Stacked CPP-MR Sensors for TDMR Skew Minimization
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Solution Overview
Problem
In two-dimensional magnetic recording (TDMR) systems, the skew of CPP-MR sensors at the inside diameter (ID) and outside diameter (OD) regions of a disk causes misalignment with target tracks, limiting the ability to read adjacent tracks effectively due to the required thickness of magnetic shields.
Innovation Solution
A stacked multi-sensor read head structure with three sensors separated by magnetic shields, where the spacing between sensors is adjusted based on the track pitch and maximum skew angle to minimize skew effects, and circuitry selects active sensors depending on the radial position of the head.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the spacing between stacked sensors is reduced to minimize skew effects, then the alignment accuracy with target tracks is improved, but the magnetic shields cannot maintain minimum effective thickness
Solution Approach 1:
The patent introduces a third dimension (vertical stacking) to accommodate multiple sensors, allowing lateral spacing to be maintained while reducing the vertical footprint. This enables the magnetic shields to maintain their minimum effective thickness in the lateral direction while sensors are stacked vertically, resolving the contradiction between alignment accuracy and shielding effectiveness.
Solution Approach 2:
The patent segments the sensing function across multiple stacked sensors (first, second, and third sensors) separated by magnetic shields. Each sensor can be independently positioned and shielded, allowing the system to maintain effective shielding thickness for each sensor while achieving compact overall structure that minimizes skew effects.
2Reliability
If the spacing between stacked sensors is increased to maintain magnetic shield thickness, then the magnetic shielding effectiveness is preserved, but the skew effect increases causing misalignment with target tracks
Solution Approach 1:
By stacking sensors vertically rather than spacing them laterally, the patent allows magnetic shields to maintain their minimum effective thickness in the lateral direction while the overall sensor assembly remains compact in the vertical direction. This dimensional reorganization resolves the trade-off between shield thickness and skew-induced misalignment.
Solution Approach 2:
The patent optimizes the vertical spacing parameter (distance D) between stacked sensors based on the maximum skew angle and track pitch. By carefully selecting this parameter, the system achieves both adequate magnetic shielding and minimized skew effects, transforming a qualitative trade-off into a quantifiable optimization.
3Quantity of substance
If more sensors are stacked to increase areal density, then the areal data bit density increases, but the device complexity and difficulty of alignment increase
Solution Approach 1:
The patent divides the sensing function into multiple segmented sensors stacked vertically, each with its own magnetic shields. This segmentation allows independent optimization of each sensor unit while achieving high areal density through vertical stacking, reducing the complexity of aligning all sensors simultaneously compared to a monolithic structure.
Solution Approach 2:
The patent implements a nested structure where magnetic shields are positioned between stacked sensors, with each shield serving dual purposes: shielding adjacent sensors and providing structural support. This nesting approach consolidates multiple functions into integrated components, reducing overall device complexity while maintaining high sensor 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 allows for accurate reading of adjacent tracks without the adverse effects of high head skew at ID and OD regions, maintaining effective magnetic shielding while allowing closer sensor spacing.
Implementation Method 1
Each of the individual CPP-MR sensors in a TDMR read head structure is required to be located between two shields of magnetically permeable material that shield the sensors from recorded data bits that are neighboring the data bit being read.
Implementation Method 2
With a sense current applied to the sensor, the rotation of the free-layer magnetization relative to the pinned-layer magnetization due to the presence of an external magnetic field is detectable as a change in electrical resistance.
Implementation Method 3
In a CPP-TMR sensor the amount of tunneling current through the layers depends on the relative orientation of the magnetizations in the two ferromagnetic layers.
Data Source
AI summary
A two-dimensional magnetic recording (TDMR) multi-sensor read head has three stacked sensors separated by magnetic shields. The lower sensor is the primary sensor that is always aligned with the target track. The middle sensor is spaced laterally from the lower sensor a distance substantially equal to the track pitch (TP). The upper sensor is aligned with the lower sensor. The spacing D between the lower and upper sensors is selected to be related to TP and a maximum skew angle, where the skew angle is the angle between a line orthogonal to the sensor and the data track that varies with radial position of the head. The read head is connected to circuitry that selects two of the three sensors to be the active sensors depending on the radial position of the head and thus the skew angle of the head.