Shape Dependence of Sensitivity and Strength on a Piezoresistive Semiconductor Accelerometer

Abstract

This paper reports the fabrication of a multi-axis accelerometer with piezoresistive detection using the bulk micromachining technique. The evaluation is attempted in the manner of using a computer simulation (FEM) and fabricating the sensors. Two-axis detection sensors were fabricated for this experiment. These sensors were estimated for two views of a ribbed structure diaphragm and a mass shape. The samples consisting of a ribbed structure diaphragm gave higher output signal than that of the sensor with diaphragm only. This result shows that the ribbed structure affords the effective stress distribution to the piezoresistive elements on the rib. On the other hand, the mass shape had influence on the sensing performance and structural strength of the samples. The samples with square shape mass didn't indicate better properties than that of polygon shape. The stress isn't effectively generated on the sensor elements, because the stress concentrates at the edge of mass. The stress at the edge of mass causes destruction to sensors in fabrication process and has a harmful effect on fabrication yield. These results are in agreement with the calculation of computer simulation (FEM) and show that the optimization of the diaphragm structure and the mass shape is important for achieving a high sensitivity and process yield for product development.