FinFET Drive Strength Modification via LDD Omission
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Solution Overview
Problem
Conventional planar MOSFETs face challenges in miniaturization due to increasing variability and short channel effects, making it difficult to manufacture SRAM arrays with acceptable yield, and finFETs struggle to independently alter the drive strengths of transistors in SRAM cells.
Innovation Solution
The method involves selectively modifying the drive strength of finFETs by omitting or forming low-density doped extension regions in the source and drain, allowing for differential drive strengths between transistors in a CMOS circuit, particularly by forming finFETs with or without LDD extension regions based on desired drive strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional planar MOSFETs are miniaturized to increase integration density, then productivity and integration density improve, but manufacturing precision deteriorates due to increasing variability and short channel effects
Solution Approach 1:
The patent transitions from planar MOSFETs to finFETs, moving the channel structure into the third dimension by forming vertical fins. This dimensional change provides better gate control over the channel, reducing short channel effects and improving manufacturing precision while maintaining high integration density.
Solution Approach 2:
The patent modifies the channel doping profile by introducing low-density doped extension regions adjacent to high-density doped source and drain regions. This parameter change in doping density distribution allows independent control of drive strength while maintaining manufacturing feasibility.
2Reliability
If finFETs are used to maintain manufacturing precision, then device reliability improves, but the ability to independently alter drive strengths of different transistors deteriorates
Solution Approach 1:
The patent applies different doping characteristics to different regions of the finFET structure. By forming low-density doped extension regions in some transistors but not others, the invention enables local differentiation of drive strength while maintaining consistent finFET reliability across the circuit.
Solution Approach 2:
The patent segments the doping profile into distinct high-density and low-density regions. This segmentation allows independent control of the extension region doping, enabling drive strength differentiation without compromising the overall device reliability provided by the finFET structure.
3Power
If transistor widths are increased to improve drive strength, then power increases, but area increases which is undesirable for compact circuits
Solution Approach 1:
The patent changes the doping density parameter in the extension regions rather than increasing transistor dimensions. By controlling the presence and characteristics of low-density doped extension regions, the invention modulates drive strength through electrical parameter adjustment while maintaining compact transistor footprints.
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 approach enables improved SRAM cell performance by allowing for the selective reduction of drive strength in pass-gate transistors relative to pull-up and pull-down transistors, enhancing static noise margin and read operation efficiency without increasing the SRAM cell area.
Implementation Method 1
a first low density doped (LDD) extension region in the substrate extending from the first high density doped (HDD) region toward the gate region and a second low density doped (LDD) extension region in the substrate extending from the second high density doped (HDD) region toward the gate region
Data Source
AI summary
A method and circuit in which the drive strength of a FinFET transistor can be selectively modified, and in particular can be selectively reduced, by omitting the LDD extension formation in the source and/or in the drain of the FinFET.One application of this approach is to enable differentiation of the drive strengths of transistors in an integrated circuit by applying the technique to some, but not all, of the transistors in the integrated circuit. In particular in a SRAM cell formed from FinFET transistors the application of the technique to the pass-gate transistors, which leads to a reduction of the drive strength of the pass-gate transistors relative to the drive strength of the pull-up and pull-down transistors, results in improved SRAM cell performance.