Graded Magnetic Free Layer for STT-MRAM Switching

Solution Overview

Problem

Conventional spin transfer torque random access memories (STT-MRAMs) face challenges with high critical switching current density, which increases power consumption and reduces thermal stability, affecting data storage reliability.

Innovation Solution

A magnetic junction with a free layer having a gradient in critical switching current density, where the switching current density is lower closer to the nonmagnetic spacer layer and higher further away, allowing for stable magnetic state switching with reduced overall switching current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If conventional uniform free layer is used, then thermal stability is maintained, but critical switching current density is significantly higher than desired

Engineering Contradiction:

Improveswitching current densityVSAvoidthermal stability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The free layer is designed with spatially varying composition: the first portion contains a magnetic alloy with lower anisotropy (e.g., CoFeB) to reduce switching current, while the second portion contains a magnetic alloy with higher anisotropy (e.g., CoFe) to provide thermal stability. This local differentiation allows each region to optimize for its specific function.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The free layer is constructed as a composite structure with two distinct magnetic alloy portions having different compositions and magnetic properties. The combination of materials with contrasting anisotropy values enables simultaneous achievement of low switching current and high thermal stability that cannot be obtained with a single uniform material.

Inventive Principle:

Principle #40Composite materials

2Ease of operation

If conventional uniform free layer is used, then结构简单性 is maintained, but switching current is three to five times higher than desired

Engineering Contradiction:

Improveswitching currentVSAvoidfree layer structure

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The free layer is designed with spatially varying composition: the first portion contains a magnetic alloy with lower anisotropy (e.g., CoFeB) to reduce switching current, while the second portion contains a magnetic alloy with higher anisotropy (e.g., CoFe) to provide thermal stability. This local differentiation allows each region to optimize for its specific function.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The free layer is constructed as a composite structure with two distinct magnetic alloy portions having different compositions and magnetic properties. The combination of materials with contrasting anisotropy values enables simultaneous achievement of low switching current and high thermal stability that cannot be obtained with a single uniform material.

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 magnetic junction achieves lower switching currents and improved thermal stability, enhancing the performance of STT-MRAMs by optimizing switching characteristics and maintaining data reliability.

Implementation Method 1

A spin polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction. As a result, layer(s) having magnetic moments that are responsive to the spin torque may be switched to a desired state.

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 2

The free layer has a gradient in a critical switching current density (Jc0) such that a first Jc0 of a first portion of the free layer is lower than a second Jc0 of a second portion of the free layer.

Methodology Applied

Scientific EffectMagnetic anisotropy gradient: Anisotropy

Implementation Method 3

The conventional tunneling barrier layer 18 is nonmagnetic and is, for example, a thin insulator such as MgO.

Methodology Applied

Scientific EffectTunneling magnetoresistance:

Data Source

PatentUS8890267B2Method and system for providing magnetic junctions having a graded magnetic free layer

Publication Date: 2014.11.18 SAMSUNG ELECTRONICS CO LTD

AI summary

A method and system provide a magnetic junction usable in a magnetic device. The magnetic junction includes a pinned layer, a nonmagnetic spacer layer, and a free layer. The nonmagnetic spacer layer is between the pinned layer and the free layer. The free layer has a gradient in a critical switching current density (Jc0) such that a first Jc0 of a first portion of the free layer is lower than a second Jc0 of a second portion of the free layer. The second portion of the free layer is further from the nonmagnetic spacer layer than the first portion is. The magnetic junction is configured such that the free layer is switchable between a plurality of stable magnetic states when a write current is passed through the magnetic junction.