Nano-Thickness Integrated Resonant Cantilevers with Surface-Stiffening Scheme for Ultra-Sensitive Detection of Trace Chemicals

The paper reports an ultra-thin silicon resonant cantilever sensor with a novel through-cantilever doped piezoresistive sensing element and a Lorentz-force resonance exciting element integrated. Torsion-mode resonance is used where shear-stress piezoresistance can be used for the 95 nm-thick silicon nano-cantilever. Thanks to the ultra-thin cantilever where surface sensing effect becomes dominant, molecule specific-adsorption induces a compressive surface-stress that further causes axial-force-induced spring-stiffening of the nano-cantilever. With the surface modified by specific SAM (self-assembled monolayer), the surface-stiffening-induced frequency-shift exhibits an much higher sensitivity to trace trimethylamine vapor, compared to the conventional mass-loading frequency-shift.