Dual-gate AlGaN/GaN modulation-doped field-effect transistors with cut-off frequencies fT>60 GHz

We demonstrate dual-gate AlGaN/GaN modulation-doped field-effect transistors (MODFETs) with gate-lengths of 0.16 μm and 0.35 μm for the first and second gates, respectively. The dual-gate device exhibits a current-gain cut-off frequency f
_T
>60 GHz, and can simultaneously achieve a high breakdown voltage of >+100 V. In comparison to single-gate devices with the same gate length 0.16 μm, dual-gate FETs can significantly increase breakdown voltages, largely increasing the maximum allowable drain bias for high power application. The continuous wave (CW) output power is in excess of 3.5 W/mm at 8.2 GHz. The corresponding large-signal gain is 12 dB and the power added efficiency is 45%. The dual-gate device with different gate lengths shows the capability of providing simultaneous high cut-off frequencies, and high breakdown voltages for broadband power amplifiers.