Magnetic Element Free Layer Engineering for Magnetoresistance
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Solution Overview
Problem
Conventional magnetic tunneling junctions (MTJs) used in hard disk drives (HDDs) face challenges with poor soft magnetic performance due to magnetostriction in amorphous CoFeB layers, which reduces magnetoresistance when trying to achieve high density recording, and the use of multilayers like CoFeB and NiFe improves soft magnetic performance but lowers magnetoresistance.
Innovation Solution
A magnetic element with a free layer comprising a first ferromagnetic layer of CoFeX or CoNiFeX, an intermediate layer with different crystalline orientations, and a MgO barrier layer, which maintains high magnetoresistance while enhancing soft magnetic properties by preventing crystalline orientation changes and atomic interdiffusion during annealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an amorphous CoFeB layer is used in the free layer to achieve high density recording, then the magnetoresistance increases, but the soft magnetic performance deteriorates due to magnetostriction
Solution Approach 1:
The free layer is constructed as a composite structure with multiple ferromagnetic layers (CoFeB, CoFe, CoFeNi) having different compositions and crystalline orientations. This composite approach allows the first CoFeB layer to provide high magnetoresistance while subsequent layers with different orientations and compositions compensate for magnetostriction effects, improving overall soft magnetic performance
Solution Approach 2:
Different regions of the free layer are assigned different properties: the first CoFeB layer (adjacent to barrier) provides high magnetoresistance, while subsequent ferromagnetic layers have engineered compositions and orientations optimized for reducing magnetostriction. Each layer serves a specific local function within the overall free layer structure
2Reliability
If a multilayer structure of CoFeB and NiFe is used to improve soft magnetic performance, then the magnetoresistance decreases
Solution Approach 1:
The invention carefully controls the composition parameters (atomic percentages of Co, Fe, B, Ni) and thickness parameters of each ferromagnetic layer. By adjusting these parameters, the structure achieves improved soft magnetic performance while maintaining high magnetoresistance, unlike conventional multilayers that sacrifice magnetoresistance for soft magnetic properties
3Measurement precision
If annealing is performed to orient the CoFeB layer to (100) direction for high magnetoresistance, then the magnetoresistance increases, but the crystalline orientation changes to (111) due to NiFe layer preference, reducing magnetoresistance
Solution Approach 1:
The first CoFeB layer is positioned adjacent to the barrier layer in a preliminary configuration that establishes the desired (100) crystalline orientation before subsequent layers are deposited. This preliminary arrangement ensures that the critical interface between the barrier and free layer maintains the optimal orientation for high magnetoresistance throughout the annealing process
Solution Approach 2:
The structure is designed to preemptively counteract the (111) orientation preference of NiFe layers during annealing. By carefully engineering the sequence and properties of ferromagnetic layers, the invention prevents the unwanted orientation change that would otherwise occur, maintaining stable (100) orientation and high magnetoresistance
4Reliability
If atomic interdiffusion occurs during annealing to improve magnetic performance, then the magnetic properties improve, but the structural stability and processing control deteriorate
Solution Approach 1:
The invention optimizes the composition parameters of each layer (atomic percentages of constituent elements) and thickness parameters to achieve the desired magnetic performance while minimizing atomic interdiffusion during annealing. These parameter optimizations allow processing control to be maintained even as magnetic properties improve through controlled thermal treatment
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 solution provides a magnetic element with improved magnetoresistance, thermal stability, and reduced magnetostriction, making it suitable for high-density HDD applications and spin transfer switching with better processing stability.
Implementation Method 1
The intermediate layer is configured such that the first ferromagnetic layer has a first crystalline orientation and the second ferromagnetic layer has a second crystalline orientation different from the first ferromagnetic layer
Implementation Method 2
The barrier layer includes MgO and resides between the pinned layer and the free layer
Implementation Method 3
The magnetization 15 of the conventional pinned layer 14 is fixed, or pinned, in a particular direction, typically by an exchange-bias interaction with the AFM layer 12
Implementation Method 4
The conventional pinned layer 14 and the conventional free layer 18 are ferromagnetic
Implementation Method 5
amorphous layers of CoFeB exhibit a large magnetostriction. This magnetostriction results in poor soft magnetic performance
Data Source
AI summary
A method and system for providing a magnetic element are described. The method and system include providing a pinned layer, a barrier layer, and a free layer. The free layer includes a first ferromagnetic layer, a second ferromagnetic layer, and an intermediate layer between the first ferromagnetic layer and the second ferromagnetic layer. The barrier layer resides between the pinned layer and the free layer and includes MgO. The first ferromagnetic layer resides between the barrier layer and the intermediate layer. The first ferromagnetic layer includes at least one of CoFeX and CoNiFeX, with X being selected from the group of B, P, Si, Nb, Zr, Hf, Ta, Ti, and being greater than zero atomic percent and not more than thirty atomic percent. The first ferromagnetic layer is ferromagnetically coupled with the second ferromagnetic layer. The intermediate layer is configured such that the first ferromagnetic layer has a first crystalline orientation and the second ferromagnetic layer has a second crystalline orientation different from the first ferromagnetic layer.