Residual stress compensated silicon nitride microcantilever array with integrated poly-Si piezoresistor for gas sensing applications

Abstract

This work reports a novel method of microfabrication for silicon nitride based piezoresistive microcantilever device, to minimize the residual stress induced bending. The microcantilever of dimension L × W ~ 250 × 100 µm2 with stack (Si3N4/Poly-Si/Si3N4/SiO2) thickness ~ 1 µm was realized, by using standard six masks and bulk silicon micromachining fabrication process. In order to compensate the residual inbuilt stress, asymmetric structure layers for microcantilever was proposed and the presence of thin oxide layer underneath the released microcantilever stack was used to control the bending. The surface profiler measurement results showed the curvature bending in the range of ~ 4 ± 3 µm. The microcantilever was characterized further to evaluate its physical parameters such as mechanical deflection sensitivity and spring constant. The deflection sensitivity and spring constant values were ~ 0.161 ppm/nm and ~ 0.2 N/m, respectively. Finally, the practical application of fabricated piezoresistive microcantilevers was demonstrated by using it for explosive vapors sensing.