Reliability of Gate Metallization in Power GaAs MESFETs

Failure modes have been studied on 0.5 ?m gate power GaAs MESFETs with Al, Ti/Al and Ti/Al/Ti gate metallization, respectively. It has been found that the dominant failure modes are gate metal disconnection for Al gate, catastrophic burn out for the Ti/Al gate and gate breakdown voltage degradation for the Ti/Al/Ti gate under D.C. operational life tests. The degradation mechanisms have been clarified using SEM, microprobe-AES and SIMS. It is shown that Ti/Al, gate is the most reliable among these three kinds of FETS.