Strain Engineering Perpendicular Magnetic Tunnel Junctions

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Solution Overview

Problem

Traditional spin torque transfer magnetoresistive random access memory (STT-MRAM) integration faces challenges due to large write switching current and voltage requirements, limiting cell size and density, and perpendicular magnetic tunnel junctions (pMTJs) need improved thermal stability and coercivity for enhanced performance.

Innovation Solution

The approach involves strain engineering of pMTJs through a recess etch and refill process, using a stress-engineered material to apply lateral strain on the switching layer, which controls the coercivity of the magnetic free layer and reduces sensitivity to hardmask stress conditions, allowing for independent modulation of thermal stability and critical current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional hardmask material is used for pMTJ fabrication, then etch masking properties are maintained, but thermal stability and coercivity are insufficient

Engineering Contradiction:

Improvethermal stabilityVSAvoidhardmask optimization complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent separates the hardmask layer into two distinct functional layers: a bottom hardmask layer that provides etch masking protection, and a top stress engineering layer that provides thermal stability and coercivity control through strain engineering. This segmentation allows each layer to be optimized independently for its specific function, resolving the contradiction between maintaining etch masking properties while improving thermal stability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The top stress engineering layer serves multiple functions: it provides thermal stability, controls coercivity through strain engineering, and can be removed after serving its purpose. This multi-functionality allows a single layer to address multiple performance requirements, reducing the need to optimize hardmask material for conflicting properties simultaneously.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If thin free magnetic layer is used to achieve perpendicular magnetic anisotropy, then PMA is established, but coercive field Hc becomes low

Engineering Contradiction:

ImprovepMTJ stabilityVSAvoidcoercive field Hc

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent changes the physical state of the free magnetic layer by introducing mechanical strain through the top stress engineering layer. This strain modifies the magnetic anisotropy energy and increases the coercive field Hc without requiring the free magnetic layer to be thicker, thereby maintaining perpendicular magnetic anisotropy while improving pMTJ stability.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If stress-engineered material is applied to pMTJ element, then lateral strain controls coercivity, but sensitivity to hardmask stress conditions increases

Engineering Contradiction:

Improvecoercivity controlVSAvoidstress condition sensitivity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

By separating the hardmask into bottom and top layers with distinct functions, the patent isolates the stress engineering function to the top layer. This allows precise control of coercivity through the top layer's stress properties without being affected by variations in the bottom layer's stress, thereby reducing sensitivity to overall hardmask stress conditions while maintaining manufacturing precision for coercivity control.

Inventive Principle:

Principle #1Segmentation

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 method enhances the flexibility and performance of pMTJs by reducing the need to optimize both stress and etch masking properties of the hardmask material, leading to improved thermal stability and coercivity, enabling higher density and efficient memory arrays.

Implementation Method 1

A lateral strain-inducing material layer 114 is disposed on the pMTJ element 102

Methodology Applied

Scientific EffectStrain engineering: Elasticity

Implementation Method 2

strain engineering of perpendicular magnetic tunnel junctions (pMTJs)... apply lateral strain on the switching layer, which controls the coercivity of the magnetic free layer

Methodology Applied

Scientific EffectMagnetostriction: Magnetostriction

Implementation Method 3

Magnetic tunnel junction (MTJ) devices... utilize a phenomenon known as tunneling magnetoresistance (TMR)... it is more likely that electrons will tunnel through the tunnel material layer when magnetizations of the two magnetic layers are in a parallel orientation

Methodology Applied

Scientific EffectTunneling magnetoresistance: Magnetoresistance

Implementation Method 4

current-induced magnetization switching may be used to set the bit states. Polarization states of a first (free) ferromagnetic layer can be switched relative to a fixed polarization of the second (fixed) ferromagnetic layer via the spin transfer torque phenomenon

Methodology Applied

Scientific EffectSpin transfer torque:

Data Source

PatentUS10868233B2Approaches for strain engineering of perpendicular magnetic tunnel junctions (pMTJs) and the resulting structures

Publication Date: 2020.12.15 TAHOE RES LTD

AI summary

Strain engineering of perpendicular magnetic tunnel junctions (PMTJs) is described. In an example, a memory structure includes a perpendicular magnetic tunnel junction (pMTJ) element disposed above a substrate. A lateral strain-inducing material layer is disposed on the pMTJ element. An inter-layer dielectric (ILD) layer disposed laterally adjacent to both the pMTJ element and the lateral strain-inducing material layer.