INVESTIGATION OF GaN HIGH ELECTRON MOBILITY TRANSISTOR FOR HIGH FREQUENCY APPLICATION

Abstract

The advancement in mobile communication, radar systems and satellite communication systems demand high power transistors that can operate at GHz to THz frequency range. These applications use microwave equipment’s to generate strong radio frequency (RF) power levels at high frequencies. AlGaN/GaN High Electron Mobility Transistors (commonly referred as GaN HEMTs) proves to be a strong competitor in both high voltage and high frequency applications because of their inherent material characteristics such as large bandgap, high electron mobility, high electron saturation velocity, and high thermal conductivity. Over the last few decades, the performance of GaN HEMTs has witnessed an unprecedented advancement, including high output power, high operation frequency, and low noise figure. So far, a cut-off frequency of more than 150 GHz has already been achieved in GaN HEMT and metal oxide semiconductor HEMT (MOS-HEMT) devices, while InAlN/GaN HEMTs further increased the cut-off frequencies exceeding 300 GHz. These demonstrations have paved pathway to realize electronic circuitry operating at mm-wave to THz frequency bands. Now, the above mentioned applications require an accurate transistor model that can be used to evaluate the transistor performance at difference frequency bands. Unfortunately, currently available GaN HEMT models are fairly accurate at low frequencies, whereas there is an urgent need to develop accurate GaN HEMT models that can precisely capture several intrinsic and parasitic effects that are dominant and high frequency and broadband frequency range. Extraction of the small-signal equivalent circuit (SSEC), which serves as a base for both noise and large-signal models, is typically the first step in microwave transistor model development. Traditionally, a lumped SSEC model consisting of constant valued circuit elements are considered for GaN (MOS)HEMTs. These models are derived from the low frequency portion of the experimentally measured Y-parameter of the device. Consequently, these models cannot faithfully capture the high frequency or broadband frequency behaviour of the device.