The 3-axis CMOS-MEMS accelerometer include accelerator sensing method of Z-axis

This study presents a 3-Axis CMOS MEMS Accelerometer include novel post CMOS MEMS processes which is used to fabricate Z-axis capacitance accelerometer, utilizing processes combined with TSMC 0.35um 2P4M Standard CMOS Process and the method of wet etching process to etch the Aluminum metal structure in order to form the suspension structure composed of multi-layer metal and via layer. The sensing space can therefore be reached to cause displacement due to the acceleration between upper and lower electrode plates, and the change of capacitance is produced. In order to prevent interference when measuring displacement and change in capacitance, the design approach of integrating three axes into one is not adopted, but rather, the accelerations of three axes are designed separately on one chip. Moreover, integrating acceleration sensing devices with CMOS circuitries to disclose processors-inside sensing system will have advantages of low cost, compact, lower power consumption and fast measuring purposes. The primary sensing range of this accelerometer is from 1G to 10G, and as can be observed after simulation, in order to achieve enough sensitivity, when a 2G acceleration is applied in the X- and Y-axes, a displacement of 23nm will occur, and so will a change in capacitance of 80fF. Moreover, from the mode analysis, the resonant frequency of the X-axis and Y-axis accelerometer was 9.3 KHz; when a 2G acceleration is applied in the Z-axis, a displacement of 35nm and a change in capacitance of 30fF will occur, the resonant frequency of the Z-axis accelerometer was 2.8KHz.