Ultrathin Reference Layer for STT-MRAM Stray Field Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional spin transfer torque magnetic random access memory (STT-MRAM) devices face challenges in minimizing stray fields on the magnetic free layer while maintaining a thin total thickness of the magnetic tunnel junction (MTJ) memory element, which affects switching currents and stability.
Innovation Solution
The STT-MRAM device incorporates a dual ultrathin reference layer structure with an anti-ferromagnetic coupling layer and a magnetic fixed layer to minimize stray fields, comprising a first magnetic reference layer made of CoFeB, a second magnetic reference layer made of CoFe, and a magnetic fixed layer with opposite magnetization direction, along with a non-magnetic tuning layer and magnetic compensation layer to reduce overall thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a thick multilayer reference layer structure is used to enhance perpendicular anisotropy, then the magnetic moment increases, but the stray field on the magnetic free layer increases and stability decreases
Solution Approach 1:
The reference layer is divided into multiple thin magnetic layers (e.g., CoFeB, CoFe) separated by non-magnetic spacer layers. This segmentation allows each thin layer to contribute to perpendicular anisotropy while the overall structure generates reduced stray field compared to a single thick layer, resolving the contradiction between enhancing anisotropy and minimizing harmful stray fields.
Solution Approach 2:
The patent employs composite multilayer structures combining magnetic layers (CoFeB, CoFe) with non-magnetic spacer layers. This composite approach enables the reference layer to maintain strong perpendicular anisotropy through the combination of materials with different magnetic and structural properties, while the non-magnetic spacers reduce the overall magnetic moment and stray field generation.
2Object-generated harmful factors
If magnetic layers with opposite magnetization direction are added to cancel stray field, then the stray field is reduced, but the total thickness of magnetic layers increases
Solution Approach 1:
Instead of adding thick compensating layers, the patent segments the reference layer into multiple thin layers with alternating or opposite magnetization directions. This segmentation achieves stray field cancellation through the distributed structure of thin layers, maintaining a compact total thickness while reducing harmful magnetic fields.
Solution Approach 2:
The patent applies local quality by creating regions with different magnetization directions within the reference layer structure. Specific thin layers are engineered with opposite magnetization to locally cancel stray fields, while maintaining the overall perpendicular anisotropy of the reference layer, thus reducing total thickness compared to uniform thick compensating structures.
3Manufacturing precision
If the total thickness of MTJ memory element is minimized, then etching process margin improves, but stray field cancellation capability is reduced
Solution Approach 1:
The reference layer is segmented into multiple ultrathin layers (each a few nanometers thick) separated by non-magnetic spacers. This segmentation achieves effective stray field cancellation within a compact total thickness, thereby improving etching process margin while maintaining the ability to reduce harmful magnetic fields through the distributed alternating magnetization structure.
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 stray fields and reduces the total thickness of the MTJ memory element, enhancing switching current stability and etching process margins while maintaining perpendicular anisotropy.
Implementation Method 1
an anti-ferromagnetic coupling layer formed adjacent to the second magnetic reference layer opposite the first magnetic reference layer
Implementation Method 2
electrons polarized by the magnetic reference layer 50 can tunnel through the insulating tunnel junction layer 54, thereby decreasing the electrical resistivity of the perpendicular MTJ 56
Implementation Method 3
The magnetic reference layer 50 and free layer 52 have a fixed magnetization direction 58 and a variable magnetization direction 60, respectively, which are substantially perpendicular to the layer planes thereof
Implementation Method 4
Upon application of an appropriate current through the perpendicular MTJ 56, the magnetization direction 60 of the magnetic free layer 52 can be switched between two directions: parallel and anti-parallel with respect to the magnetization direction 58 of the magnetic reference layer 50
Data Source
AI summary
The present invention is directed to a magnetic memory element including a magnetic free layer and a first magnetic reference layer with an insulating tunnel junction layer interposed therebetween; a second magnetic reference layer made of a material comprising cobalt and formed adjacent to the first magnetic reference layer opposite the insulating tunnel junction layer; an iridium layer formed adjacent to the second magnetic reference layer opposite the first magnetic reference layer; and a magnetic fixed layer formed adjacent to the iridium layer. The magnetic free layer has a variable magnetization direction substantially perpendicular to the layer plane thereof. The first and second magnetic reference layers have a first fixed magnetization direction substantially perpendicular to the layer planes thereof. The magnetic fixed layer has a second fixed magnetization direction that is substantially perpendicular to the layer plane thereof and is substantially opposite to the first fixed magnetization direction.