| Carbon nanotubes and field
emission display
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| Carbon nano tubes (CNT) were observed for the first time in an electron microscope by Sumio Iijima of NEC (Nature, 354 (1991), p. 56). CNT are long cylinders of rolled up graphitic layers whereby singlewalled and multiwalled nanotubes can be observed. The diameter is in the order of 1 to 10 nm. CNT show an extreme high tensile strength and high electrical conductivity (for most types of CNT). Actual links and a lot of information can be found at the “Nanotube Site” of David Tomanek http://nanotube.msu.edu . Field emission is favoured by sharp tips and edges due to physical reasons. The ends of carbon nanotubes represent extreme sharp tips of an electrical conductive material. Furthermore the individual carbon atoms are strongly bound within in the CNT resulting in a high resistance against the bombardment of residual gas ions. | ||||||||||||||||||
| Keesmann and his team are working with electrodes for corona discharges since the eighties, using electrical conductive polymers and carbon fibres. They recognized soon the potential of CNT as electrode material for field emission cathodes. The basic patent application was filed on February 23, 1994 for using CNT as a field emission cathode. Examples for applications of field emission cathodes are field emission microscopes, X-ray tubes, high frequency tubes (diodes, triodes), travelling wave tubes and especially a controllable cathode array as used in field emission displays (FED), a special sort of Flat Panel Display (FPD). | ||||||||||||||||||
Flat panel displays (FPD) are
becoming more and more important in the market of electronic displays mainly due
to the following reasons
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| The consulting
company Frost & Sullivan pronounces a triplication of annual revenues in FPD-market until 2009 (cf. Heise news from July 21, 2003 –
http://www.heise.de/newsticker/data/ola-21.07.03-000/)
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| The market of FPD is dominated
today by Active Matrix Liquid Crystal Displays. A new technology are OLED-Displays
(Organic Light Emitting Devices). OLEDs are forecasted a fast growing portion
of the market of FPD. A further new emerging technology is field emission
applied in Field Emission Displays (FED) .
In a FED, the picture is made by accelerated
electrons striking a phosphor layer as in a cathode ray tube. In contrast to
the conventional tube, in a FED each pixel has its own cathode and the
electrons are emitted by field emission and not by energy consuming thermal
emission of a glow cathode. The thickness of a FED is similar to other FPDs,
the driving electronic must control the brightness of each pixel like in LCD.
The advantages of FED are seen in the quality of the images and lower
manufacturing costs especially for large displays.
Another promising project is the application of CNTs as field emitters in flat light sources for large area LCD-TVs (so called Backlight-Units BLU). |
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| In 2000 Argus Holding ® GmbH has made an exclusive licence agreement with SI Diamond Technology, Inc. for marketing the patents. Since July 1, 2003 the name of the company has changed to Nano-Proprietary, Inc. (www.nano-proprietary.com). Sublicences for using this technology could kindly be arranged by ARGUS Holding ® GmbH.
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| For strengthening the legal position of the patent a reissue application has been filed in 2000. The Reissue Patent was granted at August 19, 2003 under patent number RE38,223. Another Reissue-Patent with patent number RE38,561 was granted on August 3, 2004. The wording of the main claim is:
10. A field emission cathode comprising an
electron-emitting part of the cathode formed at least in part as a carbon
nano-cylinder.
This means each field emission cathode comprising CNT is claimed clearly and definitely. A further continuation application has been filed in 2004 titled „Field emission cathode using carbon fibers“ – US Patent Application 20040036402, February 26, 2004. This application claims patent rights for all carbon fibers used as electron emitting. |
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| Links | ||||||||||||||||||
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Patents Europe:
http://register.epoline.org/espacenet/ep/en/srch-reg.htm
US-Patents: U.S.P.T.O. http://patft.uspto.gov/netahtml/srchnum.htm Field emission - principle: |
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| Field emission display: http://www.empa.ch/plugin/template/empa/920/22272/---/l=2 |
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| All about nanotubes - The
Nanotube Site http://www.pa.msu.edu/cmp/csc/nanotube.html |
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| Field emission cathode with CNT
for X-ray tubes: http://www.oxfordxtg.com/products/coldcath.htm |
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| Field emission cathode with CNT
for picture element tubes http://www.itron-ise.co.jp/english/new/whats2.htm |
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| Interesting informations and news can be found at CMP-Cientifica: http://www.cmp-cientifica.com | ||||||||||||||||||
| Also a useful address is the website of Nanomaterials Application Center of Texas State University San Marcos: http://www.txstate.edu/nac/index.htm | ||||||||||||||||||
| Conferences of the Society for Information Display (SID): http://www.sid.org | ||||||||||||||||||
| Market research: DisplaySearch,
Austin, Texas, USA:
http://www.displaysearch.com
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