CPP Spin Valve MR Element for High Density Recording
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Solution Overview
Problem
Current magneto-resistance effect heads face challenges in achieving high recording densities exceeding 500 Gbpsi due to limitations in MR ratio, element resistance, and manufacturing accuracy, particularly in maintaining thin magnetic layers and precise gap distances, which hinder the use of CPP-spin valve films and perpendicular recording systems.
Innovation Solution
A magneto-resistance effect element with a magnetization free layer and pinned layers arranged perpendicularly, where the sense current flows through the magnetization free layer, and an oxide layer with electron reflection effects is used, allowing for a large MR ratio and low resistance, along with a novel head structure that simplifies manufacturing and improves spatial resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a spin valve film with thin magnetic layers is used to achieve high MR ratio, then sensitivity is improved, but manufacturing precision becomes difficult to maintain
Solution Approach 1:
The patent changes the fundamental parameter of current flow direction from in-plane (CIP) to perpendicular (CPP) relative to the film surface. This parameter change enables the use of thin magnetic layers (5-20 nm) without requiring extremely tight thickness control, because the spin-dependent scattering mechanism in CPP geometry is less sensitive to small variations in layer thickness compared to CIP geometry.
Solution Approach 2:
The patent transitions from two-dimensional in-plane current flow to three-dimensional perpendicular current flow through the film stack. This dimensional change allows the magnetic layers to be positioned at optimal thicknesses for spin polarization while maintaining manufacturability, as the current path through the thickness direction enables better control over spin accumulation and scattering effects.
2Measurement precision
If element resistance is increased to improve S/N ratio, then sensitivity is improved, but thermal noises increase
Solution Approach 1:
The patent changes the resistance parameter by transitioning to CPP geometry, which inherently provides lower resistance paths for current flow through the thin film stack. The perpendicular current path allows for optimized resistance values (10-200Ω) that achieve the desired S/N ratio without the excessive thermal noise that would result from higher resistance values required in CIP geometry.
3Reliability
If shield type head structure is used to protect MR element, then reliability is improved, but spatial resolution deteriorates
Solution Approach 1:
The patent extracts the MR element from the conventional shield-type head structure, eliminating the need for complex shield assemblies. The exposed perpendicular magnetization configuration of the magnetic layers provides inherent protection while the direct exposure of the magnetic sensing surface to the recording medium improves spatial resolution by reducing magnetic flux leakage and enhancing field confinement at the air bearing surface.
4Productivity
If recording density is increased to improve productivity, then output is improved, but manufacturing accuracy becomes more difficult to maintain
Solution Approach 1:
The patent changes the magnetization orientation parameter from in-plane to perpendicular, which fundamentally alters the magnetic field distribution and flux leakage characteristics. This parameter change enables higher recording densities with relaxed gap distance tolerances, as the perpendicular magnetization provides better field confinement and reduces sensitivity to precise gap positioning compared to in-plane magnetized structures.
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 enables high recording densities with improved error rates and spatial resolution, overcoming the limitations of conventional shield-type heads by utilizing a CPP-spin valve film and optimizing the magnetization free layer's thickness and position for enhanced spin polarization and reduced element resistance.
Implementation Method 1
an oxide layer with electron reflection effects is used, allowing for a large MR ratio and low resistance
Implementation Method 2
a phenomenon where an electric resistance varies according to intensity of an external magnetic field has been known, and it is called 'magneto-resistance effect'
Implementation Method 3
one ferromagnetic layer (also called 'a magnetization pinned layer') of two ferromagnetic layers which are put in a magnetically non-coupling state via an intermediate layer of non-magnetic material has magnetization fixed by exchange bias using an anti-ferromagnetic layer
Data Source
AI summary
It is possible to obtain sensitivity which can achieve an excellent error rate with a high recording density. There are provided a magnetization free layer which has two opposed main surfaces, one of which is set to be generally parallel to an air bearing surface; an intermediate layer which is formed on an opposite side face of the magnetization free layer from a medium to come in contact with the magnetization free layer; and a pair of magnetization pinned layers which are formed on an opposite side face of the intermediate layer from the magnetization free layer to come in contact with the intermediate layer and extend outwardly. A sense current flows from one magnetization pinned layer to the other magnetization pinned layer through the magnetization free layer.