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Summary SEC555 AlGaAs:Si IRED Chip Long-Term Operating Life Study
IRED CHIP DEGRADATION STUDIES Honeywell ongoing study degradation radiant output over time function temperature current SEC555 aluminum gallium arsenide (AlGaAs) infrared emitting diode (IRED) chip. This IRED chip used variety Honeywell's commercial components assemblies. results this study through October 1987 presented below. INTRODUCTION Honeywell committed manufacture reliable, high quality optoelectronic products. ISO9001 based quality system maintained, providing necessary controls assure that products meet exceed specified requirements. assure continuing performance under conditions environmental mechanical stress, periodic reliability testing performed samples from production. products thoroughly tested characterized before introduction, with particular attention given those parameters which relate operational life reliability. Optoelectronic components, being semiconductors, share with other semiconductor devices susceptibility certain mechanical failure modes. acceptable, semiconductors must withstand stress temperature, humidity, mechanical shock vibration. industry employs established test methods reliability projection techniques ensure acceptability. Degradation radiant output reliability factor that unique infrared emitting diodes (IREDs). Honeywell pioneered development characterization model which projects effect this phenomenon component reliability. Validation this model continues Honeywell products, those other manufacturers, tested. addition, resulting knowledge factors affecting reliability aids improvement products processes. SEC555 chip aluminum gallium arsenide silicon-doped (AlGaAs:Si) infrared-emitting diode (IRED) chip. SEC555 chip widely used Honeywell component packages higher-level assemblies. This report details results ongoing study characterize fundamental long-term degradation mechanisms SEC555. results contrasted behaviour older GaAs:Si SEC450 IRED chip. MECHANICAL RELIABILITY Mechanical integrity optoelectronic components, range stress conditions over which reliable operation results, critical importance system designer. Optoelectronic components exhibit failure rates mechanical wear-out characteristics which well known "bath curve" (Figure common semiconductor devices. IRED power output degradation wear-out mechanism. Components utilizing SEC555 IRED chip available basic package types: hermetic glass-lens-to-metal-header devices plastic molded-lead-frame devices. Figure summarizes these packages their properties. Figure Semiconductor Failure Rate Function Time
Early "infant mortality" failures Random failures Useful life Wearout failures
Failure rate
Low, constant failure rate
Operating life
Figure Honeywell Optoelectronics Products Utilizing AlGaAs:Si Chip Product Package Type Hermetic TO-46 Plastic TO-46 Plastic T13/4 Thermal Resistance Heat Sink) 370°C/W 750°C/W 750°C/W Maximum Operating Temperature 125°C 125°C 100°C
SE3470 SE5470 SEP8790 SEP8703
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Honeywell Europe S.A.
Summary SEC555 AlGaAs:Si IRED Chip Long-Term Operating Life Study
SEC555 CHIP STRUCTURE SEC555 IRED chip aluminum gallium arsenide, silicon-doped (AlGaAs:Si) structure. structure based original 1977 paper Ralph Dawson, "High-Efficiency Graded Band-Gap AlGaAs Light Emitting Diodes," Journal Applied Physics 2485-92, 1977. Figure shows chip construction. AlGaAs junction formed liquid-phase-epitaxy (LPE) growth AlGaAs layers onto GaAs substrates. Wafer processing produces final chip pattern with metal contacts. Radiant emission occurs over full area chip junction with side surface emission. metal bond pads partially obstruct surface emission. Figure SEC555 Structure
0.018
QUANTUM EFFICIENCY Optical power output IRED directly proportional applied forward current: Equation Where Optical power output watts external quantum efficiency Energy photon emitted Applied forward current amps Optical power output degradation IRED fixed operating current (IF), which normal mode industrial applications, will occur result decrease IRED external quantum efficiency CHARACTERISTICS forward current-voltage characteristic semiconductor junction diode current components, diffusion current space charge recombination current: Equation A[exp(qVF/kT)] B[exp(qVF/2kT)] Where Electronic charge (1.6x10-19 Forward current Forward voltage Boltzmann's constant Junction temperature Diffusion current coefficient Space-charge recombination current coefficient IRED, only diffusion current component contributes radiative (light emission) current. space-charge recombination current contributes non-radiative current. ratio radiative non-radiative current fixed forward current, which normal mode industrial applications, directly affects IRED external quantum efficiency. Quantum efficiency directly relates IRED emitted power previously shown equation (1). AlGaAs VERSUS GaAs AlGaAs:Si IRED chip developed Dawson become popular optoelectronics industry because achieves higher quantum efficiency than industry standard GaAs:Si IRED chip developed 1960s.
0.018
surface pattern 0.005 0.005 type AlGaAs type AlGaAs
Gold bonding 0.0064 diameter
Metal header lead frame
Metallization
mechanical adhesion chip metal header employs gold-tin eutectic attach. Mechanical adhesion chip metal lead frames employs gold-filled conductive epoxy. Gold ball bonding contacts surface N-side junction. POWER OUTPUT DEGRADATION THEORY Optical power output degradation during operation been established wear-out mechanism SEC555 IRED chip. Although devices degrade this manner with time, they with widely varying rates, resulting non-constant failure rate. This process varies also with temperature operating current. Circuit system designers must have knowledge magnitude typical worst case IRED degradation assure adequate optical power output throughout intended design life system. Honeywell approach this requirement summarized following section.
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Summary SEC555 AlGaAs:Si IRED Chip Long-Term Operating Life Study
AlGaAs chip differs from GaAs chip three electro-optical characteristics: power output times higher peak wavelength instead forward voltage (VF) slightly higher higher quantum efficiency attributed photon recycling graded bandgap p-AlGaAs layer ("Photon Recycling AlGaAs:Si Graded Band-Gap LEDs," Appl. Phys. 6353-6362, 1979). theory that photons emitted downward AlGaAs layer absorbed narrower bandgap material re-emitted longer wavelength, with most downward emitting photons getting IRED chip. uniform bandgap p-GaAs layers this photon recycling does occur. peak wavelength shift increased forward voltage AlGaAs versus GaAs both wider bandgap junction with aluminum addition crystalline lattice. Previous studies have shown from experimental data that GaAs:Si (SEC450) IRED chip ages radiative ("kT") current component decreases fixed forward current decrease diffusion current coefficient radiative current decrease causes decreased IRED optical power output. mechanism degradation appears bulk diffusion which related silicon dopant since diffusion component changes only silicon doped GaAs structures. will shown later data this study, similar decreases radiative output decrease diffusion current coefficient occur AlGaAs:Si IRED chip possibly related photon recycling phenomena. Visual inspection degraded devices shows only general "dimming" radiant output both GaAs:Si AlGaAs:Si structures with dark-line-defects. Dark-line-defects well known zinc-diffused GaAs double-heterostructure AlGaAs devices. TIME DEPENDENCE Time dependence GaAs:Si IRED degradation been measured Honeywell others. Logarithmic degradation rate versus square root time wide range degradation rates been observed. degradation rate described simple one-stage equation Equation Po(t) Po(t=0)[exp(-(t/)0.5)] Where Po(t) Optical power output time (t=0) Initial optical power output Total operating time Degradation characteristic time constant will shown later experimental data, SEC555 AlGaAs:Si IRED chip exhibits multistage degradation process with time dependence more complex than above equation. TEMPERATURE/CURRENT DEPENDENCE temperature current dependence GaAs:Si IRED degradation process well described Arrhenius's Law: Equation o[exp(EA/kT)] Where current dependent assumed have power-law relationship. Equation A1(IF)n[exp(EA/kT)] Where Constant proportionality Applied forward current amps Exponent current dependence Thermal activation energy Boltzmann's constant Operating junction temperature above equations which GaAs:Si IRED work well multi-stage power output degradation mechanism AlGaAs:Si. suitable model which describes effects temperature and/or operating current AlGaAs:Si IRED been developed yet. STATISTICAL VARIATION IRED DEGRADATION Analysis IRED degradation statistical process which deals with varying degradation rates within given sample units. Using statistically significant samples, previous studies have shown log-normal distribution degradation rate GaAs:Si SEC450 IRED chip. this study actual failures (for power output drop) have been observed, projections time failure indicate log-normal failure distribution also, despite more complex degradation process. Generally, IRED operating life defined point time when power output
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Summary SEC555 AlGaAs:Si IRED Chip Long-Term Operating Life Study
drops one-half initial value (50% drop). end-of-life data IRED group tested failure plotted log-normal scales population versus logarithm operating lifetime, straight line with point population representing median half-life group should result. median half-life IRED product useful figure merit comparing products projecting system lifetimes. DESIGN ANALYSIS BURN-IN this study SEC555 IRED chip assembled hermetic TO-46 packages placed heat-sinked burn-in several temperatures forward currentconditions. Initial periodic measurements ofI-V-P data (forward current, forward voltage, optical power output) were recorded using Teradyne A360 test system. Thermal resistance measurements along with power dissipation calculations determined typical chip junction temperature each burn-in condition. Figure summarizes results date ongoing burn-in study. parallel study SEC456 GaAs:Si IRED chip compared SEC555 data Figure clear that AlGaAs:Si chip behaves differently during aging. GaAs:Si chip exhibits well-behaved temperature/current dependence degradation rate. AlGaAs:Si chip to-date does exhibit definite degradation rate temperature dependence. AlGaAs:Si chip shows some current dependence degradation parameters projected. conditions 125°C, there failures million device-hours.
Figure SEC555 Burn-In Test Summary (Chip Type: AlGaAs:Si, 0.018 0.018 in.) Temperature 80°C 100°C 125°C 125°C 125°C 125°C 125°C Forward Current Units Burn-In Hours 15,618 15,618 15,690 15,628 15,690 15,628 15,628 Units Fail Total Device Hours 390,450 390,450 392,250 390,700 392,250 390,700 390,700 Median HalfLife Hours 50,000 120,000 250,000 160,000 250,000 40,000 40,000
Figure GaAs:Si AlGaAs:Si Burn-In Comparison Chip Type: SEC456 GaAs:Si 18x18, SEC555 AlGaAs:Si 18x18 Package Type: Hermetic TO-46 Burn-In Sample: Units Burn-In Condition Burn-In Time: 15,600 Hours, 390,000 Device-Hours Failure (50%) Power Output Drop Case Temperature 80°C 100°C *125°C 125°C *125°C 125°C 125°C
Forward Current
GaAs:Si Fail Median Half-Life 150,000 hours 80,000 hours 26,000 hours 95,000 hours 26,000 hours 21,000 hours 18,000 hours Fail
AlGaAs:Si Median Half-Life 50,000 hours 120,000 hours 250,000 hours 160,000 hours 250,000 hours 40,000 hours 40,000 hours
Same group
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Summary SEC555 AlGaAs:Si IRED Chip Long-Term Operating Life Study
Figures show SEC555 IF-VF changes small large optical power output changes during burn-in. radiative current component change with significant IRED degradation clearly shown Figure Figure shows that non-radiative current component does change even significant IRED degradation. These IF-VF characteristics AlGaAs:Si agreement with earlier studies GaAs:Si. behaviour power output versus time various burn-in conditions plotted Figures 10-13. Figures clearly show two-stage degradation process which first stage rapid degradation followed second stage very slow degradation. Figures lower temperatures lower currents exhibit only stage constant degradation rate. clear whether lower stress conditions simply delay onset second stage slow degradation, remove conditions required second stage occur. power output versus time graphs indicate first stage degradation fact have temperature/current dependence degradation rate much like previous GaAs:Si studies. Figures show power output versus time plots SEC555 chip much lower temperature/current stress conditions (25°C, 100°C, where virtually degradation power output occurs during initial 1500 hours operation, which supports this conjecture first stage degradation rate. Figure shows log-normal statistical variation IRED degradation even with stage degradation rate. dashed line shows actual burn-in hours. solid circle represents units with measured half-life. open circles represent extrapolated half-life using expected logarithmic power output versus square root time behaviour. Figures demonstrate that first stage degradation process fits this behaviour. evaluation competitive AlGaAs:Si products conducted determine this stage degradation unique Honeywell product typical industry product. Figure summarizes results burn-in comparison between Honeywell competitive AlGaAs:Si suppliers, with Honeywell exhibiting slowest degradation process. power output versus time plots figures 18-20 indicate stage degradation process characteristic AlGaAs:Si product across industry, with manufacturer's process having significantly high failures during firststage degradation process. CONCLUSIONS burn-in study SEC555 AlGaAs:Si IRED chip demonstrated product fundamentally reliable with fewer failures than GaAs:Si IRED chip when failure defined drop power output. operating conditions 125°C, SEC555 IRED chip zero failures million device hours based sample size units tested over 15,600 hours (see Figures Significant differences degradation characteristics from previous GaAs:Si IRED studies were observed. two-stage degradation process with rapid initial degradation followed second stage very slow degradation exhibited. Applications which require power output change IRED chip should restricted moderate temperatures currents avoid failures. projections SEC555 product reliability over temperatures and/or currents other than burn-in study conditions made yet. burn-in comparison competitive AlGaAs:Si IRED products indicate stage degradation process unique Honeywell product, that Honeywell SEC555 IRED chip most reliable AlGaAs:Si products industry.
Honeywell reserves right make changes order improve design supply best products possible.
Summary SEC555 AlGaAs:Si IRED Chip Long-Term Operating Life Study
Figure Typical Po-VF Change During Power Output Degradation AlGaAs:Si IRED Chip
Figure Typical Po-VF Change During Power Output Degradation AlGaAs:Si IRED Chip
Relative power output
AlGaAs: UNIT 100°C 1.68 after 6500 hours 6500 hours
Relative power output
1E-1
1E-2
AlGaAs: UNIT 100°C after 6500 hours 6500 hours
1E-1
1E-2
1E-3 Forward voltage
1E-3 Forward voltage
Figure Typical IF-VF Change During Power Output Degradation AlGaAs:Si IRED Chip
1E-2
Figure Typical IF-VF Change During Power Output Degradation AlGaAs:Si IRED Chip
1E-2
Forward current
1E-3
Forward current
AlGaAs: UNIT 100°C after 6500 hours mV/decade "2KT" slope shift current 6500 hours
1E-3
AlGaAs: UNIT 100°C 1.68 after 6500 hours mV/decade "2KT" slope shift current 6500 hours
1E-4
1E-4
1E-5
1E-5
Forward voltage
Forward voltage
Figure SEC555 Power Output Time Plots (TCASE 80°C, Burn-In Time 15,618 hours)
Relative power output (dB)
Figure SEC555 Power Output Time Plots (TCASE 100°C, Burn-In Time 15,618 hours)
Relative power output (dB)
Square root time
(hours
Square root time (hours
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Summary SEC555 AlGaAs:Si IRED Chip Long-Term Operating Life Study
Figure SEC555 Power Output Time Plots (TCASE 125°C, Burn-In Time 15,691 hours)
Relative power output (dB)
Figure SEC555 Power Output Time Plots (TCASE 125°C, Burn-In Time 15,629 hours)
Relative power output (dB)
Square root time
(hours
Square root time (hours
Figure SEP8703 Plastic Package, SEC555 AlGaAs Chip 25°C, Burn-In Time 1510 hours)
Relative power output (dB)
Figure SEP8703 Plastic Package, SEC555 AlGaAs Chip 100°C, Burn-In Time hours)
Relative power output (dB)
Square root time
(hours
Square root time (hours
Figure SEC555 Plastic Package, Typical Log-Normal Distribution (TCASE 125°C, Burn-In Time 15,628 hours)
1E-6
Figure Competitive Burn-In Summary Chip Type: AlGaAs:Si Package Type: Hermetic TO-46 (TCASE 100°C, Burn-In Time 5600 hours)
Manufacturer Number units Total devicehours Number units fail Median halflife hours
Half life (hours)
1E-5 40,000 hours
Honeywell
56,000
50,000
1E-4
Actual burn-in time
56,000 20,000
1E-3
56,000 6500
Failure percentage
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Summary SEC555 AlGaAs:Si IRED Chip Long-Term Operating Life Study
Figure Competitive Burn-In, Manufacturer Power Output Time Plots 100°C, Burn-In Time 5600 hours)
Relative power output (dB)
Figure Competitive Burn-In, Manufacturer Power Output Time Plots 100°C, Burn-In Time 5600 hours)
Relative power output (dB)
Square root time
(hours
Square root time (hours
Figure Competitive Burn-In, Honeywell SE3470, Power Output Time Plots 100°C, Burn-In Time 5600 hours)
Relative power output (dB)
Square root time (hours
Honeywell reserves right make changes order improve design supply best products possible.
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