SAF Device Fabrication Using Refractory Spacer Layers

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Solution Overview

Problem

Magnetic random access memory (MRAM) devices with synthetic antiferromagnetic (SAF) structures face challenges in withstanding high-temperature annealing required for semiconductor applications, as current SAF structures either fail to maintain strong coupling at 400°C or have excessively high current densities and low activation energies.

Innovation Solution

The method involves fabricating SAF devices with a non-exchange-coupled spacer layer using refractory materials like Ta, TaN, or W, and cobalt iron boron layers, which are deposited in a specific sequence to form a storage layer that combines high anneal temperature stability with low switching currents and appropriate activation energy, allowing for improved thermal stability and switching performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional Ru-coupled SAF structures are used, then strong coupling is achieved, but the structure fails to withstand 400°C annealing and processing

Engineering Contradiction:

Improvethermal stabilityVSAvoidSAF coupling strength

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent changes the spacer material from Ru to refractory materials (Ta, TaN, W) and modifies the CoFeB layer thickness parameters to achieve both thermal stability at 400°C and maintained SAF coupling strength, resolving the contradiction between thermal withstand capability and coupling strength

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite SAF structure with alternating layers of CoFeB and refractory materials (Ta/TaN/W), forming a multi-layer composite that combines the magnetic properties of CoFeB with the thermal stability of refractory materials, enabling both high-temperature withstand capability and strong coupling

Inventive Principle:

Principle #40Composite materials

2Strength

If SAF structures with strong coupling are fabricated, then coupling strength is improved, but current density becomes excessively large for practical employment

Engineering Contradiction:

ImproveSAF coupling strengthVSAvoidswitching current density

Core Design Contradiction:

StrengthVSUse of energy by moving object

Solution Approach 1:

The patent optimizes the thickness parameters of CoFeB layers and spacer layers to achieve the right balance between coupling strength and switching current density, ensuring practical employability while maintaining strong SAF coupling

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies different material properties locally within the SAF structure, using CoFeB for magnetic coupling and refractory materials for thermal stability, with optimized local thicknesses to achieve both strong coupling and low switching current density

Inventive Principle:

Principle #3Local quality

3Temperature

If SAF structures are designed for high-temperature processing, then thermal stability is improved, but activation energy remains too low (62 kT) for sufficient data retention

Engineering Contradiction:

Improveannealing temperature withstandVSAvoiddata retention

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The patent creates a composite SAF structure where refractory materials (Ta, TaN, W) provide thermal stability for 400°C processing while CoFeB layers provide magnetic properties, achieving both high-temperature withstand capability and sufficient activation energy for data retention

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent adjusts the thickness parameters of CoFeB and spacer layers to optimize both thermal stability and activation energy simultaneously, achieving 400°C processing capability with activation energy ≥80 kT for sufficient data retention

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

This approach enables MRAM devices to maintain thermal stability at high temperatures while reducing switching currents, achieving the necessary activation energy for long-term data retention and improved performance compared to conventional Ru-coupled SAF structures.

Implementation Method 1

depositing a reference layer on a first tantalum layer and including depositing a first cobalt iron boron layer, depositing a second cobalt iron boron layer on the first cobalt iron boron layer, depositing a second Ta layer on the second cobalt iron boron layer

Methodology Applied

Scientific EffectPhysical vapor deposition: Physical Vapour Deposition

Data Source

PatentUS9015927B2Method for fabricating synthetic antiferromagnetic (SAF) device

Publication Date: 2015.04.28 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A method for fabricating a synthetic antiferromagnetic device, includes depositing a reference layer on a first tantalum layer and including depositing a first cobalt iron boron layer, depositing a second cobalt iron boron layer on the first cobalt iron boron layer, depositing a second Ta layer on the second cobalt iron boron layer, depositing a magnesium oxide spacer layer on the reference layer and depositing a cap layer on the magnesium oxide spacer layer.