Submicron piezoresistive cantilevers in a CMOS-compatible technology for intermolecular force detection

We report the design, fabrication and test of piezoresistive cantilevers for intermolecular force detection in biochemical sensing. The small forces involved in molecular recognition experiments are best detected with cantilevers with small spring constant and high force sensitivity. Both conditions can be achieved with cantilevers with submicrometre thickness and width in the micrometre range. As a first step towards the realization of a complete system integrating the cantilevers and a CMOS circuit, we have fabricated polycrystalline silicon cantilevers by using two polysilicon layers with thicknesses identical to those in a CMOS process. The upper polysilicon layer has been doped and used as piezoresistor. The cantilevers have been successfully tested by applying a known transverse displacement with an AFM tip. A gauge factor of 12 has been obtained, which is similar to values known for other micromechanical structures using polysilicon piezoresistors.