SiC Drift Region Vacancy Profile for Lower On-Resistance and Turn-Off Loss
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Solution Overview
Problem
Existing semiconductor devices using silicon carbide face a trade-off between reduced on-resistance and increased turn-off loss due to the relationship between minority carrier lifetime and depletion layers, which are not effectively managed in current manufacturing methods.
Innovation Solution
A semiconductor device with a drift region composed of regions with varying carbon vacancy densities, where the boundary between low and high carbon vacancy densities is positioned deeper than the depletion layer end, allowing for optimized minority carrier lifetime control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the minority carrier lifetime in the drift region is increased to reduce on-resistance, then the on-resistance is reduced, but the turn-off loss increases due to residual carriers discharge
Solution Approach 1:
The patent applies local quality by creating a drift region with spatially varying carbon vacancy density. The upper portion has lower carbon vacancy density (longer minority carrier lifetime) to reduce on-resistance, while the lower portion has higher carbon vacancy density (shorter minority carrier lifetime) to reduce turn-off loss. This non-uniform structural design allows simultaneous optimization of both conduction and switching characteristics.
Solution Approach 2:
The patent changes the physical parameter of carbon vacancy density within the drift region to control minority carrier lifetime. By adjusting carbon vacancy density from low in the upper region to high in the lower region, the patent achieves different carrier lifetime characteristics in different spatial zones, thereby resolving the trade-off between on-resistance and turn-off loss.
2Loss of energy
If a region with short minority carrier lifetime is formed in the depletion layer to reduce turn-off loss, then the turn-off loss is reduced, but the on-resistance increases
Solution Approach 1:
The patent applies local quality by restricting the short minority carrier lifetime region (high carbon vacancy density) to only the lower portion of the drift region that is outside the depletion layer. The upper portion within the depletion layer maintains low carbon vacancy density and long minority carrier lifetime, ensuring low on-resistance while the lower portion reduces turn-off loss.
Solution Approach 2:
The patent segments the drift region into functionally distinct zones based on their relationship to the depletion layer. The upper region (within depletion layer) is optimized for conduction with long carrier lifetime, while the lower region (outside depletion layer) is optimized for switching with short carrier lifetime. This segmentation allows independent optimization of conduction and switching performance.
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 configuration improves both on-resistance and turn-off loss, balancing the trade-off relationship by extending hole lifetime in the low carbon vacancy region and reducing turn-off loss through the high carbon vacancy region.
Implementation Method 1
a method for manufacturing a semiconductor device includes the steps of: (a) forming a drift region of a first conductivity type that includes silicon carbide as a constituent material; (b) introducing carbon atoms into an upper surface of the drift region; and (c) diffusing the carbon atoms into the drift region
Data Source
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AI summary
Provided is a technique capable of improving a trade-off relationship between reduction in on-resistance and reduction in turn-off loss. On the premise that a low carbon vacancy density region 20 having a low carbon vacancy density is formed on the upper surface side of the drift region 4 and a high carbon vacancy density region 30 having a high carbon vacancy density is formed on the lower surface side of the drift region 4, the position of an isodensity line 100 that is included in a boundary region 40 between the low carbon vacancy density region 20 and the high carbon vacancy density region 30 and has a carbon vacancy concentration corresponding to a density of 1/2 of the carbon vacancy density of the high carbon vacancy density region 30 is located deeper than an end portion 200 of a depletion layer that extends to the drift region 4 when the IGBT is turned off.