WO2017007323A1

WO2017007323A1 - In-line electrophoretic switching device

Info

Publication number: WO2017007323A1
Application number: PCT/NL2016/050498
Authority: WO
Inventors: Henricus Johannes AMESZ; Tatiana FERNÁNDEZ LANDALUCE; Johannes Petrus Van De Kamer
Original assignee: Hj Patents Bv
Priority date: 2015-07-08
Filing date: 2016-07-07
Publication date: 2017-01-12
Also published as: NL2015119B1

Abstract

The present invention is in the field of an electrophoretic device for switching between a transparent and non-transparent mode, the device having pixels, the pixels comprising a fluid and colored particles, and comprising various further elements, as well as uses thereof, in particular as a window blind and for signage.

Description

Title In-line electrophoretic switching device

FIELD OF THE INVENTION

The present invention is in the field of an electro- phoretic device for switching between a transparent and non- transparent mode, the device having pixels, the pixels comprising a fluid and colored particles, and comprising various further elements, as well as uses thereof, in particular as a window blind and for signage.

BACKGROUND OF THE INVENTION

Electronic display devices and especially electrophoretic display devices are a relatively new technique of pixi^¬ lated display devices in which charged pigment particles are moved vertically to generate a required pigmentation of a pix- el. In a first approach thereof black and white particles are encapsulated, defining a closed space wherein black particles move upwards at the same time when white particles move downwards, or vice versa; so either the white or the black parti^¬ cles are visible and hiding the other type at the same time; a transparent state is not possible. Pigment particles can not freely move, as they are enclosed in microcapsules. The pigment particles are relatively large, typically larger than 500 nm (0.5 pm) , and on average 1 μm or larger. The two electrodes typically used are located above one and anoth- er. The switching is achieved by an electric field, the particles typically being charged or chargeable; this technique is often referred to as E-ink, such as of US2002 /l 67500 Al . The microcapsules are relatively small {50 μm or less) . It is noted that despite claims colored particles are simply not available for the E-ink technology. Only by applying a col^¬ or filter a color may be provided. At best such relates to a very limited number of colors, and certainly not to full color displays. The switching is relatively fast (within 300 msec) , the stability is good (above 10 sec) , and the contrast is good as well. E-ink has as (further) disadvantage that is relatively difficult to produce, production is expensive, and production yield is too low (too much fracture, too much waste) .

In an alternative technique the colored particles can move more freely throughout a pixel, largely independently of one and another. The colored particles move from one location in the pixel to another location, also typically due to an ap^¬ plied electrical field. A first location is typically where particles accumulate, and have a high density or concentration, whereas a second location is where particles are spread out, typically evenly, and have a lower concentration or den^¬ sity. The area of the first location, often referred to as accumulation area, is relatively small. The accumulated parti- cles are badly visible for the human eye or not at all, that is the eye perceives the accumulated particles as being absent or at the most a greyish impression or the like is perceived. In addition the accumulation area may be hidden, such as be^¬ hind a cover. The second location, often referred to as field electrode and if mutually connected referred to as "common" electrode, has a larger area, compared to the accumulation ar^¬ ea, typically a few times larger. The field or common elec^¬ trode is typically kept at a constant voltage, e.g. 0 V. The particles on the field electrode are visible to the eye, giv- ing an impression of a (largely) colored pixel. Switching is achieved by moving particles from the accumulation electrode, also referred to as the "pixel" electrode, to the field electrode, typically by applying a constant voltage to the accumulation electrode of + 5-30 V or - 5-30 V, respectively. By compacting the particles towards the accumulation area the transparency of the display is changed. The movement is at least partially laterally, as the accumulation area and field area do not cover one and another in a vertical direction. In a top view the field area and accumulation area are located adjacent to one and another, contrary to the E-ink approach.

For further details of present developments in this field as well as for drawbacks of the present technology ref^¬ erence is made to recently filed NL2010936, which reference is incorporated herein by explicit reference. A main difference compared to other technologies is that the colored particles are always visible. Some details are provided below.

A benefit of the partly lateral switching of charged particles is that the electrophoretic display device may comprise a fully transparent state. In principle a choice of re- flector or possibly backlight is possible.

However, in an electrophoretic display it is rela^¬ tively difficult to control the electrical field and particle motion distribution accurately enough to provide a homogenous pixel absorbance in the "dark" state.

Also switching from a first state to a second state in the above display may be relatively slow; typically too slow for many applications, even with recently improved devices. It is noted that typically prior art particles move at a speed of less than about 1 mm per second, which is considered at least ten times too slow for certain applications.

Even further stability of the dark or transparent state is a challenge. Also contrast is not optimal, due to the presence of the accumulation area.

Recently it has been found that also the precise control and movement of particles is much more complex that apparently hypothetically possible. For instance, a small local variation in the thickness of the substrate may cause a large local variation in electrical field; in this respect note that a height of the pixel is typically some 25-50 μm, whereas perturbations of the substrate may be in the order of 1-5 μm, that is 4-20% relative. This is found to result in rather un^¬ controlled switching times and a poor distribution of colored particles. Such is partly due to the electrophoretic technolo- gy relying on electro-osmotics, which is as a consequence of the above not well controlled and not predictable enough.

For full color displays, which may comprise a stack of the above pixels, the situation is clearly even worse.

It is noted that some major companies developing displays have stopped to develop electrophoretic displays, being discouraged by negative results, complexity of the technology, and lack of prospect. For similar reason providers of pigmented particles had stopped further development as well.

As a consequence use and practical applications of the above electronic displays are so far limited, typically to relatively expensive devices, despite potential advantages. Prior art devices, such as LCD or LED type, have various limitations. For instance, such a screen has a limited viewing an^¬ gle; as a consequence typically only one person, at the most a few, can view the screen at the same time. For a relatively small screen the number of viewers is even smaller. The screen is further not optimized in terms of energy consumption; typi^¬ cally the entire screen operates in full color, or in black and white, thereby consuming more energy than strictly necessary. Further typically applications work under similar or the same boundary conditions, e.g. in full color. Resolution of screens is also limited, e.g. to 10-30 dots per inch (DPI), which is for many applications considered too low. It is noted that high end mobile phones may have a somewhat higher resolution, e.g. up to 100 DPI. In view of resolutions of e.g. photos and optical cameras such is relatively low.

Inventors have identified various documents reciting potential layouts of pixels, but these layouts typically do not solve the above problems and may even introduce further problems .

For instance, US2014/022624 (Al) recites a display device comprising a display fluid layer sandwiched between a first substrate layer and a second substrate layer, and a light-enhancing layer between the display fluid layer and the second substrate layer. The light-enhancing structure can enhance the colors displayed by the display device, especially the colors displayed through lateral switching of the charged pigment particles in an electrophoretic fluid. The charged particles are distributed throughout a fluid. Control of movement, stability and switching times still seem problematic.

WO2008/010163 (A2) recites an array device comprising an array of rows and columns of device cells, each device cell comprising a sealed region containing a fluid in which parti- cles are suspended, wherein the movement of particles within each cell is controlled to define a cell state, the cell states of all device cells together defining an output of the device. The device comprises an array of orthogonal addressing conductors. The overflow channel (32) enables the sealing of the cells can be conducted with excess cell fluid having a passageway to drain to. The electrode design also enables short and/or open circuits to be tolerated. This document relates more to switching a device and in some ways to design of pixels; it does not address the above problems. WO2007/004120 (A2) recites a method for driving an in-plane switching multi-color electrophoretic display. The display comprises a plurality of pixels and a common electrode for electrically separating the pixels from each other, each of the pixels comprises a pixel electrode for attracting or repelling pigment particles.

WO2004/008238 A2 recites an in-plan switching elec^¬ trophoretic display device (IPS-EPD), comprising a layer of electrophoretic material, being sandwiched between a first and a second substrate, a pixel of said display further comprising a first and a second electrode for locally controlling the material of said electrophoretic layer. The first and second electrodes are positioned on essentially the same distance from said first substrate, so that an essentially lateral field is generated in said electrophoretic layer when a signal is applied over said electrodes, in order to enable transflec- tive operation.

The above two displays can be regarded as typical for presenting all the disadvantages of the prior art, as indicat- ed above.

WO2003/009059 Al recites an improved EPD which comprises the in plane switching mode. More specifically, the EPD of the present invention comprises isolated cells formed from microcups of well-defined size, shape and aspect ratio and the movement of the particles in the cells is controlled by the in-plane switching mode. The EPD of the invention may be produced in a continuous manufacturing process, and the display gives improved color saturation. This document relates to an in old-fashioned mode arranged RGB pixels, provides largely irrelevant details, is limited to microcups which are most likely not suited for production purposes and reflects more the issues that needed to be solved rather than solutions thereto .

US2010/091208 Al recites a nematic bistable liquid crystal (LC) display element includes a substrate having an inner surface alignment layer and a pair of in-plane electrodes in proximity to the substrates. The display element has charged electrophoretic nanoparticles in the LC medium configured to setup a matrix with the LC when an electric field is applied to the electrodes. Apart from the electrophoretic particles, the layout is very different and reflects more the alternatives to electrophoretic displays, namely LCD.

WO2014/196853 A2 recites pixilated display devices in which charged pigment particles are moved to generate a required pigmentation of a pixel. The invention relates to a typical prior art pixel for an electrophoretic display device, to a display device, to a driver circuit for use in the electrophoretic display device and to use of the electrophoretic display device. Some figures seem to relate to in-line switch^¬ ing, but effectively the document is totally silent in this respect and effectively relates to movement of particles out of plane. In addition the device typically needs a shield for hiding accumulated particles.

Hoehla et al. in "12.3: Development of Electro-

Osmotic Color E-paper", SID Symposium Digest of technical Papers, Vol. 44, Nr. 1 (June 1 2013), p. 119-122, and slides of said presentation recites certain developments in out of plane switching devices. One of the issues with such devices is a relatively poor alignment (+ 3μm is reported) which makes the devices unsuitable for many applications. In addition the used ITO seems unsuitable as the specific resistance reported is out of range for most applications. The distance of the planes used seems to lead to unsuccessful results, hence making small distances typically unsuitable. For these type of devices a contrast ratio was typically about 5 and the transmittance was also too low (about 40%) (note these devices were produced by the present inventors) . It is mentioned that further optimization is needed.

Further, US 2012/134009 Al recites an electrophoretic display of Eink type with stacked first and second electrophoretic layers, each comprising charged particles (W, C, Y, M) in a fluid. The first layer contains particles of white (W) and first color (M) particles and has three optical states (a) white particles adjacent a viewing surface; (b) first color particles lie adjacent the viewing surface; and (c) both types of particles shuttered to allow light to pass through the first layer. The second layer contains particles having second (C) and third (Y) colors and has three optical states (d) sec- ond particles (C) adjacent the first layer; (e) third particles (Y) adjacent the first layer; and (f) second (C) and third (Y) particles intermixed within the fluid. Such devices function in a totally different manner, need a height of at least 30 μm, use much larger particles (~1 μm) , do not have a transparent status, etc.

It is an objective of the present invention to overcome disadvantages of the prior art electronic devices without jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION

The present invention relates in a first aspect to an electronic device according to claim 1, in a second aspect to use thereof, and in a third aspect a product comprising said device.

The present device comprises electrophoretic pixels, typically with a density of a few hundred DPI. Typically two substrates (41,42), which may be referred to as a bottom substrate and a top substrate, enclose pixels at two sides thereof. The pixels comprise a fluid, typically a transparent fluid. The fluid allows movement of coloured particles through the fluid. The particles are visible through an aperture area; the aperture area is "located" in the first substrate. Also "located" in the first substrate is a storage area, where particles are located when they are required to be out of sight. The aperture area and storage area define an area, the area in principle having no boundaries and mainly a functional meaning .

The pixels comprise coloured particles, being capable of moving form a first location (e.g. storage or also referred to as accumulation area) to a second location (e.g. aperture area). Thereto the particles are charged or chargeable. Also the particles are found to be relatively small, e.g. smaller than 500 nm. For improved movement and control smaller particles are preferred.

For imparting movement two electrodes are provided, a so called field electrode and an accumulation electrode, similar to the aperture area and accumulation area. These electrodes occupy an area. The at least one field electrode occupies a field electrode area, wherein the field electrode area and the aperture area largely coin^¬ cide. The accumulation electrode occupies an accumulation electrode area, wherein the at least one storage area is adjacent to the at least one aperture area, and wherein the storage area and the accumulation electrode area largely coincide. In view of the requirements to the present pixel the field electrode area is larger than the accumulation electrode area. One electrode may relate to an electrically neutral (or ground) electrode. It is noted that the terms "ac- cumulation" and "field" relate to a function intended by the respective electrodes.

For controlling movement of colored particles and stability of a status (transparent or colored) a driver circuit for applying an electro-magnetic field to the pix- els is provided.

The present pixel is characterized in that the field electrode and accumulation electrode are located at a same height on the second substrate. This provides movement of the particles in a largely lateral mode (with respect to the substrates), contrary to many prior art pixels, having at least a partial vertical mode. The present pixel is further characterized in that a distance between the first and second substrate is from 5-20 μm, such as 10 μm. The distance is much smaller than typical prior art devices. The present design, allowing lateral movement, as well as a relatively small distance provide a much better control of the movement of the particles (per unit time and per unit distance), a good control of the electrical field (< ±0.01 ν/μm) being almost insensitive to imperfections of the ma- terials used, such as perturbations (<+0.2 μm) , superior alignment (no issues whatsoever, i.e. <±0.001 μm) , no need for a shield, and providing a good stability (refreshment times > 60 sec) of the two statuses. Even further, the present design allows for stacking of pixels, contrary to pri- or art devices, such as is further detailed below. One important characteristics in view of stacking and in view of general use is a contrast ratio between a colored or black status and a white or transparent status. Light is considered to pass through a first substrate, than through the fluid, being reflected by a second substrate, passes again through the fluid and though the first substrate. A relative amount of light is considered to be reduced by a transmittance factor (T) of the fluid and a reflectance factor (R) of the second substrate (in formula T-R-T) . This factor is compared for the two statuses (e.g. black/white) and a ratio between the two statuses is calculated. The factor is determined by using white light and determining the relative amount of light that is received by a CCD- camera at a wavelength of 550 nm. Prior art devices typically report a factor of about 40%*90%*40%~12% for the white status and ~2% for the black status, hence a ratio of about 6. The present device provides 70%*90%*70%~44% for the white status and -2% for the black status, hence a ra- tio of about 22, hence significantly higher. Such is even more surprising as typically the person skilled in the art is not inclined to reduce a thickness as an amount of colored/black particles per unit volume is limited and it is typically considered that a minimum height of 50 μm for the fluid is needed to provided sufficient "coloring" to a pixel; in other words the contrast ratio is considered to become too low and hence no good distinction (for the eye) can be made between colored/white pixels. Inventors have found that a height of even 3 or 4 μm is still sufficient, e.g. in view of contrast, but for practical purposes a minimum height of 5 pm is often chosen.

The present pixel may comprise walls. The walls may fully enclose one pixel, or may have one or more gaps. Also each wall section may have one or more gaps. For in- stance, horizontal or vertical gaps may be provided. The gaps may have a size of 10-200 μm length, such as 20-100 μm, e.g. 50 μm. Such is found to improve capillary flow and filling .

The term "optical" may relate to wavelengths visi- ble to a human eye (about 380 nm- about 750 nm) , where applicable, and may relate to a broader range of wavelengths, including infrared (about 750 nm - 1 mm} and ultraviolet (about 10 nm-380 nm) , and sub-selections thereof, where applicable . Important is that the present pixel and device are fully adaptable, e.g. to changing light conditions.

The present electronic display device comprises pixels therein, which pixels can be changed instantly, i.e. within a few milliseconds, e.g. replacing an image by an^¬ other .

The present device comprises a driver circuit for changing appearance of (individual) pixels by applying an electro-magnetic field. As such also appearance of the dis- play device, or one or more parts thereof, may be changed.

The present device may further comprise a means for receiving data, such as individual pixel data, pixel color data, pixel filter data, pixel spectral data, pixel reflectivity data, pixel transmittance data, pixel intensi- ty data, and display pattern data, etc. As such the present device can be controlled on a pixel level, on a display level, on a matrix of pixels level, and combinations thereof. It is preferred to provide data in a wireless mode;

however data may also be provided by connecting a cable or the like, such as be providing a USB-port or the like. For the wireless mode preferably an RFID per display device is provided, as well as a transmitter for communicating with the display, preferably a transceiver, for also receiving data from a display. As such each individual display device and display can be adapted, e.g. according to wishes of a user, and to light conditions.

The present electronic device may comprise a unique code for identification. As such every electronic device can be identified individually.

The present display device is relatively thin and can therefore in principle be applied to e.g. a stack of devices. The display present has a thickness < 0.1 cm, preferably a thickness of 10 μm-500 μm, more preferably a thickness of 15 μm-300 μm, even more preferably a thickness of 25 μm-200 μm, such as 50 μm-100 μm. A thickness may vary, e.g. depending on a number of devices applied. As such the present display device (in a transparent mode) is not or hardly visible for a human eye.

The present device may comprise a processing unit, typically a CPU, for processing input, providing output, processing data, etc.

Also a power supply is provided, typically a battery. The present invention relies partly on earlier re- search and development by IRX Technologies B.V. For that reason and for better understanding of the underlying technology reference is made to recently filed (June 7, 2013) Dutch Patent application NL2010936. Various aspects, examples, advantages and so forth are in principle one to one applicable to the present invention. It is noted that the technology disclosed in the above patent applications has not been put into practice yet. Various obstacles have been encountered that still had to be solved. For instance bi- stability and switching times were not sufficient. Various other aspects, examples, advantages and so forth are in principle one to one applicable to the present invention. The teachings and examples of the above document are incorporated by reference herein. The present invention provides amongst others an improved layout in view of the prior art.

Thereby the present invention provides a solution to one or more of the above mentioned problems.

Advantages of the present description are detailed throughout the description.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates in a first aspect to an electronic device according to claim 1.

The pixel comprises a fluid (or liquid) . The fluid may be any suitable fluid and a combination of suitable fluids. It is preferred to use a relatively low viscosity fluid, such as having a dynamic viscosity of 1 mPa.s or less. The fluid comprises at least one type of pigment particles having a diameter smaller than 500 nm. The diameter is defined herein to be the largest distance that can be formed between two opposite parallel lines tangent to its boundary. It has been found that these particles provide a good distribution of particles over the present (field) electrode. In view of an electro-magnetic field to be applied the present particles are being chargeable or charged. Likewise magnetic particles may be used. A small charge per particle is found to be sufficient, such as from O.le to lOe per particle. A concentration of par^¬ ticles is in the order of 1-100 g/1. A size of an electric po^¬ tential is in the order of 0.5-50 V, preferably from 1-20 V, such as 5-15 V. For the present pixel a relatively large po- tential is preferred, e.g. 15-10 V. It has been found that fluid behaviour is better at a higher voltage, e.g. in terms of flow, and switching time. It is preferred to have particles charge stabilized. As such a better performance e.g. in view of distribution over the field electrode, and faster and bet- ter controllable switching times are achieved.

In an example a thin-film transistor is applied to drive a pixel, optionally in combination with other drivers.

In an example the present pixel further comprises a third electrode of a substantially transparent material for providing electro-osmotic forces to the coloured particles, wherein the third electrode is located on the first substrate. It has been found that by providing this third electrode the switching time is reduced and the movement of particles is enhanced and distribution in space thereof is improved, e.g. in terms of homogeneous distribution. Such provides a better quality images, e.g. in terms of contrast. In an example the third electrode is a spray-coated electrode. Such an electrode can be applied easily, has a good performance and reduces production costs. An example of such an electrode is an ITO elec- trode. The ITO typically has a 50-250 Ohm/square resistance, such as 100-150 Ohm/square. Preferably (Al and Ga) doped

( 10¹⁹-10²² carrier concentration/cm³) ZnO and ITO are used.

Such transparent films can be used more abundantly, thereby creating a (more) homogeneous electro-magnetic field. Such a homogeneous field is considered relevant for obtaining (sufficient) bi-stability. In terms of a more homogeneous field also smaller pixel sizes have found to contribute positively.

In an example of the present pixel conducting lines are envisaged for providing an electro-magnetic field. The lines typically have a width of 1-5 μm, such as 3-4 μm, and a thickness of 0.01-5 μm, such as 0.1-2 μm, preferably having a low electrical resistance of 50-250 Ohm/square resistance, such as 100-150 Ohm/square. Preferably transparent conducting thin films are used, such as indium-tin-oxide, (Al and Ga) doped (10¹⁹-10²² carrier concentration/cm³) ZnO. Such transparent films can be used more abundantly, thereby creating a (more) homogeneous electro-magnetic field. Such a homogeneous field is considered relevant for obtaining (sufficient) bi- stability. In terms of a more homogeneous field also smaller pixel sizes have found to contribute positively.

The above layers, and specifically the ITO layers can be spray coated as follows. The material, such as ITO, is spray coated using two targets, e.g. 90% ln₂0₃ and 10% SnC>2 composition to obtain 1:10 Sn/In ratio; in addition thereto the above dopants may be provided. A resistance of 100 Ω/cm² is obtained at 280 °C when applied during 3 min in vacuum. The thickness of the layer was found to be 23±5 nm and typically a variation in thickness is less than 10%. A micro-waviness of the layers is less than 0.2 μm/20 mm (Rt/W) . Typically no cracks and no fouls are found. Depending on a layer thickness (20-200 nm) a transmittance is found to vary from T>87% (@ 20 nm) to T > 78% (@ 300 nm) . The square resistance varies also in line with the thickness of a layer from 150 Ω/cm² (@ 20 nm) to 5 Ω/cm² (300 nm) . The etch time, e.g. in order to provide structures such as electrodes, varies from 30-280 sec (20-300 nm) . The obtained layers have a good temperature and chemical stability (e.g. versus 10% NaOH during 5 min/ 6% HCL during 2 min/ acetone or ethanol during min gives a change in re- sistance of < 10%) .

In an example the third electrode covers the first substrate fully or partly. In view of production a full coverage is preferred, albeit at the expense of a somewhat reduced control of particles. In view of control and stability it has been found that a third electrode largely coinciding in area with the field electrode provides the best results.

In an example the present device comprises a stack of 2-5 pixels (100a,b,c), such as a stack of 3 pixels, each pixel in the stack comprising different coloured particles. There- with a full colour device is provided. In an example thereof a first substrate of a second pixel and a second substrate of a first pixel are the same, i.e. are combined into one substrate. Such is a big advantage of the present device, therewith reducing the number of substrates in a stack, improving contrast and transparency, and reducing complexity. In an example the fluid is transparent. The above examples may be com^¬ bined in full or in part.

In an example of the present stack of pixels the col- oured particles are selected from cyan, magenta, and yellow particles. In an example the first pixel in the stack comprises cyan particles, the second comprises magenta particles, and the third comprises yellow particles. By individually switching pixels in the stack, i.e. cyan, magenta and yellow, full colour control is achieved.

In an example if the present pixel a density of pixels is from 2-500 pixels/cm, preferably 5-250 pixels/cm, more preferably 10-100 pixels/cm, even more preferably 25-75 pix- els/cm, such as 40-60 pixels/cm (or 120 and 160 DPI, respec- tively) . Surprisingly these dimensions provide the best results in terms of contrast, sharpness, haze factor, and brightness. In fact the present device is better than e.g. a 160 DPI LCD.

In an example of the present pixel the first and sec- ond substrate are spaced apart by (glass) beads having a diameter of 5-20 urn, preferably 7-15 pm, such as 10-12 μm. The randomly distributed beads, preferably glass beads or polymer beads, define a distance between the substrates very accurately, provide strength and flexibility to the pixel, and hardly disturb movement of the coloured particles. The beads can be produced such that a very homogenous distribution of sizes thereof is obtained, e.g. with an accuracy (and thus 3* standard deviation) of better than 0.1 μm. The average volume of beads is 0.1-15 vol.% relative to the volume of the pixel, i.e. they occupy only small volume.

In an example of the present pixel a pixel area is from 2000 μm² - 25 mm², preferably 5000 μm² - 10 mm², more preferably 10000 μm² - 5 mm², such as 1-2 mm². So a relatively large variation in size is possible, which may be relevant to an intended application of the present pixels/displays.

In an example of the present pixel the field electrode area is from 50-80% of the pixel area, preferably form 60-75%, such as 65-70%. The field electrode, and hence the aperture area, is preferably as large as possible, in view of e.g. contrast.

In an example of the present pixel the accumulation electrode area is from 10-40% of the pixel area, preferably 15-25%, such as 20%. The accumulation area is preferably as small as possible.

In an example of the present pixel the second substrate comprises a blank area of 5-30% of the pixel area. The present coloured particles "hop" over the blank area from one electrode to the other. The blank area is preferably as small as possible.

In an example of the present pixel the accumulation electrode comprising a base and at least two fingers extending from that base and the pixel electrode comprising a base and at least one finger extending from that base; as such movement of the articles is better controlled and switching times are reduced.

In an example of the present pixel the fingers of the common electrode and the pixel electrode are arranged in an interdigitated manner; and the fingers of the pixel electrode and the common electrode optionally taper outwardly in a direction away from the base of that electrode. Such contributes further to the control and switching time.

In an example of the present pixel the pixels have a rectangular form, such as square, or a hexagonal form.

In an example the present device comprises a reflector for reflecting light that has passed through at least the first transparent substrate and the liquid, such as an internal or an external reflector, wherein the reflector is white, or metallic; and an active matrix arranged on the second sub- strate on a side facing the liquid, wherein the active matrix comprises for each pixel of the electrophoretic display: at least two metal layers, such as Al; a dielectric layer, such as Si0₂; a storage capacitor formed using the at least two metal layers and the dielectric layer, and wherein the reflec- tor is preferably formed by at least one of the at least two metal layers.

In an example the present pixel comprises a scattering element configured to diffusively scatter light reflected by the reflector. Therewith contrast is improved. In an example of the present device the fluid carries a charge; therewith e.g. switching times are improved.

In an example of the present device the fluid comprises one or more of a surfactant, an emulsifier, a polar compound, and a compound capable of forming a hydrogen bond.

In an example of the present device the fluid has a relative permittivity ε_r of less than 10, and a viscosity of less than 0.1 Pa*s, such as from 0.2-10 mPa*s, e.g. 0.5-5 mPa*s, e.g. 1-2 mPa*s.

In an example of the present device the fluid is pro^¬ vided in an amount of 1-100 gr/m², preferably 2-75 gr/m², more preferably 20-50 gr/m², such as 30-40 gr/m².

In an example of the present device the coloured particles are provided in an amount of 0.02-30 gr/m², preferably 0.05-10 gr/m², more preferably 0.5-5 gr/m², such as 1-3 gr/m².

Examples of suitable combinations of fluid and col^¬ oured particles are BASF BPIG 245C (black), BPIG185 f (black), MPIG 268a (magenta), PIG269a (magenta), MPIGlli (magenta), CPIG31a (cyan), GPIG12d (yellow) and so on. Examples of BASF pigments are IRGAPHOR BLACK S0100 CF, Paliogen Schwarz EH 078, CHROMOPHTAL JET CYAN GLX, Heliogen Blau L7 460, Cinquasia Magenta L 4540, Cinquasia Magenta D4500J, Irgazin DPP Red BO Pigment, GELB 273 AKX and Cromophtal Yellow D0980J. Typically coloured particles are provided in concentrations of 0.2-5 wt.%, such as 0.5-3 wt . % (all percentages based on a total weight of the dispersion). As a solvent typically 70-95 wt.% is added, such as 75-85 wt.%. Suitable solvents are typically organic solvents comprising preferably at least one of C₈-C₁₅ alkanes, such as nonane, decane, undecane, dodecane, and tridecane, tetradecane, preferably undecane or dodecane. Typically 2-7 wt.% primary cation, such as 4-6 wt.%, is present. Suitable primary cations may be selected from at least one tertiary and quaternary ammoniums, optionally with an associated anion such as DMS . In addition 1-7 wt.% of at least one secondary ion, such as 2-6 wt.%, e.g. 3-5 wt.% of an amine, such as poly siloxane amines, such as poly dimethyl siloxane amine. In addition 2-8 wt.%, such as 3-7 wt.% of a secondary cation, such as a Si based cation, such as a siloxane, e.g. a dimethyl siloxane may be present. A total of charged agents is typically between 5-25 wt . % , such as 10-15 wt . % . Further additives, such as 0-2 wt . % rheology improvers, may be present as well. One may start from a "mother" dispersion and dilute this dispersion by adding (further) solvent. A stable suspension was typically quickly obtained (1-30 h) .

In an example of the present device the at least one type of coloured particles comprise one or more of white particles, red particles, green particles, blue particles, black particles, reflective particles, light absorbing particles, fluorescent particles, and phosphorescing particles, and/or each type of pigment particle carries a significantly different charge, such as one being charged positively, another negatively, a third with a small charge, and a fourth with a large charge, etc. In an example the charge is from 5*10^"7-0.1 C/m², such as from 1*10^"5-0.01 C/m². In an example the present pigment may change colour or appearance upon applying an electro-magnetic field, or likewise upon removing such a field.

In an example of the present device the coloured particles are smaller than 400 nm, preferably smaller than 300 nm, more preferably smaller than 200 nm, even more preferably smaller than 100 nm, such as smaller than 50 nm, and typically larger than 10 nm. It is preferred to provide a stable dispersion; as such the above sizes are preferred. The particle size is considered to be a measure of an averaged diameter thereof. It has further been found that smaller particles attribute significantly to the present characteristics of the pixels.

In an example of the present pixel the at least one field electrode is at least partly transparent to visible light, or wherein at least one field electrode is at least partly reflective to visible light.

For improved performance, e.g. in terms of switching time, distribution of particles, durability, etc. it may be preferred to have at least two accumulation electrodes and at least two field electrodes, more preferably at least one of each electrode located at a side of the pixel.

As mentioned above the present pixel may be relative^¬ ly small. When switching times and/or optical resolution become more critical smaller pixels are preferred having a length of the pixel smaller than 250 μm, preferably smaller than 150 μm, more preferably smaller than 100 μm, such as smaller than 90 pm. Present designs relate to a length of 150 μm, of 85 pm, of 75 μm, and of 50 μm. A smallest size considered at this point in time is about 25 μm. Also combinations of sizes are envisaged; such could imply a standardized unit length of e.g. 75 pm is used, and multiplicities thereof. From a production point of view somewhat larger pixels are preferred, such as having a length of 300 μm - 500 μm. From a control point of view smaller pixels are preferred. Typically a width of the pixel has a similar or the same dimension. The present pixel now provides an optical resolution that is more than sufficient for any application considered at this point in time. In an example maps may be provided on a smartphone, having sufficient optical detail to find ones way. Further a reader can continue reading for a long period of time, without getting tired. It is noted that in this respect LCD-displays provide too much light.

In an example of the present pixel the fluid carries a charge. Such has been found to be particularly advantageous, in similar terms as mentioned above.

It has been found that a disadvantage of the present pixels, and especially of smaller pixels, is that an electrical breakdown may occur. In order to prevent such a breakdown further measures may be incorporated. In an exam- pie the fluid has a reduced permittivity ε_r of less than 10, preferably of less than 5. However, such change in permittivity typically involves further compounds, such as oils, which are not (fully) compatible with other constituents. Thereto further compounds /components may be added, such as a surfac- tant, an emulsifier, a polar compound, and a compound capable of forming a hydrogen bond. In view of relatively quick switching times it has been found that the viscosity of the fluid is preferably less than 0.1 Pa*s, such as by using a mixture comprising ethylene glycol.

In an example the present pixel has a rectangular shape, such as a square shape, or a hexagonal shape. In view of switching times these layouts have been found to perform optimally. The hexagonal shape has a further advantage in that each side of the hexagon may be used for accumulating pigment particles. By varying charges or otherwise a first side can be used for red particles, a second side for green particles, and a third side for blue particles, and so further. Such could also be achieved by sub-dividing at least one side of a square pixel.

In an example of the present pixel the at least one type of pigment particles comprises one or more of white particles, red particles, green particles, blue particles, black particles, reflective particles, light absorbing particles, fluorescent particles, and phosphorescing particles. As such a combination of visible pigment particles may be provided, thereby obtaining any intended colour, in any intended brightness. In principle the same effect could be obtained by using one or more pigment particles that absorb (a specific wave- length (region) of) light. Likewise also reflective pigments may be used. The present small pixel size makes it possible to make e.g. in a matrix format a red pixel, adjacent to a blue pixel, adjacent to a green pixel, etc. As such a mixture of colours may be provided by activating an intended pixel, in an intended intensity, etc.

In an example the present pixel further comprises a UV-filter. Such is not considered yet, however, inventors have identified that some of the elements inside a pixel and possibly a transparent layer are preferably protected from environ- mental effects, such as UV-light. In an example especially an electrode needs to be protected from UV-light.

In an example of the present pixel the aperture area is more than 85%, such as 90% transparent, preferably more than 95%; typically transparency is determined at a wavelength of 550 nm. The aperture area may be made of glass and a suitable polymer, such as poly carbonate (Perspex) . The material for the aperture, e.g. glass, may have a thickness of 0.1 mm - 2 mm, such as 0.5-1 mm. If a flexible pixel and/or display are required it is preferred to use a thin material. If some strength is required, a thicker material is preferred. It has been found that with such transparency energy consumption can even be further reduced. In this respect it is noted that the present pixel uses about 0.1% of prior art pixels, such as LCD-pixels. Such provides huge advantages, e.g. in terms of usage, reduced need for loading devices, smaller charge stor^¬ ing devices, etc. Especially when a power grid is not available such will be appreciated. It is noted that power consump^¬ tion of e.g. smartphones is significant. Any reduction in pow^¬ er consumption will be beneficial to the earth.

In an example of the present pixel the at least one field electrode is at least partly transparent to visible light, preferably more than 95% transparent. In an example an upper electrode, e.g. in a stack of pixels, is preferably as transparent as possible. In a further example the at least one field electrode is at least partly reflective to visible light, preferably more than 95% reflective, such as when forming a "bottom" electrode, such as in a lowest pixel in a stack. Also combination of the above is envisaged.

In an example the present device comprises a means for processing data, such as a CPU, for making received data visible, for addressing individual pixels, for refreshing a display, etc. The device may further comprise a means for near field communication, such as a receiver and a transmitter. As such a display device may directly be addressed using a suitable signal, the signal providing updated information. Typically such communication also involves handshaking protocols, such as identifying an ID of a device and e.g. a computer or the like providing further information. The present device may in an example comprise a controller, such as a chip, a CPU. The controller, driver, power supply, means for transmitting and receiving may be integrated.

It is noted that by providing (wireless) signals like all display devices may be updated within a small time frame, if required. Such can be repeated e.g. every hour, or every minute, or every second. In fact continuous communication between device and information providing means, such as a computer, may be continuous. As such performance of the present electronic device may be adapted (almost) continuously.

As the present device and in particular an electro- phoretic display device consumes a minute amount of energy a small means of providing power, such as a battery, a capacitor, a coil, etc. may be provided. Likewise the present device may be connected to a power grid. It is noted that power con- sumption of the present device is so low that the display needs to be refreshed at the most only every two hours.

In an example the present electrophoretic display device further comprises a driver circuit for driving the one or more pixels by providing an electro-magnetic field, typically an electrical field. The applied voltage is in an example 15- 30 V, preferably being large enough to move particles. Prefer^¬ ably counter ions are present.

In an example of the present device the driver circuit comprises a means for providing a time varying electromagnetic field between the at least one field electrode and the at least one accumulation electrode, preferably a wave form varying e-m field.

In an example the electrophoretic display device comprises at least one shared field electrode. The shared field electrode may be shared by at least two pixels, typically by a row or column of pixels.

The present driver circuit for use in an electrophoretic display device according to the invention or in a pixel according to the invention, may comprise a means for providing a time varying electro-magnetic field between the at least one field electrode and the at least one accumulation electrode. Therewith movement from charged pigment particles to and from an accumulation electrode and from and to a field electrode is effected. The driver circuit may further provide an electromagnetic field for clearing pixels (removing charged particles} , for driving pixels (introducing charged particles} , for resetting pixels (moving charged particles to an initial position) . And for applying a static charge, for remaining charged pixels in position occupied at a point in time. Also a field for refreshing may be provided, e.g. for having a similar or same amount of pixels in an earlier position.

In an example the driver circuit comprises a switch for providing a static electro-magnetic field or charge to one or more of the electrodes. In an example only very scarcely a static pulse, or likewise a refresh pulse is provided, such as once every two hours. The pulse may be short and at a low intensity .

In an example the electronic display comprising pix- els is provided in a flexible polymer, and the remainder of the display device is provided in glass. The glass may be rig^¬ id glass or flexible glass. If required a protection layer is provided. If more than one colour is provided, more than one layer of flexible polymer may be provided. The polymer may be poly ethylene naphthalate (PEN) , poly ethylene terephthalate (PET) (optionally having a SiN layer) , poly ethylene (PE) , etc .

In a further example the electronic display comprising pixels is provided in at least one flexible polymer. As such the display may be attached to any surface, such as by using an adhesive.

In a second aspect the present invention relates to a use of an electronic device according to the invention, preferably an electrophoretic display device, for one or more of presenting data, projecting data and as a window blind.

The present resolution may be in the order of 300 DPI, or better. A size of a display device may be relatively small such as from 10 cm² (or smaller) , up to relatively large scale, e.g. 2000 cm².

In a third aspect the present invention relates to a product comprising the present electronic device, wherein the product is preferably selected from a window blind, a signage system, e-reader, outdoor display, electronic label, secondary screen, smart glass, colour panel, and a screen.

The invention is further detailed by the accompanying figures and examples, which are exemplary and explanatory of nature and are not limiting the scope of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

The invention although described in detailed explanatory context may be best understood in conjunction with the accompanying examples and figures.

SUMMARY OF FIGURES

Fig. la-c show top and side views of a layout of an electronic device .

Fig. 2 shows a stack of pixels. Fig. 3-6 show an electrode design.

DETAILED DESCRIPTION OF FIGURES

Fig. la shows a top view of an example of a layout of an electronic device 100. Therein a second substrate 42 is shown, having a field electrode 10 and an accumulation electrode 20.

Fig. lb shows a top view of an example of a layout of an electronic device 100. Therein a first substrate 41 is shown, having an aperture area 11 and a storage area 21.

Fig. lc shows the present pixel from a side view, having a first substrate 41, a space comprising a fluid 50, and a second substrate 42.

Fig. 2 gives a side view of an example of the present electronic device 100 having a sequence of pixels

100a, 100b, 100c stack on top of one and another.

Fig. 3 shows an electrode design. Therein electrode fingers have a spacing of 70 μm, a length from base to tip of 90 μm, a distance from base to base of 210 μm, a width of 13 μm, a bas width of 10 pm, and second electrodes positioned in between the fingers. In between the first and second electrodes a spacing of about 10 μm is provided.

In fig. 4 in addition to the layout of fig. 3 the finger tips are slightly curved, with a radius of about 5 μm. Also the finger-base attachment section is curved, with a cur- vature having a radius of 15 μm. Both the second electrodes and the spacing follow the finger curvatures.

In fig. 5, in addition to fig. 4, also a slight tapering to the fingers is provided. At a smallest section the fingers have a width of 9 μm, whereas the top section has a curvature with a radius of 8 μm. Also the finger-base attachment section is curved, with a curvature having a radius of 21.7 μm. Both the second electrodes and the spacing follow the finger curvatures.

In fig. 6, in addition to fig. 5, the finger tips are droplet shaped, the droplet having a radius of 11 μm, a curvature directly below the droplet of 20 μm. At a smallest section the fingers have a width of 9 μm. Also the finger-base attachment section is curved, with a curvature having a radius of 20 pm. Both the second electrodes and the spacing follow the finger curvatures.

For the figures 3-6 it has been found that performance of the pixels improves, e.g. in terms of contrast. It has been found that the colored particles divide much better of the surface area. Such problems do not occur with e.g. E-ink type pixels.

It should be appreciated that for commercial application it may be preferable to use one or more variations of the present system, which would similar be to the ones disclosed in the present application and are within the spirit of the invention .

Claims

1. Electronic device comprising

(a) electrophoretic pixels (100), the electrophoretic pixel comprising

a first transparent substrate (41) ,

located in the first substrate at least one aperture area (11) being visible, and

located in the first substrate at least one storage area (21) for storing the at least one type of coloured particles preferably out of sight,

a second substrate (42),

a fluid (50) in between the first (41) and second (42) substrate, the fluid comprising at least one type of coloured particles having a diameter smaller than 500 nm, the particles being chargeable or charged,

at least two electrodes (10,20) spaced apart for providing an electro-magnetic field, of which at least one electrode (20) is an accumulation electrode and at least one electrode is a field electrode (10),

wherein the at least one field electrode (10) occu- pies an field electrode area, and the at least one field electrodes optionally forming a common electrode, wherein the field electrode area and the aperture area (11) largely coincide,

wherein the accumulation electrode occupies an accu- mulation electrode area (21) ,

wherein the at least one storage area is adjacent to the at least one aperture area, and wherein the storage area (21) and the accumulation electrode area largely coincide, wherein the field electrode area is larger than the accumulation electrode area, and

(b) a driver circuit for applying an electromagnetic field to the pixels,

characterized in that

the field electrode (10) and accumulation electrode (20) are located at a same height on the second substrate (42), and

wherein a distance between the first and second substrate is from 5-20 μm.

2. Electronic device according to claim 1, further comprising a third electrode (30) of a substantially transparent material for providing electro-osmotic forces to the col- oured particles, wherein the third electrode (30) is located on the first substrate (41).

3. Electronic device according to claim 2, wherein the third electrode is a spray-coated electrode.

4. Electronic device according to any of the preced- ing claims, wherein the third electrode covers the first substrate fully or partly.

5. Electronic device according to any of the preceding claims, comprising a stack of 2-5 pixels (100a, b,c), each pixel in the stack comprising different coloured particles, and wherein optionally a first substrate of a second pixel and a second substrate of a first pixel are the same, and wherein the fluid is preferably transparent.

6. Electronic device according to claim 5, wherein the coloured particles are selected from cyan, magenta, and yellow particles.

7. Electronic device according to any of the preceding claims, wherein at least one of

a density of pixels is from 2-500 pixels/cm, the first and second substrate are spaced apart by beads having a diameter of 5-20 μm, and the average volume of beads is 0.1-15 vol.% relative to the volume of the pixel, a pixel area is from 2000 μm² - 25 mm²,

the field electrode area is from 50-80% of the pixel area,

the accumulation electrode area is from 10-40% of the pixel area, and

the second substrate comprises a blank area of 5-30% of the pixel area.

8. Electronic device according to any of the preced- ing claims, wherein the accumulation electrode comprising a base and at least two fingers extending from that base and the pixel electrode comprising a base and at least one finger extending from that base;

wherein the fingers of the common electrode and the pixel electrode are arranged in an interdigitated manner; and the fingers of the accumulation electrode and a common electrode optionally taper outwardly in a direction away from the base of that electrode, and optionally comprise a circular el- ement .

9. Electronic device according to any of the preced^¬ ing claims, wherein the pixels have a rectangular form, such as square, or a hexagonal form.

10. Electronic device according to any of the preced- ing claims, comprising a reflector for reflecting light that has passed through at least the first transparent substrate and the liquid, and

an active matrix arranged on the second substrate on a side facing the liquid, wherein the active matrix comprises for each pixel of the electronic device,

at least two metal layers;

a dielectric layer;

a storage capacitor formed using the at least two metal layers and the dielectric layer, and

wherein the reflector is preferably formed by at least one of the at least two metal layers.

11. Electronic device according to any of the preceding claims, wherein the pixel further comprises a scattering element configured to diffusively scatter light reflected by the reflector.

12. Electronic device according to any of the preceding claims, wherein one or more of

the fluid carries a charge,

the fluid comprises one or more of a surfactant, an emulsifier, a polar compound, and a compound capable of forming a hydrogen bond,

the fluid has a relative permittivity ε_r of less than 10, and a viscosity of less than 0.1 Pa*s,

the fluid is provided in an amount of 1-100 gr/m², the coloured particles are provided in an amount of

0.02-30 gr/m², and

the coloured particles are smaller than 400 nm.

13. Electronic device according to any of the preceding claims, wherein the at least one field electrode is at least partly transparent to visible light, or wherein at leas one field electrode is at least partly reflective to visible light.

14. Electronic device according to any of the preced ing claims, comprising a driver circuit, the driver circuit comprising a means for providing a time varying electromagnetic field between the at least one field electrode and the at least one accumulation electrode, preferably a wave form varying electro-magnetic field.

15. Electronic device according to claim 13, wherein the driver circuit comprises a switch for providing a static electro-magnetic field or charge to one or more of the electrodes .

16. Use of an electronic device according to any of claim 1-15 for one or more of presenting data, projecting data, and as a window blind.

17. Product comprising an electronic device accordin to any of claim 1-15, wherein the product is preferably selected from a window blind, a signage system, e-reader, outdoor display, electronic label, secondary screen, smart glass colour panel, and a screen.