Critical behavior of the piezoresistive response in RuO2-glass composites

TL;DR

This paper analyzes the critical behavior of piezoresistance in RuO2-glass composites, revealing non-universal transport exponents and divergence at the percolation threshold, explained by a new tunneling-percolating model.

Contribution

It introduces a novel tunneling-percolating theory tailored to thick-film resistor microstructures, explaining universality breakdown and divergence in piezoresistance.

Findings

Transport exponent t exceeds universal value of 2.0

Piezoresistance diverges logarithmically at percolation threshold

New model accounts for microstructure-specific tunneling effects

Abstract

We re-analyse earlier measurements of resistance R and piezoresistance K in RuO2-based thick-film resistors. The percolating nature of transport in these systems is well accounted by values of the transport exponent t larger than its universal value t=2.0. Furthermore, we show that the RuO2 volume fraction dependence of the piezoresistance data fit well with a logarithmically divergence at the percolation thresold. We argue that the universality breakdown and divergent piezoresistive response could be understood in the framework of a tunneling-percolating model proposed a few years ago to apply in carbon-black--polymer composites. We propose a new tunneling-percolating theory based on the segregated microstructure common to many thick-film resistors, and show that this model can in principle describe the observed universality breakdown and the divergent piezoresistance.