NiFeX Capping Layer for MRAM MTJ dR/R Enhancement
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Solution Overview
Problem
Conventional Magnetic Tunneling Junction (MTJ) elements face challenges in achieving a high magnetoresistive ratio while minimizing magnetostriction, as existing capping layers either enhance MR ratio at the cost of increased magnetostriction or vice versa, which is critical for high-density MRAM and TMR read head technologies.
Innovation Solution
A non-magnetic capping layer composed of NiFeX, where X is a metal with an oxidation potential greater than Ni or Fe, such as Mg, Hf, Zr, Nb, or Ta, is used in a bilayer or trilayer configuration to effectively getter oxygen atoms from the NiFe-free layer, thereby enhancing the MR ratio while maintaining low magnetostriction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional capping layer (e.g., Ta or Ru) is used to protect the MTJ stack, then the structural integrity and oxidation resistance are improved, but the magnetoresistive ratio (dR/R) is reduced due to oxygen contamination in the NiFe free layer
Solution Approach 1:
A non-magnetic intermediate layer comprising NiFeX (where X is Mg, Hf, Zr, Nb, or Ta) is introduced between the NiFe free layer and the conventional capping layer. This intermediate layer acts as a mediator that prevents oxygen diffusion from the capping layer to the NiFe free layer, thereby maintaining the magnetoresistive ratio while preserving the oxidation resistance function of the capping layer structure.
2Object-affected harmful factors
If the capping layer composition is optimized to reduce magnetostriction, then the magnetostriction is minimized, but the magnetoresistive ratio is compromised due to increased oxygen contamination
Solution Approach 1:
The NiFeX intermediate layer serves as a protective mediator that allows the use of low-magnetostriction capping layer materials without compromising the NiFe free layer quality. By blocking oxygen diffusion paths, this intermediate layer enables the system to achieve both low magnetostriction and high magnetoresistive ratio simultaneously.
3Reliability
If a thicker capping layer is used to prevent diffusion, then the diffusion barrier effectiveness is improved, but the oxygen contamination in the NiFe free layer increases due to trapped oxygen
Solution Approach 1:
The NiFeX intermediate layer acts as a first-line mediator that directly interfaces with the NiFe free layer, preventing oxygen diffusion at the critical interface. This eliminates the need for thick conventional capping layers, as the intermediate layer provides effective diffusion blocking while maintaining a thin overall structure that avoids oxygen trapping issues.
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 NiFeX capping layer achieves a high magnetoresistive ratio of over 30% while maintaining low magnetostriction, essential for advanced MRAM and TMR read head technologies, by reducing oxygen contamination in the NiFe free layer and acting as a diffusion barrier to prevent Ta diffusion into the free layer.
Implementation Method 1
A non-magnetic capping layer composed of NiFeX, where X is a metal with an oxidation potential greater than Ni or Fe, such as Mg, Hf, Zr, Nb, or Ta, is used in a bilayer or trilayer configuration to effectively getter oxygen atoms from the NiFe-free layer
Implementation Method 2
X is a metal with an oxidation potential greater than Ni or Fe
Implementation Method 3
acting as a diffusion barrier to prevent Ta diffusion into the free layer
Data Source
AI summary
An MTJ in an MRAM array or TMR read head is disclosed in which a capping layer has a bilayer configuration with a non-magnetic NiFeX inner layer on a NiFe free layer and a Ta layer on the NiFeX layer to improve dR/R and minimize magnetostriction. Optionally, a trilayer configuration may be employed where the Ta layer is sandwiched between an inner NiFeX layer and an outer Ru layer. The X component in NiFeX is preferably an element having an oxidation potential greater than Ni or Fe such as Mg, Hf, Zr, Nb, or Ta. NiFeX is preferably formed by co-sputtering a NiFe target with an X target at a forward power of about 200 W and 50 W, respectively. In an MRAM structure, the Mg content in NiFeMg may be increased to >50 atomic % to improve the gettering power of removing oxygen from the free layer.