A comparative reliability study: Aluminum gate vs. gold-base gate GaAs MESFETs

Temperature accelerated tests, with and without bias, show that the considerable MTTF advantage, at elevated temperature, of Al gate MESFETs over gold-base gate devices diminishes at lower temperatures. This is due to the difference in the activation energies, EA, of the respective gate metallization systems (EA= 0.8-1.2 ev for Al-gate and EA= 1.3-1.8 ev for gold-base gate devices). The standard deviation of the logarithms of the lifetimes, σ, was less than 0.3 in all cases. The primary mode of failure for all types of devices was a gradual degradation of IDSS. Impurity profiles indicated that the associated failure mechanism is a gate metal interaction with the epi-layer. It has been established that the degradation of the low-field resistance, RDS, is not an index of contact resistance degradation, but the logical consequence of the above failure mechanism.