72243876 Spintronic Devices

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SPINTRONIC DEVICES


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Points to be covered:

SpintronicsWhere from it came?

Magnetic materials.

What is spintronics?

Giant magnetoresistive effect. The spin valve.

The spin field effect transistor.

Why go for spintronics?

Applications of spintronic devices. Challenges in the field of spintronic devices.

Conclusion


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Nanotechnology

Deals with matter of size ranging from 1nm to 100nm.

It can be seen as an extension of existing fields of sciencesuch as material science, molecular chemistry, quantum

physics etc. to the nanoscale.

Nanotechnology

Nano-materials Nano-biotechnology Nanoelectronics


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1. Nano-materialsMaterials having unique properties arising from their

nanoscale dimensions Carbon nanotubes, fullerenes, nanorods, nanoparticles

2. Nano-biotechnology Biological or biochemical applications Study of existing elements of nature in order to fabricate

new devices Nanosensors, bionics, nanoparticles for gene delivery

3. Nanoelectronics Electronic devices of dimension less than 100nm

Takes into account the inter-atomic interactions andquantum mechanical properties

Single electron transistors, reconfigurable computing,spintronics


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Magnetic Materials

PARAMAGNETS

FERROMAGNETS

ANTIFERROMAGNETS

DIAMAGNETS

weakly repelled by magnetic field and are consideredas non-magnetic

weakly attracted by magnetic field and are alsoconsidered as non-magnetic

strongly attracted by magnetic field as domains arealigned

domains oppositely oriented canceling each othersmagnetic moment

Adapted from: M S Vijaya, and G Rangarajan, Materials Science, Tata McGraw Hill, Ed.1, 2004


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SPINTRONICS conveying the digital information by spin of the

electrons :1 by +1/2 and 0 by -1/2. involves active manipulation of spin degree of

freedom in solid state systems. magnetic materials are predominantly used.

Spin the fundamental property of electron. can be either +1/2(up spin) or -1/2(down spin).

Up-spin

Down -spin

Illustrations adapted from: Ulrich Zuelicke, New Possibilities in Semiconductor Spintronics, Mac Diarmid Inst. Workshop on Smart Materials and Smart Technologies, Nelson, NZ, 2-3 Dec03.


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Giant Magnetoresistive Effect

GMR: observed in multilayered magnetic structures.alternate ferromagnetic and non magnetic layers exhibitgreater magnetoresistive effect.

Magnetoresistancechange of electrical resistance of a conductorwhen subjected to an external magnetic field.

Schematic description of the spin-dependent scattering mechanism for the giantmagnetoresistance. Electrons are strongly scattered in magnetic layers withmagnetizations (white arrows) antiparallel (AP) to their spin (black arrows), andweakly scattered in magnetic layers with magnetizations parallel (P) to their spin.

RP < RAP

Illustrations adapted from: http://w3.rz-berlin.mpg.de/~michaeli/member/MaterialsScienceLectures/GMR-2.pdf


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Schematic description of the giant magnetoresistance effect.Blue curve: magnetization of the multilayer versus applied magnetic field.Red curve: electrical resistance of the multilayer.The insets: indicate the magnetic configuration of themultilayer in zero field and at positive and negative saturation fields.

Illustrations adapted from: http://w3.rz-berlin.mpg.de/~michaeli/member/MaterialsScienceLectures/GMR-2.pdf


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THE SPIN VALVE

NiFe

Co

CuCo

NiFe

Ferro-magneticmaterials

Ferro-magneticmaterials

Non-magnetic

material

Schematic Diagram of a Spin Valve

Illustration adapted from: Jim Daughton, Magnetic Spin Devices, Symposium X, MRS 2004 FallMeeting, Boston, MA, 1 Dec,2004


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MAGNETIC TUNNEL JUNCTION

Magnetic layer (FM)

Insulating layer

Free magneticlayer (FM)

Direction ofCurrent

AFM: Anti-Ferro MagnetFM: Ferro Magnet

Pinning layer (AFM)

Schematic Diagram of a Magnetic Tunnel Junction


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Construction of a Spin Valve Magnetoresistive Element

Illustration adapted from: Yoshihiko Kakihara et.al,Spin valve magnetoresistive element,US Patent, No.5,959,810, Sep28,1999.

AntiferromagneticLayer

Pinned Magnetic

Layer

Free MagneticLayer Non magnetic Layer


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MR trace of a 4 m spin valve resistor.The spin valve is with a structure of Ta~40 !/NiFeCo~50 !/Ta~50 !/NiFeCo~40 !/CoFe~10 !/Cu~25 !/CoFe~40 !/CrPtMn~325 !.

Adapted from: Qian et.al, MR Signal Isolators Employing Linear Spin Valve Resistors,Journal of App. Phy., Vol.93, No.10, 15 May,2003


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SPIN FIELD EFFECT TRANSISTORG (No Voltage)

G (Applied Voltage)

SD

Changed alignmentOriginal alignment

FM FM

FM FMS D

Schematic diagram of a Datta Das Spinfet

Adapted from: Prof. Supriyo Bandyopadhyay, Hybrid and Monolithic Spintronics,Available:http://www.ewh.ieee.orgr3cnced-mtt-ssc2007ProgramsSupriyo_Bandyopadhyay- Presentation.pdf


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SPIN FIELD EFFECT TRANSISTOR USING2DEG SEMICONDUCTOR CHANNEL

Adapted from: Junsaku Nitta, Semiconductor Spintronics, Selected Papers, Vol.2, No.6,NTT Basic Research Lab, Atsugi-shi, Japan, Jun 2004.


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GATE CONTROL OF SPIN ORBITINTERACTION

where,

spin precision anglespin orbit interaction parameterLdistance between source and drain ferromagnetic electrodes

which is directly proportional to which is dependent upon

gate voltageFor L = 0.5 m,

= 1.2 at Vg = 0V, = 1.8 at Vg = -5V



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Spin-orbit interaction parameter is plotted as a function of carrier

concentration Ns, which is related to gate voltage Vg.

Spin Orbit Interaction can be Controlled by GateVoltage



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Plot of source to drain current vs. gate voltagefor a Spinfet



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Advantages of Spintronic Devices:

Memory is not volatile

Power consumption is low

Better noise immunity Lesser cost than electronic devices

Also it is suggested that they are faster in

operation



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Applications of Spintronic Devices:

GMR read heads are used in hard disks. The data can beclosely packed thereby, increasing the storage capacity.(Storage capacity has increased from 1GB in 1997 to 20GB in2000.)

It is a US $100 billion/year industry producing MRAM cells,GMR read heads, GMR sensors, GMR isolators etc.

Spinfets, spin diodes, spin filters, and spin lasers.

Can be used in IC fabrication, quantum computing.

Adapted from: Ulrich Zuelicke, New Possibilities in Semiconductor Spintronics, Mac Diarmid Inst. Workshop on Smart Materials and Smart Technologies, Nelson, NZ, 2-3 Dec03.


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Challenges in the Field of Spintronic Devices:

Generation of perfectly spin polarizing currents.

How strong the channel field shouldbe?

Finding materials with high magnetism-sensitive

resistances Optimization of electron spin lifetimes

Detection of spin coherence in nano-scale structures

Transportation of spin-polarized carriers over longdistances in harsh conditions


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Conclusion:

Spintronics which originates from nanotechnology, ismainly based on principles of quantum physics.

GMR is still developing and the storage capacity and

size of devices is going to shrink further.Spin valve and Spinfet are among a few devices thateffectively use spin of the electron as their medium ofoperation.

Although some limitations are there the potential ofthis field cant be ignored.


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72243876 Spintronic Devices

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