Low-Coercivity CPP Magnetoresistive Sensor Reference Layer
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Solution Overview
Problem
Conventional CPP-GMR sensors face limitations in signal-to-noise ratio due to reference layer instability, particularly high coercivity, which is challenging to achieve with existing methods for forming simple-pinned reference layers.
Innovation Solution
A method involving the deposition of seed and antiferromagnetic layers at room temperature within a vacuum chamber, followed by controlled annealing between 200-600°C and subsequent ex-situ annealing in a magnetic field to form a simple-pinned reference layer with low coercivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional methods are used to form the simple-pinned reference layer, then the reference layer can be formed with exchange coupling to the AF layer, but the coercivity remains high which limits signal-to-noise ratio
Solution Approach 1:
The patent applies parameter changes by modifying the deposition temperature parameter - depositing the seed and AF layers at room temperature instead of elevated temperatures, followed by a controlled annealing process. This parameter change enables achieving low coercivity (improving manufacturing precision) while maintaining exchange coupling (preserving reliability).
Solution Approach 2:
The patent uses preliminary action by performing the annealing treatment after deposition but before final assembly. The annealing process pre-establishes the desired magnetic properties (low coercivity) of the reference layer, which then remains stable during subsequent sensor fabrication and operation.
2Strength
If the reference layer is well-coupled to the AF layer, then exchange bias is achieved, but coercivity increases reducing sensor performance
Solution Approach 1:
The patent changes the temperature parameter during deposition and annealing to decouple the relationship between exchange coupling strength and coercivity. By depositing at room temperature and annealing at controlled temperatures, the process achieves strong exchange coupling while maintaining low coercivity, resolving the trade-off between these two parameters.
Solution Approach 2:
The patent employs periodic action through the annealing process which applies thermal energy in a controlled time sequence. The annealing treatment is applied for a specific duration at a specific temperature, creating the desired magnetic domain structure that provides both strong coupling and low coercivity.
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 method results in a reference layer with reduced coercivity, enhancing the stability and signal-to-noise ratio of CPP-GMR sensors by ensuring only one orientation of magnetization at low magnetic fields, thereby improving sensor performance.
Implementation Method 1
Within a vacuum chamber a seed layer is deposited on a substrate without the application of heat to the substrate. This is followed by deposition of an antiferromagnetic layer on the seed layer
Implementation Method 2
The substrate with deposited layers is then subjected to a first annealing within the vacuum chamber by heating to between 200-600° C. for between 1 to 120 minutes
Implementation Method 3
Then the substrate with deposited layers is removed from the vacuum chamber and subjected to a second annealing, in the presence of a magnetic field, by heating to a temperature between 200-400° C. for between 0.5-50 hours
Data Source
AI summary
A method for making a current-perpendicular-to-the-plane (CPP) magnetoresistive (MR) sensor that has a reference layer with low coercivity includes first depositing, within a vacuum chamber, a seed layer and an antiferromagnetic layer on a substrate without the application of heat. The substrate with deposited layers is then heated to between 200-600° C. for between 1 to 120 minutes. The substrate with deposited layers is then cooled, preferably to room temperature (i.e., below 50° C., but to at least below 100° C., in the vacuum chamber. After cooling of the antiferromagnetic layer, the ferromagnetic reference layer is deposited on the antiferromagnetic layer. Then the substrate with deposited layers is removed from the vacuum chamber and subjected to a second annealing, in the presence of a magnetic field, by heating to a temperature between 200-400° C. for between 0.5-50 hours.