research issues in graphene field efffect transistors

1. Research Issues in Graphene Field
Effect Transistor
Supervised By : Presentation By :
Mr. Arvind Rajput Daljeet Singh Motton
ME(ECE) 13-703

2. Graphene
• is a 1-atom thick 2D hexagonal arrangement of carbon atoms.
• Is a zero band-gap material, thus has combined features of semi-conductor as well
as metal.
• Its physical properties include:
– Good conduction of heat
– Stronger than steel and harder than diamond
– Transparent to light
– Can be molded into any shape
• Its electronic properties include:
– Good conductor of electricity
– Capability to operate at +ve and –ve voltages due to its ambipolar property
– Charge neutrality at its dirac point.
– Resistance as function of electric field
– 10 times higher mobility than silicon at room temperature.
Ref : 1. A.K. Geim and K.S.Novoselov, “The Rise of Graphene”. Nature Materials. Vol 6, no 3,
pp 183-191, march 2007.
2. M.C. Lemme, T.J. Echtermeyer, M. Baus, H. Kurz, “A Graphene Field Effect Device”, IEEE
Electron Device Letters, Vol. 28, No. 4, April 2007.

3. Graphene field effect transistor
(construction)
• Graphene cannot be directly used as an semiconductor substrate as it is an zero
band-gap material
• But graphene can be used as an gate in silicon field effect devices.
• Reason for the use of graphene is
1. High mobility that graphene provides (103 cm2 v-1 s-1) over silicon for same operating
conditions
2. Higher current gain than silicon FETs at frequencies as high as 100Ghz for same gate length.
• The dielectric material used can be any of the following
– Hafnium oxide (HfO2), aluminum oxide (Al2O3), yttrium oxide (Y2O3), but yttrium oxide is the
most preferred dielectric due to following properties
• Easy wetting on graphene
• Good insulation property as it
has high dielectric up to 10-20.
• Low leakage current
• High breakdown voltage
Ref : WANG Zhen Xing, ZHANG ZhiYong* & PENG LianMao*, “Graphene-based ambipolar
electronics for radio frequency applications ” Key Laboratory for the Physics and
Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing
100871, China April 29, 2012

4. Research Issue 1
• There is no energy band gap in graphene
• Graphene can only act as metal but not as semi conductor
• There are a no: of methods devised for obtaining the band gap like,
– Converting graphene to graphene nano ribbons(GNRs) but it leads to lowering the ultra
high mobility of graphene
– Another method involves the use of two layers of graphene called as bi-layer graphene,
which when biased by an electric field can generate a band gap of 250meV, this leads to
the construction of dual gate device
• All these methods are not reliable and lessen the unique properties of graphene
• So, there arises the need to devise some method to induce band-gap in graphene,
which can be worked upon.
Ref : Dharmendar Reddy1, Leonard F Register1,
Gary D Carpenter2 and Sanjay K Banerjee1
1 Microelectronics Research Center, The University of Texas at Austin, Austin,
Texas 78758, USA
2 IBM Austin Research Labs, Austin, Texas 78728,
USA, “Graphene field-effect transistors”, July 2011

5. Ambipolar Property of Graphene
• The fig shows the variation of resistance of
graphene with electric field.
– The point of highest resistance is called
dirac point.
– The resistance decreases on either side of
dirac point
• The fig shows the variation of resistivity with the
voltage applied across graphene and
the corresponding fermi energy level
Ref : Melinda Y. Han, Barbaros Özyilmaz, Yuanbo Zhang
and Philip Kim,
“Energy Band Gap Engineering of Graphene ”
Department of Applied Physics, Columbia University,
New York, New York 10027.

6. Ambipolar Property of Graphene in
Practical Circuits
• GFET can be used as an amplifier operating
at GHz frequencies as shown:
• As an frequency doublers.
• As RF mixers
• As digital modulators
Ref :
WANG Zhen Xing, ZHANG Zhi Yong* & PENG LianMao
“Graphene-based ambipolar electronics for radio
frequency applications ” Key Laboratory for the
Physics and Chemistry of Nano devices and
Department of Electronics, Peking University,
Beijing 100871, China April 29, 2012

7. Research Issue 2
• To optimize high frequency performance of graphene two factors need to be
improved:
– Increasing the mobility
– Decreasing the net resistance by decreasing the contact resistance between
metal and graphene
• Mobility can be worked upon by carefully treating the surface before graphene
exfoliation or growth on.
• Contact resistance issue needs to be solved that can be worked upon.

8. Thank you