Reliability physics of compound semiconductor transistors for microwave applications

This paper reviews the reliability problems of compound semiconductor trans istors for microwave applications. These devices suffer from specific failu re mechanisms, which are related to their limited maturity, with the except ion of the GaAs MESFETs, which exhibit a stable technology and an assessed reliability. The metallizations employed in high electron mobility transist ors (HEMTs) already benefit from this assessment. However, HEMT are affecte d by concerns related to hot carriers and impact ionization. The trapping o f carriers and the generation of defects in the different layers are respon sible for the observed instabilities. The stability of the base dopant is t he main reliability concern for heterojunction bipolar transistors (HBTs). Beryllium outdiffuses from the base into the emitter and causes device degr adation. Carbon has a lower diffusivity, but is affected by the presence of hydrogen, which prompts gain variations. Finally the hot carriers reliabil ity concern in SiGe HBTs is briefly reviewed. (C) 2001 Elsevier Science Ltd . All rights reserved.