Microwave performance of ZnO/ZnMgO heterostructure field effect transistors

Abstract

AbstractWe report the first microwave performance of single crystalline ZnO/ZnMgO heterostructure field‐effect transistors (HFETs). The structure consisted of a 15‐nm‐thick ZnO channel layer was grown by molecular beam epitaxy (MBE) on an a‐sapphire substrate. Two‐finger type HFETs with 1 or 2‐µm‐long gate were fabricated and measured for microwave performance. The transconductance of the HFETs are 28 and 23 mS/mm for 1 and 2‐µm‐gate devices, respectively. The microwave measurement of ZnO‐based TFTs revealed that the current gain cutoff frequency fT of 1.75 GHz and that of unilateral power gain fmax of 2.45 GHz for 1‐µm‐gate HFET. Electron velocity obtained by two‐terminal measurements implies that the structural design is crucial for further improvement of the high‐frequency performance of ZnO/ZnMgO HFETs.magnified image Small‐signal microwave characteristics of a 1‐µm‐gate ZnO/ZnMgO heterostructure FET. The current gain cutoff frequency of 1.75 GHz and the unilateral power gain cutoff frequency of 2.45 GHz were obtained.