Microwave performance of diamond field-effect transistors

The microwave performance of diamond metal semiconductor field-effect transistors (MESFET) and metal insulator semiconductor field-effect transistors (MISFET) fabricated on hydrogen-terminated diamond surface is investigated. A cut-off frequency of 2.2 GHz is obtained on a 2 μm Cu gate MESFET with a transconductance of 70 mS/mm. A cut-off frequency of 11 GHz is obtained on a 0.7 μm gate MISFET with a transconductance of 40 mS/mm. Despite the lower transconductance, the cut-off frequency of MISFET is higher than that of MESFET due to not only gate minimization but also increased carrier mobility due to the use of CaF₂ as the gate insulator. High-frequency equivalent circuits are derived from S-parameters for MISFET with various gate lengths. Reduction of gate-source parasitic resistance and capacitance in MISFET by the improvement of device structure yield high frequency performance.