Lateral-Extended MOSFET Structure for Subthreshold Hump Suppression
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Solution Overview
Problem
The subthreshold hump effect in MOSFETs, caused by shallow-trench isolation processes, leads to non-uniformities and parasitic transistors with lower threshold voltage, resulting in higher leakage currents and undesirable noise behavior in analog circuits.
Innovation Solution
A lateral-extended MOSFET design is implemented, featuring a substrate with an active region, a gate region extended over the active region, and a source region with subregions of varying widths, which introduces additional resistance between the source/drain and channel regions, reducing the impact of parasitic transistors and eliminating the subthreshold hump effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If shallow-trench isolation (STI) processes are used in MOSFET manufacturing, then device fabrication is enabled, but divots appear along the active region edge causing non-uniformities and parasitic transistors with lower threshold voltage
Solution Approach 1:
A lateral-extended source region is introduced as an intermediary structure between the STI edge and the channel. This extended source region with varying width serves as a mediator that increases resistance in the parasitic transistor path, thereby isolating the harmful effect of STI-induced divots from the main channel while maintaining fabrication feasibility
Solution Approach 2:
The source region width is varied laterally to create different resistance zones. By changing the geometric parameter (width) of the source region, the resistance is increased in specific areas to suppress parasitic transistor conduction while maintaining the standard STI fabrication process
2Productivity
If parasitic transistors are present due to STI edge non-uniformities, then additional current paths are created, but leakage current increases due to lower threshold voltage of parasitic transistors
Solution Approach 1:
The source region width is modified to create high-resistance zones that selectively suppress parasitic transistor current while maintaining sufficient current for the main channel. This parameter change in source geometry allows differentiation between useful and parasitic current paths
3Reliability
If parasitic transistors contribute to total drain current, then device operation is maintained, but noise behavior deteriorates in analog circuits
Solution Approach 1:
Different regions of the source are given different widths to create local quality variations. The lateral-extended source region has non-uniform width that creates high resistance specifically in the parasitic transistor path while maintaining lower resistance in the main channel path, thereby locally suppressing noise without affecting overall device operation
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
The design reduces or eliminates the subthreshold hump effect, minimizing leakage currents and noise in analog circuits by increasing resistance in the parasitic transistor paths, thereby improving the overall performance of MOSFETs.
Implementation Method 1
introduces additional resistance between the source/drain and channel regions
Data Source
AI summary
A semiconductor structure may include a substrate, an active region formed on the substrate, a gate region extended over the active region along a first direction parallel to a surface of the substrate, and a source region formed within the active region and adjacent to the gate region in a second direction parallel to the surface and perpendicular to the first direction. The source region may comprise a first subregion and a second subregion such that the second subregion is between the first subregion and the gate region. The first subregion may comprise a first width along the first direction and the second subregion may comprise a second width along the first direction. The first width may be less than the second width.