New Structures Design And Characteristics Investigation Of 4H-SiC MOS-Gated Power Devices

With the progress of modern industry and the development of power semiconductor technology,silicon carbide（SiC）power devices as the rising star of the power semiconductor industry has received more and more attention,known as the green environmental protection devices to promote the revolution of new energy consumption.With its unique and superior electrical properties,SiC MOSFET plays an important role in the application fields of high frequency,high voltage and high power.Although SiC MOSFET has great advantages and a wide range of applications,the degree of commercialization is not high at present,and there are still some technical bottlenecks in design and process.First of all,in high voltage applications,there is a high electric field peak in the corner of gate oxide during the blocking state of operation,which results in degradation of both breakdown voltage and reliability.Secondly,in the continuous current applications,the turn-on voltage of the parasitic body diode is high in the reverse conduction.The turn-on of the parasitic body diode can cause the inherent bipolar degradation effect.Finally,the power loss of the device still needs to be further optimized,including conduction power loss and switching power loss.In order to improve the static and dynamic performance of SiC MOSFET,two new structures of 4H-SiC UMOSFET were proposed,and the working mechanism,electrical characteristics and key parameter optimization were explored by using Sentaurus TCAD simulation software.1.A double trench MOSFET with heterojunction diodes and split gate（HS-STMOS）is proposed.The split gate is used to reduce the coupling effect between the gate and drain,and the gate-drain capacitance is directly reduced.The"convex"P-type polysilicon is deposited in the middle and the bottom of the two split gates to form a heterojunction with the drift region.Since the barrier height of the heterojunction is lower than that of the PN junction,the heterojunction can turn on prior to the parasitic body diode in the reverse conduction,and improve the reverse conduction ability and reverse recovery characteristics.In addition,the double trenches and P-type regions,on the one hand,effectively improve the electric field distribution in the drift region to protect the gate oxide layer and heterojunction;on the other hand,part of the gate-drain capacitance is converted into the gate-source capacitance,which indirectly reduces the gate-drain capacitance and improves the switching characteristics.Simulation results show that compared with the conventional SiC MOSFET（C-TMOS）,the FOM(BV²/R_on,sp)of the new structure increases from 0.44 GW/cm² to 0.86 GW/cm²,with an increase of 95%.The reverse turn-on voltage of the new structure is only-0.82V,which is significantly lower than-2.63V.The switching loss of the new structure is reduced from 3.95 m J/cm²to 1.42 m J/cm² by a decrease of 64%.2.A double trench MOSFET with shield gate,hetero-junction diodes and semi-superjunction（SHS-DTMOS）is proposed.The source trench is injected into the P-strip region through multiple epitaxial,forming a semi-superjunction with the drift region.On the one hand,auxiliary depletion of the semi-superjunction can improve the static performance of the device and reduce the turn-on loss.On the other hand,the p-polysilicon/N-drift heterojunction above the p-strip and the gate oxide layer can be protected,and the switching characteristic can be improved by the conversion of capacitance.In addition,the gate is divided into a control gate and a shield gate,and the shield gate has a thicker oxide layer,which greatly reduces the gate-drain charge and the switching loss.Compared with the conventional SiC MOSFET（CC-TMOS）,the FOM of the new structure increases from 0.86 GW/cm² to 2.70 GW/cm²,with an increase of 214%.The reverse turn-on voltage of the new structure is only-0.42V,an 85%improvement over-2.77V.The switching loss of the new structure is reduced from 3.03 m J/cm² to 0.77m J/cm² by a decrease of 75%.