Research On 4H-SiC MOSFET With Fast Switching Speed

With the rapid development of SiC power devices,SiC Mos FETs with fast switching speed have been widely used and studied because of their excellent electrical properties,but there are still limitations in their design and technology.For example,the gate oxide layer at the bottom of the grid is broken down prematurely,the diode with SiC MOSFETs has bipolar degradation and the device’s reverse continuity ability is limited,and the device power consumption problems such as switching loss and reverse continuity loss.These problems are also the focus of research on SiC power devices.In order to solve these problems,two new types of groove-gate 4H-SiC MOSFET devices are proposed,and their internal mechanism and electrical characteristics are studied by simulation software.1.A 4H-SiC grooved MOSFET structure（LG-UMOS）with thick oxide layer and separated gate structure is presented.The main features of the structure are:the separation grid structure is adopted to reduce the width of the grid,and then reduce the longitudinal coupling area between the grid and the drain,and effectively reduce the size of the grid leakage capacity;A thicker oxide layer is adopted at the bottom of the grid,which effectively weakens the electric field concentration effect at the corner of the grooved grid,reduces the peak electric field at the corner,and increases the breakdown voltage of the structure.Finally,the current diffusion region（CSL region）is introduced below the P-base region.Compared with the N-drift region,the CSL region has a higher doping concentration,which makes the structure have better output characteristics.The simulation results show that compared with the conventional structure,the grid leakage capacity of the new device is reduced by 56.3%and the grid charge is reduced by 72%,which reduces the switching power consumption from 0.70m J/cm² to 0.437 m J/cm².In addition,the two high-frequency values of the new device HF-FOM(R_on×C_gd)and HF-FOM(R_on×Q_gd)are reduced by 58%and 73%,respectively.2.Based on the integrated diode structure of LG-UMOS,a split channel gate type4H-SiC MOSFET structure（SLG-UMOS）with integrated diode structure is proposed.The main features of the structure are as follows:the reverse diode structure is integrated on the basis of LG-UMOS structure to improve the reverse recovery ability of the structure;At the same time,a P+shield layer is added under the oxide layer of the grooved gate to protect the integrated diode structure from high electric field and improve the breakdown voltage of the device.The results show that compared with LG-UMOS structure,SLG-UMOS structure has poor output characteristics and higher specific on-off resistance,but SLG-UMOS structure has a higher breakdown voltage,the breakdown voltage increased from 1250 V to 1522 V,and the FOM value also increased.From 0.294 GW/cm²to 0.48 GW/cm².In addition,SLG-UMOS structure has better reverse recovery characteristics than LG-UMOS structure.The reverse recovery charge is reduced by 55.2%from 0.395μC to 0.177μC,and the reverse recovery power is also reduced.