Abstract
This work develops a post-CMOS (Complementary Metal Oxide Semiconductor) bulk-micromachining process for fabrication of a capacitive accelerometer and its dedicated high-performance for applications with target value: µG resolution. The important feature of the post-CMOS process is to control the thickness of proof mass by e deep anisotropic backside etch and electroless plating without an additional mask. And of course a capacitive sensing circuit will be designed to measure the acceleration. For this CMOS capacitive accelerometer, The DRIE (Deep RIE) accelerometer structure is 0.65mm by 0.65 mm in size and has a 44 μm-thick silicon and 50 μm-thick proof mass. The Brownian noise floor is around 6 μg/rtHz. which a post-CMOS bulk-micromachining process using composite microstructures made from combinations of aluminum. In this study, The CMOS MEMS has been developed for TSMC 0.35 μm CMOS processes. The released microstructure consists of multiple layers of metal, SiO2, and silicon. The microstructures have large mass in the order of 10-7 kg, resulting in high sensitivity to outside force, and several orders of magnitude higher Brownian noise than surface micromachining devices. we will design a accelerometer with standard CMOS process. The readout IC will be composed of a pre-amp, sample circuit and low-pass filter. The circuit system will help us converting the displacement of proof-mass into electrical signal. We propose to design and fabricate a novel low-noise accelerometer with a μg resolution, which compares favorably with other low-g inertial sensors in its small size. The CMOS-MEMS technology is used for monolithic integration of the sensor and the capacitive readout, in order to minimize the parasitic capacitances if implemented otherwise. A special CMOS-compatible bulk micromachining process helps to promote the capacitive sensitivity with the resultant thicker micromechanical structures. Additional sensitivity increasing is obtained via the use of a feedback control scheme, in which the accelerometer is operated in a spring-softening regime and stabilized in a controlled loop.