SOI MESFETs Fabricated Using Fully Depleted CMOS Technologies

Ultrathin channel metal-semiconductor field-effect-transistors (MESFETs) have been fabricated using fully depleted silicon-on-insulator CMOS foundries with no changes to the process flow. The Schottky gate of the MESFET is formed from a metal silicide that consumes most of the thin ( < 50 nm) FD-SOI channel and fully depletes the remaining underlying silicon. Therefore, unlike partially depleted SOI MESFETs with a thicker silicon layer ( ~ 200 nm), the conducting channel of the FD-SOI MESFET cannot be formed directly under the Schottky gate. Instead, current flow in the FD-SOI MESFET is confined between islands of silicide that deplete the conducting channel in a lateral direction. The FD-SOI MESFETs operate as depletion mode devices with a threshold voltage that can be adjusted by varying the separation between the silicide islands. Both n- and p-channel devices can be realized using the same gate material on a common FD-SOI substrate.