Domain Wall Motion Magnetic Memory Cell for Low Write Current
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Solution Overview
Problem
Magnetic random access memory (MRAM) technologies face challenges in reducing write current as memory cell size decreases, leading to increased power consumption and potential deterioration of the tunnel barrier layer, while also seeking to enhance write speed and integration density.
Innovation Solution
The proposed solution involves a magnetic memory cell structure with a ferromagnetic recording layer, a pinned layer, and a non-magnetic tunnel barrier layer, where a domain wall is moved within the recording layer using spin transfer currents that flow internally, rather than penetrating the tunnel junction, allowing for data writing without damaging the tunnel barrier and reducing write current requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the memory cell size is reduced to increase integration density, then the write current increases, but this leads to increased power consumption and tunnel barrier layer deterioration
Solution Approach 1:
The patent replaces the conventional spin transfer torque (STT) method with a domain wall motion (DWM) method. Instead of using spin-polarized current to directly switch magnetization, the invention uses current to move domain walls within the ferromagnetic layer, which then switch the magnetization state. This mechanical-like domain wall movement substitutes the direct spin transfer mechanism, enabling lower write currents that scale with device size rather than increasing as devices shrink.
Solution Approach 2:
The patent introduces a gradient in magnetic anisotropy across the ferromagnetic layer to create and control domain walls. By modifying the magnetic anisotropy parameter (through composition gradient or thickness variation), domain walls are formed at specific positions. This parameter change enables the domain wall motion mechanism to function effectively, allowing write current to control domain wall position and thus magnetization state without the high currents required by conventional STT methods.
2Reliability
If the write current is increased to maintain switching capability in smaller cells, then the magnetization switching reliability improves, but the tunnel barrier layer deteriorates due to high current stress
Solution Approach 1:
The patent replaces the spin transfer torque mechanism with domain wall motion. In the DWM method, current flows through the ferromagnetic layer to move domain walls, and the magnetization switching is achieved by the movement and annihilation of domain walls rather than direct spin transfer. This substitution eliminates the need for high current density through the tunnel barrier, preventing its deterioration while maintaining reliable magnetization switching through controlled domain wall dynamics.
Solution Approach 2:
The patent introduces domain walls as intermediary structures that mediate between the applied current and the magnetization switching. Instead of current directly acting on the magnetization through the tunnel barrier, the current first moves the domain wall (intermediary), and then the domain wall's movement and annihilation achieve the magnetization switching. This intermediary mechanism protects the tunnel barrier from high current stress while maintaining switching reliability.
3Reliability
If the conventional spin transfer method is used to write data, then the magnetization can be switched, but the write current increases as memory cell size decreases
Solution Approach 1:
The patent replaces the spin transfer torque (STT) mechanism with domain wall motion (DWM). In STT, spin-polarized current directly switches magnetization, requiring high current density that increases as device size decreases. In DWM, current moves domain walls within the ferromagnetic layer, and magnetization switching occurs through domain wall annihilation. This mechanical-like domain wall movement mechanism enables write current to scale with device size, reversing the conventional trend where write current increases as cells shrink.
Solution Approach 2:
The patent modifies the magnetic anisotropy parameter by introducing a gradient across the ferromagnetic layer. This gradient creates stable domain wall configurations that can be moved by current. By changing the magnetic anisotropy parameter spatially, the patent enables the DWM mechanism to achieve magnetization switching at lower current densities compared to uniform anisotropy structures used in conventional STT methods.
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
This approach effectively decreases write current consumption, suppresses tunnel barrier layer deterioration, and increases write speed by utilizing domain wall motion within the magnetic recording layer, thereby improving the scalability and efficiency of MRAM technology.
Implementation Method 1
the magnetization is switched by the directly interaction between a spin of a conductive electron as a carrier and magnetic moment of the conductor (hereinafter, to be referred to as a spin transfer magnetization switching)
Implementation Method 2
a domain wall is moved within the recording layer using spin transfer currents that flow internally
Data Source
AI summary
A magnetic memory cell 1 is provided with a magnetic recording layer 10 which is a ferromagnetic layer and a pinned layer 30 connected with the magnetic recording layer 10 through a non-magnetic layer 20. The magnetic recording layer 10 has a magnetization inversion region 13, a first magnetization fixed region 11 and a second magnetization fixed region 12. The magnetization inversion region 13 has a magnetization whose orientation is invertible and overlaps the pinned layer 30. The first magnetization fixed region 11 is connected with a first boundary B1 in the magnetization inversion region 13 and a magnetization orientation is fixed on a first direction. The second magnetization fixed region 12 is connected with a second boundary B2 in magnetization inversion region 13 and a magnetization orientation is fixed on a second direction. The first direction and the second direction are opposite to each other.