Optimization design and simulation of electric field at interface between substrate and electrode of photoconductive switch
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摘要: 研究电极结构、SiC与电极连接结构对界面场强的影响，通过电极边缘以及SiC晶体结构的优化降低界面处的电场增强，并通过高压试验测试优化电极结构的击穿电压。结果表明，优化电极倒角以及SiC晶体与电极的界面下埋可有效降低电场增强，在电极为圆倒角及界面使用焊料连接的结构下，使用介质环的器件在电压22 kV时击穿。Abstract: Photoconductive switch can be used in high power microwave system. The breakdown resistance field strength of SiC photoconductive switches is mainly limited by packaging. The packaging method cannot effectively solve the problem of electric field accumulation when the copper electrode leaves the SiC substrate, which leads to the application field strength of SiC far lower than the breakdown resistance strength of SiC crystal. The effects of the structure of the electrode and the connection structure of SiC to the electrode on the interfacial field intensity are studied. The electric field enhancement at the interface is reduced by optimizing the edge of the electrode and the SiC crystal structure. The breakdown voltage of optimized electrode structure is tested. The results show that the electric field enhancement can be effectively reduced by optimizing the electrode chamfering and burying under the interface between SiC crystal and electrode. Under the structure of circular chamfering and interface connecting with solder, the SiC photoconductive switch breaks down at the voltage of 22 kV.
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Key words:
- photoconductive semiconductor /
- SiC switch /
- electrode /
- interface /
- breakdown field
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图 5 不同圆柱电极结构场强
Figure 5. Electric field intensity of different cylindrical electrode structures
图 7 界面加焊料后电场强度分布图
Figure 7. Electric field intensity distribution with solder interface
图 8 不同焊料厚度电场最大值
Figure 8. Maximum electric field intensity under different solder thickness
图 9 绝缘介质介电常数30的电场分布
Figure 9. Electric field distribution of dielectric constant 30 of insulating medium
表 1 介质环绝缘材料性能表
Table 1. Insulation material performance
material dielectric strength/(kV·mm−1) dielectric constant thermal conductivity/(W·m−1·K−1) CTE/(K−1) CVD diamond 1000 5.7 1000~2000 1.1×10−6 fused silica 25~40 3.75 1.3 0.55×10−6 undoped SiC 300 10 300~500 4.0×10−6 AlN 17 9 140~180 4.5×10−6 epoxy glue 20~40 3.8~6.2 1.1 (20~60)×10−6 Al2O3 16.9 9.8 35 8.4×10−6 silicone 30~40 2.5~4 1.2 300×10−6 ZrO2 9 29 2.2 10.3×10−6 
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表 2 不同介电常数绝缘介质环材料最大场强
Table 2. Maximum electric field intensity of different dielectric constant insulation rings
material dielectric constant maximum electric field /(kV·mm−1) thickness of the solder is 0.03 mm thickness of the solder is 0.02 mm CVD diamond 5.7 39.7 36.8 Al2O3 9 37.1 32.1 undoped SiC、AlN 10 34.4 27.6 CdWO4 12.8 32.3 28.9 MnWO4 15 30.4 27.3 ZnWO4 17.6 27.7 26.1 CoNb2O6 20 27.2 25.7 Ba5Ta4O15 26 24.0 24.1 ZrO2 30 24.8 22.0 ZrO2 32 24.2 23.5
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