Temperature characteristics of thick-film resistors and its application as a strain sensor with low temperature-sensitivity

Abstract

Strain gauge made of thick-film resistors (TFRs) has great potential for civil engineering applications due to its relatively high strain sensitivity, good stability, low manufacturing cost, mass productability, and long life. Nevertheless, a persistent shortcoming of strain sensors is their thermal sensitivity. Temperature-insensitive strain measurement is important for applications. To address this issue, a thick-film resistor strain sensor with low temperature-sensitivity should be proposed and fabricated. In this paper, the effect of resistor paste components and firing temperatures on the temperature coefficient of resistance (TCR) of TFRs were studied systematically. TFRs made of various RuO2 concentrations (10 wt% to 30 wt%) fired on Al2O3 substrate at different firing temperatures (Tf) was investigated. The relationships between sheet resistivity, TCR and gauge factor (GF) were studied. The results show that hot TCR increases with increasing RuO2 concentration and firing temperature. In the vicinity of the minimum of the resistance–temperature curve (Tmin), the temperature has the least influence on the resistance value, and it can be considered that the TFR is temperature insensitive in a certain range. The effect of temperature on output strain can be evaluated by the ratio of TCR to GF. The results show that TCR, the ratio of TCR to GF and Tmin are all depended on sheet resistivity of thick-film resistors. By changing the concentration of the conductive phase and firing temperature, the sheet resistivity of TFRs can be controlled, and then strain sensors with low temperature-sensitivity for different ambient temperatures can be achieved.