SOT Layer Composition for Thermally Stable MRAM Switching
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Solution Overview
Problem
Conventional SOT materials for MRAM devices, such as topological insulators like BiSb, have low melting temperatures, making them incompatible with CMOS back-end-of-line processing, while materials like Bi2Se3 exhibit strong material diffusion during annealing, affecting adhesion and stability.
Innovation Solution
A SOT layer comprising a bismuth-based material combined with a high-melting-point metal, such as nickel, platinum, or zirconium, forming a metallic alloy or multilayer structure with controlled thickness and concentration, ensuring thermal stability and a large spin Hall angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If topological insulator materials like BiSb are used as SOT layer, then spin Hall angle is significantly increased, but melting temperature becomes below 400°C making CMOS BEOL incompatible
Solution Approach 1:
The patent uses composite materials by combining topological insulator materials (BiSb, Bi2Se3) with conventional high-melting-point metals (Ta, W, Pt) to create a hybrid SOT layer structure. This composite approach allows the system to maintain the high spin Hall angle from the topological insulator while achieving the thermal stability from the conventional metal, directly resolving the contradiction between high SHA and high melting temperature
Solution Approach 2:
The patent changes the material composition parameters by adjusting the ratio and thickness of topological insulator layers versus conventional metal layers in the composite structure. By optimizing these parameters, the system achieves a balance where the spin Hall angle remains sufficiently high while the effective melting temperature of the composite structure exceeds 400°C for CMOS BEOL compatibility
2Temperature
If bismuth selenide (Bi2Se3) is used as SOT layer, then melting temperature increases above 400°C, but strong material diffusion occurs during annealing affecting adhesion and stability
Solution Approach 1:
The patent introduces conventional metals (Ta, W, Pt) as intermediary layers between the Bi2Se3 topological insulator and the surrounding structures. These intermediary layers act as diffusion barriers that prevent material diffusion during annealing while maintaining thermal stability, thus resolving the contradiction between high melting temperature and composition stability
Solution Approach 2:
By creating a composite structure where Bi2Se3 is combined with diffusion-resistant conventional metals, the patent achieves a material system that benefits from both the high melting temperature of Bi2Se3 and the low diffusion characteristics of the conventional metal layers, maintaining adhesion and compositional stability during thermal processing
3Temperature
If conventional SOT materials like Ta, beta-W, or Pt are used, then thermal stability is achieved, but spin Hall angle is lower compared to topological insulators
Solution Approach 1:
The patent merges the advantages of conventional SOT materials (high thermal stability, CMOS compatibility) with topological insulator materials (high spin Hall angle) by creating a composite SOT layer structure. The conventional metal provides the thermal backbone while the topological insulator layer contributes enhanced spin Hall effect, achieving both thermal stability and high SHA simultaneously
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 SOT layer achieves efficient magnetization switching with thermal stability above 400°C, enabling CMOS BEOL compatibility and maintaining a high spin Hall angle, thus enhancing MRAM device performance.
Implementation Method 1
The typical figure of merit of such an SOT layer is its spin Hall angle (SHA), which quantifies how effective the SOT material of the SOT layer transfers a spin current into the magnetic free layer
Implementation Method 2
the SOT layer comprises a material combination of a bismuth-based material and a metal having a melting point of at least 1000° C.
Implementation Method 3
Bi2Se3 reveal a strong material diffusion after a 300° C. annealing sequence. FIG. 2 illustrates in this respect that Bi rich and Se rich regions develop, respectively, after performing the annealing sequence. This strong material diffusion seems to also affect the adhesion of the Bi2Se3 layer
Data Source
AI summary
The disclosure relates to spin orbit torque (SOT) magnetic random access (MRAM) devices. A magnetic structure for a SOT-MRAM device and a method for fabricating the magnetic structure are presented. The magnetic structure comprises a SOT layer and a magnetic tunnel junction (MTJ) structure arranged on the SOT layer. The SOT layer comprises a material combination of a bismuth-based material and a metal having a melting point of at least 1000° C. As a result, the SOT is thermally stable and also shows a large spin Hall angle (SHA).