Study On Surge Current Characteristic Of 1200V SiC MOSFET

The potential of SiC MOSFET in the field of power has been widely recognized due to its advantages in high voltage,frequency,and power density,making it a favored choice among researchers in electric vehicles,power transmission,and power conversion,as well as other industries.In recent years,its development has been rapid,making it a highly sought-after choice.Among commercially available SiC MOSFET,planar and trench SiC MOSFET have excellent performance,but their reliability issues have not been effectively addressed,which limits the large-scale application of SiC MOSFET.The device under the surge current stress needs to face the reliability problem at the gate oxygen and the bipolar degradation problem after the parasitic body diode is on.The failure and degradation in the surge process will seriously affect the reliability of the device.This thesis seeks to explore the surge capability of planar and trench SiC MOSFET devices in the third quadrant,utilizing a surge test platform designed and constructed independently,Silvaco TCAD,experimental results,theoretical analysis,simulation verification,and other methods.The single and repeated surge robustness of planar and trench SiC MOSFET is then systematically examined,with a focus on the failure and degradation mechanisms of the device.Exploring emphatically the surge current capability of the device under varying gate voltages,static current and surge current behavior of the third quadrant at high and low temperatures were analyzed.This enabled the current analytical models of planar and trench SiC MOSFET devices in the third quadrant to be proposed,as well as elucidating the factors impacting body diode conduction and the third quadrant current capability of the device.To begin,a self-constructed surge reliability test system is presented.Experimentally,the single and repeated surge reliability of planar and trench SiC MOSFETs under various gate voltages is evaluated.It is discovered that the gate voltage of the device has a considerable effect on the device’s single surge current capability.By detecting the static characteristics and three-terminal impedance of the device,the failure of the device during a single surge is determined to be a gate-source short-circuit or a three-terminal shortcircuit caused by melting of aluminum metal pins,which is verified by simulation.During the repeated surge reliability test,it is found that the threshold voltage of the device degrades under the positive gate voltage,and gradually recovers to the original voltage after standing for a period of time.This is because the trap in the gate oxygen captures electrons during the surge process and then releases electrons during the standing process.An examination of the static and surge current behavior of planar and trench SiC MOSFETs in the third quadrant at both high and low temperatures reveals that the channel state of the device has an influence on the turn-on voltage of the parasitic body diode.With the gradual opening of the channel,the turn-on voltage of the body diode is inhibited and the turn-on voltage increases gradually.Compared with the planar structure,the body diode in the trench structure is inhibited more seriously.When the channel in the trench structure is fully opened,the body diode could not open normally.