Carbon Nanotube Ink Technology

SouthWest NanoTechnologies Inc. (SWeNT), a leading manufacturer of single-wall and speciality multi-wall carbon nanotubes (CNT) was created in 2001 to spin off nanotube research developed at the University of Oklahoma.  Recently they have announced a partnership with Chasm Technologies Inc to provide a method for printing carbon nanotubes using commercial, high-volume printing methods and equipment, including flexographic, gravure and screen printing.  The method uses the V2V ink technology (from Chasm Technologies) as a vehicle for the CNT.  Full details can be read on their press release.

I was particularly interested in the patents around the carbon nanotubes and it turns out that most of the intellectual property for the CNT manufacture is held by the University of Oklahoma and relates to the CoMoCAT ® process.  Some of the earliest single walled CNT patents are held by IBM and NEC and it appears that SWeNT have license agreements with these companies but they have also developed the process to make it more controllable  so that specific diameter CNTs can be made.

For example, their most recent patent US 7,357,907 B2 describes a method of preferentially forming single walled carbon nanotubes having a diameter between about 0.7 nm to about 0.9 nm.  This is done by using a catalyst comprising Co and Mo on a Si support material wherein the majority of the Mo occurs as dispersed Mo oxide clusters and the majority of the Co occurs as CoMoO4 with the Co primarily in an octahedral configuration.   The ratio of Co:Mo is ideally less than 3:4.  The catalyst is exposed in a reactor to carbon monoxide gas at a temperature between about 700°C and 800°C (during which the CO disproportionates to C and CO2) and maintaining a CO2 concentration in the reactor below a threshold CO2 concentration, typically 0.9% or less, above which the conversion of ionic Co to metallic Co is inhibited.   The diameter of the carbon nanotubes thus formed can be increased by increasing the temperature range of the reaction vessel, e.g. by using a range of 800-900°C the diameter will be between about 0.9 nm to about 1.2 nm.  Some details around the mechanism of this process are provided on the SWeNT website.

The patents for the V2V ink technology are pending and so are not yet available in the public domain.

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Roll to Roll Printing for Plastic Electronics

A recent newsletter from PolyIC (18th May 2010) highlights their technology for coating thin flexible films with transparent and conductive layers in a roll-to-roll process.  A press release from 6th October  2009 further describes the potential for this technology and provides some technical details around the high resolution capability (15 micron lines).  Applications include displays, touch sensors and heating elements.

Searching the patent literature reveals that PolyIC have a few US patents already granted and more in the pipeline.  The one most closely related to this appears to be US7479670B2.  While it may not be directly relevant it is useful in that it contains many references on the subject matter.  The first four claims relate to the material and are reproduced below:

1. An electronic component made from primarily organic material, comprising: an electrically insulating substrate and/or lower layer having a depression formed by a laser; and at least one electrical conductor track and/or electrode in the depression, the depression having steep walls, sharp contours and a relatively rough bottom surface, the at least one conductor track and/or electrode comprising at least one electrically conductive material for interconnecting electrical components on the substrate.

2. The electronic component as claimed in claim 1, having at least two conductor tracks and at least two electrically conductive electrodes and a distance l smaller than 10 μm between the two conductor tracks, the at least two electrodes and/or between a conductor track and an electrode.

3. The electronic component as claimed in claim 1 wherein the conductor track and/or electrode comprises at least one metallic layer or metal alloy layer.

4. The electronic component as claimed in claim 1 wherein at least one layer of the conductor track is organic material.

You will note that claim 2 makes reference to gaps of smaller than 10 microns between the electrodes or electrode and track, although the description in the main patent section refers to this distance being smaller than 20 microns.  Interesting.  The particular significance of this distance is for construction of FETs where the source to drain distance needs to be a minimum.  This patent may therefore be specific to manufacture of OFETs.

The next claims relate to the process and are reproduced below:

5. A method for producing an organic electronic component with a conductor track or electrode, the component having an insulating lower layer and/or a substrate, the method comprising treating the lower layer and/or substrate with a laser such that at least one depression and/or one modified region are formed in the lower layer and/or the substrate, then filling the depression and/or modified region with an electrically conductive material to thereby produce the conductor track and/or electrode from the electrically conductive material for interconnecting electrical components.

6. The method as claimed in claim 5, including the step of mechanically structuring the electrically conductive material.

7. The method as claimed in claim 5 in which superfluous electrically conductive material is produced, the method including wiping off the superfluous conductive material in a process step following the application of the layer.

8. The method as claimed in claim 6 including forming the at least one depression and/or one modified region with a pulsed laser.

9. The method as claimed in claim 6 which is carried out in a continuous roll-to-roll process.

10. The method as claimed in claim 5 wherein the electrically conductive material is metallic.

These reveal that laser or mechanical patterning is used to assist in the placement of the conductive tracks which must help to achieve the high resolution.  Exact details for how the roll-to-roll process is achieved are not given.

Flexible e-Paper Modules for Displays

AU Optronics unveiled a 20-inch e-paper display at the recent  FPD2009 (28 Oct 2009) along with their 6-inch flexible e-reader  They claimed this was the world’s largest e-paper display that can be mass produced and so I was interested to see what technology was being used and what patents had been granted.  It turns out that AUO are working with technology developed by Sipix and a quick look at the Sipix website provides a nice summary of the Microcup® technology and its use for electrophoretic displays.

The first patent applications for this approach were filed in 2000 but the granted patent that covers this technology is US7112114B2 which was published on 26th Sept 2006.  The first claim reads:

1. A process for the preparation of a semi-finished display panel, which process comprises the steps of:

a) coating a layer of a thermoplastic, thermoset or precursor thereof on a temporary substrate layer followed by embossing the coated layer with a male mold or imagewise exposing a layer of a radiation curable composition coated on a temporary substrate layer followed by removing unexposed areas, to form an array of microcups;

b) filling the microcups with a charged pigment dispersion in a dielectric solvent or solvent mixture;

c) top-sealing the microcups; and

d) applying a conductor layer or a permanent substrate layer onto the top-sealed microcups.

Fig. 6 from the patent shows a schematic of the process:

Conductive Fibres for Printed Electronics

US patent application numbers 2009036012 and 2009036015 both relate to conductive webs co-formed by combining pulp fibres with conductive fibres.  According to Kimberly-Clarke another six applications are in the pipeline.  Some of the potential uses described in the patent applications include:

the conductive nonwoven material may be incorporated into any suitable electronic device. For instance, the nonwoven web can be used as a fuel cell membrane, as a battery electrode, or may be used in printed electronics. For example, in one particular embodiment, the conductive fibers may form a patterned circuit within the base webs for any suitable end use application.

It looks to me as if the technology was developed for disposable nappies that have built in electronics to provide an alarm triggered when the nappy needs changing.  Being able to offer low cost manufacture of a single-use printed electronics item is therefore key to the success of this design.

The conductive material is preferably carbon fibres, typically 3mm in length with a diameter of 5-10 microns.

Potential Benefits Summary:

  • Constructed of cost-effective, commercially available raw materials: paper, carbon, synthetics
  • Inexpensive manufacture and converting
  • Conductive; capable of resistive heating, antenna and other electronic applications
  • Non-metallic
  • Geared to low-end, semi-durable and disposable applications — a consumable
  • Holds promise as a flexible converting and end-use substrate
  • Safe for use in consumer applications

A full technical description of the potential for this approach has been provided by Yet2.com