Geometric optimisation of SU-8 piezoresistive cantilever sensors

We demonstrate the design and optimisation of polymer-based piezoresistive cantilevers used for detecting changes in surface stresses due to binding and hybridization of biomolecules on the surface of the cantilever. Various cantilever shapes (namely rectangular, T shape, inverse T shape, V shape and long- and short-based U shape) were simulated via finite element analysis using ANSYS software. Simulations were also conducted on stress concentration regions (SCRs) created by removal of segments from under the base of the cantilever. Performance was measured on the basis of both displacement sensitivity and surface stress sensitivity. It was found that the optimum shaped cantilevers were the inverse T shape and the long-based U shape. Cantilevers with stress concentration regions showed improved sensitivity. Removal of sections from under the base to leave two short legs (dual-leg design) provided superior results to removal of a single channel under the base. Overall the cantilever design that produced optimum sensitivity for use in biochemical applications was the inverse T shaped cantilever with the dual-leg SCR design. This device had very high surface stress sensitivity within an acceptable range of values for resonant frequency.