Trench Shield Connected JFET With Deeper Gate Trenches
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Solution Overview
Problem
High-voltage vertical junction field effect transistors (VJFETs) face challenges in achieving low on-resistance and low gate-drain capacitance while maintaining high voltage blocking capabilities, due to conflicting requirements of channel design and processing complexities in trench and implanted structures, which affect device speed and reliability.
Innovation Solution
The implementation of a trench shield approach using a double trench structure, where a deeper trench acts as a shield and a shallower trench as the gate, with specific implantation and connection configurations to reduce electric field stress and gate-drain capacitance, allowing for a shorter vertical channel and improved manufacturing methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional VJFET structure is used, then high voltage blocking capability is achieved, but on-resistance and gate-drain capacitance remain high
Solution Approach 1:
The device is segmented into multiple functional regions including a drift region, a first channel region, and a second channel region separated by a first trench. This segmentation allows each region to be optimized independently for its specific function, enabling the drift region to provide voltage blocking while the channel regions provide low-resistance conduction paths when activated
Solution Approach 2:
The patent introduces a vertical trench structure that extends into the channel area, creating a three-dimensional field distribution. The trench shield structure modifies the electric field in the vertical dimension, allowing the device to achieve high voltage blocking capability while maintaining low on-resistance through optimized field distribution across multiple spatial dimensions
2Reliability
If a conventional VJFET structure is used, then high voltage blocking capability is achieved, but gate-drain capacitance remains high affecting switching speed
Solution Approach 1:
The patent extracts the high-capacitance region by introducing a trench structure that physically separates the gate electrode from the drain region. The trench shield structure removes the electric field coupling between gate and drain, effectively extracting the parasitic capacitance that would otherwise limit switching speed
Solution Approach 2:
The trench shield structure acts as an intermediary element between the gate and drain regions. This intermediate structure modifies the electric field distribution and reduces direct coupling, allowing the device to maintain voltage blocking capability while minimizing gate-drain capacitance for faster switching
3Reliability
If trench and implanted structures are used, then device performance is improved, but processing complexity increases
Solution Approach 1:
The patent combines multiple functions into integrated structures: the trench structure simultaneously serves as an isolation barrier, a field modulation element, and a definition for the channel region. The implanted regions are configured to provide both electrical connection and structural definition, reducing the number of separate processing steps needed
Data Source
AI summary
A shielded junction field effect transistor (JFET) is described having gate trenches and shield trenches, the shield trenches being deeper and narrower than the gate trenches. The gate trenches may be fully aligned, partially aligned, or separated from the shield trenches.