CPP Magnetoresistance Element Free Layer Stack
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Solution Overview
Problem
Conventional CPP-type magnetic field detecting elements face limitations in reducing stack thickness and achieving high magnetoresistance while controlling the spin-torque effect, due to the requirement of synthetic pinned layers and antiferromagnetic layers, and the challenge of selecting suitable non-magnetic intermediate materials that produce both RKKY interaction and sufficient magnetoresistance.
Innovation Solution
A CPP-type magnetic field detecting element with a stack configuration including multiple free layers and non-magnetic intermediate layers, where the second non-magnetic intermediate layer allows exchange-coupling between the free layers, reducing the need for synthetic pinned layers and antiferromagnetic layers, and enabling the use of materials that limit the spin-torque effect while achieving a high magnetoresistance ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a synthetic pinned layer with antiferromagnetic layer is used to fix magnetization direction, then the magnetization direction of the pinned layer is firmly fixed, but the stack thickness cannot be reduced due to the large number of layers required
Solution Approach 1:
The invention extracts and removes the antiferromagnetic layer from the conventional synthetic pinned layer structure. By using only a pinned layer without the antiferromagnetic layer, the patent achieves magnetization direction stability through alternative means (exchange coupling between pinned and free layers) while significantly reducing the stack thickness by eliminating the thick antiferromagnetic layer
Solution Approach 2:
The invention merges the functions of the pinned layer and free layer through exchange coupling. The pinned layer and free layer are directly exchange-coupled without an intervening antiferromagnetic layer, allowing the pinned layer to fix the magnetization direction of the free layer while reducing the overall number of layers and stack thickness
2Stability of the object's composition
If a non-magnetic intermediate layer made of metal (e.g., Cu) is used to produce RKKY interaction between free layers, then exchange-coupling is achieved, but the spin-torque effect increases due to large sense current flow
Solution Approach 1:
The invention changes the material parameter (electrical resistivity) of the non-magnetic intermediate layer from metal to semiconductor. By using a semiconductor material with higher resistivity, the sense current is reduced, which in turn reduces the spin-torque effect while maintaining the exchange-coupling function through RKKY interaction
Solution Approach 2:
The invention uses composite material structure by combining semiconductor non-magnetic intermediate layer with magnetic layers. The semiconductor material provides both the necessary RKKY interaction for exchange-coupling and the high resistivity to limit spin-torque effect, achieving dual functionality
3Object-generated harmful factors
If a non-magnetic intermediate layer made of semiconductor or insulator is used to limit spin-torque effect, then the spin-torque effect is reduced, but RKKY interaction is insufficient and magnetoresistance ratio is low
Solution Approach 1:
The invention optimizes the thickness parameter of the semiconductor non-magnetic intermediate layer. By carefully controlling the thickness to be within a specific range (0.3-2.0 nm), the patent achieves sufficient RKKY interaction for exchange-coupling while maintaining the high resistivity property to limit spin-torque effect, thereby achieving both goals simultaneously
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 allows for a significant reduction in stack thickness, improved magnetoresistance ratio, and effective limitation of the spin-torque effect, enhancing the detection of external magnetic fields with improved linearity and response.
Implementation Method 1
a first non-magnetic intermediate layer which is sandwiched between the first magnetic layer and the second magnetic layer, the first non-magnetic intermediate layer producing a magnetoresistance effect between the first magnetic layer and the second magnetic layer
Implementation Method 2
the second non-magnetic intermediate layer allowing the second magnetic layer and the third magnetic layer to be exchange-coupled such that magnetization directions thereof are anti-parallel to each other under no magnetic field
Implementation Method 3
a bias magnetic layer which is provided on a side of the stack, the side being opposite to an air bearing surface of the stack, the bias magnetic layer applying a bias magnetic field to the stack in a direction that is perpendicular to the air bearing surface
Implementation Method 4
TMR elements utilizing the TMR (Tunnel Magneto-Resistance) effect
Implementation Method 5
CPP (Current Perpendicular to the Plane) elements utilizing the GMR effect
Data Source
AI summary
A magnetic field detecting element comprises: a stack which includes first, second and third magnetic layers whose magnetization directions depend upon an external magnetic field, the second magnetic layer being positioned between the first magnetic layer and the third magnetic layer, a first non-magnetic intermediate layer sandwiched between the first magnetic layer and the second magnetic layer, and a second non-magnetic intermediate layer sandwiched between the second magnetic layer and the third magnetic layer, wherein the stack is adapted such that sense current flows in a direction that is perpendicular to a film surface thereof; and a bias magnetic layer which is provided on a side of the stack, the side being opposite to an air bearing surface of the stack.