Magnetic Memory Device Using Spin-Orbit Torque for Low Current Switching
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Solution Overview
Problem
Conventional spin transfer torque magnetic memory devices face challenges in achieving both low critical current density and high thermal stability, which are essential for commercialization, and require additional external magnetic fields, leading to increased complexity and power loss.
Innovation Solution
A magnetic memory device with a tunnel junction structure that uses a conductive line with an antiferromagnetic and ferromagnetic layer to induce magnetization reversal through spin-orbit spin torque without an external magnetic field, allowing for selective switching and independent adjustment of critical current density and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the effective magnetic anisotropy energy density of the free magnetic layer is increased to meet thermal stability requirements, then thermal stability is improved, but critical current density increases making magnetization reversal more difficult
Solution Approach 1:
The patent introduces a conductive line with spin-orbit interaction as an intermediary between the current source and the free magnetic layer. This intermediary generates spin-orbit spin torque that mediates the magnetization reversal process, allowing the system to overcome the direct trade-off between thermal stability and critical current density by providing an additional torque mechanism that assists in switching.
Solution Approach 2:
The patent changes the mechanism of magnetization reversal from direct spin transfer torque to spin-orbit spin torque induced by the conductive line. This parameter change in the physical mechanism allows independent optimization of thermal stability (through magnetic anisotropy) and switching efficiency (through spin-orbit coupling in the conductive line), resolving the contradiction.
2Ease of operation
If external magnetic fields are used to control magnetization of the free magnetic layer, then magnetization control is achieved, but device complexity and power loss increase
Solution Approach 1:
The patent extracts and eliminates the external magnetic field component from the system by replacing it with a conductive line that generates the necessary magnetic effects internally through spin-orbit interaction. This removal of the external field requirement simplifies the device structure and reduces power consumption while maintaining magnetization control capability.
Solution Approach 2:
The conductive line with spin-orbit interaction serves the dual function of current conduction and magnetization control, making the system self-sufficient. The conductive line generates spin-orbit spin torque internally to control magnetization without requiring external magnetic fields, achieving self-service operation that reduces device complexity.
3Productivity
If the size of the magnetic junction unit cell is decreased to increase integration density, then integration density is improved, but superparamagnetic limit is reached causing unintended erase of written magnetic information
Solution Approach 1:
The conductive line acts as an intermediary that provides enhanced spin-orbit spin torque to overcome the reduced magnetic anisotropy energy in smaller cells. This intermediary mechanism compensates for the superparamagnetic effects that occur when cell size is reduced, allowing high integration density to be achieved while maintaining data retention reliability.
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 a highly integrated magnetic memory device with reduced power consumption and increased integration density, achieving both low critical current density and high thermal stability while eliminating the need for external magnetic fields.
Implementation Method 1
uses a conductive line with an antiferromagnetic and ferromagnetic layer to induce magnetization reversal through spin-orbit spin torque
Implementation Method 2
a magnetization direction of the free magnetic layer may be reversed or changed by using the spin transfer torque
Implementation Method 3
Electric resistance of the MTJ structure is changed depending on relative orientation between the magnetization directions of the first and second ferromagnetic layers. This is called a tunneling magnetoresistance effect
Data Source
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AI summary
A magnetic memory device may include tunnel junction unit cells, each including a pinned magnetic layer, an insulating layer, and a free magnetic layer which are sequentially stacked, a conductive line structure configured to supply an in-plane current to the unit cells and to include an antiferromagnetic layer, which is provided adjacent to the free magnetic layer, and a ferromagnetic layer, which is provided adjacent to the antiferromagnetic layer and has an in-plane magnetic anisotropy, and a voltage applying unit configured to independently apply a selection voltage to each of the tunnel junction unit cells. Each of the tunnel junction unit cells may have a magnetization direction that is selectively changed by the in-plane current and the selection voltage.