Magneto-resistance Element Trap Layer Boron Diffusion
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Solution Overview
Problem
In magnetic sensors using CoFeB layers, incomplete crystallization can lead to boron (B) diffusion from the pin and free layers to outside regions, causing characteristic changes and sensitivity issues, especially under high temperature environments.
Innovation Solution
Incorporating trap layers made of conductive oxide or nitride films, such as Ta, Ti, W, Ru, Nb, V, or Ni, to trap diffused boron, preventing its release to the outside and minimizing characteristic changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If heat-treating is performed to crystallize the pin layer and free layer, then the magneto-resistance change rate increases, but boron diffuses to outside regions causing characteristic changes
Solution Approach 1:
A trap layer is introduced as an intermediary between the CoFeB magnetic layers and the external environment. This trap layer selectively captures diffusing boron atoms during heat-treating, preventing them from reaching and reacting with external substances. The trap layer thus mediates between the need for high-temperature crystallization and the need to prevent boron contamination of surrounding structures.
Solution Approach 2:
The harmful boron diffusion process is extracted and isolated by providing a dedicated trap layer that specifically targets and captures boron atoms. Instead of allowing boron to diffuse freely and contaminate surrounding wiring and structures, the trap layer extracts boron from the diffusion path, concentrating it in a controlled region where it can be safely contained.
2Temperature
If the magnetic sensor is used under high temperature environments, then operational capability is maintained, but residual boron diffuses outward causing sensitivity changes
Solution Approach 1:
The trap layer is pre-positioned around the CoFeB magnetic layers before the sensor begins high-temperature operation. This preliminary structure is already in place to capture any boron that may diffuse during subsequent high-temperature use, preventing sensitivity degradation before it occurs. The trap layer acts as a pre-deployed defense mechanism against thermal boron diffusion.
Solution Approach 2:
The high-temperature environment, which initially causes harmful boron diffusion, is converted into a beneficial situation through the trap layer. The thermal energy that drives boron outward is now also driving boron into the trap layer, where it is harmlessly contained. The same thermal diffusion process that was problematic becomes the mechanism by which boron is safely sequestered.
3Reliability
If trap layers are added to prevent boron diffusion, then sensor stability is improved, but device complexity increases
Solution Approach 1:
Rather than modifying the entire sensor structure or all layers uniformly, the trap layer is applied locally and selectively around the specific CoFeB magnetic regions where boron diffusion occurs. This localized approach addresses the boron diffusion problem precisely where it arises, without unnecessarily complicating other parts of the sensor structure.
Solution Approach 2:
The sensor structure becomes a composite system combining the functional CoFeB magnetic layers with the protective trap layer. This composite structure integrates the magnetic functionality of CoFeB with the protective, boron-capturing properties of the trap layer materials (such as tungsten, molybdenum, or tantalum), creating a multi-functional structure that provides both sensing and protection capabilities.
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 trap layers effectively trap boron, reducing diffusion and maintaining sensor stability and sensitivity even under high temperature conditions, thus protecting the magnetic resistance film from heat and oxidation.
Implementation Method 1
residual B in the pin layer and the free layer diffuses to an outside
Implementation Method 2
a trap layer for trapping the B diffused from the resistance variable layer
Implementation Method 3
a magneto-resistance element comprising a layer including an alloy having B, wherein a resistance of the resistance variable layer changes according to a magnetic field
Data Source
AI summary
A magneto-resistance element includes a resistance variable layer and a trap layer. The resistance variable layer includes the alloy having B. A resistance of the resistance variable layer changes according to a magnetic field. The trap layer is for trapping the B diffused from the resistance variable layer. With this structure, the B in the resistance variable layer becomes easily trapped in the trap layer and becomes difficult to be diffused to an outside of the magneto-resistance element. A difficulty associated with B diffusion to the outside of the magneto-resistance element can be prevented from occurring.