CPP Magnetic Head Shunt Layer for Noise Reduction
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Solution Overview
Problem
As recording density increases, CPP structure thin-film magnetic heads face challenges such as degraded frequency characteristics, erratic spin behavior, increased thermal magnetic noise, and performance fluctuations due to reduced device size, leading to worsened S/N ratios and performance instability.
Innovation Solution
A thin-film magnetic head with a CPP structure featuring a multilayer film where a fixed magnetization layer, nonmagnetic layer, and free layer are stacked, with a shunt layer positioned deeper than the free layer and separated by a constant gap, allowing the sense current to be shunted, thereby reducing device resistance and noise, and improving frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If device size is reduced to increase recording density, then more particles are needed for pinning layer and bias magnetic field-applying layers to maintain performance, but reducing device size causes the number of particles to decline, resulting in performance fluctuations
Solution Approach 1:
The patent extends the multilayer film structure in the depth direction (perpendicular to the air bearing surface) rather than increasing lateral dimensions. The fixed magnetization layer and shunt layer are positioned at different depths, utilizing the vertical dimension to increase particle number and maintain performance while keeping the lateral device footprint small for high recording density.
2Productivity
If device size becomes small and narrow, then head resistance grows high with degradation of frequency characteristics, but reducing device size is necessary for higher recording densities
Solution Approach 1:
The shunt layer is positioned deeper in the multilayer film structure than the free layer, utilizing the depth direction to provide an additional current path. This reduces the effective resistance seen by the sense current without increasing the lateral device size, thereby maintaining frequency characteristics while enabling higher recording density.
Solution Approach 2:
The shunt layer acts as an intermediary element that provides a parallel current path for the sense current. By introducing this intermediate current route through the deeper portion of the multilayer film, the patent reduces head resistance and improves frequency response without requiring larger lateral dimensions.
3Productivity
If device size becomes small and narrow, then volume of the device decreases causing spins to get erratic and thermal magnetic noise increases, worsening S/N ratio, but device size must be reduced for higher recording densities
Solution Approach 1:
The patent utilizes the depth dimension to position the shunt layer below the free layer, effectively increasing the volume available for magnetic layer placement without increasing the lateral footprint. This additional vertical space provides more spin carriers and reduces thermal magnetic noise while maintaining the small lateral size required for high recording density.
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 maintains improved frequency characteristics, reduces thermal magnetic noise, and minimizes performance fluctuations even as device size decreases, enhancing the S/N ratio and overall performance stability.
Implementation Method 1
The free layer has its magnetization direction changing depending on an external signal magnetic field
Implementation Method 2
the fixed magnetization layer has its magnetization direction fixed by a magnetic field from the pinning layer (antiferromagnetic layer)
Implementation Method 3
a shunt layer for shunting the sense current is located at a farther distance in said depth direction than the free layer
Implementation Method 4
a magneto-resistive effect device for reading the magnetic field strength of a magnetic recording medium or the like as signals
Data Source
AI summary
The invention provides a thin-film magnetic head having a magneto-resistive effect device of the CPP (current perpendicular to plane) structure comprising a multilayer film in which a fixed magnetization layer, a nonmagnetic layer and a free layer are stacked together in order. The fixed magnetization layer, nonmagnetic layer and free layer extend away from an air bearing surface that is a plane in opposition to a medium, the length of the fixed magnetization layer in a depth direction normal to said air bearing surface is greater than the length of the free layer in the depth direction. A shunt layer for shunting the sense current is located at a farther distance in the depth direction than the free layer, and the shunt layer is separated from the free layer by a constant gap in the depth direction.