Piezoresistive cantilever force sensors based on polycrystalline silicon

We report the fabrication of polycrystalline silicon piezoresistive cantilevers with submicron width and thickness for static force measurements, using electron beam lithography (EBL) and silicon micromachining. For cantilevers with length of 150 μm, leg width of 500 nm and thickness of 320 nm, a force sensitivity of 97 μV/pN and a resolution of 30 pN have been obtained. Bigger cantilevers (leg width 6 μm, thickness 650 nm) fabricated with nominally identical processing conditions have shown a lower resistivity and a higher gauge factor. We show that the differences result from an increased effect of the grain boundaries for the smaller cantilevers. But these have a better force sensitivity and resolution due to their reduced lateral dimensions.