SRAM Array Boundary Layout Using Abutting Dummy Cells
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Solution Overview
Problem
SRAM arrays face design rule violations and process margin issues due to insufficient or non-existent keep-out regions between adjacent arrays, and large keep-out regions limit scaling capability and space efficiency.
Innovation Solution
Implementing abutting dummy cells and well strap cells to replace conventional keep-out regions, ensuring uniform operation of bit cells and reducing chip size by aligning SRAM cells symmetrically, and using N-type and P-type well strap cells to provide fixed potentials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional keep-out regions are used between adjacent SRAM arrays, then design rule compliance and process margins are improved, but chip size increases and scaling capability is limited
Solution Approach 1:
The patent extracts the essential function of keep-out regions (providing design rule compliance and process margins) and implements it through abutting dummy cells that are integrated into the SRAM array structure, rather than using separate isolated keep-out regions. This allows the functional equivalent to be achieved with minimal area overhead.
Solution Approach 2:
The patent merges the keep-out region function with the SRAM array structure by placing dummy cells at the boundaries of the array. These dummy cells serve dual purposes: they maintain design rule compliance and process margins while being physically integrated into the array structure, thereby eliminating the need for separate keep-out regions.
2Manufacturing precision
If large keep-out regions are formed between SRAM arrays, then design rule violations are prevented, but space efficiency decreases and scaling capability is limited
Solution Approach 1:
The patent applies local quality by placing dummy cells specifically at the boundary regions of the SRAM array where design rule compliance is critical, rather than using uniform keep-out regions across the entire array. This localized approach maintains manufacturing precision where needed while maximizing space efficiency in the active array regions.
Solution Approach 2:
The patent transitions from using two-dimensional keep-out regions (isolated spaces between arrays) to a one-dimensional boundary approach where dummy cells are placed only at the edges of the array. This dimensional change allows design rule compliance to be achieved with minimal area overhead.
3Stability of the object's composition
If edge/strap cells are used surrounding the bit cell array, then uniform operation of bit cells is improved, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the dummy cells to serve multiple functions: they provide uniform operating conditions for the bit cells (similar to edge/strap cells) while also maintaining design rule compliance and process margins. This multi-functionality reduces the need for separate structural elements, thereby reducing overall device complexity.
Data Source
AI summary
A semiconductor device including a static random access memory (SRAM) device includes a first SRAM array including a first plurality of bit cells arranged in a matrix; a second SRAM array including a second plurality of bit cells arranged in a matrix; and a plurality of abutting dummy cells disposed between the first SRAM array and the second SRAM array. Each of the plurality of abutting dummy cells includes a plurality of dummy gate electrode layers and a plurality of dummy contacts. The semiconductor device further includes a first-type well continuously extending from the first SRAM array to the second SRAM array. The first-type well is in direct contact with portions of the plurality of dummy contacts.