STT-MRAM Base Layer Segmentation for PMA and Thermal Endurance

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Solution Overview

Problem

Conventional techniques for improving perpendicular magnetic anisotropy (PMA) in spin transfer torque magnetic random access memory (STT-MRAM) structures lead to reduced thermal budget and endurance, while also desiring higher tunneling magnetoresistance (TMR) signals and cost-effective fabrication compatible with logic processing.

Innovation Solution

A spin transfer torque magnetic random access memory structure with a perpendicular magnetic orientation, including a base layer with a seed layer and roughness suppression layer, a hard layer, and a magnetic tunnel junction (MTJ) element, fabricated using a method that forms a transistor with a gate between source/drain regions and electrodes, enhancing PMA and thermal endurance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If conventional techniques are used to improve perpendicular magnetic anisotropy (PMA) for the fixed layer, then PMA is improved, but thermal budget and thermal endurance are reduced

Engineering Contradiction:

Improveperpendicular magnetic anisotropy (PMA)VSAvoidthermal endurance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The base layer is segmented into multiple functional sub-layers: a wetting layer (e.g., Ru or Ir) to improve adhesion and reduce roughness, a seed layer (e.g., Cr or Cr-based alloy) to promote crystalline orientation and PMA, and optionally a roughness suppression layer. This segmentation allows each sub-layer to be optimized independently for its specific function, achieving strong PMA without compromising thermal endurance.

Inventive Principle:

Principle #1Segmentation

2Strength

If conventional techniques are used to improve perpendicular magnetic anisotropy (PMA) for the fixed layer, then PMA is improved, but thermal budget is reduced

Engineering Contradiction:

Improveperpendicular magnetic anisotropy (PMA)VSAvoidthermal budget

Core Design Contradiction:

StrengthVSTemperature

Solution Approach 1:

The patent optimizes the thickness parameters of the wetting layer and seed layer to achieve the desired PMA and thermal budget balance. For example, the wetting layer thickness is controlled at 1-5 nm and the seed layer at 3-10 nm. These parameter changes allow the structure to develop strong PMA through interfacial effects while maintaining sufficient thermal budget for subsequent fabrication processes.

Inventive Principle:

Principle #35Parameter changes

3Strength

If conventional techniques are used to improve PMA, then PMA is improved, but tunneling magnetoresistance (TMR) signal is reduced

Engineering Contradiction:

Improveperpendicular magnetic anisotropy (PMA)VSAvoidtunneling magnetoresistance (TMR) signal

Core Design Contradiction:

StrengthVSMeasurement precision

Solution Approach 1:

The wetting layer acts as an intermediary between the bottom electrode and the seed layer, improving the overall interface quality. This intermediary layer promotes better adhesion and reduces roughness, which indirectly enhances the TMR signal by ensuring high-quality interfaces throughout the MTJ stack, while the seed layer directly provides the crystalline orientation needed for strong PMA.

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 solution achieves improved PMA, thermal endurance, and higher TMR signals, while being cost-effective and compatible with CMOS processes, thus addressing the limitations of conventional techniques.

Implementation Method 1

The base layer may include a wetting layer, and a seed layer over the wetting layer

Methodology Applied

Scientific EffectWetting: Wetting

Implementation Method 2

In order to obtain strong perpendicular magnetic anisotropy (PMA) for the fixed layer, a well-ordered crystalline orientation of the fixed layer is required

Methodology Applied

Scientific EffectCrystallisation: Crystallisation

Implementation Method 3

Spin transfer torque (STT) or spin transfer switching, uses spin-aligned ('polarized') electrons to directly apply a torque on the MTJ layers

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 4

A magnetic memory cell or device stores information by changing electrical resistance of a magnetic tunnel junction (MTJ) element

Methodology Applied

Scientific EffectTunneling magnetoresistance: Magnetoresistance

Data Source

PatentUS10516096B2Magnetic random access memory structures, integrated circuits, and methods for fabricating the same

Publication Date: 2019.12.24 GLOBALFOUNDRIES SINGAPORE PTE LTD

AI summary

Spin transfer torque magnetic random access memory structures, integrated circuits, and methods for fabricating integrated circuits are provided. An exemplary spin transfer torque magnetic random access memory structure has a perpendicular magnetic orientation, and includes a bottom electrode and a base layer over the bottom electrode. The base layer includes a seed layer and a roughness suppression layer. The spin transfer torque magnetic random access memory structure further includes a hard layer over the base layer. Also, the spin transfer torque magnetic random access memory structure includes a magnetic tunnel junction (MTJ) element with a perpendicular orientation over the hard layer and a top electrode over the MTJ element.