The Design And Experimental Research Of 4H-Sic FJ-JBS

With the further research on power devices,the performance of traditional 4H-SiC JBS device is getting closer to its theoretical limits,and the cost of upgrading the performance of the device in the original structure is very large.In this paper,4H-SiC FJ-JBS device with embedded P-layer is designed and fabricated.The experiment results show that the 4H-SiC FJ-JBS device can significantly improve the reverse breakdown voltage and the overall performance without greatly increasing the on-resistance of the device.In this paper,the process of the design is divided into the cell structure design and the terminal structure design.The position of the floating junctions in original cell of the device is the key to determining the performance of the device.The simulation results show that the optimal doping concentration of the upper epitaxial layer is 7.5×10¹⁵ cm^-3 while the thickness of the upper epitaxial layer is 15?m.The floating junctions will be ineffective once its doping is higher than the optimal doping concentration.The optimum thickness of the lower epitaxial layer is determined to be 14.5?m by comparing the BFOM values under different epitaxial layer thicknesses while the doping concentration of the upper and lower epitaxial layer is the same.The simulation results show that the device has the optimal comprehensive characteristics when the width W₂ and spacing S₂ of floating junctions are both 3?m with the doping concentration of upper and lower epitaxial layer 7.5×10¹⁵ cm^-3.The width W₂and spacing S₂ of floating junctions have an effect on the forward and reverse characteristics of the device.The addition of the surface junctions can greatly reduce the reverse leakage current of the device,and the simulation results show that the optimal width W₁ and spacing S₁ are 3?m.The terminals of the device are designed on the basis of the cell structure.The variable spacing field limit terminals are used after taking the efficiency,processing costs and other factors into account.The parameters such as doping type,doping concentration,doping depth and length of the limit rings are determined according to the existing design and reference literature.The simulation results show that there is an upper limit for the spacing of adjacent field rings,and it is 1.8?m when the epitaxial doping concentration is 7.0×10¹⁵cm^-3 by using the BV-d method.According to the above simulation results,different terminals are designed to verify the effect of the maximum field spacing X_max,the first ring spacing X₁ and the incremental spacing of the field?X on the device's breakdown voltage.The layouts of the floating junctions and the technological process of the device are introduced in detail.The experiment results show that the addition of the floating junctions can greatly increase the reverse breakdown voltage without significantly increasing the on-resistance of the JBS device.By comparing the forward characteristics between FJ-SBD and FJ-JBS device,it is found that the forward on-resistance of the FJ-JBS device is slightly larger than that of FJ-SBD device due to the addition of the surface junctions.FJ-SBD's reverse breakdown voltage is very close to that of the FJ-JBS device,but the leakage current of FJ-JBS device is much smaller than that of FJ-SBD device under the same reverse voltage.In addition,the experiment results show that the breakdown voltage of the device is determined by the floating junctions,the surface junctions and the device terminals together.The design process and experiment results of this paper have some guiding significance for the subsequent optimization design and fabrication of 4H-SiC FJ-JBS device.