Study Of A Novel Micromachined Capacitive Accelerometer

Micromachined accelerometers have a variety of applications in many fields due to their low cost , small size and light weight. A novel micromachined capacitive accelerometer is investigated in this dissertation, including the operating principle, design, fabrication and measurement of the device.The fundamental, dynamic characteristic and frequency characteristic of accelerometer are analyzed. By means of analyzing the air damping, the micromachined accelerometer based on slide-film damping principle, is possible to achieve high Q-value at atmospheric pressure.The mechanical structure and electric structure of the micromachined capacitive accelerometer were discussed. The U-shaped supporting beams were adopted to obtain small residual stress. The natural frequency and Q-values at atmospheric pressure are 1140Hz and 575. The expectedsensitivities of displacement and capacitance are 1.9×10^-7m·g^-1 and 1.29 ×10^-13F·g^-1.By means of comparing with bulk micromachining process, surface micromachining process and LIGA process, the accelerometers fabricated by surface micromachining process have small sensitive mass, large noise and low resolution compared to the ones fabricated by bulk micromachining process, and the LIGA process is too expensive. In this dissertation, the micromachined capacitive accelerometer was fabricated on the base of bulk micromachining process and the anodic bonding between the silicon and glass. The rooting effect of the structure in deep reactive ion etching (DRIE) process was investigated.At atmospheric pressure, the device was packaged and the performances were tested. The measured resonant frequency and Q-value of the device are 1078Hz and 215.6. The sensor obtained a measured sensitivity of 52mV/g.The analyzed and measured results show that the device designed in the dissertation has achieved high sensitivity at atmospheric pressure.