Trench MOSFET P-Shield Layout for Gate-Edge Field Relief
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Solution Overview
Problem
Conventional trench structure MOSFETs face issues with electric field concentration at the trench gate edge, leading to reduced reliability and difficulty in precisely controlling the channel area and short circuit characteristics.
Innovation Solution
The power semiconductor device incorporates a substrate with an epi layer, spaced-apart wells of a second conductivity type, a gate with a gate insulating layer, and a doped region of the first conductivity type. The wells are positioned to surround the lower edge region of the trench gate, and the second doped region is formed through an epitaxial re-growth process to control the channel length and prevent electric field concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a trench structure MOSFET is used, then the switching speed is improved, but electric field concentration occurs at the trench gate edge
Solution Approach 1:
The patent applies local quality by introducing a P-type shield region specifically at the lower edge of the trench gate where electric field concentration occurs. This localized modification addresses the harmful electric field concentration at the critical location without changing the overall trench structure that provides high switching speed. The P-type shield region creates a local field redistribution that prevents breakdown at the edge while maintaining the high-speed characteristics of the trench MOSFET.
Solution Approach 2:
The P-type shield region acts as an intermediary element between the trench gate and the drift region. It mediates the electric field distribution by introducing an intermediate layer that prevents direct field concentration at the trench gate edge. This intermediary structure allows the high-speed operation to be maintained while protecting against electric field-induced breakdown.
2Object-affected harmful factors
If a P-shield process is performed to solve electric field concentration, then electric field distribution is improved, but process complexity and cell pitch increase
Solution Approach 1:
The patent merges the P-type shield region formation with the existing trench isolation process. By combining these two functions into a single process step, the patent avoids adding separate mask layers and process steps that would increase complexity. The P-type doping is performed simultaneously with the trench isolation doping, eliminating the need for additional P-shield specific process steps while still achieving electric field distribution improvement.
Solution Approach 2:
The P-type shield region serves multiple functions: it acts as both the trench isolation structure and the electric field shielding layer. This multi-functionality eliminates the need for separate P-shield process steps, reducing overall process complexity while maintaining the electric field distribution benefits. The same doped region provides both structural isolation and electrical field management.
3Ease of manufacture
If conventional trench structure is used, then manufacturing is simplified, but channel area control precision is reduced
Solution Approach 1:
The patent replaces mechanical/channel-defined structures with an electric field-defined channel structure. Instead of relying on physical trench dimensions to define the channel area, the channel is defined by the electric field extension from the gate into the drift region. This substitution allows for more precise channel area control through electrical parameters (gate voltage, doping concentration) rather than mechanical tolerances, while maintaining manufacturing simplicity.
4Device complexity
If conventional trench structure is used, then device structure is simple, but short circuit characteristics control is difficult
Solution Approach 1:
The patent changes the controlling parameter for short circuit characteristics from geometric dimensions to doping concentration and electric field distribution. By adjusting the P-type shield doping concentration and the gate oxide thickness, the short circuit characteristics can be precisely controlled without changing the basic trench structure. This parameter-based control provides finer tuning capability while maintaining structural simplicity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively prevents electric field concentration, allows precise control of the channel length, enhances the reliability of the device during high-speed switching, and reduces the risk of damage during the doping region formation.
Implementation Method 1
the second doped region (140b) may be formed by an epitaxial re-growth process
Data Source
Figure 1~2
Figure 3
Figure 4A
AI summary
A power semiconductor device according to an embodiment and a power converter including the same may include: a substrate; an epi layer of a first conductivity type disposed on the substrate; a plurality of wells of the second conductivity types disposed spaced apart from each other on the epi layer ; and a gate disposed between the wells and a gate insulating layer disposed to surround the gate; and a doped region of the first conductivity type disposed on a side of the gate insulating layer. The doped region may include a first doped region of the first conductivity type having a first horizontal width and a second doped region of the first conductivity type disposed below the first doped region and having a second horizontal width smaller than the first horizontal width.