MRAM Oxygen Absorption Cap Layer for MTJ Stability

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Solution Overview

Problem

High temperature processes during the back-end-of-line fabrication of MRAM devices cause oxygen diffusion into the free layer, leading to degradation of magnetic performance and increased resistive area and reduced magnetoresistance percentage in magnetic tunnel junction cells.

Innovation Solution

Incorporating an oxygen absorption layer between the free layer and the oxygen-based cap layer, which absorbs oxygen and transforms into a conductive oxide, reducing oxygen diffusion and maintaining low resistive area and high magnetoresistance percentage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an oxygen-based cap layer is used during BEOL fabrication, then the structural integrity and protection of the MTJ cell is improved, but oxygen diffusion to the free layer occurs causing degradation of magnetic performance

Engineering Contradiction:

Improvestructural integrityVSAvoidoxygen diffusion

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A metal layer is introduced as an intermediary between the free layer and the oxygen-based cap layer. This metal layer acts as an oxygen sink that preferentially absorbs oxygen during high temperature BEOL processes, preventing oxygen from reaching and oxidizing the free layer. The metal layer serves as a mediator that protects the free layer while allowing the oxygen-based cap layer to remain in place for structural protection.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention converts the harmful oxygen diffusion into a beneficial process by allowing the metal layer to intentionally absorb oxygen and transform into a conductive oxide. This controlled oxidation of the metal layer prevents uncontrolled oxidation of the free layer, turning the harmful oxygen into a protective mechanism.

Inventive Principle:

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

2Productivity

If high temperature processes are performed during BEOL fabrication, then the manufacturing completeness is improved, but oxygen diffusion and magnetic performance degradation occur

Engineering Contradiction:

Improvemanufacturing completenessVSAvoidmagnetic performance

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The metal layer is deposited beforehand to perform preliminary oxygen absorption before the high temperature BEOL processes begin. This preliminary action ensures that when high temperature processing occurs, the oxygen sink is already in place to prevent oxygen diffusion to the free layer, allowing complete manufacturing without compromising magnetic performance.

Inventive Principle:

Principle #10Preliminary action

3Ease of manufacture

If the free layer is exposed to oxygen during fabrication, then the fabrication process simplicity is maintained, but the resistive area increases and magnetoresistance percentage decreases

Engineering Contradiction:

Improvefabrication process simplicityVSAvoidmagnetoresistance percentage

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The metal layer serves as a simple intermediary that can be deposited using standard sputtering techniques. This addition maintains fabrication process simplicity while effectively preventing oxygen exposure to the free layer, thereby preserving magnetoresistance percentage without complicating the overall fabrication process.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 oxygen absorption layer effectively prevents oxygen-induced degradation, maintaining the magnetic performance and reducing switching current density while ensuring interface stability during high temperature processes.

Implementation Method 1

an oxygen absorption layer between the free layer and the oxygen-based cap layer, which absorbs oxygen and transforms into a conductive oxide

Methodology Applied

Scientific EffectOxygen absorption: Absorption (physical)

Implementation Method 2

the diffused oxygen will substantially degrade the magnetic performance of free layer due to the oxidation effect from oxide cap layer

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 3

the metal layer may be transformed into a conductive oxide

Methodology Applied

Scientific EffectPhase transformation: Phase Change

Data Source

PatentUS8878318B2Structure and method for a MRAM device with an oxygen absorbing cap layer

Publication Date: 2014.11.04 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

MTJ stack structures for an MRAM device include an MTJ stack having a pinned ferromagnetic layer over a pinning layer, a tunneling barrier layer over the pinned ferromagnetic layer, a free ferromagnetic layer over the tunneling barrier layer, a conductive oxide layer over the free ferromagnetic layer, and an oxygen-based cap layer over the conductive oxide layer.