Synchronization Optimization Design Of Electrical And Thermal Properties Of Novel Power AlGaN/GaN HEMTs

Power semiconductor devices are the core components of high voltage integrated circuits（HVIC）and smart power integrated circuits（SPIC）and play an important role in energy conservation and emission reduction.With the development of the industry,as one of the research hotspots of the third-generation semiconductor power devices,AlGaN/GaN high electron mobility transistor（HEMT）has received extensive attention.However,the performance of AlGaN/GaN HEMTs is far from the theoretical value.On the one hand,the breakdown voltage（BV）of the device is limited by the lateral electric field peak at the gate edge.On the other hand,under high power operation,the high junction temperature greatly affects the heterojunction polarization,and the thermal reliability of AlGaN/GaN HEMT is problematic.This dissertation mainly focuses on improving the BV and reducing the junction temperature of AlGaN/GaN HEMTs.A series of works such as new AlGaN/GaN HEMT design,simulation optimization,modeling analysis and tape-out testing have been carried out.The performance of power AlGaN/GaN HEMTs is improved by adopting new structures,new processes technologies.While optimizing the BV,the more uniform channel temperature distribution reduces the junction temperature,thereby realizing electrothermal synchronization optimization.In this dissertation,two novel AlGaN/GaN HEMTs are designed using techniques such as electric field modulation effect（EFME）and carrier accumulation:PN junction accumulation layer mental insulator semiconductor AlGaN/GaN HEMT（am-PNAL AlGaN/GaN MIS-HEMT）and AlGaN/GaN HEMT with etched Al Ga N layer（EAL AlGaN/GaN HEMT）.Two-dimensional electro-thermal models are established for the two novel AlGaN/GaN HEMTs,respectively,which can explain the mechanism by modulating the electric field to optimize the temperature and BV.The relationship between the electrical and thermal properties of the device and the structural parameters is obtained,and the modulation factor is further obtained.The tape-out experimental verification of the EAL AlGaN/GaN HEMT was also carried out,and the electrical and thermal properties of the device were tested.The main innovations are as follows:（1）The am-PNAL AlGaN/GaN MIS-HEMT is proposed.In terms of electrical properties,the high-resistance state accumulation region can bear the high-voltage surface electric field on the off-state,which improves the BV,and electrons can be accumulated under in the accumulation layer on the on-state,which effectively reduce the specific on resistance(R_on,sp).The simulation results show that when the gate-drain length is the same,the BV of the new device is 952 V,which is 123%higher than the 420 V of the traditional f AlGaN/GaN MIS-HEMT with ield plate terminal technology.At the same time,the R_on,spof new structure is 0.61 mΩ·cm²,which still has advantages compared with the field plate structure(R_on,sp is 0.76 mΩ·cm²).Therefore,the figure of merit（FOM）of am-PNAL AlGaN/GaN MIS-HEMT has been greatly improved to 1.5 GW/cm^-2.For thermal performance,the hot spot was transfed from the gate edge to the center due to the uniform electric field,and the temperature distribution presents a uniform distribution,thus reducing the maximum junction temperature.Therefore,optimizing the electric field distribution improves the BV and at the same time reduces the maximum junction temperature,which reflects the effect of electro-thermal synchronization optimization.（2）Two dimensional electrothermal model is used to analyze the electrothermal optimization mechanism of am-PNAL AlGaN/GaN MIS-HEMT for the first time.A two-dimensional electrothermal model related to the electric field is established through the derivation of the closure formula,and the physical mechanism of the electric field distribution and temperature field distribution modulated by the accumulation layer is described.By adjusting the accumulation layer parameters,the electric field distribution can be modulated to change the BV and the hot spot position,thereby reducing the junction temperature.The relationship between the electrothermal characteristics and the structural parameters is obtained.When the accumulation layer parameter is 1/2 of the drift region,the electric field and temperature field reach the optimal value at the same time.（3）The general electric field model of AlGaN/GaN HEMTs with electric field modulation effect is summarized.According to its structural characteristics,combined with simulation analysis and solving Poisson equation,a two-dimensional electric field potential distribution model is derived.The physical mechanism of the electric field modulation technology is explained through the mathematical theory model,the relationship between the electric field distribution and the structural parameters of the device is obtained.When the etching length is 6μm and the etching depth is 15 nm,the electrothermal characteristics reach the optimal condition at the same time.（4）A two-dimensional electrothermal model of EAL AlGaN/GaN HEMT with electric field modulation is established.Combining the thermal simulation analysis with the electric field general model of AlGaN/GaN HEMTs with electric field modulation effect,the physical mechanism of optimizing the temperature field distribution of Al Ga N layer etched is expounded through the mathematical theoretical model.The relationship between the electrical and thermal characteristics and the structural parameters is obtained,and the optimal situation of the parameter design of the etched layer is expounded.When the etching length is 6μm and the etching depth is 15 nm,the electrothermal characteristics reach the optimal condition.（5）Tape-out experiments and electrical thermal tests were carried out for EAL AlGaN/GaN HEMT.After several etching process experiments,the key technology was broken through,and the samples were obtained by the layout.The samples were subjected to electrical and thermal tests respectively.The results showed that the BV of the EAL AlGaN/GaN HEMT inreaess from 371V to 621V,nearly doubled of the conventional one.Due to the improved mobility,the R_on,sp decreases,breaking the contradiction between the BV and R_on,sp of traditional power devices.The channel temperature was extracted by Raman thermometry,and the junction temperature is reduced by about 30%at the same power.The test result verifies that the electro-thermal synchronization can be achieved by etching Al Ga N layer.In this dissertation,two new types of AlGaN/GaN HEMTs are proposed.Compared with traditional AlGaN/GaN HEMT,the thermal field problem is alleviated when the BV is improved through new structure design.The modulation mechanism of electrothermal synchronization optimization is systematically discussed for the first time.Through simulation,model analysis and tape-out testing,it is verified that the proposed new AlGaN/GaN HEMT has the advantage of electrothermal synchronization optimization,which has reference significance for the design of high power AlGaN/GaN HEMT.