Silicon dioxide microcantilever with piezoresistive element integrated for portable ultraresoluble gaseous detection

Surface-stress sensing microcantilevers with on-chip signal readout are demanded for on-the-spot ultrasensitive biological/chemical detection. For enlarging the bending of the cantilever under surface stress induced by specific reaction, a novel SiO2 cantilever is developed which features much lower Young's modulus than conventional Si or SiNx cantilevers. Thin single-crystalline-silicon piezoresistors are integrated with the SiO2 cantilevers for electric readout. For improving resolution, the piezoresistors are fully encapsulated by SiO2. Thus, the piezoresistors with SiO2 isolation show much lower leakage-related noise than those with p-n junction isolation. Following the description of microfabrication process, this letter gives the sensing model and discusses the thermal mechanism of the piezoresistive SiO2 cantilever. With a specific self-assembled monolayer functionalized on the cantilever surface, on-chip detection for the vapor of trinitrotoluene is performed with a resolution of about 20 ppt (parts per trillion). (c) 2006 American Institute of Physics.