Metal-oxide devices for rapid high current switching

Abstract

Prototypes of Metal-Oxide Threshold Switches (MOTS) have been built using bulk switching effects in chips of transition metal oxides, in most cases niobium-"dioxide", NbO2(x≈2). A 3 mm diameter disc of niobium oxide can pass 100A, millisecond pulses without damage for hundreds of pulses. Chips mounted in microwave diode packages have capacitances of only a few pF, and leakage resistances ranging from the kiloohm to the megohm range in the "off" state. The "on" state occurs within 500 ps after the threshold voltage has been approached, and within a few (≈2) ns, the voltage across the device begins to drop to a "holding" voltage on the order of 20V. Threshold voltages can be varied during manufacture from 60V to the kV range for prototype MOTS. Due to their speed and low capacitance in the "off" state, MOTS devices are well suited as high current transient protectors in RF lines. Another application being studied with present prototype is the "sharpening" of pulses with undesirably long rise times for use in lasers and radars.