Magnetic Junction Bias Structure for Precessional Switching

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Solution Overview

Problem

Conventional magnetic tunneling junctions (MTJs) in spin transfer torque random access memories (STT-RAMs) face challenges with precessional switching due to the need for precise control of current timing and external magnetic fields, which are not scalable and reliable, especially as device size decreases.

Innovation Solution

A magnetic junction configuration with a first pinned layer, a nonmagnetic spacer layer, and a free layer, where the bias structure provides a magnetic bias that is exchange decoupled from the second pinned layer, allowing for stable switching between multiple magnetic states using precessional switching, with improved reliability and scalability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If precessional switching is used in conventional MTJs, then switching speed is improved, but switching reliability deteriorates due to the need for precise current timing control

Engineering Contradiction:

Improveswitching speedVSAvoidswitching reliability

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent introduces a bias structure as an intermediary component that provides a static magnetic bias field to the free layer. This mediator enables the precessional switching process to occur more reliably by providing the necessary magnetic field condition without requiring precise timing control of external fields, thus resolving the contradiction between fast switching and reliable switching.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The bias structure is configured to provide a preliminary static magnetic bias to the free layer before the spin-polarized current is applied. This preliminary action prepares the magnetic moments in the free layer to be more responsive to the spin torque, enabling more reliable precessional switching without requiring precise timing control.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If external magnetic field is applied to improve switching reliability, then switching reliability is improved, but scalability deteriorates as device size decreases

Engineering Contradiction:

Improveswitching reliabilityVSAvoidscalability

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent extracts the magnetic field generation function from external sources and integrates it into the device structure through the bias structure. By taking out the need for external magnetic fields and replacing it with an integrated bias structure that provides static magnetic bias, the solution maintains switching reliability while improving scalability to smaller device sizes.

Inventive Principle:

Principle #2Taking out (Extraction)

3Productivity

If current is driven through conventional MTJ, then switching is achieved, but switching reliability deteriorates if current timing is not precisely controlled

Engineering Contradiction:

Improveswitching operationVSAvoidswitching reliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The bias structure enables the free layer to self-precess in response to the applied spin-polarized current without requiring precise external control. The static magnetic bias creates conditions where the free layer's magnetic moments naturally precess when subjected to spin torque, making the switching process more self-regulating and reliable.

Inventive Principle:

Principle #25Self-service

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 proposed magnetic junction achieves reliable and faster switching times, with increased margins for current removal timing and improved scalability to smaller sizes, enhancing the performance and reliability of magnetic memories.

Implementation Method 1

The magnetic bias is substantially in-plane and perpendicular to the easy axis of the free layer. The magnetic portion is substantially exchange decoupled from the second pinned layer.

Methodology Applied

Scientific EffectExchange coupling:

Implementation Method 2

The bias structure provides a magnetic bias at the free layer.

Methodology Applied

Scientific EffectMagnetic bias: Magnetic Field

Implementation Method 3

A spin polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction.

Methodology Applied

Scientific EffectSpin torque:

Implementation Method 4

The conventional MTJ 10 may be written using spin transfer and used in an STT-RAM.

Methodology Applied

Scientific EffectSpin transfer:

Implementation Method 5

The free layer magnetization precesses around this nonzero demagnetization field of the free layer 20.

Methodology Applied

Scientific EffectPrecession: Precession

Implementation Method 6

Because the free layer magnetization 21 is not along the easy axis, the demagnetization field of the free layer 20 is nonzero.

Methodology Applied

Scientific EffectDemagnetization field: Magnetic Field

Data Source

PatentUS9142758B2Method and system for providing a magnetic junction configured for precessional switching using a bias structure

Publication Date: 2015.09.22 SAMSUNG ELECTRONICS CO LTD

AI summary

A method and system provide a magnetic junction usable in a magnetic device. The magnetic junction includes a first pinned layer having a first pinned layer magnetization, a first nonmagnetic spacer layer, and a free layer having an easy axis. The first nonmagnetic spacer layer is between the first pinned layer and the free layer. 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 and such that the free layer employs precessional switching.