CoFeB Free Layer with Iron Insertion for STT MRAM

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Solution Overview

Problem

Developing STT MRAM devices with magnetic materials that exhibit strong perpendicular magnetic anisotropy (PMA) at low switching currents is challenging, as existing materials do not provide sufficient switching efficiency.

Innovation Solution

The method involves forming a tunnel barrier layer and a free layer with a CoFeB alloy and an iron layer, followed by a sputtering process to create a metal oxide layer, which enhances the PMA and reduces the switching current density, thereby improving switching efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a CoFeB alloy layer is used as the free layer, then the switching current is reduced, but the perpendicular magnetic anisotropy is insufficient

Engineering Contradiction:

Improveswitching currentVSAvoidperpendicular magnetic anisotropy

Core Design Contradiction:

Use of energy by moving objectVSStrength

Solution Approach 1:

The patent combines CoFeB alloy layer with an oxide layer (such as MgO, Al2O3, or SiO2) to create a composite free layer structure. This composite structure leverages the low switching current property of CoFeB while the oxide layer provides the necessary perpendicular magnetic anisotropy, resolving the contradiction between low switching current and sufficient PMA.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent modifies the physical and chemical parameters of the free layer by introducing an oxide layer with specific thickness (1-10 nm) and composition. This parameter change transforms the magnetic properties of the free layer, enabling both low switching current and strong perpendicular magnetic anisotropy to coexist.

Inventive Principle:

Principle #35Parameter changes

2Quantity of substance

If the MTJ size is reduced, then the write current is reduced, but the switching efficiency deteriorates

Engineering Contradiction:

Improvewrite currentVSAvoidswitching efficiency

Core Design Contradiction:

Quantity of substanceVSProductivity

Solution Approach 1:

The patent changes the magnetic anisotropy parameter from in-plane to perpendicular by introducing the oxide layer. This parameter change enables efficient magnetization switching even in small-sized MTJs, maintaining high switching efficiency while using reduced write currents in scaled-down devices.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If a metal oxide layer is formed by sputtering, then the oxide layer thickness control is improved, but the process complexity increases

Engineering Contradiction:

Improveoxide layer thickness controlVSAvoidsputtering process

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent replaces conventional oxidation processes with sputtering deposition to form the oxide layer. This substitution enables precise thickness control through deposition parameter management (such as deposition rate and time) rather than relying on less controllable oxidation processes, accepting the trade-off of increased process complexity for significantly improved manufacturing precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 results in STT MRAM devices with at least 50% higher switching efficiency compared to devices with free layers of CoFeB alone, while maintaining similar energy per bit, and provides improved control over the oxide layer thickness and junction resistance-area product.

Implementation Method 1

performing a sputtering process to form a metal oxide layer on the Fe layer

Methodology Applied

Scientific EffectSputtering: Sputtering

Implementation Method 2

perpendicular magnetic anisotropy (PMA) materials in STT MRAM devices

Methodology Applied

Scientific EffectPerpendicular magnetic anisotropy: Anisotropy

Data Source

PatentUS10347827B2Perpendicular magnetic anisotropy free layers with iron insertion and oxide interfaces for spin transfer torque magnetic random access memory

Publication Date: 2019.07.09 ADEIA SEMICONDUCTOR SOLUTIONS LLC

AI summary

A method of making a spin-torque transfer magnetic random access memory device (STT MRAM) device includes forming a tunnel barrier layer on a reference layer; forming a free layer on the tunnel barrier layer, the free layer comprising a cobalt iron boron (CoFeB) alloy layer and an iron (Fe) layer; and performing a sputtering process to form a metal oxide layer on the Fe layer.