Characteristics of silicon nano wire as piezoresistor for nano electro mechanical systems

Abstract

In order to confirm ability of silicon nano wire piezoresistors as sensing element of mechanical sensors, current-voltage (I-V) characteristics and the piezoresistive effect were investigated. Electron beam (EB) direct writing and RIE were used for fabrication. Fabricated polycrystalline Si (poly-Si) nano wire piezoresistors have triangular or trapezoid cross sections. The minimum width is 53 nm and thickness is 32 nm. A remarkable phenomenon was observed. The longitudinal piezoresistive coefficient /spl pi//sub l/ of the nano wire piezoresistor increased with a decrease in the cross section area, while the transverse piezoresistive coefficient /spl pi//sub t/ was approximately zero and invariant despite variation of the cross section area. The maximum value of /spl pi//sub l/ was 22/spl times/10/sup -5/ (1/MPa) at impurity concentration N=5/spl times/10/sup 19/ (cm/sup -3/).