NTC Thermistor Ferrite Composite for Temperature Sensing with Reduced Humidity Influence

Negative temperature coefficient (NTC) thermistors, made from semiconducting oxides such as ferrites and used as resistance-based temperature sensors, remain a focus of research, as they are fundamental building blocks of many electronic systems. In this work NTC thermistor properties of a ferrite composite (MnFe
2
O
4
/Fe
2
O
3
) ceramics obtained by solid-state sintering in the form of a bulk sample were investigated. Bulk samples in the form of pellets had an average diameter of 8.7 mm and thickness of 1.8 mm. A thermal (material) constant (B
10,90
) of 4390 K calculated from measured impedance at 100 Hz in the temperature range 10 - 90 °C and temperature sensitivity of -4.87 %/K at 25 °C was obtained. These values fall within the range required for a commercial NTC thermistor material (B between 2000 and 5000, temperature sensitivity between -2 and 6% K at room temperature -25 °C). The influence of relative humidity (RH) change in the range 30-90% at the temperatures of 25 and 50 °C on impedance was monitored within the frequency range 50 Hz – 1 MHz. The obtained results showed that at 100 Hz impedance reduced from 8.15 to 3.56 MOhm at 25 °C and from 2.81 to 1.65 MOhm at 50 deg C for RH from 30 to 90%.The results indicate that the impact of humidity on impedance was less pronounced compared to the effect of temperature on impedance. Future work will focus on applying this ferrite composite in flexible printed temperature sensors.