Magnetic Memory Device with Segmented Free Layers for Multi-Valued Data
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Solution Overview
Problem
Conventional STT-MRAM and SOT-MRAM devices face challenges in controlling the magnetization direction of ferromagnetic metals, particularly in thick layers or cylindrical structures, which limits their thermal stability and structural simplicity, making it difficult to achieve high-density, multi-valued data representation.
Innovation Solution
A magnetic memory device with a two-terminal structure comprising a first and second magnetic memory device, each with a fixed layer, non-magnetic layers, and a free layer with perpendicular magnetic anisotropy, allowing for the use of pulse power and a switch to control current pulses and read multi-valued data, even with a simple device structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick ferromagnetic layer or cylindrical structure is used to improve thermal stability, then thermal stability is improved, but it becomes difficult to control the magnetization direction
Solution Approach 1:
The invention divides the ferromagnetic layer into multiple thin sub-layers (first ferromagnetic layer, second ferromagnetic layer, third ferromagnetic layer) stacked sequentially. Each sub-layer can be independently controlled by separate current paths, allowing precise control of magnetization direction while maintaining overall thermal stability through the combined thick structure.
Solution Approach 2:
The invention transitions from controlling magnetization in a single thick layer to controlling magnetization across multiple dimensions by stacking thin layers vertically. The write current paths are arranged in different spatial configurations (first write current path through first and second ferromagnetic layers, second write current path through second and third ferromagnetic layers), enabling independent control of each sub-layer's magnetization direction.
2Device complexity
If a two-terminal structure is used to simplify device structure, then device complexity is reduced, but it becomes difficult to represent multi-valued data
Solution Approach 1:
The invention segments the magnetic memory device into multiple functional units with distinct fixed layers and ferromagnetic layers. Each unit can independently store binary information, and by combining multiple units, multi-valued data representation is achieved. The first and second magnetic memory devices are connected in series, with each device containing separate read and write current paths that operate independently.
Solution Approach 2:
The two-terminal magnetic memory device structure serves multiple functions: it can store binary information in each magnetic memory device unit, represent multi-valued data through series combination of multiple units, and maintain simple structure without requiring separate read and write terminals. The same two terminals are used for both reading and writing operations by switching current paths.
3Device complexity
If conventional STT-MRAM or SOT-MRAM is used, then the device structure is simple, but it is difficult to achieve high-density data representation
Solution Approach 1:
The invention increases data density by transitioning from planar expansion to vertical stacking. Multiple ferromagnetic layers are stacked in the vertical direction, and multiple magnetic memory devices are connected in series, effectively utilizing the third dimension to pack more storage units into a smaller footprint while maintaining simple two-terminal device structures.
Solution Approach 2:
The invention segments the data storage function across multiple independent magnetic memory device units connected in series. Each unit contributes to the overall data capacity, and the series connection allows multi-valued data representation, thereby increasing effective data density without requiring more complex individual device structures.
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
Enables high thermal stability, simple structure, and high-density data representation, allowing for efficient writing and reading of multi-valued data, as well as fast calculations in neural networks and reservoir models.
Implementation Method 1
A magnetoresistance device, which has a perpendicular magnetization and executes a reading operation using a magnetoresistance effect
Implementation Method 2
a write torque exerts an influence on only a magnetization of a surface of a free layer
Implementation Method 3
Conventional STT-MRAM or spin-orbit torque (SOT)-MRAM devices
Data Source
AI summary
A magnetic memory device includes a first magnetic memory device, a second magnetic memory device, a pulse power supplying current pulses to the first and second magnetic memory devices; and a switch configured to selectively connect the pulse power to one of the first and second magnetic memory devices. A resistance value of an MTJ device composed of the first fixed layer, the first non-magnetic layer, and the free layer is different from a resistance value of a MTJ device composed of the second fixed layer, the second non-magnetic layer, and the free layer.