3-Terminal MTJ Switching via Spin Hall Effect
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional 2-terminal STT-MRAM devices face limitations in switching speed and reliability, particularly for in-plane magnetized devices, with high write error rates and incubation delays, making them unsuitable for fast and deterministic switching.
Innovation Solution
The implementation of a 3-terminal magnetic tunnel junction (MTJ) circuit using a spin Hall effect (SHE) metal layer coupled with a free magnetic layer, where a charge current generates both a spin-polarized current and an Oersted magnetic field, facilitating rapid and reliable magnetization switching through spin-transfer torque (STT) effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional 2-terminal STT-MRAM devices are used, then the device structure is simple, but the switching speed is slow and write error rates are high
Solution Approach 1:
The device is segmented into three terminals: a first terminal for applying voltage across the MTJ, a second terminal for injecting charge current into the spin Hall effect layer, and a third terminal for reading. This segmentation separates the write and read current paths, enabling independent optimization of write reliability and read operations, thereby reducing write error rates while maintaining manageable device complexity through structured terminal assignment.
Solution Approach 2:
A spin Hall effect metal layer is introduced as an intermediary component between the voltage source and the free magnetic layer. This intermediary layer converts charge current into spin-polarized current through the spin Hall effect, which then exerts spin-transfer torque on the free magnetic layer to enable reliable magnetization switching. The intermediary layer facilitates efficient spin current injection and reduces write error rates while maintaining device structural organization.
2Speed
If conventional STT-MRAM devices are used, then the device structure is simple, but the switching speed is slow with incubation delays
Solution Approach 1:
The three-terminal configuration segments the current paths, allowing the write current to flow through the spin Hall effect layer while the read current flows through the MTJ. This segmentation eliminates the incubation delay problem by enabling direct spin current injection into the free magnetic layer through the SHE layer, achieving nanosecond-timescale switching speeds while maintaining structured device complexity.
Solution Approach 2:
The spin Hall effect metal layer acts as an intermediary that converts charge current into transverse spin current, which rapidly injects spin angular momentum into the free magnetic layer. This intermediary mechanism eliminates the incubation delay by providing a direct and efficient spin current injection path, achieving fast nanosecond switching speeds while maintaining organized device structure through the intermediary layer's structured integration.
3Reliability
If charge current is applied through the MTJ for writing, then the writing operation is simple, but it causes 'write-upon-read' errors
Solution Approach 1:
The writing operation is simplified through segmentation of current paths: write current flows through the spin Hall effect layer via the second terminal, while read current flows through the MTJ via the first and third terminals. This segmentation completely separates write and read operations, eliminating write-upon-read errors while maintaining ease of operation through clear terminal assignment and independent current control paths.
Solution Approach 2:
The spin Hall effect layer serves as an intermediary for write operations, converting charge current into spin current that acts on the free magnetic layer without passing through the MTJ. This intermediary mechanism enables writing operations to be performed through the second terminal independently of the read path, eliminating write-upon-read errors while maintaining operational simplicity through the intermediary's structured integration into the three-terminal architecture.
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 configuration achieves low write error rates (≤10−5) with pulse durations as short as 2 ns, significantly faster than previous STT-MRAM devices, and allows for separate control over read and write operations, reducing the risk of 'write-upon-read' errors.
Implementation Method 1
a SHE layer that is electrically conducting and exhibits a spin Hall effect to, in response to an applied charge current, generate a spin-polarized current that is perpendicular to the applied charge current
Implementation Method 2
a spin-polarized current can be directed into a magnetic layer to cause transfer of the angular momenta of the spin-polarized electrons to the magnetic layer and this transfer can lead to exertion of a spin-transfer torque (STT) on the local magnetic moments in the magnetic layer and precession of the magnetic moments
Implementation Method 3
an Oersted magnetic field whose direction is generally in the plane of the switchable free magnetic layer across the plane of the switchable free magnetic layer
Data Source
AI summary
The disclosed technology provides various implementations of a device based on a spin Hall effect (SHE) and spin transfer torque (STT) effect. In one aspect, a device is provided to include a magnetic structure including a ferromagnetic layer having a magnetization direction that can be changed by spin transfer torque; a SHE layer that is electrically conducting and exhibits a spin Hall effect to, in response to an applied charge current, generate a spin-polarized current that is perpendicular to the applied charge current, the SHE layer located adjacent to the ferromagnetic layer to inject the spin-polarized current into the ferromagnetic layer; a first electrical contact in contact with the magnetic structure; a second electrical contact in contact with a first location of the SHE layer; a third electrical contact in contact with a second location of the SHE layer so that the first and second locations are on two opposite sides of the magnetic structure; a magnetic structure circuit coupled between the first electrical contact and one of the second and third electrical contacts to supply a current or a voltage to the magnetic structure; and a charge current circuit coupled between the second and third electrical contacts to supply the charge current into the SHE layer, wherein the device is operable at a low write error rate with pulses of a pulse duration of around 2 ns or shorter to switch a direction of the magnetization direction of the ferromagnetic layer in the magnetic structure.