SPINTRONIC DEVICESSPINTRONIC DEVICES

Presented by:Presented by:Ipsita PandaRegn. No. : 0401212073Sec-AElectronics and Telecommunication

Points to be covered:Points to be covered:

Spintronics – Where 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

NanotechnologyNanotechnology

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

1. 1. Nano-materialsNano-materials Materials having unique properties arising from their nanoscale dimensions Carbon nanotubes, fullerenes, nanorods, nanoparticles

2. Nano-biotechnology2. 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. Nanoelectronics3. Nanoelectronics Electronic devices of dimension less than 100nm Takes into account the inter-atomic interactions and quantum mechanical properties Single electron transistors, reconfigurable computing, spintronics

Magnetic MaterialsMagnetic Materials

PARAMAGNETS

FERROMAGNETS

ANTIFERROMAGNETS

DIAMAGNETS weakly repelled by magnetic field and are considered as non-magnetic

weakly attracted by magnetic field and are also considered as non-magnetic

strongly attracted by magnetic field as domains are aligned

domains oppositely oriented canceling each others magnetic moment

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

SPINTRONICSSPINTRONICS 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.

SpinSpin 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.

Giant Magnetoresistive EffectGiant Magnetoresistive Effect

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

Magnetoresistance – change of electrical resistance of a conductor when subjected to an external magnetic field.

Schematic description of the spin-dependent scattering mechanism for the giant magnetoresistance. Electrons are strongly scattered in magnetic layers withmagnetizations (white arrows) antiparallel (AP) to their spin (black arrows), and weakly 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”

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”

THE SPIN VALVETHE SPIN VALVE

NiFe

Co

Cu

Co

NiFe

Ferro-magneticmaterials

Ferro-magneticmaterials

Non-magneticmaterial

Schematic Diagram of a Spin Valve

Illustration adapted from: Jim Daughton, “Magnetic Spin Devices,” Symposium X, MRS 2004 Fall Meeting, Boston, MA, 1 Dec,2004

MAGNETIC TUNNEL JUNCTIONMAGNETIC 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

Construction of a Spin Valve Magnetoresistive ElementConstruction 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 MagneticLayer

Free MagneticLayer

Non magnetic Layer

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

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

SPIN FIELD EFFECT TRANSISTORSPIN FIELD EFFECT TRANSISTORG (No Voltage)

G (Applied Voltage)

S D

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”

SPIN FIELD EFFECT TRANSISTOR USING SPIN FIELD EFFECT TRANSISTOR USING 2DEG SEMICONDUCTOR CHANNEL2DEG SEMICONDUCTOR CHANNEL

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

GATE CONTROL OF SPIN ORBIT GATE CONTROL OF SPIN ORBIT INTERACTIONINTERACTION

where,θ – spin precision angleα – spin orbit interaction parameterL – distance between source and drain ferromagnetic electrodes

θ which is directly proportional to α which is dependent upon gate voltageFor L = 0.5 µm, θ = 1.2π at Vg = 0V, θ = 1.8π at Vg = -5V

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

Spin-orbit interaction parameter α is plotted as a function of carrier concentration Ns, which is related to gate voltage Vg.

Spin Orbit Interaction can be Controlled by Gate Spin Orbit Interaction can be Controlled by Gate VoltageVoltage

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

Plot of source to drain current vs. gate voltage Plot of source to drain current vs. gate voltage for a Spinfetfor a Spinfet

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

Advantages of Spintronic Devices: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

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

Applications of Spintronic Devices:Applications of Spintronic Devices:

GMR read heads are used in hard disks. The data can be closely packed thereby, increasing the storage capacity. (Storage capacity has increased from 1GB in 1997 to 20GB in 2000.)

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.

Challenges in the Field of Spintronic Devices:Challenges in the Field of Spintronic Devices:

Generation of perfectly spin polarizing currents. How strong the channel field should be? 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 long

distances in harsh conditions

Conclusion:Conclusion:

Spintronics which originates from nanotechnology, is mainly 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 that effectively use spin of the electron as their medium of operation.

Although some limitations are there the potential of this field can’t be ignored.