Trench MOSFET Gate Segmentation for Low On-Resistance
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Solution Overview
Problem
Trench MOSFETs face challenges in reducing on-state resistance R(DS)ON and gate-drain capacitance CGD, which affects their switching losses and speed, as represented by the Figure of Merit (FOM) that is the product of R(DS)ON and gate charge QG.
Innovation Solution
The semiconductor device incorporates a trench structure with varying gate electrode and dielectric part dimensions, where the first gate electrode part extends deeper into the semiconductor body than the second, and the gate dielectric parts have specific distance relationships, optimizing on-state resistance and gate-drain capacitance independently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the gate electrode extends deeper into the semiconductor body, then the on-state resistance is reduced, but the gate-drain capacitance increases
Solution Approach 1:
The gate electrode is divided into multiple segments at different depths within the trench structure. The first gate electrode part extends to a first depth, while the second gate electrode part extends to a second depth greater than the first depth. This segmentation allows each gate electrode part to control different regions of the semiconductor body independently, enabling the deeper part to reduce on-state resistance while the shallower part limits gate-drain capacitance coupling.
Solution Approach 2:
Different regions of the gate electrode are given different depths and functions. The first gate electrode part is positioned to control the upper region with optimized capacitance characteristics, while the second gate electrode part extends deeper to control the lower region for reduced on-state resistance. This local differentiation of gate electrode quality resolves the contradiction between these two opposing requirements.
2Speed
If the gate dielectric thickness is reduced, then the transistor switching speed is improved, but the breakdown voltage decreases
Solution Approach 1:
The gate dielectric is segmented into multiple layers with different thicknesses at different depths. The first gate dielectric part has a first thickness, while the second gate dielectric part has a second thickness greater than the first thickness. This segmentation enables the upper region to have thin dielectric for fast switching while the lower region has thick dielectric for high breakdown voltage.
Solution Approach 2:
Different thicknesses of gate dielectric are applied at different vertical positions within the trench. The shallower gate dielectric region provides low capacitance for fast switching, while the deeper gate dielectric region provides high insulation strength for breakdown voltage. This local quality variation resolves the contradiction between switching speed and breakdown voltage.
Data Source
AI summary
A semiconductor device includes a semiconductor body including a first surface and a second surface. The semiconductor device further includes a trench structure extending into the semiconductor body from the first surface. The trench structure includes a first gate electrode part and a first gate dielectric part in a first part of the trench structure, and a second gate electrode part and a second gate dielectric part in a second part of the trench structure. A width of the trench structure in the first part is equal to the width of the trench structure in the second part. The semiconductor device further includes a body region adjoining the first and second gate dielectric parts at a side wall of the trench structure. A distance d1 between a bottom edge of the first gate dielectric part and the first surface and a distance d2 between a bottom edge of the second gate dielectric part and the first surface satisfies 50 nm<d1−d2.