Single crystal silicon nano-wire piezoresistors for mechanical sensors

A p-type silicon (Si) nano-wire piezoresistor, whose minimum cross-sectional area is 53 nm×53 nm, was fabricated by combination of thermal diffusion, EB (electron beam) direct writing and RIE (reactive ion etching). The maximum value of longitudinal piezoresistance coefficient π_l[011] of the Si nano-wire piezoresistor was found to be 48×10^-5 (1/MPa) at surface impurity concentration of 5×10¹⁹ (cm^-3) and it has enough sensitivity for mechanical sensor applications. The longitudinal piezoresistance coefficient π_l[011] of the Si nano-wire piezoresistor increased up to 60% with a decrease in the cross sectional area, while transverse piezoresistance coefficient π_t[011] decreased with a increase in the aspect ratio of the cross section. These phenomena were briefly investigated based on a hole energy consideration and FEM (finite element method) stress analysis.