Fabrication of miniaturized bi-convex quartz crystal microbalance using reactive ion etching and melting photoresist

In this paper, miniaturized bi-convex quartz crystal microbalance (QCM) has been fabricated using reactive ion etching (RIE) and melting photoresist technology. Due to the convexity of the resonator surface and the small size of the excitation electrode, the energy of the oscillation is trapped at the center so that very little dissipation occurs at the edge. The fabricated bi-convex QCM has superior resonant characteristics compared with a QCM without the bi-convex formation. For example, the QCM with a high-quality value (76000) was realized for a 1mm-diameter electrode QCM with 1.6μm-deep and 2mm-diameter convex formation on both sides. A spurious mode around a fundamental vibration mode became very small or nearly negligible. This technology is useful from the viewpoint of mass production because it does not require polishing. The manufactured bi-convex QCM can be used for sensing liquid properties.