Tunnel Magnetoresistive Element Leakage Layer Current Reduction
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Solution Overview
Problem
The challenge is to reduce the reversal current required for spin injection magnetization reversal in TMR elements with perpendicular magnetic anisotropy, as the existing methods increase resistance and power consumption, and decrease reliability due to high resistivity materials used for inducing perpendicular magnetization.
Innovation Solution
A TMR element configuration that includes a reference layer, a magnetization free layer, a tunnel barrier layer, a perpendicular magnetization inducing layer, and a leakage layer, where the leakage layer has lower resistance than the perpendicular magnetization inducing layer, allowing spin-polarized current to flow through both layers and facilitate easier magnetization reversal, with the leakage layer formed from high thermal resistance metals like W, Ta, Mo, Nb, and Ru, and the tunnel and perpendicular magnetization inducing layers formed from oxide materials with spinel structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a perpendicular magnetization inducing layer formed of high resistivity oxide material is used, then perpendicular magnetic anisotropy is achieved, but resistance and power consumption increase
Solution Approach 1:
The magnetization inducing layer is segmented into two distinct layers: a first magnetization inducing layer (oxidic material) that provides perpendicular magnetic anisotropy, and a second magnetization inducing layer (conductive material) that provides low resistance. This segmentation allows each layer to perform its specific function optimally without compromise.
Solution Approach 2:
The patent uses a composite structure combining two different materials with complementary properties: an oxidic material (e.g., MgO, Al2O3) for magnetic anisotropy induction and a conductive material (e.g., Ru, Rh, Ir) for low resistance. This composite approach resolves the contradiction between achieving perpendicular magnetization and maintaining low resistance.
2Stability of the object's composition
If the film thickness of the magnetization free layer is decreased to induce perpendicular magnetization, then perpendicular magnetic anisotropy is achieved, but the layer becomes more difficult to manufacture with precise thickness control
Solution Approach 1:
Instead of relying on extremely thin film thickness (approaching the limit of manufacturing precision), the patent changes the approach by using interface magnetic anisotropy through the oxidic material layer. This allows perpendicular magnetization to be achieved at practical, manufacturable thicknesses while maintaining precision.
3Device complexity
If a conventional TMR element configuration is used, then simple structure is maintained, but spin-polarized current is insufficient for reliable magnetization reversal
Solution Approach 1:
The magnetization inducing function is segmented into two layers with different materials and positions, allowing the first layer to provide perpendicular anisotropy and the second layer to enhance spin-polarized current, thereby improving reliability without excessive complexity.
Solution Approach 2:
The patent employs a composite structure combining oxidic and conductive materials in the magnetization inducing layers, creating a system that simultaneously achieves perpendicular magnetic anisotropy and sufficient spin-polarized current for reliable magnetization reversal.
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 the reversal current needed for magnetization reversal, decreases electric power consumption, and enhances the reliability of the TMR element by allowing a sufficient spin-polarized current to flow through the leakage layer, promoting easier magnetization reversal and stabilizing the easy magnetization axis in the perpendicular direction.
Implementation Method 1
perpendicular magnetization anisotropy is imparted to the magnetization free layer such that the direction of magnetization is directed in the perpendicular direction by setting the spin-orbit interaction in the interface between the magnetization free layer and the layer in contact with the magnetization free layer to be stronger than the shape magnetic anisotropy of the magnetization free layer
Implementation Method 2
the TMR element that uses an insulation layer (tunnel barrier layer) as the non-magnetic spacer layer generally has high element resistance but can realize a high MR ratio
Implementation Method 3
a spin transfer torque (STT) is applied to the magnetization free layer from electron spins by causing a spin-polarized current to flow through the magnetization free layer
Implementation Method 4
The leakage layer is disposed on an end portion region in an in-plane direction of the magnetization free layer... allowing spin-polarized current to flow through both layers and facilitate easier magnetization reversal
Data Source
AI summary
A TMR element includes a reference layer, a magnetization free layer, a tunnel barrier layer between the reference layer and the magnetization free layer, and a perpendicular magnetization inducing layer and a leakage layer stacked on a side of the magnetization free layer opposite to the tunnel barrier layer side. A magnetization direction of the reference layer is fixed along a stack direction. The perpendicular magnetization inducing layer imparts magnetic anisotropy along the stack direction to the magnetization free layer. The leakage layer is disposed on an end portion region in an in-plane direction of the magnetization free layer. The perpendicular magnetization inducing layer is disposed on at least a central region in the in-plane direction of the magnetization free layer. A resistance value of the leakage layer along the stack direction per unit area in plane is less than that of the perpendicular magnetization inducing layer.