Abstract
The microfabrication of optical seismometer and vibrometer structures using Sandia’s silicon-based process technology is presented. The structure employs a 1.5-mm-diameter polysilicon diaphragm anchored to a 200- to 400-μm-thick bulk silicon proof mass, and suspended by surface micromachined polysilicon springs. Motion of the diaphragm is detected using an integrated polysilicon surface micromachined grating-based optical interferometer. Initial dynamic characterization of these structures in vacuum shows a fundamental resonant frequency of 250 Hz. Based on the high force sensitivity of these structures combined with interferometric motion detection, 1-μg/√Hz detection resolution in the 1-Hz frequency range is estimated. Microfabricated structures employing electrostatic actuation electrodes for the diaphragm are also presented, which enable force feedback operation for high dynamic range and enhanced dc stability. These characteristics may make these sensors well-suited for seismic and inertial navigation applications.
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