Device Design And New Structure Research Of 3300V SiC MOSFET

In recent years,with the rapid development of semiconductor technology,the performance of traditional silicon-based devices has approached its theoretical limit.In the background of silicon-based devices difficult to be greatly optimized,silicon carbide devices are favored because of its characteristics of high current,high voltage,high frequency and low loss,which can significantly improve the performance of power semiconductor.In particular,silicon carbide power devices play a very important role in efficient energy conversion.SiC MOSFET has become one of the fastest growing power semiconductor devices because of its low on resistance,good thermal stability,fast switching speed and high blocking voltage.In the current application environment of power electronics,high frequency is an extremely important application demand.In high frequency applications,the dynamic loss of SiC MOSFET becomes the main source of system loss,and determines the application efficiency and the highest working frequency of the circuit system.However,the current performance of SiC MOSFET has not reached its theoretical level.Based on the problem of large dynamic loss of SiC MOSFET at high frequency.In this thesis,a3300V SiC integrated SBD split gate MOSFET（SSG MOS）is designed.In order to further improve the High Frequency Figures-Of-Merit（HF-FOM）(_on,×₂（9）),a Buffered Gate SiC MOSFET with Integrated SBD（SBG-MOS）and a Mesa Buffered Gate SiC MOSFET with Integrated SBD（SMBG-MOS）are proposed.In addition,according to the voltage characteristics of the above devices,the field limiting ring terminal structure with gradual ring spacing is also designed.The main work of this thesis is as follows:In this thesis,a 3300V SiC split gate MOSFET（SSG-MOS）integrated with SBD is designed.The static and dynamic characteristics of the structure are simulated.The results show that the SSG-MOS has the advantages of both the split gate MOSFET and MOSFET integrated with Schottky diode,and on the basis of reducing the switching loss,it also improves the reverse recovery ability and the current continuation ability.At the same time,two kinds of new device structures with ultra-low High Frequency Figures-Of-Merit（HF-FOM）(_on,×₂（9）)are proposed,which are Buffered Gate SiC MOSFET with Integrated SBD（SBG-MOS）and Mesa Buffered Gate SiC MOSFET with Integrated SBD（SMBG-MOS）.For SBG-MOS,the main feature is to keep the width of the original gate electrode unchanged and add a p-well'region injected simultaneously with the p-well region.By setting an N-well region in the p-well'region as the path of carrier flow,the gate electrode does not overlap with the JFET region,so the gate-drain capacitance and gate-drain charge of the new structure are greatly reduced,and the high-frequency optimal value is also greatly reduced.Compared with SSG-MOS,the gate-drain charge of SBG-MOS is 50nC/cm²,which is decreased by 64.3%;HF-FOM is 945mΩ·nC,which is decreased by 60%.For SMBG-MOS,its main characteristics are similar to SBG-MOS,the difference is that the structure uses the secondary epitaxy technology to make the mesa on the JFET area,and the Schottky electrode is located on the mesa of the JFET.When conducting in the forward direction,the current enters the mesa through the channel,reducing the resistance.Compared with SSG-MOS,the specific on resistance of SMBG-MOS is14.1mΩ·cm²,which is decreased by 17%;the gate-drain charge is 75 nC/cm²,which is reduced by 46.4%;the HF-FOM is 1057mΩ·nC,which is improved by 55.3%.The 3300V SiC split gate MOSFET integrated with SBD and two new SiC MOSFET structures proposed in this thesis not only reduce the dynamic loss of the device,but also improve the dynamic capability of the device.It also solves the problem of chip area increase caused by external anti parallel Schottky diode,prevents the start of SiC MOSFET parasitic PIN diode,avoids the bipolar degradation of the device,and improves the reliability.