NiFeHf Capping Layer Oxygen Gettering for MRAM Free Layer
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Solution Overview
Problem
Conventional MTJ devices face issues with high magnetostriction and oxygen contamination in the NiFe free layer due to Ta capping, leading to poor switching field uniformity and reduced magnetoresistive change (dR/R) ratios, which are not adequately addressed by existing solutions.
Innovation Solution
A low-moment NiFeHf/Ta/Ru tri-layer capping structure is used, where NiFeHf acts as a powerful oxygen getter, reducing oxygen contamination and improving the interface sharpness between the tunnel barrier and free layers, while the Ru/Ta layer minimizes inter-diffusion and enhances dR/R ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a Ta capping layer is used, then the structure is simple and conventional, but oxygen contamination increases and magnetostriction becomes very high (λs > 5 x 10^-6)
Solution Approach 1:
A NiFeHf interlayer is introduced between the Ta capping layer and the NiFe free layer. This intermediary layer acts as an oxygen getter, preventing oxygen from reaching and contaminating the free layer, while also reducing the magnetostriction transferred to the free layer. The NiFeHf layer mediates the interaction between the capping structure and the sensitive free layer.
Solution Approach 2:
The capping structure is changed from a simple Ta layer to a composite NiFeHf/Ta structure. The NiFeHf layer provides oxygen gettering and magnetostriction reduction, while the Ta layer maintains structural stability and conventional processing compatibility. This composite approach combines the benefits of different materials to solve multiple problems simultaneously.
2Manufacturing precision
If Hf is added to NiFe free layer, then oxygen gettering improves and interface sharpness increases, but the structure complexity increases
Solution Approach 1:
The capping structure is segmented into multiple functional layers: NiFeHf for oxygen gettering and magnetostriction control, Ta for structural stability, and Ru for additional protection. This segmentation allows each layer to perform its specific function optimally while maintaining overall system performance.
Solution Approach 2:
The NiFeHf layer serves multiple functions: it acts as an oxygen getter, reduces magnetostriction, and improves interface sharpness. By combining multiple beneficial functions in a single layer, the design achieves high manufacturing precision without proportionally increasing overall device complexity.
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 NiFeHf/Ta/Ru capping structure significantly improves the dR/R ratio by 35% and reduces magnetostriction, resulting in better switching field uniformity and increased switching field, with a 30% improvement in V50 and reduced read/write error counts in MRAM devices.
Implementation Method 1
NiFeHf acts as a powerful oxygen getter, reducing oxygen contamination
Implementation Method 2
the Ru/Ta layer minimizes inter-diffusion and enhances dR/R ratios
Data Source
Figure 1~2
AI summary
A high performance MTJ, and a process for manufacturing it, are described. A capping layer of NiFeHf is used to getter oxygen out of the free layer, thereby increasing the sharpness of the free layer-tunneling layer interface. The free layer comprises two NiFe layers whose magnetostriction constants are of opposite sign, thereby largely canceling one another.