Copper Inks for Printed Electronics

I recently spotted a patent for copper based metallic inks jointly granted to Applied Nanotech Holdings, Inc. and Ishihara Chemical Co., Ltd.  The conductive inks I have previously reported on have been silver or graphene based, these can be very expensive and so there is always interest in a lower cost alternative.  Copper metal is a standard in the electronics industry and is about one tenth the cost of silver.

Patent summary:

US8404160   -  METALLIC INK

Inventor(s): LI YUNJUN [US]; ROUNDHILL DAVID MAX [US]; LI XUEPING [US]; LAXTON PETER B [US]; ARIMURA HIDETOSHI [US]; YANIV ZVI [US]

Applicant(s): APPLIED NANOTECH HOLDINGS INC [US]; ISHIHARA CHEMICAL CO LTD [JP]

Filing date: 31/03/2009
Issue date: 26/03/2013

Abstract
A metallic ink including a vehicle, a multiplicity of copper nanoparticles, and an alcohol. The conductive metallic ink may be deposited on a substrate by methods including inkjet printing and draw-down printing. The ink may be pre-cured and cured to form a conductor on the substrate.

Claim 1:

1. A conductive metal ink comprising: a vehicle comprising two or more oxygenated organic compounds; copper nanoparticles; and a medium length chain aliphatic alcohol, wherein the ink does not comprise a binder.

There are a further 23 claims giving more details of the components mentioned in claim 1.

Two figures from the patent give a flow chart for two processes which can be used:

Direct printing:

Patterning after the ink deposition:

Phil’s Comments

This is a key patent for copper inks and has a broad first claim which had to be modified from the original application by the addition of the restriction that the ink does not contain a binder and I suspect this was to get around some of the prior art identified by the patent examiner.

Six very detailed examples are given which illustrate the invention and provide further details of the printing process, the curing or sintering that is applied to produce the conductive tracks on a range of materials including flexible substrates.

Silver Nanoparticle Inks for Printed Electronics

Xerox are continuing to add to their patent portfolio of silver nanoparticle inks for printed electronics.  A new patent was granted on 4th Dec 2012 adding to the one already granted on 17th April 2012.  These two patents are summarised below:

US8158032  (B2)  -  SILVER NANOPARTICLE INK COMPOSITION FOR HIGHLY CONDUCTIVE FEATURES WITH ENHANCED MECHANICAL PROPERTIES

Abstract: A conductive ink composition comprising organic-stabilized silver nanoparticles and a solvent, and a polyvinyl alcohol derivative resin of Formula (1) wherein R1 is a chemical bond or a divalent hydrocarbon linkage having from about 1 to about 20 carbons; R2 and R3 are independently an alkyl, an aromatic or substituted aromatic group having from about 1 to about 20 carbon atoms; x, y and z represent the proportion of the corresponding repeat units respectively expressed as a weight percent, wherein each repeat unit is randomly distributed along polymer chain, and the sum of x, y and z is about 100 weight percent, and wherein the polyvinyl alcohol derivative resin is present in an amount of from 0.1 to about 5 weight percent of the ink composition.

US8324294  (B2)  -  SOLVENT-BASED INKS COMPRISING SILVER NANOPARTICLES

Abstract: High performing nanoparticle compositions suitable for printing, such as by inkjet printing, are provided herein. In particular, there is provided a conductive ink formulation comprising silver nanoparticles which has optimal performance, such as, reduced coffee ring effect, improved adhesion to substrates, and extended printhead de-cap time or latency time. The ink formulation comprises two or more solvents and a resin.

Phil’s Comments

The key technology improvements over the general prior art are for the development of inks which do not dry out and clog the printhead along with improvements in the adhesion of the ink to the substrate, reduction of the coffee ring effect and reduction of particle aggregation which leads to black dots in the printed lines.

The improved adhesion is as a result of the incorporation of a resin in the ink based on a polyvinyl alcohol derivative.  The earlier patent goes into some detail over the formulae for these resins.

The extended drying times to prevent printhead clogging are the result of incorporation of two or more ink vehicles (solvents) with vapour pressure properties as described in the second patent.  Typical compositions are based on aliphatic hydrocarbons comprising at least one cyclohexane ring, cyclic terpene, cyclic terpinene, terpineol, methyl naphthalene, and mixtures thereof.  Typical drying times are in excess of 5 hours and one claim states up to about 1 week.

The nanoparticles are stabilised with organo-amines, the first patent gives more detail on these structures,  a preferred compound is dodecylamine.

 

As always please leave a comment if you require further details or are interested in patent landscapes related to these conductive inks.

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.

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.

A Combination Patent for Electrowetting and Quantum Dot Technologies

As followers of this blog will know I keep a look out for new and interesting patents that become granted in the field of printed and plastic electronics.  This field is forever expanding as new technologies are discovered that can be created by printing functional materials.

Recently I came across a patent granted to QD Vision Inc. that is basically a combination patent of quantum dot technology and electrowetting display technology to provide a low cost, low power display that can be read under a wide variety of conditions.  Under good ambient light is relies on its reflective electrowetting display technology but as light levels are detected to drop below a critical level a UV backlight switches on (either via a sensor or manually) to activate a quantum dot (QD) light emitting display.  The electrowetting colour cells and the quantum dots are chosen so that the colours match and provide a seemless transition between the two types of display technology.

The patent is US8264777 and was published as a granted patent on 11th September 2012.   As always it is the claims that define the invention but there is a lot of technical description that can be read from the main specification as well.

Claim1:

1. An electrowetting display, comprising: a plurality of transparent layers defining a cavity; a combination of a first fluid and a second fluid positioned in the cavity; first circuitry configured to be coupled to a first voltage source for selectively repositioning the second fluid in relation to the first fluid; a first plurality of quantum dots positioned within the second fluid; a light source disposed contiguous to the plurality of layers; and second circuitry configured to be coupled to a second voltage source for selectively causing the light source to emit photons to strike the first plurality of quantum dots.

This helps us to realise that the quantum dots are included in the second fluid (the one that moves as part of the electrowetting action) and defines the way the technologies have been combined together.

In the patent FIGS. 2-5 are schematic partial cross sections illustrating four operational states for an exemplary embodiment.

Display structure

Display Structure

The images show the electrowetting display in the two main states where the second liquid is either evenly spread over the whole surface (wetting) or at the side (non-wetting).  FIGS. 2-5 are schematic diagrams of four states of a single level and a single pixel in which an electrowetting display 200, 202, 204, 206, respectively, includes QDs 208 disposed within an oil 210. Each of the FIGS. 2-5 comprise a reflective surface 211 deposited on a substrate 212. A ultraviolet (UV) light source 209 is disposed on a side of the reflective surface 211 opposed to the substrate 214 and is coupled to a voltage source 226 through switch 228 for selectively activating the UV light source 209. A transparent electrode 214 is formed over the light source 209. A transparent hydrophobic insulator 216 is formed on the electrode 214 for supporting the combination of oil 210 and water 218. A transparent electrode 220 is formed above and for containing the water 218 and oil 210 in a cavity 219. A (low frequency or DC) voltage source 222 is coupled between the electrodes 214 and 220, and is selectively applied by closing the first switch 224.

When ambient lighting is sufficient, the ambient light entering the electrowetting displays 200, 202, 204, 206 is reflected by the reflective surface 211 back out, either through the oil, or not through the oil when the oil has been moved to the side. Note that when the oil contains a color pigment, the light reflected back out will be of that color. The QDs 208 may be activated, e.g., when ambient light is insufficient, to provide additional light exiting the electrowetting displays 200, 202, 204, 206. The QDs 208 will provide a light having a color depending on the diameter of the QDs 208. Preferably, when a colored oil is used, the QDs 208 will provide light of the same frequency (color).

Phil’s Comments:

Combination patents are great ways for expanding a patent portfolio and also for ensuring that other companies don’t block you from exploiting your technology by generating their own combination patents.  The key concern is always whether the combination is obvious to anyone skilled in the art.  In this case there seems to be enough novelty in the way the technologies have been combined that the patent has been granted.  The fact that the original application claims have not been significantly amended suggests that it went through the patent process quite smoothly.

This patent was identified in a printed electronics search because various lithography processes, e.g., photolithography, electron beam lithography, and imprint lithography, ink jet printing, may be used to fabricate the light emitting device, and a printing process is preferred. In the printing process, the Freestanding Quantum Dots (FSQD) ink in liquid form is printed in desired locations on the substrate.

Can you really spray on Solar cells?

Back in January 2010 New Energy Technologies unveiled a patent pending process for “spraying” solar panels and their related components onto glass.  The spray concept seemed to catch the publics imagination and of course the idea that you could simply spray from a can onto glass and have a functioning solar window does indeed seem a fantastic breakthrough.  The reality is somewhat different and while the research does indeed show that functional organic layers can be spray coated onto a substrate this is but one step of a multi-phase process to create a fully functional solar panel.

Although the patent applications had been filed a considerable period has to elapse before they become published and available in the public domain.  Earlier this month one of the US patent applications was published and so it is possible to delve a bit deeper into the technology that is being developed.  The research is based on the work of Professor Xiaomei Jiang in the Nanostructure Optoelectronics Lab at the University of South Florida.  New Energy Technologies Inc. are in the process of developing their SolarWindow™ product using this technology.  More recently they have entered into a cooperative Research and Development agreement with the US Department of Energy’s National Renewable Energy Lab. to advance development of SolarWindow™.

The patent application is US20120156825 and summary details are shown below:

Title: Transparent Contacts Organic Solar Panel by Spray

Inventors: Jason Lewis, Jian Zhang, Xiaomei Jiang

Assignee: University of South Florida

Abstract: A method of fabricating organic solar panels with transparent contacts. The method uses a layer-by-layer spray technique to create the anode layer. The method includes placing the substrate on a flat magnet, aligning a magnetic shadow mask over the substrate, applying photoresist to the substrate using spray photolithography, etching the substrate, cleaning the substrate, spin coating a tuning layer on substrate, spin coating an active layer of P3HT/PCBM on the substrate, spray coating the substrate with a modified PEDOT solution, and annealing the substrate.

Claims: The first six claims are worth noting:

1. A method of fabricating organic solar panels with transparent contacts, comprising: applying photoresist to a substrate by spray photolithography; spin coating a tuning layer on the substrate; spin coating an active layer coating on the substrate; spray coating the substrate with a modified PEDOT solution; and annealing the substrate.

2. The method of claim 1, wherein the substrate is an ITO glass substrate.

3. The method of claim 1, wherein the substrate is plastic.

4. The method of claim 1, wherein the substrate is cloth.

5. The method of claim 1, wherein the tuning layer is Cs₂CO₃.

6. The method of claim 1, wherein in the active layer coating is P3HT/PCBM.

There are an additional 17 claims which give further details of the method.

Phil’s comments:  As you can see the concept of simply spraying a solar cell onto glass is a long way from reality.  However, this patent application does explain the technical approach quite well and indicates that the various layers including the contacts are all transparent so that the final result is a solar cell on glass that will still resemble a window.

Printing Electronic Features on Uneven Surfaces

A recently granted patent caught my eye because it made reference to a method of ink jet printing conductive inks onto non-uniform surfaces.  The patent was granted to the Cabot Corportion who currently provide a number of inkjet formulations for printed electronics applications.  This patent indicates that they have also been working on a system of direct printing which can compensate for the uneven surface of a substrate.

Patent details:

US8167393: Printable Electronic Features On Non Uniform Substrate And Processes For Making Same

Filing Information:
Inventor(s):    Karel Vanheusden, Chuck Edwards
Assignee(s):    Cabot Corporation

Filing date    13/01/2006
Issue date    01/05/2012
Prior Publication Data:     US20060158470 – 20/07/2006

Abstract:  A system and process for compensating for non-uniform surfaces of a substrate when direct printing traces is provided. The system and process provided herein measures the surface of a substrate and can determine whether the surface is substantially flat, rises or falls, or whether a mesa or valley is encountered. Depending on the surface feature (i.e., mesa, valley, falling or rising surface), the direct printing system can change the frequency of the printing timing signal, advance or retard the print timing signal, advance or retard the print data, or make repeated passes over certain areas. In addition, the process disclosed herein can determine whether two, three or all of the aforementioned steps for compensating for non-uniform substrates should be combined to most effectively and efficiently print on the non-uniform surface of the substrate as intended.

The invention seems to be primarily for printing on surfaces which have already received some printed circuit tracks or components and need to have additional conductive tracks to complete the device.  However, the text describes the situation where you might want to print directly onto an uneven or flexible substrate.  With a conventional printhead the drops will become more spaced out if the distance between the head and the substrate increases due to a downward slope.  If there was an upward slope then the drops will land closer together.

Various ways are described to overcome this problem and enable a uniform print density and line thickness to be achieved.  The distance between the printhead and the surface can be continually monitored with a laser interferometer so that the surface topography is mapped and used to control the drop delivery.

The patent has a huge number of document references and also contains a useful review of the background art associated with more traditional printing processes such as photolithography and screen printing.

This does seem to be a serious attempt at reducing the impact of an uneven surface on the reliability and quality of printed conductive tracks and I would be interested to hear from anyone who has looked at other ways of addressing this problem.

Printed electronics, tattoos and artificial skin

I came across a recent patent application from Nokia describing a haptic communication method in which labels or tattoos on the skin can be made to vibrate when triggered by a magnetic field.  In one example the magnetic field could be initiated by a mobile phone and the user could be alerted to incoming phone calls via the sensations induced on the users skin.

The patent application was published on 15th March 2012 as US20120062371

What is claimed is:
1. An apparatus comprising:
a material attachable to skin, the material capable of detecting a magnetic field and transferring a perceivable stimulus to the skin, wherein the perceivable stimulus relates to the magnetic field.
2. An apparatus according to claim 1, wherein the material comprises at least one of a visible image, invisible image, invisible tattoo, visible tattoo, visible marking, invisible marking, visible marker, visible sign, invisible sign, visible label, invisible label, visible symbol, invisible symbol, visible badge and invisible badge.
3. An apparatus according to claim 1, wherein the perceivable stimulus comprises vibration.

Several other claims go on to describe the material in more detail and indicate that it could comprise a ferromagnetic powder.

At about the same time The University of Cambridge were publishing in the Advanced Materials journal ( Vol 24, No. 12 pp. 1558-1565) an article on the progress made by researchers in the Cavendish Laboratory towards better flexible printed electronics materials.  The work was recently highlighted in the Research Features page and applications mentioned include artificial skin and interactive playing cards.  Many of these applications are a long way off yet but the groundwork to make them possible is progressing at a rapid rate.  The new circuits developed by Drs Kronemeijer and Gili exhibited the fastest operation published to date (a few hundred KHz) using a new class of ambipolar organic materials and reduced the power supply requirements by approximately one order of magnitude so that they can already be operated using a standard 9V battery.

If anyone would like to know more about the patent applications that are emerging in this highly competitive field then please contact me at IPScope (phil.coldrick@ipscope.co.uk).

Thin Printable Battery Patent

Most electronic circuits will require power to operate and for printed electronics devices to become a commercial success there is a need for a simple printed power supply that will last for the typical lifetime of the product.  Printed greeting cards with electronic add-ons are a classic example where the power is needed for a fairly short period of time but these are often powered by thin button cells which are not part of the printing process.  Several manufacturers are now providing printable power supplies and I have been keeping an eye on these developments.

Blue Spark Technologies recently announced an expansion of their manufacturing facilities for flexible carbon zinc batteries to meet the growing demand for printed electronics in commercial and industrial packaging.  The full article is here.  Back in October 2011 Blue Spark were granted a patent (US8029927) which covers the technology used in their flexible electrochemical cells and their manufacture.

The patent abstract is as follows:

A thin printed flexible electrochemical cell, and its method of manufacture, using a “picture frame” structure sealed, for example, with a high moisture and oxygen barrier polymer film and featuring, for example, a printed cathode deposited on an optional, highly conductive carbon printed cathode collector with a printed or a foil strip anode placed adjacent to the cathode. A viscous or gelled electrolyte is dispensed and/or printed in the cell, and a top laminate can then be sealed onto the picture frame. Such a construction could allow the entire cell to be made on a printing press, for example, as well as gives the opportunity to integrate the battery directly with an electronic application, for example.

Detailed descriptions cover the construction of the cells, sizes and thickness of the “frames” to contain the electrolyte and typical materials that can be used. Examples of a 14 step process are given and then ways to reduce the steps to a 9 step process for a more cost effective operation.

The first claim is quite broad but has many components:

1. A device comprising a flat, thin electrochemical cell for generating an electrical current, said cell including:

a first substrate layer comprising a polymeric film and an oxide barrier layer having a gas transmission rate that permits gas to escape;

a second substrate layer comprising a polymeric film and an oxide barrier layer having a gas transmission rate that permits gas to escape;

a cathode layer provided on at least one of said first substrate layer and said second substrate layer;

an anode layer provided on at least one of said first substrate layer and said second substrate layer;

an electrolyte layer in contact with said cathode layer and also in contact with said anode layer;

and a frame provided substantially around a perimeter of said cell and connecting said first substrate layer to said second substrate layer;

said frame together with said first and second substrate layers defining an inner space that encloses said electrolyte layer and at least portions of said cathode and anode layers.

This image from their website gives some idea of the size.

 

 

 

 

 

 

 

 

 

If you require more details or need to understand the patent landscape for this technology contact me or add any comments below.

E-reader display mimics nature to provide colour

For some time I have been watching technology developments towards colour e-reader displays which can handle rapid refresh rates for good video performance and also have a long battery life and there are some promising breakthroughs already described in this blog by Liquavista and E-ink.  I was interested to read recently of Korean’s largest bookseller, Kyobo, introducing a colour e-reader featuring Qualcomm’s Mirasol display technology.  This is the first time an e-reader has featured the mirasol technology.

The Mirasol approach essentially mimics nature’s way of producing colour.  For example the blue colour in butterfly wings is created by an interference effect caused by the photonic crystal nature of their scales.  The microstructure of the scales causes light to be coherently scattered.

In a similar way the mirasol technology uses an array of interferometric modulators (IMODs) so that light is either absorbed or reflected and depending on the state of the modulator it can be reflected as red, green or blue light.

On 29 Nov 2011 Qualcomm MEMS Technologies Inc. were granted a US patent US8068269 which describes some of the improvements to the IMOD design to enhance the colour saturation of the reflected light.  Claim 1 of the patent reads as follows:

1. A device comprising: a substrate; a fixed reflector; a movable reflector comprising an electrically conductive material, wherein an interferometric cavity is defined between the movable reflector and the fixed reflector, the movable reflector being movable between at least a first position, a second position, and a third position; and a spacing layer positioned on a side of the fixed reflector that is opposite from the movable reflector, wherein the spacing layer is positioned between the fixed reflector and the substrate, wherein the spacing layer provides a filtering cavity configured to improve color saturation of light reflected by the interferometric cavity.

Figure 10 from the patent illustrates how a tri-state modulator has been constructed with spacer layers to provide the building blocks for the colour display.

Text from the patent describes how the blue module works:

The blue modulator has three states. In the first state, the movable reflector 14 is at a first position, for example, position 81, and the blue modulator substantially reflects white light. In the second state, the movable reflector 14 is at a second position, for example, position 82, and the blue modulator substantially reflects no light. In the third state, the movable reflector 14 is at a third position, for example, position 83, and the blue modulator substantially reflects blue light.

The other colour modulators work similarly and in order to increase the saturation of the light from the red, green and blue modulators, the thickness and index of refraction of the spacing layer 103 is selected respectively for the red, green and blue modulators.  Text describing the way the spacer layer works is shown below:

The spacing layer 103 increases the distance between the movable reflector 14 and the conductive layer 102 and therefore decreases the capacitance between the movable reflector 14 and the conductive layer 102 and provides adequate protection against shorting between the movable reflector 14 and the conductive layer 102.

At the same time, the spacing layer 103 defines a second interferometric modulating cavity between the fixed reflector 16 and the conductive layer 102. The thickness and composition (index of refraction) of the spacing layer 103 can be adjusted to vary the effective optical path length of the second interferometric modulating cavity to produce a desired color filter. For example, the spacing layer 103 may be adjusted so that the second interferometric modulating cavity acts as red, green or blue band pass filters as desired, and therefore the multi-state interferometric modulator 12 reflects saturated red, green or blue light.

Full details of the approach are covered in the patent including the colour gamut response for such a device.  The other attractive features of the mirasol display are that the refresh rate for the display is extremely fast (microseconds rather than milliseconds) so that video with no motion blur is possible.  The display also works in a bi-stable mode which allows for near-zero power usage in situations where the display image is unchanged.

There are many patents now granted in the Mirasol portfolio and I have just picked out one of the recent ones.  Contact me if you are interested in details of any of the earlier granted patents.