Epitaxial Magnetic Tunnel Junctions with Controlled Oxidation
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Solution Overview
Problem
Current magnetic tunnel junctions (MTJs) lack the ability to have two epitaxial ferromagnetic layers grown on a variety of substrates, including silicon, which limits their industrial applicability and performance due to random crystallographic orientations of the second ferromagnetic layer and limited lattice match between the tunnel barrier layer and the second ferromagnetic layer.
Innovation Solution
The development of magnetic tunnel junctions with two epitaxial or textured ferromagnetic layers grown on a substrate, where a tunnel barrier oxide layer is formed by oxidizing a precursor layer between the ferromagnetic layers using a controlled oxidizing gas mixture with low oxygen partial pressure, allowing for epitaxial or textured growth without oxidizing the ferromagnetic layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional oxidation methods are used to form the tunnel barrier layer, then the oxidation process is simple and fast, but the ferromagnetic layers are oxidized and their epitaxial structure is degraded
Solution Approach 1:
The patent applies parameter changes by precisely controlling the oxygen partial pressure during oxidation. By maintaining oxygen partial pressure below a critical threshold value, the oxidation process selectively forms the tunnel barrier layer without oxidizing the ferromagnetic layers, thus preserving their epitaxial structure while achieving the desired barrier layer formation.
Solution Approach 2:
The patent implements local quality by creating different oxidation conditions at different locations within the device structure. The tunnel barrier layer precursor is selectively oxidized while the ferromagnetic layers remain protected from oxidation, achieving spatially differentiated chemical treatment that preserves the epitaxial quality of the ferromagnetic layers.
2Manufacturing precision
If a second ferromagnetic layer is grown over the tunnel barrier layer using conventional methods, then the process is simple, but the second layer becomes polycrystalline with random crystallographic orientations
Solution Approach 1:
The patent applies preliminary action by ensuring the tunnel barrier layer is formed with controlled properties before growing the second ferromagnetic layer. This preliminary formation of a high-quality tunnel barrier layer creates favorable conditions for subsequent epitaxial growth of the second ferromagnetic layer, enabling crystal orientation control that would not be achievable with conventional methods.
3Manufacturing precision
If fully epitaxial MTJs are grown to achieve high spin polarization, then the tunneling magnetoresistance ratio is improved, but the number of suitable substrates is limited due to lattice matching requirements
Solution Approach 1:
The patent applies parameter changes by controlling the oxygen partial pressure during oxidation, which enables the formation of a high-quality tunnel barrier layer that facilitates epitaxial growth. This parameter control allows achieving high spin polarization and tunneling magnetoresistance ratio while expanding substrate compatibility beyond the limited lattice-matched substrates available in conventional fully epitaxial approaches.
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 approach results in MTJs with reduced interfacial roughness, fewer defects, and controlled crystal orientations, leading to higher tunneling magnetoresistance ratios and reduced bias dependence, making them suitable for magnetic sensor and storage devices.
Implementation Method 1
The insulating layer is thin enough to permit quantum-mechanical tunneling of charge carriers between the ferromagnetic layers
Implementation Method 2
a tunnel barrier oxide layer formed by oxidizing a precursor layer between the ferromagnetic layers using a controlled oxidizing gas mixture with low oxygen partial pressure, allowing for epitaxial or textured growth without oxidizing the ferromagnetic layers
Data Source
AI summary
This invention relates to magnetic tunnel junctions and methods for making the magnetic tunnel junctions. The magnetic tunnel junctions include a tunnel barrier oxide layer sandwiched between two ferromagnetic layers both of which are epitaxial or textured with respect to the underlying substrate upon which the magnetic tunnel junctions are grown. The magnetic tunnel junctions provide improved magnetic properties, sharper interfaces and few defects.