Magnetoresistive Head with Stable Layers for Thermal Noise Reduction
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Solution Overview
Problem
High-recording-density magnetic storage devices face a challenge in maintaining a high signal-to-noise ratio (SNR) due to increased thermal noise in magnetoresistive heads, as the volume of the magnetization free layer decreases with higher areal density, leading to deteriorated head signal-to-noise ratio (SNR).
Innovation Solution
A magnetoresistive head with a laminated structure comprising a magnetization pinned layer, a non-magnetic intermediate layer, a magnetization free layer, and a magnetization stable layer, where the magnetization stable layer includes a non-magnetic coupling layer, a first ferromagnetic stable layer, and a second ferromagnetic stable layer, with their magnetizations coupled in antiparallel or parallel alignment, effectively increasing the effective volume and reducing thermal noise without compromising output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the volume of the magnetization free layer is decreased to increase areal density, then the storage capacity is improved, but the thermal noise (mag-noise) is increased and the head SNR is deteriorated
Solution Approach 1:
The patent combines the magnetization free layer with additional ferromagnetic layers (first ferromagnetic layer and second ferromagnetic layer) to form a composite magnetic structure. By merging these layers with appropriate magnetization orientations (antiparallel or perpendicular), the effective volume is increased while maintaining the same footprint, thereby reducing thermal noise without sacrificing areal density.
Solution Approach 2:
The patent utilizes out-of-plane magnetization orientation for the magnetization free layer and introduces vertical stacking of multiple ferromagnetic layers. This dimensional approach (transitioning from in-plane to out-of-plane magnetization) allows increasing the effective magnetic volume in the vertical dimension, reducing thermal noise while maintaining high areal density in the horizontal plane.
2Object-affected harmful factors
If the volume of the magnetization free layer is increased to reduce thermal noise, then the head SNR is improved, but the areal density is decreased
Solution Approach 1:
The patent segments the magnetic structure into multiple functional layers: magnetization pinned layer, non-magnetic intermediate layer, magnetization free layer, first ferromagnetic layer, and second ferromagnetic layer. Each layer serves a specific function, and their segmented arrangement allows the magnetization free layer to be coupled with additional ferromagnetic layers to increase effective volume without expanding the horizontal footprint, thus maintaining areal density while reducing thermal noise.
Solution Approach 2:
The patent creates a composite magnetic structure by combining ferromagnetic layers with different magnetization characteristics (pinned, free, and stable layers with antiparallel or perpendicular magnetization). This composite approach allows the system to achieve both high areal density and reduced thermal noise by optimizing the contribution of each material layer.
3Object-affected harmful factors
If additional ferromagnetic layers are added to increase effective volume, then the thermal noise is reduced, but the device complexity is increased
Solution Approach 1:
The additional ferromagnetic layers (first and second ferromagnetic layers) serve multiple functions: they increase the effective magnetic volume to reduce thermal noise, provide magnetic coupling through non-magnetic coupling layers, and can be configured in antiparallel or perpendicular magnetization arrangements to maintain signal output. This multi-functionality reduces the need for separate noise-reduction mechanisms, offsetting the increased structural complexity.
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
The proposed solution reduces thermal noise while maintaining the output level, thereby achieving a high head SNR by increasing the effective volume of the magnetization free layer and ensuring that the magnetization quantities of the ferromagnetic stable layers offset each other, thus reducing mag-noise.
Implementation Method 1
a magnetization of the magnetization free layer and a magnetization of the first ferromagnetic stable layer are coupled in an antiparallel alignment by the non-magnetic coupling layer
Implementation Method 2
A magnetization of the first ferromagnetic stable layer and a magnetization of the second ferromagnetic stable layer are coupled in an antiparallel alignment by the antiparallel coupling layer
Implementation Method 3
a multilayered film which is formed by stacking ferromagnetic metal layers separated by non-magnetic metal layers exhibits a large magnetoresistive effect, that is, a so-called giant magnetoresistive (GMR) effect
Implementation Method 4
The magnetization of the ferromagnetic layer which is in contact with the antiferromagnetic layer is substantially pinned due to an exchange-coupling magnetic field generated on an interface between the antiferromagnetic layer and the ferromagnetic layer
Data Source
AI summary
A magnetoresistive head which has a high head SNR by reducing generated mag-noise without deteriorating an output comprises, according to one embodiment, a magnetoresistive sensor having a laminated structure which includes an antiferromagnetic layer, a magnetization pinned layer, a non-magnetic intermediate layer, a magnetization free layer, and a magnetization stable layer arranged adjacent to the magnetization free layer. The magnetization stable layer comprises non-magnetic coupling layer, a first ferromagnetic stable layer, an antiparallel coupling layer, and a second ferromagnetic stable layer. A magnetization quantity of a first ferromagnetic stable layer and a second ferromagnetic stable layer are substantially equal, and the magnetization of the first ferromagnetic stable layer and the second ferromagnetic stable layer are magnetically coupled in the antiparallel direction from each other. The magnetizations of the first ferromagnetic stable layer and the free layer are coupled in an antiferromagnetic or a ferromagnetic alignment.