MgO Capping Layer Tuning for Low-RA PMA Magnetic Devices

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Solution Overview

Problem

Magnetic devices with out-of-plane magnetic anisotropy face challenges in reducing the resistance-area product (RA) of individual layers without compromising magnetoresistance, coercivity field (Hc), anisotropy field (Hk), and thermal stability, especially in high-density PMA spin-torque transfer MRAM applications.

Innovation Solution

A thin insulating magnesium oxide (MgO) capping layer is formed through the deposition and oxidation of a metallic magnesium layer, with plasma treatment applied before or after oxidation to reduce the oxygen necessary for oxidation, thereby reducing the RA while preserving perpendicular anisotropy, and improving the smoothness and uniformity of the interface.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a thin insulating magnesium oxide capping layer is formed to provide out-of-plane anisotropy, then the anisotropy field (Hk) is improved, but the resistance-area product (RA) increases

Engineering Contradiction:

Improveanisotropy field (Hk)VSAvoidresistance-area product (RA)

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The patent applies plasma treatment to modify the oxidation state of the magnesium oxide capping layer, changing its electrical resistance parameters while preserving the perpendicular magnetic anisotropy. This parameter change allows reduction of the RA product without sacrificing Hk, as the plasma treatment creates a less oxidized interface that has lower resistance but maintains the anisotropy-inducing properties.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention creates a gradient in oxidation state within the magnesium oxide layer, with the interface region having different properties than the bulk. The plasma treatment specifically modifies the local quality at the MgO/ferromagnetic layer interface, making it less oxidized and lower resistance, while the upper portions of the MgO layer retain sufficient oxidation to provide the necessary perpendicular anisotropy.

Inventive Principle:

Principle #3Local quality

2Strength

If the oxidation state of the magnesium oxide interface is increased to enhance perpendicular anisotropy, then the anisotropy field (Hk) is improved, but the resistance-area product (RA) increases

Engineering Contradiction:

Improveperpendicular anisotropyVSAvoidresistance-area product (RA)

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The patent uses plasma treatment to precisely control and optimize the oxidation state parameter of the magnesium oxide layer. By adjusting plasma treatment conditions (power, time, gas composition), the invention finds an optimal oxidation level that provides sufficient perpendicular anisotropy while minimizing electrical resistance, thereby reducing the RA product.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention applies partial oxidation to the magnesium layer rather than complete oxidation. The plasma treatment creates a controlled, partial oxidation state that is sufficient to generate perpendicular anisotropy but not so extensive as to create high resistance. This partial action approach optimizes the trade-off between anisotropy and resistance.

Inventive Principle:

Principle #16Partial or excessive action

3Strength

If a thick magnesium oxide layer is used to ensure sufficient perpendicular anisotropy, then the anisotropy field (Hk) is improved, but the resistance-area product (RA) increases

Engineering Contradiction:

Improveperpendicular anisotropyVSAvoidresistance-area product (RA)

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The plasma treatment changes the electrical parameters of the magnesium oxide layer by reducing its oxidation state and modifying its stoichiometry. This parameter change decreases the electrical resistance of the MgO layer, allowing for lower RA product even when sufficient thickness is maintained to provide the required perpendicular anisotropy.

Inventive Principle:

Principle #35Parameter changes

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

The method effectively reduces the RA product, enhances thermal stability, and maintains or improves Hc and Hk, making it suitable for high-density PMA Spin-Torque MRAM and other spintronic devices by ensuring compatibility with design and fabrication requirements.

Implementation Method 1

plasma treatment applied before or after oxidation to reduce the oxygen necessary for oxidation

Methodology Applied

Scientific EffectPlasma: Plasma

Implementation Method 2

formed through the deposition and oxidation of a metallic magnesium layer

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 3

formed through the deposition and oxidation of a metallic magnesium layer

Methodology Applied

Scientific EffectDeposition (physical): Deposition (physical)

Data Source

PatentUS11930716B2Reduction of capping layer resistance area product for magnetic device applications

Publication Date: 2024.03.12 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A ferromagnetic layer is capped with a metallic oxide (or nitride) layer that provides a perpendicular-to-plane magnetic anisotropy to the layer. The surface of the ferromagnetic layer is treated with a plasma to prevent diffusion of oxygen (or nitrogen) into the layer interior. An exemplary metallic oxide layer is formed as a layer of metallic Mg that is plasma treated to reduce its grain size and enhance the diffusivity of oxygen into its interior. Then the plasma treated Mg layer is naturally oxidized and, optionally, is again plasma treated to reduce its thickness and remove the oxygen rich upper surface.