Fabrication of T-shaped gate diamond metal-insulator-semiconductor field-effect transistors

Diamond metal-insulator-semiconductor field effect transistors (MISFETs) with gates of 0.2-0.9 mu m length and T-shape were realized by trilayer resist electron-beam lithography. FETs show a cut-off frequency (f(T)) of 11 GHz and maximum oscillation frequency (f(max)) of 22 GHz. The f(max)/f(T) ratio of this FET was more than double that of FETs with a conventional gate structure and the same gate length. The f(T) of 11 GHz was half the maximum for diamond FETs due to parasitic capacitance at the gate-drain and gate-source electrodes. The T-shaped gate structure and the source-to-drain spacing must be optimized to reduce parasitic capacitance between each electrode.