Reverse Complement MTJ Bit Cells with Shared Source Lines
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Solution Overview
Problem
Magnetic random access memory (MRAM) bit cells have a relatively long read sensing time, which is not sufficient for applications requiring faster data access, such as level two (L2) cache memory, and the introduction of additional circuit elements in two transistor, two magnetic tunnel junction (2T2MTJ) bit cells leads to higher parasitic resistance, limiting speed further.
Innovation Solution
Implementing reverse complement magnetic tunnel junction (MTJ) bit cells with shared source lines, allowing for a larger source line width without increasing die size, thereby reducing parasitic resistance and achieving faster read sensing times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate source lines are used for each MTJ in a 2T2MTJ bit cell, then each MTJ has dedicated current path, but parasitic resistance increases and read sensing time increases
Solution Approach 1:
The patent merges the source lines of the first and second MTJs into a single shared source line that provides current paths to both MTJs. This combining approach reduces the total number of conductive elements, thereby reducing parasitic resistance while maintaining reliable current delivery to each MTJ through the shared pathway.
2Loss of time
If additional circuit elements are introduced in 2T2MTJ bit cell, then read sensing time is reduced, but parasitic resistance increases
Solution Approach 1:
The patent combines multiple source lines into a single shared source line that serves both MTJs in the 2T2MTJ bit cell. This merging reduces the cumulative parasitic resistance that would otherwise result from having separate source lines, while the bit cell structure itself enables reduced read sensing time through the complementary MTJ configuration.
3Object-generated harmful factors
If source line width is increased to reduce parasitic resistance, then read sensing time decreases, but die size increases
Solution Approach 1:
The patent merges the source line requirements for two MTJs into a single shared source line, which allows the source line to be positioned optimally within the bit cell structure. This merging enables the source line to achieve sufficient width for low parasitic resistance without requiring the increased die area that would be needed if separate source lines were provided for each MTJ.
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
The use of shared source lines in reverse complement MTJ bit cells reduces parasitic resistance and read sensing time, enhancing the performance of MRAM bit cells by enabling faster data access and simultaneous write operations.
Implementation Method 1
magnetic random access memory (MRAM) is an example of non-volatile memory in which data is stored by programming a magnetic tunnel junction (MTJ) of an MRAM bit cell. Data is stored in an MTJ as a magnetic state
Implementation Method 2
an MTJ can store data even when power is not supplied to the MTJ (e.g., the MTJ is non-volatile). When the magnetic orientation of the pinned layer 106 and the free layer 108 are anti-parallel (AP) to each other, a first memory state exists
Data Source
AI summary
Reverse complement MTJ bit cells employing shared source lines are disclosed. In one aspect, a 2T2MTJ reverse complement bit cell employing shared source line is provided. Bit cell includes first MTJ and second MTJ. Value of first MTJ is complement of value of second MTJ. First bit line is coupled to top layer of first MTJ, and first electrode of first access transistor is coupled to bottom layer of first MTJ. Second bit line is coupled to bottom layer of second MTJ, and first electrode of second access transistor is coupled to top layer of second MTJ. Word line is coupled to second electrode of first access transistor and second access transistor. Shared source line is coupled to third electrode of first access transistor and second access transistor. Employing shared source line allows the bit cell to be designed with reduced parasitic resistance.