Second-order resonant ZnO-based film bulk acoustic resonator devices and thermal techniques to improve their resonant characteristics

Abstract

In this article, the authors describe a novel fabrication technique of ZnO-based film bulk acoustic resonator (FBAR) devices using a new type of multilayered Bragg reflector with very thin chromium (Cr) layers additionally formed between silicon dioxide (SiO2) and tungsten (W) layers. Each Cr layer is considered to enhance the adhesion between the SiO2 and W layers. The fabricated FBAR devices are shown to operate at the frequency range of 2.7–3.0 GHz, along with good return loss as well as high Q factors. Furthermore, various thermal treatments are performed to further improve the resonant characteristics of the FBAR devices, and also their effects on the device characteristics are investigated. At the second-order resonant frequency, excellent resonant characteristics are observed in terms of high return loss and good figure of merit. This feasibility study indicates that the novel fabrication technique can be useful for future broadband mobile worldwide interoperability for microwave access applications.