Thin films of the $$\alpha$$-quartz $$Si_xGe_{1-x}O_2$$ solid solution

Abstract

Abstract$$SiO_2$$SiO2with the$$\alpha$$α-quartz structure is one of the most popular piezoelectrics. It is widely used in crystal oscillators, bulk acoustic wave (BAW) devices, surface acoustic wave (SAW) devices, and so on.$$GeO_2$$GeO2can also be crystallized into the$$\alpha$$α-quartz structure and it has better piezoelectric properties, with higher piezoelectric coefficient and electromechanical coupling coefficients, than$$SiO_2$$SiO2. Experiments on bulk crystals and theoretical studies have shown that these properties can be tuned by varying the Si/Ge ratio in the$$Si_xGe_{1-x}O_2$$SixGe1-xO2solid solution. However, to the best of our knowledge, thin films of$$Si_xGe_{1-x}O_2$$SixGe1-xO2quartz have never been reported. Here we present the successful crystallization of$$Si_xGe_{1-x}O_2$$SixGe1-xO2thin films in the$$\alpha$$α-quartz phase on quartz substrates ($$SiO_2$$SiO2) with x up to 0.75. Generally, the films grow semi-epitaxially, with the same orientation as the substrates. Interestingly, the$$Si_{0.75}Ge_{0.25}O_2$$Si0.75Ge0.25O2composition grows fully strained by the quartz substrates and this leads to the formation of circular quartz domains with an ordered Dauphiné twin structure. These studies represent a first step towards the optimization of piezoelectric quartz thin films for high frequency (> 5 GHz) applications.