Micromechanical Resonant Cantilever Sensors For Bio/chemical Detection

For the detection of individual cells or bio/chemical molecules, micromechanical cantilever sensors with picogram to femtogram mass-sensing resolution in air environment have been attracting intensive research. In the investigation presented in this dissertation, high flexural mode and torsional mode mechanical resonant piezoresistive cantilevers with optimized electromagnetic excitation are developed for the application in ultrasensitive biological sensing in air environment.It is found that the ultimate mass resolution of the resonant cantilever is limited by the frequency fluctuation induced by the thermal-mechanical noise mechanisms. So, Q factor shows central effect on the mass resolution. Moreover, high mode micromechanical resonant cantilevers feature higher Q factor and sensitivity compared to the fundamental mode. Three types of cantilevers are designed to work in the 2^nd flexural mode, in the 1^st torsional mode and in the 2^nd torsional mode, which nominated as OF, CT and OT cantilever, respectively. To achieve the qualified resonance mode, the electromagnetic excitation is optimized by making Lorentz forces match their resonance mode shapes. The piezoresistive sensing schemes are investigate to detect the high resonance mode. For comparison, the cantilever with conventional electromagnetic excitation is also fabricated simultaneity and nominated as CF cantilever.The fabrication of the micromechanical cantilever is developed for the bio/chemical detection based on bulk silicon microfabrication. Several key fabrication processes are developed. To immobile Biotin molecule probe efficiently, the <111> ordered gold film is prepared by the modified electron beam evaporation. To protect aluminum from...