Acoustoelectric amplification of surface acoustic waves on ZnO deposited on AlGaN/GaN Epi

Abstract

The integration of surface acoustic wave devices with GaN HEMT technology is an area that has generated significant interest from the long-range radio and radar community. Reported devices rely on accessing the underlying epitaxial layer and then releasing it from the substrate to minimize mechanical losses [1,2]. Due to reliability concerns that arise from strain resulting from bowing, the GaN layer is grown from 1.3μm–1.7μm. This limitation can lead to less then desirable electromechanicial coupling and acoustic velocity due to the dispersion relation between the wavelength and the thickness of the piezoelectric material. Recently, amplification of surface acoustic waves by a two-dimensional electron gas in GaN has been demonstrated in [3]. This is a promising result that can compensate for high insertion loss, however, the ability to tune the thickness of the piezoelectric layer to a particular frequency is still desirable. To address this, we propose the utilization of thin-film ZnO deposited on GaN to serve as a piezoelectric. ZnO has been demonstrated to have a high electromechanical coupling and a acoustic wave velocity suitable for microwave frequencies on several substrates [4, 5]. Furthermore, acoustic gain is also achievable in this structure and its merits can be investigated by revisiting the models for gain and noise developed in [6, 7]. Figure 1 shows that the ZnO/AlGaN/GaN structure is capable of high frequency gain and lower noise figure then it's InSb/SiO 2 /LiNbO 3 predecessor. In this work, we report the observation of acoustoelectric gain in an experimental device with a greater power ratio then previously reported. We believe this structure can be a pathway that leads to the union of the versatility and signal processing power of SAW devices with the high-power high-speed III-V technology.