Ultra conformal high aspect-ratio small-gap capacitive electrode formation technology for 3D micro shell resonators

We report a new fabrication technology to form capacitive sense/drive electrodes with large area and narrow, uniform, and controllable gaps around a three-dimensional (3D) micro shell resonator. The process utilizes electroplated photoresist (EP) to form a conformal sacrificial layer on the 3D shell and electroplated metal (EM) to grow drive/sense electrodes towards the resonator until they touch the sacrificial layer and stop. Once the sacrificial layer is removed, extremely well defined and uniform capacitive gaps are formed. EP provides many desirable features as a sacrificial layer, including uniform coverage, excellent electrical insulation and chemical stability, wide thickness range, low deposition temperature, and easy removal. This post-processing technique can be applied to a variety of 3D micro devices. We demonstrate a birdbath resonator gyroscope (BRG) with ~7 μm gap and high mechanical quality factor (Q = 225,000). The development of this process is an important step toward the commercialization of high-performance 3D micro sensors and actuators.