Magnetic Memory Element With Decoupled Write Current Path
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Solution Overview
Problem
Current magnetic memory technologies face challenges in independently optimizing reading and writing processes due to the intrinsic link between spin transfer torque (STT) writing and high resistance-area product (RA) values, leading to high power dissipation and accelerated aging, as well as complexity in structuring multiple layers for efficient magnetization reversal.
Innovation Solution
A magnetic memory element with a central magnetic layer having magnetization parallel or perpendicular to its plane, sandwiched between non-magnetic outer layers, where the write current flows parallel to the plane, allowing for independent control of magnetization reversal using a magnetic field perpendicular to both the current and magnetization direction, reducing the need for high current densities and complex layer stacks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If spin transfer torque (STT) is used for writing, then magnetization reversal is achieved, but high resistance-area product (RA) values lead to high power dissipation and accelerated aging
Solution Approach 1:
The patent segments the writing and reading functions into separate operational modes. Writing is performed using spin-polarized current through a spin valve structure, while reading uses a separate magnetic tunnel junction. This segmentation allows optimization of each function independently, reducing the RA product for reading operations and thereby lowering power dissipation and aging effects during read operations.
Solution Approach 2:
The patent changes the operational parameters by using different current densities for writing and reading operations. Writing requires high current density through the spin valve, while reading uses low current density through the magnetic tunnel junction. This parameter change enables the system to achieve the desired TMR signal for reading without subjecting the junction to high stress, thereby reducing power dissipation and aging.
2Measurement precision
If high TMR values are obtained for reading, then reading sensitivity is improved, but RA values increase leading to accelerated aging
Solution Approach 1:
The patent uses separate magnetic tunnel junctions for reading operations, segmented from the writing path. This allows the reading junction to be optimized for high TMR values without being subjected to the high current densities used for writing, thereby maintaining high reading sensitivity while reducing accelerated aging.
Solution Approach 2:
The patent employs a read-only memory (ROM) structure where the magnetic tunnel junction is used exclusively for reading operations. This 'disposable' reading path is not subjected to the stress of writing operations, allowing it to maintain high TMR values and reading sensitivity without the same aging constraints as the writing path.
3Ease of operation
If multiple magnetic layers are used for STT writing, then magnetization control is improved, but device complexity increases
Solution Approach 1:
The patent segments the magnetic structure into distinct functional regions: a spin valve for writing with its specific layer stack, and a magnetic tunnel junction for reading with its own optimized structure. This segmentation allows each region to be optimized for its specific function without requiring the entire device to accommodate all functions, thereby reducing overall complexity while maintaining effective magnetization control.
Solution Approach 2:
The patent uses a unified magnetic field application mechanism that serves both writing and reading operations. The same external magnetic field system is used to assist magnetization reversal during writing and to enhance the TMR effect during reading, thereby reducing the need for separate control mechanisms and simplifying the overall device architecture.
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 configuration enables efficient magnetization reversal with reduced power consumption and extended device lifespan by decoupling writing and reading processes, allowing for more precise control over magnetization without the need for high current densities and complex layer structures.
Implementation Method 1
the current becomes spin-polarized when crossing the first magnetic layer, to then exert a torque on the magnetization of the second layer by means of the noncollinear component of the current polarization
Implementation Method 2
the element to be returned is mechanically placed in the vicinity of the magnetic field generator so as to spatially localize this field
Implementation Method 3
the reading is done by means of the magnetoresistance of the stack: giant magnetoresistance (GMR) for spin valves, and tunnel magnetoresistance (TMR) for magnetic tunnel junctions
Implementation Method 4
the reading is done by means of the magnetoresistance of the stack: giant magnetoresistance (GMR) for spin valves
Data Source
Figure 1a~2b
Figure 3a~4d
Figure 4e~6d
AI summary
The invention relates to a writeable magnetic element, comprising a stack of layers having a magnetic writing layer, characterised in that the stack comprises a such a magnetic writing layer, namely a central layer (13, 53, 70, 23, 63, 80) made of at least one magnetic material having a direction of magnetisation that is parallel or perpendicular to the plane of the central layer, which is sandwiched between a first (12, 52, 71, 22, 62) and second (14, 54, 72, 24, 64, 82) outer layer made of non-magnetic materials, the first outer layer (12, 52, 71, 22, 62) comprising a first non-magnetic material and the second outer layer (14, 54, 72, 24, 64, 82) comprising a second non-magnetic material other than the first non-magnetic material, wherein at least the second non-magnetic material is electrically conductive, and characterised in that said element comprises a device for passing a writing current only through the second outer layer and the central layer, and optionally through the first outer layer only in the event the latter is conductive, said writing current circulating in a current direction that is parallel to the plane of the central layer, as well as a device for applying a magnetic field having a component in one magnetic-field direction that is either parallel or perpendicular to the plane of the central layer (13, 53, 70, 23, 63, 80) and to the current direction, and in that the direction of magnetisation and the magnetic-field direction are mutually perpendicular.