Vertical FET Fin Structure for Positive Threshold Voltage
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Solution Overview
Problem
Conventional power FinFETs require narrow semiconductor fins to achieve a positive switch-on voltage, which is challenging to produce using conventional photolithography, especially for safety-relevant applications.
Innovation Solution
A vertical field-effect transistor design that includes a semiconductor fin with an electrically conductive region and a limiting structure, which limits the conductive channel to the area of the electrically conductive region, allowing for wider semiconductor fins while maintaining a positive switch-on voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If narrow semiconductor fins are used to achieve positive switch-on voltage, then the threshold voltage becomes positive, but the manufacturing precision becomes difficult to achieve with conventional photolithography
Solution Approach 1:
The semiconductor fin is segmented into an electrically conductive region and an electrically non-conductive region along its length. The conductive region has a first conductivity type (e.g., n-type) while the non-conductive region has a second conductivity type (e.g., p-type). This segmentation allows the fin to have a wider overall width that is manufacturable with conventional photolithography while the conductive region maintains the effective narrow width needed for positive threshold voltage.
Solution Approach 2:
Different regions of the semiconductor fin are assigned different electrical properties. The electrically conductive region is doped to have high conductivity to support current flow, while the electrically non-conductive region is doped to have low conductivity to act as a barrier. This local differentiation of properties enables the fin to simultaneously achieve manufacturable width and proper electrical characteristics for positive threshold voltage.
2Ease of manufacture
If wider semiconductor fins are used to ease manufacturing, then the lithographic requirements are reduced, but the switch-on voltage becomes negative
Solution Approach 1:
The fin is divided into conductive and non-conductive segments along its length. The non-conductive region acts as an electrical barrier that prevents the formation of a conductive channel across the entire fin width, effectively reducing the active channel width to match the conductive region width. This allows the overall fin to be wider for easier manufacturing while maintaining the narrow effective width needed for positive threshold voltage.
Solution Approach 2:
The electrically non-conductive region serves as an intermediary element between the source and drain regions. It acts as a barrier that controls the electrical connection, allowing the physical fin to be wide for manufacturability while the non-conductive region effectively narrows the electrical path to achieve the desired threshold voltage characteristics.
3Power
If the semiconductor fin width is increased, then the channel resistance decreases, but the threshold voltage becomes negative
Solution Approach 1:
The fin is segmented into conductive and non-conductive regions. The conductive region provides the current path with low resistance, while the non-conductive region acts as a barrier that maintains positive threshold voltage. The width of the conductive region determines the effective channel width for resistance calculation, while the overall fin width including the non-conductive region can be larger.
Solution Approach 2:
The fin exhibits local quality variations along its length, with the conductive region having high electrical conductivity for current flow and the non-conductive region having low conductivity to control the threshold voltage. This local differentiation allows the fin to simultaneously achieve low channel resistance through the conductive region and positive threshold voltage through the non-conductive region's barrier effect.
Data Source
AI summary
A vertical field-effect transistor. The transistor includes: a drift region having a first conductivity type; a semiconductor fin on or over the drift region; and a source/drain electrode on or over the semiconductor fin, the semiconductor fin having an electrically conductive region that connects the source/drain electrode to the drift region in electrically conductive fashion, and having a limiting structure that is formed laterally next to the electrically conductive region and that extends from the source/drain electrode to the drift region, the limiting structure being set up to limit a conductive channel of the vertical field-effect transistor in the semiconductor fin to the area of the electrically conductive region.