Design And Fabrication Of An Accelerometer With Novel "8-beams/mass" Structure

The micro machined accelerometer is a very important kind of micro inertialdevice which empowers extensive applications in aeronautics & astronautics,automobile industry, petroleum exploration, earthquake forecast and so on.Compared with other kinds of micro machined accelerometer, capacitiveaccelerometer possesses higher measurement precision,better noise characteristic,lower drift,lower temperature sensitivity and power consumption. Because of theseadvantages, capacitive accelerometer was extensively studied and has become thecurrent development mainstream.In this thesis, a new micro-silicon capacitive accelerometer with a novel "8beams-mass" structure is designed and fabricated utilizing micro-machining processbased on (111) silicon wafer. The device samples have been tested and show goodoutput signal. The proof mass of this accelerometer is supported by eight suspensionbeams which locate symmetrically on the top/bottom surface of a (111) silicon wafer.Via exploiting the extremely slow rate of Si (111) plane in anisotropic KOH etching,along with DRIE and other MEMS processes, the dimension of these beams can beaccurately controlled, and the symmetry of the "8-beams/mass" structure can beachieved. The details are given as follows:In chapter 1, based on a comprehensive survey, an introduction of the MEMStechnology, MEMS devices and their application, especially the micro machinedaccelerometers has been advanced. The prospects of the MEMS technology was givenwhereas the development of micro machined capacitive accelerometer have beenreviewed.In chapter 2, the mathematical model and principle of the capacitiveaccelerometer have been particularly introduced. Based on these, a new micro-siliconcapacitive accelerometer with novel "8 beams/mass" structure has been put forward toa focus of attention. The structure parameters of the capacitive accelerometer havebeen analyzed and optimized, and the mechanical performance of the capacitiveaccelerometer has been simulated using finite element analysis software Ansys.Compared with the traditional structures of micro machined accelerometer, such newstructure has demonstrated its advantages in mode characteristic and cross-axissensitivity.In chapter 3, several key fabrication processes such as anisotropic KOH etching,electrostatic bonding have been introduced. The entire fabrication flow of thecapacitive accelerometer has been designed and the device samples have been fabricated on (111) silicon wafer. The preliminary test results show that the capacitiveaccelerometer presents a typical resonance frequency of 2.08 KHz, a quality factor of21.4, sensitivity of 93.7 mV/g and none-linearity of 3.1ï¼…. These test results areconsistent well with the designed performances, indicating that the device design issound and the fabrication process is feasible.