Disordered Spinel Tunnel Barrier for High TMR
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Solution Overview
Problem
Conventional ferromagnetic tunnel junctions with AlOx or MgO barriers face issues with high contact resistance, interface roughness, and low TMR values due to lattice mismatches, which hinder their application in high-speed magnetic devices and spin electronics, especially under bias voltage.
Innovation Solution
A disordered spinel Mg—Al—O layer is used as the tunnel barrier, with a cubic structure and half-sized lattice constant, reducing lattice mismatch and enhancing TMR values through coherent tunnel effects, while allowing continuous modulation of lattice constants via composition control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional AlOx or MgO barrier layers are used in ferromagnetic tunnel junctions, then the device structure is simple and manufacturing is easier, but the TMR values are low and contact resistance is high due to lattice mismatches and interface roughness
Solution Approach 1:
The patent uses a composite barrier layer structure consisting of a disordered spinel Mg-Al-O layer combined with a (La, Sr)MnO3 ferromagnetic layer. This composite structure leverages the lattice-matching advantages of the spinel phase to reduce interface roughness and enhance TMR values while maintaining manufacturing feasibility through sputtering deposition.
Solution Approach 2:
The patent changes the crystal structure parameter of the barrier layer from ordered to disordered spinel phase, and adjusts the lattice constant by controlling the Mg-Al composition ratio. This parameter change optimizes the lattice matching with adjacent ferromagnetic layers, reducing misfit dislocations and enhancing coherent tunneling effects to achieve higher TMR values.
2Reliability
If the tunnel barrier layer uses a standard spinel structure with full lattice constant, then the crystal structure is stable, but the lattice mismatch with ferromagnetic layers causes interface roughness and reduces TMR value
Solution Approach 1:
The patent utilizes a disordered spinel structure where the cation arrangement lacks long-range order, effectively reducing the lattice constant to half of the standard spinel structure. This parameter change improves lattice matching with ferromagnetic layers while the short-range order maintains structural stability and chemical composition.
3Stability of the object's composition
If the tunnel barrier layer has high resistance to reduce lattice strain, then the crystal structure stability is improved, but the contact resistance increases and spin injection capability deteriorates
Solution Approach 1:
The patent optimizes the barrier layer thickness to 1-2 nm and controls the Mg-Al composition ratio to achieve optimal lattice matching. This parameter optimization reduces lattice strain while maintaining adequate barrier height, thereby improving spin injection capability without compromising crystal structure stability.
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 disordered spinel structure achieves significantly higher TMR values and improved bias voltage dependence, enabling high-performance ferromagnetic tunnel junctions with reduced lattice strain and enhanced spin injection capabilities for applications in MRAM and spin electronics.
Implementation Method 1
so-called tunnel magnetoresistance (TMR) effect is obtained in the MTJ device, where intensity of tunnel current in the direction perpendicular to the layer plane are made different in the two ferromagnetic layers by controlling magnetization of the two ferromagnetic layers in parallel or in anti-parallel
Implementation Method 2
the properties of its electronic structure results in appearance of coherent tunnel effect, where tunnel transmission of Δ1 electrons increases in ferromagnetic materials having bcc structure
Implementation Method 3
The principle of GMR mainly depends on spin-dependent scattering in the interface between the magnetic layer and the nonmagnetic layer, and includes contribution from spin-dependent scattering (bulk-scattering) in the magnetic body
Implementation Method 4
The TMR value in the tunnel junction depends on spin polarization P in the interface between the ferromagnetic body and insulator
Data Source
AI summary
A ferromagnetic tunnel junction structure comprising a first ferromagnetic layer, a second ferromagnetic layer, and a tunnel barrier layer that is interposed between the first ferromagnetic layer and the second ferromagnetic layer, wherein the tunnel barrier layer includes a crystalline non-magnetic material having constituent elements that are similar to those of an crystalline oxide that has spinel structure as a stable phase structure; the non-magnetic material has a cubic structure having a symmetry of space group Fm-3m or F-43m in which atomic arrangement in the spinel structure is disordered; and an effective lattice constant of the cubic structure is substantially half of the lattice constant of the oxide of the spinel structure.