Design Fabrication and Wet Etchant Characteristic Study on the Sensitivity Analysis of PZR Microcantilever

Abstract

Microcantilever is a Micro Electro Mechanical Systems (MEMS) micromachined device similar to the miniaturized version of a diver's board, longer as compared to width, and has a thickness much smaller than its length or width. The merits of MEMS microcantilever sensors are its high sensitivity, design simplicity, portability and high speed. In this paper, the design and fabrication of a Piezoresistive (PZR) Microcantilever sensor that is used as a platform for biological sensing such as salivary amylase-activity for human stress measurement application. In principle, adsorption of saliva amylase on a functionalized surface of the microfabricated cantilever will cause a surface stress and consequently the cantilever bending. The microcantilever beam is constructed and bending analysis is performed so that the beam tip deflection could be predicted. The device model was simulated using CoventorWare™, a commercial finite element analysis (FEA) tool designed specifically for MEMS applications. The 0.5µm-thick piezoresistive sensors are made of polysilicon. This surface micromachined microcantilever is based on silicon wafers and fabricated using 0.5µm CMOS process technology. The range of microcantilevers is 40–140 µm long, 0.5-1 µm thick, and 40 µm wide. The force sensitivity of implemented sensors ranges from 2-10Pa is corresponding to salivary amylase-activity adsorbed on the piezoresistive microcantilever. The structural variation of the piezoresistors designs on cantilever beam is also considered to increase the sensitivity of the microcantilevers sensor since the forces involved is very small. The stress distributions and the vertical displacements of the designed Piezoresistive Microcantilever were simulated and the relative resistance changes of the piezoresistors as a function of the cantilever vertical displacements were measured.