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

New high sensitivity microsensors have been developed using high-resol ution position sensors based on electron tunneling. The design of mini ature accelerometers having resolutions approaching 10(-9) g/square-ro ot Hz is discussed. A new dual-element electron tunneling structure, w hich overcomes bandwidth limitations of single-element structures, all ows design of high sensitivity accelerometers operating in a band from a few Hz to several kHz. A miniature accelerometer based on this stru cture can thus have application as a sensitive acoustic sensor. Therma l vibration of the proof mass is an extremely important constraint in miniature accelerometers, and can be the dominant limitation on the se nsitivity. Thermal noise is analyzed for the suspended masses of the d ual-element structure, and compared with electronic noise in the tunne ling circuit. With a proof mass of 100 mg noise analysis predicts limi ting resolutions better than 10(-8) g/square-root Hz between 10 and 10 0 Hz, and 10(-7) g/square-root Hz at 1 kHz. Prototype accelerometers h ave been fabricated by silicon micromachining and tested. A noise reso lution 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-freq uency responsivity of this device is 100000 V/g, decreasing to 1300 V/ g at 600 Hz.