Magnetic Stack Assist Layer Reduces Switching Current

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Solution Overview

Problem

Current magnetic memory technologies face challenges such as high switching current requirements and limited thermal stability, which hinder the development of reliable magnetic memory stacks for nonvolatile data storage and field sensors.

Innovation Solution

The development of magnetic cells with perpendicular anisotropy and a spin current-driven assist layer, featuring a ferromagnetic free layer and pinned reference layer with out-of-plane magnetization orientations, and an assist layer with low magnetic anisotropy, facilitating reduced switching currents and enhanced thermal stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of moving object

If the MTJ size is reduced to increase storage density, then the areal density is improved, but the switching magnetic field amplitude increases and switching variation becomes more severe

Engineering Contradiction:

ImproveMTJ sizeVSAvoidswitching variation

Core Design Contradiction:

Area of moving objectVSReliability

Solution Approach 1:

The invention divides the magnetic memory stack into multiple functional layers including a pinned layer, free layer, and assist layer. The assist layer is further segmented into multiple sub-layers with different magnetic properties, allowing independent optimization of switching characteristics and thermal stability while maintaining small overall MTJ dimensions for high density.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs composite magnetic structures combining different ferromagnetic materials with distinct anisotropy properties. The assist layer uses composite construction with layers having perpendicular magnetic anisotropy and in-plane magnetic anisotropy, creating a system where the combination provides both low switching field and high thermal stability, overcoming the limitations of single-material approaches in scaled devices.

Inventive Principle:

Principle #40Composite materials

2Use of energy by moving object

If the switching magnetic field amplitude is reduced to lower switching current, then the energy consumption is improved, but the thermal stability deteriorates

Engineering Contradiction:

Improveswitching currentVSAvoidthermal stability

Core Design Contradiction:

Use of energy by moving objectVSStability of the object's composition

Solution Approach 1:

The invention applies local quality by creating regions with different magnetic anisotropy characteristics within the assist layer. The first assist layer portion has perpendicular magnetic anisotropy for thermal stability, while the second assist layer portion has in-plane magnetic anisotropy for low switching field. This spatial differentiation of magnetic properties allows simultaneous achievement of low switching current and high thermal stability.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent utilizes parameter changes by varying the magnetic anisotropy type and strength across different layers. The assist layer transitions from perpendicular anisotropy (high stability) to in-plane anisotropy (low switching field), and the free layer uses materials with tunable anisotropy parameters. This parameter optimization across the stack enables reduced switching current while maintaining thermal stability.

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 design reduces the switching current needed while maintaining thermal stability, enabling the creation of high-density magnetic memory cells with improved efficiency and reliability for data storage and sensor applications.

Implementation Method 1

a ferromagnetic assist stack proximate the free layer having low magnetic anisotropy, the assist stack comprising an assist layer having a magnetic moment less than about 1000 emu/cc and a magnetization orientation that rotates in a direction of electron flow from a current

Methodology Applied

Scientific EffectSpin torque:

Implementation Method 2

The cells include a ferromagnetic free layer and a ferromagnetic pinned reference layer, each having an out-of-plane magnetic anisotropy and an out-of-plane magnetization orientation and switchable by spin torque

Methodology Applied

Scientific EffectSpin torque:

Implementation Method 3

a ferromagnetic free layer having an out-of-plane magnetic anisotropy and an out-of-plane magnetization orientation perpendicular to the substrate

Methodology Applied

Scientific EffectMagnetic anisotropy:

Data Source

PatentUS7936598B2Magnetic stack having assist layer

Publication Date: 2011.05.03 SEAGATE TECH LLC

AI summary

A magnetic memory cell having a ferromagnetic free layer and a ferromagnetic pinned reference layer, each having an out-of-plane magnetic anisotropy and an out-of-plane magnetization orientation and switchable by spin torque. The cell includes a ferromagnetic assist layer proximate the free layer, the assist layer having a low magnetic anisotropy less than about 500 Oe. The assist layer may have in-plane or out-of-plane anisotropy.