CPP Magnetoresistance Element with Three Magnetic Layers
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Solution Overview
Problem
Conventional TMR elements face limitations in reducing the thickness of the MR stack due to the requirement of a synthetic pinned layer for fixing magnetization directions, which complicates the layer configuration and hinders the reduction of the gap between shield layers, and the layer configuration using two free layers struggles with achieving high sensitivity due to ferromagnetic coupling across the tunnel barrier layer.
Innovation Solution
A magnetoresistance effect element with a stack configuration of three magnetic layers, where the first and second layers are anti-parallel under no magnetic field due to RKKY exchange coupling, and the second and third layers are ferromagnetically coupled, allowing a bias magnetic field to fix the first and third layers' magnetization directions, eliminating the need for an antiferromagnetic layer and synthetic pinned layer, enabling a thinner stack and higher sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a synthetic pinned layer is used to fix magnetization directions, then the magnetization direction is firmly fixed, but the number of layers increases and the MR stack thickness cannot be reduced
Solution Approach 1:
The invention extracts and removes the synthetic pinned layer (including outer pinned layer, inner pinned layer, and antiferromagnetic layer) from the MR stack, replacing it with a simplified configuration where only the third magnetic layer serves as the pinned layer, thereby reducing the number of layers while maintaining magnetization fixation through exchange coupling between first and third magnetic layers
Solution Approach 2:
The third magnetic layer serves dual functions: it acts as both the pinned layer (fixing magnetization direction) and eliminates the need for separate antiferromagnetic layers, as the exchange coupling between first and third magnetic layers through the non-magnetic intermediate layer provides the necessary magnetization fixation
2Length of stationary object
If the number of layers is reduced to decrease MR stack thickness, then the gap between shield layers can be reduced, but the magnetization direction cannot be firmly fixed
Solution Approach 1:
The invention introduces a non-magnetic intermediate layer as an intermediary between the first and third magnetic layers, enabling exchange coupling that fixes the magnetization direction of the third magnetic layer (pinned layer) without requiring additional layers, thus achieving both thickness reduction and reliable magnetization fixation
Solution Approach 2:
The invention creates an asymmetric layer configuration where the first and third magnetic layers are coupled through a non-magnetic intermediate layer, establishing a fixed anti-parallel magnetization relationship that provides stable pinned layer functionality without the symmetric multi-layer structure of conventional synthetic pinned layers
3Device complexity
If two free layers are used with non-magnetic intermediate layer, then the layer configuration is simplified, but ferromagnetic coupling occurs across the tunnel barrier layer preventing high sensitivity
Solution Approach 1:
The invention applies different coupling characteristics to different regions: the first non-magnetic intermediate layer provides exchange coupling (RKKY interaction) between first and third magnetic layers for magnetization fixation, while the second non-magnetic intermediate layer (tunnel barrier layer) between second and third layers maintains ferromagnetic coupling for TMR effect, with the key distinction being that the first intermediate layer enables anti-parallel alignment while the second allows parallel alignment for high sensitivity detection
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 reduced MR stack thickness, improved recording density, and enhanced sensitivity by achieving an anti-parallel state between the second and third magnetic layers, facilitating a larger magnetoresistance ratio and simplifying the layer structure.
Implementation Method 1
a first non-magnetic intermediate layer which allows the first magnetic layer and the second magnetic layer to be exchange-coupled so that the magnetization directions thereof are anti-parallel to each other when no magnetic field is applied
Implementation Method 2
a second non-magnetic intermediate layer which produces a magnetoresistance effect between the second magnetic layer and the third magnetic layer
Implementation Method 3
a bias magnetic layer provided on an opposite side of the magnetoresistive stack from an air bearing surface, the bias magnetic layer applying a bias magnetic field to the magnetoresistive stack in a direction perpendicular to the air bearing surface
Implementation Method 4
When a sense current is applied to the element in the direction of stacking, electrons pass through the energy barrier of the non-magnetic and non-conductive tunnel barrier layer due to the tunnel effect
Data Source
AI summary
A magnetoresistance effect element comprises: a magnetoresistive stack including: first, second and third magnetic layers whose magnetization directions change in accordance with an external magnetic field, said second magnetic layer being located between said first magnetic layer and the third magnetic layer; a first non-magnetic intermediate layer sandwiched between said first and second magnetic layers; and a second non-magnetic intermediate layer sandwiched between said second and third magnetic layers; wherein sense current is adapted to flow in a direction perpendicular to a film plane; a bias magnetic layer provided on an opposite side of said magnetoresistive stack from an air bearing surface.