Reliability results of HBTs with an InGaP emitter

摘要

Accelerated lifetest results are presented on HBTs with InGaP emitters. An Arrhenius plot indicates the existence of a temperature dependent activation energy, E_a. A low E_a mechanism dominates above T_j ～380℃ and a high E_a mechanism dominates at lower temperature. The critical transition temperature between regimes is determined using the method of maximum likelihood. The difference in E_a's between low and high temperature regimes is statistically significant. A comparison is made between lifetimes determined from at temperature vs. 40℃ data. No significant difference is observed indicating that beta degradation can be monitored at temperature only and cooling to low temperature is not necessary. Other comparisons indicate that junction temperatures up to 367℃ can still provide good estimates of lower temperature behavior. By the method of maximum likelihood, the predicted MTTF at T_j = 125℃ is 7.6 x 10~9 h with 95% CBs of [6.4 x 10~8, 8.9 x 10~(10)]. Given the typical industry standard of 1 x 10~6 h, the reliability requirements are easily met. It is suggested that the standard of 1 x 10~6 h does not adequately capture failure time variation and that a better specification is in terms of fails in time (FITs). The 10 year average FIT rate at 125℃ is found to be negligible. Assuming a much higher junction temperature of 210℃, the average failure rate climbs to ～5 FITs with an upper 95% confidence bound of ～40 FITs.