Improvement of structural and electrical properties of Mn-based thin film thermistors by a bilayer structure

Mn1.85Co0.3Ni0.85O4 (MCN), Mn1.85Co0.3Cu0.3Ni0.55O4 (MCCN) thin film and MCN-MCCN bilayer thermistors were prepared on Al2O3 substrates by a chemical solution deposition method. The MCN-MCCN bilayer thermistor showed better microstructure, lower resistance and smaller aging coefficient than those of the MCN and MCCN thin film thermistors. Temperature dependent ac impedance spectroscopy was employed to analyze the contributions of grain, grain boundary and interface between two layers to the conduction mechanisms in the MCN-MCCN bilayer thermistor. The results from this study showed that the bilayer structure was an effective way to improve and adjust the properties of NTC thin film thermistors.