MTJ Composite Capping Layer for Stable MRAM Anisotropy

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Solution Overview

Problem

The existing magnetic tunneling junction (MTJ) elements in MRAM devices face issues due to the hexagonal close packed (hcp) crystalline structure of ruthenium top electrodes, which cause magneto-resistance drop and increased coercivity distribution in the free layer, and the use of amorphous layers like Ta or Ti leads to reduction of perpendicular anisotropy field, affecting data retention.

Innovation Solution

A composite capping layer is introduced between the top electrode and the free layer, comprising a diffusion-stop layer, a light-element sink layer, and an amorphous layer, which forms direct interfaces with both the free layer and the top electrode, preventing element diffusion and maintaining high perpendicular anisotropy field and tunneling magneto-resistance ratio.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a ruthenium top electrode with hcp crystalline structure is used, then electrical connection is achieved, but magneto-resistance drops and coercivity distribution increases

Engineering Contradiction:

Improvemagneto-resistance ratioVSAvoidhcp crystalline structure adverse effects

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A composite capping layer comprising a diffusion-stop layer and an amorphous layer is introduced as an intermediary between the Ru top electrode and the free layer. The diffusion-stop layer (e.g., Ta, Ti, W, Mo) blocks crystalline Ru from directly contacting the free layer, preventing hcp structure-induced MR drop and coercivity distribution. The amorphous layer (e.g., Ta, Ti, Al, Si, Ge) further isolates the free layer from crystalline influence while allowing electrical connection through the Ru electrode.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If an amorphous layer like Ta or Ti is used as capping layer, then hcp crystalline structure effects are suppressed, but perpendicular anisotropy field reduces

Engineering Contradiction:

Improvehcp crystalline structure adverse effectsVSAvoidperpendicular anisotropy field

Core Design Contradiction:

Object-affected harmful factorsVSStrength

Solution Approach 1:

The capping layer is segmented into two distinct functional layers: a diffusion-stop layer and an amorphous layer. The diffusion-stop layer (Ta, Ti, W, Mo) provides strong diffusion barrier properties to prevent light element migration, preserving perpendicular anisotropy field. The amorphous layer (Ta, Ti, Al, Si, Ge) suppresses hcp crystalline structure effects from the Ru electrode. This segmentation allows each layer to optimize its specific function without compromising the other.

Inventive Principle:

Principle #1Segmentation

3Object-affected harmful factors

If Ta or Ti is used as amorphous capping layer, then hcp effects are suppressed, but element diffusion into free layer occurs

Engineering Contradiction:

Improvehcp crystalline structure adverse effectsVSAvoidelement diffusion

Core Design Contradiction:

Object-affected harmful factorsVSLoss of substance

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The composite capping layer combines materials with complementary properties: the diffusion-stop layer uses materials with high diffusion barrier characteristics (Ta, Ti, W, Mo), while the amorphous layer uses materials that effectively suppress crystalline structure effects (Ta, Ti, Al, Si, Ge). This composite structure achieves superior overall performance compared to single-material capping layers.

Inventive Principle:

Principle #40Composite materials

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 composite capping layer effectively blocks element diffusion, maintains high perpendicular anisotropy and tunneling magneto-resistance ratio, and suppresses the hcp crystalline structure's adverse effects on the free layer, enhancing the overall performance of MRAM devices.

Implementation Method 1

a diffusion-stop layer on the free layer

Methodology Applied

Scientific EffectDiffusion barrier: Diffusion Barrier

Implementation Method 2

a light-element sink layer on the diffusion-stop layer

Methodology Applied

Scientific EffectAbsorption: Absorption (physical)

Implementation Method 3

A MTJ element may be based on a tunneling magneto-resistance (TMR) effect wherein a stack of layers has a configuration in which two ferromagnetic layers are separated by a thin non-magnetic dielectric layer. If the non-magnetic dielectric layer is thin enough (typically a few nanometers), electrons can tunnel from one ferromagnet into the other.

Methodology Applied

Scientific EffectTunneling magneto-resistance: Magnetoresistance

Data Source

PatentUS12108684B2Magnetic tunneling junction element with a composite capping layer and magnetoresistive random access memory device using the same

Publication Date: 2024.10.01 HEFECHIP CORP LTD

AI summary

A magnetic tunneling junction (MTJ) element includes a reference layer, a tunnel barrier layer on the reference layer, a free layer on the tunnel barrier layer, and a composite capping layer on the free layer. The composite capping layer comprises a diffusion-stop layer on the free layer, a light-element sink layer on the diffusion-stop layer, and an amorphous layer on the light-element sink layer.