SRAM Layout Pattern with L-Shaped Gate for Charge Discharge
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Solution Overview
Problem
In static random access memory (SRAM) cells formed on silicon-on-insulator (SOI) substrates, charges can accumulate under the gate structure, leading to electrical instability due to confinement of these charges.
Innovation Solution
An improved layout pattern for SRAM is proposed, which includes additional diffusion regions with opposite conductivity types to the original regions, and gate structures designed as L-shaped or T-shaped. This configuration allows charges to flow out through the diffusion regions and be released via contact structures, preventing electrical instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional gate structures are used in SRAM cells on SOI substrates, then the device structure is simple, but charges accumulate under the gate structure causing electrical instability
Solution Approach 1:
The gate structure is divided into multiple segments (first gate structure and second gate structure) that are spatially separated. The first gate structure forms a first transistor while the second gate structure forms a second transistor, allowing independent control and charge management for each transistor, thereby preventing charge accumulation and improving electrical stability.
Solution Approach 2:
A body contact structure is introduced as an intermediary element between the substrate and the transistors. This body contact structure provides a charge discharge path for accumulated charges under the gate structures, enabling charges to flow to the substrate and be neutralized, thus eliminating electrical instability without complicating the gate structure itself.
2Reliability
If additional diffusion regions are added to enable charge discharge, then electrical stability improves, but device complexity increases
Solution Approach 1:
The body contact structure is merged with the existing diffusion regions in the SRAM cell. The body contact structure is formed over the substrate and electrically connected to the diffusion regions, combining the charge discharge function with the existing device structure. This integration allows charge management without adding separate, independent components, thus improving electrical stability while minimizing the increase in device complexity.
Data Source
AI summary
A layout pattern of static random-access memory (SRAM) includes a substrate, a plurality of diffusion regions and a plurality of gate structures are located on the substrate, each diffusion region includes a first diffusion region, a second diffusion region, a third diffusion region, a fourth diffusion region, a fifth diffusion region, a sixth diffusion region, a seventh diffusion region and an eighth diffusion region, and each gate structure spans the plurality of diffusion regions. The plurality of gate structures include a first gate structure, the first gate structure includes a first L-shaped portion, which spans the first diffusion region and the fifth diffusion region and forms a first pull-down transistor (PD1), the first diffusion region is adjacent to and in direct contact with the fifth diffusion region.