SiC MOS-IGBT Bi-directional Blocking via Substrate and Edge Termination
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Solution Overview
Problem
The fabrication of high voltage silicon carbide power devices, such as IGBTs, is challenging due to the difficulty in producing highly doped p-type substrates and the complexity of gate drive circuitry, as well as the vulnerability to premature breakdown and the limitations in forming planar edge termination structures.
Innovation Solution
The development of high voltage silicon carbide devices with a voltage blocking substrate and a boule grown substrate, incorporating a planar edge termination structure and a beveled edge termination structure, allowing for bi-directional voltage blocking and simplifying the fabrication process by eliminating the need for highly doped p-type substrates, and enabling the use of both n-type and p-type substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If highly doped p-type substrates are used to fabricate high voltage silicon carbide devices, then device performance is improved, but fabrication complexity and difficulty increase significantly
Solution Approach 1:
The patent changes the substrate doping type parameter from p-type to n-type, which is easier to manufacture in silicon carbide. This parameter change maintains device functionality while avoiding the fabrication difficulties associated with highly doped p-type substrates, thus resolving the contradiction between device performance and fabrication ease.
2Reliability
If planar edge termination structures are formed on thick substrates, then manufacturing complexity increases, but voltage blocking capability is improved
Solution Approach 1:
The patent applies beveled (angled) edge termination instead of planar edge termination. The beveled structure creates a gradual transition at the device edges, improving voltage blocking capability by reducing electric field concentration while being more manufacturable on thick substrates compared to planar structures. This resolves the contradiction between voltage blocking capability and manufacturing complexity.
3Power
If bipolar transistors are used for high power applications, then current handling capability is improved, but base drive circuitry complexity and cost increase
Solution Approach 1:
The patent extracts the high current handling capability from bipolar transistors and combines it with MOSFET gate control structures. The resulting IGBT device maintains the bipolar transistor's ability to handle high currents through minority carrier injection while using the MOSFET's voltage-controlled gate for switching, eliminating the need for complex base drive circuitry and resolving the contradiction between current handling capability and control circuit complexity.
4Power
If bipolar transistors operate at high temperatures, then power application capability is improved, but current diversion to single transistor occurs making parallel operation difficult
Solution Approach 1:
The patent changes the conduction mechanism parameter by combining bipolar and MOSFET characteristics. The IGBT's unique structure with its insulated gate and bipolar conduction region allows it to maintain stable current distribution in parallel operations at high temperatures, unlike pure bipolar transistors. This parameter change resolves the contradiction between power application capability and current distribution stability in parallel configurations.
Data Source
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Figure 2C~2D
AI summary
Silicon carbide high voltage semiconductor devices and methods of fabricating such devices are provided. The devices include a voltage blocking substrate. Insulated gate bipolar transistors are provided that have a voltage blocking substrate. Planar and beveled edge termination may be provided.