Microvaristors in thick-film and LTCC circuits

ZnO-based varistors protect electronic circuits against overvoltage. High temperature from the range of 1150–1300 °C is required for proper sintering of such material. Varistor inks with lower firing temperature are needed for application in thick-film and LTCC technology. ZnO-based thick-film composition was prepared and varistors were fabricated on alumina and LTCC substrate. Different topologies (capacitor-like or planar), electrode metallurgies (PdAg, Au or Pt-based) and firing profiles (850 °C or 950 °C) were used. Samples microstructure was investigated. Varistor I–V characteristics, long-term stability and durability to high voltage pulses were examined. Satisfactory results were achieved, because nonlinearity coefficient α up to 23 was obtained for capacitor-like varistors with Pt terminations on LTCC substrates, long-term thermally aged (150 h at 250 °C) varistors had slightly smaller nonlinearity coefficient and characteristic voltage, V1 mA and components subjected to series of high voltage pulse (1000 pulses with 10 mA amplitude and 5 ms duration each) exhibited almost the same electrical parameters.