Composite Seed Layer for Ni/Co Multilayer PMA
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Solution Overview
Problem
Current magnetic devices face challenges in achieving high perpendicular magnetic anisotropy (PMA) with materials like Ni/Co multilayers, requiring thick seed layers that are impractical due to space restrictions and performance degradation concerns, especially at elevated temperatures.
Innovation Solution
A composite seed layer configuration using Hf/NiCr, Hf/NiFeCr, NiFeCr/Hf, or NiCr/Hf is employed to induce a strong (111) crystal structure in the Ni/Co multilayer stack, ensuring high coercivity (Hc) and anisotropy field (Hk) with thermal stability up to 400°C, while maintaining a thickness compatible with device design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick seed layer is used to induce strong (111) crystal structure in Ni/Co multilayer, then perpendicular magnetic anisotropy is enhanced, but device space is excessive and performance degrades at elevated temperatures
Solution Approach 1:
The seed layer is segmented into a composite structure with multiple layers (e.g., Ta/Ru/Cu or Ta/Ti/Cu) instead of using a single thick layer. Each layer contributes differently to inducing the (111) crystal structure while maintaining thermal stability and reducing overall thickness to fit device constraints.
Solution Approach 2:
The invention uses composite seed layer materials combining different metals (Ta, Ru, Cu, Ti) to achieve the desired (111) crystal structure induction. This composite approach allows optimization of both the crystal structure induction capability and thermal stability while reducing the total seed layer thickness compared to single-material seed layers.
2Length of stationary object
If seed layer thickness is reduced to meet device space restrictions, then device integration is improved, but perpendicular magnetic anisotropy induction capability is weakened
Solution Approach 1:
Different layers within the composite seed layer have different local compositions and properties optimized for specific functions. For example, Ta provides (111) texture, Ru provides diffusion barrier and structural stability, while Cu enhances magnetic properties. This local optimization allows thin overall thickness while maintaining strong PMA induction capability.
Solution Approach 2:
The invention optimizes the thickness parameters of each individual layer within the composite seed layer to achieve the desired balance. By carefully controlling the thickness of each component layer (e.g., Ta: 10-50nm, Ru: 1-10nm, Cu: 1-10nm), the seed layer induces strong (111) structure with sufficient PMA while meeting device space constraints.
3Ease of manufacture
If conventional seed layers are used, then manufacturing is simpler, but thermal stability above 300-400°C is insufficient
Solution Approach 1:
The composite seed layer uses materials like Ta, Ru, and Cu that individually and collectively provide high thermal stability. Ta has high melting point and oxidation resistance, Ru provides structural stability at high temperatures, and Cu contributes to magnetic property stability. This composite structure maintains thermal stability above 300-400°C while remaining compatible with standard sputter deposition manufacturing processes.
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 solution enhances PMA properties, achieving higher Hc and Hk with improved thermal stability and compatibility, enabling more efficient magnetic switching and thermal stability in magnetic devices.
Implementation Method 1
a thin film made of a Ni/Co laminate or the like with a magnetization direction which is perpendicular to the plane of the film (perpendicular magnetic anisotropy or PMA)
Implementation Method 2
an improved seed layer that induces a strong (111) crystal structure in the Ni/Co multilayer stack
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
Both MRAM and STT-MRAM may have a MTJ element based on a tunneling magneto-resistance (TMR) effect
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
The spin-transfer effect arises from the spin dependent electron transport properties of ferromagnetic-spacer-ferromagnetic multilayers
Data Source
Figure 1~3
Figure 4~5
Figure 6a~6b
AI summary
A MTJ for a spintronic device is disclosed and includes a thin seed layer that enhances perpendicular magnetic anisotropy (PMA) in an overlying laminated layer with a (Co/X)n or (CoX)n composition where n is from 2 to 30, X is one of V, Rh, Ir, Os, Ru, Au, Cr, Mo, Cu, Ti, Re, Mg, or Si, and CoX is a disordered alloy. A CoFeB layer may be formed between the laminated layer and a tunnel barrier layer to serve as a transitional layer between a (111) laminate and (100) MgO tunnel barrier. The laminated layer may be used as a reference layer, dipole layer, or free layer in a MTJ. Annealing between 300°C and 400°C may be used to further enhance PMA in the laminated layer.