Symmetrical Wheatstone Microcantilever Sensor with On-chip Temperature Sensors

This work has focused on the design, finite element modeling and testing of a symmetrical Wheatstone MEMS cantilever beam with on-chip temperature sensors. The stress induced on gold surface with polysilicon piezoresistive sensing is demonstrated. In principle, adsorption of biochemical species on a functionalized surface of the microfabricated cantilever will cause a surface stress and consequently the cantilever bending. The sensing mechanism relies on the piezoresistive properties of the polysilicon wires encapsulated inside the beam. The beam is fabricated and bending analysis is performed so that the beam tip deflection could be predicted. The piezoresistor designs on the beams were varied, within certain constraints, so that external read-out circuit could measure the sensitivity of the sensing technique. The mass detection of 0.0058-0.0110 g is measured by the beam resistor series as a balanced Wheatstone bridge configuration. The voltage output of the bridge is directly proportional to the amount of bending in the MEMS cantilever. The temperature dependency and sensor performance have been characterized in experiments. Compensation by resisters on the substrate, which act as temperature sensors significantly reduces the temperature dependence effect.