High-Temperature-Recessed Millimeter-Wave AlGaN/GaN HEMTs With 42.8% Power-Added-Efficiency at 35 GHz

In this letter, a high-temperature (HT) gate recess technique is implemented into the fabrication of high-performance millimeter-wave AlGaN/GaN highelectron-mobility transistors (HEMTs). By virtue of the low damage feature of the HT recess, a high extrinsic transconductance of 422 mS/mm, a three-terminal breakdown voltage of 134 V with a source-drain separation of 2.4 μm, and a remarkable low Schottky gate leakage current of 1.6 × 10
^-6
A/mm at V
_GS
= -60 V are achieved, which is at least two orders of magnitude lower than the HEMTs with gate recessed at room temperature. By employing a 0.2-μm T-shaped gate technology, a current-gain cutoff frequency f
_T
of 81 GHz and a unit-power-gain frequency fMAX of 194 GHz are realized. The current collapse in the HT-recessed AlGaN/GaN HEMTs is significantly suppressed, contributing to a record high power-addedefficiency of 42.8%, as well as high output power density of 5.1 W/mm at 35 GHz in a continuous-wave mode.