GRAPHENE TRANSISTORS: SPEEDING UP THE ELECTRONIC CONVERSION

dehisceforkElectronics - Devices

Nov 2, 2013 (4 years and 11 days ago)

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Session B11

3114

University of Pittsburgh Swanson School of Engineering

1

March 7, 2013

GRAPHENE TRANSISTORS: SPEEDING UP THE ELECTRONIC
CONVERSION


Zachary Gannon (zjg7@pitt.edu
, Budny 10:00
)
, Jacob Guttenplan (jmg208@pitt.edu, Bon 6:00)


Abstract



In this paper we will present

and describe

graphene and its
various
qualiti
es, ranging from its
mechanical and physical
properties, such as high
malleability and durability, to its electrical
and

thermal

properties, such as
extracted mobility and
heat conductivity
.
These qualities will be compared against those of silicon, the
cu
rrent medium in many transistors, to show the
improvements in utilizing graphene as the semiconducting
substrate in future transistors.

With a graphene transistor
possibility established, we will describe
some of
the
problems
preventing

graphene transistor

production,
such
as a lack of a bandgap
. Solutions to these problems will
then
be explored via existing successful attempts
,

from companies
and universities

like

IBM and
the
University of Texas at
Austin,
at

crea
t
ing

a graphene based transistor.

With the
se cur
rent experimental successes transpiring
worldwide
, the rise of the graphene transistor and fall of the
silicon t
ransistor could occur within years
. This rise grants
the opportunity to increase energy efficiency and speed in
consumer computers
globally.


Key Words

Graph
ene, Transistors,
Graphene MOSFET,
GFET,
Metal
-
Oxide Field Effect Transistor,
Single Layer
Carbon Atom
s
, Graphene Bandgap, Silicon Carbide
,
Tungsten Disulphide


INTRODUCTION:
TRANSISTORS

TODAY
AND GRAPHENE


Computers, an integral
part of many lives around the
world, house a multitude of components


motherboards,
capacitors,

gr
aphics and video cards, optical
drives


but one
component in particular is essential for the operation of the
se

computer
s
, the transist
or.
Transistors are

mainly responsible
for controlling voltage and amplification by manipulating
the flow of electrons through th
e semiconducting material
.
These functions make the transistor a major element of not
only a computer's architecture, but
of
any electronic device
's
architecture

[1].

MOSFETs, metal
-
oxide
-
semiconductor
field effect transistors, for many years
,

have utilized silicon
for the metal
-
oxide semiconductor inside the transistor.
In
recent years however, innovations and discoveries in
electronics, specifically the realm of transistor architectures,
have brought a
new, thinner material to light:
graphene, a
single atom allotrope of carbon.

Graphene was d
iscovered in 2004
,

by
Profes
sor Kostya
Novoselov of Manchester University

and his colleague
Andre Geim
,

by peeling layer after layer of graphite from a
pencil
tip
with scotch tape, until
only an

extremely thin
layer, one atom thick
, was peeled away

[2
].
Not only is

graphene

much thin
ner than silicon, but it also has man
y
other qualities superseding silicon.

F
or example, graphene

“has extremely high carrier mobility …, can absorb light
over a range of wavelengths in the electromagnetic spectrum
from the visible to mid
-
infrared and is h
ighly transparent to
light”

[
3
]. This means that unlike the chaos and collisions
that occur

between electrons trying to flow from one
terminal to another

in the silicon transistors, the graphene
transistors allow the electrons

to

behave like beams of light

that move freely through the honeycomb lattices
. This
improved movement also prevents
the

loss of energy,
common in silicon based transistors

[
4
].

A greater degree of

free movement
ultimately
allows the
transistor to operate at much
higher

frequencies, a
s proven
by IBM’s first cultivated graphene transistors
,

"t
hat could
switch on and off at 100 billion times per second. The 100
-
gigahertz speed is about 10 t imes faster than any silicon
equivalents
"

[
5
].
Halfway around the globe, in Germany, the
University

Erlangen
-
Nuremberg

has also cultivated their
own graphene transistor using silicon carbide

[
6
]
.

Refining the graphene transistor, via
new methods in

cultivati
ng an optimal
graphene substrate
,

provides the

necessary tools to build the next generation transistor. These
new transistors present the potential
for more energy
efficient and faster computers [
6
].


TRANSISTOR BREAKDOWN


Transistors are an essential part of all modern
electronics.
Field
effect
transistors
, a very common type
,
consists

of usually three, sometimes four, terminals to which
electrons are received and released. Usually, the electrons

flow from one of the terminals, the source, through a
semiconducting substrate, which since the 1960s

has
commonly been silicon, and then
are

directed

by one or two
terminals forming the gate.
The semiconducting substrate in
transistors can either be
P
-
channel or
N
-
channel,

as shown in
figure 1. Being P
-
channel or N
-
channel refers to whether

the
electron
carrier in the semiconducting substrate is a grid of
holes or electrons

[1]
.
Voltage
from the gate charges the
semiconducting substrate

and turns the substrate either "on"
or "off", which

allows

or disallows

electrons

to flow through
the
semiconducting
material
.
Once
allowed or disallowed to
flow through

the semiconductor
, the electrons are released
throu
gh the last terminal, the drain
[1].


Zachary Gannon

Jacob Guttenplan




2


Field effect transistor diagram displaying terminal layout [7]

FIGURE 1


This movement

of electrons flowing
from


the
source
,

to

the
substrate and gate
,

and finally to
the
drain
, which occurs
constantly within the cycles of the circuit ry the transistor is
wired into,

allows transistors to operate
various

vital

mech
anis ms crucial to the success of many microelectro
nic
devices.
These mechanisms include
t wo

of many

transistor’s
main functions
:

amplification

and

switching [7].

Amplification is the ability to take an electric signal on
the gate and use that signal to control a larger signal at the
source and the drain.

Transistors acting as amplifiers take a
source voltage,
and then

through the use of various logic
gates in the gate terminals
,

augment the signal, outputting a
much greater signal.
Amplifiers are commonly used for
signal
augmentation

and sound reproductio
n

[
7
]
.

The other main fu
nction of transistors,
act
ing

as a switch,
involves a signal on the gate switching

the signal on the
source and drain, between 1 and 0, otherwise known
respectively as on and off.
Many logic gates in
microelectronics
are
comprise
d

of transistors acting as
switches, creating combinations of multiple transistors on
and/or off.
This switching is accomplished when a transistor
receives voltage at its source,
manipulates

the voltage
according to the signal it receiv
es

from the gate, and

sends
the new signal with a changed voltage out the drain.
[
7
]
.

A key factor in the entire operation of any transistor lies
ultimately in the semiconducting substrate through which the
source and the drain trans
mit to interact with the gate. One
major qua
lificat ion

of

a good semiconducting material,
for
example,

is a low bandgap value
[1]
.



WHY GRAPHENE?



Though silicon presents an acceptable medium for the
semiconductors in transistors, graphene presents a medium
bound to set new standards. Graphene's q
ualities in the
mechanical, physical, electronic, and thermal aspects greatly
surpass those of silicon. Not only are

graphene's

qualities
greatly superior

to silicon's
, but
these qualities also offer
conditions for improved sustainability in graphene based

transistors.


Sustainability holds many interpretations and definitions.
However, in the realm of graphene based transistor
sustainability,
we

interpret sustainability as
the

ability
for
something
to prove its efficacy

throughout time while
consuming minimal resources. In graphene's various
improved qualities, this interpretation holds true for many
instances.


Mechanical

Q
ualities


Since graphene is only an atom thick and nearly invisible
to the naked eye when looking
from the side, one would
expect it to be very weak or brittle. In fact, graphene is
extremely strong.

Using Atomic Force Microscopy,

a type
of scanning microscopy used
in

measuring certain criteria of
an object

at a nanoscopic scale,

s
cientists have deter
mined
that "
graphene is harder than diamond and about 300 times
harder than steel
"
[9]
.
This strength is measured by tensile
strength, t
he
amount of
tension

an object can experience
before breaking or failing.

Diamond has no definite literature
tensile
str
ength;
however, diamond

has an approximate

measured

tensile
strength of about 60 GPa, or sixty
-
billion pascals, while
g
raphene has
a
tensile strength
greater than

1TPa, or one
-
trillion p
ascal
s

[9]
.
Silicon, specifically polysilicon, the
most
commonly utili
zed allotrope of silicon in microelectronics,
only has a tensile strength of

1.2 GPa
[10]
.

While the
difference in strength between silicon and diamond is
significant, the difference in strength between silicon in
graphene is astoundingly high. This much
greater tensile
strength allows graphene to be manipulated to smaller and
smaller sizes before

fracturing and malfunctioning.
As
discovered by researchers at
the University of Texas at
Austin
, graphene is so strong it can "

survive being run over
by a movi
ng vehicle
...
without suffering damage to
[its]
outstanding properties
"

[3].

Not only is graphene extremely
strong, but it is also very pliant.
Graphene is able to stretch
to about twenty percent greater than its
natural

length
[9]
.

Graphene's pliancy
and ease of use at miniscule sizes
provides the possibility of implementing graphene based
transistors not only in computers, but span into even smaller
spaces, like in smart phones and mp3 players. These two
qualities alone allow for smaller hardwa
re, req
uiring less
raw materials
.

This lesser amount of material needed to
construct graphene transistors provides a much
higher level
of sustainability
, in that many more graphene transistors can
be made either using the same amount of material as a batch
of sil
icon transistors, or even using much less material.


Physical Q
ualities


Though the mechanical properties of graphene are vastly
impressive, t
he single atom thickness

and structure

demonstrates

one of
graphene's
greatest
advantages over
silicon.
On the ato
mic level, graphene has exceptionally high
Zachary Gannon

Jacob Guttenplan




3

quality crystal formations and an organized layer of
hexagonal lattices
, as shown in figure 2

[3]
.




G
raphene crystal lattice structure [
6
]

FIGURE 2


Graphene's

lattice structure forms the tunnels and pathways
t
hrough which electrons flow when a stream of them moves
through the semiconducting substrate and gate of the
transistor.

For example, electrons move through the tunnels
much more efficiently and quickly, allowing for greater and
much more desirable electri
cal and thermal features.
Because the crystals are of such

high quality and the lattice
is
only
a single atom thick, electrons are able to act much
more conveniently than the many atoms thick silicon

[6]
.




Silicon crystal structure
[11]

FIGURE 3


This
thickness

within the structure of silicon crystals

is
created by the crisscrossing of branches of
anisotropic
crystalline material
, as shown in figure 3
. W
ithin the cubic
symmetry of the crystal, there are certain trends to the
direction of the branches. T
hese different directional branch
trends, known as integer groups, leave tangle
d

and cluttered
tunnels for electrons to pass through, and are the main
reason for silicon's structural

inferiority to graphene
's
organized, thin crystal structure

[11]
.


Electrical

Qualities


Because graphene consists of almost perfect
crystalline
structures that form

grids of open lattice, electrons in the
electricity flowing through the graphene substrate are able to
act in

a

much mo
re favo
rable manner

electronically
tha
n
silicon.

In silicon, the channels and tunnels, through which
electrons pass from source to gate to drain, are filled with
atoms that can obstruct the path of the electrons

[4]
. These
obstructions cause collisions, thus a lack of electro
n flow.
This lack

of electron flow causes a drop in electric current,
the amount of electrons flowing through a given ci
rcuit over
a period of time, as well as an

energy leakage, when energy
dissipates from the transistor into heat energy
released
into
the atmosphere.
These current and energy drops and leaks
cause a direct drop in voltage, essential to the ideal operation
of not only transistors, but all electronics. This

drop in
voltage

presents a major issue in silicon based transistors.

Graphene, however,
can
overcom
e these issues.
Graphene's thin
, organized lattice crystalline structure grants
graphene very high carrier mobility, the extent to which
electrons can freely move through a substrate [3].
G
raphene's carrier mobility has an approximate mobility of
the order

of 10
6

cm
2
Vs
−1

[8].
According to the r
esearchers at
the University of Manchester who discovered graphene, the
carrier mobility is so high that "
electrons are able to flow
through graphene more easily than through even copper. The
electrons travel through
the graphene sheet as if they carry
no mass, as fast as just one hundr
edth that of the speed of
light"
[9]
.
This increased velocity, known a
s the electron
drift velocity,
allows for much greater current to pass
through the transistor overall
, as calculated

from

equation 1.


i
=
nAev
d







(1)
[12]


In the equation,
i

represents the current flow,
n

represents
the amount of charge carriers per unit volume of the
transmitting medium,
A

represents

an infinitesimal cross
sectional area which must be perpendi
cular to the current
flow, e
represents

the elementary charge (1.602 x 10
-
19
), and
v
d

represents

the drift velocity of the electrons

[12]
.

The
high
carrier mobility due to graphene's open hexagonal lattice
structure not only allows for greater drift velocit ies, but it
also provides a greater amount of n, the
amount

of
charge
carriers per
unit
volume. This
increased amount of charge
carriers
is al
so due to the fact that graphene, because it is
two dimensional, has a very s mall volume. Because both
v
d

and
n

are directly proportional to
i
, the high drift velocities
exhibited by beams of electrons and impressive carrier
mobility proves a higher potent
ial current flow
.

This
potentially greater current flow allows the transistor to
maintain energy and leak very little. The s mall amount of
energy leaks correlate
s to less energy radiation in the
surrounding environments, proving better efficiency and
susta
inability.


Furthermore,
the electrons' high velocities could allow
graphene to switch on and off at much greater frequencies.
This can be explained by equation

2.


f

=
v







(2)
[13]


In equation 2,
f

represents frequency,
v

represents the
velocity
of a beam of electrons, and λ (Greek letter lambda)
represents the wavelength of the
sinusoidal,
oscillatory
motion of the

electron

movement through the transistor
medium, or the number of nodes through which the path of
electrons flow in a wave

[13]
. Sinc
e graphene can be printed
Zachary Gannon

Jacob Guttenplan




4

into long sheets and
be
stretch
ed

up to twenty percent of its
natural length, one would assume the wavelength would be
very high

[9]
. This is not the case, however, because
graphene is only two
-
dimensional and has the organized gr
id
of

honeycomb lattices.
These qualities of graphene allow, as
stated before, electrons to flow in straight paths without
collision, at essentially wavelengths of one. As with
anything, error is expected, thus collisions have a chance to
occur, causing sl
ight oscillations and wavelengths greater
than one. In an ideal situation, the wavelength of one proves
an exceptionally high velocity would correspond to an
exceptionally high frequency due to their direct
proportionality.

Researchers at the University of Texas at Austin have
developed a flexible graphene transistor that
further
demonstrates graphene's increased frequency over silicon.
Their transistor design consists of layered graphene with a
plastic sheet in the middle
,
e
mbedded with mul
ti
-
finger
metal gate electrodes.

These graphene and plastic layer

transistors are capable of speeds upwards of 2.2 GHz, far
more than the typical silicon transistor
s
.

Since the University
of Texas at Austin's transistors are cult ivated

by c
hemical
vapor deposition, one of the most accurate gra
phene
production methods, the probability of consistent results is
very likely

[3]
.

With mathematically proven and research demonstrated
increases in current flow

and frequenc
y, graphene provides
more
ideal electrical conditions for the semiconducting
substrate in transistors, due largely to the extremely fast
electron drift velocity.


Thermal Qualities


In addition to the increased current flow

and frequency
,
t
he
exceedingly

fast

velocit ies

and improved carrier mobility

exhibited by electrons passing through the graphene
also
grants

it

very high

thermal conductivity

[2]
.

Thermal
conductivity is the ability

of a substance to retain a certain
amount of heat. This is a very important factor sin
ce "
even a
small increase in
[temperature]

results in reduction of
device
's

lifet ime
," according to researchers in the
e
lectrical
e
ngineering

d
epar
tment

at the

University of California
-
Riverside

in California
[14]
.
This thermal conductivity has
the
potential to allow graphene transistors to operate for
long
,
power consuming operations, before the transistor fails
or malfunctions
, directly resulting in longer lifet imes for
circuitry involving transistors
.

Aforementioned researchers at the University o
f
California
-
Riverside did many of the standard test
s

used to
measure thermal conductivity of a substance, including
thermal micro spectroscopy
, a very precise test used to make
observations at an almost atomic level. Receiving less than
satisfactory resul
ts from
standard tests, the researchers

design
ed

their own method. Th
eir new

method, based on

another topical thermal test
(
c
onfocal micro
-
Raman
spectroscopy
)
, uses a laser beam directed in the center of a
single layer of graphene (SLG) that has a diameter

of about
1 x 10
-
6

meters
[14]
.
From this test, the researchers obtained
the following data:


A fraction of the excitation light (λ = 488 nm) is
absorbed by graphene, which results in the heating power
P
G
, while the remaining light is absorbed by the tren
ch.
Since K of the air is negligible, the heat generated in
graphene laterally propagates through the layer with the
thickness of a
G

= 0.35±0.01 nm toward the heat sinks on
the sides of the flakes.
[14]
.


This very low excitation light fraction means that
graphene
utilizes most of the power sent through it, leaking very little
energy. The energy instead disperses into the graphene
medium to the edges that provide the greatest thermal
conductivity. Because graphene's cross sectional area in the
tunnels is so

small, any energy dissipation reads only as
small increments in the "rise of local temperature"
[14]
.

Another thermal property examination comes from
researchers at the University of Texas at Austin, where a
graphene transistor they cultivated is said to
"
absorb light
over a range of wavelengths in the electromagnetic spectrum
from the visible to mid
-
infrared and is highly transparent to
light”

[3]. These qualities allow graphene to experience
many different light exposures without radiating heat energy
as

a result of the exposure.

This ability to experience a
myriad of situations while preventing energy drops provides
another greater level of sustainability. The very small
amount, if any amount, of energy loss allows for a more
efficient transistor, due to

the ability to experience different
sustained and incident lights.



Graphene

Silicon

Tensile
Strength

>1 Trillion Pa

[9]

1.2 Billion
Pa [10]

Size

1 Atom Thick

(
See Figure

2)

Several atoms thick

(See Figure 3)

Electron
Mobility

1.0 ×
10
6

cm
2
Vs
−1
=
xUz
=
1.4=×=1M
3

cm
2
Vs
−1
=
xUz
=
bnergy=
ioss
=
negligible
=
R
J
㄰1
=
=
tith=the=combined=éroéerties=of=single=atom=thick
ness=
and=
near
J
éerfect= crystalline= lattice= structure
I
=
resulting= in=
tremendously=high=carrier=mobility=and=thermal=conductivityI=
graéhene= flaunts= a= éromisi
ng= array= of= enhancements= for=
transistors=imélementing=graéhene=rather=than=éurely=silicon.
=

THE PROBLEM WITH GRAPHENE


Though graphene has a multitude of features that could
enhance
a
transistor
'
s
operational capacities
to potentials
beyond
some of the
most powerful transistors of today
,
it
also

has a list of drawbacks preventing the mass production
Zachary Gannon

Jacob Guttenplan




5

of graphene transistors.
Two of these issues lie in graphene's
extreme conductivity and
lack of
a
bandgap.

Both of these
issues create strong impedances on t
he mass production and
integration of graphene transistors in consumer computers.


The Extraordinary Conductivity


Graphene is said to be the world's greatest conductor,
which creates a problem: transistors require semiconductors,
not super conductors.

Gr
aphene's super conductivity
disallows an off or zero state to be reached. With switching
being a major function of transistors, this super conductivity
a major problem needed to be fixed.


The conductivity of graphene exceeds that of most other
substances
used in electronic components today
.
With nearly
100 times the conductivity of copper, a single layer of
graphene is capable of a carrying capacity of 10
8
A/cm
2
, with
researchers at Georgia Tech
obtaining results
exceeding
10
9
A/cm
2

in certain
experiments

[1
5]
.
This high carrying
capacity is what allows graphene to experience much higher
currents.
The hexagonal nature of graphene also allows it to
have a theoretical electrical resist
ivity

of
10
-
8

Ω·m,

less than
the resistance of silver which has the lowest resistance of
any known substance

at

1.59 x 10
-
8

Ω·m

[16]
.

Because
graphene's resistivity is so small, current flows extremely
easily, to a point where there is essentially no resistance
to
current f
low. Combining
a
great
ease of flow and
an
ability
to experience very high current values produces

graphene's

inability to switch off. This inability to switch off

leads to
another of graphene's fatal flaws, a lack of a bandgap.


The Zero
Bandgap


As noted
, traditional transistors use silicon as a
semiconductor, as it has a low bandgap. Simply put, a
bandgap is the difference in the amounts of energy required
for electrons to jump into the conduction band, triggering the
transistor. Materials with high band
gaps act as insulators,
while those with low bandgaps are semiconductors. The
bandgap of silicon is 1.11 electron volts

[4]
. Graphene, in
comparison, does not have a band gap because of its perfect
hexagonal nature, without the need for additional electron
s
to excite it into the conduction band.

For this reason,
graphene i
s always in a conductive state,

meaning that it is
always in the
"
on
"

state; “
Current can be made to move
back and forth, but it can't easily be turned on and off,
meaning there'
s no easy

way to represent bits” [4]. This
inability to turn off creates problems with constructing one
of the main components transistors are used for: inverters
,
logic gates that
allow

an input voltage to change the voltage
state to be on or o
ff through different

outputs
[17]
.



"Symbol, circuit structure, and truth table of a CMOS
inverter"

[17]

FIGURE 4


A typical inverter is comprised of two CMOS transistors in
series, as shown in figure 4. Inverters rely on the ability for
one of the transistors to turn off, while allowing the other to
be on, in order to correctly manipulate current flow [17].
Inverters
happen to be a very common application of
transistors in digital logic, the conditions of microelectronic
operation. Since inverters are so common, graphene must fit
the conditions of
an inverter. However, graphene's
lack of
bandgap prevents inverter

imple
mentation
, posing a great
problem in incorporating graphene transistors in typical
electronics, especially computers.


CREATING A BANDGAP


The fact that graphene
's high electrical conductivity
causes it to lack a bandgap provides an immediate course of
act
ion; create a small bandgap to allow graphene to switch
off. Many of the methods and experiments performed utilize
a compliment to the single atom layer graphene substrate.
Many major successes branch from two methods in general
,

though, silicon carbide
an
d graphene wafers and graphene

grafted to tungsten disulphide.


Silicon Carbide Wafers


One of the first

major

successful attempts at creating a
graphene field effect transistor (GFET)

employs

the process
of cultivating wafers of silicon carbide

(SiC)
, a

complex
crystalline structure of silicon and carbon. Only the topmost
layer of silicon ions is

driven off, leaving a small layer of
just carbon in the form of graphene. With
the
wafer
cultivated, lithographic etching, engraving done by a “high
-
energy beam of charged atoms” [6], creates the paths to
which the transistor
components

will lie.


Zachary Gannon

Jacob Guttenplan




6


Silicon carbide graphene field effect transistor [8]

FIGURE 5


A key step in this etchin
g process is feeding a bit of
hydrogen gas into the etchings, changing the reactivity of the
graphene and silicon carbide.
The hydrogen gas allows the
conducting SiC doped layer to chemically bond with the
lithographically etched interface
, as shown in fig
ure 5 [8].
This change in reactivity
also
grants silicon carbide based
graphene transistors the properties of many ideal
semiconductors, especially the
creat
ion of a

bandgap

[6]
.

With this bandgap established, creating a graphene transistor
becomes a much
less arduous task, to the point where
multiple companies and research groups have successfully
crafted their own silicon carbide graphene field
-
effect
transistors.

One company showing success in silicon carbide
GFETs

is IBM.
Research at IBM
, a major
computer component
manufacturer,

has paved the way to creat ing graphene
transistors that are capable of
surpassing

the capabilities of
silicon

field
-
effect

transistors.
IBM's graphene transistor
employed the common silicon carbide wafer cult ivation, but
us
ed gold for the contacts between the etched surface and
silicon carbide wafer,

as shown in figure 6,

since gold has
favorable bonding qualities for carbon [8].
Not only have
they successfully created an operational SiC GFET, IBM has
created one with
proper
ties
surpassing

the highest measured
values of silicon based transistors, in many aspects.



Silicon carbide GFET cultivated by IBM [8]

FIGURE 6


One
of IMB's graphene transistor's

astounding
properties

lies
in the high frequency values. IBM's locally cul
t ivated
graphene field
-
effect

transistors are capable of
operating at
speeds of 100 GHz, approximately 10 t imes faster than
the
frequency capabilities of traditional silicon MOSFETs
.
These transistors are compatible with existing manufacturing
processes an
d work in the same manne
r as their silicon
counterparts

[8]
.


As described in "
The Extraordinary Conductivity
,"
researchers at Georgia Tech have created a similar silicon
carbide wafer GFET, but instead use sheets of plastic with
patterns previously drawn in. The created GFET exhibits
extreme
carrying capacit
ies upwards of
10
8

A/cm
2

[8].
The
development of this m
ethod means that the graphene can
easily be fabricated on pre
-
patterned plastic sheets and then
integrated into the transistor, instead of producing them one
at a time, allowing this to be a very viable option when it
comes to mass production options.
This

ability to mass
produce allows less waste of materials, providing great
sustainability.
With these transistors also being resistant to
liquid, this makes them a viable option in consumer
electronics, as many consumers have a tendency to spill
liquids on t
heir devices on occasion.


Tungsten Disulphide



Researchers at the University of Manchester have
designed a graphene transistor that works in much the same
way as a tradit ional silicon transistor. By designing a
transistor with an atom
-
thick layer of tung
sten disulphide
(WS2) between two atom
-
thick layers of graphene, they
have successfully designed a transistor that works in the

same

traditional sense. The use of WS2 as a barrier material
allows the transistor
to experience

the off state that most
graphen
e transistors lack

[18]
. The chemical properties of
tungsten disulphide
, namely its ability to decompose and not
melt at
1523

K (1250 C),

allow electrons to cross

the
semiconducting substrate

either by going over or under the
ba
rr
ier. When the transistor i
s off, very few electrons can
cross, but when it is turned on, electrons can cross both
under and over the barrier. The off state is achieved by
applying a negative voltage to the transistor’s gate, and is
turned on when a positive voltage is applied.
The
physical
properties of

graphene transistors
makes them one the

highest performance t ransistors ever designed, rivaling the
fastest silicon transistors on the market

[18]
.
Since grafting
things to graphene usually causes hotspots for energy
leakage, one wou
ld think grafting WS2 to graphene would
allow less efficient transistors [6]. However, this is not true
due to t
ungsten disulphide
’s layering

in nature and chemical
inactivity
, allowing it to be layered perfect ly with the
graphene.
This natural layering le
ading to less hotspots also
prevents a release of radiation into the surroundings, proving
to increase overall sustainability. Tungsten disulphide's

layering
has
implemented
it

in batteries since 1992, and has
now

found its way into transistors

[18]
.





Zachary Gannon

Jacob Guttenplan




7

CONCLU
SION: GRAPHEN
E HAS THE
POSSIBILITY TO OUST SILICON


People worldwide spend hours writ ing papers or
playing
video

games on a computer, listening to music on a mobile
device, and surfing the web on a smart phone, to the point
where these activities def
ine some social cultures. Each of
these devices essentially contain
s

a small computer with all
the similar components.
Transistors

in particular

are an
essential

part of all modern electronics. With a culture so
reliant on these devices and electronics, th
e transistor plays
one of the most important roles in maintaining operational
status.

In f
ield effect transistors, a very common type of
transistor electrons flow in from the source, through a
semiconducting substrate

where the electron's voltage is
manipulated

the gate
, and finally released through
the drain
[1]
.

The
material the semiconducting
substrate

is created
from

and orientation of the substrate is crucial in making
sure the desired voltage is

outputted, whethe
r that voltage
output needed to be amplified or switched on or off for a
logic gate. With its many qualities superior to silicon,
including qualities in the realms of mechanical, physical,
electrical, and thermal properties, graphene poses as a
promising c
andidate for that very semiconducting medium.

Like
all substances and materials known, though
,
graphene has a list of flaws and impurit ies
, such as the super
conductivity and lack of a necessary bandgap,

preventing it
from becoming that one “end all, be al
l” material.
However,
graphene
has a significant a
mount of improved qualities

outweighing many
of the

minor
faults
,
and a number of
successfully created experimental
graphene field
-
effect
transistors, utilizing complex compounds with a transition
metal or
metalloid and a non
-
metal ion. Two of these GFETs
have been successfully created using compounds of silicon
carbide and

tungsten disulphide, which can also be
reproduced.
These solutions are not only reproducible, but
they are also sustainable.
These repli
cable graphene
transistors provide revolutionary solutions to the major
problem
preventing

the mass production

of more efficient
and much faster

field effect transistors
.

Now that companies and research groups find new,
successful methods to create graphen
e transistors, graphene
has become an ext remely viable medium for the
semiconducting substrate in transistors. When graphene will
oust silicon is yet a mystery, but with continued efforts and
determination, the graphene transistors may likely become
the le
ading product speeding up the electronic conversion
within the electronic devices integrated in everyday life.


REFERENCES


[1]

Y. Cui
, Z. Zhong, D. Wang, W. Wang, C. M. Lieber.
(2003, January 1). "
High Performance Silicon Nanowire

Field Effect Transistors
."
Nano Letters.

(Online article).
DOI:
10.1021/nl025875l

[
2
] S. Connor. (2011, July 25). “Graphene discovery may
lead to faster computers.”
The Independent
. (Online article).
http://www.independent.co.uk/news/science/graphene
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discovery
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may
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lead
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to
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faster
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computers
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2319914.ht ml

[
3
] B. Dumé. (2012, December 10). “F
lexible graphene
transistor sets new records.”
Physics World
. (Online article).
http://physicsworld.com/cws/article/news/2012/dec/10/flexib
le
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graphene
-
transistor
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sets
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new
-
records

[
4
] C. Sung, J. Lee. (2012, February). “Graphene: The
Ult imate Switch.”
Spectrum.

(Online article).
http://spectrum.ieee
.org/semiconductors/materials/graphene
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the
-
ultimate
-
switch


[
5
] J. Hsu. (2010, February 5). “IBM Demonstrates 100GHz
Graphene
-
Based Transistors.”
Popsci.

(Online article).
http://www.popsci.com/technology/article/2010
-
02/graphene
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based
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computers
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may
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end
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silicon
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[
6
] J. Palmer. (2012, July 18). "
Graphene transistors in high
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performance demonstration
."
BBC

News
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http://www.bbc.co.uk/news/science
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environment
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18868848

[7] (2009, August 27). "Introduction
to FET
-
Field Effect
Transistor
." Circuits Today. (Online blog).
http://www.circuitstoday.com/fet
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field
-
effect
-
transistors
-
introduction

[
8
] S.
Hertel. (2012, July 17
). “
Tailoring the
graphene/silicon carbide interface for monolithic wafer
-
scale
electronics
.”
Nature Communications
.

(Online
article
)
.

D
OI:
10.1038/ncomms1955
. pp. 2
-
3

[9]

"Graphene: Made in Manchester."
The University of
Manchester.

(Online article).
http://www.graphene.manchester.ac.uk/story/proper
ties/

[10]

W. N. Sharpe, B
. Yuan, R. Vaidyanathan. (1997).
“Measurements of Young’s Modulus, Poisson’s Ration, and
Tensile Strength of Polysilicon.”
IEEE
Journal of
Microelectromechanical Systems
. (Online article).
http://clifton.mech.northwestern.edu/~me381/papers/mechte
st/sharpe2.pdf

[11]

M. A. Hopcroft. (2010, April). “The Young's Modulus
of Silicon

A Simple Explanation.”
IEEE Jo
urnal of
Microelectromechanical
Systems
.

(Online article).
http://silicon.mhopeng.ml1.net/Silicon/

[12]

D. Halladay
. (2012). Fundamentals of physics.
Hoboken, NJ: John Wiley and Sons Inc. (Print book). pp.
685
-
686

[13]

D. Halladay. et. al.

pp. 417
-
418

[14]

S. Ghosh, I. Calizo, D Tewelderbrhan. (2008, April 16).
"
Extremely high thermal conductivity of graphene:
Prospects for thermal management applications in
nanoelectronic circuits
."
American Institute of Physics
.
(Online article).
http://apl.aip.org/resource/1/applab/v92/i15/p151911_s1?vie
w=fulltext&bypassSSO=1

[15]

S. Bush. (2009, August 5). "
Georgia Tech claims 100x
copper conductivity for gr
aphene interconnect
."
ElectronicsWeekly.
(Online article).
Zachary Gannon

Jacob Guttenplan




8

http://www.electronicsweekly.com/Articles/05/08
/2009/466
77/georgia
-
tech
-
claims
-
100x
-
copper
-
conductivity
-
for
-
graphene
-
interconnect.htm

[16]

L. Tune. (2008, March 24). "
Physicists Show Electrons
Can Travel More Than 100 Times Faster in Graphene
."
University of Maryland Newsdesk
. (Online article).
https://newsdesk.umd.edu/scitech/release.cfm?Art icleID=16
21

[17]

"CMOS Inverter." (2013).
Sakshat Virtual Labs
.
(Online virtual lab).
http://iitg.vlab.co.in/?sub=59&brch=165&sim=901&cnt=1

[18]

L. Zyga. (2013, January 22). "
Graphene
-
based
transistor seen as candidate for post
-
CMOS technology
."
Phys.org

(Online art icle).
http://phys.org/news/2013
-
01
-
graphene
-
based
-
transistor
-
candidate
-
post
-
cmos
-
technology.html


ACKNOWLEDGMENTS


We

would like to acknowledge and extend
o
ur

heartfelt
gratitude to the following persons who have made the
completion of this possible:


Dr. Dan Budny, Head of Freshman Engineering, for writing
Introduction to Engineering Analysis
, a great source of
inspiration.


Zachary Koopmans, for providing a

great source of
background knowledge

and assistance.


Gregory Morgan, for inspiring a greater
interest

in

graphene
technology through thoughtful class discussion.