Semiconductor Device Non-Uniform Impurity Distribution
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Solution Overview
Problem
Semiconductor devices face a tradeoff between reducing ON-state resistance and maintaining high breakdown voltage, as thinner n-type drift layers decrease breakdown voltage and thicker layers increase resistance, while conventional superjunction structures suffer from decreased avalanche tolerance due to uniform impurity distributions.
Innovation Solution
A semiconductor device with a parallel pn layer structure where the impurity concentration of the n-type drift region and p-type partition region are non-uniformly distributed, with higher concentrations near the drain and lower near the source, maintaining equal total impurity amounts to enhance breakdown voltage and avalanche tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the n-type drift layer is reduced to reduce ON-state resistance, then the ON-state resistance decreases, but the breakdown voltage decreases
Solution Approach 1:
The drift layer is segmented into multiple alternating n-type and p-type layers forming a superjunction structure. This segmentation allows the electric field to be distributed across multiple pn junctions, enabling thinner overall drift layers while maintaining breakdown voltage through the cumulative effect of multiple depletion regions.
Solution Approach 2:
The patent applies different impurity concentrations locally within the drift layer structure. The n-type regions have higher impurity concentrations near the drain and lower near the source, creating optimized local electric field distributions that simultaneously reduce ON-state resistance and maintain breakdown voltage.
2Strength
If the impurity concentration distribution is made uniform to optimize breakdown voltage, then the breakdown voltage is maximized, but the avalanche tolerance decreases
Solution Approach 1:
The patent implements non-uniform impurity concentration distribution within each n-type and p-type layer, with higher concentrations near the drain and lower near the source. This local quality variation optimizes the electric field distribution to improve avalanche tolerance while maintaining overall breakdown voltage through the superjunction structure.
Solution Approach 2:
The impurity concentration profile is made asymmetric within each layer, with deliberately different concentrations at the drain-side and source-side. This asymmetry creates a more favorable electric field distribution during avalanche breakdown, improving tolerance while maintaining breakdown voltage.
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 non-uniform impurity distribution reduces ON-state resistance and increases breakdown voltage while improving avalanche tolerance by concentrating the electric field effectively, allowing for a balance between low resistance and high voltage handling.
Implementation Method 1
The non-uniform impurity distribution reduces ON-state resistance and increases breakdown voltage while improving avalanche tolerance by concentrating the electric field effectively
Implementation Method 2
in the OFF state, the breakdown voltage is sustained by the spreading of a depletion layer from a pn junction between a p-type base region and the n−-type drift layer
Data Source
AI summary
A SJ-MOSFET includes a parallel pn layer in which an n-type drift region and a p-type partition region are alternately arranged repeatedly along a direction parallel to a base main-surface. The n-type drift region and the p-type partition region have total impurity amounts that are roughly the same and widths that are basically constant over an entire depth direction. The n-type drift region is configured to have an n-type impurity concentration profile in which an impurity concentration of a portion on the drain-side is higher than an impurity concentration of a portion on the source-side by ΔCnx. The p-type partition region is configured to have a p-type impurity concentration profile in which an impurity concentration of a portion on the drain-side is higher than an impurity concentration of a portion on the source-side by ΔCph, and an impurity concentration of part of the portion on the source-side is relatively low.