Impact ionization devices

This paper discusses the fabrication and properties of a new class of microwave limiter device, based on the impact ionization of deep levels in silicon. In this device a deep lying impurity is used to provide a large number of states from which the impact generation of carriers can proceed. Nickel was used to provide the necessary deep levels because of its high solid solubility in silicon. Impact ionization is noted at a critical field of 1 to 2 × 10⁴volts per cm. Once initiated, the voltage across the device falls to a sustaining value. The mechanism of initial breakdown is relatively fast (at subnanosecond rates) while that of clamping to a low sustaining value is comparatively slow (at microsecond rates). The device exhibits an open-circuit-stable negative resistance characteristic during the transition from the high impedance state to the low impedance state.