Super Junction MOSFET Edge Termination Potential Balance
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Solution Overview
Problem
In planar gate super junction MOSFETs, the large interval between p-type pillar regions leads to potential imbalance in the edge termination region when a RESURF layer is formed, resulting in a high electric field concentration at the end of the p-type pillar region and a significant drop in breakdown voltage.
Innovation Solution
A semiconductor device with a RESURF layer of the second conductivity type formed across multiple pillar regions in the edge termination region, extending in the thickness direction from the surfaces of both the drift and pillar regions, and a high-concentration region of the second conductivity type on the surface of the RESURF layer, with no pillar region under the high-concentration region, to maintain potential balance and enhance breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the thickness of the n-type drift layer is reduced to lower on-resistance, then the on-resistance decreases, but the breakdown voltage decreases due to reduced depletion layer width
Solution Approach 1:
The drift layer is segmented into alternating n-type drift regions and p-type pillar regions in a parallel p-n super junction structure. This segmentation allows the n-type drift regions to provide low on-resistance paths while the p-n junctions generate depletion layers that extend horizontally to provide high breakdown voltage, effectively resolving the trade-off between on-resistance and breakdown voltage.
Solution Approach 2:
Different regions of the drift layer are given different conductivity types and concentrations. The n-type drift regions have high concentration for low resistance, while the p-type pillar regions have high concentration to generate wide depletion layers. This local differentiation allows each region to optimize its function: n-type regions for current conduction and p-n junctions for voltage blocking.
2Reliability
If a RESURF layer is formed across p-type pillar regions in the edge termination region, then potential balance is attempted, but large intervals between pillar regions cause potential imbalance and electric field concentration at pillar region ends
Solution Approach 1:
The high-concentration region of the second conductivity type is extracted and placed specifically in the edge termination region on the RESURF layer, separate from the pillar regions. This extracted high-concentration region acts as a dedicated potential equalization structure that compensates for the large intervals between pillar regions, preventing electric field concentration at pillar region ends and improving potential balance in the edge termination region.
Solution Approach 2:
The high-concentration region in the edge termination region serves as an intermediary structure between the pillar regions. It mediates the potential distribution across the large intervals between pillar regions, providing additional charge carriers that help equalize potentials and prevent excessive electric field concentration, thereby improving the overall breakdown voltage characteristics of the edge termination region.
3Loss of energy
If p-type pillar regions are formed with high concentration to achieve low on-resistance, then on-resistance decreases, but the large interval required between pillar regions causes potential imbalance in the edge termination region
Solution Approach 1:
The invention merges two functions into a unified structure: the RESURF layer provides potential equalization across the pillar regions, while the additional high-concentration region in the edge termination region specifically addresses potential imbalance in that region. This combination allows the pillar regions to be spaced farther apart for lower on-resistance while the merged RESURF layer plus high-concentration region structure maintains breakdown voltage by preventing potential imbalance in the edge termination region.
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 effectively secures a satisfactory breakdown voltage in both the cell and edge termination regions by preventing depletion of the high-concentration region and ensuring efficient potential sharing among pillar regions, thereby increasing the overall breakdown voltage.
Implementation Method 1
in the off state, a depletion layer is stretched in the horizontal direction from each p-n junction extending in the vertical direction of the parallel p-n structure to cause the entire drift layer to be depleted
Implementation Method 2
a high-concentration region of the second conductivity type formed in a surface of the RESURF layer, the high-concentration region being higher in impurity concentration than the RESURF layer, in which no pillar region is formed under the high-concentration region
Data Source
AI summary
An object of the present invention is to provide a semiconductor device capable of satisfactorily securing a breakdown voltage not only in a cell region but also in an edge termination region in a super junction structure. A semiconductor device according to the present invention includes a drift region of a first conductivity type and a pillar region of a second conductivity type a RESURF layer formed across a plurality of the pillar regions in an edge termination region and extending in the thickness direction from surfaces of the drift region and the pillar region, and a high-concentration region of the second conductivity type formed in a surface of the RESURF layer, the high-concentration region being higher in impurity concentration than the RESURF layer, no pillar region being formed under the high-concentration region in the thickness direction.