Tunneling Magnetic Sensor Ru-Ti Capping Layer
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Solution Overview
Problem
Tunneling magnetic sensing elements face challenges in achieving high magnetic sensitivity and stability due to increased magnetostriction and reduced rate of change in resistance (ΔR/R) caused by diffusion of tantalum (Ta) into the free magnetic layer during heat treatment, which also leads to projection issues with the protective layer, affecting the Air Bearing Surface (ABS) flatness and signal-to-noise ratio.
Innovation Solution
A tunneling magnetic sensing element is designed with a first protective layer composed of a platinum-group element, such as ruthenium (Ru), and a second protective layer of titanium (Ti), preventing Ta diffusion and maintaining a flat ABS, while the platinum-group element reduces interfacial strain and stress, allowing for a high rate of change in resistance (ΔR/R) and low magnetostriction of the free magnetic layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective layer composed of tantalum (Ta) is disposed on the free magnetic layer, then the protective layer provides protection, but Ta diffuses into the free magnetic layer during heat treatment causing increased magnetostriction and reduced rate of change in resistance
Solution Approach 1:
The protective layer is segmented into a two-layer structure: a lower protective layer (Ta, TaN, or TaOx) for protection function and an upper capping layer (Ru, Rh, Ir, Pt, Pd, or their alloys) with low magnetostriction that caps the free magnetic layer. This segmentation prevents Ta diffusion while maintaining protective functionality.
Solution Approach 2:
The capping layer acts as an intermediary between the Ta protective layer and the free magnetic layer. It mediates by preventing direct contact and diffusion of Ta into the free magnetic layer, thereby maintaining low magnetostriction while still allowing the Ta layer to provide protection.
2Reliability
If Ta is used as protective layer, then protection is provided, but the protective layer projects from the Air Bearing Surface after milling due to lower milling rate
Solution Approach 1:
The protective layer is segmented into two functional layers with different properties: the lower Ta layer provides protection and has low milling rate, while the upper capping layer has high milling rate that matches the ABS requirements, preventing projection after milling.
Solution Approach 2:
Different regions of the protective structure have different qualities: the lower protective layer uses Ta for protection, while the upper capping layer uses materials (Ru, Rh, Ir, Pt, Pd) with appropriate milling rates for ABS flatness. Each layer is optimized for its specific function.
3Reliability
If Ta diffuses into the insulating barrier layer, then protection is maintained, but crystallization is inhibited and rate of change in resistance decreases
Solution Approach 1:
The capping layer serves as an intermediary barrier that prevents Ta diffusion into the insulating barrier layer, thereby maintaining crystallization and high rate of change in resistance while the Ta layer continues to provide protection.
Solution Approach 2:
The protective structure is segmented to separate the protective function (Ta layer) from the functional performance function (capping layer), preventing harmful diffusion while maintaining both protection and high ΔR/R.
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 enhances the magnetic sensitivity and stability of the tunneling magnetic sensing element by maintaining a high rate of change in resistance (ΔR/R) and low magnetostriction, while ensuring a flat ABS and improved signal-to-noise ratio, without altering the composition or film thickness of the free magnetic layer.
Implementation Method 1
A tunneling magnetic sensing element (tunneling magnetoresistive element) causes a change in resistance utilizing a tunneling effect
Implementation Method 2
the platinum-group element reduces interfacial strain and stress, allowing for a high rate of change in resistance (ΔR/R) and low magnetostriction of the free magnetic layer
Implementation Method 3
a change in electrical resistance caused by a change in the magnetization of the free magnetic layer under an influence of an external magnetic field is captured as a change in voltage to detect a leakage magnetic field from a recording medium
Data Source
AI summary
A tunneling magnetic sensing element includes: a pinned magnetic layer whose direction of magnetization is pinned in one direction; an insulating barrier layer; and a free magnetic layer whose direction of magnetization changes in response to an external magnetic field. The pinned magnetic layer, the insulating barrier layer and the free magnetic layer are deposited in the named order. A first protective layer composed of a platinum-group element is disposed on the free magnetic layer, and a second protective layer composed of Ti is disposed on the first protective layer.