SRAM Cell FinFET Structure for Speed and Density
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Solution Overview
Problem
The increasing complexity and miniaturization of Static Random Access Memory (SRAM) cells in integrated circuits pose challenges in achieving high read and write speeds, making it difficult to meet demanding performance requirements due to the limitations in processing and manufacturing.
Innovation Solution
The use of continuous fin lines and dielectric-base fins in SRAM cell design, where transistors share semiconductor fins and have varying gate lengths, creates a balanced fin environment, improving device stability and cell matching, and allowing for reduced power supply voltage, thereby enhancing chip speed and manufacturing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If SRAM cells are downscaled to increase functional density, then chip area utilization improves, but read and write speed performance deteriorates
Solution Approach 1:
The patent transitions from planar transistor structures to vertically-oriented FinFET structures with continuous fin lines extending through multiple memory cells. This vertical dimension allows transistors to maintain effective channel control and drive strength despite horizontal downsaling, preserving read/write speeds while increasing functional density.
Solution Approach 2:
The patent merges adjacent fin structures into continuous fin lines that are shared by multiple memory cells. This consolidation reduces manufacturing variability and improves device matching between transistors in different cells, maintaining performance consistency as cells are downscaled.
2Area of stationary object
If SRAM cells are downscaled to increase functional density, then chip area utilization improves, but manufacturing complexity increases
Solution Approach 1:
The continuous fin lines serve multiple functions simultaneously: they act as channel structures for transistors in adjacent memory cells, provide mechanical support, and establish electrical connections. This multi-functionality reduces the number of separate manufacturing steps required compared to individual fin structures for each cell.
Solution Approach 2:
While the fin lines are continuous, the patent segments them into distinct regions with different doping profiles and geometries to create different transistor types (access transistors, pull-up transistors, pull-down transistors) from a single unified structure, simplifying the fabrication process.
3Manufacturing precision
If transistors share continuous fin lines to improve device matching, then manufacturing precision improves, but device stability may deteriorate due to floating sources
Solution Approach 1:
The patent applies different doping concentrations and fin geometries to specific regions of the continuous fin lines. Isolation transistor regions receive different doping than access transistor regions, allowing each transistor type to be optimized for its specific function while maintaining consistency within its category, thus preserving both matching and stability.
Data Source
AI summary
A semiconductor structure is provided. The semiconductor structure includes a substrate and a plurality of memory cells arranged in a cell array over the substrate. Each of the memory cells includes a latch circuit, a pass-gate transistor, and an isolation transistor. The latch circuit is formed by two cross-coupled inverters. The pass-gate transistor is coupled between an output terminal of the latch circuit and a bit line. The isolation transistor includes a drain and a gate, both coupled to the output terminal of the latch circuit, and a source that is floating. A first gate length of the isolation transistor is greater than a second gate length of the pass-gate transistor and a plurality of transistors within the latch circuit.