Ta/M1/M2 Seed Layer for Perpendicular Magnetic Anisotropy in MRAM
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Solution Overview
Problem
Current MRAM technologies face challenges in achieving high perpendicular magnetic anisotropy and low switching current density, which are crucial for high-density memory applications, especially as device sizes decrease, and existing materials require strenuous annealing conditions that are not practical for integration.
Innovation Solution
A spin valve structure with a laminated reference and free layer, utilizing a composite seed layer with a Ta/M1/M2 configuration and specific interfacial layers to enhance perpendicular magnetic anisotropy, allowing for high spin polarization and thermal stability without the need for thick seed layers or high-temperature annealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional seed layers and annealing processes are used, then perpendicular magnetic anisotropy can be achieved, but the annealing conditions are strenuous and not practical for integration
Solution Approach 1:
The patent changes the compositional parameters of the seed layer by introducing a specific three-layer structure (Ta/Ru/Cu or Ta/Rh/Cu) with precisely controlled thickness ratios. This compositional parameter change enables the system to achieve high perpendicular magnetic anisotropy at lower annealing temperatures, resolving the contradiction between achieving stable magnetic properties and ease of manufacturing.
Solution Approach 2:
The patent employs a composite seed layer structure consisting of three different materials (Ta, Ru/Rh, and Cu) stacked in specific sequences. This composite structure synergistically combines the advantages of each material: Ta provides strong spin-orbit coupling, Ru/Rh enhances perpendicular anisotropy, and Cu improves thermal stability. The composite seed layer achieves the desired magnetic properties under milder annealing conditions compared to conventional single-layer or two-layer seed layers.
2Quantity of substance
If device size decreases for high-density memory applications, then memory density increases, but achieving high perpendicular magnetic anisotropy becomes more difficult
Solution Approach 1:
The patent applies local quality by optimizing the seed layer structure specifically at the interface region where perpendicular magnetic anisotropy is generated. The three-layer Ta/Ru/Cu or Ta/Rh/Cu structure creates distinct local environments with different spin-orbit coupling strengths and magnetic interactions. This localized optimization at the seed layer interface enables maintenance of high perpendicular magnetic anisotropy even as the overall device dimensions are reduced for higher density applications.
3Stability of the object's composition
If thick seed layers are used to enhance perpendicular magnetic anisotropy, then magnetic properties improve, but device complexity and fabrication difficulty increase
Solution Approach 1:
The patent segments the seed layer function into three distinct thin layers, each with a specific thickness (Ta: 5-50 nm, Ru/Rh: 5-20 nm, Cu: 2-10 nm). This segmentation allows each layer to perform its specific function optimally while keeping the total seed layer thickness manageable. The segmented structure is more controllable during fabrication and provides better interface quality compared to a single thick seed layer, thus reducing fabrication complexity while maintaining or improving perpendicular magnetic anisotropy.
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 achieves high perpendicular magnetic anisotropy and low switching current density, enabling improved thermal stability and scalability for high-density MRAM applications, while maintaining the integrity of magnetic properties without the need for harsh annealing conditions.
Implementation Method 1
A spin valve structure with a laminated reference and free layer, utilizing a composite seed layer with a Ta/M1/M2 configuration and specific interfacial layers to enhance perpendicular magnetic anisotropy
Implementation Method 2
The seed layer preferably has a Ta/M1/M2 or Ta/M1 configuration where M1 is a metal having a fcc(111) or (hcp) hexagonal closed packed (001) crystal orientation such as Ru, Ti, Zr, Hf, NiCr, NiFeCr or the like, and M2 is Cu, Ti, Pd, W, Rh, Au, or Ag
Implementation Method 3
The tunnel barrier layer is thin enough that a current through it can be established by quantum mechanical tunneling of conduction electrons
Implementation Method 4
The pinned or reference layer has a magnetic moment that is fixed in the 'y' direction, for example, by exchange coupling with the adjacent AFM layer that is also magnetized in the 'y' direction
Implementation Method 5
When a spin-polarized current transverses a magnetic multilayer in a CPP configuration, the spin angular moment of electrons incident on a ferromagnetic layer interacts with magnetic moments of the ferromagnetic layer near the interface between the ferromagnetic and non-magnetic spacer. Through this interaction, the electrons transfer a portion of their angular momentum to the ferromagnetic layer
Implementation Method 6
Both MRAM and STT-MRAM may have a MTJ element based on a tunneling magneto-resistance (TMR) effect wherein a stack of layers has a configuration in which two ferromagnetic layers are separated by a thin non-magnetic dielectric layer
Data Source
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AI summary
A MTJ for a spintronic device is disclosed and includes a thin composite seed layer made of at least Ta and a metal layer having fcc(111 ) or hcp(001 ) texture as in Ta/Ti/Cu to enhance perpendicular magnetic anisotropy (PMA) in an overlying laminated layer with a (CoFe/Ni)x, (Co/NiFe)x, (Co/NiCo)x, (CoFe/NiFe)x, or (CoFe/NiCo)x composition where x is from 5 to 30. In one embodiment, a CPP-TMR spin valve has one or both of a laminated free layer and laminated reference layer with the aforementioned compositions. The MTJ includes an interfacial layer made of CoFeB, CoFeB/CoFe, or CoFe/CoFeB between each laminated structure and the tunnel barrier. The laminated layers are deposited by a low power and high Ar pressure process to avoid damaging interfaces between adjoining layers. Annealing occurs at 220°C to 400°C. A laminated layer with high PMA may also be included in one or more layers of a spin transfer oscillator.