TMR Sensor Magnetic Capping Structure Diffusion Barrier
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Solution Overview
Problem
Existing TMR sensors face a challenge with the ferromagnetic material in the capping structure diffusing into the free magnetic layer, leading to a decrease in magnetoresistance ratio and increased noise due to the ineffective nonmagnetic spacer layers like Ru, which do not form a complete solid solution with NiFe, allowing diffusion and reducing sensor performance.
Innovation Solution
A magnetic capping structure comprising a ferromagnetic capping layer and an absorption layer, such as Ir, Pd, or Pt, is introduced to absorb molecules from the ferromagnetic capping layer, preventing diffusion into the free layer and enhancing the magnetoresistance ratio by forming a complete solid solution with NiFe, thereby improving sensor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a nonmagnetic spacer layer like Ru is used to separate the ferromagnetic capping layer from the free layer, then the device structure is simplified, but the ferromagnetic material diffuses into the free layer causing decreased magnetoresistance ratio and increased noise
Solution Approach 1:
The patent introduces an absorption layer (Ir, Pd, or Pt) as an intermediary between the ferromagnetic capping layer and the free layer. This absorption layer forms a complete solid solution with NiFe, preventing ferromagnetic material diffusion while maintaining structural simplicity. The absorption layer acts as a mediator that resolves the contradiction by providing both structural integrity and diffusion barrier functionality.
Solution Approach 2:
The patent employs a composite capping structure consisting of multiple layers with distinct materials (ferromagnetic capping layer + absorption layer). This composite structure combines the magnetic properties of the ferromagnetic layer with the diffusion-blocking properties of the absorption layer, achieving both structural simplicity and high reliability through material composition rather than complex geometry.
2Ease of manufacture
If the nonmagnetic spacer layer is made thinner to reduce device complexity, then manufacturing is easier, but diffusion of ferromagnetic material into the free layer increases
Solution Approach 1:
The absorption layer serves as an intermediary that enables the use of thinner nonmagnetic spacer layers. By placing the absorption layer adjacent to the ferromagnetic capping layer, the system can use thinner Ru layers without increasing diffusion, as the absorption layer provides the primary diffusion barrier function.
Solution Approach 2:
The patent changes the material parameter of the absorption layer to Ir, Pd, or Pt, which have different diffusion characteristics compared to Ru. These materials form complete solid solutions with NiFe, fundamentally changing the diffusion parameter to prevent ferromagnetic material migration even when the spacer layer is thin.
3Productivity
If ferromagnetic material is allowed to diffuse into the free layer to simplify the capping structure, then device fabrication is easier, but noise increases and magnetoresistance ratio decreases
Solution Approach 1:
The absorption layer acts as a mediator that allows simplified fabrication processes while preventing the harmful diffusion effect. The absorption layer's ability to form a complete solid solution with NiFe creates an effective diffusion barrier that prevents noise generation, enabling simple fabrication without compromising sensor performance.
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 absorption layer effectively prevents the ferromagnetic material from diffusing into the free layer, resulting in a 5% higher magnetoresistance ratio and reduced noise, with a narrower read gap and improved sensor stability.
Implementation Method 1
The absorption layer is adapted to absorb molecules from the ferromagnetic capping layer and prevent the ferromagnetic capping layer from diffusing into the free layer
Implementation Method 2
The ferromagnetic material in the multilayer capping structure may diffuse through the nonmagnetic spacer layer into the free magnetic layer
Data Source
AI summary
Embodiments disclosed herein generally relate to a TMR sensor for reading a recording from a magnetic recording medium using TMR, and in particular, to a magnetic capping structure of the TMR sensor. The sensor comprises a free layer and a magnetic capping structure. The magnetic capping structure comprises a ferromagnetic capping layer and an absorption layer formed on the ferromagnetic capping layer. The absorption layer is adapted to absorb molecules from the ferromagnetic capping layer and prevent the ferromagnetic capping layer from diffusing into the free layer.