Design and analysis of MEMS piezoresistive SiO2 cantilever-based sensor with stress concentration region for biosensing applications

This paper uses finite element method to obtain the optimal performance of piezoresistive microcantilever sensor by optimizing the geometrical dimension of both cantilever and piezoresistor. A 250 mum times 100 mum times 1 mum SiO₂ cantilever integrated with 0.2 mum thick Si piezoresistor was used in this study. The sensor performance was measured on the basis of displacement sensitivity and surface stress sensitivity. The resulting maximum displacement value is about 0.7 nm for an applied load of 250 pN. A comparison between polySi and SiO₂ cantilever has been carried out which shows the latter gives higher displacement for the same applied load. The sensor sensitivity was investigated by varying cantilever thickness as well as piezoresistor thickness. Simulation results show that the cantilever sensitivity is maximum when both the cantilever and the piezoresistor thicknesses are at minimum. Simulations were also conducted on the effects of incorporating various stress concentration region (SCR) designs at the bottom of the cantilevers. Cantilevers with incorporated stress concentration regions shows improved sensitivity over the cantilever without SCR. The cantilever with a rectangular shaped SCR extended up to the edge of the cantilever width yields a maximum Mises stress of 0.73 kPa compares to the other designs. For the same design, the cantilever with minimum SCR thickness of 0.2 mum yields maximum stress which results in maximum sensitivity.