Magnetic Tunnel Junction Inter-layer Stack for Thermal Stability
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Solution Overview
Problem
Magnetic tunnel junctions (MTJs) face challenges in maintaining thermal robustness during elevated temperature processing steps, such as BEOL processing, which can lead to loss of magnetic anisotropy and tunnel magneto-resistance ratio (TMR) due to diffusion between layers.
Innovation Solution
Incorporating an inter-layer stack with a non-magnetic spacer sub-layer between ferromagnetic sub-layers to provide ferromagnetic coupling and act as a diffusion barrier, ensuring thermal stability and maintaining desirable magnetic and electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an MTJ structure is subjected to elevated temperature processing (BEOL processing), then large-scale fabrication is enabled, but magnetic anisotropy and TMR ratio are lost due to diffusion between layers
Solution Approach 1:
A non-magnetic spacer layer is introduced between the ferromagnetic reference layer and the hard magnetic layer. This intermediary layer prevents direct diffusion between the ferromagnetic and hard magnetic layers while maintaining ferromagnetic coupling through the spacer, thereby preserving magnetic anisotropy and TMR ratio during elevated temperature processing
Solution Approach 2:
The patent employs a composite magnetic structure consisting of multiple ferromagnetic sub-layers separated by a non-magnetic spacer layer. This composite structure combines the beneficial properties of ferromagnetic coupling (for maintaining magnetization alignment) with diffusion barrier properties (for preventing thermal degradation), enabling thermal robustness in MTJ devices
2Strength
If ferromagnetic layers are directly coupled to hard magnetic layer, then strong magnetic coupling is achieved, but diffusion occurs at elevated temperatures causing loss of magnetic properties
Solution Approach 1:
The non-magnetic spacer layer serves as a mediator that enables indirect ferromagnetic coupling between ferromagnetic layers and the hard magnetic layer while preventing direct atomic diffusion. The spacer layer thickness is optimized to maintain sufficient magnetic coupling strength while providing effective diffusion barrier protection
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 inter-layer stack enhances thermal robustness, maintains magnetic anisotropy, and achieves a sufficiently high TMR ratio, enabling reliable performance even at elevated temperatures.
Implementation Method 1
the non-magnetic spacer sub-layer is adapted to provide a ferromagnetic coupling of a magnetization of the first ferromagnetic sub-layer and a magnetization of the second ferromagnetic sub-layer
Implementation Method 2
The non-magnetic spacer sub-layer may accordingly act as a diffusion barrier, i.e. a layer counteracting or preventing diffusion
Data Source
Figure 1~2
AI summary
A magnetic layer structure for a magnetic tunnel junction (MTJ) device (100) comprises a free layer (120), a tunnel barrier layer (122), a reference layer (124), a hard magnetic layer (136), and an inter-layer stack (128) arranged between the hard magnetic layer and the reference layer, the stack including a first ferromagnetic sub-layer (130), a non-magnetic spacer sub-layer (132), and a second ferromagnetic sub-layer (134). The non-magnetic spacer provides ferromagnetic coupling of the magnetization of the first and second ferromagnetic sub-layers, such that a magnetization direction of the reference layer is fixed by the hard magnetic layer and the inter-layer stack.