IRED CHIP DEGRADATION STUDIES Honeywell engaged ongoing study degradat

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Summary SEC450 GaAs:Si IRED Chip Long-Term Operating Life Study
IRED CHIP DEGRADATION STUDIES Honeywell engaged ongoing study degradation radiant output over time function temperature SEC450 GaAs IRED (gallium arsenide infrared emitting diode) chip. This IRED chip used Honeywell's High Reliability IRED well variety commercial components assemblies. results study through July 1986 presented below. INTRODUCTION Honeywell committed manufacture reliable, high quality optoelectronic products. 9001 quality system maintained, providing necessary controls assure that product meets exceeds specified requirements. assure contin-uing 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. SEC450 chip gallium arsenide (GaAs) silicon doped (GaAs:Si) infrared emitting diode (IRED) chip which widely used component packages higher level assemblies. This report details results ongoing study characterize fundamental long-term degradation mechanisms SEC450 which will allow projection expected behavior under various conditions Honeywell packages. 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.
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Figure
Semiconductor Failure Rate Function Time
Early "infant mortality" failures
Random failures Useful life
Wearout failures
Failure rate
Low, constant failure rate
Operating life
Components utilizing SEC450 IRED chip basic package types: hermetic glass-lens-to-metal-header devices plastic molded-lead-frame devices. Figure summarizes these packages their properties. Figure Product Honeywell Products Utilizing SEC450 Chip Package Type Hermetic Pigtail Hermetic Pillpack Hermetic TO-46 Thermal Resistance Heat Sink) 785°C/W 370°C/W 670°C/W 750°C/W Maximum Operating Temperature 125°C 125°C 125°C 85°C 85°C
SE1450 SE1455 SE2460 SE3450 SE5450
SEP8505 Plastic SEP8506 Plastic Sidelooker Plastic Endlooker
SEP8507
85°C
Summary SEC450 GaAs:Si IRED Chip Long-Term Operating Life Study
SEC450 CHIP STRUCTURE Gallium arsenide, silicon doped construction shown Figure GaAs junction formed liquid-phase-epitaxy (LPE) grown GaAs layers onto GaAs substrates. Wafer processing produces final chip pattern with metal contacts. Radiance emission occurs over full area chip junction with side surface emission, with obstruction surface metal bond pad. mechanical adhesion chip metal header lead frame employs gold-tin attach. Gold ball bonding contacts surface N-side junction. Figure SEC450 IRED Structure QUANTUM EFFICIENCY Optical power output IRED directly proportional applied forward current: Equation Where Optical power output watts IRED 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 [exp(qVF/kT)] [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 POWER OUTPUT DEGRADATION THEORY Optical power output degradation during operation been established wear-out mechanism SEC450 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 being created. Honeywell approach this requirement summarized this section. 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). 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. This related silicon dopant, since diffusion component
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Summary SEC450 GaAs:Si IRED Chip Long-Term Operating Life Study
changes only silicon doped GaAs structures. Visual inspection degraded devices shows only general "dimming" radiant output, with "dark-line-defects" common zinc diffused GaAs double heterostructure GaAlAs devices. TIME DEPENDENCE Time dependence IRED degradation been measured Honeywell others. Logarithmic degradation rate versus square root time wide range degradation rates been observed. degradation rate described 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 STATISTICAL VARIATION IRED DEGRADATION Analysis IRED degradation statistical process which deals with varying degradation rates within given sample units. Using statistically significant samples, log-normal distribution degradation rate SEC450 IRED chip been observed. Gen-erally, IRED operating life defined point time when power output drops one-half initial value (50% drop). end-of-life data IRED group tested failure plotted log-normal scale population versus logarithm operating lifetime, result should straight line with point population representing median half-life group. median half-life IRED product useful figure merit comparing products projecting system lifetimes (see Figure 15). DESIGN ANALYSIS BURN-IN this study, SEC450 IRED chip assembled hermetic TO-46 packages placed heatsinked burn-in several temperatures forward current conditions. Initial periodic measurements I-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 burn-in study. data Figure plotted Figures expected straight line Figure temperature dependence half-life yields measured activation energy 0.50 current dependence half-life plotted Figure with temperature effects uncorrected, Figure with temperature effects 0.50 activation energy removed. graphs show essentially current dependence when junction heating current variations removed. These results general agreement with similar studies done here Honeywell GaAlAs fiber optic IRED structures.
TEMPERATURE/CURRENT DEPENDENCE temperature current dependence degradation process described Arrhenius's Law: Equation [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 equations describe acceleration IRED optical power output degradation increasing junction temperature and/or operating current. Because heat sinking thermal resistance have direct effect actual junction operating temperature, these parameters also affect IRED degradation rate.
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Summary SEC450 GaAs:Si IRED Chip Long-Term Operating Life Study
Figure SEC450 Burn-In Test Summary Chip Type: GaAs:Si 0.010" 0.012" Temp Figure (mA) Units Burn-In Hours 14,600 18,000 18,000 10,400 14,000 18,000 14,000 14,000 Units Fail Median Half-Life Hours 32,000 32,000 25,000 60,000 32,000 40,000 28,000 From these results, values equations determined, allowing general equation optical power output degradation SEC450 chip. Equation (t=0) exp[-t /{A1 (IF)n exp(EA /kT)}]0 Equation {0.1 (0.50 kT}]0.5 yielding median half-life tHL: Equation 0.048 [5800 This equation plotted Figure giving general Arrhenius plot SEC450 IRED chip. This plot used predict half-life performance SEC450 IRED chip various packages when junction temperature calculated using appropriate thermal resistance power dissipation values. Figures through show SEC450 changes small large optical power output changes. radiative current component change with significant IRED degradation clearly shown Figure Figures show reasonably good straight line logarithmic optical power output versus square root time. Figure Typical Current Dependence Degradation Time Constant SEC450 GaAs:Si IRED Chip
Arrhenius Plot SEC450 Burn-In Data
Figure
Current Dependence SEC450 Burn-In Data
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Summary SEC450 GaAs:Si IRED Chip Long-Term Operating Life Study
Figures show log-normal statistical variation IRED degradation. 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 behavior. Figure Arrhenius Plot SEC450 GaAs:Si IRED Chip Figure Typical Change During Power Output Degradation SEC450 IRED Chip
Figure Typical Change During Power Output Degradation SEC450 IRED Chip
Figure Typical Change During Power Output Degradation SEC450 IRED Chip
Figure Typical Change During Power Output Degradation SEC450 IRED Chip
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Summary SEC450 GaAs:Si IRED Chip Long-Term Operating Life Study
Figure SEC450 GaAs:Si 125°C, Figure SEC450 Log-Normal Distribution 125°C, Burn-In Time 14,000 Hours, Projected Median Half-life 28,000 Hours
Figure SEC450 GaAs:Si 125°C,
Figure SEP8506 GaAs Sidelooker IRED Log-Normal Distribution 100°C, Burn-In Time 2,100 Hours, Projected Median Half-life 200,000 Hours
Figure SEC450 Log-Normal Distribution 125°C, Burn-In Time 14,000 Hours, Projected Median Half-life 60,000 Hours)
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Summary SEC450 GaAs:Si IRED Chip Long-Term Operating Life Study
OPERATIONAL RELIABILITY PREDICTION IRED optical power output (PO) increases with forward current (IF). However, increasing forward current also increases power dissipation (Pd) chip junction temperature (Tj). This results decreased optical power output device operating lifetime. Data sheets IRED products allow systems designer determine optical power output switch CTR) function IRED forward current. systems designer will need also factor effect IRED forward current operating lifetime select optimum operating point. relationship chip junction temperature operating condition Equation where Chip junction temperature (°C) Ambient operating temperature (°C) Package thermal resistance-junction ambient (°C/W) Power dissipation (watts) Applied forward voltage (volts) Applied forward current (amps) Arrhenius plot SEC450 half-life (Figure along with application's calculated junction temperature used predict median half-life particular SEC450 package operating condition. example Honeywell SEP8506 sidelooker package given. SEP8506 GaAs SIDELOOKER IRED EXAMPLE common application SEC450 IRED chip plastic sidelooker package opto switch assemblies. Typically, part operated 100°C ambient temperature. maximum operating temperature 85°C operation above this temperature recommended. will calculate expected half-life 100°C compare results actual burn-in data that condition. 100°C 750°C/W 1.25 0.020 118.75°C 1,000 (°K) 2.55 From Figure determine that 1,000 2.55 that 125,000 hours. comparison, figure shows actual SEP8506 burn-in data which projects 200,000 hours 100°C indicating reasonably good agreement. Figure shows predicted variation half-life versus ambient temperature 25°C, approximately years half-life projected. Figure shows plot median half-life versus temperature three different current levels SE1450/1455 IREDs. statistical distribution IRED degradation process must considered system designer. Figure shows that even though median half-life product will 200,000 hours years) 100°C, approximately distribution will fail 8,800 hours year).
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Figure Arrhenius Plot SEP8506 Sidelooker IRED Product
Summary SEC450 GaAs:Si IRED Chip Long-Term Operating Life Study
final consideration system tolerance IRED degradation. data calculations this report half-life where drop optical power output constitutes failure. Specific system applications fail very different degradation points which will significantly shift time failure. SEC450 IRED PRODUCT'S OPERATING LIFETIME Figures previous discussion development theoretical measured long-term behavior SEC450 IRED chip summarized into projections typical operating lifetimes IRED products which utilize SEC450 chip. Three current conditions projected. Figure SE1450/1455 Typical Operating Lifetime Figure SE3450/5450 GaAs Hermetic TO-46 IRED Typical Operating Lifetime Figure SE2460 GaAs Pillpack IRED Typical Operating Lifetime
Figure SEP8505 GaAs Plastic Endlooker IRED Typical Operating Lifetime
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Summary SEC450 GaAs:Si IRED Chip Long-Term Operating Life Study
Figure SEP8506 GaAs Sidelooker IRED Typical Operating Lifetime Figure SEP8507 GaAs Plastic Endlooker IRED Typical Operating Lifetime
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