Study On Synergy Mechanism Of Hydrogen Poisoning,high Temperature And High Field Stress In AlGaN/GaN High Electron Mobility Transistors

AlGaN/GaN High Electron Mobility Transistors(HEMTs)are widely applied in radio frequency and microwave applications,which have high efficiency,high temperature resistance and high frequency performance.However,hydrogen released from the packaging material causes hydrogen poisoning of the device,and hydrogen poisoning tends to act synergically with high temperature and high field stress to degrade the device,but the synergy mechanism between them is not clear.Therefore,this paper studies the degradation mechanism of AlGaN/GaN HEMT under the synergistic action of hydrogen poisoning and high temperature and high field stress.The main results are as follows:(1)The degradation mechanism and the synergy mechanism of hydrogen poisoning and hot-electron stress after hydrogen treatment were studied.It was found that the time of hydrogen treatment had different effects on device reliability.Ga vacancies and N vacancies in the AlGaN/GaN interface and in the interior and surface of Al Ga N are obviously passivated,leading to threshold voltage shift and transconductance degradation,and subsequent hot electron stress gives the H which occupied vacancies the energy to break free,resulting in the defect dehydrogenation and more Ga vacancies,which makes the hydrogen poisoned device degrade more seriously than the non-hydrogen poisoned device.Meanwhile,hydrogen has limited passivation effect on the device after hot electron stress,indicating that hot electron stress causes irreversible damage to AlGaN/GaN interface and buffer layer;(2)The effects of high temperature and high field stress in the packaging environment on HEMT devices were investigated.Through short-term and long-term high temperature reverse bias(HTRB)experiments,the degradation process and degradation mechanism of the device under high temperature and high gate-to-drain off-state stress are studied,and it is found that the device has obvious time-dependent phenomenon under high temperature and high field stress.Under short-term stress,electrons are trapped in acceptor states and/or shallow-level defects in the Al Ga N under the gate and in the buffer layer of the device within a few seconds,resulting in depletion of the two-dimensional electron gas(2DEG),positive threshold voltage shift,2DEG away from the Al Ga N surface;when the high temperature and high field stress time is prolonged,the interface layer between the metal gate and the Al Ga N layer in the device is gradually consumed,forming a close metal-semi contact,and the donor state of the Al Ga N surface is ionized,and the threshold voltage gradually drifts negatively.At the same time,the deep level traps in the buffer layer capture electrons,and the electron decapture time is long,resulting in a decrease in the carrier concentration.After the long-term stress reaches thousands of hours,the threshold voltage of the device drifts positively,and the leakage increases under low negative bias significantly reduced.The reverse leakage mechanism in the gate region becomes frenkel-Poole(FP)tunneling,and the effective emission barrier height of the deep level defect state decreases significantly.The trapped electrons will enter the conduction band by thermal emission;(3)The effect of high temperature and high field stress on the degradation of the device after hydrogen treatment was studied,and a new degradation mechanism was proposed by the HTRB experiment in water vapor for verification and further research.In the short-term and long-term HTRB experiment after hydrogen treatment,the short-term stress makes the threshold voltage of the device change to a greater extent.There is no hot electron involved in this process.The driving force for hydrogen decapture is mainly electric field and temperature.High temperature makes a part of hydrogen detrapped in the defect.The high electric field causes vacancies to be emitted from the interface,which cross the Al Ga N barrier and enter the Schottky contact interface,forming a positive charge accumulation;with the increase of stress time,the holes are gradually consumed,the gate leakage current gradually decreases.The acceptor state in the AlGaN/GaN interface and the buffer layer region is increased,which depletes the electrons in the channel.