Improved DC and RF Performance of Novel MIS <i>p</i>-GaN-Gated HEMTs by Gate-All-Around Structure

Abstract

In this study, we report a novel structure of enhancement-mode metal-insulator-semiconductor high electron mobility transistor (E-mode MIS HEMT) with p-GaN gate by gate-all-around technology. The gate-all-around structure is fabricated by depositing an insulator and gate to surround the p-GaN mesa. The p-GaN length is smaller than the gate length, which would easily turn on the two dimensional electron gas (2DEG) of channel and result in a higher drain current and thus improve the device performance. The gate-all-around p-GaN MIS HEMT has better gate control, better transconductance, and lower gate leakage current. The device exhibits a threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) of 1.5 V, a maximum transconductance(G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m.max</sub> ) of 101 mS/mm, and a drain saturation current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS,</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) of 412 mA/mm at a gate bias (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ) of 5 V. The most important achievement is that the gate leakage current at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> = 5 V is only 10-8 mA/mm. Moreover, the ratio of drain current density to gate leakage current density (JDS/JGS) is 108 at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> = 5 V. Finally, the cutoff frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> ) and 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 microwave performance for this gate-all-around device with a 1 μm gate length are 6.0 and 9.8 GHz, respectively.