Shielded Trench MOSFET Floating Gate Termination Design
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Solution Overview
Problem
Trench MOSFETs 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 floating deep P body regions, leading to degraded electrical performance.
Innovation Solution
A trench MOSFET design featuring trenched floating gates in the termination area with depths equal to or deeper than the junction of surrounding body regions, without source regions, and using a shielded trenched gate structure with inter-electrode insulation, to maintain high breakdown voltage and reduce gate-to-drain charge, while employing the same conductive materials and trench dimensions as in the active area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the depth of trenched floating gates in the termination area is made shallower than the floating deep P body regions, then the fabrication process is simplified, but the breakdown voltage is significantly degraded
Solution Approach 1:
The patent changes the depth parameter of the trenched floating gates in the termination area, making them equal to or deeper than the floating deep P body regions, which reverses the conventional approach and resolves the breakdown voltage degradation issue while maintaining fabrication simplicity
Solution Approach 2:
Instead of making the trenched floating gates shallower than the P body regions as in prior art, the patent inverts this relationship by making the trenched floating gates equal to or deeper than the P body regions, thereby preventing leakage current while maintaining ease of manufacture
2Ease of operation
If source regions are disposed in the termination area between adjacent trenched floating gates, then the channel region can be controlled, but heavily leakage current occurs between drain and source regions
Solution Approach 1:
The patent extracts or removes the source regions from the termination area, eliminating the source of leakage current while maintaining channel control through the properly depth-matched trenched floating gates that extend to or beyond the P body region junction depth
3Quantity of substance
If multiple trenched floating gates are used in the termination area, then the gate-to-drain charge Qgd is reduced, but leakage current increases due to turned-on channel regions
Solution Approach 1:
The patent changes the depth parameter of the trenched floating gates to be equal to or deeper than the floating deep P body regions, which prevents the channel region from turning on and blocking leakage current while maintaining the low Qgd benefit of multiple trenched floating gates
Data Source
AI summary
A trench MOSFET comprising a plurality of transistor cells having shielded trenched gates and multiple 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. In some preferred embodiments, the trenched floating gates in the termination area are implemented by using shielded electrode structure.