Transient-Thermal Behavior of Pulsed High Power IMPATT and TRAPATT Diodes.

Abstract

Abstract : Results of an analytical investigation of transient and steady state temperature and current profiles within the active region of a variety of IMPATT structures are presented. The analyses are based on thermal models which assume power dissipation distributions with an axial dependence proportional to the electric field intensity E(z) and a radial dependence proportional to the local current density j(r). Examples are presented in which the local current density is assumed to decrease with the local temperature. The temperature gradients within the active region depend strongly on the doping profile. These analyses show that the maximum temperature at the edge of the active region can be as much as 25% higher than at the center of the avalanche region, especially for high efficiency, high power structures where the ionization is highly localized and the electric field intensity in the drift region is sufficiently high to prevent unsaturated drift velocities and depletion-layer modulation. Breakdown calculations using temperature dependent ionization coefficients and axial temperature profiles suggest that actual temperatures within a device can be significantly higher than those measured experimentally by using a predetermined breakdown voltage vs temperature calibration curve.