A three-dimensional thermal analysis of GaN HEMTs on diamond substrate is investigated using the finite element method. The diamond substrate thickness, area and shape, transition layer thickness and thermal conductivity of the transition layer are considered and treated appropriately in the numerical simulation. The temperature distribution and heat spreading paths are investigated under different conditions and the results indicate that the existence of the transition layer causes an increase in the channel temperature and the thickness, area and shape of the diamond substrate have certain impacts on the channel temperature too. Channel temperature reduces with increasing diamond substrate thickness and area but with a decreasing trend, which can be explained by the saturation effects of the diamond substrate. The shape of diamond substrate also affects the temperature performance of GaN HEMTs, therefore, to achieve a favorable heat dissipation effect with the settled diamond substrate area, the shape should contain as many isothermal curves as possible when the isothermal gradient is constant. The study of the thermal properties of GaN on diamond substrate is useful for the prediction of heating of high power GaN HEMTs devices and optimal designs of an efficient heat spreader for GaN HEMTs.
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