Fabrication of a nickel seismic mass microaccelerometer

摘要

In this paper, we present work on a surface micromachined opto-mechanical microaccelerometer employing Ni seimic mass. The device uses optical detection to sense motion. The microaccelerometer consists of a 500 um x 500 um electrodeposited nickel suspended by a folded beam spring on each corner over 10 pairs of 30 um x 400 um rectangular photodiodes. The seismic mass also has an array of rectangular holes parallel to the photodiodes. Each hole partially exposes a pair of adjacent photodiodes to to be illuminated by an LED. Once the mass experiences acceleration, it will act as a mechanical shutter and alters the amount of exposed area of photodiodes. For each pair of the photodiodes, as the shutter moves, it will increase the exposed area of one diode and at the same time will at the same time reduce the exposed area of the other diode by the same amount. Fully differential current signals can then be taken by appropriately biasing the photodiodes. By using differential sensing arrangement, the effects of noise and dark current can be reduced significantly. The microaccelerometer is tested on a rotating disc. The frequency response of the accelerometer is relatively flat up to 1500 Hz, then, it rise sharply at resonant frequency of approximately 1700 Hz. An open loop sensitivity of 9.2mV/g in the direction of acceleration is obtained. Cross axial sensitivity was below the noise level.