Recent progress in GaN FETs on silicon substrate for switching and RF power applications

Abstract

A GaN based field effect transistor (FET) on a silicon substrate is a promising candidate for next generation switching and RF power devices due to its high breakdown electric fields, high drift velocity and low substrate cost. A normally-off operation with a low on-resistance is important to utilize the GaN FETs as switching devices used for power supplies for computer systems and power modules for hybrid vehicles. A recessed gate structure has been reported to realize the normally-off GaN FETs with low on-resistance [1–3]. However, there still exists an issue of the insufficient uniformity in threshold voltage (Vth) due to lack of an available etch stop layer under the gate. RF power GaN FETs on Si substrates have been mainly developed for power amplifiers used for Cellular and WiMax base stations at an operating frequency of 2–5 GHz [4]. The maximum operating frequency of the reported GaN FETs on a Si substrate was up to 10 GHz [5, 6]. There is no report of a GaN FET on a Si substrate for millimeter- wave range applications such as automotive radar systems. In this paper, we describe a GaN switching device with high Vth uniformity and low on-resistance using novel piezo neutralization (PNT) technique and a 76 GHz GaN power amplifier(PA) on a Si substrate using 0.15-µm-gate GaN FETs and low-loss Coplanar Waveguide (CPW) lines.