Persons

The power of the HEMT-transistors on the substrate from silicon achieves 100 W, on the substrate from silicon carbide - 1.5 kW. This presents high requirements to the quality of heat removal from the crystal active region to case and further to the environment. In the paper the thermal resistance “junction-to-case” the measurement results for GaN HEMT-transistors have been presented. The measurements have been performed using the apparatus, which includes two methods of thermal resistance measurements. In the first method - according to the standard OCT 11 0944-96, a sequence of heating current pulses is passing through the transistor channel and the junction temperature is measured. In the second method the modulated heating power has been used and the response - variable component of the junction temperature has been measured. To exclude the influence of the heating pulses duration, that is typical for the standard method, preliminary measurements of the transient response of the thermal impedance have been performed. To reduce the influence of the delay time, caused by transient electrical processes in the transistor when it switches from the heating mode to the measurement of the thermal sensitive parameter (TSP) mode, an extrapolation of the TSP signal of this parameter has been performed by the end of the heating pulse. The comparative analysis has shown that the measurements results, obtained by the standard and modulation methods differ by less than 2%. The influence of the amplitude of pulses of the heating current heating pulses has been shown. It has been determined that with increasing the heating current the thermal resistance measured values increases, which indicates to the nonlinear nature of the dependence of the temperature in the transistor channel on the power dissipated in it.

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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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In many radiotechnical systems the microwave power amplifiers based on the monolithic integrated circuits, especially in the output power amplifiers (OPA) of transceiving modules AFAR, have become commonly used. It has been shown that selective distributions of the submodules of the output power amplifiers (OPA) of the APAL transceiving modules of the AFAR X-range on minimum and maximum output power and also on the maximum standing wave ratio (SWR) have a two-modal character, that demonstrates the existence of the prevailing factors of the assembly quality, leading to an appearance of the second mode. The distribution of the OPA submodules on the standing wave ratio by the form is close to the exponential distribution law, and on the consumed current - to the normal distribution law with a small relative average quadratic deviation. The absence of significant correlation between the consumed current and the level of the minimum output power means that the dispersion is determined by the level of the minimum output power but not by the quality of the OPA assembly, and not by the quality of monolithic integrated circuits.

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It has been analytically demonstrated that in the symmetric bipolar transistor structures with small defects with the preset full emitter current the difference between the currents, that flow through the symmetrical parts of the structure, is proportional to the value of the defect, and as a result of the structure self-heating, practically is linearly increasing with the collector voltage increase. The results of the theoretical analysis have been confirmed by computer modeling based on the program package «Workbanclm, supplemented by the block of computation of the structure parts temperatures.

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