STTMRAM Free Layer Boron Segmentation for Stiffness

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Solution Overview

Problem

Magnetic random access memory (MRAM) with magnetic tunnel junctions (MTJs) faces a challenge due to high threshold voltage/current requirements for switching the free layer magnetization, primarily attributed to low internal magnetic stiffness of the free layer in spin torque transfer-based MTJs.

Innovation Solution

A spin transfer torque magnetic random access memory (STTMRAM) element with a free layer structure is developed, featuring a multi-layered free layer structure enhanced through an annealing process that reduces boron content at the interface between sub-layers, increasing internal stiffness, thereby reducing the switching voltage/current requirements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a conventional CoFeB free layer is used in spin torque transfer MTJ, then the device can achieve magnetization switching functionality, but the internal magnetic stiffness is too low resulting in high threshold voltage/current requirements

Engineering Contradiction:

Improvethreshold voltage/currentVSAvoidinternal magnetic stiffness

Core Design Contradiction:

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

Solution Approach 1:

The free layer is segmented into multiple sub-layers with different compositions and thicknesses. The first sub-layer (adjacent to barrier) has lower B content for higher stiffness, while the second sub-layer has higher B content for optimal magnetic properties, resolving the contradiction between stiffness and switching efficiency

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the free layer are given different local compositions: the region adjacent to the barrier layer has reduced boron content for enhanced stiffness, while the upper region maintains higher boron content for desirable magnetic characteristics, allowing simultaneous optimization of both stiffness and switching properties

Inventive Principle:

Principle #3Local quality

2Productivity

If the free layer thickness is reduced to improve switching efficiency, then the device becomes more responsive, but the internal magnetic stiffness decreases further increasing threshold voltage requirements

Engineering Contradiction:

Improveswitching efficiencyVSAvoidinternal magnetic stiffness

Core Design Contradiction:

ProductivityVSStability of the object's composition

Solution Approach 1:

The thin free layer is divided into multiple sub-layers where the thickness distribution optimizes both stiffness and switching efficiency. The lower sub-layer provides stiffness while the overall thin structure maintains responsiveness, resolving the contradiction between switching efficiency and stiffness

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The free layer uses a composite structure with varying boron concentrations in different sub-layers, creating a material composition that simultaneously achieves high stiffness in critical regions while maintaining overall thin profile for efficient switching

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 enhanced internal stiffness of the free layer results in lower switching voltage/current requirements, improving the efficiency and coherence of magnetization switching, leading to easier and more efficient data storage operations in MRAM.

Implementation Method 1

annealing the STTMRAM element at a first temperature after depositing the first free sub-layer to reduce the B content at an interface between the first free sub-layer and the barrier layer

Methodology Applied

Scientific EffectThermal diffusion: Diffusion

Implementation Method 2

spin torque from electrons transmitted from the pinned layer to the free layer orientate the free layer magnetization in a direction that is parallel to that of the reference or pinned layer

Methodology Applied

Scientific EffectSpin torque transfer:

Implementation Method 3

spin torque from electrons that are reflected from the pinned layer back into the free layer orientate the free layer magnetization to be anti-parallel relative to the magnetization of the pinned layer

Methodology Applied

Scientific EffectSpin torque transfer:

Data Source

PatentUS9070464B2Magnetic random access memory (MRAM) with enhanced magnetic stiffness and method of making same

Publication Date: 2015.06.30 AVALANCHE TECHNOLOGY INC

AI summary

A spin transfer torque magnetic random access memory (STTMRAM) element and a method of manufacturing the same is disclosed having a free sub-layer structure with enhanced internal stiffness. A first free sub-layer is deposited, the first free sub-layer being made partially of boron (B), annealing is performed of the STTMRAM element at a first temperature after depositing the first free sub-layer to reduce the B content at an interface between the first free sub-layer and the barrier layer, the annealing causing a second free sub-layer to be formed on top of the first free sub-layer and being made partially of B, the amount of B of the second free sub-layer being greater than the amount of B in the first free sub-layer. Cooling down the STTMRAM element to a second temperature that is lower than the first temperature and depositing a third free sub-layer directly on top of the second free layer, with the third free sub-layer being made partially of boron (B), wherein the amount of B in the third sub-free layer is less than the amount of B in the second free sub-layer.