A surface-micromachined MEMS acoustic sensor with back-plate anchors of 100 µm depth

A surface-micromachined capacitive-type microelectro-mechanical system (MEMS) acoustic sensor with back-plate anchors of 100 μm depth is presented. The sensor is implemented by a simple front-side fabrication process of a Si substrate with a compatibility with a full CMOS process. For only the front-side process, the back-plate anchors are placed under a back-plate and inserted very deeply into the substrate by Deep Reactive-Ion Etching (DRIE), and their upper part is covered with a thick back-plate of 2.9 μm. Also, a diaphragm is composed entirely of standard CMOS process layers for a monolithic integration. It has a diameter of 500 μm and a back chamber depth of around 80 μm. After a sacrificial layer of 2.2 μm is released, the back chamber is realized by XeF2 etcher as well as the back-plate anchors, simultaneously. Thus, it shows a measured zero-bias capacitance (C_mea) of 1.1 pF at 10 kHz and a pull-in voltage (V_pull) of 35.6 V, and an open-circuit sensitivity (S₀) of 1.62 mV/Pa on a DC bias of 6 V.