Reliability evaluation of GaAs FETS

The objective of this program was to assess and establish the reliability and life characteristics of commercially available, medium power GaAs MESFETs and to identify any associated failure mechanisms. The devices chosen for this study were the TI MSX802 and laboratory devices and devices from three other manufacturers, A, B, and C. All devices were hermetically packaged and had approximately 0.5 W output power. The study included device physical, electrical (CW and pulsed), and environmental characterization; electrical (CW and pulsed) and environmental stress tests; and failure analysis. All the tests were completed during the program. During the electrical characterization no device had significant changes in electrical parameters following operation for 1000 hours at room temperature. No devices lost hermeticity or had any significant changes in dc current-voltage characteristics following any of the environmental characterization tests (mechanical and thermal stresses). There were some correlations between the various device structures and the electrical stress test results from those structures. During the environmental stress tests some of the device types did not have sufficient failures in 1000 hours, even with a 215 C heat sink, to derive an activation energy. Others had an activation energy of approximately 1.8 eV and an extrapolated median life of approximately 10 to the 12th power hours at room temperature. Both catastrophic and gradual (1 dB output power degradation) failures were observed; some could be associated with specific failure mechanisms and others could not.