Impedance properties of high-frequency pin diodes

New results of rf and microwave PIN diode modeling are presented which help to predict and explain impedance–frequency characteristics of multilayer semiconductor control devices at low and high power levels. Two techniques of different complexity based on modified physical–topological and equivalent-circuit models are developed and used. “Anomalous” amplitude characteristics of the devices including a bistability phenomenon are investigated. Two main mechanisms are shown to be responsible for the diode impedance behavior at high frequencies. The first one is connected with frequency-dependent properties of the voltage divider formed by the depleted and undepleted regions of the diode base, and with their interaction at large-signal levels. The second one is related to the transit-time phenomenon in the depletion region which results in a reduction of the effective voltage across this region. A new specific parameter is discussed — the characteristic frequency, which determines the range of a rapid and substantial change in the diode impedance properties. The concepts developed in this paper are supported by a broad scope of numerical simulations and are also consistent with real device behavior.