1.26 W/mm Output Power Density at 10 GHz for Si3N4 Passivated H-Terminated Diamond MOSFETs

In this article, the hydrogen-terminated diamond metal-oxide-semiconductor field effect transistors (MOSFETs) which can operate at high frequency of 10 GHz are demonstrated. The devices were fabricated with a 50 nm Al2O3 gate insulator and a 350 nm Si3N4 passivation layer, which is compatible with the process of monolithic microwave-integrated circuits (MMICs). The device with gate length of 0.35 mu m shows a high drain current density of -561 mA/mm. The RF small signal characteristics and power output performances at 10 GHz for the devices with different gate widths have been investigated. With the gate width increased from 100 to 200 mu m, the extrinsic maximum frequency of oscillation f(max) is slightly decreased from 23 to 21 GHz, whereas the output power density at 10 GHz is improved from 1.05 to 1.26 W/mm, with associated power added efficiency increased from less than 5% to 20.77%. Comparing with the devices fabricated by the self-aligned gate process, the power output performance is significantly improved, indicating it is a promising method to fabricate high power and high frequency diamond MOSFETs by using the thick Si3N4 passivation technique.