Study And OptimΜm Of Self-heating Effects In GaN-HEMT Device

Ga N HEMTs are very promising candidates for high frequency, high power conditions. But for now, the Ga N HEMTs operation is always associated with self-heating effect makes the channel temperature raise, and affect the device DC, RF characteristics and so on. So it has extremely important scientific research value and commercial value to research the principle of self-heating and design some of reasonable thermal optimization scheme. In this paper, we have studing and optimizing the Ga N HEMTs three dimensional thermal model, which is established by using the COMSOL Multiphysics finite element software.Firstly, the basic structure and working principle of Ga N HEMTs was introduced and the formation of self-heating effect was studied. Considering the nonlinear relationship between the semiconductor material thermal conductivity and temperature in the Ga N HEMTs modeling process, we obtained a linear equation by using the Kirchhoff transformation to convert the nonlinear heat conduction equation, and this makes it possible to solve the nonlinear heat conduction equation.Secondly, in this paper a Ga N HEMT two dimensional electrical- thermal coupling model was bulit through studied the COMSOL semiconductor module and solid heat transfer module. Employing this model, we studied the Ga N HEMTs DC characteristics including the self-heating effects, and obtained the location of the heat source in the Ga N HEMT’s three-dimensional thermal model. Then, we built a single-gate Ga N HEMTs thermal model, which was verified with the reference under the same condition. Using this model, we obtained the expression of thermal resistance in theory in the condition of the constant thermal conductivity, and verified it through the simulation. We got equivalent thermal network by fitting the device’s transient heat transfer characteristics. With the three dimensional thermal model, we have done some research on the key factors which can influence the HEMT channel temperature, and found that the substrate material and the thickness is the major factor. In addition, the width and length of gate can also affect the channel temperature to a certain extent.Finally, in order to optimize the device structure that has lower channel temperature, this paper first studied the influence of the mutual resistance on the channel temperature, and pointed out that the self-heating resistance is the main reason that leads to the channel temperature rise. This paper designs two kinds of structure to make the channel temperature decreased by adopting the method of using diamond as integrated heat-spreader. The simulation shows that a kind of structure we used can makes the channel temperature decreases 71 K, compared to the original device, while the other structure makes the channel temperature decreases 119.2K, under the condition of 1 W dissipated power.