MTJ Structure with W Buffer Layer for Thermal Stability
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Solution Overview
Problem
Current magnetic tunnel junction (MTJ) structures with vertical magnetic anisotropy face thermal instability at high temperatures due to diffusion of Pd or Pt in artificial antiferromagnetic materials during high-temperature heat treatment, degrading the overall characteristics and interfacial state with CoFeB/MgO/CoFeB bonding.
Innovation Solution
Incorporating a W-based buffer layer between the artificial antiferromagnetic layer and the ferromagnetic layers to prevent diffusion of Pd or Pt, maintaining thermal stability and ensuring coherent tunneling with the MgO tunneling oxide layer, thereby enhancing the magnetoresistance ratio and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional artificial antiferromagnetic layer structure (L1/Ru/L1) is used, then the MTJ element can achieve spin-state control, but the Pd or Pt materials diffuse during high-temperature heat treatment (400-450°C), degrading element characteristics and interfacial state
Solution Approach 1:
A buffer layer composed of Ta, W, or Mo is introduced between the artificial antiferromagnetic layer and the CoFeB/MgO/CoFeB structure. This intermediary layer prevents direct contact and diffusion between Pd/Pt in the antiferromagnetic layer and the ferromagnetic/tunneling barrier layers, while maintaining coherent tunneling through the MgO layer. The buffer layer acts as a diffusion barrier that preserves material composition stability during high-temperature heat treatment.
Solution Approach 2:
The patent creates a composite structure combining the artificial antiferromagnetic layer (with Pd or Pt), the buffer layer (Ta, W, or Mo), and the CoFeB/MgO/CoFeB structure. This composite material system leverages the specific properties of each layer: the antiferromagnetic layer provides spin-state control, the buffer layer provides diffusion prevention, and the CoFeB/MgO/CoFeB structure provides tunneling magnetoresistance, achieving both functional performance and thermal stability.
2Ease of manufacture
If high-temperature heat treatment (400-450°C) is applied to bond the selection element, then the MTJ element can be integrated with the circuit, but the Pd or Pt in the artificial antiferromagnetic layer diffuses rapidly, degrading overall characteristics
Solution Approach 1:
The buffer layer serves as a protective intermediary that enables the high-temperature bonding process to proceed without causing material diffusion. During the 400-450°C heat treatment required for selecting element integration, the buffer layer remains stable and prevents Pd/Pt atoms from migrating into the CoFeB and MgO layers, thus maintaining element characteristics while allowing manufacturing integration.
Solution Approach 2:
The buffer layer is prepared in advance before the high-temperature heat treatment process. This preliminary structural preparation ensures that when the bonding process occurs, the diffusion barrier is already in place, preventing material degradation during the thermal processing required for device integration.
3Ease of manufacture
If Pd or Pt diffusion occurs in the artificial antiferromagnetic layer, then the bonding process can proceed, but the interfacial state with CoFeB/MgO/CoFeB bonding degrades
Solution Approach 1:
The buffer layer acts as a protective intermediary at the interface between the artificial antiferromagnetic layer and the CoFeB/MgO/CoFeB structure. During bonding processes, this intermediary layer prevents Pd/Pt diffusion into the interface region, maintaining the integrity and precision of the interfacial state while allowing the bonding process to complete successfully.
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 W-based buffer layer effectively prevents material diffusion, maintaining magnetic properties and thermal stability at high temperatures, increasing the magnetoresistance ratio, and reducing power consumption in MTJ structures.
Implementation Method 1
Incorporating a W-based buffer layer between the artificial antiferromagnetic layer and the ferromagnetic layers to prevent diffusion of Pd or Pt
Implementation Method 2
a magnetic tunnel junction (MTJ) element using a change of magnetoresistance according to an MTJ effect is known
Implementation Method 3
ensuring coherent tunneling with the MgO tunneling oxide layer, thereby enhancing the magnetoresistance ratio
Implementation Method 4
MTJ structure having vertical magnetic anisotropy with thermal stability even at high temperature
Data Source
AI summary
An MTJ structure having vertical magnetic anisotropy is provided. The MTJ structure having vertical magnetic anisotropy can comprise: a substrate; an artificial antiferromagnetic layer located on the substrate; a buffer layer located on the artificial antiferromagnetic layer, and including W or an alloy containing W; a first ferromagnetic layer located on the buffer layer, and having vertical magnetic anisotropy; a tunneling barrier layer located on the first ferromagnetic layer; and a second ferromagnetic layer located on the tunneling barrier layer, and having vertical magnetic anisotropy. Accordingly, in the application of bonding the artificial antiferromagnetic layer with a CoFeB/MgO/CoFeB structure, the MTJ structure having improved thermal stability at high temperature can be provided by using the buffer layer therebetween.