Thermal Study Of GaN HEMT Devices Based On Three-dimensional Temperature Modeling

Gallium nitride(GAN)high electron mobility transistor(HEMT)devices are widely used in high-power fields because of its excellent electrical performance.However,with the rist of device power,the heating phenomenon becomes more and more obvious.GaN HEMT will form a temperature peak under the gate near the drain(gate-drain)side in the channel at work,and with the sharp increase of power,thermal breakdown will occur in serious cases.Therefore,it is of great significance to study the factors that affect the temperature rise of GaN HEMT channel.In this paper,a three-dimensional(3D)temperature model of GaN HEMT with conventional gate structure,PN junction gate stack structure and field plate structure is established,the principle of heat generation and heat conduction of the device is studied,and the factors forming the temperature peak are analyzed.The main work of the paper is as follows:Compared with the existing measured data,the error rate of the channel temperature peak value is about 5.69% when the side is set as the adiabatic condition.According to the actual situation of device packaging,the packaging material area on both sides of the boundary is added,and the actual boundary temperature is set,so that the error rate of channel temperature peak reaches 2.17%.For the phenomenon that the electric field in the drain side of the channel gate is much larger than that in the source side of the gate,an analytical formula is given based on the energy band analysis.Based on the electric field and charge distribution,it is clear that the dominant channel heat is Joule heat which concentrate on the channel gate drain side,while Thomson-Peltier heat is distributed on the source,drain,gate source side and gate drain side,and the heat generated by carrier recombination is distributed on the gate drain side.Compared with the two-dimensional simulation,the three-dimensional results show that the electric field peak is at both ends and the temperature peak is at the center along the gate width direction.At the same time,a new thermal model expression is derived to explain the relationship between the channel plane temperature and the electric field,charge distribution.Based on the 3D temperature distribution simulation of GaN HEMT device with field plate structure,the influence of channel electric field on temperature is studied.The results show that the channel temperature of field plate structure GaN HEMT device is lower than that of without field plate structure.The reason is that the formation of 2nd peak electric field in the channel makes the hot spot on the gate drain side diffuse to the drain direction;and the redistribution of electric field and charge in the heat source area along the gate drain side makes the heat generation of the hot spot more uniform along the gate width direction.The peak temperature is reduced due to the dispersed heat generation.Changing the size and structure of the field plate can reduce the temperature peak by affecting the channel electric field distribution.Based on the temperature simulation of packaged GaN HEMT devices,the packaging heat dissipation and actual boundary of GaN HEMT devices are studied.The simulation shows that the actual boundary temperature of the device is higher than the room temperature,so the boundary temperature setting of the temperature model needs to be modified.After grooves cutting around the package,it is found that the denser the grooves are,the better the heat dissipation is;the heat dissipation of trapezoidal and conical grooves is better than that of cylinder.This is because the heat dissipation area is increased and the convection heat transfer rate on the package surface is increased,thus reducing the temperature peak.