Pulse sharpening with metal-oxide bulk switching devices

Certain niobium oxide (NbO/x/, x is about 2) materials are near insulating at room temperature but undergo an 'insulator-to-metal' transition near 800 C. A similar transition can be initiated at room temperature by applying an electric field exceeding the 'threshold' value, which depends on the oxygen concentration (x) of the NbO/x/. Metal-oxide threshold switch (MOTS) prototypes are obtained by applying appropriate contacts and packaging. Threshold voltages range from 100 V to several kV. A typical MOTS has a surge current capability exceeding 100 A, an off-state capacitance of only a few pF, and a switch delay of less than 0.5 nsec. The latter two characteristics make the MOTS potentially superior to conventional devices for a number of high-speed, high-current switching functions. In particular, insertion of a MOTS into the output circuit of a conventional pulse generator can 'sharpen' the leading edge of the pulse to yield a nsec or even sub-nsec risetime.