Study On Termination Technologies Of 10-kV Silicon Carbide Diodes And Thyristors

Silicon carbide(SiC)as a wide-bandgap semiconductor have gradually attracted attentions due to its advantages in high-voltage(HV)field.SiC power devices are expected to drive the development of low-carbon and new energy fields,which is of strategic significance for national energy security.However,due to the immaturity of materials and device technology,SiC devices are still mainly applied in the medium-and low-voltage fields(≤3.3 kV),and cannot yet meet the HV requirements(≥8 kV)of several strategic equipment.Therefore,this work focuses on the key common challenges in SiC HV devices,mainly in terms of HV termination,and conducts in-depth research on the design and manufacturing technology.As technical demonstrations,two promising SiC devices in HV power grids are studied,including SiC HV diode and SiC HV thyristor.Taking them as representatives,two novel HV termination technologies are proposed for devices on single-layer and multi-layer epitaxy.Based on these two terminations,10 kV SiC diodes and thyristors are finally developed,besides several innovative achievements in key technologies with certain theoretical depth or engineering difficulty.During the research of HV diodes,the proposed termination is based on ion implantation and named exponentially varying field limiting ring(FLR).To solve the design difficulty from ring number growing in HV FLR,a design method is proposed based on relaxation iteration of depletion region and chain-like derivation of unitized model to achieve near-automatic design for nonlinear HV FLR,leading to an exponential guideline.Besides significantly lower computational consumption,this design achieves more than 90% or even near-ideal blocking capability at the target rating,and the termination length efficiency is almost maintained at a high level of 40 V/μm.Considering the high defect density in thick epitaxy for HV devices,a method to further enhance manufacturability is proposed and verified by the development of 10 kV SiC junction barrier Schottky(JBS)diodes.In this process,interdisciplinary studies on epitaxial defects and interface properties are also conducted,including the defect-related mechanism of the asymmetric breakdown in SiC HV devices,and an method of in-situ unbiased evaluation for the JBS interface barrier.During the research of HV thyristors,the proposed termination is based on epitaxial etching and named steplessly tapered junction termination extension(JTE).To solve the fabrication cylce multiplication in traditional staircase-like formation for HV JTE,a one-step solution is proposed with its design and fabrication technologies.In terms of design,an analytical model of electric field is constructed with boundary field approximation,and a hierarchical progressive optimization method is proposed to achieve near-optimal profiles with systematic steps.Simulation results show that a high termination efficiency of 35 V/μm is expected with this one-step solution,and over 46 V/μm is achievable in ideal cases.In terms of fabrication,diffraction and interference effects during photolithography are utilized with information modulation theory,by which a one-step fabrication method is proposed using a large-scale 3D photolithography as the core technology.This realizes flexibly adjustable and efficient fabrication of steplessly tapered JTEs,which is verified by the development of 10 kV SiC thyristors.The experimental results show that the termination efficiency reaches 25 V/μm,which achieves an advanced level among etching-based solutions without ion implantation.Besides one-step formation,it is much efficient in fabrication and is expected to be more advantageous at higher voltage ratings.In summary,based on SiC HV diodes and thyristors,this work provides an in-depth study of the key common challenges for SiC HV devices,mainly in terms of termination technology,and achieves several innovative achievements in the design theory and fabrication technology,providing an experimentally validated techniacal reference for the subsequent development of SiC HV devices.