Printed Electronics using Graphene based Inks

When I spotted a recent granted patent with the title Printed Electronics, it was an obvious candidate for a Phil’s Patent Pick.  US8278757 was published on 2nd October 2012 and jointly assigned to Vorbeck Materials Corp. and Univ. of Princeton.  It was originally filed on 9th January 2009 and has a priority date of 5th February 2008.

The patent has quite broad claims and describes printed electronics devices made using a conductive ink comprising functionalized graphene sheets and a binder.  I don’t always reproduce the claims but in this case they are fairly simple to follow:

1. A printed electronic device, comprising a substrate comprising at least one surface, wherein a layer of an electrically conductive ink has been applied to a portion of the surface, and wherein the ink comprises functionalized graphene sheets and at least one binder.

2. The device of claim 1, wherein the substrate comprises paper and/or cardboard.

3. The device of claim 1, wherein the substrate comprises at least one polyolefin.

4. The device of claim 1, wherein the substrate comprises at least one polyimide.

5. The device of claim 1, wherein the ink further comprises at least one dispersant.

6. The device of claim 1, wherein the binder is a polymeric binder.

7. The device of claim 6, wherein the binder is one or more of poly(ethylene oxide), poly(propylene oxide), and ethylene oxide/propylene oxide copolymers.

8. The device of claim 1, wherein the ink further comprises at least one metal component.

9. The device of claim 8, wherein the metal is silver and/or copper.

10. The device of claim 1, wherein the ink further comprises at least one electrically conductive polymer.

11. The device of claim 1, wherein the ink further comprises at least one carbonaceous material other than the functionalized graphene sheets.

12. The device of claim 1, wherein the functionalized graphene sheets have a surface area of from about 300 to about 2630 m²/g.

13. The device of claim 1, wherein the functionalized graphene sheets have a surface area of from about 400 to about 2400 m²/g.

14. The device of claim 1, wherein the functionalized graphene sheets have a carbon to oxygen ratio of about 60:40 to 20:1.

15. The device of claim 1, further comprising one or more components selected from the group consisting of processors, memory chips, batteries, resistors, diodes, capacitors, and transistors.

16. The device of claim 1 in the form of an integrated circuit.

17. The device of claim 1 in the form of a printed circuit board.

18. The device of claim 1 in the form of a light-emitting diode display.

19. The device of claim 1 in the form of a radiofrequency identification device and/or a radiofrequency device antenna.

20. The radiofrequency identification device and/or radiofrequency device antenna of claim 19 in the form of a radiofrequency identification device and/or antenna for use with ultra-high frequencies.

21. A method for forming a printed electronic device, comprising the step of applying an electrically conductive ink to a substrate, wherein the ink comprises functionalized graphene sheets and at least one binder.

22. The method of claim 21, wherein the substrate is selected from one or more of paper, cardboard, polyolefin, and polyimide.

23. The method of claim 21, wherein the electrically conductive ink further comprises a carrier.

24. The method of claim 21, wherein the electrically conductive ink further comprises a dispersant.

25. The method of claim 21, wherein the functionalized graphene sheets have a surface area of from about 300 to about 2630 m²/g.

Phil’s Comments

It is worth looking at the examples in the patent.  The printing methods and samples generated for testing are pretty crude and suggest that only simple circuits have been generated such as RFID antennas.  The type of ink suggests that printing processes will be of the gravure or flexo type rather than ink-jet.  However, the wording of the allowed claims suggests that just about any printed electronic device containing a layer that includes graphene sheets with a functional group in a binder would infringe this patent.  The majority of the claims are all about the device and not the material.  The last five claims are about the method.  Vorbeck sell the graphene based inks and with this patent they will require anyone using the inks to enter into some form of agreement with them to make the devices.  It will be interesting to see how this works in practice and whether the patent will stand the test of time.

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Inorganic Nanoparticle Inks for Printed Electronics

Silicon ink has sometimes been described as a “Dream Material” for printed electronics.  Conductive or semi-conductive inks that can be printed directly onto a variety of substrates to create transistors or other electronic devices have been talked about and promoted for a number of years but few companies have succeeded in commercializing products for the mass market.  Silicon ink has been promoted as an enhancer for the production of solar cells to squeeze an extra few percent efficiency from the panel.  One Silicon-valley company NanoGram Corp. acquired last year by the Teijin Group has developed a silicon ink using a laser pyrolysis method to create stable nanoparticles in a dispersion that can be printed by various means including spin coating and inkjet processes.

A recent patent from NanoGram US8263423 was granted on 11 Sept 2012 and completes a trio of US patents granted for their silicon ink approach.  The other patents are US7993947 and US7892872.  These patents all claim a priority date of 3 Jan 2007 for the US provisional application first filed.  The text of all three patents is more or less the same but differs in the claims, each one covering a different aspect of the invention.  The basic technology is described in the first section “Field of the Invention”:

The invention relates to dispersions/inks of silica/germania particles, such as doped silica particles. The invention further relates to inks that are suitable for ink jet printing. Additionally, the invention relates to the use of doped silica/germania particles for the doping of semiconductor substrates, such as through the drive in of dopants with heat and/or light from a silica/germania deposit formed through inkjet printing onto the semiconductor surface.

The three patents break down the invention into i) the dispersion and method for making the dispersion; ii) the method for depositing the dispersion onto a substrate (inkjet printing); and iii) the method for forming solar cells and optical components.

The following paragraph from the text was selected to describe the dispersion approach:

The dispersions comprise a liquid and the dispersed silica particles, which may or may not be surface modified. In general, silica particles formed by laser pyrolysis can be well dispersed in water or alcohols at moderate concentrations with no surface modification, although higher concentration dispersions generally can be formed with surface modification. Suitable alcohols include, for example, small aliphatic alcohols, such as methanol, ethanol, propylene glycol, butanediol, mixtures thereof and the like. Upon surface modification, the silica particles can be dispersed in a broader range of solvents and solvent blends through the matching of the chemical properties of the surface modifying agent with the liquid. Thus, following surface modification, the particles can be well dispersed in a range of less polar solvents, such as ethyl lactate, n-methylpyrrolidinone, gamma-butyl lactone, and the like.

The following paragraph was selected to illustrate the printing approach:

While various coating and printing approaches are suitable, inkjet printing offers desirable features with respect to speed, resolution and versatility with respect to real time selection of deposition patterning while maintaining speed and resolution. However, practical deposition using inkjet printing with inorganic particles requires dispersion properties that have not been available prior to development of both the techniques to form high quality silica nanoparticle along with the improved ability to form high quality dispersions from these particles. Thus, the particles produced using laser pyrolysis combined with the improved surface modification approaches and dispersion techniques provides for the formation of inks that are amenable to inkjet deposition.

The following paragraphs were selected to describe the solar cell modifications:

To deliver dopant into the semiconductor from the silica deposit, the material is heated. For example, the structure can be placed into an oven or the like with the temperature set to soften the particles such that the dopants can diffuse into the substrate. The time and temperature can be adjusted to yield a desired dopant migration into the substrate…

Following the drive in of the dopant, it may or may not be desirable to remove the silica. For photovoltaic applications it is generally desirable to remove the silica to expose the doped semiconductor for the application of conductive electrical contacts. To remove the silica, the oxide can be etched, for example, using conventional approaches, such as using wet (chemical) etching or plasma etching.

Of course, you would need to review the claims to see exactly what has been allowed by the examiner and to understand the scope of the granted patent.

Phil’s Comments

It is quite common to see a provisional patent application emerge as several patents described as continuations of the first or earlier patent.  These can also appear as divisional patents and arise because the patent examiner or inventor has noted that the original application contains more than one invention.  These days the examiners are more strict in ensuring that the method and the material inventions are separated out.  In this case the distinction between the dispersion, the printing method and the application to solar cells or optical displays has been identified and separated into the three patents reviewed here.

I have not seen any recent evidence that the Teijin group have announced any products based on this approach and about 1 year has elapsed since they were actively promoting the technology.  It has been a tough year for solar cell manufacturers and a number of promising companies exploring plastic electronics approaches have filed for bankruptcy (e.g. Konarka and Novasolar).  It remains to be seen whether the silicon ink approach will be adopted as a means to increase efficiency and lower cost of conventional solar cells.