Simulation and characterization of a piezoresistive accelerometer with self-canceling off-axis sensitivity

A six-beam piezoresistive accelerometer with self-canceling off-axis sensit ivity was fabricated on a selectively diffused (Ill)-oriented n/n(+)/n sili con substrate. A unique porous silicon micromachining technique which has s elf-stop characteristics and produces a highly selective formation of the p orous silicon layer during the anodic reaction was used. The canceling effe cts of off-axis sensitivity were investigated using the finite-dement metho d (FEM) simulation program ANSYS, and the resulting characteristics of the fabricated accelerometer were experimentally investigated. The six-beam str ucture provides a lower off-axis sensitivity than two- or four-beam structu res and is mechanically more stable due to smaller shear stress. The compar atively low sensitivity to normal accelerations, due to the additional beam s, can be simply overcome using a summing circuit. This also sharply reduce s the off-axis sensitivity.