Design,Fabrication And Application Of High-Voltage SiC JFET

Being as one typical representative of wide band material,SiC has always been regarded as an ideal material for power devices.Compared with Si devices,SiC based power devices shall have higher breakdown voltage,higher working temperature and higher switching frequency.And they are expected to expand the usage of power electronics technology in multiple areas,including power grid,renewable energy generation,train transportation and national defense.Especially in the mid-voltage range(3300V-6500V),SiC power devices and power modules show an even better working performance and application prospects.However,the research on mid-voltage range SiC power device is somehow limited.And fewer works are focused on mid-voltage range SiC power modules and their applications.In this work,based on SiC Trench-and-Implanted JFET(TI-JFET)device structure,a systematic study is presented on its structure design,fabrication process development and high voltage module.Also,this work demonstrates the fabrication and testing results of high voltage SiC TI-JFET chips and modules,and their applications in a DC-DC converter.The main contributions of this work include:1.The work presents a systemic modeling and simulation study on SiC TI-JFET structure.And a new device parameter,named "gate voltage swing" is put forward for the first time.With the electron velocity saturation model,the working modes in both linear region and saturation region are studied.And a more precious model is put forward.Also with the finite element analysis software,a series of simulation work is conducted based on SiC TI-JFET structure.And an optimized cell design and termination structure is also presented.2.The works shows the development of some key fabrication processes of SiC TI-JFET device and the process integration is also presented.By adding post annealing processes,the working temperature of passivation layer protected process is increased to 1600? for the first time.With the hard mask of Ti/Ni and SF6 based etching process,a smooth etch surface and trench profile is obtained with SiC wafer;with improved high temperature annealing process,the surface roughness is reduced by one order of magnitude.Both 1200V and 4500V SiC JFET devices are fabricated in group's laboratory.The 1200V device has a low specific on-resistance of 2.33m?cm~2,which is close to the lowest value in the same voltage range.And the 4500V device has a low specific on-resistance of 24m?cm~2.3.This work presents the development of high voltage SiC TI-JFET power module and SiC TI-JFET based all-SiC module for the first time.Difficulties about the wire bonding on trench surface and multi-chip paralleling after wire bonding is issued and addressed.Based on 4500V SiC TI-JFETs and 4500V SiC JBS,a 4500V/30A SiC TI-JFET module and a 3500V/15 A all-SiC power module are fabricated respectively.And a DC-DC converter is also demonstrated with the all-SiC module.The working performance is tested under the switching frequency of 50kHz and 100kHz.This work presents some fundamental works on SiC JFET structure designs,process developments and circuit applications,which are expected to have positive reinforcement for commercialization of SiC JFET in the near future.