Flexible thermistors: pulsed laser-induced liquid-phase sintering of spinel Mn–Co–Ni oxide films on polyethylene terephthalate sheets

Abstract

We have prepared spinel Mn_1.56Co_0.96Ni_0.48O₄ (MCN) film thermistors on flexible polyethylene terephthalate substrates at room temperature through the photoreaction of nanoparticles by using KrF laser irradiation. The MCN nanoparticles and metal organic salt solution were crystallized directly on the organic substrates via the laser irradiation. The films were well densified and planarized at 55 mJ cm⁻² for 600 pulses owing to the optimized photothermal heating effect, leading to liquid-phase sintering. This is the first report of the crystallization of MCN, which has a high crystallization temperature of 700–1200 °C, by room temperature processing on flexible substrates. We showed that the nanopores in the precursor are essential for achieving effective focal photothermal heating without damaging the organic substrate. The laser-irradiated MCN films showed negative temperature coefficient thermistor behavior with a very high B constant of 4429 K. The rapid temperature response of the MCN thermistors makes them promising candidates for temperature sensors.