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Powerful bipolar microwave transistors (PBT) operate, as a rule, in conditions close to the limiting ones, which requires controlling the release of heat from the active region of the crystal to the transistor body and further to the environment. One of the most efficient is the control of PBT heat characteristics, including the dependence of the heat resistance - the device body on the electrical mode parameters. However, the quantitative evaluations of connection of defects with measuring the heat parameters of devices in literature are absent. In the work the results of modeling using the COMSOL Multiphysics software the temperature distribution in the structures of a power bipolar microwave transistor (PBT), with defects of electrophysical and thermal nature have been presented. The dependences of the maximum overheating of the crystal working surface on the size and location of the defects have been obtained. It has been shown that the temperature dependence of power density released in the structure of PBT leads to a nonlinear dependence of the maximum and average temperature of the crystal surface on the total power dissipated in PBT. The developed thermal models can serve as the basis for creating the methods for diagnosing the PBT of thermoelectric characteristics and identifying the defective products. The comparative measurements of thermal characteristics of the serial high-power microwave transistors of the KT920B type with no defects and with an artificially introduced electrophysical-type defect in a diode switch-on using a T3Ster meter have shown that the thermal resistance of the body-to-case PBT with the defects has increased by 25-40% compared to the thermal resistance of the defect-free device. In this case, the thermal characteristics of PBT in the diode switching on of the «base-collector» transition are more sensitive to structural defects than in the diode switching on of the emitter-base transition, and more preferable for the purposes of diagnosing the PBT quality.

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