Effect of particle contact on the electrical performance of NTC-epoxy composite thermistors

TL;DR

This paper develops a flexible NTC-epoxy composite thermistor by embedding micron-sized NTC particles in an epoxy matrix, demonstrating that particle contact and connectivity significantly influence electrical performance.

Contribution

It introduces a low-stiffness, flexible NTC thermistor material and analyzes how particle contact arrangements affect its electrical properties, a novel approach for flexible temperature sensors.

Findings

Agglomerated NTC particles reduce resistivity by 4 orders of magnitude.

Parallel connectivity of particles enhances electrical performance.

Composite achieves high β-value of 2069 K with 50 vol.% agglomerates.

Abstract

As demand rises for flexible electronics, traditionally prepared sintered ceramic sensors must be transformed into fully new sensor materials that can bend and flex in use and integration. Negative temperature coefficient of resistance (NTC) ceramic thermistors are preferred temperature sensors for their high accuracy and excellent stability, yet their high stiffness and high temperature fabrication process limits their use in flexible electronics. Here, a low stiffness thermistor based on NTC ceramic particles of micron size embedded in an epoxy polymer matrix is reported. The effect of particle-to-particle contact on electrical performance is studied by arranging the NTC particles in the composite films in one of three ways: 1) Low particle contact, 2) Improved particle contact perpendicular to the electrodes and 3) dispersing high particle contact agglomerated clumps throughout the polymer. At 50 vol.\% of agglomerated NTC particles, the composite films exhibit a $\beta$-value of 2069 K and a resistivity, $\rho$, of 3.3$\cdot 10^5$ $\Omega$m, 4 orders of magnitude lower than a randomly dispersed composite at identical volume. A quantitative analysis shows that attaining a predominantly parallel connectivity of the NTC particles and polymer is a key parameter in determining the electrical performance of the composite film.