Magnetoresistive Effect Element with Graded Tunnel Barrier
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Solution Overview
Problem
Magnetic tunnel junction (MTJ) elements with MgAl2O4 spinel barrier layers face reduced magnetoresistive (MR) ratios due to band folding effects caused by lattice constant mismatches, leading to insufficient magnetoresistive effects despite attempts to suppress these effects through disordered spinel structures.
Innovation Solution
Incorporating a tunnel barrier layer with a main body region of MgAl2O4 and interface regions of DG2O4 spinel structure, where the element X (such as Ga or In) is present in higher concentrations in the interface regions than in the main body region, to suppress band folding effects and maintain a stable composition for enhanced MR ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tunnel barrier layer containing MgAl2O4 is used to achieve a large MR ratio, then the magnetoresistive effect is enhanced, but when the lattice constant difference between the tunnel barrier layer and ferromagnetic layers is approximately doubled, the MR ratio is reduced by band folding effect
Solution Approach 1:
The patent applies local quality by creating interface regions with different composition than the main body region. The interface regions contain elements (Mg, Al, Ga, In) in different ratios to match the lattice constants of adjacent ferromagnetic layers, while the main body region maintains the optimal MgAl2O4 composition for high MR ratio. This local compositional variation suppresses band folding effects at interfaces while preserving the bulk tunnel barrier properties.
Solution Approach 2:
The patent changes the compositional parameters of the tunnel barrier layer by introducing elements with different lattice constants (Ga, In) into the interface regions. This parameter modification allows tuning of the lattice constant to reduce the mismatch with ferromagnetic layers, thereby suppressing band folding effects without compromising the overall MgAl2O4 structure that provides high MR ratio.
2Reliability
If disordered MgAl2O4 is used to bring the lattice constant close to ferromagnetic layers to suppress band folding effect, then the MR ratio is increased, but the increase is still insufficient and further improvement is needed
Solution Approach 1:
The patent divides the tunnel barrier layer into distinct regions with different functions: interface regions optimized for lattice matching with ferromagnetic layers and a main body region optimized for high MR ratio. This spatial differentiation of properties allows simultaneous achievement of good interface coupling and high tunnel magnetoresistance.
Solution Approach 2:
The patent creates a composite structure within the tunnel barrier layer, combining MgAl2O4 with other elements (Ga, In) in specific regions. This composite approach allows the interface regions to have tailored lattice constants for optimal matching with ferromagnetic layers, while the main body region maintains the high-performance MgAl2O4 composition.
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 effectively suppresses band folding effects, allowing for a larger magnetoresistive effect by maintaining the MgAl2O4 composition and reducing area resistance values, thereby enhancing the MR ratio.
Implementation Method 1
An MTJ element generally includes a first ferromagnetic layer, a second ferromagnetic layer, and a tunnel barrier layer sandwiched between the two ferromagnetic layers. In the MTJ element, a difference between a resistance when a magnetization direction of the first ferromagnetic layer is parallel to a magnetization direction of the second ferromagnetic layer and a resistance when it is antiparallel thereto is used.
Data Source
AI summary
A magnetoresistive effect element includes a first ferromagnetic layer and a tunnel barrier layer. The tunnel barrier layer has a main body region and a first interface region. The main body region has an oxide material of a first spinel structure represented by a general formula LM2O4. The first interface region has at least one element X selected from a group consisting of elements having a valence of 2 and elements having a valence of 3 excluding Al and has an oxide material of a second spinel structure represented by a general formula DG2O4(D represents one or more kinds of elements including Mg or the element X, and G represents one or more kinds of elements including Al or the element X). A content of the element X contained in the first interface region is larger than that of the element X contained in the main body region.