Research Of MEMS Capacitive Accelerometer Sensitive Structure

Capacitive micromachined accelerometer is widely studied because of its simple process,high sensitivity,good performance,low power consumption,easy mass production and so on.In this paper,a capacitive biaxial accelerometer and a Z axis accelerometer based on silicon glass anodic bonding process is designed.The related work is divided into five parts:In the first paragraph of the paper,it briefly introduces the basic knowledge of MEMS and the current research status of MEMS accelerometer at home and abroad.The second part introduces the basic working principle and mathematical model of the accelerometer,according to Newton second mechanics,the accelerometer is simplified as a sensitive mass-damper-spring system.Based on the analysis of the system,some technical indicators such as mechanical sensitivity and so on are obtained.Secondly,the comparative analysis of various kinds of accelerometers,including piezoelectric accelerometer,piezoresistive accelerometer,tunnel current accelerometer,capacitive accelerometer,etc..And the two kinds of detection principle of capacitive accelerometer are compared.Variable gap detection method can obtain high sensitivity and high performance,and it is widely used in the design of the actual structure.According to the advantages and disadvantages of various types of accelerometers,to determine the final choice of capacitive variable spacing accelerometer as the structure of the article design.Secondly,in the third part of the paper,the design scheme of biaxial capacitive accelerometer and Z axis accelerometer is presented.The paper includes analysis of the beam structure,the design of the whole structure and the theory of cross coupling.And use simulation software to verify the theory design value of structure: the mechanical analysis of the accelerometer present the accelerometer is linear,and in different direction,the mechanical sensitivity is S_x=0.0845?m/g?S_y=0.1382?m/g and S_z=0.262?m/g.The impact resistance performance of the accelerometer is analyzed by the structural strength analysis.Under the large impact(1000g),the maximum stress of the structure is 337.18MPa?457.34 MPa and 349.26 Mpa appear in the support beam and the connection point of the sensitive mass is far less than the maximum stress of the silicon material 1.3GPa.The first four working modes of the structure were obtained by modal analysis,the structure first two orders modal is far less than other modes,and can effectively suppress the influence of other non sensitive direction.In accordance with the dual axis and Z axis accelerometer with MEMS machining methods,the process and corresponding details parameters are presented.Finally the accelerometer samples was fabricated,by comparing the micrographs,scanning electron microscope and theory to verify the rationality of structure parameters.At last,the test circuit of capacitive accelerometer is designed,then the principle and design of each part of the circuit are described,at last test the performance of accelerometer.