MRAM Cap Layer Structure for Low-RA Data Retention

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Solution Overview

Problem

Conventional MRAM storage elements face challenges in maintaining data retention and reducing write current due to the need for increased film thickness of the cap layer, which leads to increased Resistance Area (RA), decreased Magnetic Resistance (MR), and higher write voltage, thereby deteriorating device properties.

Innovation Solution

A storage element with a cap layer comprising conductive regions of higher conductivity than the oxide material, distributed within the cap layer to maintain low resistance and good data retention, while allowing for increased film thickness without compromising device properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the film thickness of the cap layer is increased to maintain perpendicular magnetic anisotropy after high-temperature wafer processing, then data retention property is improved, but Resistance Area (RA) increases and Magnetic Resistance (MR) decreases

Engineering Contradiction:

Improvedata retention propertyVSAvoidResistance Area (RA)

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The cap layer is constructed as a composite structure combining an oxide layer (providing perpendicular magnetic anisotropy) with a conductive material layer (providing low resistance). This composite structure simultaneously achieves both data retention and low Resistance Area, resolving the contradiction between maintaining magnetic anisotropy and minimizing resistance.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

Different regions of the cap layer structure are assigned different materials with different properties: the oxide layer provides magnetic anisotropy while the conductive material layer provides low resistance. This local differentiation of material properties allows each layer to optimize for its specific function without compromising the other.

Inventive Principle:

Principle #3Local quality

2Reliability

If the film thickness of the cap layer is increased to maintain perpendicular magnetic anisotropy, then data retention property is improved, but write voltage increases

Engineering Contradiction:

Improvedata retention propertyVSAvoidwrite voltage

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The composite cap layer structure with conductive material reduces the overall resistance, thereby reducing the write voltage required to switch the storage layer magnetization. This resolves the contradiction between maintaining data retention (requiring sufficient oxide layer thickness) and minimizing write voltage (requiring low resistance).

Inventive Principle:

Principle #40Composite materials

3Stability of the object's composition

If the film thickness of the cap layer is increased, then perpendicular magnetic anisotropy is maintained, but device property deteriorates due to superposition of series resistance

Engineering Contradiction:

Improveperpendicular magnetic anisotropyVSAvoidseries resistance

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The cap layer uses a composite structure where the oxide layer maintains perpendicular magnetic anisotropy while the conductive material layer compensates for the resistance increase caused by increased film thickness. This resolves the contradiction between maintaining magnetic anisotropy stability and minimizing series resistance effects.

Inventive Principle:

Principle #40Composite materials

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 effectively suppresses the increase in resistance value and maintains high tunnel magnetoresistance and perpendicular magnetic anisotropy, ensuring excellent data retention and write/read properties.

Implementation Method 1

it is necessary to increase the film thickness of the cap layer to keep the perpendicular magnetic anisotropy of the cap layer

Methodology Applied

Scientific EffectPerpendicular magnetic anisotropy: Anisotropy

Implementation Method 2

the cap layer includes a plurality of conductive regions having higher conductivity than conductivity of the oxide

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 3

a storage layer that is disposed on the insulation layer and changes a magnetization direction according to an applied current

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 4

increased Resistance Area (RA), decreases a Magnetic Resistance (MR)

Methodology Applied

Scientific EffectTunnel magnetoresistance: Magnetoresistance

Data Source

PatentUS20240415025A1Storage element and storage device

Publication Date: 2024.12.12 SONY SEMICON SOLUTIONS CORP

AI summary

A storage element according to an embodiment includes: a fixed layer that has a fixed magnetization direction; an insulation layer that is disposed on the fixed layer; a storage layer that is disposed on the insulation layer and changes a magnetization direction according to an applied current; and a cap layer that is disposed on the storage layer and made of an oxide, and the cap layer includes a plurality of conductive regions having higher conductivity than conductivity of the oxide.