Tunnel Magnetoresistive Element B Absorption Layer Etching
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Solution Overview
Problem
Existing tunnel magnetoresistive elements face challenges in achieving a high TMR ratio and sensitivity as a magnetic sensor due to the difficulty in accurately removing B absorption layers after magnetic annealing, which affects the exchange coupling between CoFeB and soft magnetic layers.
Innovation Solution
A method involving stacking a pinned magnetic layer, an insulating layer, and a CoFeB layer, followed by a B absorption layer, in-magnetic field heating to align magnetization axes, and precise dry etching to remove the B absorption layer, ensuring accurate endpoint detection and over-etching control to achieve a desired TMR ratio and enhance magnetic coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a B absorption layer with sufficient thickness is positioned adjacent to the CoFeB layer to achieve a huge TMR ratio, then the TMR ratio is improved, but the sensitivity of the magnetic sensor deteriorates due to poor exchange coupling between CoFeB and soft magnetic layer
Solution Approach 1:
The patent applies preliminary action by forming the B absorption layer before the soft magnetic layer, allowing the TMR ratio to be optimized first. The B absorption layer is deposited with sufficient thickness to achieve the desired TMR ratio, and then the soft magnetic layer is deposited on top. This sequential approach allows each layer to be optimized for its specific function without compromising the other.
Solution Approach 2:
The patent utilizes parameter changes by controlling the thickness of the B absorption layer within a specific range (0.5-5 nm) to balance TMR ratio and exchange coupling. By adjusting this critical parameter, the patent achieves optimal performance where the TMR ratio is sufficiently high while maintaining good exchange coupling with the soft magnetic layer.
2Manufacturing precision
If the B absorption layer is removed to improve exchange coupling and sensitivity, then the sensor sensitivity is improved, but the TMR ratio deteriorates due to insufficient B absorption
Solution Approach 1:
The patent applies partial action by providing a B absorption layer with thickness in the range of 0.5-5 nm, which is sufficient to absorb B atoms and maintain high TMR ratio, yet thin enough to allow adequate exchange coupling. This optimized thickness represents the optimal balance between the two competing requirements, avoiding both excessive thickness (which would harm coupling) and insufficient thickness (which would harm TMR ratio).
3Ease of manufacture
If conventional etching methods are used to remove the B absorption layer, then the process is simple, but the removal precision is insufficient leading to either residual layers or over-etching
Solution Approach 1:
The patent applies feedback by implementing real-time monitoring during the etching process to detect the exposure of the CoFeB layer. When the B absorption layer is completely removed and the CoFeB layer becomes visible, the etching process automatically stops. This feedback mechanism ensures precise removal of the B absorption layer without residual layers or over-etching, while maintaining process simplicity.
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 method allows for the accurate removal of B absorption layers, achieving a high TMR ratio and significantly improving the sensitivity of tunnel magnetoresistive elements for magnetic sensor applications by ensuring proper exchange coupling between CoFeB and soft magnetic layers.
Implementation Method 1
B absorption layers (Ti, MgO, and the like) with a sufficient thickness made of a material that absorbs the diffusing B from the CoFeB layers
Implementation Method 2
The resistance of the insulating layer changes by the tunnel effect depending on the angle between the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer
Implementation Method 3
magnetic annealing of the stack structure of the MTJ portion (CoFeB/MgO/CoFeB)
Data Source
AI summary
A method for producing a tunnel magnetoresistive element includes a stacking step, then in-magnetic field heating, and then dry etching. The stacking includes stacking a B absorption layer which is in contact with an upper surface of a CoFeB layer. The dry etching includes removal of layers to the B absorption layer. An end of etching is set as an end point time detected by an analysis device when a final layer before the B absorption layer directly above the CoFeB layer is exposed has reduced to a prescribed level, or when the B absorption layer directly above the CoFeB layer has increased to the prescribed level. An amount of over-etching after the end point time is specified in advance, and the B absorption layer is stacked such that the thickness from the prescribed level to the upper surface of the CoFeB layer corresponds to the over-etching amount.