CoFeB-CoFe Pinned Layer Tunnel Magnetoresistive Sensor
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Solution Overview
Problem
Tunnel magnetoresistive sensors with Mg—O as an insulating barrier layer fail to achieve a high rate of resistance change (ΔR/R) due to incomplete crystallization of the second pinned magnetic sublayer, leading to insufficient detectivity and playback head characteristics.
Innovation Solution
A layered structure with a pinned magnetic layer comprising a first magnetic sublayer of CoFeB and a second magnetic sublayer of CoFe, where the composition of B is modulated, and an insulating barrier layer of Mg—O is used, allowing for improved crystallization and increased resistance change.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the second pinned magnetic sublayer is formed of CoFeB and kept in an amorphous state, then the crystalline orientation of the insulating barrier layer and free magnetic layer is improved, but the rate of resistance change (ΔR/R) is insufficient due to incomplete crystallization
Solution Approach 1:
The second pinned magnetic sublayer is divided into two distinct layers: a lower CoFeB layer (1-3 nm thick) that provides amorphous characteristics for good crystalline orientation, and an upper CoFe layer that ensures complete crystallization for high rate of resistance change. This segmentation allows each sublayer to fulfill its specific function independently.
Solution Approach 2:
The patent uses a composite structure combining CoFeB and CoFe materials in the second pinned magnetic sublayer. The CoFeB portion contributes to amorphous state and crystalline orientation control, while the CoFe portion ensures complete crystallization, achieving both good crystalline orientation and high rate of resistance change simultaneously.
2Reliability
If the second pinned magnetic sublayer is heat treated to promote crystallization, then the rate of resistance change increases, but the crystalline orientation becomes insufficient
Solution Approach 1:
The second pinned magnetic sublayer is segmented into two functional layers: the lower CoFeB layer maintains amorphous characteristics to ensure good crystalline orientation, while the upper CoFe layer undergoes complete crystallization to provide high rate of resistance change, eliminating the need for heat treatment that would disrupt crystalline orientation.
Solution Approach 2:
Different regions of the second pinned magnetic sublayer are given different material compositions and structural qualities: the lower region uses CoFeB with amorphous characteristics for orientation control, while the upper region uses CoFe with crystalline properties for high resistance change, allowing each region to optimize its local function.
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 rate of resistance change (ΔR/R) and maintains high detectivity even at narrower track widths, improving the overall performance of tunnel magnetoresistive sensors.
Implementation Method 1
Tunnel magnetoresistive sensors generate a resistance change by utilizing a tunneling effect
Implementation Method 2
the second pinned magnetic sublayer crystallized incompletely from the amorphous state even when heat treated in a manufacturing process
Data Source
AI summary
A tunnel magnetoresistive sensor includes a pinned magnetic layer, an insulating barrier layer formed of Mg—O, and a free magnetic layer. A barrier-layer-side magnetic sublayer constituting at least part of the pinned magnetic layer and being in contact with the insulating barrier layer includes a first magnetic region formed of CoFeB or FeB and a second magnetic region formed of CoFe or Fe. The second magnetic region is disposed between the first magnetic region and the insulating barrier layer.