The deposition and wet etching of Mg-doped ZnO films and their applications for solidly mounted resonators

Abstract

In this report, a solidly mounted resonator (SMR), consisting of an Au electrode, Mg-doped ZnO (Mg_XZn_1−XO) piezoelectric film and Bragg acoustic reflector, was fabricated on a Si substrate by radio frequency (RF) magnetron sputtering. As a key processing step for the SMR, Mg_XZn_1−XO films with high c-axis orientation were fabricated and the crystalline structure, surface morphology and roughness of the films were investigated. The surface morphology, optical transmittance and shape control of Mg_XZn_1−XO films were investigated by the chemical wet-etching method with various etchants. The profiles and line patterns of Mg_XZn_1−XO films etched with FeCl₃·6H₂O solutions are satisfactory and fully meet the industrial requirements. The Bragg acoustic reflector, made entirely of metal, has small internal stress and good heat conduction. An SMR based on a Mg_XZn_1−XO piezoelectric film shows a resonant frequency of 2.402 GHz, and the k_eff², Q_S and Q_P of the SMR are 3.07%, 415 and 546, respectively.