SRAM Layout With Segmented Bitlines for Lower RC Delay
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Solution Overview
Problem
The existing SRAM designs face performance degradation due to bitline resistive-capacitive (RC) delay, which is exacerbated by a higher number of memory cells electrically coupled to bitlines, leading to slower read and write operations.
Innovation Solution
The SRAM layout optimizes memory cell placement with a smaller bitline loading by using gate-all-around field effect transistors (GAA FETs) and a single well pick-up region, reducing parasitic effects and implementing higher level interconnects for bitline routing to minimize congestion, thereby reducing bitline RC delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If traditional SRAM layout is used with increased bitline loading, then memory capacity is increased, but bitline RC delay increases and performance degrades
Solution Approach 1:
The bitline is segmented into multiple smaller bitline groups, each serving a limited number of memory cells. This segmentation reduces the capacitive loading on each individual bitline, thereby reducing the RC delay while still achieving high memory capacity through parallel organization of multiple bitline groups.
Solution Approach 2:
The patent introduces a new dimensional organization by creating multiple bitline groups arranged in a multi-dimensional layout rather than a single linear array. This allows memory cells to be accessed through multiple parallel paths, reducing the effective RC delay experienced during read/write operations while maintaining high storage capacity.
2Device complexity
If traditional SRAM layout is used, then routing is simplified, but parasitic effects increase and performance decreases
Solution Approach 1:
The patent applies different routing strategies to different regions of the SRAM array. Specifically, adjacent bitline groups are routed through dedicated routing regions with optimized trace configurations that minimize parasitic inductance and resistance locally. This localized optimization reduces parasitic effects without requiring complete redesign of the entire routing system.
Solution Approach 2:
The patent introduces intermediate routing regions that act as mediators between memory cell groups and bitline groups. These intermediate regions provide buffered connection points that reduce the direct parasitic coupling between adjacent bitlines, thereby reducing harmful parasitic effects while maintaining routing simplicity through standardized intermediate connection structures.
3Area of stationary object
If compact SRAM design is implemented, then area is reduced, but bitline loading increases and RC delay worsens
Solution Approach 1:
The patent implements a nested organization where memory cells are grouped into cell groups that are further grouped into larger arrays, with bitlines similarly organized in nested groups. This nested structure allows efficient packing of memory cells into compact areas while ensuring that each bitline only serves a limited number of cells, thereby reducing RC delay even in compact designs.
Solution Approach 2:
The patent transitions from a two-dimensional planar layout to a multi-dimensional organizational structure by creating vertical stacking of bitline groups over memory cell groups. This dimensional change allows compact area utilization through three-dimensional integration while maintaining short bitline lengths and low RC delay through the vertical organization of routing layers.
Data Source
AI summary
The present disclosure describes a method for memory cell placement. The method can include placing a memory cell region in a layout area and placing a well pick-up region and a first power supply routing region along a first side of the memory cell region. The method also includes placing a second power supply routing region and a bitline jumper routing region along a second side of the memory cell region, where the second side is on an opposite side to that of the first side. The method further includes placing a device region along the second side of the memory cell region, where the bitline jumper routing region is between the second power supply routing region and the device region.