This paper reports the DC and RF characteristics of AlN/GaN MOS-HEMTs passivated with thin Al2O3 formed by thermal oxidation of evaporated aluminium. Extraction of the small-signal equivalent circuit is also described. Device fabrication involved wet etching of evaporated Al from the Ohmic contact regions prior to metal deposition. This approach yielded an average contact resistance of ∼0.76 Ω.mm extracted from transmission line method (TLM) characterisation. Fabricated two-finger AlN/GaN MOS-HEMTs with 0.2 µm gate length and 100 µm gate width showed good gate control of drain currents up to a gate bias of 3 V and achieved a maximum drain current, IDSmax of ∼1460 mA/mm. The peak extrinsic transconductance, Gmax, of the device was ∼303 mS/mm at VDS = 4 V. Current-gain cut-off frequency, fT, and maximum oscillation frequency, fMAX, of 50 GHz and 40 GHz, respectively, were extracted from S-parameter measurements. For longer gate length, LG = 0.5 µm, fT and fMAX were 20 GHz and 30 GHz, respectively. These results demonstrate the potential of AlN/GaN MOS-HEMTs for high power and high frequency applications.

The paper presents a systematic study of in-situ passivated AlN/GaN Metal Insulator Semiconductor Field Effect Transistors (MISFETs) with submicron gates. DC, high frequency small signal, large signal and low frequency dispersion effects are reported. The DC characteristics are analyzed in conjunction with the power performance of the device at high frequencies. Studies of the low frequency characteristics are presented and the results are compared with those of AlGaN/GaN High Electron Mobility Transistors (HEMTs). Small signal measurements showed a current gain cutoff frequency and maximum oscillation frequency of 49.9 GHz and 102.3 GHz respectively. The overall characteristics of the device include a peak current density of 335 mA/mm, peak extrinsic transconductance of 130 mS/mm, a maximum output power density of 533 mW/mm with peak power added efficiency (P.A.E.) of 41.3% and linear gain of 17 dB. The maximum frequency dispersion of transconductance and output resistance of the fabricated MISFETs is 20% and 21% respectively.