Design And Optimization Of Soi Technology-based Mems Inertial Accelerometers

The MEMS(Micro Electro Mechanical System) inertial accelerometer is the key component for MIMU(Micro Inertial Measurement Unit), which has wide development and application prospects in many related fields, and occupies a decisive position in micro systems. Thus, the research of the micro inertial accelerometer has become the hot topic in the world. The MEMS inertial accelerometer, based on the SOI(Silicon-on-insulator) technology, has the good silicon mechanical characteristics and could be compatible with the CMOS(Complementary Metal Oxide Semiconductor) process, which provides the possibility of integration between the accelerometer and CMOS chips to realize the advantages for miniaturization, integration, batch production and so on.The micro capacitive accelerometer is the research subject and the structure design, modeling and simulation, structure optimization and fabrication process for device will be developed and analyzed in this paper. According to the current situations of MEMS inertial accelerometer and processing technology in the world, a comparison study is developed among the different types of micro accelerometer, and a MEMS comb capacitive accelerometer based on the SOI technology and good performances is provided. Then, the structure design and modeling of micro comb accelerometer are developed based on the basic standard for silicon microstructure. The mechanical properties, structural capacitance, dynamic characteristics of this comb accelerometer and so on are deduced and analyzed by the theoretical method. The main influence parameters for resolution, sensitivity, mechanical thermal noise of the device are presented, and structure of U-shaped elastic beam for micro-accelerometer is determined and optimization designed. The system level modeling and simulation of the structural characteristics for micro comb accelerometer are started to developed in the MEMS special software CoventorWare, mainly refers to the static analysis, modal analysis and frequency response characteristics of elastic beam structure. The structure optimization is developed based on above study and analysis. Then, the equivalent electrical model for mechanical properties and structural differential capacitance of micro-accelerometer are built, and electric simulation of micro-accelerometer structure is developed through the PSPICE software. The correctness and reasonableness for this structure are verified.Finally, the technology of bonding and etching back silicon is provided and designed based on above structure to fabricate the SOI structure, which uses the SiO2 as the middle layer, and its detailed fabrication process flow is presented. Then, the whole fabrication processes of micro-accelerometer device based on the SOI structure are designed. Meantime, a processing technology of metal ions adsorption-film is provided to remove the undercut and notching effects in the etching to good realize the fabrication for whole micro comb accelerometer, and the special and detailed fabrication process flow of the silicon suspension structure without substrate for micro-accelerometer device.