CPP MR Sensor with Antiparallel Top Shield and Side Shields
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Solution Overview
Problem
Current CPP-MR sensors face challenges in maintaining magnetic stabilization of the free layer while reducing noise during read operations, especially as data density increases and read head dimensions decrease, due to side reading of data bits from adjacent tracks and undesirable noise from moving magnetic domain walls in shields.
Innovation Solution
A CPP-MR sensor with side shields and an antiparallel structure (APS) top shield, where the APS top shield includes an antiferromagnetically exchange-coupled structure with an antiparallel coupling film and one Co or CoFe interface layer, allowing the use of NiFex (15-25 atomic percent) material for side shields without over-stabilizing the free layer, and optimizing the APS top shield to reduce noise and maintain proper magnetization rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If side shields of soft magnetic material are added to absorb magnetic flux from adjacent tracks, then spatial resolution is improved, but the free layer magnetization becomes over-stabilized and cannot rotate properly
Solution Approach 1:
An antiparallel coupled structure consisting of a first soft magnetic layer, antiparallel coupling layer, and second soft magnetic layer is introduced as an intermediary between the side shields and the free layer. This intermediary structure provides magnetic stabilization through exchange coupling while allowing the free layer magnetization to rotate properly in response to external magnetic fields, thus resolving the contradiction between spatial resolution and magnetization stability.
Solution Approach 2:
The patent employs a composite magnetic structure combining soft magnetic materials (NiFe alloy) with antiparallel coupling layers (Ru, Ir, or Cr) and interface films (Co or CoFe). This composite structure enables the side shields to provide both shielding functionality and controlled magnetic stabilization, allowing proper free layer rotation while maintaining spatial resolution.
2Productivity
If read head dimensions are decreased to handle higher data density, then productivity is improved, but side reading from adjacent tracks increases and noise from domain wall movement increases
Solution Approach 1:
The patent converts the potentially harmful magnetic flux from adjacent tracks into a beneficial effect by using soft magnetic side shields that preferentially attract and confine flux from the intended track. The antiparallel coupled structure further enhances this by providing controlled stabilization that reduces noise from domain wall movement, thus transforming harmful side reading and noise into improved signal quality at higher data densities.
3Ease of manufacture
If hard magnetic biasing material is removed to accommodate side shields, then ease of manufacture is improved, but magnetic stabilization of the free layer is lost
Solution Approach 1:
The side shields themselves, made of soft magnetic NiFe alloy material, provide the magnetic stabilization function previously performed by separate hard magnetic biasing layers. The antiparallel coupled structure enables the side shields to self-stabilize the free layer magnetization through exchange coupling, eliminating the need for additional hard magnetic biasing material and simplifying the fabrication process.
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 solution effectively reduces the magnetic track width and minimizes noise by stabilizing the free layer and shielding from adjacent tracks, achieving improved spatial resolution and reduced noise during read operations.
Implementation Method 1
an antiparallel (AP) coupled structure and an antiferromagnetic (AF) layer
Implementation Method 2
side shields of soft magnetically permeable material located on the sides of the sensor have been proposed to absorb magnetic flux from data bits in adjacent tracks
Implementation Method 3
The top and bottom shields ensure that the sensor reads only the information from the bit stored directly beneath it on a specific track of the disk by absorbing any stray magnetic fields emanating from adjacent bits and adjacent tracks
Implementation Method 4
A GMR spin-valve sensor has a stack of layers that includes two ferromagnetic layers separated by a nonmagnetic electrically conductive spacer layer... the rotation of the free-layer magnetization relative to the reference-layer magnetization due to the presence of an external magnetic field is detectable as a change in electrical resistance
Implementation Method 5
In a CPP-TMR sensor the tunneling current perpendicularly through the layers depends on the relative orientation of the magnetizations in the free and reference ferromagnetic layers
Data Source
AI summary
A current-perpendicular-to-the-plane (CPP) magnetoresistive (MR) sensor has both side shields and an antiparallel structure (APS) top shield. The APS top shield is an antiferromagnetically exchange-coupled top shield that includes an antiparallel (AP) coupled structure and an antiferromagnetic (AF) layer which permits the use of the desired NiFex (x is between 15 and 25 atomic percent) material for the side shields. The APS top shield includes lower and upper ferromagnetic layers with respective antiparallel magnetizations. The antiparallel coupling structure between the two ferromagnetic layers consists of the antiparallel coupling (APC) film, which is typically Ru, Ir or Cr, and one and only one interface film of Co or CoFe. The APS top shield with one and only one Co or CoFe interface film enables the material of the side shields to be formed of the preferred NiFex (x is between 15 and 25 atomic percent) material without over-stabilization of the free layer.