H-terminated diamond RF MOSFETs with AlOx/SiNx bi-layer passivation and selectively etched T-shaped gates

Abstract

This paper reports a novel ALD-AlOx/PECVD-SiNx bi-layer structure to passivate the surface channels of the hydrogen terminated diamond transistors. The upper SiNx was selectively etched to fabricate the robust T-shaped gates, while the lower thin AlOx with high quality was retained as the gate insulator. The fabricated device with gate length of 0.3 μm demonstrated a high current density of 715 mA/mm, a low on-resistance of 8 Ω·mm, and an extrinsic fT/fmax of 10/20 GHz. RF power output characteristics were investigated at 2 GHz and a maximum output power density of 703 mW/mm was obtained at a low drain voltage of −15 V. It reveals that it is a promising solution for high stable and high power diamond RF transistors and microwave integrated circuits by using the AlOx/SiNx passivation structure.