Reliability Study of Microwave GaAs Field-Effect Transistors

A two-phase study was performed to investigate basic failure mechanisms, alternate fabrication methods, and operational life times of low-noise microwave MESFETs fabricated on GaAs channel layers grown by liquid-phase epitaxy. The basic sub-elements of the FET were investigated, and a Cr link for connecting the Al gate to Au bond pad was developed and incorporated into an improved FET. The first high-temperature (230 to 270°C) accelerated life tests of GaAs FETs under operational low-noise bias conditions (VD = 5 V, ID = 10 mA) were performed, and decreasing saturated drain current was found to be the primary failure mode below 270°C. An activation energy Ea = 1.5 eV was determined for this mode, and an MTTF of 2 × 108 hr at 100°C is projected. At 270°C the primary failure mode is catastrophic gate failure caused by Au-Al intermetallic formations. Comparisons of parameter aging data support a relationship between dc and rf failure criteria, but considerable scatter appears to weaken its usefulness for individual devices.