Trench MOSFET Edge Layout for Higher Corner Breakdown Voltage
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Solution Overview
Problem
Existing transistor devices for power applications, such as Si MOSFETs and IGBTs, face challenges in achieving a good on-state resistance (RDS(on)) and higher breakdown voltage, particularly in the corner regions due to edge effects and manufacturing variations.
Innovation Solution
The design of the transistor device includes asymmetrical outermost trenches and edge trenches with optimized contours and radii of curvature to reduce peak electric fields, featuring a semiconductor substrate with cell fields surrounded by edge termination regions, and edge mesas with specific trench and mesa configurations to enhance breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional symmetrical trench designs are used in the cell field, then manufacturing is simpler, but breakdown voltage is reduced due to peak electric fields at corner regions
Solution Approach 1:
The patent applies asymmetry by designing the outermost trenches with different contours compared to inner trenches. Specifically, the outermost trenches have rounded outer corners facing the edge termination region while maintaining sharper inner corners facing the cell field center. This asymmetric design redistributes the electric field to eliminate peak fields at corner regions, thereby increasing breakdown voltage without significantly complicating the overall device structure
Solution Approach 2:
The patent implements local quality by applying different contour characteristics to different locations within the cell field. The outermost trenches have optimized rounded contours at their outer corners to reduce electric field peaks at the interface with the edge termination region, while inner trenches maintain standard contours. This localized optimization addresses the specific electrical stress conditions at different positions within the device
2Reliability
If standard trench configurations are used, then device structure is simpler, but edge effects cause premature breakdown in corner regions
Solution Approach 1:
The edge termination structure incorporates asymmetric trench designs where the outermost trenches have rounded outer corners that specifically address the edge effect problem. This asymmetric configuration at the periphery of the cell field, combined with the edge termination region, creates a more robust structure that resists breakdown from edge effects without requiring complete redesign of the entire device architecture
Solution Approach 2:
The patent applies curvature by rounding the outer corners of the outermost trenches. This spherical/curved geometry at the critical outer corner regions eliminates the sharp angles that concentrate electric fields, thereby preventing premature breakdown caused by edge effects. The curved contours smoothly distribute the electric field lines, enhancing the device's resistance to edge-related breakdown
3Reliability
If all trenches have identical contours, then manufacturing precision requirements are lower, but peak electric fields cause reduced breakdown voltage
Solution Approach 1:
The patent implements asymmetry by differentiating the contours of outermost trenches from inner trenches. The outermost trenches feature rounded outer corners with specific radius of curvature to eliminate peak electric fields, while inner trenches maintain standard rectangular or slightly rounded contours. This targeted asymmetric design addresses the breakdown voltage issue without requiring high-precision manufacturing across all trenches, as only the outermost trenches need the specialized contour
Data Source
AI summary
A transistor device includes a semiconductor substrate having a first major surface, a cell field, and an edge termination region laterally surrounding the cell field. The cell field includes elongate trenches that extend from the first major surface into the semiconductor substrate and that are positioned substantially parallel to one another such that one or more inner elongate trenches are arranged between two outermost elongate trenches and elongate mesas, each elongate mesa being formed between neighbouring elongate trenches. The elongate mesas include a drift region, a body region on the drift region and a source region on the body region. In a top view, one or both of the outermost elongate trenches has a different contour from the one or more inner elongate trenches.