MTJ Free-Layer Strip Structure for Precise Domain-Wall Programming
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Solution Overview
Problem
Magnetic tunnel junction (MTJ) devices with programmable domain-walls face significant variability in domain-wall location due to size, shape, and external voltage variability, hindering accurate programming for AI applications.
Innovation Solution
The MTJ structure incorporates multiple ferromagnetic strips with notches aligned along their longitudinal directions, reducing statistical variation by creating discrete domain-wall locations and utilizing a spin-orbit coupling layer to lower the threshold current for domain-wall movement, with a reference layer overlapping the sub-free layers via a tunnel barrier layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single free layer is used in the MTJ device, then the device structure is simple, but the statistical variation of domain-wall location is large, hindering accurate programming
Solution Approach 1:
The free layer is divided into multiple sub-free layers (first sub-free layer, second sub-free layer, third sub-free layer, etc.) stacked vertically. Each sub-free layer contributes to the overall magnetoresistive effect, and the segmentation reduces statistical variation in domain-wall location by averaging out random fluctuations across multiple layers, thereby improving programming precision
2Reliability
If multiple sub free layers are used, then the statistical variation of domain-wall location is reduced, but the device structure and manufacturing process become more complex
Solution Approach 1:
The free layer is segmented into multiple sub-free layers with identical or similar magnetic properties, each contributing to the magnetoresistive effect. This segmentation improves reliability by reducing statistical variation in domain-wall location through the averaging effect across multiple layers, while maintaining manageable complexity through systematic stacking
Solution Approach 2:
Multiple sub-free layers are combined in a vertical stack configuration, where each layer contributes additively to the overall magnetoresistive effect. The merging of multiple layers with individual domain-wall characteristics creates a composite structure with reduced statistical variation, improving programming reliability
3Adaptability or versatility
If domain-wall location is adjusted by external voltage, then conductance tuning is achieved, but the standard deviation of domain-wall location becomes large, hindering accurate programming
Solution Approach 1:
The free layer is divided into multiple sub-free layers that can be independently or collectively controlled by external voltage. The segmentation allows for finer control of domain-wall location by distributing the voltage-induced magnetization switching across multiple layers, reducing the standard deviation and improving location control precision while maintaining conductance tuning versatility
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 approach significantly reduces the standard deviation of domain-wall location, enhancing the certainty and accuracy of programming by increasing the number of sub-free layers, thereby improving conductance resolution and reducing the threshold current for domain-wall movement.
Implementation Method 1
each of the multiple ferromagnetic strips is covered by a spin-orbit coupling layer, the spin-orbit coupling layer being patterned to have a same shape as that of the ferromagnetic strip covered thereby. By the use of this spin-orbit coupling layer, the threshold current for driving the movement of the domain-wall location is significantly reduced.
Implementation Method 2
a tunnel barrier layer on a reference layer and a free layer on the tunnel barrier layer
Data Source
AI summary
Embodiments of present invention provide a magnetic tunnel junction (MTJ) structure. The MTJ structure includes a MTJ stack, the MTJ stack including a tunnel barrier layer on a reference layer and a free layer on the tunnel barrier layer, wherein the free layer includes multiple sub free layers, the multiple sub free layers being multiple ferromagnetic strips placed parallel to each other on the tunnel barrier layer, the multiple ferromagnetic strips having respective first ends connected to a first electrode and respective second ends connected to a second electrode. A method of forming the MTJ structure is also provided.