CPP MR Sensor Hard Bias Structure with MgO Insulating Layer
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Solution Overview
Problem
Current CPP MR sensors face challenges in achieving high coercivity and squareness for chemically-ordered L10 phase FePt alloy hard bias layers, which are essential for maintaining magnetic stabilization and signal sensitivity, especially as data density increases and read head dimensions decrease.
Innovation Solution
A hard magnet biasing structure is introduced, featuring a crystalline MgO insulating layer, an Ir or Ru seed layer, and a chemically-ordered FePt alloy hard bias layer, with a capping layer, allowing for improved magnetic properties and a thinner insulating layer, enabling increased remanence-thickness product (Mr·t) and coercivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional insulating layer is used with FePt hard bias layer, then the insulating layer provides electrical isolation, but the coercivity and squareness of the FePt layer are insufficient for high data density applications
Solution Approach 1:
The patent introduces a Cr-containing seed layer as an intermediary between the MgO insulating layer and the FePt hard bias layer. This seed layer facilitates the chemical ordering of the L10 phase in FePt by providing a suitable crystalline template, thereby achieving high coercivity and squareness without compromising the insulating properties of the MgO layer.
Solution Approach 2:
The patent changes the insulating layer material from conventional materials to crystalline MgO, which provides improved crystalline structure and chemical ordering for the FePt layer. This parameter change enables the FePt layer to achieve higher coercivity and squareness values necessary for high data density applications.
2Reliability
If the insulating layer thickness is increased to provide sufficient electrical isolation, then electrical isolation is improved, but the remanence-thickness product (Mr·t) of the hard bias layer decreases
Solution Approach 1:
The patent uses crystalline MgO with improved dielectric properties, which allows for a thinner insulating layer to achieve the same electrical isolation performance. This enables the FePt hard bias layer to be thicker, thereby increasing the remanence-thickness product (Mr·t) while maintaining adequate electrical isolation.
3Productivity
If the read head dimensions are reduced to accommodate increasing data density, then the sensor can read higher density data, but the magnetic stabilization and signal sensitivity of the sensor decrease
Solution Approach 1:
The patent employs a composite structure consisting of crystalline MgO insulating layer, Cr-containing seed layer, and FePt hard bias layer. This composite structure provides enhanced magnetic properties with high coercivity and squareness, enabling magnetic stabilization and high signal sensitivity even in reduced-dimensional read heads for high data density applications.
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 enhances coercivity and squareness of the FePt hard bias layer, allowing for thicker layers and improved magnetic stabilization, while maintaining high signal sensitivity and compatibility with existing recording head fabrication processes.
Implementation Method 1
a crystalline MgO insulating layer on and in contact with each of the side edges of the sensor free layer
Implementation Method 2
The MgO layer may be a single layer on and in contact with the side edges of the free layer
Implementation Method 3
a seed layer of either Ir or Ru on and in contact with the MgO layer, a layer of an at least partially chemically-ordered FePt alloy hard bias layer on the seed layer
Implementation Method 4
A layer of hard or high-coercivity ferromagnetic material is used as a 'hard bias' layer to stabilize the magnetization of the free layer longitudinally via magneto-static coupling
Implementation Method 5
The hard bias layer is required to exhibit a generally in-plane magnetization direction with high anisotropy (Ku) and thus high coercivity (Hc) to provide a stable longitudinal bias
Implementation Method 6
a capping layer on the FePt alloy hard bias layer
Data Source
AI summary
A hard magnet biasing structure for a CPP-GMR or CPP-TMR read head for a magnetic recording disk drive is located between the two sensor shields and abutting the side edges of the sensor free layer. The biasing structure includes a crystalline MgO insulating layer on the lower shield and the side edges of the free layer, a seed layer of either Ir or Ru on and in contact with the MgO layer, a layer of at least partially chemically-ordered ferromagnetic FePt alloy hard bias layer on the seed layer, and a capping layer on the FePt alloy hard bias layer. The MgO layer may be a single layer on and in contact with the side edges of the free layer, or an upper layer on and in contact with a base insulating layer selected from an aluminum oxide, a tantalum oxide, a titanium oxide, and a silicon nitride.