Characterization of Mass-Loaded Silicon Nitride On-Chip Resonators for Traceable Sensing of Low Amplitude Acceleration

Abstract

Low frequency (<100 Hz) acceleration sensing with low noise and traceability is critical in seismology, military surveillance, and emerging technologies. Typically, MEMS (Microelectromechanical systems) are not ideally suited for low frequency accelerometry since their fundamental thermomechanical fluctuation noise limit is higher than in macroscopic accelerometers of higher proof mass. However recent work on thin film MEMS resonators shows promising development in the reduction of damping which in turn reduces fundamental thermomechanical fluctuation noise limit. We aim to harness these low damping thin films in the context of accelerometry, by mass loading them to make them sensitive to acceleration. This work reports an experimental characterization of a mass-loaded silicon nitride membrane-based resonator, which is investigated towards the development of accelerometers for acceleration sensing at low frequencies. We experimentally demonstrate a 1.1 × 10⁻⁶ kg proof mass system achieving a 17,950 mechanical quality factor for a 526 Hz natural resonance frequency, which compares favorably to other optically interrogated on-chip accelerometers [1]-[3]. The inferred acceleration noise floor of the device is currently limited by the displacement noise of the optical fiber displacement readout, yielding a noise amplitude spectral density of 1 μg/√Hz at 10 Hz. This thesis first details a literature review of various high-performance, mass-loaded MEMS accelerometers categorized by their transduction methods, followed by a comprehensive overview of our devices design and fabrication process. Followed by an overview of the performance of our devices under different mounting conditions. Finally, a custom finite difference simulation is presented to determine the limiting factor in our device's performance along with concluding remarks and potential future work.