The Research On Electrothermal Coupling Characteristics Of Si-based GaN HEMT Power Transistor

With the rapid development of semiconductor technology,GaN transistors have promoted the era of Wide bandgap power semiconductors with their excellent conductivity and switching characteristics.However,the self-heating effects（SHEs）of Al GaN/GaN power devices has deteriorated dramatically due to the combination of conditions such as heterogeneous epitaxial device structure,degradation of thermal conductivity of semiconductor materials and heat dissipation of silicon substrate.Furthermore,due to the continuous breakthrough in process technology,the integrated circuit industry advances toward higher integration,higher power and miniaturization,which makes the device operating temperature rise significantly,leading to the degradation of GaN HEMT device electrical properties,and even triggering a series of reliability problems.Therefore,in order to realize GaN monolithic integrated power IC applications,it is very important to study the electrothermal characteristics of silicon-based GaN HEMT power devices to promote the industrialization of power integration technology.Aiming at the optimization design of electrothermal characteristics of p-GaN gate enhanced GaN HEMT devices,this thesis analyzes and studies in-depth from the aspects of establishing electrothermal coupling model,dependence of electrothermal characteristics on device structure,device structure optimization design,thermal coupling effect and temperature monitoring chip design.The main research contents are as follows:Firstly,the electro-thermal coupling model of GaN HEMT power transistor on silicon substrate is established,and then the calibration with the experimental data and the dependence of electro-thermal characteristics on the device structure are performed.The results of finite element analysis show that:（1）under the saturated working conditions,the peak operating temperature of the device under the SHEs is 453.7 K,resulting in a degradation of the on-state current of 12.9%,and the distribution of Joule heat generation along the channel depends mainly on the electric field distribution of the device.（2）the increase of the gate length,thermal conductivity of the passivation layer and substrate material and the decrease of the external ambient temperature are all beneficial to improve the thermal performance of GaN HEMT devices under the SHEs.Secondly,a vertical composite passivation structure is proposed for silicon-based GaN HEMT power device,which is beneficial to improve the switching characteristics and heat dissipation performance of the devices by using the combination of upper and lower passivation layer materials with high permittivity and high thermal conductivity,respectively.The results show that when the combined passivation structure is Hf O₂/Al N,compared with the single passivation layer,the on/off-state current ratio of the device is increased by 25.8%,and the thermal resistance is reduced by 11.3%.Thirdly,the influence of multi-gate finger structure on the electrothermal characteristics of GaN HEMT devices is studied,and a design of GaN HEMT devices with on-chip temperature sensor is proposed.The results show that:（1）due to the combined effects of Joule thermal power consumption and thermal coupling effect,the device’s heat dissipation performance continues to decline,and as the output power consumption continues to increase,the thermal coupling effect between channels becomes stronger.（2）the sensor achieves linear temperature monitoring within the operating range of the device.due to the process,the linearity error between different integrated temperature sensors is basically kept within 5%,which can be used to detect the internal temperature of the chip.