Shared-Selector SOT-MRAM for Faster, Denser Memory Cells
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Solution Overview
Problem
Existing STT-MRAM technologies face challenges with high write current requirements, slow write speeds, and low cell density, while SOT-MRAM devices require a 2T1R structure, limiting their scalability and efficiency.
Innovation Solution
A 1T1S1R SOT-MRAM design with a shared selector is introduced, utilizing a spin-orbit torque mechanism to switch the magnetic moment of the free layer, reducing device footprint and increasing cell density, and incorporating a shared selector to simplify manufacturing and reduce complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a 2T1R structure is used in SOT-MRAM, then the magnetic moment switching is achieved, but the device footprint increases and cell density decreases
Solution Approach 1:
The patent merges the selector function with the word line by making the word line itself act as the selector. This integration eliminates the need for separate selector transistors, reducing the number of components and minimizing the device footprint while maintaining the ability to control current flow to the MTJ for magnetic moment switching.
Solution Approach 2:
The word line is given multiple functions: it serves both as the word line for addressing the memory cell and as the selector switch. This multi-functionality reduces the overall component count and allows the same structural element to perform both selection and addressing tasks, thereby reducing device footprint.
2Reliability
If a 2T1R structure is used in SOT-MRAM, then the magnetic moment switching is achieved, but the manufacturing complexity increases
Solution Approach 1:
By combining the selector and word line into a single component, the patent reduces the number of fabrication steps and assembly operations required. This merging simplifies the manufacturing process while maintaining the functional capabilities of the SOT-MRAM device.
Solution Approach 2:
The patent extracts the selector function from a separate transistor component and integrates it into the word line structure. This extraction and integration eliminates the need for additional selector transistor fabrication, thereby reducing manufacturing complexity.
3Ease of manufacture
If STT-MRAM is used, then the magnetic tunneling junction can be written by current driven through the MTJ, but the write current requirement is high and write speed is slow
Solution Approach 1:
The patent replaces the direct current-driven spin transfer torque mechanism with a spin-orbit torque mechanism. Instead of driving current directly through the MTJ to generate spin transfer torque, the patent uses a spin-orbit coupled current in an adjacent layer to generate spin Hall effect, which indirectly switches the magnetization. This substitution reduces the current requirement and improves write speed.
Solution Approach 2:
The patent introduces an intermediate layer (the spin-orbit coupled current layer) between the write current source and the MTJ. This intermediate layer generates the spin Hall effect that indirectly acts on the MTJ magnetization, serving as a mediator that reduces the direct current burden on the MTJ and enables faster switching.
4Ease of manufacture
If STT-MRAM is used, then the magnetic tunneling junction can be written by current driven through the MTJ, but the cell density is low
Solution Approach 1:
By merging the selector and word line functions into a single component, the patent reduces the overall cell structure size and component count. This merging enables higher cell density by allowing more cells to be packed into the same area while maintaining the current-driven writing capability through the integrated selector structure.
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 design achieves faster switching, lower power consumption, and higher cell density, with a smaller footprint compared to SRAM and STT-MRAM, while maintaining robustness and reducing manufacturing costs.
Implementation Method 1
utilizing a spin-orbit torque mechanism to switch the magnetic moment of the free layer
Implementation Method 2
SOT-MRAM devices require a 2T1R structure, limiting their scalability and efficiency
Data Source
AI summary
A magnetic memory device includes a magnetic tunnel junction (MTJ) stack, a spin-orbit torque (SOT) induction wiring disposed over the MTJ stack, a first terminal coupled to a first end of the SOT induction wiring, a second terminal coupled to a second end of the SOT induction wiring, and a shared selector layer coupled to the first terminal.