GRAPHENE

A Revolutionary Material In ELECTRONICS

RAVI P. AGRAHARI(Science & Technology)

Introduction & History

What is GRAPHENE?

• Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D)honeycomb structure ,which works on diffraction of electrons.

• The Nobel Prize in Physics for 2010 was awarded to Andre Geim and Konstantin Novoselov "for groundbreaking experiments regarding the two-dimensional material graphene".

• Carbon-the basis of all known life on the earth-has surprised the scientific community once again with its exotic properties.

• Researchers have found that a form of carbon called graphene makes experiments possible that give new twist to electronics field.

• This devices are predicted to be substantially faster, thinner & more efficient than current silicon based devices.

Graphene as a material• Graphene as a material is completely new –not only the

thinnest ever but also the strongest.• It is the one-atom thick planar sheet of carbon atoms, which

makes it the thinnest material ever discovered.• Carbon atoms in the sheet are densely packed in a two-

dimensional(2D) honeycomb crystal lattice.• The carbon-carbon bond length in graphene is about

0.142nm.• Graphene is the basic structural element of some carbon

allotropes including graphite, charcoal, carbon nanotubes & fullerenes.

• It can be wrapped up into 0D fullerences, rolled into 1D nanotubes or stacked into 3D graphite.

• Graphene is highly conductive-conducting both heat & electricity better than any other material, copper & stronger than diamond.

• It is almost completely transparent, yet so dense that not even helium can pass through it.

˃ High electron mobility- upto 25000cm² per volt-second .˃ The theoretical mobility of electrons is 200 times that of silicon.˃ The corresponding resistivity of the graphene sheet would be 10 ⁶ Ω·cm.⁻˃ The charge storage time is less, so the operating frequency is high.˃ The near-room temperature thermal conductivity of graphene was recently measured to be between (4.84±0.44) ×10^3 to (5.30±0.48) ×10^3 Wm−1K−1.˃ The breakover voltage is less than 0.3V.

So , it can replace current devices, such as CMOS , and will give turning point to the electronics.

The below is the some allotropic structures of the carbon-

Graphene to SiliconChemical Properties of Graphene & Silicon :

Structure of Graphene & Silicon :

Two-D Graphene Silicon bond

• Graphene is two dimensional allotrope of carbon, while silicon is single dimensional metalloid found in nature.

Graphene has 6 electrons, while silicon have 14 number of electrons.

• Three carbon-carbon covalent bonds [Trivalent] form a “Graphene”, while three silica-carbon covalent bonds form a silicon as a metalliod.

• Graphene has two bands, one for empty particle & other for antiparticles[holes], & Silicon has two energy bands [conduction band & valance band] & an energy gap between them.

• Graphene is considered as hybrid between a metal & a semiconductor, Silicon is pure semiconductor.

• Doping of graphene is roughly divided into three categorie

1. hetero atom doping

2. chemical modification strategy

3. electrostatic field tuning

• Doping of silicon is roughly divided into two categorie

• 1. p-type• 2. n-type

• both process are used for extrinsic not for intrinsic semiconductor.• Density of graphene sheet is > 1 g/cm3 , while silicon has 2.57 g·cm3

Electrical Properties of Graphene & Silicon :

• Break-over voltage of graphene is less than 0.3V, & that of silicon is 0.3 Volts.

• Transmission of electrons in graphene and silicon :

✔Dirac Fermions in Graphene ✔Electrons in Conventional Silicon

• Graphene is a Zero Gap Semiconductor. So it has Electron transfer is 200 times faster than Silicon.

• Thermal conductivity of graphene was recently measured to be

between (4.84±0.44) ×103 to (5.30±0.48) ×103 Wm−1K−1, & thermal conductivity of silicon is Thermal conductivity 149 W·m−1·K−1

• Resistivity of the graphene sheet would be 10−6 Ω·cm, Electrical resistivity of the silicon 103 Ω·m.

• On-off ratio of graphene is ~30 at room temperature & which is six times greater than silicon.

• Graphene has very small voltage gain (typically, the amplitude of the output signal is about 40 times less than that of the input signal ) than silicon.

• Graphene has produced structures just 15 to 40 nanometers wide that conduct current with almost no resistance, while silicon has such structures at some micrometer wide only.

• Electrons in graphene move at an effective speed of light 300 times less than the

• speed of light in a vacuum, allowing relativistic effects to be observed without

• using particle accelerators.

GRAPHENE FABRICATIONConcept of FABRICATION• Usually Graphene can be fabricated by the methods of Chemical exfoliation,

Thermal exfoliation.

Graphene can be fabricated in the forms of :-

(I) GRAPHENE SHEETS :-

FIG.- PROCESS FLOW SCHEMATIC FOR FABRICATION OF GRAPHENE SHEETS

Fig: Graphene Sheets in layer

Fig: Single Graphene Sheet

(II) Carbon Nanotubes:-

A Carbon Nanotube is a tube made entirely carbon with a diameter of about a nanometer (1/1,00,00,00,000th of a meter). It is hard to imagine something so small, but if you zoomed in so that a nanotube was as wide as one of your hairs, then your head would be about the width of Cayuga Lake! As shown in the illustration, a carbon nanotube is a rolled tube of carbon atoms in a honeycomb arrangement

FIG-SCHEMATIC OF CARBON NANO TUBE FBRICATION FABRICATION

(III) GRAPHENE NANORIBBONS:-

How can we see a nanotube with an atomic force microscope (AFM) ?

A sharp needle attached to a diving board shaped cantilever ( a lot like a record

player needle) is scanned across the surface of the sample. Whenever the needle

hits a bump, the whole board moves up and down, and this deflection is

measured by a laser. Using our AFM, we can determine how many nanotubes

are connected between a pair of electrodes, and their diameters. Here you see an

illustration of an AFM, a real AFM , and an AFM in the CNF clean room:

Applications Graphene Transistors-

• Graphene exhibites a pronounced effect to perpendicular

external electric fields, allowing us to build FETs.

• Researchers demonstrated & built an experimental

graphene chip of single graphene transistor known as

frequency multiplier.

• However, these graphene transistor show a very poor on-

off ratio, small voltage gain & operating frequencies less

than 25kHz.

• Recently researchers have been able to create graphene

transistors with an on-off ratio rate of 100GHz.

• IBM had developed 10000 top gated transistors on 0.24

centimeter square chip.

The fabricated graphene field effect transistor.

Integrated Circuit-• Graphene has the ideal properties to become an excellent component of

integrated circuits.• Its high carrier mobility & low noise allow it to be used as a channel in FETs.• Besides, the researchers have demonstrated the first functional graphene

integrated circuit-a complementary inverter consisting of one p- & one n- type graphene transistor.

Ultra capacitors:-• Due to incredibly high surface-area-to-mass ratio of graphene, its one

potential application is in the conductive plates of ultra capacitors.• Graphene could be used to produce ultra capacitors with a greater energy

storage density than is currently available.

Anti-Bacterial:-• Sheets of graphene oxide are highly effective at killing bacteria's such as

Escherichia coli.• So, graphene could be useful in hygiene products or packaging.

Strength Applications:-• When graphene sheets are incorporated into composites, we could come up with a

material that’s many times stronger than Kevlar.• The Chinese are already working on carbon- nanotube yarn for space suits & bullet

proof vests.

T-Ray Scanners:-• Terahertz radiation, or T-ray is used for detecting hidden objects at security

checkpoints without the health risk posed by X-rays.• The fast frequencies generated by graphene circuits are the basis for chemical

sensors & generators of THz-range light.

Heat Dissipation to cool electronics:-• Overheating in laptops & other electronic gadgets is a major technological hurdle to

the speed & energy efficiency of electronic products.• Graphene behaves as a strong heat conductor, which helps chip manufacturers to

rich higher speeds with relative lower temperatures.• Scientists from University of California found that multiple layers of graphene

show strong heat conducting properties, which can help in removing dissipated heat from electronic devices.

Advantages Limitations

• Higher electron mobility • Works on principle of diffraction of

electrons.• Superb electron & heat conductivity,

greater than copper.• Very less breakover voltage, less than

0.3V• It is transparent, yet so dense as even an

atom of Helium can’t pass through it.• Stronger than diamond & steel • Can be used to make anti bacterial

materials as well as biodevices.• Can make very light weight parts for

auto bodies & armours

• Single sheet of graphene is hard to produce.

• The new fabrication & manufacturing methods has to be evolved for normal use in electronics.

• Due to small voltage gain, practical use is limited.

• While graphene can be considered semiconductor like silicon, it lacks one crucial property- the ability to act as a switch.

• Graphene research has discovered hidden interactions that will affect the way components are designed from the superfast material.

Conclusion

From above discussion it is concluded that Graphene is a material which has the

capability to eliminate the current semiconductors such as silicon and form a new

era of superfast micro electronics.

From recent researches it is observed that , the most likely applications for

Graphene will be in analogue systems , such as radar , satellite communication and

imaging devices.

There are many agencies which are working very hardly on graphene and they have

founded the new graphene devices. Some of them are- Defense Advanced

Research Projects Agency of U.S. D.O.D., Indian agencies such as D.R.D.O.,

Nanoscale science and technology group at the IBM Watson Research Centre in

Ossining, NY, etc.

Thank you…..