Development of a double-microcantilever for surface stress measurement in microsensors

Microsensors based on piezoresistive microcantilevers have been proposed to measure the surface stress change from biochemical reaction. However, the sensor performance is adversely influenced by the thermal stress induced during operation. A mechanics model is employed to analyze the piezoresistive microcantilever subject to surface stress and thermal stress loading, and a double-microcantilever design is also developed to improve the measurement sensitivity. The double-microcantilever is composed of a top immobilized cantilever and another bottom sensing cantilever such that the biaxial surface stress in the former can be converted into uniaxial strain in the latter. Analyses show that the sensitivity can be further increased by a higher length ratio and a lower thickness ratio of the two cantilevers. More than two orders of sensitivity increase can be achieved and the induced thermal effect can also be minimized.