Fabrication Of A MEMS Accelerometer Based On Area Changeable Capacitive Displacement Sensing

MEMS accelerometers have been under rapid development in recent years for its traits such as small volumes, light weights, low power consumption, easy integration and low costs. It has been widely used in the field of consumer electronics. Up to now, the high precision MEMS accelerometer is under intensive investigations because of its potential applications in inertial navigation for airborne and aerospace tasks. This thesis aims to design and manufacture such a MEMS acceleration sensor based on area changeable capacitive displacement sensing, with a range up to ±15g and a resolution < 10?g/?Hz.The acceleration sensor of this thesis takes the usual form of a 'sandwich' structure. We start with analytically calculating how the accelerometer responds to the exterior acceleration and how the area changeable capacitor senses the displacement of the proof mass. Hence, the design of the acceleration sensor is proposed including structures of the spring and the proof mass and the electrode arrays of the capacitor, according to the ultimate fabrication goal. The mechanical thermal noise of the acceleration sensor has been designed to be 6ng/?Hz and the measurement range to be ±16g. They are consistent with the results of ANSYS static and modal simulation analyses.With respect to this three-units-integrated ‘sandwich' structure, we analyze the respective function of each unit and design a dedicated process flow. This process flow contains 24 major steps, involved with a variety of micro-machining processes, such as film deposition, lift-off, lithography and etching. This thesis focuses on the photolithography and etching processes, which are used repeatedly during fabrication. At the end, the optimized process flow and processing results are presented.Finally, we test the accelerometer using external detection circuitry, and improve the accelerometer design based on test results. According to the measured intrinsic frequency and quality factor, the equivalent acceleration of the mechanical thermal noise of the acceleration sensor is deduced to be less than 10ng/?Hz, meeting the resolution goal of <10?g/?Hz; the detection sensitivity of acceleration is 203mV/g, which approaches the theoretical value of 228mV/g. The background noise power spectrum analysis shows that the acceleration resolution is 6?g in the frequency range of 1-200 Hz.