Nonrefrigerated Bulk-Semiconductor Microwave Limiters

A microwave limiter using in intrinsic silicon that is operable at room temperature is described. The microwave non-linearity observed for the device is discussed in terms of intrinsic impact ionization, a behavior that is hypothesized from low-frequency studies of the V-I characteristics for the silicon element used. Thus the operation is thought to consist of a transition from essentially a dielectric medium at low RF applied fields to a medium of substantial conductivity resulting from plasma generation by impact ionization at high RF applied electric fields in the tens of kilovolts rms per centimeter. An appropriate circuit structure for the limiter in the form of a slotted metal diaphragm, or resonant waveguide iris is also discussed. In its center is placed the silicon element. The device transmits low-power signals but, shunted by the conductive silicon medium at high incident fields, reflects high power. Details for the fabrication of the limiter as well as a microwave characterization technique to determine absolute values of electric-field strength within and conductivity of the silicon specimen are presented. Finally, the operational details of an experimental model at 9.35 GHz are presented which demonstrate limiting action of 0.4 dB at low power up to 15 dB at a burnout power of 8-kW peak, 8 watts average with l- μ s pulse width. Recovery time is about 5 μ s.