Mo Seed Layer for Perpendicular Magnetic Anisotropy Stability

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Solution Overview

Problem

Current magnetic devices with perpendicular magnetic anisotropy (PMA) face challenges in maintaining PMA properties as the magnetic layer thickness increases, as the PMA originating from a single interface is overwhelmed by demagnetizing fields, leading to instability and loss of thermal stability.

Innovation Solution

The use of a Mo transition layer between BCC and FCC crystal symmetry materials, such as in the Co/Ni multilayer system, allows PMA to originate from both the MgO/Fe interface and the top PMA layer, promoting stable perpendicular anisotropy and magnetic coupling, while avoiding diffusion issues with materials like Cr that deteriorate the MgO tunneling barrier.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If the magnetic layer thickness is increased to improve storage capacity, then the volume of magnetic material increases, but the perpendicular magnetic anisotropy is lost due to demagnetizing fields overwhelming the interface-originated PMA

Engineering Contradiction:

Improvemagnetic layer volumeVSAvoidperpendicular magnetic anisotropy stability

Core Design Contradiction:

Volume of moving objectVSStability of the object's composition

Solution Approach 1:

The magnetic layer is segmented into multiple thin sub-layers separated by non-magnetic spacer layers. This segmentation allows each sub-layer to maintain strong perpendicular magnetic anisotropy through interface effects, while the cumulative thickness provides sufficient storage capacity. The spacer layers prevent demagnetizing fields from overwhelming the PMA by breaking up the continuous magnetic material into discrete segments.

Inventive Principle:

Principle #1Segmentation

2Device complexity

If a single interface is used to generate PMA to simplify the structure, then the device complexity is reduced, but the thermal stability deteriorates when the magnetic layer becomes thicker

Engineering Contradiction:

Improveinterface structure complexityVSAvoidthermal stability of magnetization direction

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

Multiple interfaces are merged into a cooperative system where each interface contributes to the overall perpendicular magnetic anisotropy. The cumulative effect of multiple interfaces provides enhanced thermal stability compared to a single interface, while the regular periodic structure maintains relatively simple device fabrication processes.

Inventive Principle:

Principle #5Merging (Combining)

3Shape

If Cr is used as a transition layer between BCC and FCC crystal structures to promote smooth growth, then the crystal orientation is improved, but the MgO tunneling barrier deteriorates due to diffusion issues

Engineering Contradiction:

Improvecrystal orientation smoothnessVSAvoidMgO tunneling barrier quality

Core Design Contradiction:

ShapeVSReliability

Solution Approach 1:

An alternative transition layer material is introduced as an intermediary between the BCC and FCC crystal structures. This intermediary material promotes smooth crystal orientation transitions without causing diffusion damage to the MgO tunneling barrier, thereby maintaining both structural quality and barrier integrity.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The harmful diffusion effect of Cr into the MgO barrier is converted into a benefit by selecting a different transition layer material that achieves the same crystal structure transition function without the harmful diffusion side effect. The harmful property of Cr (diffusion into MgO) is avoided while maintaining the beneficial function (crystal structure transition).

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 maintains stable perpendicular magnetic anisotropy and thermal stability across thicker layers, enhancing magnetic coupling and tunnel magnetoresistance, as demonstrated by annealed multilayer configurations measured in a polar Kerr magnetometer and magnetoresistance curves.

Implementation Method 1

A seed layer (as in Fig's. 1(a) and (c)), on the other hand, is defined as a layer that operates as a template to produce a certain crystal-oriented growth of the following deposited layer

Methodology Applied

Scientific EffectTemplate effect for crystal growth: Epitaxy

Implementation Method 2

The PMA in this system arises from electronic band matching at the FCC (face centered cubic) (111)-oriented Co/Ni interface

Methodology Applied

Scientific EffectElectronic band matching:

Implementation Method 3

annealed multilayer configurations measured in a polar Kerr magnetometer

Methodology Applied

Scientific EffectMagneto-optic Kerr effect: Magneto-Optic Kerr Effect

Data Source

PatentEP2987189B1Seed layer for perpendicular magnetic anisotropy (PMA) thin film

Publication Date: 2021.09.29 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

Figure 1(a)~2
Figure 3~4
Figure 5a~5b

AI summary

A magnetic thin film deposition having PMA (perpendicular magnetic anisotropy) is a multilayered fabrication of materials having differing crystal symmetries that smoothly transition by use of a seed layer that promotes symmetry matching. An interface between layers in the deposition, such as an interface between a layer of MgO and an Fe-containing ferromagnetic layer, is a source of perpendicular magnetic anisotropy which then propagates throughout the remainder of the deposition by means of the symmetry matching seed layer.