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Graphene Transistor By Shital Badaik
The document discusses graphene and its potential use in transistors. It describes graphene as a single sheet of carbon atoms arranged in a honeycomb lattice. Researchers have shown that stacking a few layers of graphene could enable optical switches that are 100 times faster than current technologies. The document also details experiments where graphene field-effect transistors were fabricated with gate lengths down to 150nm, achieving a cutoff frequency of 26GHz. Scaling to smaller gate lengths allows higher frequencies, with cutoff frequency scaling inversely with the square of the gate length. Graphene has potential for high-frequency and versatile applications due to its high carrier mobility and small channel lengths.
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Graphene Transistor By Shital Badaik
- 1. GRAPHENE TRANSISTOR 19th September 2014 VSSUT,Burla Shital Prasad Badaik Reg. No-11010240 Section:ETC-2 Branch-E.T.C.E
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- 6. “BREAKTHROUGH MATERIAL” (Hint: It’snot Silicon)
- 7. GRAPHENE IS COMPOSEDOF A SHEET OF CARBON ATOMS ARRANGED IN A HONEY-COMB CRYSTAL LATTICE GRAPHENE- THE RISE OF THE SUPER MATERIAL
- 8. Researchers have shownthat 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
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- 13. Ultrafast Switching •Conventional 1/ffrequency 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
- 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 Characteristicsof 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 signalcurrent 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 DCbias 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 usingMetal 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 carriermobility Fig.1 Cross-section of N-channel Si MOSFET Fig.2 transfer Characteristics of Si MOSFET
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- 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