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Standard IGBT Series What HiPerFET Power Mosfet? 1600 BIMOSFET Transistors Open Appl. Comparative Performance BIMOSFET Back Converter Circuits Reliability Power Semiconductor lowest forward voltage drop real Schottky diodes always best choice? Fast, Faster, Fastest, Hiperfast diodes ISOPLUS Fast Recovery Epitaxial Diodes (FRED) Input Rectifiers with Semifast Diodes Link ISOPLUS247 Power Package Features 2500V Internal Isolation Combining Features Modules Discretes Power Sem. Package; i4-PAC Package Pressure Mounting Power Stage Boost Converters Rectifier with Power Factor Correction Insulated Gate Bipolar Transistors (IGBT) with high Short-Circuit capability Revolution Discrete Isolation Technique Parallel operation IGBT discrete device chipset 300V IGBT diode Electrical Vehicles MiniBLOC polyvalent power package Power Mosfet Module with Ultra RDSon Automotive Applications Choosing Appropriate Component from Data Sheet Ratings Characteristics (IGBT Mod.) Electrical Behaviour GaAs Power Schottky Diode Semiconductor Current Regulators Protect Circuits Power Cycle capability Modules Made with Solder Contacts Investigations Electromagnetic Compatibility Power Sem.Modules Integrated Converter
System. Approach testing todays Power Sem. obtain generally applicable Characterization Appl. Oriented Testing Power Semiconductors Quality Control Status Technniques Three Phase Rect. Systems with Effects Mains Design Experimental Investigation Vienna Rectifier
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Standard IGBT, Series
IGBTs class power semiconductors that combine advantages gated drive simplicity with current handling capability bipolar devices. basic cell design characteristics IGBT very similar Power MOSFETs. drive circuitry required control 1200 basically same Power MOSFET with 9000 input capacitance. During turn-on IGBT, minority carrier injection into N-base region modulates body on-resistance level times lower than equivalently sized MOSFET, resulting proportionate times increase current handling capability. Minority carrier recombination during turn-off results fall time 0.2-1.0 which similar bipolar devices. Therefore, IGBT more suitable medium frequency, high current, power switching applications ranging from kHz. HDMOSis planar, high density process which incorporates techniques improve operating characteristics stability high voltages. This technology, combined with unique polysilicon gate cell structure, gives IGBT peak current capability times 90°C current rating. This advantage makes IGBT ideal many industrial commercial applications power conversion motor control. family products feature IGBT with ultra-fast diode connected emitter-collector (Fig. handle reverse currents that occur motor controls other similar applications. Devices rated encapsulated standard TO-220, TO-247 TO-264 packages while higher current versions come miniBLOC(SOT-227B) package. many advantages this package include electrically isolated mounting base plate, inductance leads, reduced collector-to-case capacitance. Either package combination saves space, reduces parts count assembly costs, increases reliability efficiency.
Definition Switching Times Energies Fig. shows typical circuit schematic testing dynamic parameters such switching times energies. Typical current voltage waveforms shown fig. with definition switching times specified data sheets. Turn energy Eoff defined integral within limits rise fall. Normally Eoff plays major part total switching losses. amount turn energy depends reverse recovery behaviour free wheeling diode, special attention must paid. there free wheeling diode within package IGBT (Co-Pack), same type used measuring Eon, otherwise turn energy derived from resistive test. defined integral within limits rise fall. Estimating switching energies other than specified easily done multiplying datasheet value with relation actual current voltage specified one. otherwise stated IXYS IGBTs tested with gate voltage switched from reduce switching losses recommended switch gate with negative voltage (-15
Fig. Switching Time Test Circuit
Fig. IGBT with Diode package, Co-Pack
fast recovery epitaxial diodes were designed provide optimized performance with ultra-fast recovery times soft recovery behavior. This combination IGBT diode minimizes losses power conversion motor control circuits.
td(on) td(off) toff
Fig. Definition Switching Times
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What HiPerFETPower MOSFET?
HiPerFETfamily Power MOSFETs designed provide superior intrinsic rectifier dv/dt ruggedness while eliminating need discrete, fast recovery "freewheeling" diodes broad range power conversion control applications. This class Power MOSFET uses IXYS' HDMOS IIprocess, improving ruggedness while reducing reverse recovery time intrinsic rectifier less than performance intrinsic rectifier comparable discrete high voltage fast recovery rectifiers, tailored minimize power dissipation switching stress MOSFET. HiPerFETsoffer extended dv/dt ruggedness. These devices have improved stress withstand capability applications where intrinsic rectifier used freewheeling diode. Both static commutating dv/dt have been improved significantly typically V/ns V/ns, respectively. This offers significant margin safety high stress conditions found many types inductive power switching applications. HDMOS IIeliminates trade-offs. This fifth generation Power technology been developed IXYS, incorporating ultra-low RDS(on), high unclamped inductive energy capability (UIS), high transconductance original HDMOSprocess. HDMOS IInow includes proprietary lifetime control, reducing recovery time (trr) intrinsic rectifier without increasing on-resistance MOSFET. addition, HDMOS IIhas improved cell design, improving dv/dt ruggedness. Figure shows cross-sectional view DMOS cell, many thousands that operate parallel form Power MOSFET. MOSFET subject failure parasitic transistor turns-on because this dramatic increase drain current will burn this MOSFET cell. This failure mechanism triggered whenever base-emitter voltage exceeds This occur three different ways: High drain current flow avalanche voltage breakdown. Base current flow during reapplied forward voltage dv/dt). Reverse recovery current after intrinsic diode conducted. HiPerFETis IXYS Power MOSFET with intrinsic rectifier that been improved with proprietary lifetime control process. This process makes several important changes MOSFET's operating characteristics:
di/dt A/µs
21N50 HiPerFET
Time (ns)
Fig. HiPerFETand Standard MOSFET intrinsic diode reverse recovery. reverse recovery internal, intrinsic diode markedly improved. Diode reverse recovery time decreased more reverse recovery current decreased correspondingly. Figure illustrates dramatic improvement reverse recovery HiPerFETcommutating rated diode current di/dt A/µs. Intrinsic rectifier Commutating Safe Operating Area (CSOA), sometimes called commutating dv/dt, markedly improved. Commutating Safe Operating Area (CSOA) measure capability transistor withstand intrinsic diode reverse recovery stresses, which combination reverse recovery current dv/dt while diode regains reverse blocking capability MOSFET becoming forward biased. HiPerFETcarry V/ns commutating dv/dt rating. They capable reliable, efficient operation variety power circuits that Standard MOSFETs alone have never been able address. These include brushless motor controls, inverters, welding equipment, resonant power converters sonar amplifiers. HiPerFETAdvantage past, order Power MOSFET applications mentioned above, necessary provide external path reverse diode currents. illustrated Figure this usually accomplished blocking intrinsic rectifier (typically with series Schottky diode) placing external fast recovery rectifier antiparallel with this series combination MOSFET Schottky.
Fig. Cross-sectional view Power MOSFET
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versus
(125°C) (25°C) (125°C)
Fig. Reduction parts count with HiPerFET100 diode HiPerFEThas been improved point that rugged, reliable, efficient enough eliminate these external components. 3-phase motor control, this eliminates twelve power components, their heatsink insulator pads, mounting hardware, labor required mount them. This significant cost parts count reduction, resulting reduction size, weight, assembly labor cost improvement performance reliability. HiPerFETCharacteristics Figures illustrate typical behavior HiPerFETintrinsic rectifier under wide range operating conditions. This data taken same device shown Figure Figure shows dependence diode forward current temperature. current increases, more charge injection occurs that more minority carriers stored parasitic collector region. This increases higher temperatures, junction injection efficiency increases again more carriers stored collector with same result before. Avalanche Voltage Testing well known, standard industrial test ruggedness avalanche voltage testing, also known Unclamped Inductive Switching (UIS) testing. test circuit shown Figure Peak test current normally 25°C current rating D.U.T. D.U.T. checked electrically after test ensure that degradation occurred during test. This test guarantees that HiPerFETwill survive voltage transients that excess repetitive collector-drain voltage rating some abnormal switching condition, (e.g. open circuit short circuit operation, lightening load bank switching, etc.). Design Handling Considerations MOSFET Switching Speeds: Device Switching speeds dependent drive circuit impedance. driving gate from impedance voltage source, extremely fast switching speeds attained. Turn-on turn-off times essentially independent device temperature.
(25°C)
Fig. Dependence diode current
(125°C)
(25°C) (125°C)
(25°C)
A/µs di/dt Fig. commutation di/dt
Gate Termination: Because gate essentially capacitor, circuits that leave gate open-circuit floating result unwanted turn-on device gate overvoltage damage. Voltage buildup input capacitance occur from device board leakage currents capacitive coupling from drain other circuit nodes. gate drive impedance high, frequently advisable external Zener diode from gate source protect device. Gate protection ESD: IXYS HiPerFETsdo have internal Zener diode from Gate Source, subject damage from static discharge. Reasonable precautions handling packaging, similar those required ICs, must employed.
Intrinsic Diode Switching Speed: Intrinsic rectifier trr, strong functions diode operating temperature power circuit operating conditions, including turn-off di/dt, gate drive impedance, stay source inductance. Gate Voltage Ratings: important exceed gate voltage ratings VGSS (continuous) VGSM (transient). Exceeding VGSM poses immediate risk permanent damage gate oxide layer MOSFET chip.
Fig. test circuit 2000 IXYS rights reserved
1600V BIMOSFET Transistors Open Applications
Ralph Locher IXYS Corporation Santa Clara, Introduction There many applications today using high voltage MOSFETs IGBTs, which would benefit from higher voltage part. Examples sweep circuits, radar pulse modulators, capacitor discharge circuits, solid state relays, auxiliary power supplies traction equipment other high voltage switch mode power supplies. MOSFETs connected series-parallel strings overcome their voltage high RDS(on) limitations. High voltage IGBTs slow some applications. family high voltage BIMOSFETtransistors fulfilling these needs. conventional construction both MOSFETs IGBTs commonly referred DMOS which consists layer epitaxial silicon grown thick, resistivity silicon substrate, shown Fig. However, voltages excess 1200V, thickness Nsilicon layer required support these blocking voltages makes more attractive less costly non-epitaxial construction illustrated Fig. This type construction also known "homogeneous base" "non-punch through" (NPT). Referring Figure typical pnpn-structure IGBT been maintained, note that collector-short pattern been introduced order reduce current gain transistor consequently turn-off switching behavior. However, there "free" intrinsic diode from emitter collector unlike that found MOSFET, which coin acronym 'BIMOSFETtransistor.' turn-off behavior BIMOSFETtransistor controlled amount collector shorting. order diode usable cause commutating dV/dt problems, lifetime minority carriers must reduced irradiation. result device, which optimized either high frequency frequency switching tailoring collector short pattern along with suitable amounts
Figure Comparison BIMOSFETIXBH40N160 cross-section IGBT with epitaxial construction (b).
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Table Comparative Electrical Performance
3DUDPHWHU Parameters 25C) BVces Vge(th) Vce(sat) Qg(on) Ic(on) Switching 125C) Turn-on (Note td(on) E(on) 7XUQRII 1RWH E(off)
Notes:
,;%+1
,;/+1
1600V 5-9V 121nC 110A
1600V 5-9V 2.5V 108nC 100A
50ns 195ns 0.78mJ
50ns 168ns 0.66mJ
195ns 240ns 3.0mJ
335ns 1980ns 29mJ
Turn-on test conditions: 960V; 30A; 2.7; Resistive load Turn-off test conditions: 1440V; 25A; Inductive load
radiation. Since there many applications which electrical characteristics intrinsic diode optimum application, e.g. high onvoltage reverse recovery current high power dissipation, modified fabrication process been developed block intrinsic diode without impacting effectiveness collector shorts. first member family with diode blocked 1600V rated IXLH45N160 BIMOSFETtransistor intended high current applications with repetition rates. This part much lower saturation voltage (3.5V 30A) because irradiated. switching speed controlled amount collector shorting; more shorting reM1
sults higher saturation voltages loss conducting area faster switching performance. Electrical Performance foreseen that BIMOSFETtransistor family will span range high voltage applications, from simple high voltage switch increasing upper frequency performance high voltage IGBTs. Table offers comparison their electrical performances. examining this table some figures below, note following: typical threshold voltage BIMOSFETtransistor family higher than normal IGBTs Qg(on) comparable. This
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,;/+1
,;%+1
Figure Gate charge
Figure VCE(sat) IXLH45N160 showing effect increasing
Figure IXLH45N160 output current gateemitter voltage
relatively Miller gate capacitance resulting Miller gate charge seen Figure sense, high threshold voltage considered advantage electrically noisy environments. VCE(sat) version also higher VGE(on). Figure plots transconductance room elevated temperatures shows that output current relatively independent temperature. VCE(sat) IXLH45N160 almost one-third IXBH40N160, 2.5V 7.0V respectively 25A. saturation voltage both parts strong, positive temperature coefficient evidenced Fig. depicting VCE(sat) curves IXLH45N160. Fig. plots diode voltage drop IXBH40N160
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Figure Forward voltage drop IXBH40N160 intrinsic diode.
shows that positive tempco. Consequently easier operate BIMOSFETtransistors parallel than either DMOS IGBTs MOSFETs. order survive short circuit testing (SCSOA) higher voltages, transconductance, yielding short circuit current ICE(on) required. with ICE(on) values order 100A, BIMOSFETtransistors used applications where survivability this type fault must. However many pulse applications, capability conduct high peak currents more
Figure Saturation voltage curve IXBH45N160. Note increased output current capability lower VCE(sat) voltage with gate drive.
Figure Turn-off current voltage waveforms IXBH40N160.
important than SCSOA. overcome transconductance increase gate voltage. Figure shows that IC(on) almost doubles from 100A over 200A increased from 20V, while gate charge only increases 20nC. This easily done using either discrete MOSFETs bipolar transistors gating circuit using commercially available drivers, such Telcom TC4431 TC4432 MOSFET drivers.
8G6HQ
Switching Performance Comparison Both BIMOSFETtransistors switch exceptionally fast 1600V rated parts. resistive turn-on time IXLH45N160 with gate resistor typically 168ns, which edges IXBH40N160 (tri 195ns) because latter irradiated. Figure illustrating IXBH40N160 turning inductive load into 1000V clamp elevated temperature 125OC, shows where shines. There relatively little tail current that E(off) 2.4mJ, which less than comparable IGBT. Figure plots turn-off energy function series gate resistor This resistor primarily determines rate-of-rise collecM1
Figure Turn-off energy versus gate resistor IXBH40N160.
Figure Series connection
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Figure Bi-directional switch.
Static voltage sharing resistors unequal leakage currents switches; Dynamic voltage sharing capacitors compensate differences turn-on turn-off times; Resitor also required dampen voltage ringing limit capacitor in-rush current turn-on; Zener diodes protect IGBTs against overvoltage transients; Duplicate gating circuit components Eight these components eliminated when using only high voltage switch! addition, pulse transformer easier wind since there only secondary winding. When switch does have current handling capability, semiconductor switches used parallel. While both MOSFETs IGBTs used parallel, both require matching achieve satisfactory operation.
Figure current control using diode bridge.
voltage, which increases decreases correspondingly E(off) decreases. VCE(sat) IXLH45N160 much longer tail current, which only marginally affected Consequently operating frequency range less than 5kHz. Applications Some many applications have already been mentioned review advantages availability high voltage switches. fast growing type application capacitor discharge circuits, such found laser power supplies, defibrillators, spot welders similar circuits. high voltage advantage because energy stored capacitor proportional voltage squared fast current rise times easier achieve. Figure shows typical circuit using IGBTs series string. Note necessity following duplicate components:
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Figure Dynamic break configuration.
Figure Boost configuration.
BIMOSFETtransistor family facilitates paralleling positive voltage temperature coefficient both saturation voltage forward voltage drop intrinsic diode shown Figure traditional usage thyristors solid state switches. possible circuits shown Figures Figure shows connection diagram IXLH45N160 BIMOSFETtransistors high voltage diodes while Figure circuit uses BIMOSFETtransistor inside full-wave bridge. Both circuits used mains 600V(RMS) both also provide additional functions precise current control overcurrent protection. circuit Figure carry more current because current shared BIMOSFETtransistors will more efficient because current only flows through diode. circuit Figure will cost less because there only BIMOSFETtransistor.
Finally Figures show usage BIMOSFETtransistors rapidly growing applications, namely motor control featuring dynamic braking boost inverters. Again high voltage fast switching capability IXBH40N160, design these circuits operate 600V(RMS) produce output voltages 1200V. Just anticipated that applications BIMOSFETtransistors will proliferate, IXYS will continue grow BIMOSFETtransistor family additions both higher lower current devices with range switching speeds meet requirements power conversion market. (Acknowledgement: author wishes recognize thank co-workers, Messrs. Arnold, Jankovic, Lindemann Zschieschang, their contributions suggestions make this article possible.)
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Technical Application
Comparative Performance BIMOSFETs Fly-Back Converter Circuits
typical applications flyback converter auxiliary power supply IGBT gate driver inverter. essential requirement switch flyback converter drives inverter high breakdown voltage combined with fast switching speed. minimize predominant switching losses, switch-on -off energies have low. main advantage BIMOSFET lies first lower turn- losses secondarily lower conduction losses. comparison total energy losses between MOSFET BIMOSFET results less total losses BIMOSFET.
Flyback Operation Flyback Converter most simple converter types. minimum configuration consists only switch, transformer, diode capacitors shown fig.
Flyback Application typical applications flyback converter auxiliary power supply IGBT gate driver inverter. This application requirements, which fulfilled ideally flyback converter.
500-800
Input Rectifier
Brake Chopper Inverter
Start Circuit
Driver
BIMOSFET
0-50
Inrush Current Limitation IGBT Driver
Micro Controller
Figure inverter
Figure flyback
energy this converter type stored ferrite core. Primary current ramps during state switch storing magnetic energy, which then transferred output diodes when switch turns off. power range this converter type limited approximately advantages this circuit very wide input-output voltage ratio feasibility adding more secondary windings create multiple output voltages. Furthermore, advantageous have galvanic insulation between primary secondary side. disadvantages high breakdown voltage required switch emission generated transformer. flyback converter work without load closed regulation loop otherwise output voltage will exceed allowable limits. 2000 IXYS rights reserved
shaded area fig. shows converter with start-up circuit part drives inverter. auxiliary power supply built very cost effectively with relatively elements. Since input voltage converter DC-power bus, there wide voltage variation. During precharge capacitors, power supply work properly with very DC-bus voltages, well under braking operation motor, when voltage reaches high values output voltage easily regulated varying transistor duty cycle. insulated outputs generated adding more separated secondary windings. example supply micro controller, current sensors, common +15V supply driver three lower IGBTs three separate +15V supplies upper IGBT drivers.
Requirements Switch essential requirement switch flyback converter drives inverter high breakdown voltage. flyback converter maximum voltage applied switch approximately input voltage. Therefore, minimum breakdown voltage must higher than Vin. standard inverters motor control used mains DC-bus voltage reach motor braking mode operation. Here breakdown voltage least 1600 needed. Flyback converters normally with switching frequencies between kHz. minimize predominant switching losses switch-on -off energies have low. achieve this, high switching speed switch obvious. common trick avoid switch-on losses back topology turn transistor until current output diode reached zero (discontinuous mode). There must deadtime until next cycle starts. advantage here less transistor diode commutation losses, which allows higher switching frequency order reduce size transformer. BIMOSFETChip Technology Standard high voltage IGBTs slow flyback applications. family high voltage BIMOSFET transistors fulfilling these needs. conventional construction both MOSFETs IGBTs commonly referred DMOS which consists layer epitaxial silicon grown thick, resistivity silicon substrate, shown Fig.
Referring Fig. typical pnpn structure IGBT been maintained, note that collector- short pattern been introduced order reduce current gain transistor consequently turn-off switching behavior. However, there "free" intrinsic diode from emitter collector, unlike that found MOSFET, which coin acronym BIMOSFET transistor. turn-off behavior BIMOSFET transistor controlled amount collector shorting. order diode usable cause commutating dV/dt problems, lifetime minority carriers must reduced irradiation. result device, which optimized either high frequency frequency switching tailoring collector short pattern along with suitable amounts irradiation. Driver requirements tests have shown there significant influence losses gate resistor gate voltage. rule, have found that series gate resistor less than tendency oscillate while switching above increases mainly turn-on losses. Therefore, IXBH 9N160 BIMOSFET operates best gate drive using gate resistor between achieve full conduction, gate drive necessary, because threshold voltage relatively high compared MOSFETs. Static behavior When comparing output curves linear characteristic MOSFET (fig.4a) bipolar behavior BIMOSFET (fig.4b).
Mosfet 1500V,
Epitaxial IGBT crossection
T_vj=125°C
V_GS=4 V_GS=5 V_DS
Figure Cross section
However, voltages excess 1200 thickness N-silicon layer required suppport these blocking voltages makes more attractive less costly non-epitaxial construction illustrated Fig. This type construction also known "homogeneous base" "Non Punch Through" (NPT).
V_GS=6 V_GS=15
Figure output characteristics
IXBH9N160; V_GE=7V V_GE=9 T_vj=125°C
Homogeneous Bimosfet crossection
V_GE=11 V_GE=15
Figure Cross section
Figure output characteristics
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seen from figure MOSFET conduct with only gate drive. Comparing this BIMOSFET output characteristic fig. sees that there current flow with gate drive. Here lies major difference BIMOSFET. need least switch properly currents below higher peak currents, need gate voltage proper conduction. There significant difference on-state losses. gate drive, MOSFET voltage drop BIMOSFET only volt drop. This leads times less conduction losses. also much higher current capability BIMOSFET, which easily conduct more than compared MOSFET, which limited Switching behavior have done several comparative measurements quantify performance standard high voltage MOSFET BIMOSFET. figures show full switching cycle allow calculation total losses. parameters drain current, drain voltage gate voltage have been measured. power dissipation total energy have been calculated from these data.
Mosfet 1500V, R_G=40 Ohm, T_vj=125°C
test equipment double pulse tester, which freewheeling diode still conducting when MOSFET switched Consequently, turn-on waveform impacted diode's recovery behavior. However, performance comparable because diode`s influence MOSFET BIMOSFET same. conditions follows: Turn-off current amplitude Voltage Gate drive Junction temperature 125°C time from conduction phase. this phase rise energy curve (solid line below), which caused higher state losses MOSFET. next step turn-off. dotted line (Ptot) below shows significant difference turn-off losses although they might slightly less BIMOSFET. After turn- t3), there visible tail current BIMOSFET. slight increase energy that during off-state might measurement error, since have same MOSFET, which definitely tail current. next phase turn-on from easily that major losses occur during turn-on. upper solid line shows high peak current, which mainly caused commutation diode. comparison, turn-on time MOSFET longer than BIMOSFET. peak power MOSFET approximately peak power BIMOSFET only duration Therefore, total switch energy MOSFET only BIMOSFET. This less BIMOSFET. last from beginning conduction phase. energy curve MOSFET shows rise caused high resistance. BIMOSFET curve almost flat, which sign saturation voltage (compare fig.4b).
A/div] V_DS [200 V/div] V_GS V/div] Energy [0,2 mJ/div]
[250 ns/div]
IXBH9N160; R_G=40 Ohm, T_vj=125°C
[250 ns/div]
A/div] V_CE [200 V/div] V_GE V/div] Energy [0,2 mJ/div]
Figure switching curves
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Product range Type BVCES min. 1600 1400 1600 1400 1600 1400 1600 1400 VCEsat 25°C max. IC25 Eoff @125°C typ. 0.72 1.04 1.52 @125°C typ. 0.56 1.52 2.15
IXBH 9N160 IXBH 9N140 IXBH 15N160 IXBH 15N140 IXBH 20N160 IXBH 20N140 IXBH 40N160 IXBH 40N140
summary main advantage BIMOSFET lies first lower turn- losses secondarily lower conduction losses. total energy loss pulse shown time where that MOSFET value 0.95 BIMOSFET, only 0.62 This results less total losses BIMOSFET.
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Reliability
Reliability
General Power semiconductors used high power electronic equipment exposed different conditions compared plastic encapsulated components applied equipment used communication electronics. Controlling converting high power simultaneously requires reliable control both high voltage high current. Control electrical drives additionally results frequent repetition switch-on switch-off processes that must meet special demands with respect internal mechanical design. While electrical losses occur components applied communication electronics these order high power silicon semiconductor components. These really considerable losses existing during entire operation time converter equipment must dissipated environment cooling surfaces. semiconductors must designed interior such withstand continuously arising temperature gradients resulting from losses. Finally, safe electrical isolation electrical circuits modules must ensured. Failure Rate, Reliability Prediction difficult find distribution function which will allow whole bathtub curve. However, each section Weibull distribution applicable. F(t) F(t) probability that device fails interval [0,t] characteristic life shape parameter time; number cycles
From this equation follows failure rate hazard function tb-1 shape parameter means: constant failure rate decreasing failure rate increasing failure rate random failures early failures wear-out, fatigue
Random failures terms electrical failures usually shape parameter applicable. This particular Weibull distribution then called Exponential distribution F(t) where MTTF constant failure rate. Failure rate often estimated experiment using formula =r/(n*t) MTTF number failures sample size test time Mean Time Failures, time which 62.3 devices failed
Reliability, Life According international standards term quality defined totality characteristics entity that bear ability satisfy stated implied needs. this case entity power semiconductor. Reliability property semiconductor maintain functions during usage. Since possible determine long range reliability power semiconductor components prior production release under realistic conditions accelerated life tests must applied which allow reliable results about reliability components after short test period. achieve acceleration effect reliability tests carried under greater stress than application. According familiar failure rate curve (bathtub curve) distinguish between early failures, random failures (failures with constant failure rate) failures resulting from wear-out fatigue. While applying so-called "burn-in" integrated circuits catch early failures prior final application equipment this does make sense power semiconductors because substantial higher costs. Provided there misapplication caused user early failures must avoided complete control mastery manufacturing processes. Excluding short time overload during operation random failures determined reproducibility safety margins manufacturing parameters. early design phase product already decides about failures caused wear-out fatigue designing parts processes selecting material.
Because statistical nature this number extended formula taking into account confidence limit (Upper Confidence Limit [UCL] common value) used. Moreover, possible calculate reliability data computer models. available computer models, however, have been developed power semiconductors. failure rate model according MIL-HDBK serves therefore time being only rough estimate. depending confidence limit number failures Failures Time, failures device hours
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Constant failure rates allow reliability prediction using acceleration factor. This acceleration factor calculated means Arrhenius equation: activation energy HTRB, HTGB Boltzmann's constant 10-5 eV/K absolute application junction Temperature absolute test junction Temperature
Early Failures Constant failure rate allows simple computation prediction life. regime early failures prediction failure rate practible. failure rate strongly time dependent. example evaluation power cycle test parts with early failures given Fig.2; (Temperature difference: failure critera: initial value
failure rate [1/10^3cycle]
Fig. shows acceleration factors [125°C]
Acceleration Factor
number cycles
Fig. Power Cycle: Early Failures, 0.353
Wear-Out
[°C]
Fig. Acceleration Factor
above mentioned acceleration factor applicable constant temperatures mainly HTRB HTGB. case temperature differences (temperature cycle, power cycle) other formulas have used. estimate life times different frequently MansonCoffin relation used which been established originally metals under plasic stress [2]. plastic strain dominates, then number cycles failure temperature difference extended formula known from literature incorporate cycle period maximum junction temperature [2]: )1/3 (Tmax) laboratory test field application cycle frequency (Tmax) TAmax TLmax
Power semiconductors rarely come fatigue wear-out. Even accelerated tests take long time show this. Usually reliability tests stopped time number cycles from fatigue. Fig. shows result power cycle test that carried thyristor module thermal fatigue; after month cycles, temperature difference failure criteria: test stopped. Weibull analysis significantly points wear-out.
failure rate [1/10^6cycle]
number cycles
Fig. Power Cycle: Wear-Out, 8.82
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Reliability Tests Table shows reliability tests which performed continuously power semiconductors relation failure mode important process parameters. Further tests carried request particular cases, High Temperature Storage, Temperature Storage, HAST Mechanical tests (vibration,schock,acceleration) performed changed basic constructions. HAST mechanical tests will performed outdoor test house.
Test High Temperature Reverse Bias (HTRB) High Temperature Gate Bias (HTGB) Temperature Cycle Power Cycle Humidity Test Failure Mode Degradation breakdown characteristics Rupture gate oxide Thermal fatigue silicon- metal metal-metal interfaces Thermal fatigue silicon- metal metal-metal interfaces Degradation electrical leakage characteristics Test Sensitive Process Parameter Passivation Gate Oxide Metallization Assembling Isolation Encapsulation
Temperature Cycle results multiple temperature cycles ranging between minimum maximum storage temperatures listed data sheet show evidence good different materials like plastics, metals, ceramic silicon match wether harmful thermomechanical stress occurs. devices tested brought into cradle two-chamber temperature cycle cabinet.The cradle containing devices moves perodically from heat chamber cooling chamber (IEC -2-14, Method Na). Power Cycle Power cycle tests carried prove reliability power semiconductors after frequent switching off. semiconductors tested mounted heatsinks. With known thermal resistance power semiconductor cooling system time current flow adjusted such reach junction temperature each power cycle resulting amplitude chip temperature difference (IEC 60747). Humidity Test climatic test required determine wether power semiconductors meet specifications when exposed continuously humidity. Humidity influence blocking capability attack internal connections corrosion. This climatic test performed plastic encapsulated devices only. test conditions device depending: module 1000 hrs, (IEC 60749) single device: hrs,
Table Reliability tests, failure mode test sensitive process parameters Reliability Data High Temperature Reverse Bias (HTRB) HTRB applied silicon chips devices, these chips must withstand continuous blocking load junctions. this case protective functions passivation encapsulation system examined. temperature then adjusted such allow temperature blocking junction taking account blocking losses. diodes thyristors voltage applied which rated voltage. FRED's, IGBT's MOSFET's applied voltage rated voltage. evaluation done after monitoring test after 1000 qualification tests respectively (IEC 60747). High Temperature Gate Bias HTGB This test only performed MOSFET, HYPERFET IGBT. this case gate oxide examined must withstand continuous positve voltage. applied voltage rated continuous gate voltage. temperature adjusted modules single devices (MIL-STD750). results reliability tests great importance user. determine reliability equipment user needs data from supplier with regard failure rates each individual part. Results reliability tests summarised special publication "Reliability Report". This report available request.
Literature 8402
Quality management quality assurance Vocabulary ;1995
Norris, Landzberg, Reliability Controlled Collapse Interconnections. Res. Devel., Vol. page 266-271 (1969)
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Technical Application
lowest forward voltage drop real schottky diodes always best choice?
Berndes; IXYS Semiconductor GmbH)
According thermionic emission model, pure Schottky barriers exhibit forward voltage drop, which decreases linearly barrier height diminishes; whereas reverse current increases exponentially barrier height decreases. Consequently, there exists optimum barrier height, which minimize forward reverse power dissipation particular application. However, discussions with users Schottky diodes reveal that they search minimum forward reverse power dissipation always minimum forward voltage drop. Values reverse current very rarely asked for. must know Schottky diode being applied order objectively select most appropriate part.
voltage level applications high power applications with circuit voltages using Schottky diodes with blocking voltages less than 25V, forward power losses diodes still dominate balance power losses. prevailing applications switched mode power supplies (SMPS). Here argued that decrease forward voltage drop results reduction forward power losses approximately Therefore, components created this application have barrier heights (less than 0.74 highly doped, thin epitaxial drift layers. This results device with forward voltage drop high still acceptable reverse current. Medium high voltage level applications other hand, reverse power losses high power applications using medium high voltage Schottky types (VRRM ranging from comparable even higher than forward power losses. Nevertheless, most users don't reverse currents again only forward voltage drop. Diode with ideal dynamic behavior addition forward reverse power losses, there apparently third quality, that difficult quantify. Nevertheless impact forward voltage drop shown experience. suppose that this quality exhibited dynamic properties switching loss real Schottky diode. their short appearance range only nanoseconds, they only measured with costly test equipment moreover, slight differences their dependencies cannot made evident. With regard dynamic properties, Schottky diode generally considered ideal diode with junction capacitance connected parallel. Concerning switching
characteristics, ideal diode pure majority-carrier component (only electrons n-region). After zero crossing current from forward state reverse state, ideal diode fully ignores previous conductive state blocks reverse voltage immediately after current crosses zero. Fast reverse recovery pn-diodes contrast ideal diode, pn-diodes with minority-carrier current components still "remember" their previous on-state after forward current decreased zero. This injected minority carriers (holes n-region), which will decay exponentially with adjusted minority carrier lifetime swept reverse current. pn-diode regains reverse blocking capability with delay after zero crossing current. minority carrier lifetime decreased diffusing lifetime killers (gold platinum) into region exposing diode chip radiation. Real Schottky diodes Real Schottky diodes also have minority-carrier injection through their barriers although smaller several orders magnitude. This phenomenon called modulation epitaxial layer. injection increases barrier height, voltage type, forward current density junction temperature increase. above-mentioned, technical measuring difficulties, have simulated switch-off behavior real Schottky diodes. figure below, resulting current voltage waveforms Schottky diode with type voltage active area 0.323 plotted versus time. preset operating conditions forward current, A/µs during commutation, reverse bias voltage 25°C junction temperature. Three different materials with barrier heights 0.74, 0.86 considered. turn-off energies 0.86, respectively. simulation model clearly shows that remaining minority carriers from conduction phase n-doped
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Simulated reverse recovery behavior Schottky diode
Fig.
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epitaxial layer determine initial conditions general solution differential equation circuit, which consists switch-off inductive coil, junction capacitance forcing reverse voltage bias delayed capability real Schottky diode block reverse voltage after commutation growing with increasing barrier height resonant circuit reacts with excessive reverse current (i.e. greater than commutation switching-off slope multiplied square root LC), excessive reverse voltage (i.e. more than twice driving reverse voltage) steeply starting, excessive dv/dt (i.e. more than driving reverse voltage divided square root LC). excess dynamic parameters switching loss becomes more evident barrier height increased. reaction barrier height 0.74 with respect dynamic behavior switching loss almost ideal example chosen above. Thus having above mentioned rule mind lower barrier lower forward voltage drop pure Schottky barrier shows that search minimum forward voltage drop only diminishes forward power loss also switching loss real Schottky diodes.
explains demand forward voltage drop even with high reverse current. this simple rule that forward voltage drop corresponds switching loss does hold real Schottkys type voltage above approximately have take into account that forward voltage drop drops over actual barrier epitaxial drift layer. second term becomes more pronounced with respect first term with increasing type voltage. other hand, increasing barrier heights type voltage, increased modulation epitaxial layer lowers resistivity forward voltage drop over epitaxial drift layer. This lowering become more pronounced than increase voltage drop over actual barrier figure indicates. Numbers example A/cm2 room temperature are: diodes with lowest forward voltage drop 0.78 highest barrier 0.86 have worst dynamic values, and; highest forward drop lowest barrier 0.74 have best dynamic values. Thus real Schottky diodes type voltage above with lowest forward voltage drop fastest. Application-specific adjustment barrier height opinion that, circuit designer, deviations dynamic behavior corresponding switching loss from ideal diode with junction capacitance represent more disadvantageous behavior than very high reverse current. fact, reverse current diode with barrier height 0.74 about times higher than that diode with 0.86 Above certain limit, exponentially increasing reverse currents, typical barrier heights, become unacceptable. However, this depends respective application. objective meet special application requirements customers' needs offering components with mixed barriers (values between 0.66 0.86 eV).
Fig.
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Technical Application
Fast, faster, fastest!
Optimised diodes switching applications
Steinebrunner, IXYS Semiconductor GmbH
Great efforts have been made improve power switches MOSFETs IGBTs decrease forward voltage drop, well decrease turn-off energy. switching inductive loads, turn-on losses depend strongly behavior companion freewheeling diode form major part over-all power losses. developments like series connected diodes single package greatly improve given design. This article shows choose optimum diode using example circuit. efforts importante faits pour disjoncteurs MOSFET IGBT dons chute tension directe ainsi coupure. Lors commutations charges inductives, pertes mise marche fortement comportement diode adjointe roue libre constituent actuellement part essentielle pertes courant totales. nouveaux tels diodes serie dans boitier unique, peuvent significativement conception article explique comment choisir diode optimale base d'un circuit correcteur F.P. Leistungsschalter MOSFETs IGBTs verbessern, also Abschaltenergie reduzieren, wurden grosse Anstrengungen unternommen. Beim Schalten induktiven Lasten Einschaltverluste stark Verhalten Freilaufdiode spielen wesentliche Rolle totalen Verlustleistung. Neue Entwicklungen Serienschaltungen Dioden gegebenes Design erheblich verbessern. Artikel zeigt Auswahl einer optimalen Diode anhand einer PFC-Schaltung.
FRANCAIS
DEUTSCH
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hard switching applications with inductive load, free-wheeling diode causes high losses during turn-on transition power switch. Power factor correction resonant mode typical example such hard inductive switching. very common topology boost configuration (Fig. using MOSFET usual power switch higher frequencies. Fig. shows idealised current voltage waveforms during diode's turn-off MOSFET's turn-on. These waveforms also valid inverter designs, where diode power switch parts phase leg. results obtained with this example also used designing drive inverters, switched mode power supplies, line inver ters other similar applications. known method achieve better performance rectifiers given blocking voltage connect lower voltage diodes series [1]. equal voltage sharing, sometimes
FAVM (VT1 V)T0 FAVM
IFAVM
-IRRM -VOUT IRRM VOUT
Real Curve Linear
Fig. Linear model forward voltage drop output curve: deriving Fig. Idealised current voltage waveforms; current commutates from diode switch
VOUT
Fig. Boost converter principle, power factor correction (PFC)
energy loss. Energy times frequency gives total power-loss, increasing junction-temperature semiconductor which sets limit switching frequency fsw. reduce weight, volume costs passive components like inductors capacitors (and which designer power supply does want this), necessary higher switching frequencies fsw. over-all losses switch have reduced this better free-wheeling diode. high switching frequencies, turn-off time reverse recovery current should possible save energy while power switch turns estimation switching energies easily derived from curves Fig. following formulas [2]: Eoff(diode) Vout Eon(MOSFET) (IRM Vout obvious that turn-on losses switch will higher than turn-of losses rectifier this example. Turn-on energy diode mostly small, turnoff static losses MOSFET independent diode they from interest this case. compare different diode types, also necessary calculate their on-state blocking losses. first obtained using linear model output curve (Fig. IF(AV) IF(RMS)2 Poff (Note: duty cycle)
good compromise between improved reliability optimized chip size optimized costs) achieved with around 125°C 150°C. Therefore values parameters formulas must interpolated operating junction temperature from values given data sheet. power losses affected freewheeling diode derived, following formula should used: Ptot(diode affected) [Eoff(diode) Eon(MOSFET)] Poff Having derived necessary formulas, possible draw some conclusions: Diode selection depends strongly upon switching frequency. lower frequency applications, forward voltage drop plays major role diode's power loss. higher frequencies, switching losses become more more important. Losses commutating switch will rise with frequency dynamic behavior diode. maintain junction temperatures increased reliability lifetime, either power loss thermal resistance must decreased even both). APPROACHES DIODE OPTIMISATION addition well-known IXYS Fast Recovery Epitaxial Diodes (named DSEI. single diodes DSEK. common cathode configuration), High Performance FRED series been developed called HiPerFRED(respectively DSEP. DSEC.). Blocking currents have been reduced high temperatures while dynamic parameters, like tB), were improved. Forward voltage drop decreases with increased giving lower static losses when device running working temperature. Combining these diodes with latest package development IXYS, called ISOPLUS247TM, possible achieve acceptable junction temperatures even high switching frequencies. ISOPLUS247is isolated, discrete housing which standard copper
necessary connect snubber networks parallel each single diode, thereby making this solution rarely used. newly developed housing makes possible connect more diodes series within single package. Matching testing dice voltage sharing allows user design these diodes without additional snubber circuits. depends application switching frequency single series connected diode better choice. POWER LOSSES JUNCTION TEMPERATURE rectifier carrying forward current needs non-negligible time change from on-state blocking state. Until reverse recovery charge been removed from junction, diode behaves like short circuit causing high current flowing only through self, also through power switch that turning diode. seen from Fig. maximum reverse recovery current diode added load current drain current MOSFET reaches maximum voltage drop short zero, switch carries only high current also sees full output voltage Vout, resulting enormous instantaneous power dissipation thus turn-on 2000 IXYS rights reserved
Dynamic losses calculated multiplying switching energy with switching frequency, total diode losses become: Ptot(diode) Eoff(diode) Poff junction temperature diode, power loss multiplied thermal resistance from junction case (C): Ptot(diode) Rth(JC)
lead frame been replaced DirectCopper-Bonded alumina, same isolation material used high power modules. This package meets JEDEC standard TO-247 outline recognised package. ceramic isolation unbeatable thermal resistance junction heatsink while providing 2500 VRMS isolation voltage from leads backside. ISOPLUS247also allows interesting method decreased dynamic parameters: series connection diodes. Because DCB-substrate patterned like printed circuit board, easy connect more chips series single package. Fig. shows impact series connection IRM. higher blocking voltage same chip size, higher also dynamic parameters forward voltage drop. Connecting three devices
100% single chip chips series single chip
Table V-diodes suitable similar applications Type DSEP 8-06A DSEP 9-06CR DSEP 30-06B Competition VRRM IFAV Total chip size 100% Package TO-220 ISOPLUS247TO-247 TO-220 Remarks single chip chips series, isolated single chip, high speed chips series, isolated
Table Static dynamic parameters tested diodes Type IF=10 TJ=150°C DSEP 8-06A DSEP 9-06CR DSEP 30-06B Competition 1.24 3.09 0.99 2.17 [ns] [ns]
IF=10 VR=400 -di/dt=300 A/µs, TJ=150°C
single chip, this case only half value device (b). table there three examples diodes shown representing above mentioned technologies [3,4]. rated blocking voltage suited application described below. DSEP 8-06A single chip diode with normal switching speed (suffix "A"). DSEP 9-06CR series connection three diodes package which exhibits very dynamic parameters "HiPerDynTMFRED"). Suffix corresponds "Lightspeed" IGBT series IXYS, while stands ISOPLUS247package. DSEP 3006B finally again single chip device with improved switching speed (suffix "B"). competitive, series-connected diode listed last. CHOOSE OPTIMUM DIODE single phase circuit which from input voltage draws current gives nominal input power simplify calculation current assumed rectangular with constant duty cycle D=0.5 constant amplitude Ipeak= (RMS rectangular waveform equals Ipeak thus giving value mentioned above).
Static losses investigated diodes were calculated from formulas (4), dynamic losses diode turn-on losses switch from (2). Parameters needed calculations found datasheets: were derived from curve forward current voltage drop shown Fig. were read directly from their curves. rough approximations, trr/2. This method getting necessary parameters useful first approximation power losses. Having choosen suitable devices, recommended measure dynamic losses within application prove theoretical assumptions. Results Table have been measured using circuit shown Fig. under equal conditions that direct comparison different types possible. With measured values above calculations, optimum diode given design found. Fig. shows total diode power losses switching frequency according equation using values Table seen that above kHz, series connected diodes lead lowest power losses.
100% single chip
IRRM
chips series
single chip
Fig. Effect series connection forward voltage drop reverse recovery current
series results blocking diode. resulting voltage drop increased factor when compared actual diode, value only doubled (a). However, advantage that reverse recovery current
P_tot DSEP 8-06A f_sw [kHz] DSEP 9-06CR DSEP 30-06B Competition
f_sw [kHz] [°C] DSEP 8-06A DSEP 9-06CR DSEP 30-06B Competition
Fig. Diode affected power losses switching frequency using Table data
Fig. Maximum allowed case temperature switching frequency using Table data; TJ=150°C
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DSEP 9-06CR produces only losses single chip diodes. total efficiency circuit increased, should series connected diodes. Fig. maximum allowed case temperature switching frequency shown calculated formula (6), again using values Table Junction temperature 150°C, which still well below maximum value 175°C IXYS HiPerFREDdiodes. diode with largest chip size (DSEP 30-06B) requires lowest cooling effort therefore should used ambient temperatures high cooling problem. series connected diode DSEP 9-06CR starts outperform smaller DSEP 8-06A single chip type above kHz. Because this diagram only diode losses appear, cross-over point higher than Fig. turn-on losses power switch play major rule total diode affected losses! Within frequency range from (which typical most applications), make decision depending upon design goal. type switch already fixed efficiency cooling problem, DSEP 8-06A would best choice because least expensive. switching device been chosen yet, maybe smaller part taken when using series connected diodes because reduced turn-on losses switch. this case, overall costs lower compared solution with single chip diode larger transistor. Above high system efficiency required, there alternative series connected diodes. also possible discard active snubber networks that `discharge' diode junction before main switch turns that there superimposed reverse recovery current main switch's drain current. Replacing conventional rectifier with series connected diodes with their very reverse recovery current provides similar effect without additional circuitry.
A/div]
competition
ns/div]
Fig. Turn-off behavior competitive type; IF=10 -diF/dt=300 A/µs, VR=400 TJ=150°C
When connecting devices series, normally necessary ensure voltage sharing. This achieved connecting RC-networks parallel each single part resistors static, capacitors dynamic voltage sharing. above introduced, single package, series connected diode, there more need external networks. Chips built into housing were matched that parameter differences kept low. 100% testing both static dynamic voltage sharing gives additional safety devices replace single chip parts without restriction need additional parts. SUMMARY been shown that, depending switching frequency, there optimised solutions. frequency range, single chip diodes best because their static losses. medium frequency range, user choose suitable diode according main goal. cost required, single chip part maybe first choice should determine better performing series connected diode allows smaller switch leading lower overall costs. High ambient temperature poor cooling ability leads large chip device with good heat transfer characteristic. High efficiency total system achieved when using series connected diodes with dynamic parameters. this reason they also unbeatable high very high frequency range. method described enables designer choose perfect rectifier application. REFERENCES Rivet: Advantages Fast Recovery Epitaxial Diode (FRED) Power Conversion, June 1997 Proceedings IXYS Technical Information Fast Recovery Epitaxial Diodes IXYS Semiconductor Databook 2000, CD-ROM http://www.ixys.com
A/div]
ns/div] DSEP 9-06CR, serial diode DSEP 8-06A, single chip
Fig. Comparison series connected diode single chip type; IF=10 -diF/ dt=300 A/µs, VR=400 TJ=150°C
competitive diode type requires less cooling effort than IXYS series diode DSEP 9-06CR. This very short second portion recovery time what leads according formula diode losses. price which paid this very snappy turn-off behavior which might cause problems seen Fig. DSEP 9-06CR slightly slower much softer, oscillations negligible. Fig. shows clearly much better reverse recovery behaviour compared single chip diode DSEP 8-06A.
2000 IXYS rights reserved
Fast Recovery Epitaxial Diodes (FRED)
Characteristics Applications Examples
During last years, power supply topology undergone basic change. Power supplies kinds constructed that heavy bulky mains transformers longer necessary. These transformers represented major part volume weight traditional power supply. Today they have been replaced with smaller lighter transfomers, whose core materials consist sintered ferrites instead iron laminations which operate kHz. same power rating, high frequency operation significantly reduces weight volume transformer. This development been significantly influenced new, fast switching power transistors, such MOSFETS IGBTs, working high blocking voltages (VCES Technologies abbreviation FRED (Fast Recovery Epitaxial Diodes) stands series ultrafast diodes, which have gained wide acceptance during last years. There exist several methods control switching characteristics diodes each leads different interdependency forward voltage drop blocking voltage VRRM values. these interdependencies compromises) that differeniate ultrafast diodes available market today. Fig.1 shows qualitative relationship forward voltage reverse recovery time trr. most important parameters turn-on turn-off behavior diode (Fig. VFR, IRM, will influenced different manufacturing
However, nearly topologies equipped with these transistors also need ultrafast diodes conduct reactive load current rectify output when voltage required. switching behavior these diodes must tailored match switching charcteristics transistors. This only true switch mode power supplies also inverter circuits. these inverters, manufacturers have chosen frequencies about create smooth sinoidial waveform output current have used frequency above order operate above audible level. Apart from characteristics transitor switches, on-state dynamic characteristics free processes. shown Fig. each technology must come with compromise between forward voltage recovery time obtain device that will operate satisatisfac-torily. Figure shows typical switching cycle diode. During forward conduction, resistivity epitaxial layer (see Fig. decreased excess minority
wheeling diodes have significant impact power loss, efficiency degree safety operation whole equipment. They also play decisive role when comes increasing efficiency SMPS reduce losses inverter, which clearly mandates that ultrafast diodes used. ultrafast diodes described here embrace characteristics modern epitaxial diodes, such soft recovery, reverse recovery current with short reverse recovery times.
MOSFET Metal Oxide Semiconductor Field Effect Transistor IGBT Insulated Gate Bipolar Transistor
charges this case holes) being stored there. When this forward current commutated another switch, diode cannot regain reverse blocking capability until this excess stored charge removed, which only done recombination stored holes with background electrons reverse current flow through diode. Since ideal diode zero reverse recovery
Fig. Typical switching waveforms FRED diode
Fig. Qualitative correlation show this compromise various FRED technologies
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Technologies
Characteristics
Anode
Characteristics most important processes speed turn-off behavior bipolar diode gold platinum doping electron irradiation. case ultrafast diodes, n-layer that supports reverse voltage, should made thin possible minimize forward voltage drop well stored charge pn-junction. obtain wafer thickness that allows good mechanical handling wafers, epitaxial technology most favorable choice. This technology makes relatively thick doped wafer substrate mechanical strength, which thin, monocrystal n-layer (the so-called epitaxial layer), grown. epi-layer thickness resistivity adjusted according desired blocking voltage capability. passivation pn-junction uses planar technology, which similar manufacturing process transistors. Guard rings reduce electric field strength prevent voltage break-down surface glass-coated ensure blocking voltage stability. improve turn-off behavior, either gold platinum atoms diffused interstitially into epilayer these atoms trapping sites, which excess holes recombine with electrons. Recombination centers also created electron irradiation, which displaces silicon atoms from their normal cyrstalline lattice sites. Very high temperatures will allow displaced silicon atoms vibrate back into lattice structure. Therefore, irradiation often followed annealing process anneal
Planar epitaxial diode, DWEP. Glasspassivation Guard ring Anode
pitaxie Epitaxy Slayer- stra Substrate atho
Cathode
Metalization
Cathode Kathode
Fig. Cross-sectional view FRED junction diode with planar passivation
Fig. Cross-sectional view Schotty diode current, recombination stored charge must accelerated, which done introduction recombination centers into epitaxial layer. course, result will that stored charge both recombines swept reverse current, resulting short negative current pulse, called reverse recovery current. reverse recovery current reaches maximun (IRM), areas free carriers develop pn-junction, which then start block voltage. ensuing decrease recovery current essentially determined actual distribution remaining carriers n-region. decrease recovery current (diR/dt) versus time special importance, because determines peak voltage dv/dt transients that will occur. This will discussed more detail below. already mentioned, recombination centers created within diode decrease reverse recovery current. Schottky diode, whose cross-section shown Fig. majority carrier diode, which switched very quickly, similar MOSFET. observed reverse current charging metal barrier-silicon capacitance, which independent temperature. now, Schottky diodes have only been used applications with reverse voltages (typically less than However, newer types with higher blocking voltages more already available. applications requiring ultrafast diodes with blocking voltages excess bipolar pn-junction FREDs only answer.
temperature sensitive portion crystal disturbances. process parameters, irradiation energy annealing temperature properly chosen, switching characteristic will remain stable. Table shows essential characteristics ultrafast diodes process technologies. course, manufacturing process ultrafast diodes advantages well disadvantages. FRED diodes, using gold doping control minority carrier lifetime, represent excellent compromise between forward voltage, peak reverse recovery currents with soft recovery. These diodes charac-terized soft recovery behavior from -40°C +150°C, showing even very high -diF/dt A/µs) tendency "snap-off." higher leakage current gold doped diode compari-son platin doped irradiated diode, only disadvantage. However most applications, power loss caused leakage current small comparison forward current reverse recovery losses (Fig. [1].
Table Comparative advantages ultrafast diodes process technologies
Gold Doped Soft reverse recovery Good trade-off, very short with much higher High high temperatures (100°C) Platinum Doped Tendency snapp-off Good trade-off nearly same gold; higher same than gold Electron Irradiation Tendency snapp-off trade-off good doping; clearly longer Schottky Diodes Much better turn-off than gold Very small IRM,
Very high even room temperature, relatively
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Free Wheeling Diodes
Free Wheeling Diodes These diodes mainly used free wheeling diodes, connected parallel fast switching transistors working with inductive load such e.g. inductors boost buck converter, transformers motors. majority these circuits controlled pulse width modulation working fixed frequency. Forced inductive load, current must continue flow free wheeling circuit. case transistor turned-on, free wheeling path must blocked prevent short circuit. typical interaction between power transistor free wheeling diode described following example. Fig. shows simplified circuit buck converter. This circuit provides output voltage Vout which lower than supply voltage Vin. Fig. shows control signals voltage current waveforms conducting blocking phases active elements devided follows:
F/dt 250A/us DSEI 12-10A SPEED 87-1000 12PI1000
Vout
Last load
Cout
Sollwerte
input value
controller Regler
Fig. Buck-converter circuit diagram switching action Diode characterized four important phases: diode blocks while onstate, transition from blocking conducting mode: turn-on, blocking voltage cabability, temperature diode chip and, above all, technology diode. Together with applied reverse voltage reverse power loss
Turn-On With transistor switched off, current inductor must keep flowing. voltage across diode drops down diode takes over current inductor. current rise time equals current fall time volume charge formed pnjunction diode during blocking phase flooded carriers causing change resistance pn-junction during current rise time. This turn-on diode accompanied short overvoltage forward direction which depends chip temperature, -diF/dt again chip technology. Compared blocking voltage, overvoltage very most applications, important operation diode (waveform Fig. However, this dynamic turn-on voltage diode does peak voltage that appears across transistor adds turn-off losses. overvoltage determines turnon losses diode. These turn-on losses increase linearly with switching frequency.
Fig. Comparison reverse recovery currents several different FREDs certain time controller switches series circuit Cout connected supply voltage makes current increase linearly. This current deter-mined inductor output voltage Vout. After certain time, fixed controller, switched again. discontinuous mode operation, energy stored IL2) transferred free wheeling path into capacitor Cout. certain time switched again whole precedure repeated. diode conducts forward current while blocked, transition from conducting blocking mode: turn-off.
Blocking Mode While MOSFET conducting, supply voltage appears reverse voltage diode with semiconductors, current diode flows from cathode anode (leakage current IR). leak-age current depends
2000 IXYS rights reserved
On-State Once turn-on phase over, diode conducts forward current There forward voltage drop threshold voltage pn-junction resistance semi-conductor. This voltage drop depends, already mentioned, chip temperature, forward current process technology. indicate forward voltage drop various currents and, consequently, calculate on-state losses, parameters often appear datasheets. simplified model forward voltage drop shown Fig. on-state power dissipation then calculated accordingly: calculated losses, however, only
Turn-Off Apart from on-state characteristic, turn-off behavior considered most important parameter determining suitability diode high frequency application. current commutated transistor, decreases linearly with di/dt which transistor turns current. case
What results reverse recovery current whose waveform depends chip temperature, forward current -diF/dt technology. Fig. shows reverse recovery current depends chip temperature gold doped (9a) platinum doped (9b) epitaxial diode same forward characteristic.
25°C 125°C
Fig. Typical forward voltage drop versus current model,
Gate 25°C 125°C
Fig. Transistor gate signals, current voltage waveforms along with diode current voltage waveforms switching cycle buck-converter shown Fig.
Fig. Reverse recovery current voltage FRED diodes 25°C 125°C gold-doped diode platinum-doped diode
approximate values, depend great deal temperature only given certain temper-ature (TVJM). Since this temperature differ from actual operating temper-ature, calculated losses only valid given temperature.
power MOSFETs IGBTs, -diF/dt values more than 1000 A/µs easily reached. mentioned before, carriers which have flooded pn-junction during on-state phase must removed before diode start block reverse voltage.
difference between technologies really striking, compares recovery behavior various diF/dt same temperature.
2000 IXYS rights reserved
Example
Whereas, case platinum, decrease recovery current speeds (Fig. 10b), gold diodes with controlled minority carrier reduction keep their soft recovery behavior, even high -diF/ values (Fig. 10a). faster decrease recovery current (the diode gets "snappy"), higher overvoltage caused stray inductances circuit lay-out. maximum voltage reaches maximum blocking voltage transistor, snubbers must used guarantee safety operation equipment. Furthermore, much high dv/dt values cause EMI/RFI problems, which complicate shielding, certain limits have kept. reverse recovery current flowing diode does only determine turn-off losses diode also adds turn-on losses transistor, which carries diode current.
reverse recovery current must added current inductor turn-on time extended some portion (Fig. Figures emphasize significance peak recovery current accompanied soft recovery behavior. first place, soft recovery behavior gold doped diodes entails small overvoltage reverse recovery current. Therefore diode marked turn-off losses. Secondly, reverse recovery current leads essentially reduced turn-on losses transistor. Thus, choice diodes decisively influences power losses both devices.
Operating conditions buckconverter: DC-link voltage Current fall time MOSFET Output voltage Vout Switching frequency Inductor current Duty cycle MOSFET Max. junction temperature 125°C
Maximum Blocking Losses From datasheet page IRmax 125°C, IRmax
Turn-on Losses calculation actual turn-on losses much more difficult than calculation blocking losses on-state losses. There static operation, current voltage diode functions time only calculated approximately using exponential hyberbolic equations.
Last
10%V
Fig. Reverse recovery waveforms free-wheeling diode Fig. Transistor current voltage waveforms showing impact reverse recovery current commu-tates free-wheeling diode
Example following example illustrates calculate power losses free wheeling diode buck-converter (Fig. epitaxial diode, type DSEI 30-10 described slightly shortened datasheet (page D1-16), where also find respective data calculate power losses.
Fig. Reverse recovery currents different -diF/dt 125°C gold-doped diode platinum-doped diode
Fig. Actual diode turn-on waveforms their linearized approximations simplify turn-on power loss calculations 2000 IXYS rights reserved
Further Applications
estimate diode turn-on losses, turn-on waveform given simplified form Fig. This simplification conservative, i.e. actual turn-on losses smaller than calculated ones, makes possible calculation using datasheet values. current rise time determined turn-off time MOSFET load current: diF/dt IF/tf A/60 A/µs diagram Fig. datasheet shows turn-on recovery time turn-on overvoltage -diF/dt A/µs 31.5 calculate turn-on energy, current which assumed constant, multiplied triangle waveform overvoltage time tfr: 31.5 turn-on power losses calculated multiplying pulse energy switching frequency:
Turn-off Losses Similar turn-on losses, turn-off losses only calculated approximately using datasheet values. Once again, waveforms voltage current simplified (Fig.13). assumes same diF/dt given during switch-on, diagrams Fig. Fig. datasheet show: These data valid 100°C must multiplied factor adjusting these data 125°C. This factor given diagram Fig. datasheet. 125°C data multiplied 1.1. This simplified calculation turn-off behavior results turn-off energy Eoff trr/2 Eoff Eoff multiplication switching frequency results turn-off power loss: Poff Eoff Poff 12.5
total losses diode buckconverter are: Ptot Poff Ptot 13.3 12.4 Ptot 32.1 Using thermal resistance RthJC which shown data-sheet, chip temperature 29°C above case temperature. Assuming thermal resistance RthCK 0.25 chip temperature less than 125°C, maximum heatsink temperature exceed 88°C: TKmax TVJM (RthJC RthCK) Ptot TKmax 125°C (0.9+0.25) 32.1 TKmax 88°C While this application used buck-converter circuit example, same approximations calculations used boost-converter.
Further Applications Rectifier Diodes Ultrafast epitaxial diodes used rectifier diodes only switching frequency higher than blocking voltage exceeds These conditions very common switchmode power supplies delivering output voltages more than because there Schottky barrier diodes with required blocking voltage capability (Fig. 14). Switch-mode power supplies generally operate with controller. Therefore mode operation epi-diode used rectifier very similar that free wheeling diode. current voltage waveforms rectangular, calculation power losses carried described case free wheeling diode.
On-State Losses on-state forward voltage 125°C shown diagram Fig. page on-state forward voltage given curve 100°C: 1.77
Thus following on-state losses calculated: 1.77 13.3
Eoff
calculates on-state losses using formula (VT0 IF2) (1-d), gets smaller value: 12.5 12.5 0.52 2000 IXYS rights reserved
Fig. Actual diode reverse recovery waveforms their linearized approximations
Fig. Center-tapped output circuit with common-cathode diode connection
Snubber Diodes
Summary
FRED Modules
Snubber Diodes "Snubber" circuits used protect power semiconductors from being destroyed short overvoltage spikes. di/dt values more than 1000 A/µs, which reached with transistors (MOSFETs IGBTs), cause overvoltages parasitic stray inductances circuit wiring. equation di/dt underlines high these overvoltages even very stray inductances. example, case -di/dt 1000 A/µs during switch-off with stray inductance computed voltage spike 1000 A/µs This spike, which will added voltage, will require higher voltage MOSFET IGBT. These devices only cost more efficiency circuit will decrease their higher switching losses. Snubber circuits limit generated overvoltage transferring energy stored stray inductances capacitor. Apart from capaci-tance, turn-on behavior diode determines remaining overvoltage. diagram Fig. datasheet illustrates forward recovery voltage VFR, which expected, forward recovery time various di/dt values.
Summary depicted detail, ultrafast diodes have different characteristics depending manufacturing process. These characteristics should considered make best them various applications. standard FREDs existing circuit replaced DSEI diodes, power losses both diode transistor thus reduced. soft recovery behavior DSEI diodes also prevents transistor from being overloaded high dv/dt overvoltage spike also reduces EMI/RFI. market ultrafast diodes constantly expanding. Apart from their standard application free wheeling diode inverters, these diodes also more more used snubber circuits rectifier circuits switch-mode power supplies. FRED diodes delivered IXYS characterized very reverse recovery currents, even high /dt. Simultaneaously, they show soft decrease reverse recovery current, thus avoiding inductive overvoltages with very high dv/dt. These overvoltages could cause malfunction even destruction active switching device, MOSFET, IGBT bipolar transistor. given example buck-converter shows, that when choosing ultrafast diode, operating modes taken together must considered only individual parameters. losses diode buckconverter divided illustrated Fig. on-state turn-off losses make total losses diode. determining factors these losses are: Poff trr, IXYS offers ultrafast diodes (FRED Fast Recovery Epitaxial Diodes) TO-220, TO-247 SOT-227B packages. These diodes available with blocking voltages from 1200 Furthermore, IXYS provides FRED modules various topologies 1200 (table page 10).
FRED Modules FRED modules type MEO, MEE, (Fig. extension discrete DSEI higher current while sharing same diode characteristics mentioned before. They applied circuits with MOSFETs, IGBTs bipolar Darlingtons, working switching frequencies more than about kHz. paralleling several discrete diodes miniBLOCs necessary, these modules represent possible alternative minimize assembly time size final equipment. Generally FRED modules used free wheeling diodes high current IGBTs bipolar Darlingtons fast rectifiers power supplies welding equipments. What follows series applications showing FRED modules.
(6.5%)
(13.5%)
Fig. Circuit diagrams available FRED modules
Poff (38.6%)
(41.4%)
Fig. Comparative losses freewheeling diode buck-converter example
2000 IXYS rights reserved
Applications
Parallel Series Connection Modules
Application rectifier power supplies welding equipments Half-wave rectifier (Fig. 19a). Depending load current, several modules paralleled. Common cathode topology (Fig. 19b). Depending load current, several modules paralleled. Common anode topology (Fig. 19c). Depending load current, several modules paralleled. Full bridge rectifier (Fig.19 Depending load current, either modules paralleled. Full bridge rectifer higher output voltages (Fig. 19e). Here both diodes module connected series obtain higher/blocking voltage. FRED modules continuous current FAVM given heatsink temperature 65°C junction temperature TVJM 125°C (difference temperature 60°C). When comparing these modules with types competition, make sure that modules compared share same difference temperature between heatsink (case) junction, because this what determines maximum allowable forward current. Furthermore, current ratings FRED modules include blocking losses diode 125°C duty cycle Parallel Series Connection Modules Fig. type type FRED modules consist several individual diode chips, which connected parallel internally obtain desired current rating module. order good current sharing between diode chips, they selected such that forward voltage drop nearly same chips parallel. This selection facilitates parallel connection well series connection several modules.
Fig.
Fig.
Fig. type type Application free wheeling diode three phase inverters drive systems, working with controlling switching frequen-cies range (Fig.
Fig.
Fig.
Fig.
Fig. type type
Fig. 19a-e Examples different FRED modules output rectfiiers power supplies
Application free wheeling diode switch-mode power supplies servo drives symmetrical full bridge with MOSFETs Schottky blocking diodes (Fig. 18a) assymmetrical full bridge with MOSFETs forward converters motor drives (Fig. 18b)
2000 IXYS rights reserved
Parallel Series Connection Modules
Parallel Connection simplify parallel connection several modules, they tested categories which indicated type label. part number followed digit letter, which stands category device. Example: MEO260-12DA3 MEK160-06DAD. several modules connected parallel higher output current, only modules same category should used. There are, course, exceptions rule: also possible adjoining categories; however, saftey operation, this should only exception. current handling capability modules connected parallel calculated follows: number modules current module (see table total current modules parallel Example: modules 260-12DA1 connected parallel: allowable continuous forward current IFAVM 65°C equals: Series Connection series connection FRED modules requires static resistor circuit equalize different blocking currents diodes dynamic snubber circuit equalize different reverse recovery charges (Qr) diodes. calculation these snubber circuits take into account great number conditions which differ from application application. snubber circuits only optimized, really familiar with these conditions. rough setup these snubber circuits illustrated Fig. What special interest that, individual diode chips within module, selection categories also means that there exists selection thus detailed databook (publication D94013DE) whole range ultrafast diodes exists help design engineer choose right diode application. Literature Heumann, Impact turn-off Semiconductor devices power electronics, Journal, Vol. (1991), page
Fig. Voltage sharing networks FRED modules when diodes used series
2000 IXYS rights reserved
Input Rectifiers with Semifast Diodes Link
Switching power semiconductors used inverter systems with DC-link. high switching frequencies, harmonics line distortion generated. important that designs reduce these influences fullfil filtering requirements according 0871.
Input rectifiers have charge link capacitor inverter system with highly constant voltage. there request feeding back energy mains, rectification voltage mostly done using uncontrolled singleor three phase rectifier bridges. peak current level when loading capacitor during switching system must limited incritical values input rectifier. This realized applying: NTC-resistors connected input rectifier. That, however, makes sense only power applications. Using starting resistor either side which continuous operation must shorted reduce losses heat dissipation increase efficiency. Very often shortcircuit resistor done mechanical relais with limited lifetime. better load DC-link capacitor using half controlled rectifier bridges type which available currents voltages 1600 When using half controlled rectifier bridges soft start achieved slowly increasing trigger angle bridge thyristors thus limiting charging current link capacitor. During normal operation after having reached full wave control thyristors operate like diodes. cathodes thyristors have same voltage potential shown Fig. triggering thyristors easy realize using impuls transformer only. Since thyristors need positiv triggerpuls during reverse time recommended only triggerimpulses nearly factor -value given datasheet order avoid high increase reverse current thus resulting increase blocking losses, too. Other softstart facilities using mechanical devices with limited lifetime series series inrush current rectifier uncritical values. When DC-link resistor reached maximum charge soft start thyristor parallel resistor will triggered thus shortcircuiting resistor. Using this technology mechanically operated relais replaced electronic switch with almost unlimited lifetime. gate triggervoltage thyristor will easily formed through transistor circuit with impuls transformer using link voltage. thyristor designed operated continuously with load current datasheet. thyristor operated under phase control conditions, problems concerning turn-off will occur. input rectifier equipped with semifast diodes therefore optimized turn-off, resulting lower peak recovery current compared non-optimized normal
Fig. Reverse revocery with standard rectifier semifast rectifier
rectifier diodes (Fig. This behaviour direct influence design filter network with capacitors inductivites which size costs reduced. Fig. show that turn-off optimized diodes have less snap-off behaviour compared turn-off optimized diodes rectifier modules when same EMI-filter will used. snapping behaviour proportional peak recovery current, higher rises bigger snapping behavour will These peaks always appear when diode current commutate from diode branche other branche rectifier bridge. During commutation periode there always exists short circuit some nanoseconds. rate rise current (di/dt) this case only limited stray inductances. capacitor within filter circuitry (necessary acc. 0871) input voltage rectifier bridge became very "hard" thus resulting high di/dt levels during commutation. peak recovery current diode depends di/dt value will increased accordingly. minimize this influence rectifiers should equipped with diode chips which optimized short reverse delay time small peak recovery current. modules therefore equipped with such optimized diode chips. Fig. shows influence optimized optimized input rectifier built SMPS application Iout Vout= -marked line shows voltage level frequency turn-off optimized input rectifier module where marked
Fig. Circuit different input rectifier bridges
necessary. applications with softstart resistor mentioned above, modul Type (Fig. with controlled rectifier bridge including integrated soft start thyristor recommended. This module available with voltages 1600 softstart will realized with load resistor placed positive outline input rectifier. This resistor limits 2000 IXYS rights reserved
filter network
Test point
Test point
Fig. Test circuit with filter network
compared input rectifier equipped with optimized rectifier diode chips. This result will help design engineer design smaller, compact less expensive power supplies systems. Using optimized input rectifier module type with integrated soft start thyristor other controlled rectifier bridges like module type avoids disadvantage
Fig.
Input current with standard rectifier test point Input current with standard rectifier test point
with standard rectifier with semifast rectifier
voltage level
line gives results rectifier equipped with optimized diode chips. curves show that noise level reduced 15dB when using reverse recovery optimized rectifiers. circuit diagram both cases shown Fig. results clearly prove that module equipped with semifast diode chips shows lower level interference voltage thus resulting necessity less filter equipment
Level class
Level class
frequency
Fig.
measurement 0871
using many discrete components allows realize produce electronic concepts cost effective high quality level. IXYS prepared develop other rectifier bridges with semifast diodes according customer's request. noise level could again reduced another when using rectifier bridges equipped with Fast Recovery Epitaxial Diodes (FRED) like modules type (single phase bridge) (three phase bridge) which however more expensive necessary some applications fulfill other standards.
Fig.
Input current with semifast rectifier test point Input current with semifast rectifier test point
2000 IXYS rights reserved
ISOPLUS247Power Package Features 2500V Internal Isolation
Revolutionary Approach Improves Thermal Conductance Reliability capability because thermal expansion IXYS Corporation introduced new, isocoefficient silicon matches that lated plastic encapsulated package types DCB; discrete power semiconductors, which prom6. Small chip-to-heatsink stray capacitance ises change power devices attached reduced EMI/RFI emissions; heatsinks. ISOPLUS247has in7. substrate etched like ternally isolated mounting with 2500V(RMS) board allowing more circuit configurations than normally found nonisolated TO-247, e.g. epitaxial ultra-fast Plastic housing Silicon recovery diodes Schottky connected common anode series, multiple diodes series, MOSFET connected series with Schottky diode with without antiparallel diode. primary advantage ISOPLUS247 packDCB lead frame aging very thermal resistance achievable rugged, high voltage, isolated mounting system. Table compares thermal resistance Figure Cut-away view ISOPLUS247 package 55A/500V MOSFET chip ISOPLUS247 isolation voltage rating. package meets package (IXFR55N50) hole-less TO-247 standard JEDEC TO-247 outline intended version (IXFX55N50) when isolated with various pressure mounting applications since there interface material. Figure shows allowable mounting screw hole. seen Figure current handling capabilities various usual copper lead frame been replaced mounting conditions. direct-copper-bonded (DCB) alumina subInspection this table shows that depending strate possessing both high thermal conductance upon mounting technique, allowable output high electrical isolation (2500V). current increased about same There multiple advantages this isolated junction temperature. Conversely, chip hole-less packaging concept. 29OC cooler same operating conditions that translates into more reliable operation. Because dielectric breakdown voltage there such potentially large decrease juncis 6,000V although package only rated tion-to-case thermal resistance, possible 2500V(RMS) creep strike distances smaller chip same current, which TO-247 outline; would more than cover extra price (approxi2. electrical insulation barrier plastic enmately $0.50 production volumes) capsulated therefore protected from eninternal isolation. vironment; 3.Very low, isolated thermal resistance junctionIXYS plans introducing over part to-heatsink only types this revolutionary package during 1999. non-soldered interface between silicon chip Initial product will consist high power heatsink; MOSFETs offering industry's lowest on4.Ease assembly pressure mounting resistance this package outline. Future product screws) additional isolation interface mawill include IGBTs, IGBTs co-packaged with terial required mounting heatsink; diodes, ultra-fast Schottky diodes. Increased temperature power cycling
2000 IXYS rights reserved
Table: Performance Comparison ISOPLUS247 IXFR55N50 IXFX55N50 Mounted Using Various Interface Materials
Part Type Isolation Thickness Isolation R(th)js Tj=150C (K/W) 0.52 Tj=150C 28.1 Idc=15A
SIL-PAD trademark Bergquist
Material (mm) IXFR55N50 (Internal alumina DCB) External alumina Kapton SIL-PAD 2000(TM) Softface(TM) 0.63
Voltage (kV)
IXFX55N50 IXFX55N50 IXFX55N50 IXFX55N50 IXFX55N50
0.63 0.05 0.13 0.38 0.127
0.68 0.96 0.78 1.24 0.61
24.6 20.7 23.0 18.2 26.0
Figure Graphical comparison showing current handling capability ISOPLUS247 IXFR55N50 MOSFET IXFX55N50 MOSFET function heatsink mounting conditions. 125OC
Drain Current Amperes
IXFR55N50 IXFX55N50+ext.DCB
IXFX55N50 Kapton IXFX55N50 SIL-PAD 2000
IXFX55N50
Heatsink Temperature
2000 IXYS rights reserved
Technical Application
Combining Features Modules Discretes Power Semiconductor Package
Andreas Lindemann IXYS Semiconductor
Abstract
package power semiconductors been developed: Power semiconductor chips soldered onto ceramic substrate together with lead frame with five pins. Subsequently chips covered molding compound. This packaging method combines technologies module discrete assembly. Thus resulting component provides combination characteristics both families devices: components internally isolated from heatsink they will clamped onto. pins soldered into printed circuit board; circuit with adequate number pins incorporated package, using kind chip such MOSFETs, IGBTs, thyristors, diodes topology. pinouts defined according requirements electrical circuit design example avoiding current loops which together with very compact volume package faciliates inductive design power section. Designing scalable power sections broad range nominal power easy possibility connecting devices parallel. Reliability expected comparable modules' because matched thermal expansion coefficients silicon chips ceramic substrate they soldered onto. These features described this paper make family components advantageously applicable variety converters, such industrial automotive drives power supplies.
Packaging Technology
package will named ISOPLUS I4-PACin following. bottom view shown figure Basically, looks similar conventional discrete components such TO-247; however significant differences become obvious regarding cross section figure chips mounted solid metal leadframe, substrate [1]. consists ceramic substrate with copper layers bonded onto bottom side. bottom copper, used transfer operational power dissipation heatsink, visible package's bottom view figure ceramic isolates from copper layer, which structured corresponding printed circuit board visible figure copper carries chips, whose upper side wire bonded towards pattern pins. provide electrical mechanical protection, this subassembly transfer molded, thus creating typical black plastic package. versions package with different distances have been successfully introduced. Their outlines shown figure Height length correspond TO-247, width TO-264 industry standard packages. experiences gained IXYS' proprietary production discrete assembly, together with manufacturing already introduced TO-247 like ISOPLUS I4-PACTM, have helped install assembly process.
2000 IXYS rights reserved
Fig. bottom view five version
Fig. Cross section five version
Fig. Dimensional drawing three (left) five (right) version
construction described offers several benefits user components: large variety topologies with kinds power semiconductor switches incorporated. pinout defined electrically favourable way. power circuit internally isolated from heatsink. heatsink with appropriate geometry permits obtain creepage distance between pins ground more than without additional measures. Standard mounting processes used: pins soldered into printed circuit board. package simply directly clamped onto heatsink with industry standard spring [3], generally using some thermal compound achieve good heat transfer between package sink. This mounting procedure allows considerable savings, because external isolator required. High reliability achieved corresponding thermal expansion coefficients silicon chips substrate. following section gives more details several products with reference general features previously outlined. Section shows their significance exemplary applications.
Topologies, Components
This section presents some components ISOPLUS I4PACpackage recently developed currently under development. course there variety further possibilities. Numbering pins used following shown figure
Fig. pinout three (left) five (right) version
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Single Switches Single switches manufactured using types power semiconductors with three different kinds pinouts: three package figure (left) will used with same pinout TO-247 TO-264 components, drop replacement latters isolated components with larger chips smaller footprint respectively. high voltage version will realized based five package, omitting pins thus enlarging strike creepage distances required length figures (right) Please also note position gate besides source emitter terminal, which layout friendly will increase noise immunity. high current version will realized with five package, paralleling pins each main current path figures (right)
Fig. Phaselegs with MOSFETs (left), IGBTs with diodes (center) thyristors (right)
neighbouring gate source, emitter cathode pins respectively easy noise immune drive which enhance user friendlyness these components above market standards known from discrete components. course, boost- buck choppers generated based phaselegs, replacing transistor diode. However, possibilities even further, because structurability explained section permits introduce series connected thus exceptionally fast free wheeling diode. examples, this kind boost buck choppers with MOSFETs IGBT shown figure
Fig. high voltage single switches with diode (left), MOSFET (center) IGBT with diode (right)
Fig. high current single switches with diode (left), MOSFET (center) IGBT with diode (right)
Table gives basic ratings exemplary single switch ISOPLUS I4-PACpackage.
Fig. Buck chopper with MOSFET (left), boost chopper with MOSFET (center) IGBT (right), with series connected free wheeling diodes
Phaselegs Choppers five package incorporate complete phaseleg using MOSFETs, IGBTs with free wheeling diodes thyristors respectively shown figure Please note features small current loop between plus minus (2), thus inductance
Table single switches ISOPLUS I4-PAC
Please additionally note, that bridge configurations phaseleg, boost buck choppers with different types chips have same pinout. This faciliates designers' layout work enhances flexibility printed circuit board layouts several times different purposes.
Name IXFF24N100 IXBF9N160 IXBF40N160 IXDF30N120D1
Type MOSFET BIMOSFET BIMOSFET IGBT diode
Voltage rating UDSS 1000 UCES 1600 UCES 1600 UCES 1200V
Current rating ID90 IC90 IC90 IC90
Pinout, fig. fig. (right) fig. (right)
2000 IXYS rights reserved
table again basic ratings exemplary phaseleg chopper components ISOPLUS I4-PACpackage given.
Table phaselegs choppers ISOPLUS I4-PAC
Name FMM75-01F FDM21-05QC FMD21-05QC FID35-06C FCC21-08io
Type MOSFET phaseleg MOSFET buck MOSFET boost IGBT boost thyristor phaseleg
Voltage rating UDSS UDSS UDSS UCES URRM
Current rating ID90 ID90 ID90 IC90 ITAVM90
Pinout, fig. fig. (left) fig. (left) fig. (center) fig. (right) fig. (right)
Table rectifiers ISOPLUS I4-PAC
Name FBO16-08N FUO22-08N
Type single phase three phase
Voltage rating URRM URRM
Current rating IFAVM90 IFAVM90
Pinout, fig. fig. (left) fig. (right)
Rectifiers Another obviously advantageous topology ISOPLUS I4PACpackage single three phase rectifier shown figure rated table Again application friendly pinout been achieved with pins being separated from pins.
Proceeding features using ISOPLUS I4-PACcomponents will same described drives. industrial drives, inverter bridge complemented brake chopper again figure table single three phase rectifier figure table advantages this kind converter brake inverter power stage using ISOPLUS I4-PACcomponents compared standard discrete solutions obvious such lower design mounting expense, better operational behaviour increased reliability. Components like FMM75-01F aiming different kind electrical drives, mainly vehicle applications: ISOPLUS I4-PACcomponents contribute optimize automotive auxiliary drives with adaptable nominal power particularly supply drives battery supplied vehicles.
Power Supplies Power Factor Correction
Fig. single (left) three phase rectifier (right
Applications
Some typical applications ISOPLUS I4-PACcomponents with topologies using components desribed section discussed following:
Figure table deal with single three phase rectifier components ISOPLUS I4-PACpackage; they used variety power supplies. recent trend power supply technology leads power factor corrected rectification. This partially standards [5], limiting harmonic distortion mains input currents, additionally this topology offers benefits provide wide input voltage range gain highest amount active power plug with given fuse. availability incorporating control functions such single phase rectifiers built simple cost effective way. Their power section consists single phase rectifier series with boost converter [7]. While this topology advantageously integrated into power semiconductor module nominal powers above some 1kW, mainly discretes have been used lower power levels. However part count again mounting effort high conventional discrete solutions. This avoided using Isoplus ISOPLUS I4PACcomponents single phase rectifier such FBO1608N according figure (left), table boost chopper such FMD21-05QC FID35-06C according figure (center right), table chopper consists MOSFET with gate charge fast IGBT series connected 2000 IXYS rights reserved
Industrial Automotive Electrical Drives Self commutated converters drives phaseleg configurations shown figure (left center). This means, that very compact power section drive built, using three ISOPLUS I4-PACcomponents listed table power range easily enlarged parallelling several components without penalty thus increase stray inductances between printed circuit board chips, which avoided phaseleg topology. Switched reluctance drives require several boost buck components according figure table drives boost buck chopper thyristor bridge according figure (right) table
fast diodes representing free wheeling diode with reverse recovery behaviour outperforming single chip solutions [9], which particularly important switching frequencies 50kHz 100kHz typically used. user friendly pinout both components leads current flow avoiding wire crossings printed circuit board.
Conclusion
family power semiconductor components recently developed package been presented. package combines outline comparable discrete components with features multi chip modules, such isolation from heatsink capability integrate variety circuits. Topologies have been suggested power semiconductor components have been rated; typical applications have been discussed. features packaging concept make expect broad components belonging ISOPLUS I4-PACproduct family existing emerging applications.
References
Neidig: Neue Montagetechnik Leistungsmodule; Mikroelektronik, Vol. Issue Fachbeilage Mikroperipherik, 1991 Arnold, Locher: Revolution Discrete Isolation Technique; PCIM Europe, Issue 3/1999 Grafham: Cutting-Edge Moundown Methods Discrete Semiconductor Power Packages Boost Performance System Cost; PCIM Conference, 1998 IEC61000-3-2: 1995; /A1: 1997; /A2: 1998 IEC61000-3-4: 1998 Todd: Boost Power Factor Corrector Design with UC3853; Texas Instruments, 1999 Schneider, Chrystowski: Power Stage Boost Converters Perfect Match Controller ICs; PCIM Conference, 1993 Lutz al.: Applikationshandbuch IGBT- MOSFET-Leistungsmodule; Hrsg. Martin, Verlag Isle, Ilmenau, 1998 Rivet: Dioden Spar-PFC-Schaltungen; Design\Elektronik, 1999
2000 IXYS rights reserved
Packages Pressure Mounting
APPLICATION BRIEF AB-9801
Prepared Ralph Locher Introduction
pressure mount discrete power semiconductor packages heat sinks been rapidly growing many reasons. When properly executed, proven cost effective technique been shown that improve overall performance discrete power semiconductor. recognition this trend, IXYS brought discrete packages housing power MOSFETs, IGBTs FREDs further enhance overall performance equipment using these parts. Examples pressure mounted packages spring clip assemblies shown picture left. This application brief will discuss advantages these packages their mounting considerations.
Pressure Mounting Trends
spring clips bars secure TO-220, TO-247 TO-264 parts heatsink new. Screwing these parts heatsink seems easy suffers from following disadvantages: Their laborious because only part mounted time each screw must accompanied lock spring washer plus flat washer distribute force from screw head. Torque limiting screw drivers must used damage silicon chip within package interface used. Self-tapping screws should used wide variance applied pressure that either heatsink must drilled tapped additional will required secure screw. popular discrete packages mentioned above suffer from having only screw hole that screw tendency lift non-secured resulting increased case-to-sink thermal resistance R(th)cs. Finally specifications creep strike distances meet safety standards various safety agencies increases difficulties using screws mounting these packages grounded heatsink surfaces. Pressure mounting presents solutions these disadvantages follows: Elimination screw associated hardware facilitates agency approval; Springs apply pressure directly over silicon chip decrease R(th)cs; springs used gang mount multiple devices; Hardware minimized;
Pressure Mounted Packages
pressure mounting comes into own, IXYS brought packages designed take advantage this trend. They are: PLUS247package, also known `holeless' TO-247 should have been called `whole' TO-247; leaded TO-268 package, also known PAK. Their package designations letters respectively shown following illustration well picture above. major advantage these packages that they allow
PLUS-247 (IX_X)
package (IX_J)
semiconductor manufacturer completely fill package with more silicon maximum power efficiency. example, PLUS247 package, IXYS offer 500V HiPerFETMOSFETs with Rds(on)=0.08 (IXFX55N50) 600V/75A rated IGBT with companion FRED diode (IXGX50N60BU1). Likewise package, insert 500V MOSFET with Rds(on) 0.15 (IXFJ32N50) place pressure mounted TO-220. Indeed driving force J-package recognition that easiest, high power package upgrade power conversion equipment using TO-220 packages other equipment with limited headroom above board. Additionally preferred package high voltage since strike distance between pins 3.7mm (0.145"), greater than TO247, creep distance been increased 4.5mm (0.177"), partly enhanced barrier ridge between each pair pins.
2000 IXYS rights reserved
TO-264 Plus TO-247 Pack
Figure Comparison allowable current ratings 1000V/12A rated MOSFET chip four different packages. power semiconductors limited junction temperature that their maximum power output only good overall thermal design equipment. total thermal resistance junction-to-ambient R(th)ja subdivided into three components, namely thermal resistances between junction-to-case, case-to-sink sink-to-ambient. equation form: R(th)ja R(th)jc R(th)cs R(th)sa larger larger silicon chips have been encapsulated into discrete housings, importance R(th)cs grown because decreased same rate R(th)jc. R(th)cs function many factors, explained next section, important contributor area heat flow path. turns that PLUS247 package same area TO-264 package, that they share same value R(th)cs 0.15K/W. shown Figure this results immediate increase about current handling capability same size silicon chip housed standard TO247 package. smaller package shares same value TO-247. Pressure Mounting Considerations R(th)cs function many factors, such flatness surface preparation both discrete package heatsink, type insulating washer thermally conductive compound, mountdown pressure and, already mentioned, area heat flow path. best conducting contact metal metal there always voids contact surface finish. Depending upon thermal electrical requirements system, packaging engineer will choose thermal grease and/or some form lubricating insulating washer between device heatsink eliminate voids. requirements preparation mounting area heatsink pressure mounted parts depends upon selection thermally conducting compound washer.
2000 IXYS rights reserved
Thermal Grease Thermal greases effective reducing R(th)cs where maximum between surfaces less than 25µm (0.001"). This means that extruded aluminum heatsinks will require some surface milling housings larger than TO-220 because nominal flatness specification 4µm/mm (0.004"/in). minimize effects heatsink finish, heatsink mounting surfaces should flat within 0.001"/in roughness should exceed microinches. IXYS recommends Corning heatsink compound Berulub FZ1E3 (Bechem, silicone free) which contains zinc oxide particles reduce R(th)cs. R(th)cs `greased' interface typically 30-50% less than joint varies less with pressure. grease should rolled onto heatsink surface thickness 50µm (0.001" 0.002"). range 150kPa 300kPa (20-40 PSI) usually sufficient ensure good thermal conduction. Thermally Conductive Pads Today packaging engineer literal cornucopia pads choose from meet needs isolation voltage, environmental restrictions, moisture thermal conductance. Reference more thorough comparison various materials used these pads. Mica washers coated with thermal grease both sides provide very cost, good thermal conductive joint with high dielectric strength. major disadvantage brittleness susceptibility puncture burrs either heatsink semiconductor package. better choice meet high isolation voltage requirements ceramic washers because they combine high dielectric strength with good thermal conductivity. However, they also brittle require thermal grease fill voids between interface layers. IXYS manufactures Direct-Copper-Bonded (DCB) ceramic substrates multitudinous power module families products. developed pads TO-247 TO-264 packages, which bought individually. Again either thermal grease non-insulating grease replacement material such Q-Pad from Bergquist Thermstrate® from Power Devices. Both materials conform mating surfaces when exposed modest heat pressure achieve relatively thermal resistance. There many objections thermal greases their messiness, incompatibility with soldering systems, possibility outgassing drying with time. There also been much research work performed develop `low pressure' types interface tabs, which power industry probably thank industry developing high speed digital products that requir
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