Magnetic Exchange Coupled MTJ Free Layer for Low Switching Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing spin transfer torque magnetic tunnel junction (STT-MRAM) devices face a trade-off between fast switching currents, which require high currents for minimal pulse widths, and data retention, where low moment free layers provide low activation energy, leading to poor retention and high error rates.
Innovation Solution
The implementation of a magnetic exchange coupled composite free layer with a low moment region and a high energy barrier region, separated by a nonmagnetic spacer, allows for efficient switching with reduced overdrive current while maintaining high data retention through magnetic exchange coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a low moment free layer is used to reduce switching current, then switching current is reduced, but activation energy becomes low leading to poor data retention
Solution Approach 1:
The free layer is divided into two separate magnetic layers (first free layer and second free layer) with different magnetic moment characteristics. The first free layer has low magnetic moment to reduce switching current, while the second free layer has high magnetic moment to provide high activation energy for data retention. This segmentation allows each layer to fulfill its specific function independently.
Solution Approach 2:
Different regions of the free layer structure are assigned different magnetic moment properties. The first free layer region is designed with low magnetic moment density, while the second free layer region is designed with high magnetic moment density. This local differentiation enables the structure to simultaneously achieve low switching current and high data retention.
2Reliability
If a high moment free layer is used to increase activation energy, then data retention is improved, but switching current increases
Solution Approach 1:
The free layer is divided into two separate magnetic layers (first free layer and second free layer) with different magnetic moment characteristics. The first free layer has low magnetic moment to reduce switching current, while the second free layer has high magnetic moment to provide high activation energy for data retention. This segmentation allows each layer to fulfill its specific function independently.
Solution Approach 2:
Different regions of the free layer structure are assigned different magnetic moment properties. The first free layer region is designed with low magnetic moment density, while the second free layer region is designed with high magnetic moment density. This local differentiation enables the structure to simultaneously achieve low switching current and high data retention.
3Use of energy by moving object
If magnetic exchange coupling is increased to improve switching efficiency, then switching current is reduced, but data retention may be compromised
Solution Approach 1:
A nonmagnetic spacer layer is introduced as an intermediary between the first and second free layers. This spacer layer provides controlled magnetic exchange coupling that enables efficient switching while maintaining the distinct magnetic moment properties of each layer. The spacer acts as a mediator that transmits spin torque from the low moment layer to the high moment layer without compromising the high activation energy provided by the second layer.
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 minimizes switching current while ensuring high data retention by optimizing the magnetic exchange coupling strength and layer thicknesses, achieving efficient switching and error rate performance.
Implementation Method 1
STT is a phenomenon that can be leveraged in MTJ-based storage elements to assist in switching the storage element from one storage state (e.g., '0' or '1') to another storage state (e.g., '1' or '0'). For example, STT-MRAM 100 shown in FIG. 1 uses electrons that have been spin-polarized to switch the magnetic state (i.e., the magnetization direction 110) of a free layer 108 of MTJ 102.
Implementation Method 2
The MTJ 102 is configured to include a reference/fixed magnetic layer 104, a thin dielectric tunnel barrier 106 and a free magnetic layer 108. The MTJ 102 has a low resistance when the magnetization direction 110 of its free layer 108 is parallel to the magnetization direction 112 of its fixed layer 104.
Implementation Method 3
The first spacer material is between the first region and the second region, and the first spacer material is configured to provide magnetic exchange coupling between the first region and the second region. The implementation of a magnetic exchange coupled composite free layer with a low moment region and a high energy barrier region, separated by a nonmagnetic spacer, allows for efficient switching with reduced overdrive current while maintaining high data retention through magnetic exchange coupling.
Data Source
AI summary
Embodiments of the invention are directed to a magnetic tunnel junction (MTJ) storage element that includes a reference layer, a tunnel barrier and a free layer on an opposite side of the tunnel barrier layer from the reference layer. The reference layer has a fixed magnetization direction. The free layer includes a first region, a second region and a third region. The third region is formed from a third material that is configured to magnetically couple the first region and the second region. The first region is formed from a first material having a first predetermined magnetic moment, and the second region is formed from a second material having a second predetermined magnetic moment. The first predetermined magnetic moment is lower that the second predetermined magnetic moment.