Design and verification of quartz resonators with quasi-convex structure

Recently, AT-cut quartz resonators have found widespread use as RF and high-sensitivity devices. In these applications, further miniaturization and high-frequency stability are required. To achieve a high quality (Q)-factor and high productivity, the authors have proposed a novel resonator shape in which the surface is machined as a three-dimensional stripe-like structure. This shape is called quasi-convex. In this paper, we discuss the design and fabrication of quasi-convex resonators to verify their effectiveness. First, with regard to the height of the convex part and the pitch of the quasi-convex pattern, the optimal resonator design is discussed on the basis of the results of a finite-element method simulation. Then, prototypes of the quasi-convex resonators fabricated by deep reactive-ion etching and micro electro-mechanical systems fabrication technology are presented. In our experiments, the highest Q-factor is obtained when the height ratio of the convex part was 5% and the pitch is 100 μm. In addition, the Q-factor of the quasi-convex resonators is seven times greater than that of ordinary plane-shaped resonators, as confirmed using vacuum equipment.