Multi-layered Magnetic Memory Structure for Low Coercivity
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Solution Overview
Problem
Magnetic memory cells face challenges with increased coercivity as they shrink, requiring higher write currents, which leads to higher power consumption, electromigration concerns, and increased costs, while reducing thickness for lower coercivity compromises thermal stability.
Innovation Solution
A multi-layered magnetic memory structure is developed with a first ferromagnetic layer, a non-magnetic separating layer, and a second ferromagnetic layer, where the first layer has higher coercivity and the second layer has lower coercivity, allowing for data storage by reversing the magnetic moment of the first layer with a specific magnetic field and reading by sensing resistance changes between the second layer and a reference layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the memory cell area is decreased to reduce chip size and cost, then the coercivity increases, but higher write current is required which increases power consumption and electromigration concerns
Solution Approach 1:
The data layer is segmented into two separate ferromagnetic layers (first and second ferromagnetic layers) with different coercivities, allowing independent optimization of thermal stability and writeability. The first layer has higher coercivity for stability while the second layer has lower coercivity for easier switching.
Solution Approach 2:
Different regions of the data layer are assigned different magnetic properties - the first ferromagnetic layer has higher coercivity for thermal stability while the second ferromagnetic layer has lower coercivity for reduced write current requirements. This local differentiation resolves the contradiction between stability and ease of writing.
2Length of stationary object
If the ferromagnetic layer thickness is reduced to lower coercivity, then write current decreases, but thermal stability deteriorates
Solution Approach 1:
The data layer is divided into two ferromagnetic layers with different thicknesses and coercivities. The first layer can be thicker for stability while the second layer is thinner for easier switching, or both layers can be thin but combined they provide sufficient thermal stability through their composite magnetic moment.
Solution Approach 2:
The data layer is constructed as a composite of two ferromagnetic materials or two ferromagnetic layers with different magnetic properties. This composite structure allows the system to achieve both low coercivity (for reduced write current) and high thermal stability simultaneously, as the combined magnetic properties of the composite layer satisfy both requirements.
3Device complexity
If a single ferromagnetic layer is used, then the structure is simple, but both coercivity and thermal stability cannot be optimized simultaneously
Solution Approach 1:
Rather than using a single ferromagnetic layer, the data layer is segmented into two distinct ferromagnetic layers with different coercivities. This segmentation allows independent optimization of thermal stability (first layer) and writeability (second layer), resolving the contradiction between simplicity and performance optimization.
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 reduces coercivity and improves thermal stability, allowing for easier data switching with lower write currents and maintaining thermal stability, thus addressing the challenges of power consumption and cost while enhancing operational efficiency.
Implementation Method 1
a second ferromagnetic layer spaced apart from the first ferromagnetic layer by a non-magnetic separating layer and being magnetically coupled to the first ferromagnetic layer by demagnetizing fields from the first ferromagnetic layer
Implementation Method 2
The degree of parallelism affects the resistance of the cell, and this resistance can be determined by sensing (e.g., via a sense amplifier) an output current or voltage produced by the memory cell in response to the read current
Data Source
AI summary
An exemplary memory array including a plurality of memory cells, each of the memory cells comprises a first ferromagnetic layer, a second ferromagnetic layer spaced apart from the first ferromagnetic layer by a non-magnetic separating layer and being magnetically coupled to the first ferromagnetic layer by demagnetizing fields from the first ferromagnetic layer, a spacer layer above the second ferromagnetic layer, and a reference layer above the spacer layer. The first ferromagnetic layer, non-magnetic separating layer, and second ferromagnetic layer in combination function as a data layer of the memory cell.