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A surface-micromachined MEMS acoustic sensor with X-shape bottom electrode anchor

A surface-micromachined capacitive-type micro-electro-mechanical system (MEMS) acoustic sensor with X-shape bottom electrode anchor on a Si substrate is presented. As it is designed to be implemented on only one side of a substrate for a simple monolithic integrated process, this sensor has X-shape bottom electrode anchor fabricated. The anchor operates to remove the back side process of wafer for a conventional back chamber because the chamber is formed through Si surface etching by an isotropic dry etcher of XeF2. The Si MEMS acoustic sensor proposed in this paper has a diameter of 300 µm and a back chamber depth of 25 µm. It shows a pull down voltage of 9.1 V at 1 kHz and a zero-bias capacitance of 1.87 pF. Additionally, the sensor has an open-circuit sensitivity of 0.57 mV/Pa at 1 kHz on a bias of 5 V.