Effects of Si3N4, SiO, and polyimide surface passivations on GaAs MESFET amplifier RF stability

The effects of silicon nitride, silicon monoxide, and polyimide MESFET passivations on amplifier RF stability have been examined. GaAs MESFET amplifiers subjected to biased life tests show a time dependent "drift" in RF performance from turn on to hundreds of hours. These short- and long-term instabilities in performance have been correlated with surface effects. It was found that passivation with a surface dielectric such as Si
3
N
4
can eliminate this drift mechanism, while other dielectrics either delayed the onset of drift or had no desirable effects. Methods for deposition of these dielectrics and the relative merits of these methods are discussed.