The mechanics of polymer swelling on microcantilever sensors

This paper investigates the swelling mechanics of polymer capture layers integrated into piezoresistive cantilever biochemical sensors. A finite element model investigates mechanical deformations in a polymer layer affixed to a silicon microcantilever. The polymer swells during analyte absorption, inducing deformations in the silicon cantilever which are sensed by a piezoresistive sensor integrated into the cantilever. The highest sensitivity is predicted for short and wide cantilevers that are coated with stiff polymer whose thickness is twice that of the cantilever. While the polymer swelling induces the deformations, the silicon carries most of the load. When portions of the silicon beam are removed to introduce stress concentrations, the system sensitivity can increase by 18% compared to the cantilever without stress concentrations. This study of stress distributions in the cantilever system allows sensor optimization that considers the full 3D effects of polymer swelling mechanics.