SiC Semiconductor Drift Layer Relaxing Region Breakdown Voltage
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Solution Overview
Problem
Silicon carbide semiconductor devices face challenges in achieving high breakdown voltage due to electric field concentration, which is different from silicon semiconductor devices, and existing techniques do not fully utilize the physical properties of silicon carbide to improve breakdown voltage.
Innovation Solution
Increasing the impurity dose amount in the relaxing region to satisfy Drx > Ld ● Nd, ensuring a sufficient depletion layer is formed between the relaxing region and the main surface, thereby reducing electric field intensity and increasing the breakdown voltage, with specific conditions such as Ld ≥ 5 µm and Drx ≥ 1×10^13 cm^-2, and using a single crystal substrate with higher impurity concentration to lower contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the impurity concentration in the drift layer is lowered to increase breakdown voltage, then the breakdown voltage increases, but the ON resistance increases
Solution Approach 1:
The drift layer is divided into multiple regions with different impurity concentrations: a first drift layer region with lower impurity concentration (for high breakdown voltage) and a second drift layer region with higher impurity concentration (for low ON resistance). This segmentation allows each region to optimize for its specific function, resolving the trade-off between breakdown voltage and ON resistance.
Solution Approach 2:
Different regions of the drift layer are assigned different local properties (impurity concentrations) to fulfill different functional requirements. The first drift layer region has low impurity concentration to withstand high electric fields, while the second drift layer region has high impurity concentration to reduce resistive losses, achieving both high breakdown voltage and low ON resistance simultaneously.
2Device complexity
If existing Si-based techniques are applied to SiC devices, then the device structure is simplified, but the breakdown voltage cannot be fully optimized for SiC's physical properties
Solution Approach 1:
The invention modifies the impurity concentration parameters within the drift layer by introducing a multi-region structure with different doping levels. This parameter change optimizes the electric field distribution to fully utilize SiC's high breakdown field strength, achieving breakdown voltages that reflect SiC's superior physical properties compared to Si.
3Reliability
If the depletion layer length is increased to reduce electric field intensity, then the breakdown voltage increases, but the device area increases
Solution Approach 1:
The drift layer is segmented into regions with different impurity concentrations to create optimized electric field distribution. This allows the depletion layer to extend effectively through the low-doped first drift layer region, achieving high breakdown voltage without requiring a proportional increase in overall device area, as the high-doped second drift layer region provides compact current conduction paths.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively raises the breakdown voltage of silicon carbide semiconductor devices to at least 600 V by reducing electric field intensity at critical points, preventing breakdown and enhancing electrical resistance.
Implementation Method 1
when a voltage across the first and second electrodes becomes higher as the silicon carbide semiconductor device is set to an OFF state, the relaxing region is prevented from being completely depleted before a depletion layer sufficiently extends from the relaxing region to the first main surface of the silicon carbide layer
Data Source
Figure 1~2
Figure 3
Figure 4~6
AI summary
A drift layer (81) forms a first main surface (P1) of a silicon carbide layer (101) and has a first conductivity type. A source region (83) is provided to be spaced apart from the drift layer (81) by a body region (82), forms a second main surface (P2), and has the first conductivity type. A relaxing region (71) is provided within the drift layer (81) and has a distance Ld from the first main surface (P1). The relaxing region (71) has a second conductivity type and has an impurity dose amount Drx. The drift layer (81) has an impurity concentration Nd between the first main surface (P1) and the relaxing region (71). Relation of Drx > Ld•Nd is satisfied. Thus, a silicon carbide semiconductor device having a high breakdown voltage is provided.