MRAM Cell With Synthetic Storage Layer For Dipolar Coupling Reduction
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Solution Overview
Problem
Conventional MRAM cells face challenges in scaling down due to increased dipolar coupling between storage and sense layers, which requires high magnetic fields for read operations, leading to power consumption issues and hysteresis loop shifts.
Innovation Solution
The MRAM cell design incorporates a synthetic storage layer with anti-parallel ferromagnetic layers and a reversible sense layer, optimized thicknesses to minimize net local magnetic stray fields, and controlled magnetic fields for writing and reading, allowing for reduced power consumption and scaled-down functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MRAM cell design is used, then data storage functionality is achieved, but dipolar coupling between storage and sense layers increases, requiring high magnetic fields for read operations
Solution Approach 1:
The storage layer is segmented into two separate ferromagnetic layers (first storage layer and second storage layer) with anti-parallel magnetization directions. This segmentation allows the magnetic fields from each layer to partially cancel each other, reducing the net dipolar coupling field acting on the sense layer while maintaining the necessary storage functionality.
Solution Approach 2:
The first storage layer and second storage layer are designed to produce opposing magnetic fields (anti-weight) that counterbalance each other's dipolar coupling effect on the sense layer. By positioning these layers with anti-parallel magnetization, the harmful magnetic field is neutralized, reducing the read operation field requirement.
2Use of energy by moving object
If dipolar coupling between storage and sense layers is reduced, then power consumption decreases, but achieving the required magnetic field control becomes more difficult
Solution Approach 1:
The patent applies different magnetization directions to different local regions (the first and second storage layers) to create a specific magnetic field distribution. By making the magnetization quality local (anti-parallel in different layers) rather than uniform, the dipolar coupling is reduced while maintaining controllable magnetic field characteristics for read operations.
Solution Approach 2:
The invention changes the magnetic field parameters by introducing anti-parallel magnetization configurations in the storage layers. This parameter change (from parallel to anti-parallel magnetization) fundamentally alters the magnetic field distribution, reducing the net field at the sense layer while maintaining writability and readability through controlled field application.
3Area of moving object
If feature size is reduced for scaling, then device density increases, but dipolar coupling increases requiring even higher magnetic fields
Solution Approach 1:
By segmenting the storage layer into two anti-parallel magnetized layers, the patent creates internal field cancellation that scales with device size reduction. As feature size decreases, the opposing fields from the segmented layers continue to cancel each other, preventing the dipolar coupling from increasing proportionally with scaling.
Solution Approach 2:
The anti-weight principle is applied by designing the first and second storage layers to produce counterbalancing magnetic fields. This counterweight mechanism ensures that even as device dimensions are reduced for higher density, the dipolar coupling field does not increase because the opposing layers continuously neutralize each other's field contribution.
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
This design enables low-power writing and reading operations with reduced magnetic field requirements, minimizing dipolar coupling and maintaining efficient data storage even at smaller feature sizes.
Implementation Method 1
a dipolar coupling between the storage and sense layers occurs due to local magnetic stray field, coupling the magnetization of the storage and sense layers
Implementation Method 2
the reference layer is 'exchange biased' to an adjacent antiferromagnetic reference layer characterized by a critical temperature (above which the exchange bias vanishes) known as the blocking temperature
Implementation Method 3
Writing is then performed by heating the magnetic tunnel junction above T BS but below T BR, preferably but not limited to by sending a heating current through the magnetic tunnel junction
Implementation Method 4
When the respective magnetisations of the reference layers and the storage layer are antiparallel, the resistance of the magnetic tunnel junction is high (R max ), corresponding to a low logic state '0'. On the other hand, when the respective magnetizations are parallel, the resistance of the magnetic tunnel junction becomes low (R min )
Data Source
Figure 1
Figure 2
Figure 3~4(a)
AI summary
The present disclosure concerns a magnetic random access memory (MRAM) cell (1) comprising a magnetic tunnel junction (2) comprising a synthetic storage layer (23); a sense layer (21) having a sense magnetization (211) that is reversible; and a tunnel barrier layer (22) between the sense layer (21) and the storage layer (23); wherein a net local magnetic stray field couples the storage layer (23) with the sense layer (21); and wherein the net local magnetic stray field being such that the net local magnetic stray field coupling the sense layer (21) is below 50 Oe. The disclosure also pertains to a method for writing and reading the MRAM cell (1). The disclosed MRAM cell (1) can be written and read with lower consumption in comparison to conventional MRAM cells.