Field Emission Display: a good application for carbon nano tubes Jean Dijon LETIDOPTSTCO CEAGrenoble

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Field Emission Display a good application for
carbon nano tubesJean DijonLETI/DOPT/STCO
CEA/Grenoble 17 rue des martyrs F 38054
Grenoble cedex 9 France
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OUTLINE

• Introduction
• What technology and what market for CNT displays?
• A Bottom up as grown CNT display technology
• Display structure
• CVD versus PECVD for displays
• To date achieved performances
• Current density
• Life time
• Scalability
• Conclusions

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The CRT TV market is dominated by Flat display
technologies
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The first generation of FED is not really
compatible with large area (40)

• FED structure

anode
Gate
cathode
TIP (emitter)
1µm

• Two technological steps are troublesome
• Gate hole lithography (1µm)
• Tip growth (normal incidence)
• Next generation

Carbon Nano tubes as emitters
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Why CNT as emitters?

• The aspect ratio h/r produce enormous field
  amplification factor ß

The threshold of field emission is very low
µTips ß 30 V100 d1µm
CNT ß 300 V100 d10µm
CNT devices allow the manufacturing of displays
with large design rules High beta CNT materials
are needed MWCNT electrically connected
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The Breakthrough

• A scalable FED technology to address the large TV
  display market
• Low cost Technology as simple as possible
• Simple Cathode Structure (No focusing gate)
• Proximity photolithography
• CNT Bottom up approach As grown CNT
• Self assembly localisation of the CNT
• Demonstrators development road map
• 1.2 cm2 test vehicle 2001
• 6 inches video displays 2004

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The CNT cathode design developed at LETI is
compatible with large area photolithography

• No critical photolithographic step
• Only 3 masks
• Embedded ballast resistor
• Carbon Nanotubes are located on catalyst pads
  (55µm2)

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6 inches FED display cathode structure
350µm
Pixel Structure
Made with 1x mask (5µm resolution) CNT filling
factor 6
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Bottom up approach CNT are grown by thermal CVD
directly on the cathode
Self assembled CNT

• Ni catalyst pad (thickness,3 to 10nm)
• Droplets formation during heating

• Thermal CVD (500C lt T lt 600C)
• C2H2 fast growth (below one minutes)

Why thermal CVD process?
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Key property (1) of CVD the height of the tubes
is inversely proportional to the tube diameter
Growth Limiting factor Carbon diffusion in the
catalyst (1)
Very High beta value tubes Sparse tubes above the
background low screening
(1) R. Baker J. of catalysis 30, 86, 1973
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Key property (2) of CVD The beta distribution of
CNT is an exponential law

• Exponential distribution of beta measured by
  Nilsson (1)
• Exponential distribution of beta is due to the
  exponential distribution of h

3µm

• The exponential distribution of h is related
  to growth mechanism and poisoning of catalyst (2)
• This distribution is reproducible

As grown CNT layers are well suited for high
current emission
(1) Nilsson et al. J.A.P 2001, 90,768 (2) G.G.
Tibbets J. Crystal Growth 73,431,1985
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Drawback (1) of PECVD The height of the tubes is
proportional to the tube diameter
Slow growth Medium beta value Gaussian
distribution of Beta (1)
(1) K. Teo et al Nanotechnology 14, (2003),204
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Drawback (2) of PECVD Screening impairs emission
of the CNT

• With VACNT High density means no emission

Sparse VACNT are needed

• Known solution patterning of the catalyst

• Problem low cost solution for sparse growth?

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CVD versus PECVD electrical benchmarking
2µm
As grown PECVD films are not compatible with
remote gates
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CVD process is more suitable for low cost display
technology
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The achieved current density is within the
specifications for HDTV
CVD CNT films reach in triode mode an emission
current density of 500mA/cm2 _at_ 9.5V/µm (filling
factor 6)
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The basic CEA LETI technology shows 12000h
lifetime
Conditions Oxidizing phosphor (Y2SiO5Tb)
standard getter, full brightness Ageing
mechanism No change of work function, decrease
of site density Non critical burning of CNT
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6 inches monochrome video display performances
6 inches video CNT FED CEA LETI 2005
The technology is easy to scale up
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Conclusion(1) Proof of concept of CNT FED
demonstrated

• Technology Low cost Large area
• Simple scalable structure (no focusing gate)
• Low resolution photolithography (no stepper)
• Simple growth process (without post
  activation)
• Integration of CNT onto the devices
• Display Performances close to the target
• Current density (25mA/cm2 demonstrated)
• Low driving voltage (85V)
• Brightness (3000Cd/m2
  demonstrated)
• Very reliable emission (15000h
  demonstrated)
• Uniformity (5 with 0.1mm2
  pixels)
• Scalability 6 inches video

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CNT FED Displays How to go from nano to macro?

• Material development
• Optimization of the material on the criteria of
  interest (current emission)
• Not on material structure
• Overcome current knowledge limitations
• No control of individual CNT properties required
• Material integration
• Good matching of the Micro structure
• With nano material
• With macro component
• High redundancy
• robustness
• large area compatible

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Thank you for your attention