A Millimeter-Wave AlGaN/GaN HEMT Fabricated With Transitional-Recessed-Gate Technology for High-Gain and High- Linearity Applications

A high-linearity and high-gain AlGaN/GaN HEMTs with a 100-nm gate were demonstrated. The device employs transitional recessed gate (TRG) along the gate width for millimeter wave power application. The gradually changing gate recess depth was created using transitional dosed photoetching. Accurate etching ensured that the FET-elements have a continued V_ts offset in the local equivalent threshold voltage (V_th) in different areas. The device exhibits a high I_d,max of 1.12 A/mm and a high peak extrinsic gm of 374 mS/mm with an improved gate swing > 2.6 V, much higher than that of Fin-HEMT. Excellent RF performance was shown, including f_T/f_max = 61.8/148.8 GHz, G_as/G_linear = 9.98/ 12dB at 30 GHz. To the best of our knowledge, this is the best associated gain and linearity performance reported to date for AlGaN/GaN HEMTs. This letter has great potential for high gain and linearity millimeter wave power applications, which are needed for future communication systems.

I. Introduction

Gallium nitride (GaN) based high electron mobility transistors (HEMTs) are one of the most expected devices for high-voltage, high-frequency and high-temperature applications due to its remarkable natural material advantages [1], [2]. However well suited those properties may be for the increasing demand of faster mobile devices’ radio communications, its linearity needs to be improved. The sources of its non-linearity is its transconductance () drop at high current [3], [4]. Researchers have tried many methods [5]–[11] to achieve a broader curve for transistor linearity, targeting amplifiers with a linear output over a wide bias range [6]–[8]. Recently, Fin-HEMTs have widely captured attention and interest of the industry, due to their steady , continuous power output, and high normalized current density [10]–[12].