Equivalent-Circuit Model for CMOS-Based Resonant Cantilever Biosensors

We present the modeling and characterization of a CMOS-based resonant cantilever biosensor operating in fluid environments. The device, which is fabricated in a 0.8-mum CMOS process with subsequent CMOS-compatible micromachining, consists of four resonant cantilevers (resonance frequency about 200 kHz in water) monolithically integrated with dedicated analog and digital signal processing and conditioning circuitry. The integrated cantilevers feature electromagnetic actuation and piezoresistive readout. In the first part of the paper an equivalent circuit model of the resonant cantilever is developed. The model allows a full characterization of the complete system comprising the cantilevers and the circuitry using commercial circuit simulation software. As will be shown, the presented model shows good agreement with actual measurements. At the end of the paper the application of the monolithic sensor system to the detection of prostate specific antigen (PSA) at clinically significant concentration levels will be presented.