Semi-spin valve magnetic memory switching

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Solution Overview

Problem

Conventional spin transfer torque random access memories (STT-RAMs) require high currents for switching, which can lead to write error issues and damage to magnetic junctions, and result in reduced read signals due to magnetoresistance cancellation in the antidual state.

Innovation Solution

Incorporating semi-spin valve (SSV) lines with ferromagnetic and nonmagnetic layers adjacent to magnetic junctions to exert spin accumulation induced torque, allowing for switching using in-plane spin polarized current and reducing the need for high perpendicular currents, while also utilizing magnetoelectric selection devices.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high perpendicular current is driven through the magnetic junction to switch magnetization, then switching can be achieved, but write error rates increase and magnetic junctions may be damaged

Engineering Contradiction:

Improvewrite error rateVSAvoidcurrent requirement

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent introduces a semi-spin valve (SSV) line as an intermediary structure between the current path and the magnetic junction. The SSV line includes a ferromagnetic layer and a nonmagnetic layer that generates spin accumulation, which then exerts torque on the magnetic junction's free layer. This mediator converts charge current into spin current more efficiently, reducing the direct current burden on the magnetic junction while achieving the same switching effect.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the direct spin transfer torque mechanism (which requires high perpendicular current through the junction) with a spin accumulation induced torque mechanism. Instead of driving current directly through the magnetic tunnel junction, the system uses the SSV line to generate spin accumulation that indirectly acts on the free layer, substituting a less harmful mechanical stress-free switching mechanism.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If reference layers are configured in the antidual state to enhance spin torque, then switching torque is improved, but magnetoresistance signal is reduced due to cancellation

Engineering Contradiction:

Improveswitching torqueVSAvoidread signal

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent applies different magnetic configurations to different parts of the system. The reference layers can be configured in the antidual state locally where spin torque is needed, while the read operation uses a different configuration path. The SSV line structure allows selective activation of spin torque in specific regions without affecting the overall magnetoresistance signal detection.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent segments the magnetic memory structure into distinct functional components: the SSV line with its ferromagnetic and nonmagnetic layers, the magnetic junction with free and reference layers, and the read/write paths. This segmentation allows the reference layers to serve dual purposes - providing spin torque enhancement in one configuration while maintaining read signal integrity through proper structural design and selective operation modes.

Inventive Principle:

Principle #1Segmentation

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 approach enables more efficient switching with lower current requirements, reduces write error rates, and maintains higher read signal integrity by minimizing magnetoresistance cancellation, thus improving the performance of spin transfer torque based memories.

Implementation Method 1

The SSV line(s) are configured to exert a spin accumulation induced torque on at least a portion of the magnetic junctions due to an accumulation of spin polarized current carriers from a current that is substantially in-plane

Methodology Applied

Scientific EffectSpin accumulation induced torque:

Implementation Method 2

The current carriers are spin polarized and exert a torque on the magnetization 21 of the conventional free layer 20 as the current carriers pass through the conventional free layer 20

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 3

utilizing magnetoelectric selection devices

Methodology Applied

Scientific EffectMagnetoelectric effect:

Data Source

PatentUS9076954B2Method and system for providing magnetic memories switchable using spin accumulation and selectable using magnetoelectric devices

Publication Date: 2015.07.07 SAMSUNG ELECTRONICS CO LTD

AI summary

A magnetic memory is described. In one aspect, the magnetic memory includes magnetic junctions and at least one semi-spin valve (SSV) line adjacent to the magnetic junctions. Each magnetic junction includes a magnetic free layer. The SSV line(s) include a ferromagnetic layer and a nonmagnetic layer between the ferromagnetic layer and the magnetic junctions. The SSV line(s) are configured to exert a spin accumulation induced torque on at least a portion of the magnetic junctions due to an accumulation of spin polarized current carriers from a current that is substantially in-plane. The free layer is configured to be written using at least the spin accumulation induced torque. In another aspect, the magnetic memory includes magnetic memory cells and at least one spin torque (ST) line that is analogous to the SSV line. Each magnetic memory cell includes magnetic junction(s) analogous to those above and magnetoelectric selection device(s).