Investigation into a novel humidity sensor operating at room temperature

Abstract

The investigation into a novel thick film material, a combination of MnO, ZnO and Fe2O3, is documented for humidity sensing applications. To date, no other accounts using this combination for humidity sensing have been reported in the literature. Different paste preparations have been investigated in full, including the effect of increasing polymer content for the polymer samples, and the effect of different firing profiles for the cermet samples. RuO2 has been considered as a method for improving the conductivity of the samples. DC and AC conduction studies have been carried out on different polymer and cermet pastes. From the AC conduction studies, it is confirmed that electronic tunnelling is the dominant conduction mechanism. From the DC conduction studies, space charge limited conduction has been observed. A large number of sensor samples have been manufactured and tested. The fabrication and characterization of three typical sensor samples is presented and discussed in this paper, sample 1: vacuum-fired cermet sensor, sample 2: air-fired cermet sensor and sample 3: 10:1 polymer sensor. The sensor pattern consists of an interdigitated conductor on top of which a 30μm thick sensing layer is printed using screen-printing technology. The thermal effect of the sensors is quite low, ranging from a minimum of 0.0037%/°C (sample 1) to a maximum of 0.0085%/°C (sample 3). In comparison, the measured humidity sensitivity values are much higher, ranging from 0.0356%/RH% (sample 1) to 1.697%/RH% (sample 2). All the samples exhibit a low drift over a 1 year span, low hysteresis, high linearity and reasonably fast response times.