TW202329062A - Coordinated top electrode - drive electrode voltages for switching optical state of electrophoretic displays using postive and negative voltages of different magnitudes - Google Patents

Abstract

A system for simplified driving of electrophoretic media using a positive and a negative voltage source, where the voltage sources have different magnitudes, and a controller that cycles the top electrode between the two voltage sources and ground while coordinating driving at least two drive electrodes opposed to the top electrode. The resulting system can achieve roughly the same color states as compared to supplying each drive electrode with six independent drive levels and ground. Thus, the system simplifies the required electronics with only marginal loss in color gamut. The system is particularly useful for addressing an electrophoretic medium including four sets of different particles, e.g., wherein three of the particles are colored and subtractive and one of the particles is light-scattering.

Description

Coordinated top electrode-drive electrode voltages for switching optical states of electrophoretic displays using positive and negative voltages of different magnitudes

[Related applications]

This application claims priority to U.S. Provisional Application Serial No. 63/320,524, filed March 16, 2022. This application also claims priority to US Patent Application Serial No. 17/474,375, filed September 14, 2021. The entire contents of the patents and published patent applications disclosed herein are incorporated by reference.

Electrophoretic displays (EPDs) change color by changing the position of charged colored particles relative to a light-transmissive viewing surface. Such electrophoretic displays are often called "electronic paper" or "ePaper" because the resulting display has a high contrast ratio and is readable in sunlight, much like ink on paper. Electrophoretic displays have been widely adopted in eReaders such as Amazon KINDLE® because they provide a book-like reading experience with low power consumption and allow users to carry a collection of hundreds of volumes in a lightweight handheld device.

For many years, electrophoretic displays consisted of only two types of charged colored (black and white) particles. (Of course, "color" as used herein includes black and white.) White particles are typically light scattering and contain, for example, titanium dioxide, while black particles are absorptive throughout the visible spectrum and may contain carbon Black or absorbing metal oxides (such as copper chromite). In the simplest sense, a black-and-white electrophoretic display requires only a light-transmitting electrode on the viewing side, a back electrode, and an electrophoretic medium containing oppositely charged white and black particles. When a voltage of one polarity is applied, the white particles move to the viewing surface, and when a voltage of the opposite polarity is applied, the black particles move to the viewing surface. If the back electrode comprises controllable areas (pixels) (segmented electrodes controlled by transistors or an active matrix of pixel electrodes), the pattern can be made to appear electronically on the viewing surface. The pattern can be, for example, the text of a book.

Recently, electrophoretic displays have been available in the market in a variety of colors, including three-color displays (black, white, red; black, white, yellow) and four-color displays (black, white, red, yellow). Similar to the operation of a black and white electrophoretic display, an electrophoretic display with three or four reflective pigments operates like a simple black and white display in that the desired color particles are driven to the viewing surface. The driving scheme is far more complex than just black and white, but in the end, the optical function of the particles is the same.

Advanced Color Electronic Paper (ACeP™) also contains four particles, but the cyan, yellow and magenta particles are subtractive rather than reflective, so each pixel can produce thousands of colors. Color processing is functionally equivalent to long-used printing methods in offset printing and inkjet printers. Produces a given color by using the correct proportions of cyan, yellow, and magenta on a sharp 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 of each pixel. While this type of electrophoretic display allows the rendering of thousands of colors per pixel, each pigment (50 to 500 nanometers in size) is carefully controlled within a working space of about 10 to 20 micrometers (micrometers) thick The location is critical. Obviously, a shift in the position of the paint will result in an incorrect color being displayed at a given pixel. Accordingly, such systems require fine voltage control. Further details of such systems are provided in the following US patents, all of which are incorporated herein by reference in their entirety: US Patent Nos. 9,361,836, 9,921,451, 10,276,109, 10,353,266, 10,467,984, and 10,593,272.

The present invention relates to use in color electrophoretic displays, particularly but not limited to electrophoretic displays capable of displaying more than two colors using a single layer of electrophoretic material comprising a plurality of colored particles such as white, cyan, yellow and magenta. In some instances, two of the particles are positively charged and two of the particles are negatively charged. In some instances, three of the particles are positively charged and one is negatively charged. In some examples, the positively charged particles have a thick polymer shell and the negatively charged particles have a thick polymer shell.

The term "grayscale state" is used herein in its conventional sense in the imaging arts to refer to a state between two extreme optical states of a pixel, and does not necessarily imply a black-to-white transition between these two extreme states ( black-white transition). For example, several of the E Ink patents and published applications mentioned below describe electrophoretic displays in which the extreme states are white and dark blue, such that the intermediate "gray state" is actually light blue. Indeed, as stated, 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 two extreme optical states of a display, and should be understood to generally include extreme optical states that are not black and white at all, such as 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 a display comprising first and second components having at least one optical property that differs. Two display state display elements such that after any given element is driven, it assumes its first or second display state by an addressing pulse of finite duration, while the addressing pulse After the wave has terminated, the state will persist for at least a few times (eg, at least 4), ie, the shortest duration of the addressing pulse that changes the state of the display element. US Patent No. 7,170,670 shows that some particle-based electrophoretic displays with gray scales are stable not only in extreme black and white states, but also in intermediate gray scale states, and the same is true for some other types of electro-optic displays. This type of display may properly be called multi-stable rather than bistable, but for convenience the term "bistable" may be used here to cover both bistable and multi-stable. monitor.

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 during which the display is driven.

Particles that absorb, scatter or reflect broadband or selected wavelengths of light are referred to herein as colored or pigment particles. Various light-absorbing or reflective materials (in the strict sense of the term, refer to insoluble colored materials) other than pigments can also be used in the electrophoretic medium and display of the present invention, such as dyes or photonic crystals.

Particle-based electrophoretic displays have been the subject of intensive research and development for several years. In such displays, a plurality of charged particles, sometimes called pigment particles, move through a fluid under the influence of an electric field. Compared with liquid crystal displays, electrophoretic displays can have properties such as excellent brightness and contrast, wide viewing angles, state bistability, and low power consumption. However, problems with the long-term image quality of these displays have hindered their widespread use. For example, the particles that make up electrophoretic displays are prone to sedimentation, resulting in insufficient lifetime of these displays.

As mentioned above, the electrophoretic medium requires the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but gaseous fluids can be used to create the electrophoretic media; 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 US Patent Nos. 7,321,459 and 7,236,291. Such gas-based electrophoretic media appear to be susceptible to the same settling effects of particles as liquid-based electrophoretic media when the media are used in an orientation that allows particle settling, such as in a label that arranges the media in a vertical plane. Caused by the type of problems affected. Indeed, particle settling appears to be a more serious problem in gas-based electrophoretic media than in liquid-based electrophoretic media, since the lower viscosity of gas-suspended fluids allows for faster settling of the electrophoretic particles compared to liquid-based suspending fluids.

Numerous patents and applications assigned to or in the name of the Massachusetts Institute of Technology (MIT) and E Ink Corporation describe various techniques used in capsule electrophoresis and other electro-optic media. Such capsule-type media comprise a plurality of small capsules, each of which itself comprises an inner phase containing electrophoretically mobile particles in a fluid medium and a wall surrounding the inner phase. Typically, the capsules themselves are held in a polymeric adhesive to form a coherent layer between the two electrodes. Such technologies described in these patents and patent applications include: (a) Electrophoretic particles, fluids and fluid additives; see, eg, US Patent Nos. 7,002,728 and 7,679,814; (b) Capsules, adhesives, and encapsulation processes; see, eg, US Patent Nos. 6,922,276 and 7,411,719; (c) Microcellular structures, wall materials, and methods of forming cells; see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906; (d) methods for filling and sealing micelles; see, e.g., U.S. Patent Nos. 7,144,942 and 7,715,088; (e) Films and sub-assemblies comprising electro-optic materials; see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564; (f) backplanes, adhesive layers, and other auxiliary layers and methods used in displays; see, for example, U.S. Patent Nos. 7,116,318 and 7,535,624; (g) Color formation and color adjustment; see, e.g., U.S. Patent Nos. 1, 7,075,502, 7,167,155, 7,385,751, 7,492,505, 7,667,684, 7,684,108, 7,791,789, 7,800,813, 7,821,702, 7,839,564, 7,910,175, 7,952,790, 7,956,841, 7,982,941, 8,040,594, 8,054,526, 8,098,418, 8,159,636, 8,213,076, 8 ,363,299 8,422,116 8,441,714 8,441,716 8,466,852 8,503,063 8,576,470 8,576,475 8,593,721 8,605,354 8,649,084 8,670,174 4,756, 8,717,664, 8,786,935, 8,797,634, 8,810,899, 8,830,559, 8,873,129, 8,902,153, 8,902,491, 8,917,439, 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, 9,36 1,836, 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, 20 13/0278995, 2014/0055840, 2014/ 0078576, 2014/0340430, 2014/0340736, 2014/0362213, 2015/0103394, 2015/0118390, 2015/0124345, 2015/0198858, 2015/0234250, 2015/0268 531, 2015/0301246, 2016/0011484, 2016/0026062, Nos. 2016/0048054, 2016/0116816, 2016/0116818 and 2016/0140909; (h) Methods of driving displays; see, for example, U.S. Pat. , 7,034,783, 7,061,166, 7,061,662, 7,116,466, 7,119,772, 7,177,066, 7,193,625, 7,202,847 ,7,242,514,7,259,744,7,304,787,7,312,794,7,327,511,7,408,699,7,453,445,7,492,339,7,528,822,7,545,358,7,583,251,7,602,374, 7,612,760,7,679,599,7,679,813,7,683,606,7,688,297,7,729,039,7,733,311,7,733,335,7,787,169,7,859,742,7,952,557,7,956,841,7,9 82,479 , 7,999,787, 8,077,141, 8,125,501, 8,139,050, 8,174,490, 8,243,013, 8,274,472, 8,289,250, 8,300,006, 8,305,341, 8,314,784, 8,373,649, 8,384,658,8,456,414,8,462,102,8,514,168,8,537,105,8,558,783,8,558,785,8,558,786,8,558,855,8,576,164,8,576,259,8,593,396,8,6 05,032 , 8,643,595, 8,665,206, 8,681,191, 8,730,153, 8,810,525, 8,928,562, 8,928,641, 8,976,444, 9,013,394, 9,019,197, 9,019,198, 9,019,318, 9,082,352,9,171,508,9,218,773,9,224,338,9,224,342,9,224,344,9,230,492,9,251,736,9,262,973,9,269,311,9,299,294,9,373,289,9,3 90,066 , 9,390,661, and 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, 2009/0322721, 2010/0194733, 2010/0194789, 2010/0220121, 2010/0265561, 2010 /0283804, 2011/0063314, 2011/0175875, 2011/ 0193840, 2011/0193841, 2011/0199671, 2011/0221740, 2012/0001957, 2012/0098740, 2013/0063333, 2013/0194250, 2013/0249782, 2013/0321 278, 2014/0009817, 2014/0085355, 2014/0204012, 2014/0218277, 2014/0240210, 2014/0240373, 2014/0253425, 2014/0292830, 2014/0293398, 2014/0333685, 2014/0340734, 2015/0070744, 2015 /0097877, 2015/0109283, 2015/0213749, 2015/ 0213765, 2015/0221257, 2015/0262255, 2015/0262551, 2016/0071465, 2016/0078820, 2016/0093253, 2016/0140910 and 2016/0180777 (these patents and applications are hereinafter May be called MEDEOD (MEthods for Driving Electro-optic Displays) applications, method for driving electro-optic displays) applications); (i) Display applications; see, eg, US Patent Nos. 7,312,784 and 8,009,348; and (j) Non-electrophoretic displays as described in US Patent No. 6,241,921, US Patent Application Publication No. 2015/0277160, and US Patent Application Publication Nos. 2015/0005720 and 2016/0012710.

Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in capsule-type electrophoretic media can be replaced by a continuous phase, resulting in so-called polymer-dispersed electrophoretic displays, where the electrophoretic medium comprises a plurality of discrete droplets of electrophoretic fluid and continuous phase of polymeric material, and the discrete droplets of electrophoretic fluid within such polymer-dispersed electrophoretic displays can be viewed as capsules or microcapsules even though there is no discrete capsule membrane associated with each individual droplet; see For example US Patent No. 6,866,760. Thus, for the purposes of this application, such polymer-dispersed electrophoretic media are considered subspecies of capsule-type electrophoretic media.

A related type of electrophoretic display is the so-called "microcell electrophoretic display". In microcell electrophoretic displays, charged particles and fluids are not encapsulated in microcapsules, but are held in cavities formed within a carrier medium (usually a polymeric film) . See, eg, US Patent Nos. 6,672,921 and 6,788,449.

Although electrophoretic media are generally opaque (because, for example, 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 operated in a so-called "shutter mode". )" in which one display state is substantially opaque and one display state is transmissive. See, eg, US Patent Nos. 5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; Dielectrophoretic displays (which are similar to electrophoretic displays, but rely on changes in electric field strength) can operate in a similar mode; see US Patent No. 4,418,346. Other types of electro-optic displays can also operate in raster mode. Electro-optic media that operate in a raster pattern can be used in multilayer structures for full-color displays; in such structures, at least one layer adjacent to the viewing surface of the display operates in a raster pattern to expose or hide a second layer further from the viewing surface. layer.

A capsule-type electrophoretic display generally does not suffer from the clustering and settling failure modes of conventional electrophoretic devices and offers additional advantages, such as the ability to print or coat the display on a 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 coatings (e.g. patch die coating, slot die coating) or extrusion coating (slot or extrusion coating), inclined plate or cascade coating (slide or cascade coating) and curtain coating (curtain coating)); roll coating (roll coating) (for example: roller lining knife coating ( knife over roll coating and 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 manufacturing (thermal printing processes); ink jet printing processes (ink jet printing processes); electrophoretic deposition (electrophoretic deposition) (see U.S. Patent No. 7,339,715); and other similar techniques). Therefore, the completed display can be flexible Furthermore, since the display medium can be printed (using various methods), the display itself can be manufactured cheaply.

As noted above, most simple prior art electrophoretic media exhibit essentially only two colors. Such electrophoretic media use a single type of electrophoretic particle of a first color in a colored fluid of a second, different color (in this case, the first color is displayed when the particle is adjacent to the viewing surface of the display, and the first color is displayed when the particle is in contact with the viewing surface of the display. displaying a second color when the viewing surfaces are spaced apart) or using first and second types of electrophoretic particles of different first and second colors in a colorless fluid (in this case, when particles of the first type are adjacent When the viewing surface of the display is displayed, a first color is displayed, and when particles of the second type are adjacent to the viewing surface, a second color is displayed). Usually these two colors are black and white. If a full color display is desired, a color filter array can be deposited on the viewing side of a monochrome (black and white) display.

Displays with color filter arrays rely on area sharing and color mixing to generate color stimuli. Share the available display area between three or four primary colors such as Red/Green/Blue (RGB) or Red/Green/Blue/White (RGBW), and the filters can be one-dimensional (striped) or two-dimensional (2x2 ) repeating patterns to arrange. Other primary colors or a selection of more than three primary colors 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 to be small enough that at the expected viewing distance they visually blend together into a stimulus of uniform color ( "color blending") individual pixels. The inherent disadvantage of area sharing is that the colorant is always present, and the color can only be modulated by switching the corresponding pixel of the underlying monochrome display to white or black (turning the corresponding primary color on or off). For example, in an ideal RGBW display, each of the red, green, blue, and white primary colors occupies a quarter of the display area (one of four sub-pixels), with the white sub-pixel matching the underlying monochrome display white as bright as , and each color sub-pixel is no brighter than a third of the white of a monochrome display. The white brightness displayed by the display as a whole cannot be greater than half of the brightness of the white sub-pixel (the white area of the display is obtained by displaying one white sub-pixel in every four sub-pixels plus each color sub-pixel equivalent to the white sub-pixel in its color form 1/3, so the combined contribution of the three colored sub-pixels is no more than one white sub-pixel). The brightness and saturation of the color will be reduced by sharing the area with the color pixel that is switched to black. Area sharing is particularly problematic when mixing yellow, since yellow is brighter than any other color of the same brightness and saturated yellow is almost as bright as white. Switching the blue pixels (a quarter of the display area) to black makes the yellow too dark.

A system for quantifying color characteristics (including both luminance and hue) is the CIELAB system, which specifies the CIE standard illuminant D65 (for example: a color temperature of 6500K) corresponding to the color displayed by a general color reflective display device Color coordinate values (ie, L*, a* and b*). L* represents lightness from black to white on a scale of 0 to 100, and a* and b* represent chromaticity without specific numerical limits. The negative number a* corresponds to green, the positive number a* corresponds to red, the negative number b* corresponds to blue, and the number b* corresponds to yellow. L* can be converted to reflectance using the following formula: L*=116(R/R ₀ ) ^1/3 -16, where R is the reflectance and R ₀ is the standard reflectance value.

US Patent Nos. 8,576,476 and 8,797,634 describe multicolor electrophoretic displays having a single backplane comprising individually addressable pixel electrodes and a common light-transmissive front electrode. This common light-transmitting front electrode is also called top electrode. A negative number electrophoretic layer is disposed between the back plate and the front electrode. The displays described in these applications can render any primary color (red, green, blue, cyan, magenta, yellow, white, and black) at any pixel location. However, there are several disadvantages to using 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 in the case of a single electrophoretic layer addressed using the same voltage. Additionally, optical losses (eg, caused by light scattering or unwanted absorption) of the electrophoretic layer closest to the viewing surface may affect the appearance of images formed in the underlying electrophoretic layer.

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 comprising one or two types of pigment particles dispersed in a transparent colorless or colored solvent, the electrophoretic fluid being disposed between a common electrode and a plurality of pixels or drive between the electrodes. The drive electrodes are configured to expose the background layer. US Patent No. 9,116,412 describes a method for driving a display unit filled with an electrophoretic fluid comprising two types of charged particles of opposite charge polarity and two contrasting colors. Both types of pigment particles are dispersed in a colored solvent or in a solvent with uncharged or slightly charged colored particles. The method includes driving the display unit by applying a driving voltage of about 1 to about 20% of the full driving voltage to display the color of the solvent or the color of the uncharged or slightly charged colored particles. US Patent Nos. 8,717,664 and 8,964,282 describe an electrophoretic fluid and a method for driving an electrophoretic display. The fluid includes 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 have opposite charge polarities, and the charge level of the third type of pigment particles is less than about 50% of the charge level of the first or second type of pigment particles. These 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 of the term used hereinafter, which achieves the display of at least 8 independent colors (white, red, green, blue, cyan, yellow, magenta and black).

This specification discloses improved methods for driving full-color electrophoretic displays and full-color electrophoretic displays using these driving methods. In one aspect, the invention relates to a color electrophoretic display comprising a light-transmitting electrode at a viewing surface, a backplane comprising an array of thin film transistors coupled to pixel electrodes, wherein each thin film transistor comprises a layer of metal oxide Semiconductor and colored electrophoretic media disposed between the light-transmitting electrodes and the backplane. The color electrophoretic medium includes (a) fluid; (b) a plurality of first and a plurality of second particles in the dispersion fluid, the first and second particles have opposite charges, and the first particles are optical scattering particles with a second particle having a subtractive primary color; and (c) a plurality of third and a plurality of fourth particles in a dispersed fluid, the third and fourth particles having charges of opposite polarity, and the fourth particles The third and fourth particles are each of a different subtractive primary color from each other and from the second particles.

In some embodiments, the first electric field required to separate aggregates formed from the third and fourth types of particles is greater than the second electric field required to separate aggregates formed from the 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 particles are 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 colors of 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 negatively charged. Tether is positively charged. In some embodiments, yellow, magenta, and cyan pigments exhibit diffuse reflectances at 650, 550, and 450 nm, respectively, when the pigments are approximately isotropically distributed at 15% by volume in an area containing the pigment and with a refractive index less than 1.55 in a layer of liquid with a thickness of 1 µm, which is measured on a black background as less than 2.5%. In some embodiments, the fluid is a non-polar fluid with a dielectric constant of less than about 5. In some embodiments, the polymer in which the fluid has been dissolved or dispersed has a number average molecular weight in excess of about 20,000 and is substantially nonabsorbent to particles. In some embodiments, the metal oxide semiconductor is indium gallium zinc oxide (IGZO). The invention described above can be incorporated into an e-book reader, portable computer, tablet computer, mobile phone, smart card, sign, watch, shelf label or flash drive.

In another aspect, a color electrophoretic display includes a controller, a light-transmitting electrode at a viewing surface, and a backplane including an array of thin film transistors coupled to pixel electrodes, each thin film transistor comprising a layer of metal oxide semiconductor . A colored electrophoretic medium is arranged between the light-transmitting electrode and the back plate, and the colored electrophoretic medium includes (a) a fluid; (b) a plurality of first particles and a plurality of second particles in the dispersion fluid, and the first and second particles are (c) a plurality of third particles and a plurality of fourth particles in a dispersed fluid, the first particles being light-scattering particles, and the second particle having a subtractive primary color; The fourth particles are oppositely charged, and the third and fourth particles are each of a different subtractive primary color from each other and from the second particles. The controller is configured to provide a plurality of drive voltages to several pixel electrodes so that white, yellow, red, magenta, blue, cyan, green and black can be displayed at each pixel electrode while maintaining the light-transmitting electrode at a constant voltage. In some embodiments, the controller is configured to provide a voltage greater than 25 volts and less than −25 volts to the pixel electrodes. In some embodiments, the controller is configured to additionally provide a voltage between 25 V and 0 V, and a voltage between -25 V and 0 V. In some embodiments, the metal oxide semiconductor is indium gallium zinc oxide (IGZO).

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 includes (a) fluid; (b) a plurality of first and a plurality of second particles in the dispersion fluid, the first and second particles have opposite charges, and the first particles are optical scattering particles with a second particle having a subtractive primary color; and (c) a plurality of third and a plurality of fourth particles in a dispersed fluid, the third and fourth particles having charges of opposite polarity, and the fourth particles The third and fourth particles are each of 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 such that White, yellow, red, magenta, blue, cyan, green and black are displayed, wherein the magnitude of one of the first high voltage, the first low voltage, the second high voltage and the second low voltage is different. In some embodiments, the magnitude of the first high voltage is the same as that of the second high voltage. In some embodiments, the magnitude of the first low voltage is the same as that of the second low voltage, and the magnitude of the first high voltage is different from that of the first low voltage.

In another aspect, a color electrophoretic display includes a controller, a light-transmitting electrode at a viewing surface, a backplane electrode, and a color electrophoretic medium disposed between the light-transmitting electrode and the backplane electrode. The color electrophoretic medium includes (a) fluid; (b) a plurality of first and a plurality of second particles in the dispersion fluid, the first and second particles have opposite charges, and the first particles are optical scattering particles with a second particle having one of the subtractive primary colors; and (c) a plurality of third and a plurality of fourth particles in the dispersed fluid, the third and fourth particles having charges of opposite polarity, And the third and fourth particles are each different subtractive primary colors from each other and from the second particles. The controller is configured to cause white, yellow, red, magenta, blue, cyan, green, and black colors to be displayed at the viewing surface by providing a plurality of time-dependent drive voltages to the backplane electrodes while simultaneously The following driving voltages are provided to the light-transmitting electrode: 1) a high voltage is provided for a first time, a low voltage is provided for a second time, and a high voltage is provided for a third time, or 2) a low voltage is provided for a first time and a high voltage is provided for a second time , and provide a low voltage for the third time.

In another aspect, a system for driving an electrophoretic medium includes an electrophoretic display and a power supply capable of providing positive and negative voltages, wherein the positive and negative voltages are different in magnitude; and a controller coupled to the top electrode driver, the first driving electrode driver and the second driving electrode driver. The electrophoretic medium includes a light-transmissive top electrode at the viewing surface, a first drive electrode, a second drive electrode, and the electrophoretic medium disposed between the top electrode and the first and second drive electrodes. The controller is configured to: A) in a first frame, provide the positive voltage to the top electrode, provide the negative voltage to the first drive electrode, and provide the positive voltage to the second drive electrode; B) 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; C) in a third frame, providing the 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; and D) in a fourth frame, providing the positive voltage to the top electrode, providing the positive voltage to the first driving electrode, and provide the positive voltage to the second driving electrode. In one embodiment, the controller is configured to further E): in a fifth frame, provide the negative voltage to the top electrode, provide the ground voltage to the first drive electrode, and provide the negative voltage to the a second drive electrode; and F) 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. In one embodiment, the electrophoretic medium is encapsulated in a plurality of microcapsules, and the microcapsules are dispersed in a polymer binder between the top electrode and the first and second driving electrodes. In one embodiment, the electrophoretic medium is encapsulated in a microcell array having openings, wherein the openings are sealed with a polymer binder, and the microcell array is disposed between the top electrode and the second electrode. between the first and second drive electrodes. In one embodiment, the electrophoretic medium includes a non-polar fluid and four groups of particles with different optical properties. In one embodiment, the first and second groups of particles are charged with opposite polarities, the third and fourth groups of particles are charged with opposite polarities, the first particles are light scattering particles, and the second, The third and fourth sets of particles are each of a different subtractive primary color from the other. In one embodiment, the controller is configured to provide a combination of the positive voltage, the negative voltage and the ground voltage to the top electrode and the first drive electrode such that white, yellow , Red, Magenta, Blue, Cyan, Green, and Black. In one embodiment, the first and second groups of particles have opposite charges, the third and fourth groups of particles have the same charge as the second particles, the first particles are light scattering particles, and The second, third and fourth sets of particles are each of a different subtractive primary color from the other. In one embodiment, the controller is configured to provide a combination of the positive voltage, the negative voltage and the ground voltage to the top electrode and the first drive electrode such that white, yellow , Red, Magenta, Blue, Cyan, Green, and Black. 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.

In another aspect, a system for driving an electrophoretic medium includes an electrophoretic display; and a power supply capable of providing a positive voltage and a negative voltage, wherein the positive and negative voltages are different in magnitude; and a controller coupled to the a top electrode driver, the first driving electrode driver and the second driving electrode driver. The electrophoretic medium includes a light-transmissive top electrode at the viewing surface, a first drive electrode, a second drive electrode, and the electrophoretic medium disposed between the top electrode and the first and second drive electrodes. The controller is configured to: A) in a first frame, provide the positive voltage to the top electrode, provide the negative voltage to the first drive electrode, and provide the positive voltage to the second drive electrode; B) 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; C) in a third 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; and D) in a fourth frame, providing the positive voltage to the top electrode, providing the positive voltage to the first driving electrode, and provide the positive voltage to the second driving electrode. In one embodiment, the controller is configured to further: E) in a fifth frame, provide the negative voltage to the top electrode, provide the ground voltage to the first drive electrode, and provide the negative voltage to the a second drive electrode; and F) 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. In one embodiment, the electrophoretic medium is encapsulated in a plurality of microcapsules, and the microcapsules are dispersed in a polymer binder between the top electrode and the first and second driving electrodes. In one embodiment, the electrophoretic medium is encapsulated in a microcellular array having openings, wherein the openings are sealed with a polymeric binder, and the microcellular array is disposed between the top electrode and the first and second electrodes. Between the two drive electrodes. In one embodiment, the electrophoretic medium includes a non-polar fluid and four groups of particles with different optical properties. In one embodiment, the first and second groups of particles are charged with opposite polarities, the third and fourth groups of particles are charged with opposite polarities, the first particles are light scattering particles, and the second, The third and fourth sets of particles are each of a different subtractive primary color from the other. In one embodiment, the controller is configured to provide a combination of the positive voltage, the negative voltage and the ground voltage to the top electrode and the first drive electrode such that white, yellow , Red, Magenta, Blue, Cyan, Green, and Black. In one embodiment, the first and second groups of particles have opposite charges, the third and fourth groups of particles have the same charge as the second particles, the first particles are light scattering particles, and The second, third and fourth sets of particles are each of a different subtractive primary color from the other. In one embodiment, the controller is configured to provide a combination of the positive voltage, the negative voltage and the ground voltage to the top electrode and the first drive electrode such that white, yellow , Red, Magenta, Blue, Cyan, Green, and Black. 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.

A system for simplified driving of electrophoretic media using positive and negative voltage sources, wherein the voltage sources are of different sizes, and a controller which cycles the top electrode between the two voltage sources and ground voltage while coordinating the drive with the top At least two driving electrodes opposite to each other. Compared to providing 6 independent driving levels and ground voltages for each driving electrode, the completed system can achieve roughly the same color state. Thus, the system simplifies the required electronics with only a marginal loss of color gamut. The system is particularly suitable for addressing electrophoretic media comprising four different groups of particles, for example, where three of the particles are colored and subtractive and one of the particles is light scattering.

The present invention proposes an improved method of driving electro-optic devices with so-called top-plane switching, ie, where the voltage on the top (common) electrode varies during the device refresh process. In some embodiments, the present invention is used with electrophoretic media comprising four particles, where two of the particles are colored and subtractive, and one of the particles is light scattering. Generally, such systems include white particles and cyan, yellow and magenta subtractive primary color particles. 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 schematically in Figure 5 and it can provide white, yellow, red, magenta, blue, cyan, green and black at each pixel.

Using the electrophoretic fluids of the present invention, display devices can be constructed in several ways known in the art. The electrophoretic fluid can be encapsulated in microcapsules, or incorporated into a cellular structure, which is then sealed with a polymer layer. The microcapsule or cell layer can be coated or imprinted on a transparent coated plastic substrate or film loaded with conductive material. The assembly can be laminated to a backplane carrying the pixel electrodes using a conductive adhesive. Alternatively, the electrophoretic fluid can be dispensed directly onto a thin grid of openings already disposed on the backplane including the active pixel electrode array. The filled grid can then be top-sealed with an integrated protective sheet/light-transmissive electrode.

Referring to Figures 1 and 2, an electrophoretic display (101, 102) generally includes a top light-transmissive electrode 110, an electrophoretic medium 120, and bottom drive electrodes 130/135, which are usually pixels of an active pixel array controlled by thin film transistors (TFTs). electrode. Alternatively, the bottom drive electrodes 130/135 may be wired directly to a controller or other switch that provides a voltage to the bottom drive electrodes 130/135 to enable the optical state of the electrophoretic medium 120 (eg, segmented electrodes) Make a change. Importantly, it is not necessary that the junctions between the drive electrodes 130/135 correspond to the intersections of the microcapsules, or the walls of the cells 127 . Because the electrophoretic medium 120 is thin enough and the capsules or cells are wide enough, when the display is viewed from the viewing side, the pattern (square, circular, hexagonal, wavy, text or other) of the driving electrodes will be seen, while not the pattern of the container described. The electrophoretic medium 120 includes at least one electrophoretic particle 121 , however, the second electrophoretic particle 122 , the third electrophoretic particle 123 , the fourth electrophoretic particle 124 or more particles are feasible. [It should be noted that the third electrophoretic particle 123 and the fourth electrophoretic particle 124 may be included in the microcapsule 126 of FIG. 1 , but are omitted for clarity. ] The electrophoretic medium 120 generally includes solvents, such as isoparaffins (isoparaffins), and may also include dispersed polymers and charge control agents to promote state stability, such as bistability (bistability), that is, without inputting any additional The ability to maintain an electro-optical state in the absence of energy.

The electrophoretic medium 120 is generally separated by walls of microcapsules 126 or cells 127 . The entire display stack is generally configured on a substrate 150, which may be a rigid or flexible substrate. The display (101, 102) generally also includes a protective layer 160, which may simply protect the top electrode 110 from damage, or it may also surround the entire display (101, 102) to prevent water ingress and the like. The electrophoretic display (101, 102) may also include one or more adhesive layers 140, 170 and/or sealing layer 180, as desired. In some embodiments, the adhesive layer may include a primer component to enhance the adhesion to the electrode layer 110 , or a separate primer layer (not shown in FIG. 1 or 2 ) may also be used. (The structures of electrophoretic displays and components, pigments, adhesives, electrode materials, etc. are described in many patents and patent application publications of E Ink Corporation (for example: U.S. Patent Nos. 6,922,276, 7,002,728, 7,072,095, 7,116,318, 7,715,088, and 7,839,564) , the entire contents of which are incorporated herein by reference.)

Each pixel electrode or propulsion electrode of a thin film transistor (TFT) backplane usually has only one transistor. Conventionally, each pixel electrode has a capacitor electrode associated therewith such that the pixel electrode and the capacitor electrode form a capacitor, see eg International Patent Application Publication WO 01/07961. In some embodiments, an N-type semiconductor (eg, amorphous silicon) can be used to form the transistor, and the "select" and "non-select" voltages applied to the gate electrodes can be positive and negative, respectively.

As shown in Figure 3, each transistor (TFT) is connected to gate lines, data lines and pixel electrodes (push electrodes). When the positive voltage on the TFT gate is large enough (or negative voltage, depending on the type of transistor) to make the scanning line and the pixel electrode coupled to the TFT drain (ie, Vg "ON" or "turn on") have a small gap The voltage on the scan line is thus transferred to the electrode of the pixel when the impedance is lower. However, when there is a negative voltage on the TFT gate, the pixel storage capacitor has a higher impedance and stores voltage and is not scanned while other pixels are addressed (i.e., Vg "OFF" or "OFF"). voltage on the line. Therefore, generally speaking, the TFT should be used as a digital switch. In practice, the TFT still has a certain amount of resistance when it is in the "ON" setting, so it takes some time to charge the pixels. In addition, when the voltage is in the “OFF” setting, current may leak from V _S to V _pix , causing cross-talk. Increasing the capacitance of the storage capacitor C _s reduces crosstalk, but at the cost of making it more difficult to charge the pixel and increasing the charging time. As shown in FIG. 3, a separate voltage (V _TOP ) is supplied to the top electrode, thereby establishing an electric field between the top electrode and the pixel electrode (V _FPL ). Finally, it is the value of V _FPL that determines the optical state of the associated electro-optic medium. When the first side of the storage capacitor is coupled to the pixel electrode, the second side of the storage capacitor is coupled to a separate line (V _COM ), so that charge is removed from the pixel electrode. See, eg, US Patent No. 7,176,880, which is hereby incorporated by reference in its entirety. [In some embodiments, an N-type semiconductor (eg, amorphous silicon) can be used to form the transistor, and the "select" and "non-select" voltages applied to the gate electrodes can be positive and negative, respectively. ] In some embodiments, ground may be used, however, there are many different designs for draining charge from charging capacitors, such as described in US Patent No. 10,037,735, the entire contents of which are incorporated herein by reference.

The problem with conventional amorphous silicon TFTs is that the operating voltage is limited to about ±15V, so that the transistor starts to leak and eventually fails. While an operating voltage range of ±15V is available for many two-particle electrophoretic systems, it has been found that the increased voltage range makes it easier to separate particles with different zeta potentials, enabling advanced electrophoretic displays to update faster and have more reproducible colors . A solution to increase the voltage range of the pixel electrode is to use top-plane switching, ie whereby the voltage on the top (common) electrode varies as a function of time.

The principle of top plane switching is shown 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 as having four different types of electrophoretic particles, however, the electrophoretic medium 420 may have fewer or more types of different particles than depicted. In the simplified embodiment of FIG. 4, both the top electrode 410 and the drive electrode 430 are powered by different power supplies 440 and 460, which may be from the same power source (not shown). In addition, a ground voltage 470 is also available. Generally, one power supply is positive with respect to ground voltage, and one power supply is negative with respect to ground voltage. Which power supply (or ground voltage) is connected to which electrode at a given unit of time (one frame) is controlled by the controller 470 . The controller may be a commercially available electrophoretic display controller, such as that manufactured by UltraChip, or it may be a research controller, such as that provided by E Ink Corporation (HULK controller, ARC30™ controller), or it may be a virtual Controller, using eg LABVIEW® to control the output of the voltage board.

As shown in the equation below the electrophoretic display 401 of FIG. 4, each combination of voltages supplied to the top electrode 410 and to the drive electrode 430 results in a voltage difference ΔV=V(drive electrode) across the electrophoretic medium 420 – V (top electrode). It can be seen from the equations (described below) that by modifying the voltage on the top electrode, a wider range of voltages on the electrophoretic medium 420 can be achieved. Furthermore, where the magnitudes of 440 and 460 are different, intermediate differential voltage values across the electrophoretic medium can be obtained. As shown in FIG. 4, by carefully coordinating which power source the top electrode 410 and drive electrode 430 are connected to, seven different voltages can be supplied to the electrophoretic medium 420.

Although FIG. 4 only shows a single drive electrode 430, it is understood that this principle can be extended to a system with many drive pixels, for example provided with an active matrix backplane. However, coordinating the necessary top electrode voltages to achieve the desired voltage difference across a particular pixel becomes very complex as the number of pixels increases. In practice, top plane switching with an active matrix backplane uses separate voltage controllers for the top plane and pixel electrodes, and requires cycling the top electrode voltage for multiple frames while individual pixel electrodes are switched to generate the desired waveform. Further details of this approach are described in US Patent No. 10,593,272, the entire contents of which are incorporated herein by reference.

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 can only See those colored pigments that are on the viewing side of the white pigments (ie, the only pigments that scatter light). More specifically, when cyan, magenta, and yellow particles are below a white particle (scenario [A] in Figure 5), there are no particles above the white particle, and the pixel only displays white. When there is only a single particle above the white particle, the color of the single particle is displayed, which are yellow, magenta and cyan respectively in situations [B], [D] and [F] in Fig. 5 . When two particles are above a white particle, the displayed color is the combination of the two particles, in situation [C] of Figure 5, magenta and yellow particles display red, and in situation [E], cyan and magenta particles shows blue, while in situation [G] yellow and cyan particles show green. Finally, when all three colored particles are located below the white particles (scenario [H] in FIG. 5), all incident light is absorbed by the three subtractive primary color particles, and the pixel appears black.

A subtractive primary color may be represented by light-scattering particles, so that the display will include two types of light-scattering particles, one white and one colored. In this case, however, the position of the light-scattering colored particle relative to other colored particles covering the white particle becomes important. For example, when rendering black (when all three colored particles are on white particles) the scattering colored particles cannot sit on non-scattering colored particles (otherwise they would be partially or completely hidden behind the scattering particles, the rendered color will be the color of the scattered colored particles, not black). If more than one type of colored particle scatters light, it is not easy to render the color as black.

It has been found that sorting the four pigments into appropriate configurations to make waveforms for these colors results in at least seven voltage levels (high positive level, middle positive level, low positive level, zero level, low negative level). Standard, Medium Negative Level and High Negative Level) to achieve the best. Figure 6 shows typical waveforms (in a simplified manner) used to drive the 4-particle color electrophoretic display system described above. This type of waveform has a "push-pull" structure, ie, it consists of a dipole formed by two pulses of opposite polarity. The size and length of these pulses determine the color achieved. In general, the higher the magnitude of the "high" voltage, the better the color gamut achieved by the display. The "high" voltage is typically between 20V and 30V, more typically around 25V, eg 24V. The "middle" (M) level is typically between 10V and 20V, more typically around 15V, such as 15V or 12V. The "low" (L) voltage is typically between 3V and 10V, more typically around 7V, eg 9V or 5V. Of course, the values of H, M, and L depend to some extent on the composition of the particles, as well as the environment of the electrophoretic medium. In some applications, H, M, L can be set by the cost of the components used to generate and control these voltage levels.

As shown in Figure 6, if the top electrode is held at a constant voltage (i.e., non-top-plane switching), even the simple waveform of the ACeP® system requires the drive electronics to provide seven Different voltages (+H, +M, +L, 0, -L, -M, -H). While multi-level source drivers capable of supplying seven different voltages are available, most commercially available source drivers for electrophoretic displays only allow three different voltages (typically positive, zero, and negative) to be supplied during a single frame. Voltage).

Of course, achieving the desired color using the drive pulses of Figure 6 depends on starting the process from a known state of the particle, which is unlikely to be the last color displayed on the pixel. Accordingly, a series of reset pulses takes precedence over drive pulses, increasing the amount of time required to update a pixel from a first color to a second color. This reset pulse is described in more detail in US Patent No. 10,593,272, which is incorporated herein by reference. The lengths of these pulses (resetting and addressing) and any rests (i.e., periods of zero voltage between them) can be chosen such that the overall waveform (i.e., the integral of voltage over time over the entire waveform) is direct current (DC) balanced (ie, the integral of voltage over time is essentially zero). DC balance can be achieved by adjusting the length of the pulses and the rest during the reset phase so that the net pulses provided by the reset phase are equal in magnitude and opposite in sign to the net pulses provided by the address phase, which are switched to a specific During the desired color phase.

In addition, the previous discussion of waveforms, especially the discussion of DC balance, ignored the problem of kickback voltage. In practice, as mentioned above, each backplane voltage is the voltage provided by the power supply, offset by an amount equal to the kickback voltage V _KB . Therefore, if the power supply used provides the three +V, 0, and -V voltages, the backplane actually receives voltages of V+V _KB , V _KB , and –V+V _KB (note that in amorphous In the case of silicon TFTs, V _KB will actually be negative). However, this same power supply would provide +V, 0 and -V to the front electrodes without backshoot voltage offset. Thus, for example, when -V is supplied to the front electrode, the display will experience a maximum voltage of 2V+V _KB and a minimum voltage of V _KB . Instead of using a separate power supply to supply V KB to the front electrodes (which can be expensive and inconvenient), the waveform can be divided into V _KB parts where the front electrodes are supplied with positive voltage, negative voltage and V _KB . In addition to the kickback voltage. Higher Voltage Addressing Using a Metal Oxide Backplane

Although modifying the rail voltages provides some flexibility to achieve different electro-optical performances than the four-particle electrophoretic system, it still brings many constraints on the top surface switching. For example, it is generally preferred that the lower negative voltage V _M- be less than half of the maximum negative voltage V _H- for the display of the present invention to be in a white state. However, as shown in the above equation, top-plane switching requires a lower positive voltage constant of at least half of the maximum positive voltage, typically higher than half.

An alternative solution to the complexity of top-plane switching can be provided by fabricating control transistors using uncommon materials with higher electron mobility, allowing the transistors to directly switch larger control voltages, e.g. +/- 30V. Newly developed active matrix backplanes may include thin film transistors incorporating metal oxide materials such as tungsten oxide, tin oxide, indium oxide and zinc oxide. In these applications, such metal oxide materials are used to form a channel forming region for each transistor, allowing faster switching of higher voltages. This type of transistor generally includes a gate electrode, a gate insulating film (usually SiO ₂ ), a metal source electrode, a metal drain electrode, and a metal oxide semiconductor film above the gate insulating film, and the gate electrode, the source electrode, and the drain electrode are at least partially overlap. Such backplanes are supplied by manufacturers such as Sharp/Foxconn, LG and BOE.

A preferred metal oxide material for such applications is Indium Gallium Zinc Oxide (IGZO). The electron mobility of IGZO-TFT is 20 to 50 times higher than that of amorphous silicon. By using IGZO TFTs in an active matrix backplane, voltages greater than 30V can be provided by suitable display drivers. Furthermore, at least five (preferably seven) levels of source drivers can be provided to provide different driving paradigms for the four-particle electrophoretic display system. In one embodiment, it has two positive voltages, two negative voltages, and several zero volts. In another embodiment, it has three positive voltages, three negative voltages, and several zero volts. In one embodiment, it has four positive voltages, four negative voltages, and several zero volts. These levels can be selected in the range of about -27V to +27V without imposing the constraints of top plane switching as described above.

Using an advanced backplane, such as a metal oxide backplane, it is possible to directly address each pixel in a suitable push-pull waveform, ie, as described in FIG. 6 . This drastically reduces the time it takes to update each pixel, converting a six-second update to less than a second in some cases. While, in some cases, it may be necessary to use a reset pulse to establish a starting point for addressing, reset can be done faster at higher voltages. Furthermore, 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 specific waveform that is only slightly longer than the push-pull waveform shown in FIG. 6 . Simplified Top Plane Switching

To reduce update length and flashiness, the complexity of the front plane switching can be reduced in exchange for a smaller number of available colors. Furthermore, since the particles have a finite velocity in the electrophoretic medium, the amount of time the dipole is applied also affects the size of the color gamut.

Figure 7 shows a solution using a simplified top-plane switching pulse sequence (top left), with a simplified backplane switching pulse sequence (bottom left) matched to a single top-plane sequence, thereby providing at least distinct colors. The top plane switches between two voltages (one positive and one negative), while the backplane can take three different voltages: positive, negative and zero. (In Figure 7, the voltage levels are relative (i.e., 1, 0, and -1), but in many instances the actual are 15V, 0, and -15V.) Note that the eight color sequences in Figure 6 (right in Figure 7) can be achieved by subtracting the pulse sequence for the top plane from the backplane pulse sequence (left in Figure 7). . It will be appreciated that for the pulse sequences in Figures 6 and 7, the electrophoretic fluid includes negatively charged white pigments, positively charged magenta and cyan pigments, and may be positively or negatively charged or substantially neutral. yellow paint. Other color/charge combinations are possible and the waveform can be adjusted accordingly.

As explained above, in the waveform of FIG. 7, at least five different voltages are required. In an active array drive environment, this can be achieved either (a) by providing a selection of five different voltages to the row when a particular column is selected at a particular time, or (b) by selecting a particular column at a first time and then selecting it at a second When a different set of voltages is provided when the same column is time selected, this is achieved by providing a selection of fewer (eg, 3) different voltages to the row, or (c) by simultaneously applying the same row at the first and second time The same selection of three voltages is provided, but achieved by changing the potential of the front electrode between the first and second times. Option (c) is particularly useful when at least one voltage needs to be provided that is higher than what the backplane electronics can support.

Since, with top plane switching, it is not possible to assert both high positive and high negative potentials, it is necessary to offset the +/- dipole of the top plane relative to the -/+ dipole of the backplane. In the wave pattern shown in Figure 7, there is only one dipole per transition. This provides as few "momentary" waveforms as possible, since each dipole produces two visible optical changes to the display. In cases where five different voltage levels can be provided to the backplane electrodes when each column is selected, and the backplane electronics can support the highest voltage required, it is not necessary to shift the dipoles in the manner shown in FIG. 7 . Driving with Cyclic Top Plane Voltage

For the driving sequence in Figure 7, the voltages applied to the top plane are denoted as V _t+ and V _t- , and the voltages applied to the backplane are denoted as V _{b +} and V _{b -} , respectively, and | V _t+ |=| V _{t -} |=| V _{b +} |=| V _{b -} |=V. According to this, when the maximum supply voltage is +/-15 volts (as in typical commercially available backplanes), the voltages across the electrophoretic medium become 30V, 28V, 0V, -28V and -30V.

However, the magnitude of the maximum voltage (ie rail voltage) of the top plane electrode and the back electrode need not be the same. For example, the rail voltage offset can be calculated from some nominal maximum voltage amplitude V. The offset of each rail can be denoted as w, x, y and z, while assuming that the zero voltage rail remains at zero and is not applied to the top plane. therefore:

Referring to the backplane voltage, when the top plane is set to V _t+ , three negative voltages of high, medium and low sizes can be applied to the electrophoretic medium, denoted as V _H- , V _M- and V _L- (that is, V _b -V _t , where V _b can take one of the three values shown above). These voltages are: When the voltage of the top plane is set to V _t- , these equal voltages are available: When the voltage of the top plane is set to 0, the equivalent voltage is available:

It can be seen from the above that when w=y and x=z, no matter the top plane system is set to V _t+ , V _t- or 0, the zero voltage condition can be maintained. In practice, waveforms need to be significantly greater in complexity and length if the best color is to be achieved. Accordingly, the top-plane switching scheme thus requires greater complexity than the scheme shown in FIG. 7 . However, as the difficulty increases, in applications that require simultaneous updates in different areas of the display, the start times are interleaved with intervals smaller than the length of one waveform. Because the top plane potential is established across the display, it may not be possible to initiate a new update in one area of the display until a previously initiated update in another location has completed.

The problem of coordinating multiple simultaneous updates each requiring top-plane switching can be solved by cycling the top-plane voltage while stretching the waveform, as shown in Figure 8. (V _TE = top electrode voltage, V _DE1 = first drive electrode voltage, V _DE2 = second drive electrode voltage, ΔV _DE1 = voltage difference on the electrophoretic medium between first drive electrode and top electrode, ΔV _DE2 = second The voltage difference across the electrophoretic medium between the two drive electrodes and the top electrode.) previously targeted a seven-level backplane capable of delivering +/-24V, +/-15V, +/-9V, or 0V at any pixel location in any frame The established green and yellow waveforms have been modified for cyclic top-plane drive. The controller provides successive frames of +15V, -9V and 0V (ie, V=15V, w=y=0V and x=z=6V in the above equation) to the top electrode as shown in FIG. 9 . By stretching the waveform, and coordinating the voltage supplied to the first and second drive electrodes with the top voltage cycling, it is possible to effect simultaneous color refresh at two different drive electrodes using top switching.

When the top electrode is +15V, the voltage difference supplied to the electrophoretic medium is -24V, -15V and -0V. When the top electrode is -9V, the voltage difference supplied to the electrophoretic medium is 24V, 9V and 0V. When the top electrode is at ground voltage (0V), the voltage difference supplied to the electrophoretic medium is 15V, 0V and -9V. [Conventionally, the voltage difference is ΔV=V(drive electrode)−V(top electrode). ] In this way, seven voltages can be provided: +/-24V, +/-15V and +/-9V, and 0V. It should be noted 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 such that for that frame the voltage difference across the electrophoretic medium is zero. Obviously this makes the waveforms much longer, each "simple" waveform now takes three times as long to update as the original multilevel waveform.

Using a model of a four-particle electrophoresis system, tests were performed against the same system with seven individual drive levels and a static top electrode using top electrode cyclic drive trains of +15V, -9V, and 0. The results are shown in Tables 1 and 2, and presented in the graph of Figure 9A and the simulated color table of Figure 9B. Table 1. Calculated L*a*b* values for a modeled ACeP system using a dedicated seven-stage driver . color L* a* b* color black 20.4 0.3 -17.5 black blue 37.3 -0.4 -22.3 blue red 49.4 18 8 red magenta 39.5 28.5 -11.3 magenta green 52.9 -14.5 11.6 green blue 44.9 -12.7 -9.2 blue yellow 64.5 -8.6 36.1 yellow White 67.2 -6.7 15.2 White color gamut 14565 CR 11.9 Table 2. Calculated L*a*b* values for the modeled ACeP system using top electrode cycling and +15V and -9V power supplies. color L* a* b* color black 18.1 -2.5 -6.6 black blue 30.5 -12.7 -15.8 blue red 48.5 10.9 14.6 red magenta 38 26.3 -7.7 magenta green 46 -21.4 7.9 green blue 35 -18 -13.6 blue yellow 59.7 -8.9 27.9 yellow White 61.7 -2.8 1.7 White color gamut 15991 CR 11.8

Comparing Tables 1 and 2, it appears that in addition to the longer update time, there is a slight loss of top electrode cycling. In fact, the color gamut (color space) of the top electrode cycling method is actually slightly larger. The difference between the two methods can be further visualized by considering Figures 9A and 9B. In FIG. 9A , the solid circles represent the L*a*b* measurements for the seven-level drive, while the open circles represent the L*a*b* measurements for the cyclic top electrode drive. It can be seen from Figures 9A and 9B that the resulting primary color states are very similar. (Compare the positions of the open and filled circles.) The greatest change can be seen in the green primary (left center portion of Figure 9A), where the green primary shifts a lot towards yellow. The color state difference of the green primary color can be demonstrated by Fig. 9B.

Accordingly, the present invention provides full color electrophoretic displays capable of directly addressing electrophoretic media with and without top plane switching, and waveforms for such electrophoretic displays. Several aspects and embodiments of the technology of the present application have been described here. It should be understood that those skilled in the art will easily think of various changes, modifications and improvements. Such alterations, modifications and improvements are intended to be within the spirit and scope of the technology described in this application. For example, various other means and/or structures for performing the functions described herein and/or obtaining the results and/or one or more advantages described herein will be readily conceivable by those skilled in the art, Each of such alterations and/or modifications are therefore considered 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 their equivalents, embodiments of the 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 within the scope of the present invention unless mutually inconsistent.

101,102: Electrophoretic displays 110: top transparent electrode 120: Electrophoretic medium 121: Electrophoretic particles 122: the second electrophoretic particle 123: The third electrophoretic particle 124: The fourth electrophoretic particle 126: Microcapsules 127:Microcell 130,135: Bottom drive electrodes 140,170: Adhesive layer 150: Substrate 160: protective layer 180: sealing layer 401: Electrophoretic display 410: top electrode 420: Electrophoretic medium 430: drive electrode 440,460: Power 470:Controller

Figure 1 is a schematic cross-sectional view illustrating an embodiment of a capsule-type electrophoretic display suitable for use with the method of the present invention. Figure 2 is a schematic cross-sectional view illustrating an embodiment of a capsule-type electrophoretic display suitable for use with the method of the present invention. FIG. 3 shows an exemplary equivalent circuit of a single pixel of an electrophoretic display, where the voltage on the single pixel is controlled by a transistor. The circuit in Figure 3 is commonly used in active array backplanes. FIG. 4 illustrates how a positive voltage source and a rich voltage source are applied to the top electrode and two separate drive electrodes to achieve the desired drive voltage on the two separate drive electrodes. Fig. 5 is a schematic cross-sectional view showing the positions of various colored particles in a colored electrophoretic medium displaying black, white, three subtractive primary colors and three additive primary colors. Figure 6 depicts an exemplary push-pull drive scheme for addressing an electrophoretic medium comprising tri-subtractive particles and scattering (white) particles. Figure 7 depicts a simplified top-plane drive waveform for the generation of eight colors in an electrophoretic medium comprising trisubtractive particles and scattering (white) particles. 8 illustrates an exemplary drive mode for achieving a green optical state at the viewing face above the first electrode and a yellow optical state at the viewing face above the second electrode using only two voltage sources. Figure 9A shows the variation of L*a*b* values for eight color indices when the same four-particle electrophoretic medium was driven with seven independent driving voltages or with two voltage sources and using coordinated top electrode voltage cycling. FIG. 9B depicts dates as simulated colors in the graph of FIG. 9A.

101: Electrophoretic display

110: top transparent electrode

120: Electrophoretic medium

121: Electrophoretic particles

122: the second electrophoretic particle

126: Microcapsules

130,135: Bottom drive electrodes

140: Adhesive layer

150: Substrate

160: protective layer

170: Adhesive layer

Claims (20)

A system for driving an electrophoretic medium comprising: Electrophoretic displays, including light-transmitting top electrode at the viewing face, the first drive electrode, the second driving electrode, an electrophoretic medium disposed between the top electrode and the first and second drive electrodes; a power source capable of providing positive and negative voltages, wherein the positive and negative voltages are of different magnitudes; and a controller coupled to the top electrode driver, the first drive electrode driver and the second drive electrode driver, the controller being configured to: In a first frame, providing the positive voltage to the top electrode, providing the negative voltage to the first drive electrode, and providing the positive voltage to the second drive electrode, 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 the 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, and In a fourth frame, the positive voltage is provided to the top electrode, the positive voltage is provided to the first drive electrode, and the positive voltage is provided to the second drive electrode. The system of claim 1, wherein the controller is configured to further: 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, and In a sixth frame, the ground voltage is provided to the top electrode, the ground voltage is provided to the first driving electrode, and the ground voltage is provided to the second driving electrode. The system of claim 1, wherein the electrophoretic medium is encapsulated in a plurality of microcapsules, and the microcapsules are dispersed in the polymer binder between the top electrode and the first and second driving electrodes. The system of claim 1, wherein the electrophoretic medium is encapsulated in an array of microcells having openings, wherein the openings are sealed with a polymer binder, and the array of microcells is disposed between the top electrode and the second electrode. between the first and second drive electrodes. The system according to claim 1, wherein the electrophoretic medium includes non-polar fluid and four groups of particles with different optical properties. The system of claim 5, wherein the first and second groups of particles have opposite charges, the third and fourth groups of particles have opposite charges, the first particles are light scattering particles, and the second The second, third and fourth groups of particles are subtractive primary colors that are different from each other. The system of claim 6, wherein the controller is configured to provide a combination of the positive voltage, the negative voltage, and the ground voltage to the top electrode and the first drive electrode so that a white color can be displayed at the viewing surface , yellow, red, magenta, blue, cyan, green, and black. The system of claim 5, wherein the first and second groups of particles have opposite charges, the third and fourth groups of particles have the same charge as the second particles, and the first particles are light-scattering particles , and the second, third, and fourth sets of particles are each different subtractive primary colors from each other. The system of claim 8, wherein the controller is configured to provide a combination of the positive voltage, the negative voltage, and the ground voltage to the top electrode and the first drive electrode so that a white color can be displayed at the viewing surface , yellow, red, magenta, blue, cyan, green, and black. The system of claim 1, wherein the positive voltage is +15V, and the negative voltage is -9V. The system of claim 1, wherein the positive voltage is +9V, and the negative voltage is -15V. A system for driving an electrophoretic medium comprising: Electrophoretic displays, including light-transmitting top electrode at the viewing face, the first drive electrode, the second driving electrode, an electrophoretic medium disposed between the top electrode and the first and second drive electrodes; a power source capable of providing positive and negative voltages, wherein the positive and negative voltages are of different magnitudes; and a controller coupled to the top electrode driver, the first drive electrode driver and the second drive electrode driver, the controller being configured to: In a first frame, providing the positive voltage to the top electrode, providing the negative voltage to the first drive electrode, and providing the positive voltage to the second drive electrode, 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 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, and In a fourth frame, the positive voltage is provided to the top electrode, the positive voltage is provided to the first drive electrode, and the positive voltage is provided to the second drive electrode. The system of claim 12, wherein the controller is configured to further: 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, and In a sixth frame, the ground voltage is provided to the top electrode, the ground voltage is provided to the first driving electrode, and the ground voltage is provided to the second driving electrode. The system of claim 12, wherein the electrophoretic medium is encapsulated in a plurality of microcapsules, and the microcapsules are dispersed in a polymer binder between the top electrode and the first and second driving electrodes. The system of claim 12, wherein the electrophoretic medium is encapsulated in a microcell array with openings, wherein the openings are sealed with a polymer binder, and the microcell array is configured between the top electrode and the first and the second drive electrode. The system of claim 12, wherein the electrophoretic medium includes a non-polar fluid and four groups of particles with different optical properties. The system according to claim 16, wherein the first and second groups of particles have opposite charges, the third and fourth groups of particles have opposite charges, the first particles are light scattering particles, and the first The second, third and fourth groups of particles are subtractive primary colors that are different from each other. The system of claim 17, wherein the controller is configured to provide a combination of the positive voltage, the negative voltage and the ground voltage to the top electrode and the first drive electrode so that a white color can be displayed at the viewing surface , yellow, red, magenta, blue, cyan, green, and black. The system according to claim 16, wherein the first and second groups of particles have opposite charges, the third and fourth groups of particles have the same charge as the second particles, and the first particles are light scattering particles , and the second, third, and fourth sets of particles are each different subtractive primary colors from each other. The system of claim 19, wherein the controller is configured to provide a combination of the positive voltage, the negative voltage and the ground voltage to the top electrode and the first drive electrode so that a white color can be displayed at the viewing surface , yellow, red, magenta, blue, cyan, green, and black.

Images