Vertical Semiconductor Buffer Layer Segmentation for Turn-Off Loss Reduction
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Solution Overview
Problem
Conventional vertical semiconductor devices face issues with poor controllability of turn-off operations and reduced blocking capability due to steep impurity gradients in buffer layers, leading to increased turn-off losses and leakage currents.
Innovation Solution
A semiconductor device with a vertical structure featuring a buffer layer with a peak impurity concentration lower than the drift layer, and an energy level acting as a recombination center in the band gap, improving voltage blocking capability and reducing leakage current during turn-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a buffer layer with high impurity concentration and steep gradient is used in conventional vertical semiconductor devices, then manufacturing is simplified, but turn-off controllability deteriorates and blocking capability is reduced
Solution Approach 1:
The buffer layer is divided into multiple distinct layers (first buffer layer with higher impurity concentration, second buffer layer with lower impurity concentration) to resolve the contradiction. This segmentation allows each layer to perform its specific function: the first buffer layer provides manufacturing ease while the second buffer layer ensures turn-off controllability by having lower impurity concentration that prevents excessive carrier generation during turn-off.
Solution Approach 2:
Different regions of the buffer layer structure are assigned different impurity concentrations tailored to their specific functional requirements. The first buffer layer adjacent to the drift layer has higher impurity concentration for ease of manufacture, while the second buffer layer has lower impurity concentration for improved turn-off controllability. This local quality differentiation resolves the contradiction between manufacturing ease and reliability.
2Ease of manufacture
If a buffer layer with high impurity concentration is used, then manufacturing is easier, but leakage current increases during turn-off
Solution Approach 1:
The buffer layer structure is segmented into multiple layers with different impurity concentrations. The second buffer layer with lower impurity concentration is specifically designed to reduce leakage current during turn-off, while the first buffer layer maintains manufacturing ease. This segmentation resolves the contradiction between ease of manufacture and reduction of harmful leakage current.
Solution Approach 2:
The buffer layer structure implements local quality differentiation where the second buffer layer has optimized lower impurity concentration specifically in the region where leakage current control is critical. This local optimization reduces leakage current during turn-off while maintaining overall manufacturing feasibility through the first buffer layer.
3Device complexity
If a buffer layer with steep impurity gradient is used, then manufacturing process is simplified, but blocking capability at turn-off is reduced
Solution Approach 1:
The buffer layer is segmented into multiple layers with controlled impurity gradients. Rather than using a single steep gradient, the structure uses multiple gentler gradients across different layers. This segmentation reduces device complexity by avoiding the need for complex single-layer gradient control while improving blocking capability through the cumulative effect of multiple controlled transitions.
Solution Approach 2:
Different regions of the buffer layer structure have different impurity concentration profiles optimized for their specific functions. The first buffer layer has a steeper gradient for manufacturing simplicity, while the second buffer layer has a gentler gradient for improved blocking capability. This local quality differentiation resolves the contradiction between device complexity and reliability.
4Ease of manufacture
If conventional buffer layer structure is used, then manufacturing is simpler, but turn-off loss increases
Solution Approach 1:
The buffer layer is segmented into multiple layers with different impurity concentrations. The second buffer layer with lower impurity concentration reduces carrier generation during turn-off, thereby reducing turn-off energy loss. The first buffer layer maintains manufacturing simplicity. This segmentation resolves the contradiction between ease of manufacture and reduction of energy loss.
Solution Approach 2:
The buffer layer structure implements local quality optimization where the second buffer layer has specifically optimized lower impurity concentration in the region critical for turn-off operation. This local optimization reduces turn-off loss by minimizing excess carrier generation while maintaining overall manufacturing feasibility through the first buffer layer.
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
The solution achieves stable withstand voltage characteristics, reduces turn-off loss, and enhances controllability and blocking capability during turn-off operations.
Implementation Method 1
The second buffer layer has an energy level, which is a recombination center, in a band gap of a semiconductor constituting the second buffer layer
Data Source
AI summary
The present invention has an object of, in a semiconductor device having a vertical structure, providing stable withstand voltage characteristics, reducing a turn-off loss with reduction in leakage current at a time of turn-off, and improving a controllability of a turn-off operation and a blocking capability at a time of turn-off.A buffer layer includes a first buffer layer being joined to an active layer and having one peak point of an impurity concentration and a second buffer layer being joined to the first buffer layer and a drift layer, having at least one peak point of an impurity concentration, and having a maximum impurity concentration lower than that of the first buffer layer, and the maximum impurity concentration of the second buffer layer is higher than the impurity concentration of the drift layer and equal to or lower than 1.0×1015 cm−3.