Micromachined tunneling accelerometer with a low-voltage CMOS interface circuit

Three types of low-voltage CMOS interface circuitry for a micromachined tunneling accelerometer have been designed, fabricated, and tested. One of these uses a pn-junction diode as a logarithmic current-to-voltage converter and has the best performance. Only one single 12 V power supply is required for device operation and the total power dissipation is 2.5 mW. With an active area of 400×400 μm ² (the proof-mass and support cantilever beams), the accelerometer has an on-axis sensitivity of 125 mV/g, 3 dB bandwidth of 2.5 kHz, and measurement range of 30 g. The noise equivalent acceleration with a 1/f behavior drops from 4 mg/√Hz to 0.1 mg/√Hz, thus corresponding to a minimum resolution of 8 mg and dynamic range of 71 dB. After one month of continuous operation, the device shows a sensitivity and offset drift of less than 0.5%. The hybrid sensor-circuit module requires a much simpler interface circuit than capacitive accelerometers, which generally need monolithic sensor-circuit integration and complex design of signal processing to provide comparable performance