Magnetic Sensor Stack Body with Stepwise Hard Bias
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Solution Overview
Problem
The challenge in magnetic sensor stack bodies is maintaining a sufficient bias magnetic field as the size of magnetic bits decreases, leading to reduced sensitivity and increased noise due to the miniaturization of the reader stack and hard bias stack body, where the thickness of the magnetic layers and insulating layers limits the application of bias to the free layer, and the orientation of crystal grains affects magnetic flux direction.
Innovation Solution
The magnetic sensor stack body is designed with a stepwise-shaped magnetoresistive element and a hard bias stack body where the crystal c-axes in the magnetic layers near the junction wall face are oriented almost perpendicular to the junction wall face, achieved by optimizing the material, thickness, and sputter incident angle of the underlayer, allowing for effective condensation of magnetic fluxes and maintaining magnetic anisotropy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the reader stack thickness is reduced to increase recording density, then the recording capacity increases, but the bias magnetic field strength decreases
Solution Approach 1:
The patent applies local quality by creating a stepwise structure where the magnetic layer has different thicknesses in different regions. The magnetic layer is thicker at the junction wall face (contact region with reader stack) and thinner toward the shield layer. This local variation ensures strong bias field at the critical interface while maintaining overall miniaturization for high recording density.
Solution Approach 2:
The patent transitions from a uniform two-dimensional magnetic layer to a three-dimensional stepwise structure. By adding the thickness dimension variation, the magnetic layer can provide enhanced bias field strength at the junction wall face without increasing the overall footprint area, thus resolving the contradiction between miniaturization and field strength.
2Volume of moving object
If the magnetic layer volume is reduced for miniaturization, then the device size decreases, but the bias magnetic field application capability deteriorates
Solution Approach 1:
The magnetic layer employs local quality through spatially varying thickness. The thicker region at the junction wall face provides sufficient magnetic moment for reliable bias field application, while the overall reduced volume achieves miniaturization. This localized thickness optimization ensures reliability where it matters most without sacrificing compactness.
3Measurement precision
If the read gap is reduced to increase magnetic bit resolution, then the resolution increases, but the space for magnetic layer thickness is reduced
Solution Approach 1:
The patent resolves this contradiction by utilizing the vertical thickness dimension of the magnetic layer. Instead of being constrained by the reduced read gap in the horizontal plane, the magnetic layer extends vertically with varying thickness, providing sufficient magnetic moment for bias field application even when the read gap is minimized for high resolution.
4Measurement precision
If the reader width and stripe height are reduced to decrease sensitivity to track edges, then the track edge sensitivity decreases, but the available space for bias field application is reduced
Solution Approach 1:
The patent applies local quality by concentrating the magnetic layer thickness in the junction wall face region, which is the critical area for bias field application to the reader stack. This localized thickness enhancement ensures adequate bias field strength even when the overall reader width and stripe height are reduced for improved track edge sensitivity.
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 enhances the uniformity of the magnetic field applied to the free layer, reducing noise and improving sensitivity by effectively directing magnetic fluxes, even at reduced dimensions, thus addressing the limitations of miniaturization in magnetic sensor stacks.
Implementation Method 1
the crystal c-axes in the magnetic layers near the junction wall face are oriented almost perpendicular to the junction wall face... maintaining magnetic anisotropy
Implementation Method 2
allowing for effective condensation of magnetic fluxes and maintaining magnetic anisotropy
Implementation Method 3
achieved by optimizing the material, thickness, and sputter incident angle of the underlayer
Data Source
AI summary
The present invention is directed to align crystal c-axes in magnetic layers near two opposed junction wall faces of a magnetoresistive element so as to be almost perpendicular to the junction wall faces. A magnetic sensor stack body has, on a substrate, a magnetoresistive element whose electric resistance fluctuates when a bias magnetic field is applied and, on sides of opposed junction wall faces of the magnetoresistive element, field regions including magnetic layers for applying the bias magnetic field to the element. The magnetoresistive element has at least a ferromagnetic stack on a part of an antiferromagnetic layer, and width of an uppermost face of the ferromagnetic stack along a direction in which the junction wall faces are opposed to each other is smaller than width of an uppermost face of the antiferromagnetic layer in the same direction.