Thick-Film Thermistor and Its Applications

The electrical properties, reliability, and several successful applications of a thick-film thermistor are described. The thick-film thermistor is composed of a semiconducting oxide, precious metal (RuO2), and glass. The resistivity and thermistor constant are affected to a great extent by the electrical properties of the semiconducting oxide, the particle size of RuO2, and the characteristics of the glass. The thermal expansion coefficient of the semiconducting oxide is required to be less than 105 x 10^-7K^-1in order to prevent the cracks in as-fired film. A resistivity ranging from I\Omega2.cm to 10 M\Omega.cm together with a thermistor constant from 100 to 4500 K can be obtained by controlling these factors. These glass coated thick-film thermistors exhibit extremely high stability. An accelerated life test shows the drift rate as less than 0.02 percent/year in the resistance of a thick-film thermistor with a crystallized glass coating. A thick-film thermistor can be used widely as an accurate and stable temperature sensor and as an exact temperature compensating element in a thick-film hybrid circuit.