Power MOSFET Ring Field Plate Corner Breakdown
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Solution Overview
Problem
In semiconductor devices with a super-junction MOSFET structure, the asymmetrical column layout at chip corners leads to curved equipotential lines, causing a reduction in breakdown voltage due to density points, which affects the reliability of power type semiconductor devices.
Innovation Solution
A ring-shaped field plate is disposed around the active cell region in power MOSFETs, with ohmic contact along the sides but not at the corners, to prevent breakdown voltage reduction by managing equipotential line distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ring-shaped field plate with ohmic contact parts is disposed around the active cell region, then the breakdown voltage is improved, but the device complexity increases
Solution Approach 1:
The field plate structure implements different contact configurations at different locations: ohmic contact parts are provided at straight portions of the ring-shaped field plate, while corner portions are designed without ohmic contacts. This local differentiation optimizes the electric field distribution specifically at corner regions where breakdown voltage is compromised, while maintaining simplicity at straight portions.
Solution Approach 2:
The ring-shaped field plate is segmented into distinct functional zones: straight portions with ohmic contact parts and corner portions without ohmic contacts. This segmentation allows each portion to be optimized independently for its specific electrical characteristics, preventing uniform design from causing breakdown at corner regions.
2Ease of manufacture
If ohmic contact parts are disposed along all sides of the ring-shaped field plate, then the manufacturing process is simplified, but the breakdown voltage at corner parts is reduced
Solution Approach 1:
The field plate structure implements different contact configurations at different locations: ohmic contact parts are provided at straight portions of the ring-shaped field plate, while corner portions are designed without ohmic contacts. This local differentiation optimizes the electric field distribution specifically at corner regions where breakdown voltage is compromised, while maintaining simplicity at straight portions.
Solution Approach 2:
The design accepts that complete ohmic contact coverage would simplify manufacturing, but converts the potential harm of corner breakdown into a benefit by strategically omitting contacts only at corner portions while maintaining them at straight portions, achieving both manufacturing feasibility and electrical performance.
Data Source
AI summary
Super-junction MOSFETs by trench fill system requires void-free filling epitaxial growth. This may require alignment of plane orientations of trenches in a given direction. Particularly, when column layout at chip corner part is bilaterally asymmetrical with a diagonal line between chip corners, equipotential lines in a blocking state are curved at corner parts due to column asymmetry at chip corner. This tends to cause points where equipotential lines become dense, which may cause breakdown voltage reduction. In the present invention, in power type semiconductor active elements such as power MOSFETs, a ring-shaped field plate is disposed in chip peripheral regions around an active cell region, etc., assuming a nearly rectangular shape. The field plate has an ohmic-contact part in at least a part of the portion along the side of the rectangle. However, in the portion corresponding to the corner part of the rectangle, an ohmic-contact part is not disposed.