Wedge-Shaped Free Layer CPP-MR Sensor Read Gap Reduction
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Solution Overview
Problem
Conventional CPP-MR sensors face challenges in reducing the read gap without compromising magnetoresistance and readback signal amplitude, limiting their ability to detect smaller data bits and achieve higher data density.
Innovation Solution
The free layer is designed to be wedge-shaped with a tapered thickness from the back edge to the front edge, reducing the read gap while maintaining the volume of ferromagnetic material for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the free layer thickness is reduced at the front edge to reduce the read gap, then the sensor resolution is improved, but the volume of ferromagnetic material decreases which would reduce the readback signal amplitude
Solution Approach 1:
The free layer is designed with non-uniform thickness, being thinner at the front edge (facing the disk) and thicker at the back edge. This local variation in thickness allows the front edge to reduce the read gap for improved resolution while the back edge maintains sufficient ferromagnetic material volume for adequate signal amplitude.
Solution Approach 2:
The free layer employs an asymmetric wedge-shaped profile rather than a uniform thickness. The thickness transitions from a minimum value at the front edge to a maximum value at the back edge, creating an asymmetric structure that simultaneously achieves reduced read gap and maintained signal strength.
2Productivity
If the read gap is reduced to improve resolution and allow closer bit placement, then data density increases, but the magnetoresistance and readback signal amplitude may be compromised
Solution Approach 1:
The wedge-shaped free layer provides local quality optimization by having different thicknesses at different positions. The thinner front edge enables reduced read gap for higher data density, while the thicker back edge ensures sufficient magnetoresistance and signal amplitude for reliable 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 design enhances the sensor's resolution, allowing closer placement of data bits along the track without sacrificing readback signal amplitude, thereby improving data density and detection capabilities.
Implementation Method 1
A conventional magnetoresistive (MR) sensor used as the read head in magnetic recording disk drives is a 'spin-valve' sensor based on the giant magnetoresistance (GMR) effect
Implementation Method 2
The barrier layer is sufficiently thin that quantum-mechanical tunneling of charge carriers occurs between the two ferromagnetic layers. This quantum-mechanical tunneling process is electron spin dependent
Implementation Method 3
One ferromagnetic layer adjacent the spacer layer has its magnetization direction fixed, such as by being pinned by exchange coupling with an adjacent antiferromagnetic layer
Data Source
AI summary
A current perpendicular-to-the-plane magnetoresistive (CPP-MR) sensor for a magnetic recording medium has a substantially wedge-shaped free ferromagnetic layer. The free layer thickness is tapered from the back edge (the edge recessed from the medium-facing surface) to the front edge at the medium-facing surface. The thinner free layer front edge thickness reduces the read gap (the spacing between the two sensor magnetic shields), which improves the resolution of the sensor, which in turn allows the bits to be placed closer together in the along-the-track direction. The free layer is thicker at the back edge so the volume of free layer ferromagnetic material can be maintained at the level required for high amplitude of the readback signal.