A percolation model of conduction in segregated systems of metallic and insulating materials: Application to thick film resistors

An expression relating the resistivity, R, of a segregated system of conducting and non-conducting media to the volume fraction, V, of the conducting component has been derived by applying percolation theory to a simple but realistic model of the system microstructure. It is proposed that R varies as (p'-p_c)^-mu where p_c is the percolation threshold, mu is the conductivity critical exponent for 3D systems and p' is the fraction of sites in the conducting region that are filled by conducting particles; p' is related to V. The expression can be used to fit the observed R-V curves (blending curves) of thick film resistor systems, which are known to have a segregated structure. The model is valid over a useful range of volume fractions and employs typical values for p_c and mu .