Study On Surge Resistance Of 4H-SiC JBS Diode

4H-SiC JBS diode has the advantages of fast switching speed,high voltage resistance and high operating temperature.It is widely used in high-frequency rectifier and switching power supply circuit.In practical application,it often faces the adverse impact of surge impact on the reliability of the device,so that the device appears micro or macro damage.At present,there are few researches on the degradation mechanism of static electrical parameters and anti-surge ability of 4H-SiC JBS diodes caused by the change of internal defects during the surge process.In this paper,the surge resistance of 4H-SiC JBS diode is studied by numerical simulation and experiment.The main research contents and conclusions of this paper are as follows:1.The influence of device structure parameters on anti-surge capability is studied,and a 4HSiC JBS diode structure with high anti-surge capability is proposed.The simulation shows that the P+area by doping concentration 1×1018cm-3 increases to 1×1019cm-3,The heating power of the device increases from 31.23W to 31.59W in the surge process of 20A,but decreases from 192.62W to 186.46W in the surge process of 40 A where the bipolar conduction mode is dominant.When the Schottky zone width is increased from 1.0μm to 1.8μm,the heating power of the device increases by 1.82W in the 20A surge process,but decreases by 3.13W in the 50A surge process dominated by the bipolar conduction mode.When the doping concentration in the drift region is lower and the drift region thickness is thicker,the heating power of the device in the single and bipolar conduction mode increases.Then,the structure parameters of the device are optimized to meet the requirements of static electrical characteristics,and a 4H-SiC JBS diode with high surge resistance is proposed for the flow plate experiment.2.The influence of drift defects on the surge process dominated by the bipolar conduction mode of the device is studied.The simulation results show that the existence of bulk defects enhances the carrier recombination,leads to the reduction of carrier lifetime,decreases the positive conduction capability of the device,and increases the I-V traj ectory hysteretic degree of the device during the surge process.In the process of 40 a surge current,body defect concentration for 1×1015 cm-3 has the highest device junction temperature reached 1008.6 K,the device of the anode metal has been great damage and lead to device failure.The higher the volume defect concentration,the higher the heating power in the surge process dominated by bipolar conduction mode,so the premature failure of the device will reduce the anti-surge capability of the device.3.The influence of SiC/SiO2 interface states in the field limiting ring(FLR)terminal region on the reverse blocking characteristics of the device is studied.The simulation results show that when the SiC/SiO2 interface traps positive and negative charges,the electric field distribution in the FLR terminal region changes,leading to the degradation of the reverse blocking characteristics of the device.4.The mechanism of the device failure after a single surge impact and the degradation of electrical characteristics after repeated surge impact are experimentally studied.A single surge test of a self-developed device shows that the specific on-going resistance of the device increases from 5.529mΩ·cm2 to 5.635mΩ·cm2 when the surge current increases to 51 A,and the device fails when the surge current increases to 53 A.The repeated surge test showed that the conduction voltage drop VF increased from 1.362V to 1.365V and the breakdown voltage VR decreased from 905.5V to 902.4V after 400 repeated 45A surge tests.After 400 repeated 49A surge tests,the conduction voltage drop VF increased from 1.388V to 1.394V,the breakdown voltage VR decreased from 907.7V to 876.3V,and the static electrical characteristics of the device deteriorated significantly.DLTS test shows that E22 and E23 trap energy levels are generated inside the device after repeated surge impact,and the corresponding activation energies are"0.297eV" and "0.782eV",indicating that the surge test results in damage inside the device and degradation of electrical characteristics.C-V test shows that after repeated surge test,negative charge accumulation occurs at the SiC/SiO2 interface in FLR terminal area,which is one of the reasons for the degradation of blocking characteristics.