T-Shaped Gate GaN HFETs on Si With Improved Breakdown Voltage and $f_{\rm MAX}$

In this letter, we have fabricated GaN heterostructure field-effect transistors (HFETs) with submicrometer T-shaped gate on Si substrate to realize compact solid-state power amplifiers used in Ku-band and higher. An AlGaN buffer layer was incorporated under the GaN channel layer, which was expected to enhance the breakdown voltage without decreasing the gain. The fabricated GaN HFETs with a gate length (L
_G
) of 0.16 μm showed a three-terminal breakdown voltage (BV
₃
) of 98 V and a peak maximum oscillation frequency (f
_MAX
) of 226 GHz, with a simultaneous current gain cutoff frequency ( f
_T
) of 63 GHz at VDS = 15 V. In addition, a minimum noise figure (N
_Fmin
) of 1.01 dB with an associated gain of 16 dB at 14 GHz was obtained at V
_DS
= 5 V. A 0.1-mm-wide GaN HFETs exhibited a saturated power density of 3.82 W/mm at V
_DS
= 30 V, indicating the successful reduction of current collapse. To the best of our knowledge, this is the first demonstration of a GaN HFETs on Si, which combines high BV
₃
, high f
_MAX
, high power density, and low NF
_min
at the Ku-band.