Patent Application
20250006146
An electrophoretic display (EPD) changes color by modifying the position of one or more charged colored particles with respect to a light-transmissive viewing surface. Such electrophoretic displays are typically referred to as “electronic paper” or “ePaper” because the resulting display has high contrast and is sunlight-readable, much like ink on paper. Electrophoretic displays have enjoyed widespread adoption in eReaders because the electrophoretic displays provide a book-like reading experience, use little power, and allow a user to carry a library of hundreds of books in a lightweight handheld device. Such devices are increasingly being adapted to display out-of-home (OOH) digital content, such as shelf labels, outdoor advertisement and transportation signage.
For many years, electrophoretic displays included only two types of charged color particles, black and white. (To be sure, “color” as used herein includes black and white.) The white particles are often of the light scattering type, and comprise, e.g., titanium dioxide, while the black particle are absorptive across the visible spectrum, and may comprise carbon black, or an absorptive metal oxide, such as copper chromite. In the simplest sense, a black and white electrophoretic display only requires a light-transmissive electrode at the viewing surface, a back electrode, and an electrophoretic medium including oppositely charged white and black particles. When a voltage of one polarity is provided, the white particles move to the viewing surface, and when a voltage of the opposite polarity is provided the black particles move to the viewing surface. If the back electrode includes controllable regions (pixels)—either segmented electrodes or an active matrix of pixel electrodes controlled by transistors—a pattern can be made to appear electronically at the viewing surface. The pattern can be, for example, the text to a book.
More recently, a variety of color option have become commercially available for electrophoretic displays, including three-color displays (black, white, red; black white, yellow), and four color displays (black, white, red, yellow). Similar to the operation of black and white electrophoretic displays, electrophoretic displays with three or four reflective pigments operate similar to the simple black and white displays because the desired color particle is driven to the viewing surface. The driving schemes are far more complicated than only black and white, but in the end, the optical function of the particles is the same.
Advanced Color electronic Paper (ACeP™) also includes four particles, but the cyan, yellow, and magenta particles are subtractive rather than reflective, thereby allowing thousands of colors to be produced at each pixel. The color process is functionally equivalent to the printing methods that have long been used in offset printing and ink-jet printers. A given color is produced by using the correct ratio of cyan, yellow, and magenta on a bright white paper background. In the instance of ACeP, the relative positions of the cyan, yellow, magenta and white particles with respect to the viewing surface will determine the color at each pixel. While this type of electrophoretic display allows for thousands of colors at each pixel, it is critical to carefully control the position of each of the (50 to 500 nanometer-sized) pigments within a working space of about 10 to 20 micrometers in thickness. Obviously, variations in the position of the pigments will result in incorrect colors being displayed at a given pixel. Accordingly, exquisite voltage control is required for such a system. More details of this system are available in the following U.S. Patents, all of which are incorporated by reference in their entireties: U.S. Pat. Nos. 9,361,836, 9,921,451, 10,276,109, 10,353,266, 10,467,984, 10,593,272, and 10,657,869.
As described in the aforementioned patents, the waveforms (i.e., electric fields provided across the electrophoretic medium as a function of time) typically require substantial swings in voltage polarity in a short time. Because of this, in some instances, the colored electrophoretic display “flashes,” “flickers,” or “looks flashy” when switching between color images. This shortcoming is particularly pronounced when a full-color eReader is quickly switched (i.e., in less than 1 second) between full-color images. U.S. Pat. No. 10,657,869 addressed a similar issue, however the '869 patent does not suggest to use look up tables to store offset waveforms, as described below. Other patents owned by E Ink Corporation, such as U.S. Pat. No. 8,593,396 also provided solutions for shifting the initiation of a waveform or reducing (or increasing) the size of the waveform in order to improve gray scale control, however these patents did not appreciate that such adjustments would decrease flash when properly coordinated.
In particular, this invention relates to color electrophoretic displays, especially, but not exclusively, to electrophoretic displays capable of rendering more than two colors using a single layer of electrophoretic material comprising a plurality of colored particles, for example white, cyan, yellow, and magenta particles. In some instances, two of the particles will be positively-charged, and one (or two) of the particles will be negatively-charged. In some instances one of the particles will be positively-charged, and three particles will be negatively-charged. In some instances one of the particles will be negatively-charged, and three particles will be positively-charged. The particles may additionally different in the type of charge species on the particle surface and/or the type of polymer(s) functionalized on the surface. The particles may comprise organic or inorganic pigments or dyes.
The term gray state is used herein in its conventional meaning in the imaging art to refer to a state intermediate two extreme optical states of a pixel, and does not necessarily imply a black-white transition between these two extreme states. For example, several of the E Ink patents and published applications referred to below describe electrophoretic displays in which the extreme states are white and deep blue, so that an intermediate gray state would actually be pale blue. Indeed, as already mentioned, the change in optical state may not be a color change at all. The terms black and white may be used hereinafter to refer to the two extreme optical states of a display, and should be understood as normally including extreme optical states which are not strictly black and white, for example the aforementioned white and dark blue states.
The terms bistable and bistability are used herein in their conventional meaning in the art to refer to displays comprising display elements having first and second display states differing in at least one optical property, and such that after any given element has been driven, by means of an addressing pulse of finite duration, to assume either its first or second display state, after the addressing pulse has terminated, that state will persist for at least several times, for example at least four times, the minimum duration of the addressing pulse required to change the state of the display element. It is shown in U.S. Pat. No. 7,170,670 that some particle-based electrophoretic displays capable of gray scale are stable not only in their extreme black and white states but also in their intermediate gray states, and the same is true of some other types of electro-optic displays. This type of display is properly called multi-stable rather than bistable, although for convenience the term bistable may be used herein to cover both bistable and multi-stable displays.
The term impulse, when used to refer to driving an electrophoretic display, is used herein to refer to the integral of the applied voltage with respect to time during the period in which the display is driven.
A particle that absorbs, scatters, or reflects light, either in a broad band or at selected wavelengths, is referred to herein as a colored or pigment particle. Various materials other than pigments (in the strict sense of that term as meaning insoluble colored materials) that absorb or reflect light, such as dyes or photonic crystals, etc., may also be used in the electrophoretic media and displays of the present invention.
Particle-based electrophoretic displays have been the subject of intense research and development for a number of years. In such displays, a plurality of charged particles (sometimes referred to as pigment particles) move through a fluid under the influence of an electric field. Electrophoretic displays can have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared with liquid crystal displays. Nevertheless, problems with the long-term image quality of these displays have prevented their widespread usage. For example, particles that make up electrophoretic displays tend to settle, resulting in inadequate service-life for these displays.
As noted above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but electrophoretic media can be produced using gaseous fluids; see, for example, Kitamura, T., et al., Electrical toner movement for electronic paper-like display, IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y, et al., Toner display using insulative particles charged triboelectrically, IDW Japan, 2001, Paper AMD4-4). See also U.S. Pat. Nos. 7,321,459 and 7,236,291. Such gas-based electrophoretic media appear to be susceptible to the same types of problems due to particle settling as liquid-based electrophoretic media, when the media are used in an orientation which permits such settling, for example in a sign where the medium is disposed in a vertical plane. Indeed, particle settling appears to be a more serious problem in gas-based electrophoretic media than in liquid-based ones, since the lower viscosity of gaseous suspending fluids as compared with liquid ones allows more rapid settling of the electrophoretic particles.
Numerous patents and applications assigned to or in the names of the Massachusetts Institute of Technology (MIT) and E Ink Corporation describe various technologies used in encapsulated electrophoretic and other electro-optic media. Such encapsulated media comprise numerous small capsules, each of which itself comprises an internal phase containing electrophoretically-mobile particles in a fluid medium, and a capsule wall surrounding the internal phase. Typically, the capsules are themselves held within a polymeric binder to form a coherent layer positioned between two electrodes. The technologies described in these patents and applications include:
Many of the aforementioned patents and applications recognize that the walls surrounding the discrete microcapsules in an encapsulated electrophoretic medium could be replaced by a continuous phase, thus producing a so-called polymer-dispersed electrophoretic display, in which the electrophoretic medium comprises a plurality of discrete droplets of an electrophoretic fluid and a continuous phase of a polymeric material, and that the discrete droplets of electrophoretic fluid within such a polymer-dispersed electrophoretic display may be regarded as capsules or microcapsules even though no discrete capsule membrane is associated with each individual droplet; see for example, U.S. Pat. No. 6,866,760. Accordingly, for purposes of the present application, such polymer-dispersed electrophoretic media are regarded as sub-species of encapsulated electrophoretic media.
A related type of electrophoretic display is a so-called microcell electrophoretic display. In a microcell electrophoretic display, the charged particles and the fluid are not encapsulated within microcapsules but instead are retained within a plurality of cavities formed within a carrier medium, typically a polymeric film. See, for example, U.S. Pat. Nos. 6,672,921 and 6,788,449.
Although electrophoretic media are often opaque (since, for example, in many electrophoretic media, the particles substantially block transmission of visible light through the display) and operate in a reflective mode, many electrophoretic displays can be made to operate in a so-called shutter mode in which one display state is substantially opaque and one is light-transmissive. See, for example, U.S. Pat. Nos. 5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; 6,225,971; and 6,184,856. Dielectrophoretic displays, which are similar to electrophoretic displays but rely upon variations in electric field strength, can operate in a similar mode; see U.S. Pat. No. 4,418,346. Other types of electro-optic displays may also be capable of operating in shutter mode. Electro-optic media operating in shutter mode can be used in multi-layer structures for full color displays; in such structures, at least one layer adjacent the viewing surface of the display operates in shutter mode to expose or conceal a second layer more distant from the viewing surface.
An encapsulated electrophoretic display typically does not suffer from the clustering and settling failure mode of traditional electrophoretic devices and provides further advantages, such as the ability to print or coat the display on a wide variety of flexible and rigid substrates. (Use of the word printing is intended to include all forms of printing and coating, including, but without limitation: pre-metered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating; roll coating such as knife over roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; silk screen printing processes; electrostatic printing processes; thermal printing processes; ink jet printing processes; electrophoretic deposition (See U.S. Pat. No. 7,339,715); and other similar techniques.) Thus, the resulting display can be flexible. Further, because the display medium can be printed (using a variety of methods), the display itself can be made inexpensively.
As indicated above most simple prior art electrophoretic media essentially display only two colors. Such electrophoretic media either use a single type of electrophoretic particle having a first color in a colored fluid having a second, different color (in which case, the first color is displayed when the particles lie adjacent the viewing surface of the display and the second color is displayed when the particles are spaced from the viewing surface), or first and second types of electrophoretic particles having differing first and second colors in an uncolored fluid (in which case, the first color is displayed when the first type of particles lie adjacent the viewing surface of the display and the second color is displayed when the second type of particles lie adjacent the viewing surface). Typically the two colors are black and white. If a full color display is desired, a color filter array may be deposited over the viewing surface of the monochrome (black and white) display. Displays with color filter arrays rely on area sharing and color blending to create color stimuli. The available display area is shared between three or four primary colors such as red/green/blue (RGB) or red/green/blue/white (RGBW), and the filters can be arranged in one-dimensional (stripe) or two-dimensional (2×2) repeat patterns. Other choices of primary colors or more than three primaries are also known in the art. The three (in the case of RGB displays) or four (in the case of RGBW displays) sub-pixels are chosen small enough so that at the intended viewing distance they visually blend together to a single pixel with a uniform color stimulus (‘color blending’). The inherent disadvantage of area sharing is that the colorants are always present, and colors can only be modulated by switching the corresponding pixels of the underlying monochrome display to white or black (switching the corresponding primary colors on or off). For example, in an ideal RGBW display, each of the red, green, blue and white primaries occupy one fourth of the display area (one sub-pixel out of four), with the white sub-pixel being as bright as the underlying monochrome display white, and each of the colored sub-pixels being no lighter than one third of the monochrome display white. The brightness of the white color shown by the display as a whole cannot be more than one half of the brightness of the white sub-pixel (white areas of the display are produced by displaying the one white sub-pixel out of each four, plus each colored sub-pixel in its colored form being equivalent to one third of a white sub-pixel, so the three colored sub-pixels combined contribute no more than the one white sub-pixel). The brightness and saturation of colors is lowered by area-sharing with color pixels switched to black. Area sharing is especially problematic when mixing yellow because it is lighter than any other color of equal brightness, and saturated yellow is almost as bright as white. Switching the blue pixels (one fourth of the display area) to black makes the yellow too dark.
U.S. Pat. Nos. 8,576,476 and 8,797,634 describe multicolor electrophoretic displays having a single back plane comprising independently addressable pixel electrodes and a common, light-transmissive front electrode. Between the back plane and the front electrode is disposed a plurality of electrophoretic layers. Displays described in these applications are capable of rendering any of the primary colors (red, green, blue, cyan, magenta, yellow, white and black) at any pixel location. However, there are disadvantages to the use of multiple electrophoretic layers located between a single set of addressing electrodes. The electric field experienced by the particles in a particular layer is lower than would be the case for a single electrophoretic layer addressed with the same voltage. In addition, optical losses in an electrophoretic layer closest to the viewing surface (for example, caused by light scattering or unwanted absorption) may affect the appearance of images formed in underlying electrophoretic layers.
Attempts have been made to provide full-color electrophoretic displays using a single electrophoretic layer. For example, U.S. Pat. No. 8,917,439 describes a color display comprising an electrophoretic fluid that comprises one or two types of pigment particles dispersed in a clear and colorless or colored solvent, the electrophoretic fluid being disposed between a common electrode and a plurality of pixel or driving electrodes. The driving electrodes are arranged to expose a background layer. U.S. Pat. No. 9,116,412 describes a method for driving a display cell filled with an electrophoretic fluid comprising two types of charged particles carrying opposite charge polarities and of two contrast colors. The two types of pigment particles are dispersed in a colored solvent or in a solvent with non-charged or slightly charged colored particles dispersed therein. The method comprises driving the display cell to display the color of the solvent or the color of the non-charged or slightly charged colored particles by applying a driving voltage that is about 1 to about 20% of the full driving voltage. U.S. Pat. Nos. 8,717,664 and 8,964,282 describe an electrophoretic fluid, and a method for driving an electrophoretic display. The fluid comprises first, second and third type of pigment particles, all of which are dispersed in a solvent or solvent mixture. The first and second types of pigment particles carry opposite charge polarities, and the third type of pigment particles has a charge level being less than about 50% of the charge level of the first or second type. The three types of pigment particles have different levels of threshold voltage, or different levels of mobility, or both.
Electrophoretic displays capable of rendering any color at any pixel location have been described in U.S. Pat. Nos. 10,475,399 and 10,678,111. In the '399 patent, a display is described in which a white (light-scattering) pigment moves in a first direction when addressed with a low applied voltage and in the opposite direction when addressed with a higher voltage. In the '111 patent, a full-color electrophoretic display is described in which there are four pigments: white, cyan, magenta and yellow, in which two of the pigments are positively-charged and two negatively charged. U.S. Patent Publication 2022/0082896 describes a full-color electrophoretic display in which there are four pigments: white, cyan, magenta and yellow, in which the three colored pigments are positively-charged and white pigment negatively charged. Embodiments of the present invention of this type are referred to as CMYW embodiments.
In addition, there are multi-particle display designs in which the color pigments scatter light (i.e., reflective color particles). U.S. Pat. No. 10,339,876 describes a display of this type having black, white and red particles capable of rendering three states. Similar display designs including four pigments can render four different colors, see, e.g. U.S. Pat. No. 9,922,603, or, by using a semi-transparent colored particle, such displays can render six colors, see, e.g., U.S. Pat. No. 11,640,803. Many of the multi-particle display designs using light-scattering particles incorporate lengthy and “flashy” updates, which some viewers find unappealing. The solutions described below can be used to decrease the “flashiness” of the updates in such displays, and typically require very little additional cost in terms of new controllers or drivers.
Disclosed herein are improved methods of driving full color electrophoretic displays and full color electrophoretic displays using these drive methods. In one aspect, the invention includes an electrophoretic display, which includes a light-transmissive electrode, an active matrix backplane comprising a plurality of rows of pixel electrodes, each pixel electrode being coupled to a thin-film transistor comprising a gate line and a source line, an electrophoretic medium disposed between the light-transmissive electrode and the active matrix backplane, wherein the electrophoretic medium includes at least three different types of charged pigment particles. The electrophoretic display additionally includes a controller coupled to a plurality of gate lines, each gate line being coupled to the thin-film transistors of one of the plurality of rows of pixel electrodes, and the controller being coupled to a plurality of source lines, the controller further being configured to address the pixel electrodes in a row-by-row fashion by providing both a gate voltage and a source voltage to each thin-film transistor, and non-transitory memory coupled to the controller and comprising a look-up table, wherein for a transition between a first color and a second color, wherein the look-up table includes a first waveform for causing the electrophoretic medium to transition between the first color and the second color, and a second waveform for causing the electrophoretic medium to transition between the first color and the second color, wherein the first and second waveforms are identical with respect to a number of voltage pulses and a polarity and magnitude of each of the voltage pulses, but wherein the first and second waveforms are time-shifted by at least 1 ms, e.g., 5 ms, e.g., 8 ms, e.g., 12 ms. Additionally, the controller performs the following steps when updating the electrophoretic display between the first image and the second image: receiving the first waveform from the look up table; providing the first waveform to a first row of pixel electrodes; receiving the second waveform from the look up table; and providing the second waveform to a second row of pixel electrodes adjacent the first row of pixel electrodes.
In one embodiment, the look-up table further comprises a third waveform for causing the electrophoretic medium to transition between the first color and the second color, wherein the first, second, and third waveforms are identical with respect to a number of voltage pulses and a polarity and magnitude of each of the voltage pulses, but wherein the first and second and third waveforms are time-shifted by at least 5 ms from each other, and the controller further performs the step of receiving the third waveform from the look-up table and providing the third waveform to a third row of pixel electrodes adjacent to the second row of electrodes, wherein the second row of electrodes are between the first row of electrodes and the third row of electrodes. In one embodiment, the look-up table further comprises a fourth waveform for causing the electrophoretic medium to transition between the first color and a third color, wherein the third waveform is not identical with respect to a number of voltage pulses and a polarity and magnitude of each of the voltage pulses of the first and second waveforms, but wherein the first and second and third waveforms are time-shifted by at least 1 ms from each other. In one embodiment, the first waveform and the second waveform are time-shifted by at least 5 ms, optionally at least 10 ms, optionally time shifted by between 12 ms and 20 ms. In one embodiment, the first waveform and the second waveform are time-shifted by a frame, wherein a frame is the time required to address every pixel in the active matrix backplane one time when addressing the active matrix backplane in a row-by-row fashion. In one embodiment, the magnitudes of the voltage pulses are between −15V and +15V, or between −24V and +24V. In one embodiment, the electrophoretic medium includes a reflective white particle and at least one subtractive color particle or a reflective white particle and at least one reflective color particle. In one embodiment, the electrophoretic medium includes a fourth type of electrophoretic particle. In one embodiment, two of the types of particles are negatively charged and two of the types of particles are positively charged, or wherein one of the types of particles is negatively charged and three of the types of particles are positively charged, or wherein three of the types of particles are negatively charged and one of the types of particles is positively charged. In one embodiment, the electrophoretic medium is encapsulated in microcapsules or microcells.
The invention includes electrophoretic displays with multi-particle electrophoretic media, and improved methods for driving such multi-particle electrophoretic media. Displays of the invention typically include an active matrix backplane of pixel electrodes controlled with thin-film transistors. Typically, each pixel electrode is also couple to a storage capacitor. While the driving methods of displays are generalizable to all different types of electrophoretic displays (segmented, direct drive, indirect drive, active matrix) and may be used with a variety of waveforms, the inventive displays are often used for driving more complicated electrophoretic media, e.g., which require precise control of three, four, or more particles simultaneously. In preferred embodiments, the displays of the invention use active matrix backplanes controlled with an array of thin-film transistors and the driving waveforms are repetitive “push-pull” types. Using the techniques described herein, electrophoretic displays incorporating the disclosed drive schemes will typically appear less “flashy” as compared to addressing with traditional row-by-row updating using a single “best” waveform for a particular color transition, which has been the state of the art for some time. Such displays may include multiple subtractive colored electrophoretic particle and/or multiple reflective colored electrophoretic particles. In a preferred embodiment, the electrophoretic medium includes a white particle and cyan, yellow, and magenta subtractive primary colored particles, i.e., a WCMY system.
Methods for fabricating an electrophoretic display including four (or more) particles have been discussed in the prior art. The electrophoretic fluid may be encapsulated in microcapsules or incorporated into microcell structures that are thereafter sealed with a polymeric layer. The microcapsule or microcell layers may be coated or laminated to a plastic substrate or film bearing a transparent coating of an electrically conductive material. Alternatively, the microcapsules may be coated onto a light transmissive substrate or other electrode material using spraying techniques. (See U.S. Pat. No. 9,835,925, incorporated by reference herein). The resulting assembly may be laminated to a backplane bearing pixel electrodes using an electrically conductive adhesive. The assembly may alternatively be attached to one or more segmented electrodes on a backplane, wherein the segmented electrodes are driven directly.
This invention provides, among other things, an architecture and method for using a thin film transistor array to address an electrophoretic display with dipoles. Larger look-up tables are used, which include a plurality of time-shifted waveforms for each color transition. The controller can thus easily cause a phase shift in the color flashes across the display, which ultimate diminishes or removes the perception that the device is “flashing” during an update from a first image to a second image. Accordingly, a variety of multi-particle (color) electrophoretic displays can be addressed without visible flickering or flashing.
Electrophoretic media used herein include charged particles that vary in color, reflective or absorptive properties, charge density, and mobility in an electric field (measured as a zeta potential). A particle that absorbs, scatters, or reflects light, either in a broad band or at selected wavelengths, is referred to herein as a colored or pigment particle. Various materials other than pigments (in the strict sense of that term as meaning insoluble colored materials) that absorb or reflect light, such as dyes, photonic crystals, quantum dots, etc., may also be used in the electrophoretic media and displays of the present invention. For example, the electrophoretic medium might include a fluid, a plurality of first and a plurality of second particles dispersed in the fluid, the first and second particles bearing charges of opposite polarity, the first particle being a light-scattering particle and the second particle having one of the subtractive primary colors, and a plurality of third and a plurality of fourth particles dispersed in the fluid, the third and fourth particles bearing charges of opposite polarity, the third and fourth particles each having a subtractive primary color different from each other and from the second particles, wherein the electric field required to separate an aggregate formed by the third and the fourth particles is greater than that required to separate an aggregate formed from any other two types of particles.
The electrophoretic media of the present invention may contain any of the additives used in prior art electrophoretic media as described for example in the E Ink and MIT patents and applications mentioned above. Thus, for example, the electrophoretic medium of the present invention will typically comprise at least one charge control agent to control the charge on the various particles, and the fluid may have dissolved or dispersed therein a polymer having a number average molecular weight in excess of about 20,000 and being essentially non-absorbing on the particles to improves the bistability of the display, as described in the aforementioned U.S. Pat. No. 7,170,670.
In one embodiment, the present invention uses a light-scattering particle, typically white, and three substantially non-light-scattering particles. There is of course no such thing as a completely light-scattering particle or a completely non-light-scattering particle, and the minimum degree of light scattering of the light-scattering particle, and the maximum tolerable degree of light scattering tolerable in the substantially non-light-scattering particles, used in the electrophoretic of the present invention may vary somewhat depending upon factors such as the exact pigments used, their colors and the ability of the user or application to tolerate some deviation from ideal desired colors. The scattering and absorption characteristics of a pigment may be assessed by measurement of the diffuse reflectance of a sample of the pigment dispersed in an appropriate matrix or liquid against white and dark backgrounds. Results from such measurements can be interpreted according to a number of models that are well-known in the art, for example, the one-dimensional Kubelka-Munk treatment. In the present invention, it is preferred that the white pigment exhibit a diffuse reflectance at 550 nm, measured over a black background, of at least 5% when the pigment is approximately isotropically distributed at 15% by volume in a layer of thickness 1 μm comprising the pigment and a liquid of refractive index less than 1.55. The yellow, magenta and cyan pigments preferably exhibit diffuse reflectances at 650, 650 and 450 nm, respectively, measured over a black background, of less than 2.5% under the same conditions. (The wavelengths chosen above for measurement of the yellow, magenta and cyan pigments correspond to spectral regions of minimal absorption by these pigments.) Colored pigments meeting these criteria are hereinafter referred to as “non-scattering” or “substantially non-light-scattering”. Specific examples of suitable particles are disclosed in U.S. Pat. Nos. 9,921,451, which is incorporated by reference herein.
Alternative particle sets may also be used, including four sets of reflective particles, or one absorptive particle with three or four sets of different reflective particles, i.e., such as described in U.S. Pat. Nos. 9,922,603 and 10,032,419, which are incorporated by reference herein. For example, white particles may be formed from an inorganic pigment, such as TiO2, ZrO2, ZnO, Al2O3, Sb2O3, BaSO4, PbSO4 or the like, while black particles may be formed from CI pigment black 26 or 28 or the like (e.g., manganese ferrite black spinel or copper chromite black spinel) or carbon black. The third/fourth/fifth type of particles may be of a color such as red, green, blue, magenta, cyan or yellow. The pigments for this type of particles may include, but are not limited to, CI pigment PR 254, PR122, PR149, PG36, PG58, PG7, PB28, PB15:3, PY138, PY150, PY155 or PY20. Specific examples include Clariant Hostaperm Red D3G 70-EDS, Hostaperm Pink E-EDS, PV fast red D3G, Hostaperm red D3G 70, Hostaperm Blue B2G-EDS, Hostaperm Yellow H4G-EDS, Hostaperm Green GNX, BASF Irgazine red L 3630, Cinquasia Red L 4100 HD, and Irgazin Red L 3660 HD; Sun Chemical phthalocyanine blue, phthalocyanine green, diarylide yellow or diarylide AAOT yellow.
As shown in
In some embodiments, e.g., as shown in
Conventionally, in high resolution arrays, the pixels are arranged in a two-dimensional array of rows and columns, such that any specific pixel is uniquely defined by the intersection of one specified row and one specified column. (See
It should be noted that the magnitude of the voltage that can be provided in such row-column driving can be limited by the materials from which the non-linear element, e.g., thin film transistor, is fabricated. In many embodiments the semiconductor material is silicon, especially amorphous silicon, which is able to control driving voltages on the order of ±15 V. In other embodiments, the semi-conductor of the thin-film-transistor may be a metal oxide, such indium gallium zinc oxide (IGZO), which allows for a wider range of driving voltages, e.g., up to ±30 V e.g., as described in U.S. Patent Publication No. US 2022/0084473. This design feature is particularly pertinent when driving waveforms to sort the pigments of a multi-particle system. In such systems, it is beneficial to provide at least five voltage levels (high positive, low positive, zero, low negative, high negative), and with higher total voltages, it is easier to separate the particles. For greater details, see U.S. Patent Publication 2021-0132459.
In a conventional electrophoretic display using an active matrix backplane, each pixel electrode has associated therewith a capacitor electrode (storage capacitor) such that the pixel electrode and the capacitor electrode form a capacitor; see, for example, International Patent Application WO 01/07961. In some embodiments, N-type semiconductor (e.g., amorphous silicon) may be used to from the transistors and the “select” and “non-select” voltages applied to the gate electrodes can be positive and negative, respectively.
Additional details of the row-column addressing used in an “active matrix” display are shown in
Conventionally, in high resolution arrays, the pixels are arranged in a two-dimensional array of rows and columns, such that any specific pixel is uniquely defined by the intersection of one specified row and one specified column. The sources of all the transistors in each column are connected to a single column (scan) line 406, while the gates of all the transistors in each row are connected to a single row (gate) line 408; again the assignment of sources to rows and gates to columns is conventional but essentially arbitrary, and could be reversed if desired. The gate lines 408 are optionally connected to a gate line driver 412, which essentially ensures that at any given moment only one row is selected, i.e., that there is applied to the selected row electrode a select voltage such as to ensure that all the transistors in the selected row are conductive, while there is applied to all other rows a non-select voltage such as to ensure that all the transistors in these non-selected rows remain non-conductive. The column scan lines 406 are optionally connected to scan line drivers 410, which place upon the various scan lines 406 voltages selected to drive the pixels in the selected row to their desired optical states. (The aforementioned voltages are relative to a common top electrode, and is not shown in
The active matrix backplane described with respect to
Waveforms (discussed below) are typically stored in the non-transitory memory 70, however they can also be incorporated into the controller 60 or the processor 50 or they can be stored on the cloud and downloaded via communications 85. A number of look-up tables can be used to facilitate the methods of the invention, especially to provide time shifted waveforms to the controller 60 as appropriate. In particular for a given transition from a first color to a second color in an electrophoretic medium having eight primaries a look up table could include instructions for updating from color 1 to a later color (with no time offset) in look-up slots 1 to 8, while instructions for updating from color 1 to a later color (with a first time offset) in look-up slots 9 to 16, and instructions for updating from color 1 to a later color (with a second time offset) in look-up slots 17 to 24, and so on. Of course, this type of look-up table can also be indexed for improved performance in view of operating conditions, such as device temperature, battery health, front-light color, front-light intensity, etc.
Once the desired image has been converted for display on the display module 55, the specific image instructions are sent to a controller 60, which facilitates voltage sequences being sent to the respective thin film transistors (described above). Such voltages typically originate from one or more power supplies 80, which may include, e.g., a power management integrated chip (PMIC). The electrophoretic display 40 may additionally include communication 85, which may be, for example, WIFI protocols or BLUETOOTH, and allows the electrophoretic display 40 to receive images and instructions, which also may be stored in memory 70. The electrophoretic display 40 may additionally include one or more sensors 90, which may include a temperature sensor and/or a photo sensor, and such information can be fed to the processor 50 to allow the processor to select an optimum look-up-table when such look-up-tables are indexed for ambient temperature or incident illumination intensity or spectrum. In some instances, multiple components of the electrophoretic display 40 can be embedded in a singular integrated circuit. For example, a specialized integrated circuit may fulfill the functions of processor 50 and controller 60.
As shown in
More specifically, when the cyan, magenta and yellow particles lie below the white particles (Situation [A] in
It is possible that one subtractive primary color could be rendered by a particle that scatters light, so that the display would comprise two types of light-scattering particle, one of which would be white and another colored. In this case, however, the position of the light-scattering colored particle with respect to the other colored particles overlying the white particle would be important. For example, in rendering the color black (when all three colored particles lie over the white particles) the scattering colored particle cannot lie over the non-scattering colored particles (otherwise they will be partially or completely hidden behind the scattering particle and the color rendered will be that of the scattering colored particle, not black).
Notably with the dipole waveforms of
As can be seen in
One way to decrease the flash for a given transition from a first color to a second color is to provide waveforms for the same transition that are offset (slightly) in time. Similar to noise-cancelling headphones, by providing coordinated peaks when the dominant waveform has valleys, a viewer does not perceive the large swings between color, i.e., the image is optically quieter. The method for this improvement is shown in more detail in
It should be noted that the techniques of
The invention allows a non-flashing update of a multi-pigment color display without requiring substantial modification to the driving electronics. Having thus described several aspects and embodiments of the technology of this application, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those of ordinary skill in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the technology described in the application. For example, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the embodiments described herein. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described. In addition, any combination of two or more features, systems, articles, materials, kits, and/or methods described herein, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present disclosure.
This application claims priority to U.S. Provisional Application No. 63/523,484, filed Jun. 27, 2023. All patents and publications disclosed herein are incorporated by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 63523484 | Jun 2023 | US |
