Thick-film, niobate-glass threshold switches have been made in reducing gas atmospheres at high temperatures (1100-1400°C) using SiO2and B2O3as glass formers. Their temperature characteristics are far superior to those of similar vanadate switches previously reported [1,2], and they are stable at low ON currents (< mA) if they are protected from atmospheric oxidation. They do not require forming. The process consists in pre-firing the printed, powdered glass in air and then reducing in argon/hydrogen gas. While the reducing conditions are not critical and virtually full reduction to tetragonal NbO2occurs, the pre-firing conditions in air are critical if high-resistance devices are to be obtained. Many devices can be made on a single alumina chip and the results of a statistical analysis are given. The electrical characteristics - measured, chiefly, using a double-pulse technique to examine the change in delay time with pulse separation, ON current, pulse width, etc. - are similar to those previously reported for the vanadate switches . These measurements, together with the results of a microscope and electron-microprobe examination, indicate that a thermal mechanism of switching with filament or channel formation is the most likely. A steady-state computer simulation based on the thermal model indicates the temperatures to be expected during switching, and these are calculated to be less than the NbO2semiconductor-metal transition temperature of roughly 800°C, for all the cases examined. © 1977.
Higgins, J. K. (1977). Threshold switching in niobate glass - thick-film devices. Journal of Non-Crystalline Solids, 23(3), 321–348. https://doi.org/10.1016/0022-3093(77)90117-X