Depletion Mode GaAs IC Reliability

This work presents results of MSI GaAs reliability testing. Previously reported methods of element-based IC reliability prediction are verified and additional element results are briefly described. This report is the culmination of reliability testing on over 2700 circuit elements and 100 ICs. Each of the failures have been classified and failure rate distributions have been established where appropriate. Element studies confirmed gate metal diffusion is the primary failure mechanism. These findings are used in the determination of IC failure distributions. Two accelerated lifetests, totaling over 100,000 (non-derated) device-hours, have been completed on MSI (30 gate equivalency) four-bit ripple counters. An additional lifetest has been completed on a larger scale (300 gate equivalency) ASIC digital circuit. A comparison of IC and element median lives reveals a nonlinear relationship between integration level and reliability. For example, the single FET median life at 150°C was found to be only 3 times longer than the median life of the 300 gate equivalency (1000 MESFET) device. Thus, IC failure rates are less than whole multiples of FET failure rates. IC lifetests have also indicated that reliability levels vs fabrication date are rapidly improving for GaAs ICs. 30 Gate devices tested in the most recent lifetest have 150°C median lives ten times longer (6.5E5 vs 6.0E4 hrs) than ICs manufactured six months earlier. Preliminary data on microwave ICs indicate similar results.