DC and RF Performance of AlN/GaN MOS-HEMTs

Abstract

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 ∼0.76Ω.mm extracted from transmission line method (TLM) characterisation. Fabricated two-finger AlN/GaN MOS-HEMTs with 0.2µm gate length and 100µm gate width showed good gate control of drain currents up to a gate bias of 3V and achieved a maximum drain current, IDSmax of ∼1460mA/mm. The peak extrinsic transconductance, Gmax, of the device was ∼303mS/mm at VDS =4V. Current-gain cut-off frequency, fT, and maximum oscillation frequency, fMAX, of 50GHz and 40GHz, respectively, were extracted from S-parameter measurements. For longer gate length, LG =0.5µm, fT and fMAX were 20GHz and 30GHz, respectively. These results demonstrate the potential of AlN/GaN MOS-HEMTs for high power and high frequency applications.