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. (C) 1998 Elsevier Science Ltd. All rights reserved.