A MINIATURE HIGH-SENSITIVITY BROAD-BAND ACCELEROMETER BASED ON ELECTRON-TUNNELING TRANSDUCERS

New high sensitivity microsensors have been developed using high-resolution position sensors based on electron tunneling. The design of miniature accelerometers having resolutions approaching 10(-9) g/square-root Hz is discussed. A new dual-element electron tunneling structure, which overcomes bandwidth limitations of single-element structures, allows design of high sensitivity accelerometers operating in a band from a few Hz to several kHz. A miniature accelerometer based on this structure can thus have application as a sensitive acoustic sensor. Thermal vibration of the proof mass is an extremely important constraint in miniature accelerometers, and can be the dominant limitation on the sensitivity. Thermal noise is analyzed for the suspended masses of the dual-element structure, and compared with electronic noise in the tunneling circuit. With a proof mass of 100 mg noise analysis predicts limiting resolutions better than 10(-8) g/square-root Hz between 10 and 100 Hz, and 10(-7) g/square-root Hz at 1 kHz. Prototype accelerometers have been fabricated by silicon micromachining and tested. A noise resolution of 10(-7) g/square-root Hz between 4 and 70 Hz and 6 x 10(-7) g/square-root Hz at 400 Hz is observed in a damped device. The low-frequency responsivity of this device is 100000 V/g, decreasing to 1300 V/g at 600 Hz.