T-Shaped Gate GaN HFETs on Si With Improved Breakdown Voltage and <inline-formula> <tex-math notation="TeX">$f_{\rm MAX}$ </tex-math></inline-formula>

Abstract

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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> ) of 0.16 μm showed a three-terminal breakdown voltage (BV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) of 98 V and a peak maximum oscillation frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MAX</sub> ) of 226 GHz, with a simultaneous current gain cutoff frequency ( f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) of 63 GHz at VDS = 15 V. In addition, a minimum noise figure (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Fmin</sub> ) of 1.01 dB with an associated gain of 16 dB at 14 GHz was obtained at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> = 5 V. A 0.1-mm-wide GaN HFETs exhibited a saturated power density of 3.82 W/mm at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> = 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , high f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MAX</sub> , high power density, and low NF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> at the Ku-band.