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We report a novel palladium (Pd)-based micro electro-mechanical system (MEMS) capacitive hydrogen gas sensor that has an inverted T-shaped electrode and a ring-shaped Pd alloy layer, which enable high sensitivity and low power consumption. Thanks to these structures, deformation of the membrane as a result of hydrogen absorption can be efficiently transduced to capacitance change. The capacitance change of the proposed sensor is found to be three times larger than that of the conventional structure. Prototype sensors were fabricated by a CMOS-compatible surface micromachining process. The proposed sensor offers a broad design window for attaining high sensitivity. Finally, we show that our sensor provides fast response, is hysteresis-free, and has excellent hydrogen selectivity characteristics despite not employing a heater by using PdCuSi metallic glass.

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An RF MEMS variable capacitor using hybrid actuation of piezoelectric and electrostatic forces is presented. A surface micromachining process is used to fabricate the device. The piezoelectric actuator, which uses thin film PZT, enables low voltage actuation while the electrostatic actuator realizes large capacitance ratio. The measured capacitance ratio is Cmax/Cmin=14 at 5V. We demonstrate that the hybrid actuation enables to lower the pull-in voltage without changing the pull-out voltage. We also show that the shift of pull-out voltage due to dielectric charging can be reduced drastically at actuation voltages below 1OV. In this sense, the hybrid actuation can realize low voltage operation with enhanced robustness for stiction.