| Name: Xin Li (Microelectronics and Solid State Electronics) Directed by Prof. Yuelin WangMEMS-based sensors have some special advantages, such as low fabrication cost, easily to be integrated, and good reliability. Compared with piezoresistive sensor, the capacitive sensor has higher sensitivity and low temperature effect. To match the requirement of the low detection range differential pressure sensor with low detection range, capacitive structure is used. In the thesis, basic principle, fabrication process and testing are presented in detail.A movable diaphragm is the kernel of the pressure sensor, and analysis of the diaphragm structure is very important. With Finite Element Method (FEM), characteristics of some kinds of diaphragms structures are studied. Considering the sensitivity, linearity and fabrication process, an optimized movable diaphragm is desired, its thickness is 4 n m and its dimension is 4mm*4mm.The quality of the diaphragm is very important to the sensor. By using heavy boron doping, KOH boron etch-stop and LPCVD, we succeed to make a very flat compounded diaphragm which is composed with Si(P++) and SisN^ The dimension of the diaphragm is 4mm*4mm and its thickness is 2-5 w m.Based on the method of fabrication of the Si(P++)/ SisN4 diaphragm and Si/Glass bonding technology, differential pressure sensor with single capacitance is obtained. Result shows that the sensor has high sensitivity of 4fF/Pa and works well repeatedly within 0-200Pa. Also, some reasons that would affect the result are analyzed and corresponding resolving methods are discussed.Then we present a new force-balanced tiny differential pressure sensor which extends the dynamic detection range by using a servo structure. The fabrication process is decided and some experiences are made. Some valuable results are gained. In the future research, we should advance the method of package and test, and develop the interface IC. A microsystem for detecting tiny differential pressure wouldbe obtained. |
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