Variable Resistance Memory Free Layer Composition

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Solution Overview

Problem

Existing semiconductor memory devices face challenges in achieving high TMR and low magnetization reversal current while maintaining perpendicular magnetic properties, as increasing the thickness of the free layer to enhance these characteristics can exceed limits that compromise the magnetic properties.

Innovation Solution

The implementation of a variable resistance element with a free layer having a variable magnetization direction, a pinned layer with a fixed magnetization direction, and a tunnel barrier layer, where the free layer includes a CoFeB alloy and additional elements like Cd, Ni, Sn, Sb, or Pd to reduce saturation magnetization and maintain interface magnetic anisotropy, allowing for increased thickness without compromising perpendicular magnetic properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the thickness of the free layer is increased to enhance TMR and reduce magnetization reversal current, then the magnetization reversal current decreases and TMR improves, but the perpendicular magnetic properties are compromised

Engineering Contradiction:

Improvemagnetization reversal currentVSAvoidperpendicular magnetic properties

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent applies local quality by creating a non-uniform composition within the free layer, where elements like Co, Fe, and B are distributed with varying concentrations at different positions (interface vs. bulk). This allows the interface region to maintain perpendicular magnetic anisotropy while the bulk region contributes to lower saturation magnetization, enabling thicker layers without losing magnetic properties.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent uses composite materials by combining multiple ferromagnetic elements (Co, Fe, B) in specific ratios within the free layer. This composite structure enables simultaneous achievement of perpendicular magnetic anisotropy (through interface effects) and reduced saturation magnetization (through bulk composition), resolving the contradiction between layer thickness and magnetic property stability.

Inventive Principle:

Principle #40Composite materials

2Reliability

If the thickness of the free layer is increased to improve TMR ratio, then the TMR ratio increases, but the device complexity increases due to composition control requirements

Engineering Contradiction:

ImproveTMR ratioVSAvoidcomposition control

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies parameter changes by optimizing the thickness and composition ratios of the free layer within specific ranges (e.g., Co:Fe:B atomic ratios and thickness values). By establishing quantitative parameter windows, the patent simplifies the composition control process while maintaining high TMR ratios, transforming a complex qualitative control problem into a more manageable quantitative optimization task.

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 configuration improves the characteristics of the variable resistance element by enhancing TMR and reducing magnetization reversal current while maintaining the necessary magnetic properties, enabling efficient data storage in semiconductor memory devices.

Implementation Method 1

a variable resistance element exhibiting different resistance states for storing data

Methodology Applied

Scientific EffectTunnel magnetoresistance (TMR): Magnetoresistance

Implementation Method 2

a first free layer adjacent to the tunnel barrier layer and having a perpendicular magnetic anisotropy at an interface with the tunnel barrier layer

Methodology Applied

Scientific EffectPerpendicular magnetic anisotropy (PMA): Anisotropy

Implementation Method 3

a second free layer spaced apart from the tunnel barrier layer by the first free layer and having a saturation magnetization lower than a saturation magnetization of the first free layer

Methodology Applied

Scientific EffectMagnetization reduction through alloying: Ferromagnetism

Data Source

PatentUS10367137B2Electronic device including a semiconductor memory having a variable resistance element including two free layers

Publication Date: 2019.07.30 SK HYNIX INC

AI summary

Disclosed are an electronic device comprising a semiconductor memory. The semiconductor memory includes a variable resistance element including a free layer having a variable magnetization direction; a pinned layer having a fixed magnetization direction; and a tunnel barrier layer interposed between the free layer and the pinned layer, wherein the free layer includes: a first free layer adjacent to the tunnel barrier layer and having a perpendicular magnetic anisotropy at an interface with the tunnel barrier layer; and a second free layer spaced apart from the tunnel barrier layer by the first free layer and having a saturation magnetization lower than a saturation magnetization of the first free layer.