Spin Hall Effect Metal Layer for MRAM Switching
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Solution Overview
Problem
Current spin-transfer torque (STT) technologies face challenges in efficiently switching magnetic layers with perpendicular magnetic anisotropy, requiring large spin torques and charge currents, and struggle with reliable writing and reading operations in magnetic random access memory (MRAM) devices due to the need for high current through the tunnel barrier, which degrades the memory cell.
Innovation Solution
The development of 3-terminal magnetic circuits and devices utilizing the spin Hall effect (SHE) to generate a spin-polarized current with both in-plane and perpendicular components, allowing for efficient spin-transfer torque with lower charge currents and independent control of writing and reading operations through a gate voltage and charge current in a spin Hall effect metal layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional spin-transfer torque (STT) is used to switch magnetic layers with perpendicular magnetic anisotropy, then magnetization switching can be achieved, but large spin torques and charge currents are required which degrade the memory cell
Solution Approach 1:
The patent introduces a spin Hall effect metal layer as an intermediary between the charge current source and the magnetic tunnel junction. This intermediary layer converts the charge current into a spin-polarized current via the spin Hall effect, which then exerts spin-transfer torque on the free magnetic layer. This mediator approach allows the charge current to flow through the SHE metal layer rather than directly through the tunnel barrier, reducing degradation while maintaining switching effectiveness.
Solution Approach 2:
The patent replaces the conventional direct spin-transfer torque mechanism (where charge current flows through the tunnel barrier) with an indirect mechanism using the spin Hall effect. Instead of relying on direct electron tunneling through the barrier to generate spin torque, the system uses spin-dependent scattering in the SHE metal layer to generate the necessary spin-polarized current, substituting a different physical mechanism that achieves the same goal with less damage to the memory cell.
2Ease of operation
If high charge current is applied through the tunnel barrier to achieve magnetization switching, then writing operation can be performed, but the tunnel barrier degrades and reading operation becomes unreliable
Solution Approach 1:
The patent segments the current path by introducing a separate spin Hall effect metal layer through which the writing current flows. This divides the original single current path (through the tunnel barrier) into two separate paths: one for writing (through the SHE metal layer) and one for reading (through the tunnel barrier). This segmentation allows the writing operation to occur without subjecting the tunnel barrier to degrading high currents, preserving its integrity for reliable reading operations.
Solution Approach 2:
The spin Hall effect metal layer serves as an intermediary that handles the high-current writing operation, protecting the tunnel barrier from direct exposure to degrading currents. The intermediary converts the charge current into spin torque indirectly, allowing the tunnel barrier to remain intact for its primary function of enabling reliable read operations through tunnel magnetoresistance.
3Adaptability or versatility
If conventional 2-terminal MTJ structure is used, then device simplicity is maintained, but independent control of writing and reading operations is not possible
Solution Approach 1:
The magnetic tunnel junction structure is designed to serve multiple functions through different terminal configurations. The same MTJ structure can perform writing operations when current flows through the spin Hall effect metal layer and reading operations when current flows through the tunnel barrier, enabling one structure to handle both write and read functions with independent control, rather than requiring separate structures for each function.
Solution Approach 2:
The patent adds a third terminal dimension to the conventional 2-terminal MTJ structure by introducing the spin Hall effect metal layer with its own electrical contacts. This transforms the device from a 2-terminal to a 3-terminal structure, adding a new dimension of control that enables independent writing and reading operations. The additional terminal provides an independent current path for writing that does not interfere with the reading path through the tunnel barrier.
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 enables efficient anti-damping switching of magnetic layers with perpendicular magnetic anisotropy, reduces the need for high current through the tunnel barrier, and improves the reliability and efficiency of MRAM devices by allowing separate control of writing and reading operations, thereby enhancing the performance and longevity of memory cells.
Implementation Method 1
an electrically conducting magnetic layer structure exhibiting a spin Hall effect (SHE) and, in response to an applied in-plane charge current, generating a spin-polarized current of a magnetic moment oriented in a predetermined direction having both an in-plane magnetic moment component parallel to a surface of the electrically conducting magnetic layer structure and a perpendicular magnetic moment component perpendicular to the surface
Implementation Method 2
The magnetization direction of the free magnetic layer is capable of being switched by the spin-polarized current via a spin-transfer torque (STT) effect
Implementation Method 3
The free magnetic layer (FL) and the pinned magnetic layer (PL) are separated by an insulating barrier layer (e.g., a MgO layer) that is sufficiently thin to allow electrons to transit through the barrier layer via quantum mechanical tunneling when an electrical bias voltage is applied between the electrodes
Data Source
AI summary
A device based on a spin Hall effect and spin-transfer torque (STT) effect is provided to include a magnetic tunneling junction (MTJ) element including a free magnetic layer structured to have a magnetization direction that can be changed by spin-transfer torque; an electrically conducting magnetic layer structure exhibiting a spin Hall effect (SHE) and, in response to an applied in-plane charge current, generating a spin-polarized current of a magnetic moment oriented in a predetermined direction having both an in-plane magnetic moment component parallel to a surface of the electrically conducting magnetic layer structure and a perpendicular magnetic moment component perpendicular to the surface of the electrically conducting magnetic layer structure. The magnetization direction of the free magnetic layer is capable of being switched by the spin-polarized current via a spin-transfer torque (STT) effect. This device can be configured in a 3-terminal configuration.