A CMOS cantilever platform using adsorption-induced surface stress and piezoresistive transduction for biosensing

This work proposes a biosensing platform based on a microcantilever operating in static mode. The microcantilever transforms the adsorption-induced surface stress into a deflection which is then transformed in an electrical signal by means of a piezoresistive element that is embedded in the structure. A non-destructive and independent-of-fabrication-processes method to characterize residual stress within composite micromachined beams has been proposed. The method was validated by comparing available experimental data and simulation results from fourteen microbeams obtaining an average of 27% absolute error concerning the maximum deflection of the structures. A multipysics model incorporating a suspended beam, a piezoresistor and a Wheatstone bridge has been created in Comsol and used to explore performance of different piezoresistor geometries. A serpentine piezoresistor compared favorably among different geometries and showed a sensibility of 116Ω/µm. Finally, several Bandgap references were designed to be used in conjunction with the Wheatstone bridge in order to get low sensibilities to temperature and voltage supply variations. The best reference showed sensibilities of 18 ppm/ ◦C and 3.2mV/V. This platform was entirely designed to be fabricated in a CMOS process, and is expected to be used in the future to detect and quantify different analytes for environmental monitoring, food industry and biomedicine.