Simulation Study On A New Type Of Injection Enhanced SiC IGBT

SiC power devices exhibit greater performance because of its wide bandgap,high breakdown field,high resistance to radiations and high thermal conductivity.Insulated gate bipolar transistor(IGBT)is the latest type of power electronic device.It combines the advantages of MOSFET and BJT.It is praised by the industry as the"CPU"of power converters.Therefore,applying SiC materials to IGBTs,combined with the dual advantages of new materials and new device structures,makes SiC IGBTs both hot fronts and general trends.For SiC IGBTs,the contradiction between reducing the forward voltage drop and reducing the turn-off loss has been a research difficulty.Based on the above problems,this paper proposes a novel injection-enhanced SiC IGBT structure for reducing total power consumption,and analyzes the performance of the new structure in detail.The main work obtained are as follows:In this paper,the working principle of SiC IGBT is described in detail.And the simulation parameter model of the SiC IGBT device is given in detail,and the transfer characteristics,on-state characteristics and switching characteristics of the conventional SiC IGBT structure were given by simulation.Then we summarize the calculation method of the characteristic parameters.After that,the thickness of the collector region,the doping concentration of the collector region,the buffer layer thickness,the doping concentration of the buffer layer,drift thickness and the doping concentration of the p-well as several key parameters were simulated respectively.Then the design rules of the SiC IGBT structure were discussed in detail through simulation of key structural parameters.Finally,a conventional SiC IGBT structure is designed and compared as a reference for the new structure simulation in Chapter 3.The working principle of the novel injection-enhanced SiC IGBT structure is described in detail.In the new structure,a top surface Schottky contact is added to the p-base area as a holes barrier to enhance the conductivity modulation effect.And the P-P+-P(shaped like island structure)is formed by multiple ion implantation process steps.Afterwards,the on-state characteristics and switching characteristics of the novel injection-enhanced SiC IGBT structure and the SiC IGBT conventional structure are simulated respectively.The simulation results show that the forward voltage drop and the turn-off loss of the new structure decrease at the same time.The new structure of SiC IGBT offers a forward voltage drop(V_F)decrease of 14%and a turn-off loss reduction of 18%when compared with a conventional IGBT structure on SiC substrate.After that,several key parameters of novel structure such as Schottky barrier height,the ratio of the Schottky contact to the ohmic contact,the depth of the Schottky contact region,and the doping concentration of the Schottky contact region were determined.The simulation results by comparing forward voltage drop and turn-off loss respectively show that the Schottky barrier height and the depth of Schottky contact zone are two key parameters of the new structure,they effects the forward voltage drop and turn-off loss significantly.The increase of SB makes an increase in the turn-off loss,drop in the V_F.The V_F and turn-off loss show a rapid change when Hpp=0.14?m.The V_F increase and turn-off loss decrease when Hpp?0.14?m.In the simulation conditions designed in this study,the optimal Schottky barrier height is 1.79eV,and the total power loss of the device decreases when Hpp?0.14?m.A detailed study was conducted on the latch-up resistance of the novel injection-enhanced SiC IGBT structures.Firstly,the mechanism of latch-up effect,the generation conditions and improvement measures were introduced.For the trench-gate SiC IGBT structure,measures to improve the latch-up effect mainly include reducing the resistance of the well region,reducing the common base current gain of the PNP transistor,and increasing the potential difference tolerance between the emission area and well region.The specific improvement measures for the three aspects were described in detail.After that,the latch current levels of the conventional structure and the novel structure were compared.Several key parameters affecting the latch-up effect of novel SiC IGBTs were discussed such as Schottky contact region doping concentration(Np),Schottky contact region thickness(Hpp)and Schottky barrier height(SB).The simulation results show that reducing the Schottky contact region thickness and the Schottky barrier height significantly improves the latch-up current level of the new structure,but it deteriorates the power loss level of the device.Only by appropriately increasing the doping concentration of the Schottky contact region can make the new structure take into account the latch-up resistance performance without affecting the power consumption performance.