A capacitive type uncooled infrared detector structure with new capacitance reading scheme is investigated. The structure has two parts: infrared absorber and bi-material legs. The infrared absorber has an insulator-metal-insulator structure, and acts as a top electrode of a variable capacitor composed of two bottom electrodes and top electrode (infrared absorber) which is separated electrically from the substrate. The absorber is posted to the substrate through bi-material legs which are designed to have electrical insulation, low thermal conductance and temperature dependent deformation characteristics. Thermal energy from absorbed infrared rays is transferred to the bi-material legs, resulting in leg bending, top floating electrode (absorber) lifting, and capacitance change of the variable capacitor. Electrical signal part and mechanical moving part of a MEMS structure can be separated with this scheme. Therefore, it is applicable to high Q-factor capacitors of other devices such as ultrasonic sensors.
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