Trench MOSFET Floating Gate Depth for Leakage Reduction
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Solution Overview
Problem
Trench MOSFETs with trenched floating gates in the termination area face issues of high leakage current and low breakdown voltage due to poor isolation between the drain and source regions, caused by floating gates not being shorted with source regions and having shallower depths than body regions, leading to degraded electrical performance.
Innovation Solution
The design features trenched floating gates in the termination area with depths equal to or deeper than the body region junctions, without source regions, and includes a substrate with epitaxial layers and specific body and gate structures to maintain high breakdown voltage and reduce gate-to-drain charge, while preventing leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If trenched floating gates are made shallower than body regions to reduce fabrication complexity, then manufacturing precision is improved, but breakdown voltage is significantly degraded
Solution Approach 1:
The patent applies local quality by making the trenched floating gates in the termination area deeper than body regions, while keeping trenched gates in the active area at standard depths. This localized depth differentiation maintains high breakdown voltage in the termination area without compromising the overall device performance or requiring complete redesign of the fabrication process.
2Reliability
If source regions are disposed between adjacent trenched floating gates in termination area, then electrical isolation is improved, but leakage current increases due to turned-on channel regions
Solution Approach 1:
The patent extracts the source regions from the termination area, eliminating the harmful leakage current path that would exist if source regions were present between adjacent trenched floating gates. The termination area contains only the deeper trenched floating gates surrounded by P body regions, removing the conflicting requirement for electrical isolation while preventing leakage.
3Strength
If trenched floating gates are made deeper than body regions to maintain high breakdown voltage, then breakdown voltage is improved, but device complexity increases
Solution Approach 1:
The patent segments the device into two distinct areas with different trench depths: the active area with standard-depth trenched gates and the termination area with deeper trenched floating gates. This segmentation allows each area to be optimized independently for its specific function while using a unified fabrication process, managing device complexity through spatial differentiation rather than process complexity.
Data Source
AI summary
A trench MOSFET comprising a plurality of transistor cells, multiple trenched floating gates in termination area is disclosed. The trenched floating gates have trench depth equal to or deeper than body junction depth of body regions in active area. In some preferred embodiments, the trench MOSFET further comprises a gate metal runner surrounding outside the source metal and extending to the gate metal pad. Furthermore, the termination area further comprises an EPR surrounding outside the trenched floating gates.