A piezoresistive accelerometer with a novel vertical beam structure

A micromachined piezoresistive accelerometer sensitive to an acceleration component in the chip plane and vertical to the beam direction has been developed. To sense a lateral acceleration, a beam with a cross section vertical to the (001) wafer surface has been developed by anisotropic etching in aqueous KOH. The vertical beam is along the [100] direction and has a high aspect ratio. Two n-type piezoresistors instead of p-type ones are positioned on the top edge (wafer top surface) of the beam with one resistor on each side of the neutral line of the beam. The top edge of the beam is widened slightly to make enough room to accommodate the piezoresistors and their interconnections so that, in fact, the beam has a T-shaped cross section. The sensitivity of the device fabricated is about 0.5 mV g(-1) 5 V-1 and the resonance frequency is about 1.2 kHz. As the sensitivity is comparable to and the fabrication process is compatible with the conventional piezoresistive accelerometers for normal acceleration, this design leads the way to developing a monolithic piezoresistive multi-axis accelerometer. (C) 1997 Elsevier Science S.A.