Trench MOSFET Floating Gate Termination for Leakage Reduction
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Solution Overview
Problem
Trench MOSFET designs with trenched floating gates face issues of high leakage current and low breakdown voltage due to poor isolation between drain and source regions, particularly in the termination area, where the depth of trenched floating gates is shallower than the deep P body regions.
Innovation Solution
The design features trenched floating gates in the termination area with a depth equal to or deeper than the junction of the surrounding body region, without a source region, and wider and deeper trenched gates compared to those in the active area, to maintain high breakdown voltage and reduce gate-to-drain charge, while preventing current leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the depth of trenched floating gates in termination area is made shallower than deep P body regions, then the fabrication process is simplified, but the breakdown voltage is significantly degraded and leakage current increases
Solution Approach 1:
The patent applies different trench depths to different regions: the trenched floating gates in the termination area have a first depth, while the body regions have a second depth greater than the first depth. This local differentiation allows the body regions to provide adequate breakdown voltage while the trenched floating gates simplify the fabrication process by not requiring equal depth matching.
2Ease of operation
If n+ source region is disposed between adjacent trenched floating gates in termination area, then the channel conduction is improved, but heavily leakage current occurs between drain and source regions
Solution Approach 1:
The patent removes the n+ source region from the termination area between adjacent trenched floating gates. By extracting this conductive element from the termination region, the patent eliminates the leakage current path that would otherwise exist between drain and source regions when the channel is turned on, while maintaining channel conduction in the active transistor areas.
3Manufacturing precision
If trenched floating gates are made shallower than body regions, then the fabrication alignment is easier, but poor isolation between drain and source regions causes low breakdown voltage
Solution Approach 1:
The patent implements local quality by assigning different depths to different structural elements: trenched floating gates have a first depth while body regions have a second depth greater than the first. This depth differentiation simplifies fabrication alignment requirements while the body regions extend deeper to provide the necessary isolation and maintain breakdown voltage in the termination area.
Data Source
AI summary
A trench MOSFET comprising a plurality of transistor cells with a plurality of wide trenched floating gates as termination region is disclosed. The trenched floating gates have trench depth equal to or deeper than body junction depth of body regions in termination area. Each body region between two adjacent said trenched floating gates has floating voltage.