Metal-semiconductor field-effect transistors (MESFETs) have long been studied for their extreme environment applications, with the most widely developed technologies making use of compound semiconductor materials such as GaAs, and gallium nitride and silicon carbide. This chapter describes one such approach based on silicon-on-insulator and silicon-on-sapphire (SOS) CMOS technologies that has been demonstrated at a variety of different foundry services. The MESFET architecture requires a Schottky barrier to control the depletion region under the gate, and thereby the current flowing in the conducting channel. The CMOS process flow cannot be adjusted to optimize the performance of the SOI MESFETs. An important property of the SOI MESFETs is their enhanced voltage operation which exceeds that of the CMOS technology being used for the fabrication. The voltage tolerance of the MESFET is attributed to the fact that the Schottky gate can support substantial current flow under forward and reverse bias without suffering permanent damage.
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