Preparation and influence of highly concentrated screen-printing inks on the development and characteristics of thick-film varistors

The preparation of screen-printing inks with a high solids load was studied for the development of thick-film varistors. A high solids load can ensure a higher green density of the films for enhanced densification and microstructure development in order, to obtain good current-voltage (I-U) characteristics for the thick-film varistor, even after short firing times at temperatures below 1000 °C. The inks with a solids load of 50, 60 and 70 wt.% enabled the preparation of thick-film varistors on an alumina substrate with a homogenous microstructure, a uniformly distributed Bi2O3-rich phase and a good varistor film-electrode contact after firing at 900 °C for 15 min. However, the porosity of the films gradually decreased with the increasing solids load and a varistor film prepared from the ink with the highest solids load of 70 wt.% had minimal porosity and improved I-U characteristics in comparison with the other samples.