Improved wave switching for electro-optic displays

Abstract

Methods for driving "spaced-contact" and "isolated-electrode" electro-optic displays, such as electrophoretic displays comprising charged pigment particles disposed in a solvent, the charged pigment particles moving in response to an applied electric field. The improved method provides a "wave-switching" waveform with less visual "dead time" compared to prior art wave-switching methods. The improved method provides a DC-balanced waveform that allows a horizontal display to wave-switch from a first color to a second color along a first direction, and then back to the first color in the opposite direction. Such switching is not feasible in prior art devices due to concerns about the accumulation of runaway residual voltages that could damage the display.

Description

Cross-references to related applications

[0001] This application claims priority to U.S. Provisional Application No. 63 / 559,515, filed February 29, 2024. All patents and publications mentioned herein are incorporated herein by reference in their entirety. Technical Field

[0002] This invention relates to methods for driving electro-optic displays, particularly bistable electro-optic displays. The 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 alter the appearance of the display. The methods described herein allow the electrophoretic display to exhibit changes in optical state from one side of the display to the other, as if a “wave” of color change were passing through the display. Such methods are particularly valuable in digital signage (e.g., segmented digital signage), where wave updates draw the observer's attention to the signage. Background Technology

[0003] When applied to materials or displays, the term "electro-optic" is used herein in its conventional meaning in the field of imaging, referring to a material having a first display state and a second display state that differ in at least one optical property, the material transitioning from its first display state to its second display state by the application of an electric field. While the optical property is typically color perceptible to the human eye, it can also refer to other optical properties such as optical transmittance, reflectance, luminescence, or, in the case of machine-readable displays, pseudo-color in the sense of variations in electromagnetic reflectance within the non-visible wavelength range.

[0004] The term "gray state" is used herein in its conventional meaning in the field of imaging, referring to the state between the two extreme optical states of a pixel, and does not necessarily imply a black-and-white transition between these two extreme states. For example, in the electrophoretic displays described in several IENK patents and publications mentioned below, where the extreme states are white and dark blue, the intermediate gray state is actually light blue. In fact, as already mentioned, a change in optical state may not be a color change at all. The terms black and white may be used below to refer to the two extreme optical states of a display, and should be understood to generally include extreme optical states that are not strictly black and white, such as the aforementioned white and dark blue states. The term "monochrome" may be used below to refer to a driving scheme that drives pixels only to their two extreme optical states, without an intermediate gray state. The methods described herein are not limited to monochrome displays and can be used for displays capable of displaying multiple different colors, such as three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen, or more colors.

[0005] The terms “bistable” and “bistable” are used herein in their conventional sense within the art, referring to a display comprising display elements having a first display state and a second display state that are different in at least one optical property, such that after either given element is driven to present its first or second display state using an addressing pulse of finite duration, the state persists for at least several times (e.g., at least four times) the minimum duration of the addressing pulse required to change the state of the display element. As shown in U.S. Patent No. 7,170,670, some particle-based electrophoretic displays supporting grayscale are stable not only in their extreme black and white states but also in their intermediate gray states, as are some other types of electro-optical displays. Such displays are aptly referred to as “multistable” rather than “bistable,” but for convenience, the term “bistable” may be used herein to encompass both bistable and multistable displays.

[0006] The term "impulse" is used herein in its conventional sense as the integral of voltage over time. However, some bistable electro-optic dielectrics are used as charge transducers, and for such dielectrics, an alternative definition of impulse can be used, namely the integral of current over time (which equals the total applied charge). The appropriate definition of impulse should be used depending on whether the dielectric is used as a voltage-time impulse transducer or a charge impulse transducer.

[0007] The majority of the discussion below will focus on methods for driving an electro-optic display from an initial gray level to a final gray level (which may be different from or the same as the initial gray level). The term "waveform" will be used to refer to the entire voltage-to-time curve that influences the transition from a particular initial gray level to a particular final gray level. Such a waveform may include multiple waveform elements; where these elements are substantially rectangular (i.e., where a given element involves the application of a constant voltage over a period of time); these elements may be referred to as "pulses" or "drive pulses." The term "drive scheme" refers to a set of waveforms sufficient to influence all possible transitions between gray levels of a particular display. A display may utilize more than one drive scheme; for example, the aforementioned U.S. Patent No. 7,012,600 teaches that the drive scheme may need to be modified based on parameters such as the temperature of the display or the time it has been operating during its lifespan, thus providing the display with multiple different drive schemes for use under conditions such as different temperatures. A set of drive schemes used in this way may be referred to as a "set of related drive schemes." It is also possible to use more than one drive scheme simultaneously in different areas of the same display; a set of drive schemes used in this way may be referred to as a "set of simultaneous drive schemes."

[0008] One type of electro-optic display that has been extensively researched and developed is the particle-based electrophoretic display, in which multiple charged particles move through a fluid under the influence of an electric field. Compared to liquid crystal displays (LCDs), electrophoretic displays offer superior brightness and contrast, wide viewing angles, state-dependent stability, and low power consumption. However, long-term image quality issues hinder their widespread adoption. For example, the particles constituting an electrophoretic display tend to settle, leading to a shorter lifespan for these displays.

[0009] 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 also be used to generate the electrophoretic medium; see, for example, Kitamura, T., et al., "Electrical toner movement for electronic paper-like display", IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y., et al., "Toner display using insulative particles charged triboelectrically", IDW Japan, 2001, Paper AMD4-4. See also U.S. Patents 7,321,459 and 7,236,291. When the electrophoretic medium is used in an orientation that allows such sedimentation (e.g., in a sign where the medium is positioned in a vertical plane), such gas-based electrophoretic media appear to be prone to the same type of problems caused by particle sedimentation as liquid-based electrophoretic media. In fact, particle sedimentation appears to be a more serious problem in gas-based electrophoresis media than in liquid-based electrophoresis media because gaseous suspensions have lower viscosity than liquid suspensions, which causes electrophoretic particles to settle faster.

[0010] Numerous patents and applications transferred to or in the name of MIT and Einkel describe various techniques for encapsulating electrophoretic and other electro-optic media. Such encapsulated media comprise a plurality of small capsules, each capsule containing 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 polymer binder to form a coherent layer located between two electrodes. The techniques described in these patents and applications include:

[0011] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814;

[0012] (b) Encapsulation, adhesives, and encapsulation processes; see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719;

[0013] (c) Films and subassemblies containing electro-optic materials; see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564;

[0014] (d) Backsheets, 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;

[0015] (e) Color formation and color adjustment; see, for example, U.S. Patent Nos. 7,075,502 and 7,839,564;

[0016] (f) A method for driving a display; see the aforementioned MEDEOD application;

[0017] (g) Applications of displays; see, for example, U.S. Patent Nos. 7,312,784; and 7,312,784; and

[0018] (h) Non-electrophoretic displays, as described in U.S. Patent Nos. 6,241,921, 6,950,220, 7,420,549, 8,319,759, 8,994,705 and 10,372,008.

[0019] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby producing a so-called polymer dispersion electrophoretic display, wherein the electrophoretic medium comprises a plurality of discrete droplets of electrophoretic fluid and a continuous phase of polymeric material, and the discrete droplets of electrophoretic fluid within such a polymer dispersion electrophoretic display can be considered as capsules or microcapsules, even without a discrete capsule membrane associated with each individual droplet; see, for example, U.S. Patent No. 6,866,760. Therefore, for the purposes of this application, such polymer dispersion electrophoretic media are considered a subclass of encapsulated electrophoretic media.

[0020] One related type of electrophoretic display is the so-called microcell electrophoretic display. In a microcell electrophoretic display, charged particles and fluids are not encapsulated within microcapsules, but are held in multiple cavities formed within a carrier medium (typically a polymer film). See, for example, U.S. Patents 6,672,921 and 6,788,449, both assigned to SiPix Imaging, Inc.

[0021] Although electrophoretic media are typically opaque (because, for example, in many electrophoretic media, particles essentially block visible light transmission through the display) and operate in reflective mode, many electrophoretic displays can be fabricated to operate in a so-called shutter mode, in which one display state is substantially opaque and the other display state is light-transmitting. 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. Dielectric electrophoretic displays (similar to electrophoretic displays but dependent 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 may also be able to operate in shutter mode. Electro-optic media operating in shutter mode may be useful in multi-layered structures of full-color displays, in which at least one layer adjacent to the viewing surface of the display operates in shutter mode to expose or conceal a second layer further away from the viewing surface.

[0022] Encapsulated electrophoretic displays typically do not suffer from the aggregation and sedimentation failure modes of conventional electrophoretic equipment and offer several advantages, such as the ability to print or coat displays on a variety of flexible and rigid substrates. (The term "printing" is intended to include all forms of printing and coating, including but not limited to: pre-metering coatings such as patch die coating, slot or extrusion coating, slide or stack coating, curtain coating; roller coatings such as doctor blade roller coating, forward and reverse roller coating; concave coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing; electrostatic printing; thermal printing; inkjet printing; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques.) Therefore, the resulting display can be flexible. Furthermore, because the display medium can be printed (using a variety of methods), the display itself can be manufactured inexpensively.

[0023] Other types of electro-optic media can also be used in the display of this invention.

[0024] The bistable or multistable behavior of particle-based electrophoretic displays, and the bistable or multistable behavior of other electro-optic displays exhibiting similar behavior (hereafter referred to as "impulse-driven displays" for convenience), contrasts sharply with the behavior of conventional liquid crystal ("LC") displays. Twisted nematic liquid crystals are not bistable or multistable but are used as voltage transducers, such that applying a given electric field to a pixel of such a display produces a specific gray level at that pixel, regardless of its prior gray level. Furthermore, LC displays are driven in only one direction (from nontransmissive or "dark" to transmissive or "bright"), achieving the opposite transition from a brighter to a darker state by reducing or eliminating the electric field. Finally, the gray levels of pixels in LC displays are insensitive to the polarity of the electric field, only to its amplitude, and in practice, commercial LC displays typically reverse the polarity of the driving field at frequent intervals due to technological reasons. Conversely, bistable electro-optic displays are approximated as impulse transducers, such that the final state of a pixel depends not only on the applied electric field and the time at which the field is applied, but also on the state of the pixel before the electric field is applied.

[0025] Regardless of whether the electro-optic medium used is bistable, to achieve a high-resolution display, the individual pixels of the display must be addressable without interference from neighboring pixels. One way to achieve this is to provide an array of nonlinear elements (such as transistors or diodes), with each pixel associated with at least one nonlinear element to produce an "active matrix" display. The addressing electrode, or pixel electrode, that addresses a pixel is connected to a suitable voltage source via the associated nonlinear element. Typically, when the nonlinear element is a transistor, the pixel electrode is connected to the drain of the transistor, and this arrangement will be used 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 are arranged in a two-dimensional array of rows and columns, such that any particular pixel is uniquely defined by the intersection of a designated row and a designated column. The sources of all transistors in each column are connected to a single column electrode, and the gates of all transistors in each row are connected to a single row electrode; again, it is conventional to assign sources to rows and gates to columns, but this is essentially arbitrary and can be reversed if necessary. Row electrodes are connected to row drivers, which essentially ensure that only one row is selected at any given time. That is, a voltage is applied to the selected row electrode to ensure all transistors in the selected row are turned on, while voltages are applied to all other rows to ensure all transistors in these unselected rows remain off. Column electrodes are connected to column drivers, which apply selected voltages to different column electrodes to drive the pixels in the selected row to their desired optical state. (The aforementioned voltages are relative to a common front electrode, which is conventionally provided on the side of the electro-optic medium opposite the nonlinear array and extends throughout the display.) After a preselection interval called the “row addressing time,” the selected row is deselected, the next row is selected, and the voltage on the column driver is changed to write the next row to the display. This process is repeated, thus writing to the entire display row by row.

[0026] Alternatively, for electro-optic media with a substantial threshold voltage (which most electrophoretic media do not possess), passive matrix driving can be used. In this type of driving, two sets of parallel, elongated electrodes are arranged on opposite sides of the electro-optic layer, perpendicular to each other, such that each pixel is defined by the intersection of one electrode from each of the two sets. Finally, electro-optic displays can utilize so-called "direct driving," where multiple pixels each have a separate conductor connecting the pixel electrode to a display controller, allowing direct control of the potential of each pixel electrode.

[0027] Active and passive matrix displays are complex and expensive, especially in the case of large-area displays, because the cost of the required electrodes tends to be a function of the display area rather than the number of pixels. However, active and passive matrix displays do offer the flexibility to display arbitrary images and can therefore represent pictures and text in different point values. Direct-drive displays tend to be cheaper but lack flexibility and, if they can display text, are typically limited to a single point value and require a very large number of connections between the pixel electrodes and the controller; see, for example, U.S. Design Patent No. D485,294, which requires 63 pixels to represent a single character of various versions of the Latin alphabet in a single point value.

[0028] To date, most commercial applications of electrophoresis and similar bistable electro-optic displays have been in small products such as electronic document readers, watches, and solid-state storage devices. However, there is growing interest in applying such displays to furniture and architectural applications. In many furniture and architectural applications, electro-optic displays are designed to provide simple, often moving, geometric patterns. This invention aims to provide a display and driving method useful in furniture and architectural applications. Furthermore, the described waveform allows for “reciprocating” wave switching, a type of wave switching not available in previous art, i.e., as described in U.S. Patent Nos. 10,197,883 and 10,551,713, which are incorporated herein by reference in their entirety.

[0029] As discussed in the aforementioned applications, if the waveform applied to an electro-optic display is not DC balanced, it can lead to damage to the electrodes, especially in the case of light-transmitting electrodes, which are typically very thin, less than 1 µm. (The term "light transmission" is used herein in its conventional meaning in the field of displays, such as as described, for example, in U.S. Patent No. 6,982,178, meaning the transmission of sufficient visible light to allow an observer to observe the electro-optic material through the light-transmitting electrode to observe changes in the optical state of the electro-optic material.) To reduce or eliminate such damage to the electrodes, at least a portion of one of the first and second electrodes may be provided with a passivation layer disposed between the electrode and the electro-optic material layer. Suitable passivation layers are described, for example, in U.S. Patent No. 6,724,519. However, to further prevent the possibility of electrode damage, there is a need to develop a DC-balanced waveform for operation of the electro-optic display. Such damage can cause the display to display incorrect colors, or the display may cease operation entirely. Summary of the Invention

[0030] The present invention provides an improved method for driving a spaced-contact display, such as a spaced-contact electrophoretic display, wherein the spaced-contact display includes: an electro-optic material layer, and a first electrode and a second electrode on opposite sides of the electro-optic material layer, at least one of the first electrode and the second electrode being light-transmitting, and at least one of the first electrode and the second electrode having at least two spaced contacts, and a voltage controller arranged to provide a driving voltage signal between the two spaced contacts attached to the same electrode.

[0031] In a first aspect, the present invention provides a method for driving an interleaved contact electro-optic display, comprising: providing an interleaved contact electro-optic display including an electro-optic material layer, a first electrode layer and a second electrode layer on opposite sides of the electro-optic material layer, wherein the first electrode layer or the second electrode layer is light-transmitting, a first contact and a second contact spaced apart on the first electrode layer and electrically coupled to the first electrode layer, and a voltage controller coupled to the first contact and the second contact; providing a first time-varying drive signal to the first contact via the voltage controller, wherein the first time-varying drive signal starts from a duty cycle of zero, slopes to a duty cycle of 1, and then returns to a duty cycle of zero; and providing a second time-varying drive signal to the second contact via the voltage controller, wherein the second time-varying drive signal starts from a duty cycle of zero, slopes to a duty cycle of -1, then slopes to a duty cycle of 1, and then returns to a duty cycle of zero. In some embodiments, the slope of the second time-varying drive signal from a duty cycle of -1 to a duty cycle of 1 includes two different slopes of the duty cycle per unit time. In some embodiments, the method further includes: providing a third time-varying drive signal to a first contact via a voltage controller, wherein the first time-varying drive signal starts with a duty cycle of zero, slopes to a duty cycle of -1, and then returns to a duty cycle of zero; and providing a fourth time-varying drive signal to a second contact via a voltage controller, wherein the second time-varying drive signal starts with a duty cycle of zero, slopes to a duty cycle of 1, slopes to a duty cycle of -1, and then returns to a duty cycle of zero. In some embodiments, the first time-varying drive signal and the second time-varying drive signal simultaneously reach a duty cycle of 1. In some embodiments, the frequencies of the first drive signal and the second drive signal are 30 Hz or higher. In some embodiments, the voltage amplitudes of the first drive signal and the second drive signal are 15 V to 30 V. In some embodiments, the first electrode and the second electrode each have at least two spaced contacts, and the voltage controller is arranged to change the potential difference between the two spaced contacts attached to each electrode. In some embodiments, the electro-optic material includes an electrophoretic material comprising a plurality of charged particles disposed in a fluid and capable of moving through the fluid under the influence of an electric field. In some embodiments, charged particles and fluid are confined within multiple capsules or microunits or discrete droplets surrounded by a continuous phase comprising a polymeric material. In some embodiments, at least one of the first and second electrodes is interrupted by at least one non-conductive region, such that the current must follow a non-linear path between the two contacts on the electrode. In some embodiments, at least one of the first and second electrodes is divided into multiple segments having different resistances per unit length. In some embodiments, at least one of the first and second electrodes is divided into multiple segments having different capacitances per unit area. In some embodiments, at least a portion of one of the first and second electrodes is provided with a passivation layer disposed between the electrode and the electro-optic material layer.In some embodiments, the first time-varying drive signal or the second time-varying drive signal includes a sine wave, a triangular wave, a sawtooth wave, or a square wave.

[0032] In another aspect, the present invention provides a method for driving an interleaved contact electro-optic display, comprising: providing an interleaved contact electro-optic display, comprising: an electro-optic material layer, a first electrode layer and a second electrode layer on opposite sides of the electro-optic material layer, wherein the first electrode layer or the second electrode layer is light-transmitting, a first contact and a second contact spaced apart and electrically coupled to the first electrode layer, and a voltage controller coupled to the first contact and the second contact; providing a first time-varying drive signal to the first contact via the voltage controller, wherein the first... A time-varying drive signal starts with a duty cycle of zero, ramps to a duty cycle of -1, maintains a duty cycle of -1 for a sufficient time to provide DC balance to the first time-varying drive signal, then ramps to a duty cycle of 1, and then returns to a duty cycle of zero; and a second time-varying drive signal is provided to a second contact via a voltage controller, wherein the second time-varying drive signal starts with a duty cycle of zero, transitions to a duty cycle of 1 by experiencing a negative duty cycle impulse until the first time-varying drive signal is maintained at a duty cycle of -1, then proceeds to a duty cycle of 1, and then returns to a duty cycle of zero. In some embodiments, the method further includes: providing a third time-varying drive signal identical to the second time-varying drive signal to the first contact; and providing a fourth time-varying drive signal identical to the first time-varying drive signal to the second contact. In some embodiments, the first time-varying drive signal and the second time-varying drive signal simultaneously reach a duty cycle of 1. In some embodiments, the frequencies of the first drive signal and the second drive signal are 30 Hz or higher. In some embodiments, the voltage amplitudes of the first drive signal and the second drive signal are 15 V to 30 V. In some embodiments, both the first electrode and the second electrode have at least two spaced contacts, and a voltage controller is arranged to change the potential difference between the two spaced contacts attached to each electrode. In some embodiments, the electro-optic material includes an electrophoretic material comprising a plurality of charged particles disposed in a fluid and capable of moving through the fluid under the influence of an electric field. In some embodiments, the charged particles and the fluid are confined within a plurality of capsules or microunits or discrete droplets surrounded by a continuous phase comprising a polymeric material. In some embodiments, at least one of the first electrode and the second electrode is interrupted by at least one non-conductive region, such that the current must follow a non-linear path between the two contacts on the electrode. In some embodiments, at least one of the first electrode and the second electrode is divided into a plurality of segments having different resistances per unit length. In some embodiments, at least one of the first electrode and the second electrode is divided into a plurality of segments having different capacitances per unit area. In some embodiments, at least a portion of one of the first electrode and the second electrode is provided with a passivation layer disposed between the electrode and the electro-optic material layer. In some embodiments, the first or second time-varying drive signal includes a sine wave, a triangular wave, a sawtooth wave, or a square wave.

[0033] In a preferred form of the spaced-contact display of the present invention, both the first electrode and the second electrode have at least two spaced contacts, and a voltage controller is arranged to change the potential difference between the two spaced contacts attached to each electrode. Each electrode may, of course, have more than two spaced contacts; if so, the voltage controller need not be arranged to change the potential of all but one of these contacts independently; for example, the contacts may be divided into two or more groups, with the contacts in each group remaining at the same potential, but a potential difference applied between the different groups.

[0034] The spaced-contact display of the present invention can have more than one electrode on each side of the electro-optic dielectric layer. In practice, in the case of very large displays (potentially covering very large walls), it may be necessary or desirable to divide the display into a series of separate modules, each module having an electro-optic layer sandwiched between a first electrode and a second electrode. Furthermore, the spaced-contact display of the present invention can have a different number of electrodes on each side of the electro-optic dielectric layer.

[0035] The method disclosed herein is also applicable to “isolated electrode” displays, which include an electro-optic material layer, a sequence of at least three electrodes disposed adjacent to the electro-optic material layer and configured to apply an electric field across the electro-optic material layer, the electrodes on at least one surface of the electro-optic material layer being light-transmitting, and a voltage controller arranged to change the potential difference between a first electrode and a last electrode of the sequence, wherein: (a) each electrode of the sequence is located on a side of the electro-optic material layer opposite to both the electrode preceding it in the sequence and the electrode following it in the sequence; (b) each electrode of the sequence has a first edge overlapping or adjacent to the electrode preceding it in the sequence and a second edge overlapping or adjacent to the electrode following it in the sequence; and (c) each electrode of the sequence other than the first electrode and the last electrode is electrically isolated such that its potential is controlled by the passage of current through the electro-optic material layer. Attached Figure Description

[0036] In the attached diagram Figure 1 This is a schematic top view of the spaced-touch banner display of the present invention, showing the positions of the contacts of the top (T) and bottom (B) electrode layers.

[0037] Figure 2 It is along Figure 1 The image shows a schematic cross-sectional view of the height as seen in the direction of the arrow, with line II-II in the image. It is noteworthy that the contacts of the top electrode layer are at the bottom of the display, while the contacts of the bottom electrode layer are at the top of the display.

[0038] Figure 3This is a schematic top view of an alternative construction of an interleaved contact display, in which a gap is provided in an electrode layer such that the current must follow a non-linear path between two interleaved contacts of the electrode layer.

[0039] Figure 4 This is a schematic top view of an alternative construction of an interleaved contact display, in which one electrode is divided into segments with different resistances per unit length.

[0040] Figure 5 This is a side view of an alternative construction of an interleaved contact display, in which one electrode layer has a region with varying capacitance per unit area.

[0041] Figure 6 This is a side view of the isolated electrode display of the present invention, wherein a series of electrodes are alternately located above and below an electro-optic material layer. Each electrode in the sequence is located on the side of the electro-optic material layer opposite to both the electrodes preceding and following it in the sequence.

[0042] Figures 7A to 7D A schematic top view of each layer of the electrode layer applicable to the present invention is shown.

[0043] Figure 8 An exemplary driving scheme used in the prior art is shown, in which two different time-varying driving waveforms are provided by a voltage controller to electrodes spaced at both ends of a banner display. For both waveforms, the voltage and frequency remain constant, however, the duty cycle varies as a function of time (which is determined by the number of frames).

[0044] Figure 9 The duty cycle variation under constant voltage and frequency is shown.

[0045] Figure 10 An embodiment of the improved driving method of the present invention is shown, which provides a DC balanced waveform and also allows for less “dead time” during the driving cycle.

[0046] Figure 11 An embodiment of the improved driving method of the present invention is shown, which provides a DC balanced waveform and also allows for less “dead time” during the driving cycle.

[0047] Figure 12 An exemplary wave-shaped toggling banner sign indicating the location of a train station is shown. The sign alternates between black text on a white background and white text on a black background, moving from left to right in a wave-like pattern over approximately 3 seconds. Detailed Implementation

[0048] This invention relates to an improved method for driving "interval contact type" electro-optic displays and "isolated electrode type" electro-optic displays. The improved method provides a DC balanced waveform that reduces the amount of residual voltage remaining between the electrodes at the end of the drive cycle. Additionally, the improved method allows banner-type displays to switch "wave-like" in a first direction and then return in the opposite direction.

[0049] In a spaced-contact display, two electrode layers are disposed on either side of an electro-optic dielectric layer. Each electrode layer may include two contacts, and each electrode layer may simply be in the form of a uniform strip of conductive film (transmissive or non-transmissive) extending between the two contacts. A voltage controller is coupled to the contacts and configured to apply a time-varying potential difference between the paired contacts attached to at least one electrode layer. For example, the voltage controller may vary the potential difference (voltage) applied to the first and second contacts at different frequencies. The voltage controller may vary the potential difference into, for example, a sine wave, triangle wave, sawtooth wave, or square wave with a fixed or varying frequency or a varying duty cycle.

[0050] Additionally, interesting visual effects can be produced in spaced-contact displays by using non-uniform electrode layers. For example, at least one of the first and second electrode layers can be interrupted by at least one non-conductive region, causing the current to follow a non-linear path between the two contacts on the electrode. Examples of possible geometric arrangements of such non-linear paths include strips, spirals, and staggered electrodes, which are discussed below with reference to the accompanying drawings. Alternatively, at least one of the first and second electrode layers can be divided into multiple segments with different resistances per unit length and / or into multiple segments with different capacitances per unit area. The electrode layer with two contacts can also be provided in the form of multiple conductive traces or regions on a backplane and configured to serve as a busbar. In some embodiments, the electrode layer may include a first plurality of conductive lines, an insulating material layer applied above the first plurality of conductive lines, a second plurality of conductive lines applied on the insulating material layer, and a resistive material layer in electrical contact with the second plurality of conductive lines. The insulating material layer may be configured to electrically connect each conductive trace of the first plurality of conductive lines to a single conductive line of the second plurality of conductive lines, and to electrically connect each conductive line of the second plurality of conductive lines to a single conductive line of the first plurality of conductive lines. In another embodiment, the electrode layer may include a plurality of conductive lines, an insulating material layer applied above the first plurality of conductive lines, a plurality of conductive regions applied above the insulating material layer, and a resistive material layer electrically contacting the plurality of conductive regions. The insulating material layer may be configured to electrically connect each of the plurality of conductive lines to a single conductive region and each conductive region to a single conductive line. To reduce or eliminate such damage to the electrode layer, at least a portion of one of the first electrode layer and the second electrode layer may be provided with a passivation layer disposed between the electrode layer and the electro-optic material layer. Suitable passivation layers are described, for example, in U.S. Patent No. 6,724,519.

[0051] The method disclosed herein is also applicable to "isolated electrode" displays, which include an electro-optic material layer, a sequence of at least three electrodes disposed adjacent to the electro-optic material layer and configured to apply an electric field across the electro-optic material layer, the electrodes on at least one surface of the electro-optic material layer being light-transmitting, and a voltage controller arranged to change the potential difference between the first and last electrodes of the sequence, wherein:

[0052] (a) Each electrode of the sequence is located on the opposite side of the electro-optic material layer to both the electrode preceding it in the sequence and the electrode following it in the sequence;

[0053] (b) Each electrode in the sequence has a first edge that overlaps with or is adjacent to an electrode preceding it in the sequence and a second edge that overlaps with or is adjacent to an electrode following it in the sequence; and

[0054] (c) Each electrode in the sequence, except for the first and last electrodes, is electrically isolated such that its potential is controlled by the passage of current through the electro-optic material layer.

[0055] In most instances, isolated contact displays (as defined above) are driven by a voltage controller configured to apply a potential difference between the first and last electrodes of the display. The voltage controller can be arranged to apply a time-varying potential difference between the first and last electrodes.

[0056] The display and driving method of the present invention can utilize any type of electro-optic medium discussed above. In a preferred embodiment, the electro-optic display may include an electrophoretic material comprising a plurality of charged particles disposed in a fluid and capable of moving through the fluid under the influence of an electric field. The charged particles and fluid may be confined within a plurality of capsules or microcells. Alternatively, the charged particles and fluid may exist as a plurality of discrete droplets surrounded by a continuous phase comprising a polymer material. The fluid may be a liquid or a gas. A spaced-touch display includes an electro-optic material layer, a first electrode and a second electrode located on opposite sides of the electro-optic material layer, at least one of the first electrode and the second electrode having at least two spaced contacts, and a voltage controller arranged to change the potential difference between two spaced contacts attached to the same electrode.

[0057] As described above, most conventional electro-optic displays, whether active matrix or direct-drive, use a single light-transmitting "common" electrode on the front (top; viewing) side of the electro-optic layer, and an array of electrodes (pixel electrodes or direct-drive electrodes) on the opposite side (backplate). The potential difference between each array electrode and the common electrode is controlled by a display driver or voltage controller, such that each array electrode (in principle) controls the optical state of the electro-optic medium region located between that array electrode and the common electrode. That is, the optical state depends on the polarity and amplitude of the potential difference and the duration for which the potential difference is applied. Typically, the potential on the "common" front electrode is controlled by a so-called "topplate connection," which can be connected to or even through the backplate to provide a robust connection. See also Figure 2 The common practice is to provide multiple connections to the front electrode to reduce the risk of poor contact, but these multiple connections are not independently controllable.

[0058] Compared to displays with multiple top plate connections, the spaced-touch display using the method of this invention relies on the potential difference between two or more spaced contacts on a single electrode layer (typically an elongated electrode layer) to generate a potential gradient within that electrode layer. This time-dependent potential difference between different regions of a single electrode layer and electrodes on the opposite side of the electro-optic layer will result in... Figure 12The "wave switching" is illustrated. Furthermore, if, as is typically the case, both electrode layers of the display have multiple contacts, a potential gradient will exist within both electrodes, and the potential difference applied to any point in the electro-optic layer will be the difference between the instantaneous potentials at selected portions of the electro-optic material between the two electrode layers. That is, the potential difference applied to the electro-optic material across the electro-optic layer will continuously change, resulting in a corresponding continuous change in the optical state of the electro-optic medium. For example... Figure 12 As shown, the effect is striking and quite rapid.

[0059] Since the display of this invention is designed to operate by generating a potential gradient within the electrodes (by providing a potential gradient between two or more contacts attached to the electrode within one electrode), the resistance provided by the electrodes is crucial. Too low an electrode resistance will generate excessive current within the electrode, which may short-circuit the electronics in the voltage controller and may cause other problems, such as excessive localized heating that could damage the electro-optic layer. On the other hand, too high an electrode resistance may cause the voltage from the spaced contacts to propagate only short-range, resulting in switching occurring only in a very small area adjacent to the contacts, and requiring a large number of contacts if the entire display area needs to be switched. This situation is similar to embodiments with isolated electrodes, where the influence range of a single contact is limited.

[0060] Furthermore, since various display embodiments manufactured according to the present invention may rely on reflected ambient light to observe the image generated by the electro-optic material, light loss from the light-transmitting electrodes should be minimized. For example, in displays according to various embodiments of the present invention, ambient light will pass through the light-transmitting electrodes twice: first when the ambient light propagates from its source to the surface of the electro-optic material, and second when the light is reflected from the electro-optic material to the observer. As mentioned above, the electrode material should form a front electrode with sufficiently high conductivity to ensure sufficient current for uniformly driving the display. A thicker layer of electrode material will have higher conductivity; however, a thicker layer will also result in greater light loss because the material is not colorless. Indium tin oxide (ITO) is highly colored, but this color effect can be minimized by applying an extremely thin layer, for example, on the order of about 1000-2000 Å.

[0061] While the optimal electrode resistance will vary with the display size, the number of contacts, and the properties of the specific electro-optic medium used, the sheet resistance of the light-transmitting electrode material is preferably from about 500 to about 50,000 Ohm / sq, more preferably from about 1,000 to about 15,000 Ohm / sq, and most preferably from about 300 to about 5,000 Ohm / sq. If desired, light-transmitting conductors such as PEDOT, carbon nanotubes, graphene, and nanowires can certainly be used.

[0062] The electro-optic materials used in the displays of this invention are typically bistable display materials, such as electrochromic, rotating dichromatic elements, or electrophoretic materials. Such bistable materials only change their electro-optic state after exposure to an electric field for a significant period of time (typically on the order of 0.1 to 1 second). Therefore, the appearance of the display of this invention is controlled not only by the potential changes on each region of the individual electrodes with the change in potential at the spaced contacts, but also by the response speed of the electro-optic materials used to the electric field they are exposed to. Furthermore, as discussed in the preceding applications, some electro-optic materials experience a phenomenon known as “halo,” through which changes in potential at the electrodes affect the electro-optic state of the material in areas larger than the electrode itself. Although halo is generally considered a problem in electro-optic displays because it tends to distort the displayed image, in at least some displays of this invention, halo can actually be beneficial in masking areas of the display that would otherwise be inactive. For example, as mentioned in some displays of this invention, the first and / or second electrodes can be interrupted by at least one non-conductive region, causing the current to follow a non-linear path between the two contacts on that electrode. Halo can be used to conceal the optical effects of such non-conductive regions. In fact, in some cases, it is desirable to design electro-optical materials that increase halos to aid in this concealment.

[0063] A typical display of the present invention may include the following layers in sequence:

[0064] (a) Forming a transparent conductive layer (“front electrode”) on the display viewing surface;

[0065] (b) Encapsulating the electrophoretic dielectric layer;

[0066] (c) the laminated adhesive layer; and

[0067] (d) “Backsheet”, which includes a substrate (usually a polymer film) and a conductor that does not need to be transparent.

[0068] At least two regions of each electrode in layers (a) and (d) are cleaned to expose conductors for electrical contacts that can be addressed independently. Finally, the display includes a voltage controller for driving the front electrode and backplate to positive and negative potentials relative to each other, and generating a potential gradient within each electrode.

[0069] This display has been manufactured using the following materials. The front electrode is formed of 5 mil (127 µm) polyethylene terephthalate, one surface of which is coated with ITO of grade OC300 or 450. Alternatively, the front electrode can be coated onto the remaining layers of the display without any supporting substrate. The encapsulating electrophoretic medium is substantially as described in U.S. Patent No. 8,270,064, and the laminating adhesive is a 25 µm layer substantially as described in U.S. Patent No. 7,012,735, containing 5000 ppm of tetrabutylammonium hexafluorophosphate dopant to control electrical properties. The backsheet is a PET / ITO film similar to that used for the front electrode, but can be replaced with printed carbon conductors or other low-cost transparent or opaque conductors.

[0070] A thin banner "interval contact" display is schematically shown in the attached diagram. Figure 1 and Figure 2 As shown in the image. Figure 1 As shown, the elongated, spaced-out contact display (typically designated 100) includes elongated rectangular light-transmitting electrodes 102, which are typically commercially available PET-ITO (Saint-Gobain). An electro-optic display material (typically designated 106) is supported from below by a substrate 118.

[0071] like Figure 2 As shown, the elongated, spaced-out contact display 100 includes an elongated rectangular light-transmitting electrode 102, which includes a PET film 108 with an ITO front electrode 110 extending across the entire area of ​​the display 106. In contact with the front electrode 110 is an electro-optic display material 106, which may be an encapsulating electrophoretic medium. The lower surface of the electro-optic display material 106 is in contact with a laminating adhesive layer 114, which secures the encapsulating electrophoretic medium 112 to a backplane including an ITO electrode layer 116 on a glass substrate 118. Figure 1 As shown, the front electrode 102 is provided with four contacts T1-T4 arranged near the corner of the elongated-spaced contact display 100, while the rear electrode 116 is similarly provided with four contacts B1-B4 arranged in a similar manner.

[0072] Figure 2The construction of contacts T1-T4 and B1-B4 is shown. Contacts B1-B4 are created by making a kiss-cut opening through the PET film 108 (typically using a laser cutter) and cleaning the lower portion of the electrophoretic medium 106 and laminating adhesive 114. Similarly, contacts T1-T4 are created by cutting an opening through the glass substrate 118 and cleaning the upper portion of the electrophoretic medium 106 and laminating adhesive 114 using solvent and manual or mechanical methods (such as an electric toothbrush). The resulting openings are filled with a conductive material, such as a carbon-filled adhesive, conductive ink, or silver paste, to create individually addressable contacts. Optionally, an insulating material 119, such as a transparent, non-conductive polymer, may be applied around the vias in the opposing electrode layers to prevent short circuits. A voltage controller (not shown) is provided to independently drive contacts T1-T4 and B1-B4 to positive and negative potentials in a time-dependent manner. This controller has 12 outputs, each capable of providing any independently programmable voltage and waveform on each channel between ±30V, and also has high impedance or floating states. The controller has one drive line for each output, providing direct drive.

[0073] Figure 1 and Figure 2 The display shown can be constructed substantially as described in the aforementioned U.S. Patent No. 6,982,178. A PET / ITO film (i.e., PET film 108 and ITO electrode 110) is coated or laminated onto an electrophoretic medium 106 to form a PET / ITO / electrophotonic assembly. An ITO-glass substrate (i.e., lower substrate 118 and bottom ITO electrode 116) is laminated to this sub-assembly with a lamination adhesive layer 114. In an alternative embodiment, the bottom ITO electrode 116 can be replaced with a non-transmissive electrode without adverse effects because the electrophoretic medium 112 is opaque. The resulting structure is a complete electro-optic display capable of switching given the correct electrical connections. Using this technique, single displays of 16 × 60 inches (406 × 1523 mm) or larger can be manufactured. Other construction methods can also be used, such as forming a front planar laminate (FPL) as described in the aforementioned U.S. Patent No. 6,982,178, then cutting the FPL to size and laminating it onto a backplate. The substrate in the cutting area is removed, and then the electrophoretic medium is cleaned. The more contacts there are, and the more spatially distributed these contacts around the display, the more complex the switching patterns can be achieved.

[0074] Figure 1 and Figure 2The display 100 shown can be driven by a voltage controller (not shown) by setting the top contacts T2 and T3 (at opposite corners of the display 100) to -20V and +20V respectively, while grounding the back panel contacts B2 and B3, and allowing all other remaining contacts (T1, T4, B1, B4) to float. If this driving mode is maintained for more than about 1 second, the optical state of the electrophoretic layer will be half dark and half white, with a diffuse gradient region in the middle (see...). Figure 12 (At 1.5 seconds). If the driven contacts T2 and T3 are fed a variable voltage mode instead of a fixed voltage, a moving pattern is generated in the electrophoretic layer. For example, if one contact receives a sine wave with an amplitude of 20V and a frequency of 0.1Hz, and another driven contact on the same electrode receives a sine wave with an amplitude of 20V and a frequency of 0.09Hz, the black-to-white switching wave will slowly move across the display at different speeds and in different directions, from left to right or from right to left, varying over time due to the different frequencies of the two applied sine waves. By making the two sine waves have the same frequency and giving them a constant phase difference, the speed and direction of the black-to-white or white-to-black moving wave can be made constant and repeatable. More complex patterns can be formed by driving two contacts at opposite ends of the display diagonally, especially when using opposite diagonal contacts on the top and bottom electrodes. More complex patterns can be produced by providing a greater number of contacts around the perimeter of the display.

[0075] although Figure 1 and Figure 2 The illustrated display has electrodes in a simple rectangular form, such that each electrode layer is substantially uniform between the spaced contacts at its two ends. However, it should be understood that the method for improving wave switching (described below) is not limited to rectangular or any particular shape of display, and interesting effects can be produced using polygonal (e.g., hexagonal or octagonal) displays, or circular or elliptical displays. In this case, one or more contacts can be arranged around the perimeter of the display, and another contact can be arranged at the center of the display, causing the change in the electro-optic material to propagate radially rather than linearly. Furthermore, the invention is not limited to planar two-dimensional displays, but can be applied to three-dimensional objects. Both the electrodes and the electro-optic medium can be deposited on the three-dimensional object; for example, electrodes formed of organic conductors can be deposited from a solution, and electrophoretic media can be deposited using a spraying technique.

[0076] Furthermore, interesting optical effects can be achieved by setting gaps in one or both electrodes, for example by removing or chemically altering the electrode material, so that the current must follow a non-linear path between the two contacts on the electrode. Figure 3 This is a schematic top view of this type of monitor (typically specified as 300). Figure 1 and Figure 2Similar to the elongated, spaced-out contact display 100 shown, the display 300 has an elongated rectangular shape with strip contacts 302 and 304 at opposite ends. (The contacts do not need to be pads, and there does not need to be more than one contact at each end.) The electrode layer 306 extending between contacts 302 and 304 is interrupted by multiple non-conductive regions 308, such that the current (and therefore the electro-optic effect) must follow a basic sinusoidal path between contacts 302 and 304. The non-conductive regions 308 do not require special materials and can be achieved by simply scraping a sufficiently wide (e.g., 5 mm) layer of ITO from PET to prevent short circuits across the removed ITO.

[0077] Such as Figure 3 The non-conductive region 308 can be used to "guide" the electro-optic effect into various interesting patterns. For example, a circular, elliptical, or polygonal display may have a single contact at the periphery of the display, a second contact at the center of the display, and a spiral non-conductive region to guide the electro-optic effect along a spiral electrode extending between the two contacts. In the case of a three-dimensional display, there is even greater design freedom; for example, a display formed on a cylindrical substrate can use a helical non-conductive region to guide the electro-optic effect along a spiral path between contacts provided at opposite ends of the cylindrical substrate. As previously described, in the spaced-contact display of the present invention, at least one of the first and second electrodes can be divided into multiple segments with different resistances per unit length, a schematic top view of which (typically designated as 400) is shown below. Figure 4 As shown. The monitor 400 is generally similar to Figure 3 The display 300 shown is different because the display 400 has an elongated rectangular shape with contacts 402 and 404 provided at its opposite ends. Also, like the display 300, the display 400 provides a non-conductive region 408. However, the arrangement of region 408 differs from that of the display 300. Figure 3 The arrangement of region 308; region 408 is in the form of two adjacent region pairs extending from the opposite long sides of display 400, so as to leave a narrow “neck” or “islet” of conductive material 410 or 412 between each pair of adjacent regions. Therefore, the current passing between contacts 402 and 404 passes successively through low-resistance region 414, high-resistance neck 410, low-resistance region 416, high-resistance neck 412 and low-resistance region 418.

[0078] Figure 4 This illustration shows a variable resistance region formed by varying the width of the electrodes, but other techniques for changing resistance can certainly be employed. For example, it could be modified by replacing each neck region 410 and 412 with contacts provided on adjacent regions and interconnected via appropriate resistors. Figure 4The display shown. To avoid the unsightly presence of visible electrical components, resistors and associated conductors can be housed within a bezel surrounding the display, such as those typically found in logo bezels. The ability to "invisibly" interconnect electrode areas by placing electrical components within such a bezel does indeed provide additional design freedom, namely the ability to electrically arrange electrode segments in a sequence different from their physical locations. For example, consider a modified version of display 400 where the electrodes are divided into five segments (for convenience, in...) Figure 4 (Read from left to right as A, B, C, D, and E) instead of Figure 4 The three sections 414, 416, and 418 shown are interconnected, with section AE interconnected via conductors and resistors hidden within the bezel. The electrical interconnections can be arranged such that the electrode sections are electrically interconnected in, for example, the order A, D, B, C, E, which will produce an appearance of jumping around the display rather than... Figure 1 and Figure 2 The electro-optic effect, as shown in the display 100, travels linearly along its path.

[0079] A variable capacitance region can be provided within the electrodes instead of a variable resistance region. A schematic cross-sectional illustration of such a display (typically specified as 500) is shown in [illustration missing]. Figure 5 In the middle. The monitor 500 is generally similar to those in... Figure 3 and Figure 4 The displays 300 and 400 shown are elongated rectangular in shape, with electrodes 506 having contacts 502 and 504 at their opposite ends. However, unlike the electrodes shown in displays 300 and 400, the electrodes 506 of display 500 are continuous. However, the electrodes 506 are provided with a capacitance region varying per unit area by providing a series of spaced electrodes 512 (all of which are grounded) on the electro-optic dielectric side opposite to the electrodes 506. It will be apparent that the region of electrode 506 opposite to the electrodes 512 will have a substantially larger capacitance per unit area than the region of electrode 506 not opposite to the electrodes 512, thus providing a variation in electro-optic performance of display 500 that is generally similar to that provided by the variable resistance region in display 400. (Generally, similar to...) Figure 2 The adhesive layer 114 shown will exist between the electro-optic layer 510 and the electrode 506, or between the electro-optic layer 510 and the electrode 512. For ease of explanation, Figure 5 The adhesive layer is omitted, but its presence or absence has no impact on the basic operation of the display 500.

[0080] Now refer to Figure 6 This invention describes one embodiment of an isolated electrode display. Conceptually, an isolated electrode display can be considered as... Figure 4A modification to the variable resistance electrode display of the type shown is included, which involves using the electro-optic layer itself as a high-resistance region between low-resistance electrodes. This modification places continuous high-resistance regions (electrodes) on opposite sides of the electro-optic layer, thus requiring only a single set of electrodes.

[0081] More specifically, such as Figure 6 As shown, the isolated electrode display (generally designated 600) has an elongated rectangular shape similar to a display, comprising an electro-optic material layer 610 and a sequence of seven electrodes 612-624, each electrode having the form of an elongated strip extending across the entire width of the display. The first and last electrodes 612 and 624 are respectively connected to a voltage control unit (schematically shown at 626), which enables the application of a time-varying potential difference between electrodes 612 and 624. The remaining electrodes 614-622 are electrically isolated such that their potential is controlled by a current flowing through the electro-optic material layer 610. Electrodes 612-624 alternate between the lower and upper surfaces of layer 610 (as shown), and electrodes 614, 618, and 622 on the upper surface (which is the viewing surface of the display) are light-transmitting; electrodes 612, 616, 620, and 624 may or may not be light-transmitting. Figure 6 It can be seen that each of electrodes 614-622 has a first edge that overlaps with the previous electrode (e.g., Figure 6 (as shown by its left-hand edge) and the second edge overlapping with the next electrode (as shown by the ... Figure 6 (As shown by its right-hand edge). Adjacent edges do not need to overlap, as long as they are provided close to each other to leave a conductive path of reasonable length through layer 610. It should be understood that the first and second edges of the electrodes do not need to be on opposite sides of the electrodes. For example, electrodes 612-624 can be in the form of isosceles triangles, such that the first and second edges will not be parallel, or the electrodes can be arranged in a checkerboard pattern, in which case some electrodes will have first and second edges perpendicular to each other.

[0082] Applying a time-varying potential difference between electrodes 612 and 624 via voltage controller 626 will cause complex changes in the potential of electrodes 614-622, depending on factors such as the resistivity of layer 610, the capacitance between the electrodes, and the polarization within layer 610. Furthermore, the optical state of various parts of layer 610 will undergo even more complex changes. Most commonly, when the voltage applied by voltage controller 626 changes, various parts of layer 610 will be perceived as "flickering".

[0083] In yet another embodiment, the display may be fabricated to include a backplane configured to enable low-power wave switching. (See reference...) Figures 7A to 7DThe backplane may include a rectangular substrate 700 on which a first plurality of conductive lines or traces 710 of varying lengths may be printed. One end of each conductive line 710 may be connected to a drive circuit or voltage controller (not shown). An insulating material layer 720 may then be applied over the first plurality of conductive lines 710, except for a plurality of gaps 730, exposing the unconnected ends of the first plurality of conductive lines 710. A second plurality of conductive lines or traces 740 may be applied over the insulating material layer 720 such that each conductive line 740 traverses and electrically contacts a corresponding first conductive line 710, but only one of the first conductive lines 710. This can be achieved by printing the second plurality of conductive lines 740 over the gaps 730 in the insulating material 720. The positions of the gaps in the insulating material layer and the second plurality of conductive lines are precisely positioned to prevent electrical short circuits between unrelated wires. Thus, each of the first plurality of conductive lines is electrically contacted by only one of the second plurality of conductive lines, and vice versa. One or more contact pads 751, 752 may also be applied to the exposed ends of the first conductive lines 710. One or more contact pads 751, 752 may provide locations for electrically connecting the backplane to the light-transmitting front electrode (not shown) of the display. Finally, a resistive material layer 760 may be applied to the second plurality of conductive lines 740, such that this resistive material layer 760 is in electrical contact with the second plurality of conductive lines 740. This resistive material layer is preferably the top layer of the backplane and will be in direct contact with the front plane laminate (FPL) of the display.

[0084] Each component in the backplane can be readily fabricated using techniques known to those skilled in the art, such as methods for manufacturing multilayer printed circuit boards. Various materials can be used for the different layers of the backplane. For example, materials used for insulating layers include, but are not limited to, dielectric materials, preferably photocurable solvent-free organic or silicon-based oligomers. Examples of materials that can be used for resistive layers include, but are not limited to, resistive carbon, ITO-filled polymers, PEDOT-filled polymers, and metal fillers. Similarly, any conductive material can be used to print first or second conductive lines, such as carbon or conductive metals like silver, nickel, and copper.

[0085] The material used to form the second plurality of conductive lines preferably has higher conductivity than the material used to form the resistive material layer. The combination of the second plurality of conductive lines and the resistive material layer essentially provides a series of highly conductive busbars, where the conductive lines act as individual busbars because the resistive material layer ensures uniform voltage around each line. The resistance of the resistive material layer can be selected relative to the length and spacing of the busbars. Preferably, the total resistance between the busbars is greater than or equal to 1 kOhm, more preferably greater than or equal to 10 kOhm to reduce power consumption. For example, in a configuration where the ratio of busbar length to spacing is 10, providing a resistive layer with a resistivity of 10 kOhms / square results in a total resistance of 1 kOhms between the busbars.

[0086] In another embodiment of the invention, a method for driving a display having the aforementioned backplane is provided. To drive the display, a driver with dual-level or tri-level output capability can be used, which preferably also has a floating (high-impedance) output capability. (See again...) Figures 7A to 7D The driver can be connected to the first plurality of conductive lines 710 along the left side of the substrate 700. In the first step, the driver can apply a voltage to the leftmost bus bar (“first bus bar”) of the second plurality of conductive lines 740 and short-circuit or leave the remaining bus bars floating. As used herein, “short-circuit” or “short-connected” means grounding a conductive line or conductive area, while “floating” or “floating” means electrically isolating a conductive line or conductive area. The electro-optic medium within the FPL located near the leftmost bus bar will switch immediately, and a color gradient from the switched electro-optic medium to the unswitched electro-optic medium will appear between the first bus bar and the subsequent bus bar (“second bus bar”). If the voltage controller is capable of pulse width modulation (PWM) or voltage modulation (VM) output, the driver can gradually increase the duty cycle or voltage to produce a more slowly developing gradient. After a period of time (the length of which can be determined by the switching speed required by the application), the driver can apply a voltage to the second bus bar while ending the voltage application to the first bus bar, and so on. In this way, the driver can gradually switch the electro-optical medium across the entire display in a controlled manner, while limiting the voltage application to a region where only the gradient exists between the switched and unswitched electro-optical media. Fortunately, PWM and VM outputs do not require a high-end function generator and can be implemented using, for example, a LabVIEW programming kit, an Arduino board coupled to a suitable voltage source, or certain off-the-shelf EPD drivers (e.g., available from ULTRACHIP).

[0087] If a wider gradient is needed, for example, the driver can continuously apply voltages at timed intervals on multiple adjacent busbars to gradually diffuse the gradient across the entire display. Finally, gradients can be created at any location on the display, and multiple gradients can exist simultaneously by applying patterns of opposite voltages on multiple busbars. Gradients can start and stop at any point on the display or at any time, and if multiple gradients are generated simultaneously, they can propagate in multiple directions at multiple speeds. Therefore, the complexity of the wave depends on the busbar spacing and the software control of the driver.

[0088] As described above, the insulating layer between the first and second plurality of conductive lines connects the drive circuitry to a distant region of the backplane. The different conductive lines can cross each other without short-circuiting. This configuration allows for a variety of backplane designs. For example, a backplane with a printed layer similar to the aforementioned rectangular backplane can alternatively be provided on a circular substrate.

[0089] For Figures 7A-7D The (existing) PWM drive scheme for displays is Figure 8 Depicted in [the text]. Figure 8 In this context, the drive signal with a frequency of 30Hz and ±15V has a variable duty cycle ranging from -1 to 1, which can be determined by referring to... Figure 9 As can be seen, a duty cycle of 0 to -1 (i.e., a negative duty cycle) corresponds to... Figure 9 The duty cycle shown is 0 to 1, the difference being that the voltage is -V, i.e., -15V. Applying a blue drive signal to one corner contact (e.g., pad 751) of the elongated-pitch contact display 700, while simultaneously applying an orange drive signal to the other corner contact (e.g., pad 752), produces... Figure 8 The toggle effect shown at the bottom. It should be understood that... Figure 8 The described method is generally applicable to driving displays with narrow, spaced contact points or isolated electrode displays (e.g., Figure 6 In addition, the blue drive signal has been supplemented with a solid black line for easier observation.

[0090] Back Figure 8 The transition will begin on the side with the blue drive signal (also known as the "left side") and will appear to end on the side where the orange trace is applied (also known as the "right side"). The orange drive signal has been supplemented with a black dashed line for easier observation. This diagram illustrates a single transition from one track state to another, such as from black to white, as along... Figure 8 As depicted at the bottom. Once in white mode, the display can be driven from white to black by reversing the duty cycle signal provided to the two contacts. However, the wave switching will again proceed from left to right.

[0091] Importantly, such as Figure 8As shown, the transition appears to be complete at approximately frame 40, at which point the trailing (orange) waveform has risen significantly above 0. [As used herein, a "frame" is a unit of time representing the step from the first duty cycle to the next adjacent duty cycle. The size of a frame is somewhat arbitrary; however, for optimal performance and to prevent damage to the display, ...] Figure 8 Each frame is approximately 100ms, for example, 80ms. Therefore, the number of voltage pulses at a given duty cycle is on the order of 2-5 at ±V; unlike... Figure 9 As long as it is described Figure 9 [For illustrative purposes only.] However, from frame 40 to frame 66, the visual appearance of the display will change negligibly, meaning there is an inherent static period before the banner can switch back to the opposite color. If Figure 8 Immediately after the transition shown, there is a wave in the same direction (from left to right) from (now) white to black, and the visual effect does not begin until about frame 67, or more than two seconds after the first switch appears to be complete.

[0092] Fortunately, the two transitions (from black to white and from white to black) of the combination of movements in the same direction (from left to right) result in a DC balance pair, which reduces wear and tear on the monitor, although there is no discernible visual effect for about 2 / 5 of the time. However, DC balance is only achieved when moving from (black to white and white to black) in the same direction (from left to right). Note in Figure 8 In the image, the orange trace is DC balanced, while the blue trace is completely positive and therefore not DC balanced. Therefore, if the monitor doesn't switch back to its original colors, excessive charge can damage it. Worse still, if the direction of the transition back (from white to black) is reversed (from right to left), i.e., the opposite polarity of the blue trace is applied to the right and the opposite polarity of the orange trace to the left, the DC imbalance is doubled (!), which will cause the monitor to deteriorate rapidly. Therefore, using... Figure 8 The driving scheme cannot achieve reciprocating wave switching, i.e., "ping-pong switching," without significantly degrading the display. Finally, it should be noted that the orange trace ends with a 100% duty cycle, which is essentially the rail voltage (see...). Figure 9 If there is a delay or "static" after the unidirectional transition, the electrophoretic medium will bounce back from the orbital state of the destination, resulting in the final state not being as saturated as expected.

[0093] Given the limitations of existing technology, there is a need for improved wave switching methods for spaced contact and isolated electrode displays (i.e., the types mentioned above). Figure 10 An improved waveform is shown that can be used for elongated-pitch contact displays driven by PWM or VM. Specifically, Figure 10 The waveform significantly reduces the relative time amount during which the display does not noticeably change its optical state, from a relative perspective... Figure 8 Approximately 40% of the driver solutions do not show a significant switch relative to Figure 10 Approximately 10% of the driver solutions do not show significant switching. Figure 10 The waveform also reduces bounce when the drive ends and the device is inserted to rest. Compared with existing methods ( Figure 8 Two significant changes are visible in the blue and orange lines at the beginning and end of the transition. Initially, the duty cycle of the orange line (right side) smoothly (but rapidly) increases from 0 to -1, eliminating the... Figure 8 The orange line experiences a sudden jump in its state. At the end of the transition, the duty cycle of the orange line (right) smoothly decreases from 1 to 0, eliminating the bounce. Furthermore, the visual transition occurs approximately between frames 0 and 55, providing a significant reduction in inactivity time. DC imbalance still exists at each end of the waveform, but it does provide the shortest possible smooth transition between consecutive updates in each rail state. Meanwhile, the blue line (left) has been extended for the visual transition to match the orange line, while the blue line still returns from duty cycle 1 to duty cycle 0, as... Figure 8 As shown, however, this occurs after the visible transformation is complete.

[0094] Figure 11 Alternative driving schemes for elongated-pitch contact displays using PWM or VM driving are shown. Figure 11 The drive scheme provides additional DC balancing at the end of each wave switching, however, the drive ratio is higher. Figure 10 More complex and potentially requiring more sophisticated voltage controllers. While both the blue (left) and orange (right) drive schemes resemble... Figure 10 Both start with a zero duty cycle, but the first 28 frames of the transition are used for DC balancing of both the blue and orange waveforms. Then, around frame 30, the wave will begin on the left side of the display. Around frame 55, the right side of the display will appear to have completed its transition. To achieve DC balancing, both drive schemes need to run until completion, resulting in approximately 20% of the switching time being imperceptible. Figure 10 Poor. However, Figure 11 The DC balance in the drive scheme allows the display to reverse direction in the next transition, achieving the desired "ping-pong switch". Reversing direction drive can be achieved by essentially providing the blue drive scheme at the right contact and the orange drive scheme at the left contact, or by flipping both the direction and polarity of the blue and orange drive schemes, while providing the modified blue and orange drive schemes to the left and right contacts, as done with the previous drive scheme.

[0095] As will be seen from the foregoing, the present invention provides a display and a driving method that enable the optical states of an electro-optic medium (especially a bistable medium, such as an electrophoretic medium) to shift and change, and to generate visually interesting patterns using very simple and inexpensive electrodes. Visually interesting patterns can be used to guide the observer or draw attention to otherwise static content, such as the content provided by a segmented electrode display, for example... Figure 12 As shown.

[0096] 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 invention. For example, the variable voltage is certainly not limited to a simple sine wave; a triangular wave, sawtooth wave, or square wave with a fixed or varying frequency can be used. Therefore, the entire foregoing description should be interpreted as illustrative rather than restrictive.

Claims

1. A method for driving an intermittent contact electro-optic display, comprising: Provides an intermittent contact electro-optical display, comprising: An electro-optic material layer, a first electrode layer and a second electrode layer on opposite sides of the electro-optic material layer, wherein the first electrode layer or the second electrode layer is light-transmitting. A first contact and a second contact spaced apart and electrically coupled to the first electrode layer on the first electrode layer, and A voltage controller coupled to the first contact and the second contact; The voltage controller provides a first time-varying drive signal to the first contact, wherein the first time-varying drive signal starts with a duty cycle of zero, scales up to a duty cycle of 1, and then returns to a duty cycle of zero; and The voltage controller provides a second time-varying drive signal to the second contact, wherein the second time-varying drive signal starts from a duty cycle of zero, scales to a duty cycle of -1, then scales to a duty cycle of 1, and then returns to a duty cycle of zero.

2. The method according to claim 1, wherein the slope of the second time-varying drive signal from a duty cycle of -1 to a duty cycle of 1 includes two different slopes of the duty cycle per unit time.

3. The method according to claim 1, further comprising: A third time-varying drive signal is provided to the first contact via the voltage controller, wherein the first time-varying drive signal starts with a duty cycle of zero, scales down to a duty cycle of -1, and then returns to a duty cycle of zero; and The voltage controller provides a fourth time-varying drive signal to the second contact, wherein the second time-varying drive signal starts from a duty cycle of zero, scales to a duty cycle of 1, then scales to a duty cycle of -1, and then returns to a duty cycle of zero.

4. A method for driving an intermittent contact electro-optic display, comprising: Provides an intermittent contact electro-optical display, comprising: An electro-optic material layer, a first electrode layer and a second electrode layer on opposite sides of the electro-optic material layer, wherein the first electrode layer or the second electrode layer is light-transmitting. A first contact and a second contact spaced apart and electrically coupled to the first electrode layer on the first electrode layer, and A voltage controller coupled to the first contact and the second contact; The voltage controller provides a first time-varying drive signal to the first contact, wherein the first time-varying drive signal starts with a duty cycle of zero, scales down to a duty cycle of -1, maintains a duty cycle of -1 for a sufficient time to provide DC balance to the first time-varying drive signal, then scales down to a duty cycle of 1, and then returns to a duty cycle of zero; and The voltage controller provides a second time-varying drive signal to the second contact, wherein the second time-varying drive signal starts with a duty cycle of zero, transitions to a duty cycle of 1 by experiencing a negative duty cycle impulse until the first time-varying drive signal is maintained at a duty cycle of -1, then proceeds to a duty cycle of 1, and then returns to a duty cycle of zero.

5. The method according to claim 4, further comprising: A third time-varying drive signal, identical to the second time-varying drive signal, is provided to the first contact. as well as A fourth time-varying drive signal, identical to the first time-varying drive signal, is provided to the second contact.

6. The method according to any one of the preceding claims, wherein the first time-varying drive signal and the second time-varying drive signal simultaneously achieve a duty cycle of 1.

7. The method according to any one of the preceding claims, wherein the frequency of the first driving signal and the second driving signal is 30 Hz or higher.

8. The method according to any one of the preceding claims, wherein the voltage amplitude of the first driving signal and the second driving signal is 15V to 30V.

9. The method according to any one of the preceding claims, wherein both the first electrode and the second electrode have at least two spaced contacts, and the voltage controller is arranged to change the potential difference between the two spaced contacts attached to each electrode.

10. The method according to any one of the preceding claims, wherein the electro-optic material comprises an electrophoretic material, the electrophoretic material comprising a plurality of charged particles disposed in a fluid and capable of moving through the fluid under the influence of an electric field.

11. The method of claim 10, wherein the charged particles and the fluid are confined within a plurality of capsules or microunits or discrete droplets surrounded by a continuous phase comprising a polymeric material.

12. The method according to any one of the preceding claims, wherein at least one of the first electrode and the second electrode is interrupted by at least one non-conductive region, such that the current must follow a non-linear path between the two contacts on the electrode.

13. The method according to any one of the preceding claims, wherein at least one of the first electrode and the second electrode is divided into a plurality of segments having different resistances per unit length.

14. The method according to any one of the preceding claims, wherein at least one of the first electrode and the second electrode is divided into a plurality of segments having different capacitances per unit area.

15. The method according to any one of the preceding claims, wherein at least a portion of one of the first electrode and the second electrode is provided with a passivation layer disposed between the electrode and the electro-optic material layer.

16. The method according to any one of the preceding claims, wherein the first time-varying drive signal or the second time-varying drive signal comprises a sine wave, a triangular wave, a sawtooth wave, or a square wave.

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