Study on thick-film PTC thermistor fabricated by micro-pen direct writing

Micro-pen direct-write technique has been used to fabricate thick-film PTC thermistor. Thick-film PTC thermistors were fired at 700, 750, 800, 850 and 900 °C. The microstructure and the development of the conductive phase were investigated by optical microscope, scanning electron microscopy and X-ray powder-diffraction analysis. Sheet resistivities and temperature coefficients of resistivity were measured as a function of firing temperature. The conductive phase of the PTC thermistor is based on a mixture of RuO2, CuO and ruthenate. Pb2Ru2O6.5 decomposes and the cubic-like CuO particle grows up to spinel-like particle during firing at temperature over 750 °C, while the sheet resistivities decrease from high values to a lowest values.