Study On Hot-electron-effects And Life-prediction Of GaN-based HEMT Devices

GaN-based high electron mobility transistors?HEMTs?are the new generation of microwave and millimeter-wave power devices.It have shown remarkable advantages in frequency,gain and noise performance,which are regarded as the key electronic device for the fifth generation mobile communication technology?5G?eras in the future.However,there are still some reliability issues to be solved urgently about GaN-based HEMTs,especially the hot electron effects and life prediction of HEMT devices have become one of the key factors affecting their industrial application.In this dissertation,the hot electron effects about AlGaN/GaN HEMTs were studied by the simulation methods,and the effects of trap states in different semiconductor layers on the hot electron effects of GaN HEMTs are clarified.Aiming at the problem of the life issue about HEMTs,the life prediction of GaN-based HEMT devices has carried out through the constant temperature accelerated life test.Firstly,the influence of trap states in different semiconductor layers,such as GaN buffer layer,AlGaN barrier layer and the surface trap states of HEMTs,for the thermal electron effect of GaN HEMT devices have been strdied under the same hot electron stresses,by Sentaurus TCAD software.In order to study the influence of different trap states on the hot electron effects of HEMT devices independently,the transient hot electron stresses:gate electrode floated,V_DS?stress?=15V,were established in the simulation experiments.With the stress basis,the acceptor traps were set in the GaN buffer layer,AlGaN barrier layer and the surface of AlGaN barrier layer,with different concentrations and different energy levels respectively.Forthermore,the simulation experiments about hot electron stresses are carried out to the initial simulation model of devices by using the control variable method.With the same hot electron stresses,the datas show that the higher concentration of acceptor traps and the deeper energy level of the traps in the HEMTs'buffer and barrier layers,the more severe degradation of device characteristics,which were manifested by the decrease of device I_DS?sat?and the posistive drift of the threshold voltage V_TH.However,for the same density or energy level of acceptor traps,the degradation of I_DS?sat?in the buffer layer was greater than that in the barrier layer where the trap was located.The positive drift of V_TH in the AlGaN layer was larger than that in the GaN layer where the trap was located.And it was found that the surface state trap had a little effects about HEMTs'electrical properties with the same hot electron stresses.In addition,the scheme of constant temperature accelerated life test have been formulated.The acceleration coefficient of HEMT device under temperature stress have been calculated by Weibull distribution probability diagram method,and the corresponding acceleration equation of life is determined.Then the average life?MTTF?of GaN HEMTs has been predicted at the specified temperature stress level.In conclusion,based on the simulation results,it can be found that both buffer traps and barrier traps could exacerbate the hot electron degradation of GaN-based HEMT devices under the same hot electron stresses.The former has the greatest impact on the I_DS?sat?degradation of HEMT,while the latter has the most significant effect on the V_TH positive drift,while the surface traps have a lettle effect on the thermal electron effect of HEMT.In addition,through accelerated life test,the MTTF reference index of GaN-based HEMT devices under temperature stress of 150oC is given.