Thermal analysis of AlGaN/GaN high-electron mobility transistors on silicon has been performed with emphasis on the influence of the field-plate configuration on power dissipation and temperature profiles along a 2-D electron gas. The results highlight the importance of the field plates in power dissipation and show the difference between various field-plate configurations. Consequently, their design is important for a good thermal behavior and reliability of the transistors. By means of coupled technology computer aided design and finite element modeling simulations, a model is developed and used to characterize test structures in the saturation regime for power densities up to 12 W/mm. In addition, experiments are presented providing RF extraction of the ac output conductance and showing the influence of self-heating in a wide frequency range. In this way, the thermal resistance is extracted. The measured results are in good agreement with the electrothermal model.
The temperature dependence of Raman shifts for different layers and different optical phonon modes in an AlGaN/GaN stack was examined in this study. The slopes of the Raman shifts as a function of temperature for the GaN and Al x GaN layers were found to vary, especially for the E 2 high mode compared with that for the A 1 (LO) mode. To further investigate these fluctuations in the temperature dependence of Raman shifts, a detailed evaluation was conducted for the depth distribution of in-plane strains in the AlGaN/GaN stack by detecting each of the layers simultaneously in a single Raman spectrum. The temperature dependence fluctuations for the E 2 high modes of the Al x GaN layers are considered to be related to the in-plane strain distribution with depth.
A new thermal model based on a distributed and fast modeling approach for the modeling of gallium nitride (GaN) power devices is presented in this paper. The model is based on the application of Green's function theory to obtain an analytical solution of the heat conduction equation. The model comprises an accurate, spatially distributed, and fast algorithm that calculates a 2-D thermal response at the 2-D electron gas level of GaN power devices in the steady-state and the transient regime. In comparison with finite element method finite-element model simulations, the model achieves a significant reduction of the computational time while retaining very good accuracy. The model shows strong capabilities for thermal analysis with respect to parameters that have a significant impact on the thermal behavior. Moreover, the nonlinear effect associated with the temperature-dependent thermal conductivity is encompassed together with the impact of package and ambience. As a validation study, the thermal behavior of packaged GaN devices is experimentally characterized by means of infrared thermography. An excellent agreement between the model results and experiments is observed.
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