7. GRAPHENE IS COMPOSED OF A
SHEET OF CARBON ATOMS
ARRANGED IN A HONEY-COMB
CRYSTAL LATTICE
GRAPHENE- THE RISE OF THE SUPER MATERIAL
8. Researchers have shown that
a few layers of graphene
stacked on top of each other
could act as formidable
material for optical switches
delivering speed up to 100
times faster than current
technology
13. Ultrafast Switching
•Conventional 1/f frequency dependence
•high carrier mobility
•IGAIN 1/f
• 26GHz at Gate length(l)=150nm
THE EXPERIMENT:
Mechanical
exfoliation
Source and
drain (1nm)
12nm Al
(ALD),250ºC
TMA+NO2
Metal
deposition
14.
15. EXPERIMENTAL RESULTS
TRANSCONDUCTANCE(Gm) Gm= Id/Vd
FIELD EFFECT MOBILITY(μ) ∆ =q. ∆n.
μ
μ= 400 cm2/V.s (estimated)
•Distortion in field mobility can mainly arise due to deposition of
Top Gate Dielectric which reduces both field effect mobility &
device Gm
•Charge impurity scattering
16. DC Electrical Characteristics of GFET
•Vds=Vgs-Vt at Drain bias ,Vd=100mV
• for the sub-threshold region i.e. Vgs<Vt
•Terminal voltage=1.6V
•-Gm denotes p-type transport dominance
• +Gm denotes n- type transport dominance
• Gm=Vd at Vd=1.6V
17. Fig(4a): h21=small signal current gain
h21= iD/iG
fig(4b): 1/f dependence of h21 and also
ft=h21xf for h21=1(figure of merit)
High Frequency Response Measurement of GFETs
(HP8510- vector network analyzer)
•AC current and Voltages are directly related by
scattering parameter for drain and source
• Open, Short and Load calibration employed to
network analyzer to de-embed signals to
calculate parasitic gate capacitance
•h21 1/f
•Ft= h21 x f (here ~4Ghz)
• -20dB slope for c. FET for Z=1/j.w.Cg
18. Figure5: At DC bias condition
Graph 1 :ft vs. Vg showing 1/f dependence all the way
Graph2: gm vs. Vt graph with max. cut off at gm=1.6 at
Vt=0.5v
•For graph 2 maximum Cut off of ~4GHz at Gm=1.6mS
•In FET, ft=Gm/2 .Cg
• Cg=~80fF for gate area 360nm x 40μm
Figure 6: ft varies inversely with square
of gate length (l)
DC Bias Condition
• Gate Length(l): 500nm 150nm
•fcutoff=4GHz 26Ghz
19. f 1/ɭ²
Generally, fcutoff =1/ ζ = Vd/lg
Now, for linear region operation of GFET(Id-Vd) Vd= μ.Ed
and Ed 1/l for given drain bias
So the final Equation is f μ .(1/lg).(1/lg)
20. Effect of using Metal Contacts
Contact Induced Defect
•BAND ALTERATION: Charge transfer takes place from Co contact to source and drain
•In negative Gate region, anomaly in Transfer characteristics is reported
•Shift in Fermi level
• Diffusion of Co atoms into graphene channels
21. Skepticism of carrier mobility
Fig.1 Cross-section of N-channel Si
MOSFET
Fig.2 transfer Characteristics of Si
MOSFET
24. References
1. Graphene Electronics: Materials, Devices, and Circuits by Yanqing Wu,
Damon B. Farmer, Fengnian Xia, and Phaedon Avouris
2. Graphene put down still decades to replace current Si-tech an article by
Joel Hruska
3. Operation of Graphene Transistors at GHz Frequencies by Yu-Ming Lin*,
Keith A. Jenkins, Alberto Valdes-Garcia, Joshua P. Small, Damon B.
Farmer, and Phaedon Avouris
4. Transfer Characteristics in Graphene Field-Effect Transistors with Co
Contacts by Ryo Nouchi, Masashi Shiraishi and Yoshishige Suzuki
5. Graphene-Fundamental and Emergent Applications by Jamie H. Warner,
Franziska Schaffel, Alicia Bachmatiuk, Mark H. Rummeli
6. Direct Growth of Graphene Film on Germanium Substrate by Gang
Wang, Miao Zhang, Yun Zhu, Guqiao Ding, Da Jiang, Qinglei Guo,Su Liu,
Xiaoming Xie, Paul K. Chu, Zengfeng Di & Xi Wang
7. Graphene transistors by Frank Schwierz, Nature Nanotechnology
