1. Graphene Based Transistors-Theory and Operation; Development State
Alex Van Eck
EE4611
04/12/17

2. Overview Moore’s Law Properties of Graphene Band Gap
Graphene Nanoribbons
Future of Graphene

3. Introduction
Major milestone in electronics was the discovery of the transistor in 1948 by physicists at Bell Labs
Moore’s Law
Speed of integration is decreasing
Stability gets poorer at sizes below 10nm
Graphene could replace silicon to help this issue

4. “Moore’s Law” at an end?
Putting more transistors on a chip keeps getting more and more difficult : shortening the distance between conductive channels greatly increases the possibility of current leakage/ heat
Getting to the point where there is little room to improve
Intel: working on 10nm chips
Solve using graphene?

5. Graphene 1 Atom Thick Layer of carbon (2-Dimensional)
Honeycomb Lattice
Best Thermal Conductor
Best Electrical Conductor
Strongest Thinnest Material Known To Exist
Electron mobility 250,000cm^2/Vs
~200 times greater than silicon
Lower heat production and energy consumption
International Journal of Advanced Research in Computer and Communication Engineering
Vol. 1, Issue 4, June 2012

6. Graphene vs Silicon High mobility at room temperature
Symmetric properties for holes and electrons
Thickness
One issue: zero energy gap

7. Bandgap
Graphene’s main problem for use in Semiconductor industry is having zero bandgap
Bandgap allows movement of electrons from the valence to conduction bands
in order for the material to switch currents on and off
In graphene (1 atom thick) valence and conduction bands meet
No bandgap= can not stop current flow
Bilayer Graphene
Graphene Nanoribbon

8. Bilayer Graphene Lamination of two layers of graphene
Zero bandgap, but apply an external electric field across the bilayer graphene to open the bandgap
Bandgap is tunable by the applied electric field strength
Bandgap has been tuned up to .3eV
Widening of the Bandgap has also been confirmed

9. Graphene Nanoribbons Grown Chemically
Synthesize rings of carbon atoms similar in structure to benzene
Heating, under the right condition encourages them to bind together
Heat again stripping most of the hydrogen atoms freeing carbon to form the honeycomb structure of graphene
This process allows control over where each atom of carbon goes into the final ribbon
Could potentially increase the density of transistors on a chip as much as 10000x
Human Hair is 10,000 times wider than nanoribbon

10. Decrease the width of the graphene sheet
Graphene is called a nanoribbon when the width is several times the unit cell of graphene
Graphene nanoribbons exhibit semiconductor or metallic properties: bandgap is larger than 0 depending on how the nanoribbon is structured
Armchair configuration exhibits semiconductor properties

11. Graphene Transistor
Graphene exhibits a pronounced effect to perpendiciular external electric fields, which allows us to use it to build FETs
The graphene transistors show very poor on-off ratios- small voltage gain, but operating frequencies are greater than 25GHz
Researchers have been able to create transistors with an on-off ratio of 100GHz
IBM developed 10k top gated transistors on a .24cm square chip

12. GFET MOSFET-most commonly used Si based device
Electron and hole mobilities In GFETs are almost equal, making the transfer characteristics symmetric
Operation reported higher than Si based FETS
IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 62, NO. 10, OCTOBER 2015

13. Advantages High Frequency Operation Work without much noise
Self cooling
Operate with little voltage
Consume little power
Wide temp range
Great conductor

14. Disadvantages Difficult to turn off
Single sheet of graphene is hard to produce
Small voltage gain
Hard to create on large scale

15. Most Likely/Future Applications
Replace traditional Semiconductors in RF applications
Touch Screens
Rollable e-paper
Foldable OLED
Flexable, thin transistors

16. Conclusion
Graphene transistors could make smaller, faster electronic chips that are achievable with Si
Time will only tell if we can make the use of graphene in semiconductors a reality

17. References
Abe Michelen. “Is Graphene—Finally—A Replacement for Silicon?” Consumer Electronics. 11 Novermber < a-replacement-for-silicon>
“Enhanced performance of graphene transistor with ion-gel top gate”, Carbon 2014
Javad Bavaghar Chahardeh. “A Review on Graphene Transistors” International Journal of Advanced Research in Computer and Communication Engineering Vol. 1, Issue 4, June 2012
Max Lemme. “Potential Applications for Graphene Devices in Nanoelectronics” 2012
Yashushi Iyechikca, “Application of Graphene to High-Speed Transistors: Expectations and Challenges” Science and Technology Trends Quarterly Review No.37 October 2010

18. Topics Issue with using graphene in a transistor? No band gap
Ways to fix the band gap problem with graphene? Nanoribbons, Bilayer graphene
How does one induce a bandgap in bilayer graphene? Apply an electric field
Pros and Cons of using graphene in transistors
Advantages of Graphene vs Silicon