Electro-optical display and driving method

Abstract

A driving method for driving a display comprising an electrophoretic material having at least one type of colored pigment particles, the method comprising applying at least one pulse pair to reset the at least one type of colored pigment particles, applying a separation pulse, and applying a second pulse pair to reset the at least one type of colored pigment particles.

Description

[0001] Citation of Related Applications

[0002] This application claims the benefit of U.S. Provisional Application No. 62 / 699,117, filed Jul. 17, 2018.

[0003] The entire disclosure of the foregoing application is incorporated herein by reference. TECHNICAL FIELD

[0004] The subject matter presented herein relates to a method of driving an electro-optical display device. BACKGROUND OF THE INVENTION

[0005] To achieve color display, color filters are often used. The most common method is to add color filters on top of the black / white sub-pixels of a pixelated display to display red, green, and blue. When red is desired, the green and blue sub-pixels are turned to a black state so that the only color displayed is red. When blue is desired, the green and red sub-pixels are turned to a black state so that the only color displayed is blue. When green is desired, the red and blue sub-pixels are turned to a black state so that the only color displayed is green. When a black state is desired, all three sub-pixels are turned to a black state. When a white state is desired, the three sub-pixels are turned to red, green, and blue respectively, and as a result, the observer sees a white state.

[0006] The biggest drawback of this technique is that since the reflectivity of each sub-pixel is about one-third (1 / 3) of the desired white state, the white state is rather dark. To compensate for this, a fourth sub-pixel that can only display black and white states can be added so that the white level is doubled at the expense of the red, green, or blue levels (where each sub-pixel now only occupies one-fourth of the pixel area). A brighter color can be achieved by increasing the light from the white pixels, but this is achieved at the expense of the color gamut, resulting in a very bright and unsaturated color. A similar result can be achieved by reducing the color saturation of the three sub-pixels. Even with these methods, the white level is typically much less than half of the white level of a black and white display, making it an unacceptable choice for display devices such as e-readers or displays that require good readable black and white brightness and contrast. SUMMARY OF THE INVENTION

[0007] The subject matter disclosed herein relates to a method of driving a display that includes an electrophoretic material having at least one type of colored pigment particle. One such method can include applying at least one pulse pair to reset the at least one type of colored pigment particle, applying a separation pulse, and applying a second pulse pair to reset the at least one type of colored pigment particle. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Aspects and embodiments of the present application will be described with reference to the following drawings. It should be understood that the drawings are not necessarily to scale. Items that appear in multiple figures are denoted by the same reference numeral in all figures in which they appear.

[0009] Figure 1 A schematic representation of an electro-optic display in accordance with the subject matter presented herein is shown;

[0010] Figure 2 Shows a representation Figure 1 of the equivalent circuit of the electro-optic display shown;

[0011] Figure 3 A cross-sectional view of an electro-optic display in accordance with the subject matter presented herein is shown;

[0012] Figure 4 An embodiment of a driving method for driving an electro-optic display in accordance with the subject matter presented herein is shown; and

[0013] Figure 5 Another embodiment of a driving method for driving an electro-optic display in accordance with the subject matter presented herein is shown. Detailed Description

[0014] The present invention relates to a method of driving an electro-optic display (particularly a bistable electro-optic display) in a dark mode and to an apparatus for such a method. More particularly, the present invention relates to a driving method that can allow for a reduction in "ghosting" and edge artifacts and a reduction in flicker in such a display when displaying white text on a black background. The present invention is particularly but not exclusively intended for use with particle-based electrophoretic displays in which one or more types of charged particles are present in a fluid and move through the fluid under the influence of an electric field to change the appearance of the display.

[0015] As used herein, the term "electro-optic" as applied to a material or a display has its conventional meaning in the imaging art and refers to a material having first and second display states, at least one of the optical properties of which is different, and which is caused to change from its first display state to its second display state by the application of an electric field to the material. Although the optical property is typically a color perceptible to the human eye, it can be another optical property, such as light transmission, reflection, luminescence, or, in the case of a display for machine reading, a change in reflectivity of electromagnetic wavelengths outside the visible light range in the sense of a pseudo-color.

[0016] The term "gray state" is used here in its conventional meaning in the field of imaging, referring to a state between the two extreme optical states of a pixel, but does not necessarily mean a black and white transition between the two extreme states. For example, several patents and published applications of Iink Corporation referred to above describe electrophoretic displays in which the extreme states are white and dark blue, so that the intermediate "gray state" is actually light blue. In fact, as already mentioned, the change in optical state may not be a color change at all. The terms "black" and "white" may be used hereinafter to refer to the two extreme optical states of the display, and should be understood to generally include extreme optical states that are not strictly black and white, such as the white and dark blue states mentioned above. The term "monochrome" may be used hereinafter to refer to a drive scheme in which pixels are driven only to their two extreme optical states, without an intermediate gray state.

[0017] Much of the discussion below will focus on methods of driving one or more pixels of an electro-optical display through a transition from an initial gray scale (or "gray tone") to a final gray scale (which may or may not be different from the initial gray scale). The terms "gray state," "gray scale," and "gray tone" are used interchangeably herein and include extreme optical states as well as intermediate gray states. Due to limitations such as the discreteness of the drive pulses applied by the frame rate of the display driver and temperature sensitivity, the number of possible gray scales in current systems is typically 2-16. For example, in a black and white display with 16 gray scales, typically, gray scale 1 is black and gray scale 16 is white; however, the designations of black and white gray scales can be reversed. Here, gray tone 1 will be used to designate black. As the gray tone advances toward gray tone 16 (i.e., white), gray tone 2 will be a lighter black.

[0018] The terms "bistable" and "bistable" are used herein in their conventional sense in the art to refer to a display including a display element having first and second display states, the first and second display states differing in at least one optical property such that after any given element is driven to assume its first or second display state with an addressing pulse of finite duration, that state will persist after termination of the addressing pulse for at least several times (e.g., at least 4 times) the minimum duration of the addressing pulse required to change the state of the display element. It is shown in U.S. Patent No. 7,170,670 that some particle-based electrophoretic displays supporting gray scales can be stable not only in their extreme black and white states, but also in intermediate gray states, as well as some other types of electro-optical displays. This type of display is properly referred to as "multistable" rather than bistable, but for convenience, the term "bistable" will be used herein to cover both bistable and multistable displays.

[0019] The term "pulse" is used herein in its conventional sense, i.e., the integral of voltage with respect to time. However, some bistable electro-optic media function as charge converters, and for such media, an alternative definition of a pulse can be used, i.e., the integral of current with respect to time (which is equal to the total charge applied). Depending on whether the media functions as a voltage-time pulse converter or as a charge pulse converter, the appropriate definition of a pulse should be used.

[0020] The term "waveform" will be used to denote the entire curve of voltage versus time used to effect a transition from a particular initial gray level to a particular final gray level. Typically, such a waveform will consist of a plurality of waveform elements; where these elements are substantially rectangular (i.e., a given element comprises the application of a constant voltage over a period of time); and the element may be referred to as a "pulse" or a "drive pulse". The term "driving scheme" denotes a set of waveforms sufficient to effect all possible transitions between the gray levels of a particular display. A display may utilize more than one driving scheme; for example, the aforementioned U.S. Patent No. 7,012,600 teaches that the driving scheme may need to be modified according to parameters such as the temperature of the display or the time it has been operated during its lifetime, and thus a display may be provided with a plurality of different driving schemes for use at different temperatures, etc. A set of driving schemes used in this manner may be referred to as a "set of related driving schemes". As described in several of the aforementioned MEDEOD applications, more than one driving scheme may also be used simultaneously in different regions of the same display, and a set of driving schemes used in this manner may be referred to as a "set of simultaneous driving schemes".

[0021] Several types of electro-optic displays are known. One type of electro-optic display is the rotating bichromal member type, as described, for example, in U.S. Patent Nos. 5,808,783, 5,777,782, 5,760,761, 6,054,071, 6,055,091, 6,097,531, 6,128,124, 6,137,467, and 6,147,791 (although displays of this type are commonly referred to as "rotating bichromal ball" displays, the term "rotating bichromal member" is preferred as being more precise since in some of the patents mentioned above, the rotating member is not spherical). Such displays use a number of small bodies (usually spherical or cylindrical) and internal dipoles, the bodies comprising two or more portions having different optical properties. These bodies are suspended within liquid-filled vesicles within a matrix, the vesicles being filled with liquid such that the bodies are free to rotate. The appearance of the display is changed by applying an electric field to the display, thereby rotating the bodies to various positions and changing which portion of the bodies is seen through the viewing surface. Electro-optic media of this type are typically bistable.

[0022] Another type of electro-optic display uses an electrochromic medium, such as an electrochromic medium in the form of a nanochromic film, which includes an electrode formed at least in part of a semiconducting metal oxide and a plurality of dye molecules attached to the electrode that are capable of reversibly changing color; see, e.g., O'Regan, B. et al., Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24 (March 2002). See also Bach, U. et al., Adv. Mater., 2002, 14(11), 845. This type of nanochromic film is also described, for example, in U.S. Patent Nos. 6,301,038; 6,870,657; and 6,950,220. This type of medium is also typically bistable.

[0023] Another type of electro-optic display is the electrowetting display developed by Philips, which is described in Hayes, R.A. et al., "Video-Speed Electronic Paper Based on Electrowetting", Nature, 425, 383-385 (2003). Such an electrowetting display is shown in U.S. Patent No. 7,420,549 to be manufacturable as bistable.

[0024] One type of electro-optic display that has been the subject of intensive research and development for many years is the particle-based electrophoretic display, in which a plurality of charged particles move through a fluid under the influence of an electric field. Compared to liquid crystal displays, electrophoretic displays can have the attributes of good 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 tend to settle, resulting in insufficient service life for these displays.

[0025] As described above, an electrophoretic medium requires the presence of a fluid. In most prior art electrophoretic media, the fluid is a liquid, but an electrophoretic medium can be produced using a gaseous fluid; see, for example, Kitamura, T. et al., "Electronic toner movement for electronic paper-like display", IDW Japan, 2001, Paper HCS 1-1, 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. When such gas-based electrophoretic media are used in a direction that permits particle sedimentation, such as in a sign where the medium is arranged in a vertical plane, due to the same particle sedimentation as in liquid-based electrophoretic media, such gas-based electrophoretic media are prone to the same types of problems. In fact, the particle sedimentation problem in gas-based electrophoretic media is more severe than in liquid-based electrophoretic media because the lower viscosity of the gaseous suspension fluid compared to liquid allows electrophoretic particles to sediment faster.

[0026] Numerous patents and applications assigned to or in the name of the Massachusetts Institute of Technology (MIT) and E Ink Corporation describe various techniques for encapsulating electrophoretic and other electro-optic media. Such encapsulated media include a number of small capsules, each capsule itself including an inner phase and a capsule wall surrounding the inner phase, wherein the inner phase contains electrophoretically mobile particles in a fluid medium. Typically, the capsules themselves are held in a polymeric binder to form a coherent layer located between two electrodes. The techniques described in these patents and applications include:

[0027] (a) electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814;

[0028] (b) capsules, binders, and encapsulation processes; see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719;

[0029] (c) films and sub-assemblies containing electro-optic materials; see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564;

[0030] (d) backplanes, adhesive layers, and other auxiliary layers and methods for use in displays; see, for example, U.S. Patent Nos. 7,116,318 and 7,535,624;

[0031] (e) Color formation and color adjustment; see, for example, U.S. Patent No. 7,075,502 and U.S. Patent Application Publication No. 2007 / 0109219;

[0032] (f) Method for driving a display; see, for example, 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; 7,202,847; 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; 7,982,479; 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; 8,537,105; 8,558,783; 8,558,785; 8,558,786; 8,558,855; 8,576,164; 8,576,259; 8,593,396; 8,605,032; 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; 9,390,066; 9,390,661; and 9,412,314; and U.S. Patent Application Publication No.2003 / 0102858; 2004 / 0246562; 2005 / 0253777; 2007 / 0070032; 2007 / 0076289; 2007 / 0091418; 2007 / 0103427; 2007 / 0176912; 2007 / 0296452; 2008 / 0024429; 2008 / 0024482; 2008 / 0136774; 2008 / 0169821; 2008 / 0218471; 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 / 0321278; 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; 2016 / 0071465; 2016 / 0078820; 2016 / 0093253; 2016 / 0140910; and 2016 / 0180777;.

[0033] (g) Applications of displays; see, for example, U.S. Patent No. 7,312,784; and U.S. Patent Application Publication No. 2006 / 0279527; and

[0034] (h) Non-electrophoretic displays, as described in U.S. Patent No. 6,241,921; 6,950,220; and 7,420,549 and U.S. Patent Application Publication No. 2009 / 0046082.

[0035] Many of the foregoing patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, resulting in so-called polymer dispersed electrophoretic displays, where the electrophoretic medium includes a plurality of discrete microdroplets of electrophoretic fluid and a continuous phase of polymeric material, and the discrete microdroplets of electrophoretic fluid within such polymer dispersed electrophoretic displays can be considered capsules or microcapsules even though no discrete capsule membrane is associated with each individual microdroplet; see, for example, the foregoing U.S. Patent No. 6,866,760. Thus, for the purposes of the present application, such polymer dispersed electrophoretic media are considered a subclass of encapsulated electrophoretic media.

[0036] A related type of electrophoretic display is the so-called "microcell electrophoretic display". In a microcell electrophoretic display, charged particles and fluid are not encapsulated within microcapsules, but rather are held within a plurality of cavities formed within a carrier medium (typically a polymeric film). See, for example, U.S. Patent Nos. 6,672,921 and 6,788,449, both assigned to Sipix Imaging, Inc.

[0037] Although electrophoretic media are typically opaque (because, for example, in many electrophoretic media, the particles substantially block visible light from passing 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 display state is light transmissive. See, for example, U.S. Patent Nos. 5,872,552, 6,130,774, 6,144,361, 6,172,798, 6,271,823, 6,225,971 and 6,184,856. Dielectrophoretic displays, which are similar to electrophoretic displays but rely on changes in electric field strength, can operate in a similar mode; see U.S. Patent No. 4,418,346. Other types of electro-optic displays are also capable of operating in the shutter mode. Electro-optic media that operate in the shutter mode can be used in a multi-layer structure for a full-color display; in such a structure, at least one layer adjacent to the viewing surface of the display operates in the shutter mode to expose or hide a second layer that is further from the viewing surface.

[0038] Encapsulated electrophoretic displays are generally not plagued by the aggregation and sedimentation failure modes of conventional electrophoretic devices and offer additional benefits such as the ability to print or coat the display on a variety of flexible and rigid substrates. (The use of the word "print" is intended to include all forms of printing and coating, including but not limited to: pre-metered coating such as patch die coating, slot or extrusion coating, slide or curtain coating, meniscus coating; roll coating such as rod blade coating, forward and reverse roll coating; gravure coating; dip coating; spraying; meniscus coating; spin coating; brush coating; air knife coating; screen printing processes; electrophotographic processes; thermal printing processes; inkjet printing processes; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques.) As a result, the resulting display can be flexible. Additionally, because the display medium can be (using a variety of methods) printed, the display itself can be manufactured inexpensively.

[0039] Other types of electro-optic media can also be used in the displays of the present invention.

[0040] The bistable or multistable behavior of particle-based electrophoretic displays and other electro-optic displays that exhibit similar behavior (hereinafter, for convenience, such displays may be referred to as "impulse-driven displays") stand in sharp contrast to conventional liquid crystal ("LC") displays. Twisted nematic liquid crystals are not bistable or multistable, but rather act as voltage converters, and thus, applying a given electric field to a pixel of such a display produces a specific gray scale at the pixel, independent of the gray scale that previously appeared at the pixel. Additionally, LC displays are driven in only one direction (from non-transmissive or "dark" to transmissive or "bright"), and the reverse transition from a brighter state to a darker state is achieved by reducing or eliminating the electric field. Finally, the gray scale of the pixels of an LC display is insensitive to the polarity of the electric field and is only sensitive to the magnitude of the electric field, and in fact, for technical reasons, commercial LC displays typically reverse the polarity of the drive field at frequent intervals. In contrast, bistable electro-optic displays act approximately as impulse converters, such that the final state of a pixel depends not only on the applied electric field and the duration for which the electric field is applied, but also on the state of the pixel prior to the application of the electric field.

[0041] Regardless of whether the electro-optic medium used is bistable or not, in order to obtain a high-resolution display, each pixel of the display must be addressable and not be interfered with by adjacent pixels. One way to achieve this is to provide an array of nonlinear elements (such as transistors or diodes), and at least one nonlinear element is associated with each pixel to produce an "active matrix" display. The addressing or pixel electrode used to address a pixel is connected to an appropriate voltage source through the associated nonlinear element. Generally, when the nonlinear element is a transistor, the pixel electrode is connected to the drain of the transistor, and this arrangement will be assumed in the following description, although it is essentially arbitrary and the pixel electrode can be connected to the source of the transistor. Conventionally, in a high-resolution array, pixels can be arranged in a two-dimensional array having rows and columns such that any particular pixel is uniquely defined by the intersection of a particular row and a particular column. The sources of all the transistors in each column are connected to a single column electrode, and the gates of all the transistors in each row are connected to a single row electrode; similarly, the source-to-row and gate-to-column assignments are conventional but essentially arbitrary and can be reversed if desired. The row electrodes are connected to a row driver, which substantially ensures that only one row is selected at any given moment, i.e., a voltage is applied to the selected row electrode, for example to ensure that all the transistors in the selected row are conducting, while voltages are applied to all the other rows, for example to ensure that all the transistors in these unselected rows remain non-conducting. The column electrodes are connected to a column driver, which applies voltages to different column electrodes, the voltages being selected to drive the pixels in the selected row to their desired optical states. (The voltages mentioned above are with respect to a common front electrode, which is conventionally provided on the opposite side of the electro-optic medium from the nonlinear array and extends across the entire display.) After a preselected interval called the "row address time", the selected row is deselected, the next row is selected, and the voltages on the column driver are changed so that the next row of the display is written. This process is repeated, thereby writing the entire display in a row-by-row manner.

[0042] It should be understood that even though the various embodiments presented below use electrophoretic materials with microcells to illustrate the working principles of the subject matter presented herein, the same principles can be readily applied to electrophoretic materials with microencapsulated particles (such as pigment particles). The electrophoretic materials with microcells are used herein for illustration and not for limitation.

[0043] Figure 1A schematic model of a display pixel 100 of an electro-optical display in accordance with the subject matter presented herein is shown. Pixel 100 may include an imaging film 110. In some embodiments, imaging film 110 may be an electrophoretic material layer and is bistable in nature. The electrophoretic material may include a plurality of charged pigment particles (e.g., black, white, or red) disposed in a fluid and capable of moving through the fluid under the influence of an electric field. In some embodiments, imaging film 110 may be an electrophoretic film having micro-cells with charged pigment particles. In some other embodiments, imaging film 110 may include, but is not limited to, an encapsulated electrophoretic imaging film, which may include, for example, charged pigment particles. It should be understood that the driving methods presented below may be readily used with any type of electrophoretic material (e.g., encapsulated or film with micro-cells).

[0044] In some embodiments, imaging film 110 may be disposed between a front electrode 102 and a rear electrode or pixel electrode 104. Front electrode 102 may be formed between the imaging film and the front of the display. In some embodiments, front electrode 102 may be transparent and light transmissive. In some embodiments, front electrode 102 may be formed of any suitable transparent material, including but not limited to indium tin oxide (ITO). Rear electrode 104 may be formed on the side of imaging film 110 opposite to front electrode 102. In some embodiments, a parasitic capacitance (not shown) may be formed between front electrode 102 and rear electrode 104.

[0045] Pixel 100 may be one of a plurality of pixels. The plurality of pixels may be arranged in a two-dimensional array of rows and columns to form a matrix such that any particular pixel is uniquely defined by the intersection of a particular row and a particular column. In some embodiments, the matrix of pixels may be an "active matrix" in which each pixel is associated with at least one non-linear circuit element 120. The non-linear circuit element 120 may be coupled between the backplane electrode 104 and the addressing electrode 108. In some embodiments, the non-linear element 120 may be a diode and / or a transistor, including but not limited to a metal oxide semiconductor field effect transistor (MOSFET) or a thin film transistor (TFT). The drain (or source) of the MOSFET or TFT may be coupled to the backplane or pixel electrode 104, the source (or drain) of the MOSFET or TFT may be coupled to the addressing electrode 108, and the gate of the MOSFET or TFT may be coupled to the driver electrode 106, which is configured to control the activation and deactivation of the MOSFET or TFT. (For simplicity, the terminal of the MOSFET or TFT coupled to the backplane electrode 104 will be referred to as the drain of the MOSFET or TFT, and the terminal of the MOSFET or TFT coupled to the addressing electrode 108 will be referred to as the source of the MOSFET or TFT. However, one of ordinary skill in the art will recognize that in some embodiments, the source and drain of the MOSFET or TFT may be interchanged.).

[0046] In some embodiments of the active matrix, the addressing electrodes 108 of all the pixels in each column may be connected to the same column electrode, and the driver electrodes 106 of all the pixels in each row may be connected to the same row electrode. The row electrodes may be connected to a row driver, which may select one or more rows of pixels by applying a voltage to the selected row electrodes, the voltage being sufficient to activate the non-linear elements 120 of all the pixels 100 in the selected row. The column electrodes may be connected to a column driver, which may apply a voltage suitable for driving the pixels to a desired optical state to the addressing electrodes 106 of the selected (activated) pixels. The voltage applied to the addressing electrode 108 may be relative to the voltage applied to the front plate electrode 102 of the pixel (e.g., a voltage of approximately zero volts). In some embodiments, the front plate electrodes 102 of all the pixels in the active matrix may be coupled to a common electrode.

[0047] In use, the pixels 100 of the active matrix may be written in a row-by-row manner. For example, the row driver may select a row of pixels, and the column driver may apply a voltage corresponding to the desired optical state of the row of pixels. After a preselected interval referred to as the "row address time", the selected row may be deselected, another row may be selected, and the voltage on the column driver may be changed such that another row of the display is written.

[0048] Figure 2 Shows a circuit model of an electro-optic imaging layer 110 according to the subject matter presented herein, the electro-optic imaging layer 100 being disposed between a front electrode 102 and a rear electrode 104. Resistors 202 and capacitors 204 may represent the resistance and capacitance of the electro-optic imaging layer 110, including any adhesive layer, the front electrode 102, and the rear electrode 104. Resistors 212 and capacitors 214 may represent the resistance and capacitance of the laminated adhesive layer. Capacitor 216 may represent the capacitance that may be formed between the front electrode 102 and the rear electrode 104, for example, an interfacial contact region between layers, such as an interface between the imaging layer and the laminated adhesive layer and / or an interface between the laminated adhesive layer and the backplane electrode. The voltage Vi across the imaging film 110 of a pixel may include the residual voltage of the pixel.

[0049] In Figure 3 is shown a cross-sectional view of an exemplary imaging film 310 (e.g., an electrophoretic film) similar to Figure 1 the imaging layer 110 shown. The imaging film 310 may include micro-units that enclose an electrophoretic fluid. It should be understood that an electrophoretic material having micro-units is used herein to illustrate the general working principle of the subject matter presented herein, where the same principle may be applied to electrophoretic films having capsules. As shown, the imaging film 310 may include three types of pigment particles dispersed in a dielectric solvent or solvent mixture. For ease of illustration, the three types of pigment particles may be referred to as white particles 311, black particles 312, and colored particles 313, where the colored particles are non-white and non-black.

[0050] However, it should be understood that the scope of the subject matter presented herein broadly encompasses pigment particles of any color, provided that the three types of pigment particles have visually distinguishable colors. Thus, the three types of pigment particles may also be referred to as a first type of pigment particle, a second type of pigment particle, and a third type of pigment particle.

[0051] It should also be understood that even though a three-particle system is used herein to illustrate the general principle of the subject matter, the same principle may be readily applied to systems having a different number of particles (e.g., 4 particles, 5 particles, 6 particles, etc.).

[0052] For the white particles, they may be composed of such as TiO 2 , ZrO 2 , ZnO, Al 2 O 3 , Sb 2 O 3 , BaSO 4 , PbSO 4formed from inorganic pigments such as etc. For black particles, they can be formed from Cl Pigment Black 26 or 28 etc. (such as iron manganese black or copper chromium black) or carbon black.

[0053] The third type of particles can be colors such as red, green, blue, magenta, cyan or yellow. Pigments for the particles of this type can include but are not limited to CI Pigment PR254, PR122, PR149, PG36, PG58, PG7, PB28, PB15:3, PY138, PY150, PY155 or PY20. Those are common organic pigments described in the Pigment Index manuals "New Pigment Application Technology" (CMC Publishing Co., Ltd. 1986) and "Printing Ink Technology" (CMC Publishing Co., Ltd. 1984). Specific examples include Hostaperm Red D3G 70-EDS, Hostaperm Pink E-EDS, PV fast red D3G, Hostaperm Red D3G 70, Hostaperm Blue B2G-EDS, Hostaperm Yellow H4G-EDS, Hostaperm Green GNX of Clariant; Irgazine Red L 3630, Cinquasia Red L 4100HD and Irgazin Red L 3660HD of BASF; phthalocyanine blue, phthalocyanine green, aniline yellow or benzidine yellow of Sun Chemical.

[0054] In addition to color, the first, second and third types of particles can have other different optical properties, such as light transmission, reflection, luminescence, or in the case of a display for machine reading, pseudo-color in the sense of a change in the reflectance of electromagnetic wavelengths outside the visible light range.

[0055] The solvent in which three types of pigment particles are dispersed can be transparent and colorless. For high particle mobility, the solvent preferably has a low viscosity and a dielectric constant in the range of about 2 to about 30, preferably in the range of about 2 to about 15. Examples of suitable dielectric solvents include hydrocarbons such as isopar solvents, decalin, 5-ethylidene-2-norbornene, fatty oils, paraffin oils, silicone oils; aromatic hydrocarbons such as toluene, xylene, phenylxylene ethane, dodecylbenzene or alkylnaphthalenes; halogenated solvents such as perfluorodecalin, perfluorotoluene, perfluoroxylene, dichlorotrifluorobenzene, 3,4,5-trichlorotrifluorotoluene, chloropentafluorobenzene, dichlorononane or pentachlorobenzene; and perfluorinated solvents such as FC-43, FC-70 or FC-5060 from 3M Company, St. Paul, MN; low molecular weight halogen-containing polymers such as poly(perfluoroepoxypropane) from TCI America, Portland, Oregon; poly(trifluorochloroethylene) such as Halocarbon Oils from Halocarbon Product Corp., River Edge, NJ; perfluoropolyalkyl ethers such as Galden from Ausimont or Krytox Oils and Greases K-Fluid series from DuPont, Delaware, and polydimethylsiloxane-based silicone oils (DC-200) from Dow-Corning.

[0056] The display layer using the display fluid of the present invention has two surfaces, a first surface 316 on the viewing side and a second surface 317 on the opposite side of the first surface 316. Thus, the second surface is on the non-viewing side. The term "viewing side" refers to the side on which the image is viewed.

[0057] The display fluid is sandwiched between the two surfaces. On the side of the first surface 316, there is a common electrode 314, which is a transparent electrode layer (e.g., ITO), distributed over the entire top of the display layer. On the side of the second surface 317, there is an electrode layer 315, which includes a plurality of pixel electrodes 315a.

[0058] The display fluid is filled in the display unit. The display unit may or may not be aligned with the pixel electrodes. The term "display unit" refers to a microcontainer filled with an electrophoretic fluid. Examples of "display unit" may include cup-shaped micro-units as described in U.S. Patent No. 6,930,818 and microcapsules as described in U.S. Patent No. 5,930,026. The microcontainer can have any shape or size, all of which are within the scope of this application.

[0059] The region corresponding to the pixel electrode may be referred to as a pixel (or sub-pixel). Driving of the region corresponding to the pixel electrode is achieved by applying a voltage potential difference (or referred to as a driving voltage or an electric field) between the common electrode and the pixel electrode.

[0060] The pixel electrode may be an active matrix driving system having a thin film transistor (TFT) backplane, or may be other types of addressing electrodes, as long as the electrode provides the required functions.

[0061] The interval between two vertical dotted lines represents a pixel (or sub-pixel). For simplicity, when the term "pixel" is mentioned in the driving method, this term also covers "sub-pixel".

[0062] In some embodiments, two of the three types of pigment particles may carry opposite charge polarities, and the third type of pigment particles may be slightly charged. The term "slightly charged" or "lower charge intensity" is intended to refer to a charge level of particles that is approximately 50% less, preferably about 5% to 30%, than that of more strongly charged particles. In one embodiment, the charge intensity may be measured according to the ζ (zeta) potential. In one embodiment, the ζ potential is determined by a Colloidal Dynamics AcoustoSizer IIM having a CSPU-100 signal processing unit and an ESA flow cell (K: 127). Instrument constants are input before testing, such as the density of the solvent used in the sample, the dielectric constant of the solvent, the speed of sound in the solvent, the viscosity of the solvent, all at the test temperature (25 °C). The pigment sample is dispersed in a solvent (which is typically a hydrocarbon fluid having fewer than 12 carbon atoms) and diluted to 5-10% (by weight). The sample also contains a charge control agent (Solsperse which can be purchased from Lubrizol Corporation of Berkshire Hathaway company; "Solsperse" is a registered trademark), and the weight ratio of the charge control agent to the particles is 1:10. The mass of the diluted sample is determined, and then the sample is loaded into a flow through cell to determine the ζ potential.

[0063] For example, if the black particles are positively charged and the white particles are negatively charged, the colored pigment particles may be slightly charged. In other words, in this example, the charge levels carried by the black and white particles are higher than the charge level carried by the colored particles.

[0064] In addition, the charge polarity of the colored particles carrying a slight charge is the same as that carried by one of the other two types of more strongly charged particles.

[0065] Note that among the three types of pigment particles, preferably, the slightly charged type of particles can have a larger size.

[0066] Also, in the context of the subject matter presented herein, a high driving voltage can be defined as a driving voltage sufficient to drive a pixel from one extreme color state to another extreme color state. If the first and second types of pigment particles are highly charged particles, the high driving voltage refers to a driving voltage sufficient to drive a pixel from the color state of the first type of pigment particles to the color state of the second type of pigment particles, and vice versa.

[0067] In practice, the white pigment particles 311 can be negatively charged, while the black pigment particles 312 are positively charged, and both types of pigment particles can be smaller than the colored particles 313. The colored particles 313 can carry the same charge polarity as the black particles, but are slightly charged. As a result, at certain driving voltages, the black particles move faster than the colored particles 313.

[0068] In practice, multiple problems can occur that affect the quality of each of the three color states. One problem is the tinting of the black and white states. For example, if the colored particles are red, the white state may suffer from red tinting (i.e., a high a* value) because the red particles are not well separated from the white particles. Although the white and red particles can carry opposite charge polarities, a small amount of red particles displayed on the viewing side in the white state can cause red tinting, which can be unpleasant for the observer. The black state also suffers from red tinting. Although the black and red particles carry the same charge polarity, they have different levels of charge intensity. It is expected that the more highly charged black particles move faster than the less highly charged red particles to display a good black state without red tinting; however, in practice, red tinting is difficult to avoid.

[0069] A second problem that can occur is the ghosting phenomenon, which can be caused by pixels driven from different color states to the same color state, and the resulting color state typically shows a difference in L* (i.e., ΔL*) and / or a difference in a* (i.e., Δa*) because the previous states had different colors.

[0070] In one example, two groups of pixels can be driven to the black state simultaneously. The first group of pixels driven from the white state to the black state can display an L* of 15, and the other group of pixels driven from the black state to the end black state can display an L* of 10. In this case, the ΔL* of the end black state is 5.

[0071] In another example of a three-color system, three groups of pixels are simultaneously driven to a black state. The first group of pixels driven from a red state to a black state can display an L* of 17 and an a* value of 7 (where the high a* value also indicates color tinting). The second group of pixels driven from a black state to an end black state can display an L* of 10 and an a* value of 1. The third group of pixels driven from a white state to an end black state can display an L* of 15 and an a* of 3. In this case, the worst ghosting results from a ΔL* of 7 and a Δa* of 6.

[0072] Another problem that may occur is color degradation over time. For example, after approximately 50 image updates, a display using a front-plane laminate with a high-resistance sealant material may experience gradual color degradation. This degradation is generally not permanent but is still easily reproducible.

[0073] The subject matter presented herein includes driving methods that can provide improvements to all of the above problems. In other words, the driving methods presented herein can not only reduce / eliminate color tinting (i.e., reduce the a* value of the black and / or white states), but also reduce / eliminate the ghosting effect (i.e., reduce ΔL* and Δa*), while improving color purity and reducing color degradation that may occur over time.

[0074] In practice, one way to reduce or eliminate the above unwanted optical defects (e.g., color tinting, ghosting, and color degradation) is to "reset" or "preprocess" the particles before driving the pixels to the desired color state. Figure 4 and Figure 5 illustrates a driving method that can be used to perform "resetting" or "preprocessing" according to the subject matter disclosed herein.

[0075] As used herein, the symbol "msec" represents milliseconds.

[0076] In some embodiments, the resetting or preprocessing of the particles can include a vibration waveform, where such a vibration waveform can include repeating many cycles of drive pulse pairs having opposite polarities. For example, as Figure 4 shown, the vibration waveform 400 can consist of a pulse pair having a +15V pulse for 20 milliseconds and a -15V pulse for 20 milliseconds, and such a pulse pair can be repeated more than 80 times, where the total duration of the vibration waveform will exceed 3200 milliseconds.

[0077] In some embodiments, the time for which each drive pulse in the vibration waveform can be applied does not exceed half of the drive time required to drive the display pixel from the fully black state to the white state (or vice versa). For example, if it takes 300 milliseconds to drive a pixel from the fully black state to the fully white state (or vice versa), the vibration waveform can consist of positive and negative pulses, with the application time of each pulse not exceeding 150 milliseconds. In practice, it is generally preferred that the duration of these pulses is short.

[0078] In some other embodiments, it may be preferred that the vibration waveform includes one or more isolated pulses. This means that instead of repeatedly and continuously applying the +15V / -15V pulse pair as shown Figure 4 isolated pulses can be introduced to reset or separate the pulse pairs. The term "isolated pulse" as used herein refers to a pulse with a constant voltage amplitude and polarity that is different from the above-mentioned pulse pair. In other words, a constant voltage pulse can be set between the repeated +15V / -15V pulse pairs, and depending on the intended display application, the duration of the reset or isolated pulse can be longer or shorter than that of the +15V / -15V pulse pair. For example, the +15V / -15V pulse pair can consist of a 20-millisecond +15V pulse and a 20-millisecond -15V pulse, with a total duration of 40 milliseconds. Among them, the duration of the isolated pulse can be 2 times or 3 times or more times that of the pulse pair. Preferably, the duration of the isolated pulse is not long enough to drive the display pixel to an extreme optical state (e.g., fully black or fully white). In Figure 5 In one embodiment shown, a vibration waveform with multiple +15V / -15V pulse pairs can be divided into 8 groups, and these groups are separated by isolated pulses. In this embodiment, the vibration pulse pair consists of a +15V pulse and a -15V pulse.

[0079] In some other embodiments, the groups of pulse pairs in the vibration waveform as described above do not have to be evenly spaced. This means that each group of pulse pairs within the vibration waveform can include a different number of pulse pairs (e.g., the above-mentioned +15V / -15V pulse pairs). For example, one group can have 20 pulse pairs, while another group can have 30 such pulse pairs.

[0080] In still some other embodiments, for the purpose of optimizing display performance, the isolated pulses can have different durations. For example, one isolated pulse can have a first duration, while another isolated pulse within the same vibration waveform can have a second duration different from the first duration. In addition, the isolated pulses can have different voltage amplitudes. For example, the first isolated pulse can have a first voltage amplitude, while the second isolated pulse within the same vibration waveform can have a second amplitude different from the first amplitude.

[0081] It should also be understood that asFigure 5 As shown, the separation pulses can carry different polarities. Figure 5 A separation pulse 510 with a negative polarity (e.g., -15 volts) is shown. It should be noted that the separation pulses can well carry a positive polarity (e.g., +15 volts). And it should also be noted that the separation pulses within the vibration waveform can carry a polarity opposite to that of another separation pulse. For example, the amplitude and polarity of the first separation pulse can be +15 volts, while the amplitude and polarity of a different separation pulse within the same vibration waveform can be -15 volts. Similarly, the separation pulses can have different voltage amplitudes from another separation pulse. For example, the amplitude of one separation pulse can be +10 volts, while the amplitude of the second separation pulse can be 15 volts.

[0082] It should also be noted that the duration or length of the vibration pulses can depend on the physical properties of the electrophoretic material and / or the display itself. For example, depending on the resistance of the sealing material used on the display, the duration of the vibration pulses can increase or decrease.

[0083] It should also be noted that in Figure 4 and 5 the vibration waveform can be shortened (i.e., the number of pulses is less than the actual number in some driving methods).

[0084] After completing the "reset" or "pre-treatment" with vibration, the three types of particles should be in a mixed state in the display fluid. Subsequently, the pixel can be driven to the desired color state (e.g., black, red, or white). For example, a positive pulse can be applied to drive the pixel to black; a negative pulse can be applied to drive the pixel to white; or a negative pulse can be applied followed by a positive pulse with a lower amplitude to drive the pixel to red.

[0085] When comparing the driving methods with or without the "reset" or "pre-treatment" of the present invention, the method with the "reset" or "pre-treatment" of the present invention has an additional advantage that the waveform time is shorter when achieving the same level of optical performance (including ghosting).

[0086] In practice, before driving the pixel to the desired color state (e.g., red), a period of 0-volt driving can follow the vibration waveform as shown in Figure 4 and 5

[0087] It should be noted that Figure 4 and 5 ​The pulse pairs shown are DC balanced, meaning that the amplitudes of the positive pulses (e.g., +15 V pulses) and the negative pulses (e.g., -15 V pulses) are equal, resulting in a DC balanced overall vibration waveform. As such, no excessive charge is introduced into the display medium (e.g., electrophoretic medium) or the display itself due to the applied vibration waveform, which can prevent display performance degradation. However, in some applications, DC unbalanced pulse pairs can be used to achieve various purposes (e.g., better particle separation). For example, the pulse pair can consist of a +15 V positive pulse and a -10 V negative pulse. And similar to Figure 4 and 5 the subject matter shown, the vibration waveform composed of such pulse pairs can also include separation pulses. In the case where the pulse pairs and the vibration waveform are DC unbalanced, a charge discharge process (e.g., residual voltage discharge process) can be applied at the end of the update. Exemplary methods for discharging residual voltage and charge are discussed in more detail in U.S. Patent Application No. 15 / 266,554, the entire content of which is incorporated herein.

[0088] It will be apparent to those skilled in the art that many changes and modifications can be made to the specific embodiments of the present invention described above without departing from the scope of the present invention. Accordingly, the entirety of the foregoing specification is to be construed in an illustrative rather than a limiting sense.

Claims

1. A driving method for driving a display comprising an electrophoretic material having at least one type of colored pigment particles, wherein: The display has a front plane laminate including a sealing material, The driving method comprises: applying a first vibration waveform comprising at least one first pulse pair to reset the at least one type of colored pigment particles, wherein a duration of the first vibration waveform is based on the resistance of the sealing material; applying a first separation pulse after the at least one first pulse pair, wherein the duration of the first separation pulse is not long enough to drive the at least one type of colored pigment particles to an extreme optical state; applying a second vibration waveform comprising at least one second pulse pair to reset the at least one type of colored pigment particles, wherein the duration of the second vibration waveform is based on the resistance of the sealing material, wherein the first separation pulse separates the at least one first pulse pair from the at least one second pulse pair; and A second separation pulse is applied after the at least one second pulse pair, wherein the duration of the second separation pulse is not long enough to drive the at least one type of colored pigment particles to an extreme optical state.

2. The driving method according to claim 1, wherein: The at least one first pulse pair includes a pulse having a positive amplitude and a pulse having a negative amplitude.

3. The driving method according to claim 2, wherein: The pulse with the positive amplitude and the pulse with the negative amplitude have the same duration.

4. The driving method according to claim 1, wherein: The first separation pulse has a longer duration than the at least one first pulse pair.

5. The driving method according to claim 1, wherein: The at least one first pulse pair has a different duration than the at least one second pulse pair.

6. The driving method according to claim 1, wherein: The at least one first pulse pair is DC balanced.

7. The driving method according to claim 1, wherein: The driving method is DC balanced.

8. The driving method according to claim 2, wherein: The first separation pulse has the same amplitude as the pulse having the negative amplitude.

9. The driving method according to claim 2, wherein: The first separation pulse has the same amplitude as the pulse having the positive amplitude.

10. The driving method according to claim 2, wherein: The first separation pulse has an amplitude different from the pulse having a negative amplitude.

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