Fabrication of Two-Axis Quartz MEMS-Based Capacitive Tilt Sensor

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The design, fabrication packaging and evaluation of a two-axis quartz MEMS-based capacitive tilt sensor is described. Two same sensing elements are microfabricated using bulk anisotropic wet etching technique on one quartz chip. Sensing element 1 detects the tilt angle around Y axis giving the output θ and sensing element 2 detects the information of Y axis and X axis, giving output γ. Microfabrication efforts are made on wet etching high aspect ratio gap between comb electrodes, good metal step coverage on the side wall of comb electrodes, and patterning surface leading wire and pads. The sensor is mounted on a designed ceramic package by flip chip method. A special spring structure is inserted between the two sensing elements for absorbing the residual stress caused by reflow process. The sensitivity of the fabricated sensor is evaluated using diode bridge capacitance detection circuit. In the range of ±1°, voltage outputs are 529 mV/° for sensing element 1 and 394 mV/° for sensing element 2 respectively. The detection accuracy of 0.001° was also examined.
2008-03-01