Micromachined Isolators for Shock and Vibration Reliability of MEMS Sensors: Fabrication, Damping, and Integration
Type of DegreePhD Dissertation
Electrical and Computer Engineering
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This dissertation details the design, FEA simulation, fabrication, and testing of three variations of micromachined vibration isolators (MVIs). The vibration isolators serve as low pass filters to attenuate high frequency mechanical excitation in order to improve both MEMS sensor fidelity and lifespan. Isolators are designed for integration of a small (~3mm x ~3mm) MEMS sensor package and boast a sub-1 sq.cm footprint. For all isolator variations, the fundamental geometry consists of an outer frame to be fixed to the substrate of interest, a central platform to accommodate the isolated sensor, and springs for attachment of the frame and platform. Devices are fabricated via a double-sided lithography process using <100> silicon-on-insulator (SOI) wafers. Laser Doppler vibrometry is performed to investigate the frequency response of each isolator variation across a 6.2 kHz bandwidth. Alternative methods of MVI fabrication including fused deposition molding (FDM), stereolithography (SLA), and two-photon polymerization (TPP) are discussed. Additionally, this dissertation introduces the use of nickel (Ni) and copper (Cu) microfibrous meshes (MFMs) and Sorbothane and polydimethysiloxane (PDMS) viscoelastic polymers to damp the dynamic response of MVIs for shock and vibration reliability in mechanically harsh environments. The MFMs are attached to the microisolators post-fabrication via solder attachment. We then investigate the transmissibility of the undamped and damped vibration microisolators using laser Doppler vibrometry. The peak transmissibility of the microisolator is significantly reduced for all four cases of polymer or MFM damping. Experimental results are compared to the FEA simulated transmissibility and to the analytically calculated transmissibility. Lastly, MVI performance is validated by the integration of a wide bandwidth piezoelectric acclerometer. The accelerometer output for the isolated and unisolated cases are compared. The experimental results confirm successful isolation of the accelerometer from high frequency excitation.