Graphene Seminar

8/2/2019 Graphene Seminar

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Seminaron

Graphene: The Ultimate Switch


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Contents

About transistors

Electrons can be made to bend and bounce

What can we do with this light- mimicking behavior?

How Graphene works?

Reconfigurable logic Honey comb like lattice of hexagons

Creating artificial bandgap.

Moore's law

Gate test Conclusion

References


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About Transistor

From the outside, transistors seem so simple

and straightforward. But inside, they're

actually a mess. Electrons moving through

even the best transistor channel can't go in

straight lines. Instead they're buffeted

continually by a host of imperfections and

vibrations, which together put a strict limit onspeed and generate a lot of heat in the

process.


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Electrons can be made to bend and

bounce

The good news is that it doesn't have to be thatway. By a quirk of quantum mechanics, electronsmoving through atom-thick sheets of carbon

known as graphenedon't suffer much at allfrom these sorts of collisions. Instead, theybehave like massless particles, speeding along instraight lines for long distances just like photons

do. And just like light, these electrons can bemade to bend or bounce back when they movefrom one medium to another.


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What can we do with this light-

mimicking behavior?Well, here's what we'd like to do: Replace thelogic circuitry at the heart of every computer

processor. After 50 years of steady

miniaturization, chipmakers have just about

shrunk the device to its limits. we know that

to continue making faster, cheaper, and more

energy efficient chips, we'll need a newtechnology.


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How Graphene works?

Graphene logic will be extraordinarily fast.Instead of manipulating information byturning the flow of current on and off through

a transistor channel, graphene logic couldperform calculations by bending, reflecting,focusing, and defocusing electrons moving at1/300th the speed of lightabout 10 times as

fast as electrons in silicon CMOS devices.Logic devices built from graphene willconsume less power


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Reconfigurable logic

Unlike any other technology being considered,

graphene devices have the potential to

simplify and speed up chips by creating truly

reconfigurable logic. Such logic would be able

to change its type on the fly: In response to

electronic signals, an AND gate, for example,

could be transformed into an OR gate andthen back again.


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As you might imagine, no ordinary

semiconductor can be used to shuttle

electrons around like beams of light. In the

silicon CMOS transistors that make up today's

chips, electrons can barely move a few

nanometers before they bounce off an

impurity. Other semiconductor materialsaren't much better.


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But graphene is different. First isolated in

2004, the material consists of a single sheet of

carbon atoms arranged in a honeycomb-like

lattice of hexagons. Roll it up and you've got a

carbon nanotube. Stack it and you can make

graphite. Graphene's symmetrical, two-

dimensional crystalline structure isresponsible for most of its unique qualities.


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Honey comb like lattice of hexagons
http://en.wikipedia.org/wiki/File:Graphen.jpg


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Creating artificial bandgap.

Graphene isn't really a semiconductor. Becausegraphene in its natural state has no bandgap, avanishingly small amount of energy is needed toknock an electron free of its valence band.

Engineers have some tricks that can be used tocreate an artificial bandgap. They can, forexample, pattern graphene into very thinribbons or apply an electric field across two layersof graphene stacked one on top of the other. Butwhile these sorts of approaches do create abandgap, they have the side effect of reducingelectron speed.


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Ref

[4]


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By using graphene technology we can end up

with a new technology than can keep the

world on Moores law like- like progression

toward cheaper, lower power and betterperforming processors


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Two triangles of a graphene


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One of the first designs explored was the simplebinary switch. we can build such a switch with

just a square of graphene. If you draw animaginary diagonal across the square, you create

two triangles of graphene. Under each of thesetriangles you place a triangular wedge ofconducting materialsuch as copper or heavilydoped siliconthat can be either positively or

negatively charged. These buried wedges act asgates, altering the electronic properties of thegraphene above them.


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If both wedges have the same charge, the

switch is on, and an electron coming from one

side of the graphene square can move in a

straight line from one side of the square to theother. But if opposite biases are applied, the

two graphene regions will become oppositely

doped, and nearly all the electrons will bereflected at the interface. Now the switch is

off.


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Gate test
http://spectrum.ieee.org/img/02OLGraphenef4b-1327597721263.jpg


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Laboratory experiments have shown that

graphene's resistance to the flow of current

varies, depending on how it is angled when

placed atop a pair of gates. The results suggestthat the fraction of electrons that pass

through the gate interface changes with the

angle, just like light.


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Conclusion

We might see graphen based reconfigurable

logic prototypes with in the next five years

that can replace CMOS circuits.


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References:-

1) IEEE journal magazine february 2012

2) IEEE spectrum(http://spectrum.ieee.org/semiconductors/mate

rials/graphene-the-ultimate-switch/0)3) Wikipedia(http://en.wikipedia.org/wiki/Graphen

e)

4) http://en.wikipedia.org/wiki/Moore's_law

5)ftp://download.intel.com/museum/Moores_Law/Printed_Materials/Moores_Law_2pg.pdf
http://spectrum.ieee.org/http://spectrum.ieee.org/semiconductors/materials/graphene-the-ultimate-switch/0http://spectrum.ieee.org/semiconductors/materials/graphene-the-ultimate-switch/0http://en.wikipedia.org/wiki/Graphenehttp://en.wikipedia.org/wiki/Graphenehttp://en.wikipedia.org/wiki/Moore's_lawftp://download.intel.com/museum/Moores_Law/Printed_Materials/Moores_Law_2pg.pdfftp://download.intel.com/museum/Moores_Law/Printed_Materials/Moores_Law_2pg.pdfftp://download.intel.com/museum/Moores_Law/Printed_Materials/Moores_Law_2pg.pdfftp://download.intel.com/museum/Moores_Law/Printed_Materials/Moores_Law_2pg.pdfhttp://en.wikipedia.org/wiki/Moore's_lawhttp://en.wikipedia.org/wiki/Moore's_lawhttp://en.wikipedia.org/wiki/Graphenehttp://en.wikipedia.org/wiki/Graphenehttp://spectrum.ieee.org/semiconductors/materials/graphene-the-ultimate-switch/0http://spectrum.ieee.org/semiconductors/materials/graphene-the-ultimate-switch/0http://spectrum.ieee.org/semiconductors/materials/graphene-the-ultimate-switch/0http://spectrum.ieee.org/semiconductors/materials/graphene-the-ultimate-switch/0http://spectrum.ieee.org/semiconductors/materials/graphene-the-ultimate-switch/0http://spectrum.ieee.org/semiconductors/materials/graphene-the-ultimate-switch/0http://spectrum.ieee.org/semiconductors/materials/graphene-the-ultimate-switch/0http://spectrum.ieee.org/semiconductors/materials/graphene-the-ultimate-switch/0http://spectrum.ieee.org/


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Thank you for listening

Graphene Seminar

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