MTJ Diffusion Barrier for Coercivity Retention at 400°C
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Solution Overview
Problem
Current magnetic tunnel junction (MTJ) stacks face challenges in maintaining coercivity (Hc) and thermal stability at elevated temperatures, particularly during high-temperature semiconductor processes up to 400°C, due to diffusion of hard mask materials and reduced perpendicular magnetic anisotropy (PMA), which degrades the performance of magnetic memory devices.
Innovation Solution
Incorporating a diffusion barrier between the metal oxide cap layer and the hard mask in the MTJ stack to prevent non-magnetic metal diffusion and maintain PMA, using non-magnetic metals or alloys like Mo, Zr, Nb, or TaN to block metal migration, and employing a metal oxide layer to enhance perpendicular anisotropy, thereby maintaining coercivity and thermal stability during high-temperature processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If high temperature annealing (400°C) is applied to improve semiconductor process compatibility, then thermal stability and oxidation resistance are improved, but coercivity and perpendicular magnetic anisotropy deteriorate due to metal diffusion
Solution Approach 1:
A diffusion barrier layer comprising TaN, Mo, Zr, or Nb is introduced between the metal oxide cap layer and the hard mask layer. This intermediary layer prevents non-magnetic metal diffusion into the free layer during high temperature annealing, thereby maintaining coercivity and perpendicular magnetic anisotropy while allowing the system to withstand 400°C processing temperatures.
2Stability of the object's composition
If metal oxide cap layer is used to enhance perpendicular anisotropy, then PMA is improved, but metal diffusion occurs at high temperature causing coercivity loss
Solution Approach 1:
The diffusion barrier layer is positioned between the metal oxide cap layer and the hard mask layer to block the diffusion path of non-magnetic metals. This allows the metal oxide cap layer to maintain its function of enhancing perpendicular magnetic anisotropy at the free layer interface while preventing harmful metal diffusion during high temperature processing.
Solution Approach 2:
The patent employs a composite structure consisting of multiple layers with distinct functions: the metal oxide cap layer provides perpendicular magnetic anisotropy enhancement, while the diffusion barrier layer (TaN, Mo, Zr, or Nb) provides diffusion protection. This composite approach allows simultaneous achievement of high PMA and coercivity retention after 400°C annealing.
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 diffusion barrier effectively prevents metal diffusion, maintaining high coercivity and thermal stability of the free layer, ensuring optimal magnetic memory performance even after annealing at 400°C, thus enhancing the retention time and scalability of MTJ-based memory devices.
Implementation Method 1
Incorporating a diffusion barrier between the metal oxide cap layer and the hard mask in the MTJ stack to prevent non-magnetic metal diffusion
Implementation Method 2
The tunnel barrier is typically about 10 Angstroms (1 Angstrom = 0.1 nm) thick so that a current through the tunnel barrier can be established by a quantum mechanical tunneling of conduction electrons
Implementation Method 3
Magnetoresistive Random Access Memory (MRAM) has a read function based on a tunneling magnetoresistive (TMR) effect in a MTJ stack
Implementation Method 4
MTJ elements wherein one or both of the free layer and reference layer have perpendicular magnetic anisotropy (PMA)
Data Source
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AI summary
A magnetic tunnel junction (MTJ) is disclosed wherein a free layer has an interface with a tunnel barrier and a second interface with a metal oxide layer to promote perpendicular magnetic anisotropy (PMA) therein. A diffusion barrier is formed on a side of the metal oxide layer opposite the second interface to prevent non-magnetic metals in a hard mask or electrode from migrating to the second interface and degrading free layer PMA. A second diffusion barrier may be formed between a second electrode and a reference layer. The diffusion barrier may be a single layer of SiN, TiN, TaN, Mo, or CoFeX where X is Zr, P, B, or Ta, or is a multilayer such as CoFeX/Mo wherein CoFeX contacts the metal oxide layer and Mo adjoins a hard mask. As a result, coercivity is maintained or increased in the MTJ after annealing at 400°C for 30 minutes.