A wafer-bonded silicon load cell operating in the tensioned-wire regime

The authors have used wafer-bonding techniques to fabricate a dielectrically isolated single-crystal silicon version of a dual-port, H-shaped resonant load cell operating in the tensioned-wire regime. The typical geometry reported here is 1.1 mu m thick and has four 1200 mu m long tethers connected at their center by a cross-bar. The resonators are made of p/sup +/ single-crystal silicon which has been determined to be under a net tensile strain of 260 p.p.m. The high length-to-thickness ratio of the resonator, combined with high strain, yield a gage factor which approaches that of a tensioned wire, namely 1/2 epsilon , where epsilon is the strain. In this limit, the gage factor is essentially independent of geometry, and solely dependent on the residual strain in the p+ silicon. It may be possible to take advantage of this tensioned-wire regime to achieve highly repeatable gage factors even in the presence of small geometric variations between devices.<>