Design and Fabrication Issues in Affinity Cantilevers for bioMEMS Applications

Microfabricated cantilevers are widely used for biomedical sensing applications. In this paper, for the first time, design guidelines have been provided for composite polymeric microcantilevers with embedded piezoresistors. Optimization guidelines have been provided from the point of reducing their stiffness and to increase their deflection and the DeltaR/R response. Choice of the piezoresistive material and the location of this layer with respect to the neutral axis are shown to impact the stiffness and DeltaR/R of a microcantilever. Differences in the behavior of DeltaR/R and deflection, when surface stresses are applied to polymer based microcantilevers and oxide/nitride based ones, are brought out. We also show that it is essential to have the immobilization layer and the piezoresistor on the same side of the neutral axis particularly when these microcantivelers are used for sensing small surface stresses in the order of a few mN/m, typical of many molecular markers used in biomedical applications