Composite Seed Layer Stack for Thermally Stable PMA Multilayers
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Solution Overview
Problem
Current magnetic technologies face challenges in achieving high thermal stability and perpendicular magnetic anisotropy (PMA) at elevated temperatures, particularly in reducing the thickness of seed layers while maintaining robust magnetic properties, which is crucial for advanced MRAM and spintronic devices.
Innovation Solution
A magnetic element with a seed layer stack comprising TaN and Mg or MgZr, along with a growth promoting layer like NiCr, induces a strong (111) crystal structure in overlying PMA layers, enhancing coercivity (Hc) and anisotropy field (Hk) while maintaining thermal stability up to 400°C and ensuring compatibility with other device layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the thickness of the seed layer is reduced to enable scaling and higher packing density, then device integration and packing density are improved, but the ability to induce strong (111) crystal structure and maintain PMA properties deteriorates
Solution Approach 1:
The patent employs a composite seed layer structure consisting of multiple materials (Ta, TaN, Mg, MgZr, NiCr) arranged in specific configurations. This composite approach allows each layer to contribute different functions: Ta/TaN provides thermal stability and adhesion, Mg/MgZr promotes (111) crystal structure formation, and NiCr enhances PMA. The combination achieves reliable crystal structure induction at reduced thickness compared to conventional single-material seed layers.
Solution Approach 2:
The seed layer is designed with spatially varying properties where different materials are positioned at specific locations to achieve local functions. The Mg or MgZr layer is positioned specifically to induce (111) structure in the PMA layer, while Ta/TaN layers provide thermal stability at the substrate interface. This local optimization allows thin overall thickness while maintaining necessary functions at each interface.
2Volume of moving object
If the seed layer thickness is reduced, then device scaling and packing density are improved, but thermal stability at elevated temperatures up to 400°C deteriorates
Solution Approach 1:
The composite seed layer incorporates Ta and TaN which have high melting points and excellent thermal stability. These materials form a thermally stable base that can withstand 400°C processing temperatures. The combination of thermally stable materials (Ta/TaN) with structure-promoting materials (Mg/MgZr) in a thin composite structure achieves both reduced thickness and maintained thermal stability.
Solution Approach 2:
The patent changes the compositional parameters of the seed layer by incorporating specific ratios of different materials. The Mg or MgZr content is optimized to provide sufficient (111) structure promotion while keeping the total thickness low. The TaN/Mg or TaN/MgZr configuration with specific thickness ratios achieves the right balance between thermal stability and structure induction capability at elevated temperatures.
3Ease of manufacture
If conventional seed layers are used, then manufacturing simplicity is maintained, but the ability to achieve high coercivity (Hc) and anisotropy field (Hk) deteriorates
Solution Approach 1:
The composite seed layer uses materials that can be deposited using standard sputtering techniques, maintaining manufacturing simplicity. The NiCr layer specifically enhances PMA and magnetic properties, while Ta/TaN/Mg combinations provide the necessary crystal structure. This composite approach achieves high Hc and Hk values without requiring complex manufacturing processes, as each layer can be deposited using conventional thin-film techniques.
Solution Approach 2:
The patent optimizes the thickness parameters of each seed layer component to achieve high magnetic properties. The NiCr layer thickness is specifically controlled to maximize PMA induction, while the Mg or MgZr layer thickness is optimized for (111) structure formation. These parameter optimizations enable high Hc and Hk values while maintaining compatibility with standard fabrication processes.
4Volume of moving object
If the seed layer is made thinner, then device scaling is improved, but surface roughness of overlying layers increases
Solution Approach 1:
The composite seed layer structure with Ta/TaN base layers and Mg/MgZr intermediate layers provides a smooth foundation for the PMA layer. The different materials in the composite structure have complementary properties that collectively minimize surface roughness. The Ta/TaN layers provide a stable base, while the Mg/MgZr layers promote epitaxial growth, resulting in smooth interfaces even at reduced overall thickness.
Solution Approach 2:
The seed layer is designed with local quality optimization where specific materials are positioned to address specific interface quality issues. The Mg or MgZr layer is positioned specifically to promote smooth epitaxial growth of the PMA layer, reducing roughness at the critical interface. This local optimization of interface quality allows thin seed layers while maintaining smooth surfaces for subsequent layers.
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 proposed solution achieves improved magnetic properties, including higher Hc and Hk, with enhanced thermal stability and reduced roughness, enabling better compatibility with high-temperature processing and scaling for higher packing density in MRAM and spintronic devices.
Implementation Method 1
induce a strong (111) crystal structure in an overlying multilayer stack thereby improving perpendicular magnetic anisotropy (PMA)
Data Source
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Figure 7a~7h
AI summary
A magnetic element is disclosed wherein a composite seed layer such as TaN/Mg enhances perpendicular magnetic anisotropy (PMA) in an overlying magnetic layer that may be a reference layer, free layer, or dipole layer. The first seed layer is selected from one or more of Ta, Zr, Nb, TaN, ZrN, NbN, and Ru. The second seed layer is selected from one or more of Mg, Sr, Ti, Al, V, Hf, B, and Si. A growth promoting layer made of NiCr or an alloy thereof may be inserted between the seed layer and magnetic layer. The magnetic element has thermal stability to at least 400°C.