  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.

Applied Physics;Materials Science