An in-plane low-noise accelerometer fabricated with an improved process flow |
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| Authors: | Xu-dong Zheng Zhong-he Jin Yue-lin Wang Wei-jun Lin Xiao-qi Zhou |
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| Institution: | (1) Department of EECS, Glennan 510, Case Western Reserve University, 10900 Euclid Avenue, 44106 Cleveland, OH, USA;(2) Department of Electrical Engineering and Computer Science, Case Western Reserve University, 10900 Euclid Avenue, 44106 Cleveland, OH, USA;(3) Department of Electrical Engineering and Computer Science, Case Western Reserve University, 44106 Cleveland, OH, USA |
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| Abstract: | We present a bulk micromachined in-plane capacitive accelerometer fabricated with an improved process flow, by etching only one-fifth of the wafer thickness at the back of the silicon while forming the bar-structure electrode for the sensing capacitor. The improved flow greatly lowers the footing effect during deep reactive ion etching (DRIE), and increases the proof mass by 54% compared to the traditional way, resulting in both improved device quality and a higher yield rate. Acceleration in the X direction is sensed capacitively by varying the overlapped area of a differential capacitor pair, which eliminates the nonlinear behavior by fixing the parallel-plate gap. The damping coefficient of the sensing motion is low due to the slide-film damping. A large proof mass is made using DRIE, which also ensures that dimensions of the spring beams in the Y and Z directions can be made large to lower cross axis coupling and increase the pull-in voltage. The theoretical Brownian noise floor is 0.47 μg/Hz1/2 at room temperature and atmospheric pressure. The tested frequency response of a prototype complies with the low damping design scheme. Output data for input acceleration from-1 g to 1 g are recorded by a digital multimeter and show very good linearity. The tested random bias of the prototype is 130 μg at an averaging time of around 6 s. |
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| Keywords: | MEMS accelerometer Deep reactive ion etching (DRIE) Footing effect Capacitive sensing |
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