Inorganic-metal composite body exhibiting reliable PTC behavior

摘要

An inorganic-metal composite body exhibiting PTC behavior at a trip point temperature ranging from 40°C - 300°C, including an electrically insulating inorganic matrix having a room temperature resistivity of at least 1 x 10⁶ Ω·cm, and electrically conductive particles uniformly dispersed in the matrix and forming a three-dimensional conductive network extending from a first surface of said body to an opposed second surface thereof wherein the composite body has a room temperature resistivity of no more than 10 Ω·cm and a high temperature resistivity of at least 100 Ω·cm. Preferably, the electrically conductive particles are made of a Bi-based alloy containing at least 50 wt % Bi, and have an average diameter, ϕ_ave, of 5-50µm and a 3σ particle size distribution of 0.5 ϕ_ave-2.0 ϕ_ave. Also disclosed is an inorganic PTC device including an intermediate electrode layer to insure adhesion of outer termination electrodes to the PTC composite body, and a method of forming the composite body, which method effectively deals with the volatility of the electrically conductive particles.