Polymer/Ceramic Wireless MEMS Pressure Sensors for Harsh Environments: High Temperature and Biomedical Applications
Fonseca, Michael Agapito
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This dissertation presents an investigation of miniaturized sensors, designed to wirelessly measure pressure in harsh environments such as high temperature and biomedical applications. Current wireless MEMS pressure sensors are silicon-based and have limited high temperature operation, require internal power sources, or have limited packaging technology that restricts their use in harsh environments. Sensor designs in this work are based on passive LC resonant circuits to achieve wireless telemetry without the need for active circuitry or internal power sources. A cavity, which is embedded into the substrate, is bound by two pressure-deformable plates that include a parallel-plate capacitor. Deflection of the plates from applied pressure changes the capacitance, thus the resonance frequency varies and is a function of the applied pressure. The LC resonant circuit and pressure-deformable plates are fabricated into a monolithic housing that servers as the final device package (i.e. intrinsically packaged). This co-integration of device and package offers increased robustness and the ability to operate wirelessly in harsh environments. To intrinsically packaged devices, the fabrication approach relies on techniques developed for MEMS and leverage established lamination-based manufacturing processes, such as ceramic and flex-circuit packaging technologies. To demonstrate operation in high temperatures applications, LTCC and HTCC ceramic pressure sensors were fabricated and characterized, operating up to 450°C under 5 bars of pressure while HTCC devices demonstrated electrical functionality up to 600°C. To demonstrate operation in biomedical implantable applications, polymer-based and polymer-ceramic flexible designs were fabricated and characterized. Bench testing for > 300 millions pressure cycles (simulated 7 years of pulse pressure) confirmed the reduction of frequency drift for polymer-ceramic pressure sensors compared to purely polymer-based pressure sensors. Finally, LCP-based pressure sensors were delivered in vivo into canine models with mock abdominal aortic aneurysms and monitored wirelessly over 30 days. The animal results confirmed both catheter deliverability and wireless telemetry in real biomedical applications.