GRAPHENE TRANSISTOR

19th September 2014VSSUT, Burla

Shital Prasad Badaik Reg. No-11010240

Section:ETC-2 Branch-E.T.C.E

A BREAKTHROUGH MATERIAL

REVOLUTIONARY TRANSISTOR

APPLICATIONS

“BREAKTHROUGH MATERIAL” (Hint: It’s not Silicon)

GRAPHENE IS COMPOSED OF A SHEET OF CARBON ATOMS ARRANGED IN A HONEY-COMB CRYSTAL LATTICE

GRAPHENE- THE RISE OF THE SUPER MATERIAL

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

FABRICATION TECHNIQUES

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

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

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

Fig(4a): h21=small signal current gainh21= 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

Figure5: At DC bias conditionGraph 1 :ft vs. Vg showing 1/f dependence all the wayGraph2: 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

f 1/ɭ²Generally, fcutoff =1/ ζ = Vd/lgNow, for linear region operation of GFET(Id-Vd) Vd= μ.Ed

and Ed 1/l for given drain biasSo the final Equation is f μ .(1/lg).(1/lg)

Effect of using Metal ContactsContact 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

Skepticism of carrier mobility

Fig.1 Cross-section of N-channel Si MOSFETFig.2 transfer Characteristics of Si MOSFET

HIGH FREQUENCY OPERATION

CHANNEL LENGTH

BAND

GAP

CARRIER MOBILIT

Y

CONCLUSION

Versatile properties

Leapfrog applications & products

Engineering Euphoria

References 1. Graphene Electronics: Materials, Devices, and Circuits by Yanqing Wu,

Damon B. Farmer, Fengnian Xia, and Phaedon Avouris2. Graphene put down still decades to replace current Si-tech an article by Joel

Hruska3. 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