Plasma CVD Carbon Nanotubes CNTs

1
Plasma CVD Carbon Nanotubes (CNTs)

• Michael .A. Awaah
• Elec 7730 Advanced Plasma Processing for
  Microelectronic Fabrication
• Instructor Dr. Y. TZENG
• Fall 2003

2
Outline

• CNTs
• CNTs Properties
• Mechanical Properties
• Electrical Properties
• Growth of CNTs
• Application

3
Questions

• Why are carbon nanotubes so strong
• What re the current limitation in CNT VLSI
  fabrication

4
Carbon Nanotubes (CNTs)

• Carbon nanotubes are one of the most fascinating
  material in recent years, since they show
  exceptional electronic and mechanical properties
  that have triggered an ever stronger effort
  towards application.
• The possibilities are promising and range from
  nanotube composite materials, nanoelectronics,
  scanning microscope probes, chemical and /or
  biological sensors, to cold electron sources.

5
CNTs

• Nanotubes have a unique property in that their
  electronic behavior (semiconducting or metallic)
  is determined by their structure, which also
  determines to a great extent the overall
  properties of devices as wide ranging as field
  effect transistors, flat panel displays, or
  chemical sensor
• This implies a precise of nanotube diameter and
  chirality for molecular electronics.

6
Helicity and sp2 bonding
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Single-walled nanotubes (SWNT)
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Types of SWNT
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Types of SWNT

• Cna1 ma2
• m is zero for all zigzag SWNT
• mn for all armchair nanotubes
• All other SWNT are chiral, chiral angle
• q sin-1 m(3)1/2/ 2(n2 nm m2)1/2

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CNTs Properties

• Electrical properties depends on geometry of
  nanotube
• Roughly 2/3 are semiconductors and 1/3 are
  metallic in random growth
• Tremendous current carrying capability
• 1 billion Amps/cm2
• Excellent heat conductor
• twice as good as diamond

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CNTs Properties

• High strength
• much higher than high-strength steel
• Youngs Modulus 1 Pa (DWNT) and 1.25 TPa (MWNT)
  ( Steel 230 Gpa)
• High Aspect Ratio 1000 10,000
• Density 1.3 1.4 g/cm3
• Maximum Tensile Strength 30 Gpa
• Thermal Conductivity 2000 W/m.K ( Cu has 400
  W/m.K)

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Thermal Property of CNT
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Nanotube Conductance

• Semiconducting when (m, n) indices
• m n ? 3 integer
• The rest are metallic
• Carbon Nanotubes are intrinsically p-type
  semiconductors.

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CNT Conductance Variation
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Quantum Effect

• Conductance appears to be ballistic over micron
  scales, even at room temp.
• Ballistic, no dissipation , very high current
  densities are possible
• Frank et al., Science 280, 1744(1998)

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Electron Field Emission From CNTs

• Low turn-on electric field and threshold electric
  field
• High field enhancement factor
• High current density
• High current stability, low degradation rate

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Synthesis of carbon nanotubes

• There are three commonly means by which carbon
  nanotubes are synthesize
• Laser ablation
• Arc-discharge method
• Chemical vapor deposition (CVD)

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Arc-discharge method
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Laser ablation
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CVD

• CVD synthesis is achieved by taking a carbon
  species in the gas phase and using an energy
  source , such as plasma or a relatively heated
  coil, to import energy to a gaseous carbon
  molecule
• The energy source is used to crack the molecule
  into a reactive radical species
• Carbon nanotubes are formed if proper parameters
  are maintained

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Plasma CVD

• Plasma CVD has an advantage of low temperature
  synthesis over thermal CVD
• Carbon nanotubes can be synthesized on soda lime
  glass.
• The power supplies for discharge of plasma are
  DC and High Frequency
• RF(13.56 MHz) and Microwave (2.47 GHz) are
  typical of high frequency applied are both
  electrodes.

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Plasma CVD apparatus
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Plasma CVD Nanotubes

• Carbon nanotubes are grown on the metal particles
  by glow discharge generated from high frequency
  power
• Reaction is supplied to the chamber during the
  discharge
• A substrate is placed on the grounded electrode

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Plasma CVD Nanotubes

• The reaction gas is supplied from the opposite
  plate
• C2H2, CH4, C2H4, C2H4,, CO gases are used for
  synthesis carbon nanotubes
• Catalytic metal, such as Fe, Ni, and Co are used
  on a Si, SiO2 , or glass substrate using thermal
  CVD or sputtering

25
SEM, TEM, AFM, STM
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EELS Images of CNTs
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Space elevator
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CNTFET transistor
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TUBFET
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Intramolecular CNTFET Inverter
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TUBFET
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Nanotube single electron transistor
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Conclusion

• Carbon nanotubes
• exceptional potential to replace Silicon based
  semiconductor
• Tremendous current carrying capability
• 1 billion Amps/cm2
• Excellent heat conductor
• twice as good as diamond
• High strength
• much higher than high-strength steel

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Conclusion Ctd

• Potential 50A gate length , THz switching speed
• The possibilities of CNT are promising and range
  from nanotube composite materials,
  nanoelectronics, scanning microscope probes,
  chemical and /or biological sensors, to cold
  electron sources.

35
Questions

• Strong SP2 bond
• CNT VLSI drawbacks
• Large scale replacement, parallel fabrication
  techniques
• Lithography require for source, gate, drain etc

36
Reference

• 1 P. J Harris, Carbon Nanotubes and Related
  Structures, Cambridge Press, (Cambridge,
• London, 1999)
• 2 M. S. Dresselhaus, G. Dresselhaus, and P. C.
  Ecklund, Science of Fullerenes and
• Carbon Nanotubes, AP, (New York, 1996)
• 3 H. O Pierson, Handbook of Chemical Vapor
  Deposition, Noyes, (Norwich, 1999)
• 4 M. Yudasaka, R. Kikuchi,T.Matsui, Y Ohki, S
  Yoshimura, and E. Ota, Appl. Phys. Lett.

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Reference

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Reference

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