A piezoresistive bridge-microcantilever biosensor by CMOS process for surface stress measurement

Microsensors based on piezoresistive microcantilevers have been proposed to measure the surface stress change by molecule adsorption from biochemical reaction on an immobilized surface. However, the sensor performance is adversely influenced by the biaxial effect of the surface stress and the thermal effect of the piezoresistor during operation. A bridge-microcantilever design based on standard CMOS fabrication process is developed to improve the measurement sensitivity. The design is an immobilized cantilever connected to the sensing cantilever by a transmitter such that biaxial surface stress can be converted into uniaxial strain similar to AFM operation and the thermal effect can be isolated. The design based on standard CMOS process also facilitates on-chip signal processing electronics and stable batch fabrication. Analyses show that the sensitivity can be increased by the design parameters of the length ratio of the two cantilevers and the transmitter rigidity.