Tuned top electrode-driving electrode voltages for switching the optical states of electrophoretic displays using different magnitude positive and negative voltages

Abstract

A system for simplified driving of an electrophoretic medium using positive and negative voltage sources, the voltage sources having different magnitudes, and a controller that coordinates driving at least two drive electrodes opposite the top electrode while cycling the top electrode between the two voltage sources and ground. The resulting system can achieve nearly the same color states as one that provides six independent drive levels and ground to each drive electrode. Thus, the system simplifies the required electronics with only a minor loss in color gamut. The system is particularly useful for addressing an electrophoretic medium that includes four sets of different particles, for example, three of the particles are colored and subtractive and one of the particles is light scattering.

Description

[Background technology]

[0001] (Related Applications) This application claims priority to U.S. Provisional Patent Application No. 63 / 320,524, filed March 16, 2022. This application additionally claims priority to U.S. Patent Application No. 17 / 474,375, filed September 14, 2021. All patents and publications disclosed herein are incorporated by reference in their entirety.

[0002] Electrophoretic displays (EPDs) change color by modifying the position of charged colored particles relative to a light-transmissive viewing surface. Such electrophoretic displays are typically referred to as "electronic paper" or "e-paper" because the resulting display has high contrast and is readable in sunlight, much like ink on paper. Electrophoretic displays have been widely adopted in e-readers, such as the AMAZON KINDLE®, because they provide a book-like reading experience, use low power, and allow users to carry a library of hundreds of books in a lightweight, portable device.

[0003] For many years, electrophoretic displays have included only two types of charged color particles: black and white (for clarity, "color" as used herein includes black and white). The white particles are often light scattering and comprise, for example, titanium dioxide, while the black particles are absorptive across the visible spectrum and may comprise carbon black, or an absorbing metal oxide such as copper chromite. In the simplest sense, a black and white electrophoretic display requires only a light-transmissive electrode at the viewing surface, a back electrode, and an electrophoretic medium that includes 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 split electrodes or an active matrix of pixel electrodes controlled by transistors - a pattern can be made to appear electronically at the viewing surface. This pattern can be, for example, the text for a book.

[0004] More recently, a variety of color options have become commercially available for electrophoretic displays, including three-color displays (black, white, red, and 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 similarly to simple black and white displays, as the desired color particles are driven relative to the viewing surface. This driving scheme is much more complicated than just black and white, but ultimately the optical function of the particles is the same.

[0005] Advanced Color Electronic Paper (ACeP TM) also contains 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 long used in offset and inkjet printers. A given color is produced by using the correct ratios of cyan, yellow, and magenta colors on a bright white paper background. In the case 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. This type of electrophoretic display allows thousands of colors at each pixel, but careful control of the position of each of the pigments (50-500 nanometers in size) within a working space about 10-20 microns thick is crucial. Obviously, variations in the position of the pigments will result in the wrong color being displayed at a given pixel. Hence, precise voltage control is required for such systems. Further details of this system are available in the following U.S. patents, all of which are incorporated by reference in their entirety: U.S. Patent Nos. 9,361,836, 9,921,451, 10,276,109, 10,353,266, 10,467,984, and 10,593,272.

[0006] The present invention relates to color electrophoretic displays, and particularly, but not exclusively, to electrophoretic displays capable of rendering three or more colors using a single layer of electrophoretic material comprising a plurality of colored particles, e.g., white, cyan, yellow, and magenta particles. In some cases, two of the particles will be positively charged and two particles will be negatively charged. In some cases, three of the particles will be positively charged and one particle will be negatively charged. In some cases, one positively charged particle has a thick polymer shell and one negatively charged particle has a thick polymer shell.

[0007] The term "gray state" is used herein in its conventional sense in the imaging arts to refer to a state intermediate between two extreme pixel optical states, and does not necessarily imply a black-white transition between these two extreme states. For example, some of the E Ink patents and published applications referenced below describe electrophoretic displays whose extreme states are white and dark blue, such that an intermediate gray state would actually be light blue. In fact, as already mentioned, a change in optical state may not be a change in color at all. The terms "black and white" may be used hereinafter to refer to the two extreme optical states of a display, and should generally be understood to include extreme optical states that are not strictly black and white, such as the white and dark blue states mentioned above.

[0008] The terms "bistable" and "bi-stable" are used herein in their conventional sense in the art to refer to a display comprising display elements having first and second display states differing in at least one optical property, where any given element is driven with an address pulse of finite duration to exhibit either its first or second display state, which state will persist after the address pulse is terminated for at least several times, e.g., at least four times, the minimum duration of the address pulse required to change the state of the display element. It has been 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 for some other types of electro-optic displays. Displays of this type are appropriately referred to as "multistable" rather than "bistable", although for convenience the term "bistable" may be used herein to encompass both bistable and multistable displays.

[0009] The term "impulse", when used to refer to driving an electrophoretic display, is used herein to refer to the integral of an applied voltage versus time during the period that the display is driven.

[0010] Particles that absorb, scatter, or reflect light, either broadband or at selected wavelengths, are referred to herein as colored or pigmented particles. A variety of materials other than pigments (in the strict sense of the term as meaning insoluble colored materials) that absorb or reflect light, such as dyes or photonic crystals, may also be used in the electrophoretic media and displays of the present invention.

[0011] Particle-based electrophoretic displays have been the subject of intense research and development for many 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 to liquid crystal displays. Nevertheless, problems with the long-term image quality of these displays have prevented their widespread use. For example, the particles that make up electrophoretic displays tend to settle, resulting in poor service life for these displays.

[0012] As mentioned above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but electrophoretic media can also 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. Patent Nos. 7,321,459 and 7,236,291. It is believed that such gas-based electrophoretic media are susceptible to the same types of problems as liquid-based electrophoretic media, due to particle settling, when the media is used in an orientation that allows such settling, such as, for example, a sign where the media is placed on a vertical surface. In fact, particle settling is believed to be a more severe problem in gas-based electrophoretic media than in liquid-based ones, since the lower viscosity of the gaseous suspending fluid allows for faster settling of electrophoretic particles compared to that of liquids.

[0013] Numerous patents and applications assigned to or in the name of Massachusetts Institute of Technology (MIT) and E Ink Corporation describe various techniques used in encapsulated electrophoretic and other electro-optic media. Such encapsulated media comprise a number of 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, forming a coherent layer that is positioned between two electrodes. Techniques described in these patents and applications include the following: (a) electrophoretic particles, fluids, and fluid additives (see, e.g., U.S. Pat. Nos. 7,002,728 and 7,679,814); (b) capsules, binders, and encapsulation processes (see, e.g., U.S. Pat. Nos. 6,922,276 and 7,411,719); (c) microcell structures, wall materials, and methods of forming the microcells (see, e.g., U.S. Pat. Nos. 7,072,095 and 9,279,906); (d) methods of filling and sealing microcells (see, e.g., U.S. Pat. Nos. 7,144,942 and 7,715,088); (e) films and subassemblies containing electro-optical materials (see, e.g., U.S. Pat. Nos. 6,982,178 and 7,839,564); (f) backplanes, adhesive layers, and other auxiliary layers and methods used in displays (see, e.g., U.S. Pat. Nos. 7,116,318 and 7,535,624); (g) Color formation and color control (e.g., U.S. Patent Nos. 6,017,584, 6,545,797, 6,664,944, 6,788,452, 6,864,875, 6,914,714, 6,972,893, 7,038,656, 7,038,670, 7,046,228, 7,052,571, 7,075,502, 7,167,155, 7,385,751, 7,492,505, 7,667,684, 7,6 No. 84,108, No. 7,791,789, No. 7,800,813, No. 7,821,702, No. 7,839,564, No. 7,910,175, No. 7,952,790, No. 7,956,841, No. 7,982,941, No. 8, No. 040,594, No. 8,054,526, No. 8,098,418, No. 8,159,636, No. 8,213,076, No. 8,363,299, No. 8,422,116, No. 8,441,714, No. 8,441,716, No. 8 ,466,852, No.8,503,063, No.8,576,470, No.8,576,475, No.8,593,721, No.8,605,354, No.8,649,084, No.8,670,174, No.8,704,756, No. No. 8,717,664, No. 8,786,935, No. 8,797,634, No. 8,810,899, No. 8,830,559, No. 8,873,129, No. 8,902,153, No. 8,902,491, No. 8,917,439, Nos. 8,964,282, 9,013,783, 9,116,412, 9,146,439, 9,164,207, 9,170,467, 9,170,468, 9,182,646, 9,195,111, 9,199,441, 9,268,191, 9,285,649, 9,293,511, 9,341,916, 9,360,733, 9,361,836, 9,383,623, and 9,423,666, and U.S. Patent Application Publication Nos. 2008 / 0043318, 2008 / 0048970, 2009 / 0225398, 2010 / 0156780, 2011 / 0043543, 2012 / 0326957, 2013 / 0242378, 2013 / 0278995, 2014 / 0055840, 2014 / 0078576, 2014 / 0340430, 2014 / 0340736, 2014 / 0362 213, No. 2015 / 0103394, No. 2015 / 0118390, No. 2015 / 0124345, No. 2015 / 0198858, No. 2015 / 0234250, No. 2015 / 0268531, No. 2015 / 0301246, No. 2016 / 0011484, No. 2016 / 0026062, No. 2016 / 0048054, No. 2016 / 0116816, No. 2016 / 0116818, and No. 2016 / 0140909); (h) methods of driving displays (e.g., U.S. Patent Nos. 5,930,026; 6,445,489; 6,504,524; 6,512,354; 6,531,997; 6,753,999; 6,825,970; 6,900,851; 6,995,550; 7,012,600; 7,023,420; 7,034,783; 7,061,166; 7,061,662; 7,116,466; 7,119,772; 7,177,066; 7,193,625; 7,202,84 No. 7, No. 7,242,514, No. 7,259,744, No. 7,304,787, No. 7,312,794, No. 7,327,511 , No. 7,408,699, No. 7,453,445, No. 7,492,339, No. 7,528,822, No. 7,545,358, No. 7 , No. 583,251, No. 7,602,374, No. 7,612,760, No. 7,679,599, No. 7,679,813, No. 7,6 No. 83,606, No. 7,688,297, No. 7,729,039, No. 7,733,311, No. 7,733,335, No. 7,787, No. 169, No. 7,859,742, No. 7,952,557, No. 7,956,841, No. 7,982,479, No. 7,999,78 No. 7, No. 8,077,141, No. 8,125,501, No. 8,139,050, No. 8,174,490, No. 8,243,013, No. 8,274,472, No. 8,289,250, No. 8,300,006, No. 8,305,341, No. 8,314,784, No. 8 ,373,649, No.8,384,658, No.8,456,414, No.8,462,102, No.8,514,168, No.8,53 No. 7,105, No. 8,558,783, No. 8,558,785, No. 8,558,786, No. 8,558,855, No. 8,576, No. 164, No. 8,576,259, No. 8,593,396, No. 8,605,032, No. 8,643,595, No. 8,665,206 No. 8,681,191, No. 8,730,153, No. 8,810,525, No. 8,928,562, No. 8,928,641, No. 8,976,444, No. 9,013,394, No. 9,019,197, No. 9,019,198, No. 9,019,318, No. 9,082,352, No. 9,171,508, No. 9,218,773, No. 9,224,338, No. 9,224,342, No. 9,224,344, No. 9,230,492, No. 9,251,736, No. 9,262,973, No. 9,269,311, No. 9,299,294, No. 9,373,289, No. 9,390,066, No. 9,390,661, and No. 9,412,314, and U.S. Patent Application Publication Nos. 2003 / 0102858, 2004 / 0246562, 2005 / 0253777, 2007 / 0091418, 2007 / 0103427, 2007 / 0176912, 2008 / 0024429, 2008 / 0024482, 2008 / 0136774, 2008 / 0291129, 2008 / 0303780, 2009 / 0174651, 2009 / 0195568, and 2009 / 0322721 No., No. 2010 / 0194733, No. 2010 / 0194789, No. 2010 / 0220121, No. 2010 / 0265561, No. 2010 / 0283804, No. 2011 / 0063314, No. 2011 / 0175875, No. 2011 / 0193840, 2011 / 0193841, 2011 / 0199671, 2011 / 0221740, 2012 / 0001957, 2012 / 0098740, 2013 / 0063333, 2013 / 0194250 No., No. 2013 / 0249782, No. 2013 / 0321278, No. 2014 / 0009817, No. 2014 / 0085355, No. 2014 / 0204012, No. 2014 / 0218277, No. 2014 / 0240210, No. 2014 / 0240373, 2014 / 0253425, 2014 / 0292830, 2014 / 0293398, 2014 / 0333685, 2014 / 0340734, 2015 / 0070744, 2015 / 0097877 Nos. 2015 / 0109283, 2015 / 0213749, 2015 / 0213765, 2015 / 0221257, 2015 / 0262255, 2015 / 0262551, 2016 / 0071465, 2016 / 0078820, 2016 / 0093253, 2016 / 0140910, and 2016 / 0180777 (which patents and applications may hereinafter be referred to as the MEDEOD (Methods of Driving Electro-Optical Displays) Applications); (i) display applications (see, e.g., U.S. Pat. Nos. 7,312,784 and 8,009,348); (j) Non-electrophoretic displays (see, e.g., U.S. Pat. No. 6,241,921, and U.S. Patent Application Publication Nos. 2015 / 0277160, and U.S. Patent Application Publication Nos. 2015 / 0005720 and 2016 / 0012710).

[0014] Many of the aforementioned patents and applications recognize that the walls surrounding the separate microcapsules in an encapsulated electrophoretic medium may be replaced with a continuous phase, thus giving rise to so-called "polymer-dispersed electrophoretic displays" in which the electrophoretic medium comprises a plurality of separate droplets of electrophoretic fluid and a continuous phase of polymeric material, and that the separate droplets of electrophoretic fluid in such polymer-dispersed electrophoretic displays may be considered capsules or microcapsules, even though no separate capsule membrane is associated with each individual droplet. See, for example, U.S. Patent No. 6,866,760. Thus, for purposes of this application, such polymer-dispersed electrophoretic media are considered a subspecies of encapsulated electrophoretic media.

[0015] A related type of electrophoretic display is the so-called "microcell electrophoretic display." In a microcell electrophoretic display, the charged particles and fluid are not encapsulated in microcapsules, but instead are held within a plurality of cavities formed in a propagation medium, typically a polymer film. See, for example, U.S. Patent Nos. 6,672,921 and 6,788,449.

[0016] Although electrophoretic media are often opaque (e.g., in many electrophoretic media, the particles substantially block the 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 are similar to electrophoretic displays, but rely on variations in electric field strength and 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 a shutter mode. Electro-optic media operating in shutter mode can be used in multi-layer structures for full color displays, where at least one layer adjacent the viewing surface of the display operates in shutter mode to expose or conceal a second layer further away from the viewing surface.

[0017] Encapsulated electrophoretic displays typically do not suffer from the clustering and settling failure modes of conventional electrophoretic devices and offer additional advantages such as the ability to print or coat the display on a wide variety of flexible and rigid substrates (the use of the word "printing" is intended to include all forms of printing and coating, including, but not limited to, pre-metered coating, e.g., patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating, etc., roll coating, e.g., knife-over-roll coating, forward-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. Furthermore, because the display medium can be printed (using a variety of methods), the display itself can be inexpensively made.

[0018] As shown above, the simplest prior art electrophoretic media essentially display only two colors. Such electrophoretic media use either a single type of electrophoretic particles having a first color in a colored fluid having a second, different color (wherein the first color is displayed when the particles are adjacent to 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 different first and second colors in a non-colored fluid (wherein the first color is displayed when the first type of particles are adjacent to the viewing surface of the display and the second color is displayed when the second type of particles are adjacent to the viewing surface). Typically, the two colors are black and white. If a full color display is desired, a color filter array can be deposited over the viewing surface of a monochrome (black and white) display.

[0019] 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 (stripes) or two-dimensional (2×2) repeating patterns. Other alternative primary colors or more than three primary colors are also known in the art. The three (for RGB displays) or four (for RGBW displays) subpixels are chosen to be small enough so that at the intended viewing distance, they visually blend together into a single pixel with a uniform color stimulus ("color blending"). An inherent disadvantage of area sharing is that the colorants are always present and the color 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 primary colors occupies one-quarter of the display area (one subpixel out of four), the white subpixel is as bright as the white of the underlying monochrome display, but each of the colored subpixels is no brighter than one-third of the white of the monochrome display. The brightness of the white color shown by the display as a whole cannot exceed one-half the brightness of the white subpixel (the white area of ​​the display is produced by displaying each one-out-of-four white subpixel plus each colored subpixel in its colored form equal to one-third of the white subpixel, so that the three colored subpixels combined do not contribute more than one white subpixel). The brightness and saturation of the colors are reduced by area sharing with color pixels switched to black. Area sharing is particularly problematic when mixing yellow, because it is brighter than any other color of equal brightness, and saturated yellow is nearly as bright as white. Switching a blue pixel (a quarter of the display area) to black makes it a noticeably darker yellow.

[0020] A commonly used system for quantifying the color characteristics of displays, including both luminance and hue, is the CIELAB system, which defines color coordinate values ​​(i.e., L, λ, λ′, λ′) corresponding to colors displayed by a typical color-reflective display device under a CIE standard illuminant D65 (e.g., with a color temperature of 6500 K). * , a * , b * ) is assigned. * represents the brightness from black to white on a scale of 0 to 100, while a * and b * represents a chromaticity without any specific numerical limits. * corresponds to green, and positive a * corresponds to red, and negative b * corresponds to blue, and positive b * corresponds to yellow. * is represented by the following formula: * = 116(R / R0)1 / 3-16, where R is the reflectance and R0 is the standard reflectance value.

[0021] U.S. Patent Nos. 8,576,476 and 8,797,634 describe multicolor electrophoretic displays having a single backplane with independently addressable pixel electrodes and a common light-transmitting front electrode. The common light-transmitting front electrode is also known as the top electrode. Multiple electrophoretic layers are disposed between the backplane and the front electrode. The 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 address electrodes. The electric field experienced by 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 (caused, for example, by light scattering or unwanted light absorption) in the electrophoretic layer closest to the viewing surface can affect the appearance of the image formed in the underlying electrophoretic layer.

[0022] Attempts have been made to provide a full-color electrophoretic display using a single electrophoretic layer. For example, U.S. Patent No. 8,917,439 describes a color display comprising an electrophoretic fluid comprising 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 drive electrodes. The drive electrodes are positioned to expose a background layer. U.S. Patent No. 9,116,412 describes a method of driving a display cell filled with an electrophoretic fluid comprising two types of charged particles that carry opposite charge polarities and are two contrasting colors. The two types of pigment particles are dispersed in a colored solvent or a solvent with dispersed uncharged or weakly charged colored particles. The method includes driving the display cell by applying a drive voltage that is about 1 to about 20% of the total drive voltage to display the color of the solvent or the color of the uncharged or weakly charged colored particles. US Patent Nos. 8,717,664 and 8,964,2822 describe electrophoretic fluids and methods of driving electrophoretic displays. The fluid comprises first, second, and third types 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 that is less than about 50% of the charge level of the first or second types. The three types of pigment particles have different levels of threshold voltage, or different levels of mobility, or both. None of these patent applications discloses a full-color display, in the sense that term is used below, that is capable of achieving at least eight independent colors (white, red, green, blue, cyan, yellow, magenta, and black). [Prior art documents] [Patent documents]

[0023] [Patent Document 1] U.S. Pat. No. 9,361,836 Summary of the Invention [Means for solving the problem]

[0024] Disclosed herein are improved methods of driving full-color electrophoretic displays, and full-color electrophoretic displays using these driving methods. In one aspect, the invention involves a color electrophoretic display including a light-transmissive electrode at a viewing surface, a backplane including an array of thin film transistors coupled to pixel electrodes, each thin film transistor comprising a metal oxide semiconductor layer, and a color electrophoretic medium disposed between the light-transmissive electrode and the backplane. The color electrophoretic medium includes (a) a fluid; (b) a first plurality and a second plurality of particles dispersed in the fluid, the first and second particles carrying charges of opposite polarity, the first particles being light scattering particles and the second particles having one of the subtractive primary colors; and (c) a third plurality and a fourth plurality of particles dispersed in the fluid, the third and fourth particles carrying charges of opposite polarity, and each of the third and fourth particles having a different subtractive primary color from each other and from the second particles.

[0025] In some embodiments, the first electric field required to separate the population formed by the third and fourth types of particles is greater than the second electric field required to separate the population formed from any other two types of particles. In some embodiments, at least two of the second, third, and fourth particles are non-light scattering. In some embodiments, the first particle is white and the second, third, and fourth particles are non-light scattering. In some embodiments, the first and third particles are negatively charged and the second and fourth particles are positively charged. In some embodiments, the first, second, third, and fourth particles are white, cyan, yellow, and magenta, respectively, and the white and yellow particles are negatively charged and the magenta and cyan particles are positively charged. In some embodiments, the yellow, magenta, and cyan pigments exhibit less than 2.5% diffuse reflectance (measured over a black background) at 650, 550, and 450 nm, respectively, when the pigments are distributed approximately isotropically at 15% by volume in a 1 μm thick layer comprising the pigment and a liquid with a refractive index less than 1.55. In some embodiments, the liquid is a non-polar liquid having a dielectric constant less than about 5. In some embodiments, the fluid has an average molecular weight value greater than about 20,000 and has a polymer dissolved or dispersed therein that is essentially non-adsorbing on the particles. In some embodiments, the metal oxide semiconductor is indium gallium zinc oxide (IGZO). The above invention may be incorporated into an e-book reader, a portable computer, a tablet computer, a mobile phone, a smart card, a sign, a watch, a shelf label, or a flash drive.

[0026] In another aspect, a color electrophoretic display includes a controller, a light-transmissive electrode at a viewing surface, and a backplane including an array of thin film transistors coupled to the pixel electrodes, each thin film transistor comprising a metal oxide semiconductor layer. A color electrophoretic medium is disposed between the light-transmissive electrode and the backplane and includes (a) a fluid, (b) a plurality of first and a plurality of second particles dispersed in the fluid, the first and second particles carrying charges of opposite polarity, the first particles being light scattering particles, and the second particles having one of the subtractive primary colors, and (c) a plurality of third and a plurality of fourth particles dispersed in the fluid, the third and fourth particles carrying charges of opposite polarity, and each of the third and fourth particles having a different subtractive primary color from each other and from the second particles. The controller is configured to provide a plurality of driving voltages to the pixel electrodes such that white, yellow, red, magenta, blue, cyan, green, and black can be displayed at each pixel electrode while maintaining the light-transmissive electrode at a constant voltage. In some embodiments, the controller is configured to provide a voltage greater than 25 volts and a voltage less than -25 volts to the pixel electrodes. In some embodiments, the controller is configured to additionally provide a voltage between 25V and 0V and a voltage between -25V and 0V. In some embodiments, the metal oxide semiconductor is indium gallium zinc oxide (IGZO).

[0027] In another aspect, a color electrophoretic display includes a controller, a light-transmissive electrode at a viewing surface, a backplane electrode, and a color electrophoretic medium disposed between the light-transmissive electrode and the backplane electrode, the color electrophoretic medium including (a) a fluid, (b) a plurality of first and a plurality of second particles dispersed in the fluid, the first and second particles carrying charges of opposite polarity, the first particles being light scattering particles, and the second particles having one of the subtractive primary colors, and (c) a plurality of third and a plurality of fourth particles dispersed in the fluid, the third and fourth particles carrying charges of opposite polarity, and each of the third and fourth particles having a different subtractive primary color from each other and from the second particles. The controller is configured to provide a first high voltage and a first low voltage to the light-transmissive electrode and a second high voltage, zero voltage, and a second low voltage to the backplane electrode, whereby white, yellow, red, magenta, blue, cyan, green, and black can be displayed at the viewing surface, and the magnitude of at least one of the first high voltage, the first low voltage, the second high voltage, and the second low voltage is not the same. In some embodiments, the magnitude of the first high voltage and the magnitude of the second high voltage are the same. In some embodiments, the magnitude of the first low voltage and the magnitude of the second low voltage are the same, and the magnitude of the first high voltage and the magnitude of the first low voltage are not the same.

[0028] In another aspect, a color electrophoretic display includes a controller, a light-transmissive electrode at a viewing surface, a backplane electrode, and a color electrophoretic medium disposed between the light-transmissive electrode and the backplane electrode, the color electrophoretic medium including (a) a fluid, (b) a plurality of first and a plurality of second particles dispersed in the fluid, the first and second particles carrying charges of opposite polarity, the first particles being light scattering particles, and the second particles having one of the subtractive primary colors, and (c) a plurality of third and a plurality of fourth particles dispersed in the fluid, the third and fourth particles carrying charges of opposite polarity, and each of the third and fourth particles having a different subtractive primary color from each other and from the second particles. The controller is configured to cause white, yellow, red, magenta, blue, cyan, green, and black to be displayed at the viewing surface by providing one of a plurality of time-dependent drive voltages to the backplane electrode while providing one of the following drive voltages to the light-transmissive electrode: 1) a high voltage for a first time, a low voltage for a second time, and a high voltage for a third time, or 2) a low voltage for the first time, a high voltage for a second time, and a low voltage for a third time.

[0029] In another aspect, a system for driving an electrophoretic medium includes an electrophoretic display, a power supply capable of providing a positive voltage and a negative voltage, the positive and negative voltages having different magnitudes, and a controller coupled to the top electrode driver, the first drive electrode driver, and the second drive electrode driver. The electrophoretic medium includes a light-transmissive top electrode at a viewing surface, the first drive electrode, the second drive electrode, and an electrophoretic medium disposed between the top electrode and the first and second drive electrodes. The controller is configured to: A) provide a positive voltage to the top electrode, a negative voltage to the first drive electrode, and a positive voltage to the second drive electrode in a first frame, B) provide a negative voltage to the top electrode, a negative voltage to the first drive electrode, and a negative voltage to the second drive electrode in a second frame, C) provide a ground voltage to the top electrode, a ground voltage to the first drive electrode, and a positive voltage to the second drive electrode in a third frame, and D) provide a positive voltage to the top electrode, a positive voltage to the first drive electrode, and a positive voltage to the second drive electrode in a fourth frame. In one embodiment, the controller is further configured to: E) provide a negative voltage to the top electrode, a ground voltage to the first drive electrode, and a negative voltage to the second drive electrode in a fifth frame, and F) provide a ground voltage to the top electrode, a ground voltage to the first drive electrode, and a ground voltage to the second drive electrode in a sixth frame. In one embodiment, the electrophoretic medium is encapsulated in a plurality of microcapsules, the microcapsules being dispersed in a polymer binder between the top electrode and the first and second drive electrodes. In one embodiment, the electrophoretic medium is encapsulated in an array of microcells having openings, the openings being sealed with a polymer binder, and the array of microcells being disposed between the top electrode and the first and second drive electrodes. In one embodiment, the electrophoretic medium comprises a non-polar fluid and four sets of particles having different optical properties.In one embodiment, the first and second sets of particles carry charges of opposite polarity, the third and fourth sets of particles carry charges of opposite polarity, the first particles are light scattering particles, and each of the second, third and fourth sets of particles are different subtractive primary colors. In one embodiment, the controller is configured to provide combinations of positive, negative and ground voltages to the top electrode and the first drive electrode such that white, yellow, red, magenta, blue, cyan, green and black can be displayed on the viewing surface. In one embodiment, the first and second sets of particles carry charges of opposite polarity, the third and fourth sets of particles carry the same charge as the second particles, the first particles are light scattering particles, and each of the second, third and fourth sets of particles are different subtractive primary colors. In one embodiment, the controller is configured to provide a combination of positive, negative, and ground voltages to the top electrode and the first drive electrode such that white, yellow, red, magenta, blue, cyan, green, and black can be displayed on the viewing surface. In one embodiment, the positive voltage is +15V and the negative voltage is -9V. In one embodiment, the positive voltage is +9V and the negative voltage is -15V.

[0030] In another aspect, a system for driving an electrophoretic medium includes an electrophoretic display, a power supply capable of providing a positive voltage and a negative voltage, the positive and negative voltages having different magnitudes, and a controller coupled to the top electrode driver, the first drive electrode driver, and the second drive electrode driver. The electrophoretic medium includes a light-transmissive top electrode at a viewing surface, the first drive electrode, the second drive electrode, and an electrophoretic medium disposed between the top electrode and the first and second drive electrodes. The controller is configured to: A) provide a positive voltage to the top electrode, a negative voltage to the first drive electrode, and a positive voltage to the second drive electrode in a first frame, B) provide a negative voltage to the top electrode, a negative voltage to the first drive electrode, and a negative voltage to the second drive electrode in a second frame, C) provide a ground voltage to the top electrode, a ground voltage to the first drive electrode, and a positive voltage to the second drive electrode in a third frame, and D) provide a positive voltage to the top electrode, a positive voltage to the first drive electrode, and a positive voltage to the second drive electrode in a fourth frame. In one embodiment, the controller is further configured to: E) provide a negative voltage to the top electrode, a ground voltage to the first drive electrode, and a negative voltage to the second drive electrode in a fifth frame, and F) provide a ground voltage to the top electrode, a ground voltage to the first drive electrode, and a ground voltage to the second drive electrode in a sixth frame. In one embodiment, the electrophoretic medium is encapsulated in a plurality of microcapsules, the microcapsules being dispersed in a polymer binder between the top electrode and the first and second drive electrodes. In one embodiment, the electrophoretic medium is encapsulated in an array of microcells having openings, the openings being sealed with a polymer binder, and the array of microcells being disposed between the top electrode and the first and second drive electrodes. In one embodiment, the electrophoretic medium comprises a non-polar fluid and four sets of particles having different optical properties.In one embodiment, the first and second sets of particles carry charges of opposite polarity, the third and fourth sets of particles carry charges of opposite polarity, the first particles are light scattering particles, and each of the second, third and fourth sets of particles are different subtractive primary colors. In one embodiment, the controller is configured to provide combinations of positive, negative and ground voltages to the top electrode and the first drive electrode such that white, yellow, red, magenta, blue, cyan, green and black can be displayed on the viewing surface. In one embodiment, the first and second sets of particles carry charges of opposite polarity, the third and fourth sets of particles carry the same charge as the second particles, the first particles are light scattering particles, and each of the second, third and fourth sets of particles are different subtractive primary colors. In one embodiment, the controller is configured to provide a combination of positive, negative, and ground voltages to the top electrode and the first drive electrode such that white, yellow, red, magenta, blue, cyan, green, and black can be displayed on the viewing surface. In one embodiment, the positive voltage is +15V and the negative voltage is -9V. In one embodiment, the positive voltage is +9V and the negative voltage is -15V. The present invention provides, for example, the following items. (Item 1) 1. A system for driving an electrophoretic medium, the system comprising: 1. An electrophoretic display comprising: a light transmissive top electrode at the viewing surface; A first drive electrode; A second drive electrode; an electrophoretic medium disposed between the upper electrode and the first and second drive electrodes; an electrophoretic display comprising: a power supply capable of providing a positive voltage and a negative voltage, the magnitude of the positive voltage and the magnitude of the negative voltage being different; a controller coupled to the top electrode driver, the first drive electrode driver, and the second drive electrode driver; Equipped with The controller: providing the positive voltage to the top electrode, the negative voltage to the first drive electrode, and the positive voltage to the second drive electrode in a first frame; in a second frame, providing the negative voltage to the top electrode, providing the negative voltage to the first drive electrode, and providing the negative voltage to the second drive electrode; in a third frame, providing a ground voltage to the top electrode, providing the ground voltage to the first drive electrode, and providing the positive voltage to the second drive electrode; in a fourth frame, providing the positive voltage to the top electrode, providing the positive voltage to the first drive electrode, and providing the positive voltage to the second drive electrode; A system configured to: (Item 2) The controller: in a fifth frame, providing the negative voltage to the top electrode, providing the ground voltage to the first drive electrode, and providing the negative voltage to the second drive electrode; in a sixth frame, providing the ground voltage to the top electrode, providing the ground voltage to the first drive electrode, and providing the ground voltage to the second drive electrode; 2. The system of claim 1, further configured to: (Item 3) 2. The system of claim 1, wherein the electrophoretic medium is encapsulated in a plurality of microcapsules, the microcapsules being dispersed in a polymer binder between the top electrode and the first and second drive electrodes. (Item 4) 2. The system of claim 1, wherein the electrophoretic medium is encapsulated in an array of microcells having openings, the openings being sealed with a polymer binder, and the array of microcells is disposed between the top electrode and the first and second drive electrodes. (Item 5) Item 10. The system of item 1, wherein the electrophoretic medium comprises a non-polar fluid and four sets of particles having different optical properties. (Item 6) Item 6. The system of item 5, wherein the first and second sets of particles carry opposite polarity charges, the third and fourth sets of particles carry opposite polarity charges, the first particles are light scattering particles, and each of the second, third, and fourth sets of particles are a different subtractive primary color. (Item 7) 7. The system of claim 6, wherein the controller is configured to provide combinations of the positive voltages, the negative voltages, and the ground voltages to the top electrode and the first drive electrode such that white, yellow, red, magenta, blue, cyan, green, and black can be displayed on the viewing surface. (Item 8) 6. The system of claim 5, wherein the first and second sets of particles carry opposite polarity charges, the third and fourth sets of particles carry the same charge as the second particles, the first particles are light scattering particles, and each of the second, third, and fourth sets of particles are a different subtractive primary color. (Item 9) 9. The system of claim 8, wherein the controller is configured to provide combinations of the positive voltages, the negative voltages, and the ground voltages to the top electrode and the first drive electrode such that white, yellow, red, magenta, blue, cyan, green, and black can be displayed on the viewing surface. (Item 10) 2. The system of claim 1, wherein the positive voltage is +15V and the negative voltage is -9V. (Item 11) 2. The system of claim 1, wherein the positive voltage is +9V and the negative voltage is -15V. (Item 12) 1. A system for driving an electrophoretic medium, the system comprising: 1. An electrophoretic display comprising: a light transmissive top electrode at the viewing surface; A first drive electrode; A second drive electrode; an electrophoretic medium disposed between the upper electrode and the first and second drive electrodes; an electrophoretic display comprising: a power supply capable of providing a positive voltage and a negative voltage, the magnitude of the positive voltage and the magnitude of the negative voltage being different; a controller coupled to the top electrode driver, the first drive electrode driver, and the second drive electrode driver; Equipped with The controller: providing the positive voltage to the top electrode, the negative voltage to the first drive electrode, and the positive voltage to the second drive electrode in a first frame; in a second frame, providing the negative voltage to the top electrode, providing the negative voltage to the first drive electrode, and providing the negative voltage to the second drive electrode; in a third frame, providing a ground voltage to the top electrode, providing the ground voltage to the first drive electrode, and providing the ground voltage to the second drive electrode; in a fourth frame, providing the positive voltage to the top electrode, providing the positive voltage to the first drive electrode, and providing the positive voltage to the second drive electrode; A system configured to: (Item 13) The controller: in a fifth frame, providing the negative voltage to the top electrode, providing the ground voltage to the first drive electrode, and providing the negative voltage to the second drive electrode; in a sixth frame, providing the ground voltage to the top electrode, providing the ground voltage to the first drive electrode, and providing the ground voltage to the second drive electrode; Item 13. The system of item 12, further configured to: (Item 14) Item 13. The system of item 12, wherein the electrophoretic medium is encapsulated in a plurality of microcapsules, the microcapsules being dispersed in a polymer binder between the top electrode and the first and second drive electrodes. (Item 15) Item 13. The system of item 12, wherein the electrophoretic medium is encapsulated in an array of microcells having openings, the openings being sealed with a polymer binder, and the array of microcells is disposed between the top electrode and the first and second drive electrodes. (Item 16) Item 13. The system of item 12, wherein the electrophoretic medium comprises a non-polar fluid and four sets of particles having different optical properties. (Item 17) Item 17. The system of item 16, wherein the first and second sets of particles carry opposite polarity charges, the third and fourth sets of particles carry opposite polarity charges, the first particles are light scattering particles, and each of the second, third, and fourth sets of particles are a different subtractive primary color. (Item 18) Item 18. The system of item 17, wherein the controller is configured to provide combinations of the positive voltages, the negative voltages, and the ground voltages to the top electrode and the first drive electrode such that white, yellow, red, magenta, blue, cyan, green, and black can be displayed on the viewing surface. (Item 19) Item 17. The system of item 16, wherein the first and second sets of particles carry opposite polarity charges, the third and fourth sets of particles carry the same charge as the second particles, the first particles are light scattering particles, and each of the second, third, and fourth sets of particles are a different subtractive primary color. (Item 20) 20. The system of claim 19, wherein the controller is configured to provide combinations of the positive voltages, the negative voltages, and the ground voltages to the top electrode and the first drive electrode such that white, yellow, red, magenta, blue, cyan, green, and black can be displayed on the viewing surface. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating an embodiment of an encapsulated electrophoretic display suitable for use with the method of the present invention.

[0032] [Diagram 2] FIG. 2 is a schematic cross-sectional view illustrating an embodiment of an encapsulated electrophoretic display suitable for use with the methods of the present invention.

[0033] [Diagram 3] Figure 3 illustrates an exemplary equivalent circuit of a single pixel of an electrophoretic display, where the voltage at the single pixel is controlled using a transistor. The circuit of Figure 3 is commonly used in active matrix backplanes.

[0034] [Figure 4] FIG. 4 illustrates how positive and negative voltage sources can be applied to the top electrode and two separate drive electrodes to achieve the required drive voltages at the two separate drive electrodes.

[0035] [Diagram 5] FIG. 5 is a schematic cross-sectional view showing the positions of various colored particles in a colored electrophoretic medium when displaying black, white, the three subtractive primary colors, and the three additive primary colors.

[0036] [Figure 6] FIG. 6 shows an exemplary push-pull drive scheme for addressing an electrophoretic medium containing three subtractive particles and a scattering (white) particle.

[0037] [Figure 7] FIG. 7 depicts simplified top-plane drive waveforms for the production of eight colors in an electrophoretic medium containing three subtractive particles and one scattering (white) particle.

[0038] [Figure 8] FIG. 8 shows an example drive pattern for achieving a green optical state at the viewing surface above the first drive electrode and a yellow optical state at the viewing surface above the second drive electrode using only two voltage sources.

[0039] [Figure 9A] FIG. 9A shows the change in the L*a*b* values ​​of the eight color indices when the same four-particle electrophoretic medium is driven with seven independent driving voltages or two voltage sources and uses coordinated top electrode voltage cycling.

[0040] [Figure 9B] FIG. 9B shows the dates in the graph of FIG. 9A as simulated colors. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] A system for simplified driving of an electrophoretic medium, the system using positive and negative voltage sources, the voltage sources having different magnitudes, and a controller that coordinates driving at least two drive electrodes opposite the top electrode while cycling the top electrode between the two voltage sources and ground. The resulting system can achieve nearly the same color states as compared to providing six independent drive levels and ground to each drive electrode. Thus, the system simplifies the required electronics with only a slight loss in color gamut. The system is particularly useful for addressing an electrophoretic medium containing four sets of different particles, for example, three of the particles are colored and subtractive and one of the particles is light scattering.

[0042] The present invention provides an improved method of driving electro-optic media devices using so-called top-plane switching (i.e., the voltage at the top (common) electrode is varied during the process of updating the device). In some embodiments, the present invention is used with an electrophoretic medium that includes four particles, two of which are colored and subtractive, and at least one of which is scattering. Typically, such a system includes white particles and subtractive primary color particles of cyan, yellow, and magenta. In some embodiments, two of the particles are positively charged and two of the particles are negatively charged. In some embodiments, three of the particles are positively charged and one of the particles is negatively charged. In some embodiments, one of the particles is positively charged and three of the particles are negatively charged. Such a system is shown diagrammatically in FIG. 5, which can provide white, yellow, red, magenta, blue, cyan, green, and black at every pixel.

[0043] Display devices can be constructed using the electrophoretic fluids of the present invention in several ways known in the art. The electrophoretic fluid can be encapsulated in microcapsules or incorporated into a microcell structure, which can then be sealed with a polymer layer. The microcapsules or microcell layer can be coated or embossed onto a plastic substrate or film bearing a transparent coating of conductive material. This assembly can be laminated, using a conductive adhesive, to a backplane bearing pixel electrodes. Alternatively, the electrophoretic fluid can be dispensed directly onto a thin open cell grid disposed on a backplane containing an active matrix of pixel electrodes. The filled grid can then be top-sealed with an integrated protective sheet / light-transparent electrode.

[0044] 1 and 2, an electrophoretic display (101, 102) typically includes a top light-transmissive electrode 110, an electrophoretic medium 120, and bottom drive electrodes 130 / 135, which are often pixel electrodes of an active matrix of pixels controlled with thin film transistors (TFTs). Alternatively, the bottom drive electrodes 130 / 135 may be wired directly to a controller or some other switch, which provides a voltage to the bottom drive electrodes 130 / 135 to effect a change in the optical state of the electrophoretic medium 120, i.e., the split electrodes. Importantly, it is not necessary that the junctions between the drive electrodes 130 / 135 correspond to the intersections of the microcapsules or the walls 127 of the microcells. The electrophoretic medium 120 is sufficiently thin and the capsules or microcells are sufficiently wide so that the pattern of the drive electrodes (squares, circles, hexagons, waves, strings, or otherwise) will be visible when the display is viewed from a viewing surface, rather than the pattern of the containers. The electrophoretic medium 120 includes at least one electrophoretic particle 121, however a second electrophoretic particle 122 or a third electrophoretic particle 123, a fourth electrophoretic particle 124, or more particles are feasible [note that the third electrophoretic particle 123 and the fourth electrophoretic particle 124 may be included within the microcapsules 126 of FIG. 1, but have been omitted for clarity]. The electrophoretic medium 120 typically includes a solvent such as isoparaffin, and may include a dispersion polymer and a charge control agent to promote state stability, e.g., bistability (i.e., the ability to maintain an electro-optical state without the input of any additional energy).

[0045] The electrophoretic medium 120 is typically compartmentalized, such as by walls of microcapsules 126 or microcells 127. The entire display stack is typically disposed on a substrate 150, which can be rigid or flexible. The displays (101, 102) also typically include a protective layer 160, which may simply protect the top electrode 110 from damage, or which may surround the entire display (101, 102) to prevent water ingress, etc. The electrophoretic displays (101, 102) may also include one or more adhesive layers 140, 170 and / or sealing layers 180, as required. In some embodiments, the adhesive layer may include a primer component to improve adhesion to the electrode layer 110, or a separate primer layer (not shown in FIGS. 1 or 2) may be used. (The structure of electrophoretic displays and their component parts, pigments, adhesives, electrode materials, etc. are described in many patents and patent applications published by E Ink Corporation, such as U.S. Pat. Nos. 6,922,276, 7,002,728, 7,072,095, 7,116,318, 7,715,088, and 7,839,564, all of which are incorporated herein by reference in their entireties.)

[0046] Thin film transistor (TFT) backplanes typically have only one transistor per pixel or drive electrode. Conventionally, each pixel electrode has a capacitor electrode associated with it, whereby the pixel electrode and the capacitor electrode form a capacitor; see, for example, International Patent Application No. WO01 / 07961. In some embodiments, N-type semiconductors (e.g., amorphous silicon) may be used to form the transistors, and the "select" and "unselect" voltages applied to the gate electrodes may be positive and negative, respectively.

[0047] As illustrated in FIG. 3, each transistor (TFT) is connected to a gate line, a data line, and a pixel electrode (drive electrode). When there is a sufficient positive voltage (or negative voltage, depending on the type of transistor) on the TFT gate, there is a low impedance between the scan line and the pixel electrode coupled to the TFT drain (i.e., Vg is in the "on" or "open" state), and thus the voltage on the scan line is transferred to the pixel's electrode. However, when there is a negative voltage on the TFT gate, there is a high impedance, and the voltage is stored on the pixel storage capacitor, and is not affected by the voltage on the scan line when other pixels are addressed (i.e., Vg is "off" or "closed"). Thus, ideally, the TFT should act as a digital switch. In practice, when the TFT is in the "on" setting, there is still a certain amount of resistance, and thus the pixel takes some time to charge. In addition, when the TFT is in the "off" setting, the voltage is V S From V pix Increasing the capacitance of the reservoir capacitor Cs reduces crosstalk, but at the cost of making it more difficult to charge the pixel, increasing the charging time. As shown in Figure 3, a separate voltage (V TOP ) is provided to the top electrode, so that an electric field (V FPL ) which ultimately determines the optical state of the associated electro-optic medium, V FPL The first side of the storage capacitor is coupled to the pixel electrode, while the second side of the storage capacitor is coupled to a separate line (V COM ) in a transistor. See, e.g., U.S. Pat. No. 7,176,880, incorporated by reference in its entirety. [In some embodiments, an N-type semiconductor (e.g., amorphous silicon) may be used to form a transistor, with "select" and "unselect" voltages applied to the gate electrodes, which may be positive and negative, respectively.] In some embodiments, V COMcan be grounded, however, there are many different designs for draining charge from the charge capacitor, as described, for example, in U.S. Pat. No. 10,037,735 (incorporated by reference in its entirety).

[0048] One problem with conventional amorphous silicon TFTs is that the operating voltage is limited to approximately ±15V, at which the transistors begin to leak current and eventually fail. While an operating range of ±15V is suitable for many two-particle electrophoretic systems, it has been found that having an increased voltage range makes it easier to separate particles with different zeta potentials, resulting in advanced electrophoretic displays that update faster and have more reproducible colors. One solution for increasing the voltage range for the pixel electrodes is to use top-plane switching, whereby the voltage at the top (common) electrode is varied as a function of time.

[0049] The principle of top-plane switching is illustrated in FIG. 4. An exemplary electrophoretic display 401 includes an electrophoretic medium 420 disposed between a top electrode 410 and a (bottom) drive electrode 430. The electrophoretic medium 420 in FIG. 4 is shown with four different types of electrophoretic particles, however, the electrophoretic medium 420 can have fewer or more types of different particles than shown. In the simplified embodiment of FIG. 4, both the top electrode 410 and the drive electrode 430 are supplied by two different power supplies 440 and 460, which may be from the same power supply (not shown). In addition, a ground voltage 470 is available. Typically, one power supply is positive with respect to ground and one power supply is negative with respect to ground. Which power supply (or ground) is connected to which electrode in a given unit of time (frame) is controlled by a controller 470. The controller can be a commercially available electrophoretic display controller, such as that manufactured by UltraChip, to control the output of the voltage board, or it can be a laboratory controller, such as that provided by E Ink Corporation (HULK Controller, ARC30 TM Controller) or it can be a virtual controller using, for example, LABVIEW®.

[0050] As illustrated in the equation below electrophoretic display 401 in FIG. 4, each combination of voltages provided to top electrode 410 and drive electrode 430 results in a voltage difference of ΔV=V(drive electrode)-V(top electrode) at electrophoretic medium 420. As can be seen by the equation (and as discussed below), by modifying the voltage at the top electrode, a larger dynamic range of voltages at electrophoretic medium 420 can be achieved. In addition, if the magnitudes of 440 and 460 are different, intermediate differential voltage values ​​on the electrophoretic medium can be achieved. As shown in FIG. 4, by carefully adjusting when top electrode 410 and drive electrodes 430 are connected to which power supplies, seven different voltages are available to electrophoretic medium 420.

[0051] Although FIG. 4 illustrates only a single drive electrode 430, it should be understood that the principles can be extended to systems with many driven pixels, such as those available with active matrix backplanes. However, adjusting the top electrode voltage required to achieve a desired voltage difference across a particular pixel becomes very complicated very quickly as the number of pixels increases. In practice, top plane switching with active matrix backplanes uses separate voltage controllers for the top plane and pixel electrodes, and requires top electrode voltage cycling that continues for many frames while individual pixel electrodes are switched to produce the desired waveform. Further details of the method are described in U.S. Pat. No. 10,593,272, which is incorporated by reference in its entirety.

[0052] In the case of ACeP®, each of the eight primary colors (red, green, blue, cyan, magenta, yellow, black, and white) corresponds to a different arrangement of the four pigments, so that the viewer sees only those colored pigments (i.e., only light-scattering pigments) that are on the viewing side of the white pigment. More specifically, when cyan, magenta, and yellow particles are present below the white particle (situation [A] in FIG. 5), there are no particles above the white particle, and the pixel simply displays white. When a single particle is above the white particle, the color of the single particle is displayed as yellow, magenta, and cyan in situations [B], [D], and [F] in FIG. 5, respectively. When two particles are present above the white particle, the displayed color is the combination of those two particles. That is, in situation [C] in Figure 5, the magenta and yellow particles display red, in situation [E] the cyan and magenta particles display blue, and in situation [G] the yellow and cyan particles display green. Finally, when all three colored particles are above the white particle (situation [H] in Figure 5), all the incident light is absorbed by the three subtractive colored particles and the pixel displays black.

[0053] It is possible that one subtractive primary color can be rendered by light-scattering particles, whereby the display will have two types of light-scattering particles, one of which is white and the other is colored. However, in this case, the position of the light-scattering colored particles relative to the other colored particles that cover the white particles will be important. For example, in rendering black (when all three colored particles are located over the white particles), the scattering colored particles cannot be located over the non-scattering colored particles (otherwise they will be partially or completely hidden behind the scattering particles, and the color rendered will be the scattering colored particles, not black). If more than one type of colored particles scatter light, it will not be easy to render black.

[0054] It has been found that waveforms for rearranging the four pigments into the appropriate configuration to create these colors are best achieved with at least seven voltage levels (high positive, medium positive, low positive, zero, low negative, medium negative, high negative). Figure 6 shows a typical waveform (in simplified form) used to drive the four-particle color electrophoretic display system described above. Such waveforms have a "push-pull" structure, i.e. they consist of a dipole with two pulses of opposite polarity. The magnitude and length of those pulses determine the color obtained. In general, the higher the magnitude of the "high" voltage, the better the color gamut achieved by the display. The "high" voltage is typically 20V to 30V, more typically about 25V, e.g. 24V. The "medium" (M) level is typically 10V to 20V, more typically about 15V, e.g. 15V or 12V. The "low" (L) level is typically 3V to 10V, more typically about 7V, e.g., 9V or 5V. Of course, the values ​​of H, M, L will depend somewhat on the composition of the particles and the environment of the electrophoretic medium. In some applications, H, M, L may be set by the cost of the components to produce and control these voltage levels.

[0055] As shown in Figure 6, when the top electrode is held at a constant voltage (i.e., not top-plane switched), even the "simple" waveform for the ACeP® system requires the drive electronics to provide seven different voltages (+H, +M, +L, 0, -L, -M, -H) to the data lines during the update of a selected pixel of the display. Although multi-level source drivers capable of delivering seven different voltages are available, many commercially available source drivers for electrophoretic displays allow only three different voltages to be delivered during a single frame (typically a positive voltage, zero, and a negative voltage).

[0056] Of course, achieving a desired color using the drive pulses of FIG. 6 depends on the particles starting the process from a known state, which is unlikely to be the final color displayed on the pixel. Thus, a series of reset pulses precede the drive pulses, which increase the amount of time required to update the pixel from a first color to a second color. Reset pulses are described in more detail in U.S. Pat. No. 10,593,272, which is incorporated by reference. The lengths of these pulses (refresh and address) and any rests (i.e., the period of zero voltage between pulses) can be chosen such that the entire waveform (integral of voltage with respect to time over the entire waveform) is DC balanced (i.e., the integral of voltage over time is substantially zero). DC balance can be achieved by adjusting the length of the pulses and rests in the reset phase such that the net impulse delivered in the reset phase is equal in magnitude and opposite in sign to the net impulse delivered in the address phase (during which the display is switched to a particular desired color).

[0057] In addition, the above discussion of waveforms, and specifically, the discussion of DC balance, ignores the issue of kickback voltage. Indeed, as mentioned above, all backplane voltages are subject to a kickback voltage V KB The backplane is offset from the voltage provided by the power supply by an amount equal to V+V. Thus, if the power supply being used provides three voltages, +V, 0, and -V, the backplane will actually be at a voltage of V+V KB , V KB , and -V+V KB (V KB (Note that for amorphous silicon TFTs, V is typically a negative number.) However, the same power supply will supply +V, 0, and -V to the front electrode without any kickback voltage offset. So, for example, when the front electrode is supplied with -V, the display will only supply a maximum voltage of 2V +V KB and the minimum voltage V KB Using a separate power supply, V KBInstead of supplying V to the front electrodes (which can be costly and inconvenient), the waveform can be split into sections, with the front electrodes receiving positive voltage, negative voltage, and V KB In addition to the kickback,

[0058] (High Voltage Addressing with Metal Oxide Backplane) While modifying the rail voltages offers some flexibility in achieving different electro-optical performance than four-particle electrophoretic systems, there are many limitations introduced by top-plane switching. For example, typically a lower negative voltage V M- is the maximum negative voltage V H- However, as shown in the equation above, top plane switching requires that the lower positive voltage be at least half, and typically more than half, of the maximum positive voltage at all times.

[0059] An alternative solution to the complexities of top-plane switching can be provided by fabricating the control transistors from less common materials with higher electron mobility, thereby allowing the transistors to directly switch larger control voltages, e.g., + / - 30V. Newly developed active matrix backplanes can include thin film transistors incorporating metal oxide materials such as tungsten oxide, tin oxide, indium oxide, and zinc oxide. In these applications, a channel forming region is formed for each transistor using such metal oxide materials, allowing faster switching of higher voltages. Such transistors typically include a gate electrode, a gate insulating film (typically SiO2), a metal source electrode, a metal drain electrode, and a metal oxide semiconductor film that covers the gate insulating film that at least partially overlaps the gate electrode, source electrode, and drain electrode. Such backplanes are available from manufacturers such as Sharp / Foxconn, LG, and BOE.

[0060] One preferred metal oxide material for such applications is indium gallium zinc oxide (IGZO). IGZO-TFTs have 20-50 times the electron mobility of amorphous silicon. By using IGZO TFTs in an active matrix backplane, it is possible to provide voltages greater than 30V via a suitable display driver. Furthermore, a source driver capable of providing at least five, preferably seven, levels provides different driving paradigms for a four-particle electrophoretic display system. In one embodiment, there will be two positive voltages, two negative voltages, and zero volts. In another embodiment, there will be three positive voltages, three negative voltages, and zero volts. In one embodiment, there will be four positive voltages, four negative voltages, and zero volts. These levels may be selected within the range of about -27V to +27V, without the limitations imposed by the switching of the top plane as described above.

[0061] With advanced backplanes such as metal oxide backplanes, it is possible to address each pixel directly using a suitable push-pull waveform (i.e., as illustrated in FIG. 6). This significantly reduces the time required to update each pixel, turning a 6 second update into less than 1 second in some cases. The reset can be done more quickly at higher voltages, although in some cases it may be necessary to use a reset pulse to establish a starting point for the address. In addition, in a four-color electrophoretic display with a reduced color set, it is possible to drive directly from a first color to a second color using a particular waveform that is only slightly longer than the push-pull waveform shown in FIG. 6.

[0062] (Simplified top plane switching) To reduce the length of time and flashiness of updates, the complexity of the frontplane switching can be reduced at the expense of fewer available colors. Additionally, because particles have a finite speed in the electrophoretic medium, the amount of time the dipoles are applied also affects the size of the color gamut.

[0063] FIG. 7 shows such a solution in which a simplified top-plane switching pulse sequence (top left panel) is used, and a simplified back-plane pulse sequence (left side; bottom) is matched to a single top-plane sequence, thereby providing at least different colors. The top-plane is switched between two voltages, one positive and one negative, while the back-plane can take three different voltages, positive, negative, and zero (in FIG. 7 the voltage levels are relative, i.e., 1, 0, -1, but in many cases they are actually 15V, 0, and -5V, as is typical for commercial back-planes containing amorphous silicon thin-film transistors). Note that by subtracting the top-plane pulse sequence from the back-plane pulse sequence (FIG. 7 left), the eight-color sequence of FIG. 6 (FIG. 7 right) is achieved. With respect to the pulse sequences of Figures 6 and 7, it should be understood that the electrophoretic fluid includes a white pigment that is negatively charged, magenta and cyan pigments that are positively charged, and a yellow pigment that can be either positively or negatively charged or essentially neutral. Other color / charge combinations are possible and the waveforms can be adjusted accordingly.

[0064] As discussed above, in the waveforms of Figure 7, at least five different voltages are required. In an active matrix driving environment, this can be achieved by (a) supplying a choice of five different voltages to the columns when a particular row is selected at a particular time, or (b) providing a choice of fewer (e.g., three) different voltages to the columns when a particular row is selected a first time, and providing a different set of voltages when the same row is selected a second time, or (c) providing the same choice of three voltages to the columns in both the first and second times, but changing the potential of the front electrodes between the first and second times. Option (c) is particularly useful when at least one of the voltages required to be supplied is higher than the backplane electronics can support.

[0065] With top-plane switching, it is not possible to assert a high positive potential and a high negative potential simultaneously, so it is necessary to offset the top-plane + / - dipoles with respect to the backplane - / + dipoles. In the waveform shown in Figure 7, there is only one dipole per transition. This provides the least "flash-like" waveform possible, since each dipole results in two visible optical changes in the display. In this case, if five different voltage levels can be supplied to the backplane electrodes when each row is selected, and if the backplane electronics can support the highest voltages required, there is no need to offset the dipoles in the manner shown in Figure 7.

[0066] (Driving with a Cycled Top Plane Voltage) For the driving sequence of FIG. 7, the voltages applied to the top plane are V t+ and V t- The voltages applied to the backplane are V b+ and V b- and |V t+ |=|V t- |=|V b+ |=|V b-|=V. Thus, when the maximum supply voltage is + / - 15 volts, as is typical for commercial backplanes, the voltages across the electrophoretic medium will be 30V, 28V, 0V, -28V, and -30V.

[0067] However, the maximum voltage magnitudes (i.e., "rails") of the top plane and backplane electrodes need not be the same. For example, the rail voltage offsets can be calculated from some nominal maximum voltage magnitude value, i.e., V. The offsets per rail may be expressed as w, x, y, and z, with the zero voltage rail assumed to be maintained at zero and not applied to the top plane. Therefore, it is as follows:

number

[0068] When referring to the backplane voltage, the top plane is V t+ When the electrophoretic medium is set to 0, three different negative voltages of high, medium, and low magnitude can be applied to the electrophoretic medium, which are designated V H- , V M- , and V L- (i.e., V b -V t and V b can take one of the three values ​​shown above). These voltages are as follows:

number

number

number

[0069] When w=y and x=z, the top plane is V t+ or V t- It is clear that it is possible to maintain the zero voltage state regardless of whether the top plane potential is set to 0 or 1. In practice, if optimal color is to be obtained, the waveforms will require significantly greater complexity and length. Hence, the top plane switching pattern will require to be significantly more complex than that illustrated in FIG. 7. However, in applications requiring simultaneous updates in different regions of the display with staggered start times separated by less than the length of one waveform, certain difficulties arise. Because the top plane potential is asserted across the entire display, it may not be possible to begin a new update in one region of the display before the completion of a previously initiated update elsewhere.

[0070] The problem of coordinating multiple simultaneous updates, each of which requires a top-plane switch, can be solved by cycling the top-plane voltage while stretching the waveform, as shown in FIG. 8 (V TE = top electrode voltage, V DE1 = first drive electrode voltage, V DE2 = second driving electrode voltage, ΔV DE1 = voltage difference in the electrophoretic medium between the first drive electrode and the top electrode, ΔV DE2= voltage difference in the electrophoretic medium between the second drive electrode and the top electrode). The green and yellow waveforms created earlier for a 7-level backplane, capable of providing + / -24V, + / -15V, + / -9V, or 0V at any pixel location in any frame, were modified for cycled top-plane drive. The controller provides successive frames of +15V, -9V, and 0V to the top electrode (i.e., V=15V, w=y=0V, and x=z=6V in the above equations), as shown in FIG. 9. By stretching the waveforms and coordinating the voltages to the first and second drive electrodes with the top electrode cycle, it was possible to use top-plane switching to effect simultaneous color updates at two different drive electrodes.

[0071] When the top electrode is at +15V, the voltage differences available to the electrophoretic medium are -24V, -15V, -0V. When the top electrode is at -9V, the voltage differences available to the electrophoretic medium are 24V, 9V, and 0V. When the top electrode is at ground (0V), the voltage differences available to the electrophoretic medium are 15V, 0V, and -9V in a third [by convention, the voltage difference is ΔV=V(drive electrode)-V(top electrode)]. Thus, seven voltage levels were available: + / -24V, + / -15V, and + / -9V+0V. Note that when a particular drive electrode needs to "wait" for the next top electrode frame, that drive electrode is set to the same voltage as the top electrode so that the voltage difference across the electrophoretic medium is zero for that frame. Obviously, this makes the waveform longer in time; each "simple" waveform now requires an update three times longer than the original multi-level waveform.

[0072] Using a model of a four-particle electrophoretic system, top electrode cyclic drive with +15V, -9V, and 0 was tested against the same system with seven individual drive levels and a static top electrode. The results are shown below in Tables 1 and 2 and represented in the graph of Figure 9A and the simulated color chart of Figure 9B. [Table 1] [Table 2]

[0073] Comparing Tables 1 and 2, there appears to be little sacrifice for top electrode cycling other than a longer update time. In fact, the color gamut (color space) is actually slightly larger for the top electrode cycling method. The difference between the two methods can be further visualized by examining Figures 9A and 9B. In Figure 9A, the filled circles represent the L * a * b * The open circles represent the L * a * b * 9A and 9B represent measured values. As can be seen from Figures 9A and 9B, the resulting primary color states are very similar (compare the positions of the open circles versus the filled circles). The largest change is seen in the green primary (left center of Figure 9A), where the green primary drifts significantly toward yellow. The difference in color state for the green primary is also evident in Figure 9B.

[0074] Thus, the present invention provides full-color electrophoretic displays capable of directly addressing an electrophoretic medium with and without top-plane switching, and waveforms for such electrophoretic displays. Although several aspects and embodiments of the present technology have been described, it should be understood that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the technology described herein. For example, one skilled in the art will readily envision a variety of other means and / or structures for performing the functions and / or obtaining one or more of the results and / or 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. Thus, the foregoing embodiments are presented by way of example only, and it should be understood that within the scope of the appended claims and equivalents thereof, the embodiments of the present invention 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 is also included within the scope of the present disclosure, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent.

Claims

1. 1. A system for driving an electrophoretic medium, the system comprising:

1. An electrophoretic display comprising: a light transmissive top electrode at the viewing surface; A first drive electrode; A second drive electrode; an electrophoretic medium disposed between the upper electrode and the first and second drive electrodes; an electrophoretic display comprising: a power supply capable of providing a positive voltage and a negative voltage, the magnitude of the positive voltage and the magnitude of the negative voltage being different; a controller coupled to the top electrode driver, the first drive electrode driver, and the second drive electrode driver; Equipped with The controller: providing the positive voltage to the top electrode, the negative voltage to the first drive electrode, and the positive voltage to the second drive electrode in a first frame; in a second frame, providing the negative voltage to the top electrode, providing the negative voltage to the first drive electrode, and providing the negative voltage to the second drive electrode; in a third frame, providing a ground voltage to the top electrode, providing the ground voltage to the first drive electrode, and providing the positive voltage to the second drive electrode; in a fourth frame, providing the positive voltage to the top electrode, providing the positive voltage to the first drive electrode, and providing the positive voltage to the second drive electrode; A system configured to:

2. The controller: in a fifth frame, providing the negative voltage to the top electrode, providing the ground voltage to the first drive electrode, and providing the negative voltage to the second drive electrode; in a sixth frame, providing the ground voltage to the top electrode, providing the ground voltage to the first drive electrode, and providing the ground voltage to the second drive electrode; The system of claim 1 , further configured to:

3. 10. The system of claim 1 , wherein the electrophoretic medium is encapsulated in a plurality of microcapsules, the microcapsules being dispersed in a polymer binder between the top electrode and the first and second drive electrodes.

4. 2. The system of claim 1, wherein the electrophoretic medium is encapsulated in an array of microcells having openings, the openings being sealed with a polymer binder, and the array of microcells is disposed between the top electrode and the first and second drive electrodes.

5. The system of claim 1 , wherein the electrophoretic medium comprises a non-polar fluid and four sets of particles having different optical properties.

6. 6. The system of claim 5, wherein the first and second sets of particles carry opposite polarity charges, the third and fourth sets of particles carry opposite polarity charges, the first set of particles are light scattering particles, and each of the second, third, and fourth sets of particles are a different subtractive primary color.

7. 7. The system of claim 6, wherein the controller is configured to provide combinations of the positive voltages, the negative voltages, and the ground voltages to the top electrode and the first drive electrode such that white, yellow, red, magenta, blue, cyan, green, and black can be displayed on the viewing surface.

8. 6. The system of claim 5, wherein the first and second sets of particles carry opposite polarity charges, the third and fourth sets of particles carry the same charge as the second set of particles, the first set of particles are light scattering particles, and each of the second, third, and fourth sets of particles are different subtractive primary colors.

9. 9. The system of claim 8, wherein the controller is configured to provide combinations of the positive voltages, the negative voltages, and the ground voltages to the top electrode and the first drive electrode such that white, yellow, red, magenta, blue, cyan, green, and black can be displayed on the viewing surface.

10. 2. The system of claim 1, wherein the positive voltage is +15V and the negative voltage is -9V.

11. 2. The system of claim 1, wherein the positive voltage is +9V and the negative voltage is -15V.

12. 1. A system for driving an electrophoretic medium, the system comprising:

1. An electrophoretic display comprising: a light transmissive top electrode at the viewing surface; A first drive electrode; A second drive electrode; an electrophoretic medium disposed between the upper electrode and the first and second drive electrodes; an electrophoretic display comprising: a power supply capable of providing a positive voltage and a negative voltage, the magnitude of the positive voltage and the magnitude of the negative voltage being different; a controller coupled to the top electrode driver, the first drive electrode driver, and the second drive electrode driver; Equipped with The controller: providing the positive voltage to the top electrode, the negative voltage to the first drive electrode, and the positive voltage to the second drive electrode in a first frame; in a second frame, providing the negative voltage to the top electrode, providing the negative voltage to the first drive electrode, and providing the negative voltage to the second drive electrode; in a third frame, providing a ground voltage to the top electrode, providing the ground voltage to the first drive electrode, and providing the ground voltage to the second drive electrode; in a fourth frame, providing the positive voltage to the top electrode, providing the positive voltage to the first drive electrode, and providing the positive voltage to the second drive electrode; A system configured to:

13. The controller: in a fifth frame, providing the negative voltage to the top electrode, providing the ground voltage to the first drive electrode, and providing the negative voltage to the second drive electrode; in a sixth frame, providing the ground voltage to the top electrode, providing the ground voltage to the first drive electrode, and providing the ground voltage to the second drive electrode; The system of claim 12 , further configured to:

14. 13. The system of claim 12, wherein the electrophoretic medium is encapsulated in a plurality of microcapsules, the microcapsules being dispersed in a polymer binder between the top electrode and the first and second drive electrodes.

15. 13. The system of claim 12, wherein the electrophoretic medium is encapsulated in an array of microcells having openings, the openings being sealed with a polymer binder, and the array of microcells is disposed between the top electrode and the first and second drive electrodes.

16. The system of claim 12 , wherein the electrophoretic medium comprises a non-polar fluid and four sets of particles having different optical properties.

17. 17. The system of claim 16, wherein the first and second sets of particles carry opposite polarity charges, the third and fourth sets of particles carry opposite polarity charges, the first set of particles are light scattering particles, and each of the second, third, and fourth sets of particles are a different subtractive primary color.

18. 18. The system of claim 17, wherein the controller is configured to provide combinations of the positive voltages, the negative voltages, and the ground voltages to the top electrode and the first drive electrode such that white, yellow, red, magenta, blue, cyan, green, and black can be displayed on the viewing surface.

19. 17. The system of claim 16, wherein the first and second sets of particles carry opposite polarity charges, the third and fourth sets of particles carry the same charge as the second set of particles, the first set of particles are light scattering particles, and each of the second, third, and fourth sets of particles are different subtractive primary colors.

20. 20. The system of claim 19, wherein the controller is configured to provide combinations of the positive voltages, the negative voltages, and the ground voltages to the top electrode and the first drive electrode such that white, yellow, red, magenta, blue, cyan, green, and black can be displayed on the viewing surface.

Images