Achieving Mode Detection and Precise Mechanical Trimming of Uncoated Micro Shell Resonator Using Interdigital Electrode

This article presents a new method to achieve mode detection for an uncoated microshell resonator (MSR) made of fused silica using an interdigital electrode (IDE) for the first time. The high-frequency axis and low-frequency axis of wineglass mode can be determined by frequency response analysis (FRA) along different electrodes using IDE. Finite element modeling is used to demonstrate the effectiveness of the mode detection approach. Mechanical frequency trimming is applied on an uncoated resonator based on the mode FRA results. In order to improve the driving and detecting efficiency of IDEs, structural parameters are optimized with finite element method (FEM). Then, an uncoated fused silica resonator is assembled on a fabricated IDE substrate using a soluble glue. Frequency sweep is used to detect the low-frequency axis and laser trimming is applied to reduce the frequency split. Experiments show that frequency split is successfully reduced to 87 mHz. Finally, the trimmed resonator is detached from the IDE and assembled with the electrode substrate after the cleaning and coating process. Test results indicate that the trimmed coated resonator has a small frequency split of 0.17 Hz without any damage on the metal layer of the electrode substrate.