Classifications

• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
  • G09G3/3433—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using light modulating elements actuated by an electric field and being other than liquid crystal devices and electrochromic devices
  • G09G3/344—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using light modulating elements actuated by an electric field and being other than liquid crystal devices and electrochromic devices based on particles moving in a fluid or in a gas, e.g. electrophoretic devices
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/1675—Constructional details
  • G02F1/1676—Electrodes
  • G02F1/16766—Electrodes for active matrices
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2300/00—Aspects of the constitution of display devices
  • G09G2300/04—Structural and physical details of display devices
  • G09G2300/0421—Structural details of the set of electrodes
  • G09G2300/043—Compensation electrodes or other additional electrodes in matrix displays related to distortions or compensation signals, e.g. for modifying TFT threshold voltage in column driver
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2300/00—Aspects of the constitution of display devices
  • G09G2300/08—Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
  • G09G2300/0809—Several active elements per pixel in active matrix panels
  • G09G2300/0819—Several active elements per pixel in active matrix panels used for counteracting undesired variations, e.g. feedback or autozeroing
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2310/00—Command of the display device
  • G09G2310/06—Details of flat display driving waveforms
  • G09G2310/068—Application of pulses of alternating polarity prior to the drive pulse in electrophoretic displays
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2320/00—Control of display operating conditions
  • G09G2320/02—Improving the quality of display appearance
  • G09G2320/0204—Compensation of DC component across the pixels in flat panels
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2330/00—Aspects of power supply; Aspects of display protection and defect management
  • G09G2330/02—Details of power systems and of start or stop of display operation
  • G09G2330/027—Arrangements or methods related to powering off a display

Definitions

• U.S. Patent Application No. 17/388,417 is related to U.S. Patent Application No. 17/032,189 (now U.S. Patent No. 11,107,425) filed on September 25, 2000, U.S. Patent Application No. 16/745,473 (now U.S Patent No. 10,825,405) filed on January 17, 2020, and U.S. Patent Application No. 15/992,363 (now U.S. Patent No. 10,573,257) filed on May 30, 2018 which claimed priority to U.S. Provisional Patent Application No. 62/512,212 filed on May 30, 2017.
• This application is also related to U.S. Patent Application 15/015,822 filed on Feb. 04, 2016 (now U.S. Patent No. 10,163,406); U.S.
• Patent Application 15/014,236 filed on Feb. 03, 2016 (now U.S. Patent No. 10,475,396); and U.S. Patent Application 15/266,554 filed on September 15, 2016 (now U.S. Patent No. 10,803,813).
• All of the above-listed patents and applications are incorporated by reference in their entireties.
• the subject matter disclosed herein relates to means and methods to drive electro-optic displays. Specifically, the subject matter is related to backplane designs for electro-optic displays and methods for driving and/or discharging such displays.
• Electrophoretic displays or EPDs are commonly driven by so-called DC- balanced waveforms.
• DC-balanced waveforms have been proven to improve long-term usage of EPDs by reducing severe hardware degradations and eliminating other reliability issues.
• the DC-balance waveform constraint limits the set of possible waveforms that are available to drive the EPD display, making it difficult or sometimes impossible to implement advantageous features via a waveform mode. For example, when implementing a “flash-less” white-on-black display mode, excessive white edge accumulation may become visible when gray-tones that have transitioned to black are next to a non-flashing black background.
• a DC-imbalanced drive scheme may have worked well, but such drive scheme requires breaking the DC-balance constraint.
• DC- imbalanced drive schemes or waveforms can cause hardware degradations over time which shortens display devices’ lifetime.
• electro-optic displays capable of operating with DC-imbalanced waveforms or drive schemes without suffering hardware degradations.
• an electrophoretic display having a plurality of display pixels, each of the plurality of display pixels may include a pixel electrode for driving the display pixel, a single thin film transistor (TFT) coupled to the pixel electrode for transmitting waveforms to the pixel electrode, a front plane laminate (FPL) coupled to the single thin film transistor, and a storage capacitor coupled to the pixel electrode and placed in parallel with the FPL, where the storage capacitor is configured to be sufficiently ohmiealfy conductive to allow the discharge of remnant voltages from the FPL through the storage capacitor.
• TFT thin film transistor
• FPL front plane laminate
• the storage capacitor’s resistance is approximately the same as the FPL resistance.
• the storage capacitor’s resistance value is between one third and three times the FPL resistance.
• the electrophoretic display may further comprising a discharge capacitor in parallel to the storage capacitor.
• Figure 1 is one embodiment of an equivalent circuit of a display pixel in accordance with the subject matter presented herein;
• Figures 2 A and 2B are graphs illustrating graytone and ghosting shifts of a display due to shifts in TFT performance
• Figure 3 is an exemplary pixel design in accordance with the subject matter presented herein to enable the use of post-drive discharging without introducing optical shifts
• Figure 4 is another pixel design in accordance with the subject matter presented herein to enable the use of post-drive discharging without introducing optical shifts
• Figure 5 are voltage sequences for an active update followed by a discharge
• Figure 6 is another pixel design in accordance with the subject matter presented herein to enable the use of post-drive discharging without introducing optical shifts
• Figure 7 is yet another pixel design in accordance with the subject matter presented herein to enable the use of post-drive discharging without introducing optical shifts;
• Figure 8 are voltage sequences for an active update followed by discharging;
• Figure 9 is another pixel design in accordance with the subject matter presented herein;
• Figure 10a illustrates one experimental set up for measuring FPL voltages
• Figures 10b- 10c illustrate measured FPL voltages using the setup illustrated in Figure 10a
• Figure lOd illustrates one example of simulated active matrix driving during a drive phase
• Figures lla-lle illustrate measured FPL voltages and display lightness using different Rd values using the setup illustrated in Figure 10a;
• Figure 12 illustrates a cross sectional view of one configuration for a display pixel in accordance with the subject matter presented herein;
• Figure 13 illustrates yet another pixel design in accordance with the subject matter presented herein.
• Figure 14 illustrates a cross sectional view of another configuration for a display pixel in accordance with the subject matter presented herein.
• the subject matter disclosed herein relates to improving electro-optic display durability. Specifically, it is related to improving optical performance shifts such as mitigating gray-tone shifts and ghosting shifts caused by component stresses.
• optical property is typically color perceptible to the human eye, it may be another optical property, such as optical transmission, reflectance, luminescence or, in the case of displays intended for machine reading, pseudo-color in the sense of a change in reflectance of electromagnetic wavelengths outside the visible range.
• gray state is used herein in its conventional meaning in the imaging art to refer to a state intermediate two extreme optical states of a pixel, and does not necessarily imply a black-white transition between these two extreme states.
• E Ink patents and published applications referred to below describe electrophoretic displays in which the extreme states are white and deep blue, so that an intermediate "gray state” would actually be pale blue. Indeed, as already mentioned, the change in optical state may not be a color change at all.
• black and “white” may be used hereinafter to refer to the two extreme optical states of a display, and should be understood as normally including extreme optical states which are not strictly black and white, for example, the aforementioned white and dark blue states.
• the term “monochrome” may be used hereinafter to denote a display or drive scheme which only drives pixels to their two extreme optical states with no intervening gray states.
• each pixel is composed of a plurality of sub-pixels each of which can display less than all the colors which the display itself can show.
• each pixel is composed of a red sub-pixel, a green sub-pixel, a blue sub-pixel, and optionally a white sub-pixel, with each of the sub-pixels being capable of displaying a range of colors from black to the brightest version of its specified color.
• electro-optic displays are known.
• One type of electro-optic display is a rotating bichromal member type as described, for example, in U.S. Patents 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 this type of display is often referred to as a "rotating bichromal ball" display, the term "rotating bichromal member" is preferred as more accurate since in some of the patents mentioned above the rotating members are not spherical).
• Such a display uses a large number of small bodies (typically spherical or cylindrical) which have two or more sections with differing optical characteristics, and an internal dipole. These bodies are suspended within liquid-filled vacuoles within a matrix, the vacuoles being filled with liquid so that the bodies are free to rotate. The appearance of the display is changed by applying an electric field thereto, thus rotating the bodies to various positions and varying which of the sections of the bodies is seen through a viewing surface.
• This type of electro-optic medium is typically bistable.
• an electrochromic medium for example an electrochromic medium in the form of a nanochromic film comprising an electrode formed at least in part from a semi-conducting metal oxide and a plurality of dye molecules capable of reversible color change attached to the electrode; see, for example O'Regan, B., et ah, Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24 (March 2002). See also Bach, U., et ah, Adv. Mater., 2002, 14(11), 845. Nanochromic films of this type are also described, for example, in U.S. Patents Nos. 6,301,038; 6,870,657; and 6,950,220. This type of medium is also typically bistable.
• Electrophoretic display One type of electro-optic display, which has been the subject of intense research and development for a number of 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. Electrophoretic displays can have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared with liquid crystal displays.
• electrophoretic media require the presence of a fluid.
• this fluid is a liquid, but electrophoretic media can be produced using gaseous fluids; see, for example, Kitamura, T., et al., "Electrical toner movement for electronic paper-like display", IDW Japan. 2001, Paper HCSl-1, and Yamaguchi, Y., et al., "Toner display using insulative particles charged triboelectrically", IDW Japan. 2001, Paper AMD4-4). See also U.S. Patents Nos. 7,321,459 and 7,236,291.
• Such gas-based electrophoretic media appear to be susceptible to the same types of problems due to particle settling as liquid-based electrophoretic media, when the media are used in an orientation which permits such settling, for example in a sign where the medium is disposed in a vertical plane. Indeed, particle settling appears to be a more serious problem in gas- based electrophoretic media than in liquid-based ones, since the lower viscosity of gaseous suspending fluids as compared with liquid ones allows more rapid settling of the electrophoretic particles.
• Microcell structures, wall materials, and methods of forming microcells see for example United States Patents Nos. 7,072,095 and 9,279,906; and
• microcell electrophoretic display A related type of electrophoretic display is a so-called "microcell electrophoretic display".
• the charged particles and the fluid are not encapsulated within microcapsules but instead are retained within a plurality of cavities formed within a carrier medium, typically a polymeric film. See, for example, U.S. Patents Nos. 6,672,921 and 6,788,449, both assigned to Sipix Imaging, Inc.
• electrophoretic media are often opaque (since, for example, in many electrophoretic media, the particles substantially block transmission of visible light through the display) and operate in a reflective mode
• many electrophoretic displays can be made to operate in a so-called "shutter mode" in which one display state is substantially opaque and one is light-transmissive. See, for example, U.S. Patents Nos. 5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; 6,225,971; and 6,184,856.
• Di electrophoretic displays which are similar to electrophoretic displays but rely upon variations in electric field strength, can operate in a similar mode; see U.S. Patent No. 4,418,346.
• Electro-optic media operating in shutter mode may be useful in multi-layer structures for full color displays; in such structures, at least one layer adjacent the viewing surface of the display operates in shutter mode to expose or conceal a second layer more distant from the viewing surface.
• An encapsulated electrophoretic display typically does not suffer from the clustering and settling failure mode of traditional electrophoretic devices and provides further advantages, such as the ability to print or coat the display on a wide variety of flexible and rigid substrates.
• the word “printing” is intended to include all forms of printing and coating, including, but without limitation: pre-metered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating; roll coating such as knife over roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; silk screen printing processes; electrostatic printing processes; thermal printing processes; ink jet printing processes; electrophoretic deposition (See U.S. Patent No. 7,339,715); and other similar techniques.)
• pre-metered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating
• roll coating such as knife over roll coating, forward and reverse roll coating
• gravure coating dip coating
• spray coating meniscus coating
• spin coating spin coating
• brush coating air knife coating
• silk screen printing processes electrostatic printing processes
• thermal printing processes ink jet printing processes
• electrophoretic deposition See U.S. Patent No. 7,339,715); and other similar
• An electrophoretic display normally comprises a layer of electrophoretic material and at least two other layers disposed on opposed sides of the electrophoretic material, one of these two layers being an electrode layer. In most such displays both the layers are electrode layers, and one or both of the electrode layers are patterned to define the pixels of the display. For example, one electrode layer may be patterned into elongate row electrodes and the other into elongate column electrodes running at right angles to the row electrodes, the pixels being defined by the intersections of the row and column electrodes.
• one electrode layer has the form of a single continuous electrode and the other electrode layer is patterned into a matrix of pixel electrodes, each of which defines one pixel of the display.
• one electrode layer has the form of a single continuous electrode and the other electrode layer is patterned into a matrix of pixel electrodes, each of which defines one pixel of the display.
• only one of the layers adjacent the electrophoretic layer comprises an electrode, the layer on the opposed side of the electrophoretic layer typically being a protective layer intended to prevent the movable electrode damaging the electrophoretic layer.
• electrophoretic displays may be constructed with two continuous electrodes and an electrophoretic layer and a photoelectrophoretic layer between the electrodes. Because the photoelectrophoretic material changes resistivity with the absorption of photons, incident light can be used to alter the state of the electrophoretic medium.
• FIG. 1 Such a device is illustrated in FIG. 1.
• the device of FIG. 1 works best when driven by an emissive source, such as an LCD display, located on the opposed side of the display from the viewing surface.
• the devices of U.S. Pat. No. 6,704,133 incorporated special barrier layers between the front electrode and the photoelectrophoretic material to reduce “dark currents” caused by incident light from the front of the display that leaks past the reflective electro-optic media.
• the light- transmissive electrically-conductive layer will be carried on a light-transmissive substrate, which is preferably flexible, in the sense that the substrate can be manually wrapped around a drum (say) 10 inches (254 mm) in diameter without permanent deformation.
• the term "light-transmissive" is used in this patent and herein to mean that the layer thus designated transmits sufficient light to enable an observer, looking through that layer, to observe the change in display states of the electro-optic medium, which will normally be viewed through the electrically-conductive layer and adjacent substrate (if present); in cases where the electro-optic medium displays a change in reflectivity at non-visible wavelengths, the term "light-transmissive" should of course be interpreted to refer to transmission of the relevant non-visible wavelengths.
• the substrate will typically be a polymeric film, and will normally have a thickness in the range of about 1 to about 25 mil (25 to 634 pm), preferably about 2 to about 10 mil (51 to 254 pm).
• the electrically-conductive layer is conveniently a thin metal or metal oxide layer of, for example, aluminum or ITO, or may be a conductive polymer.
• PET poly (ethylene terephthalate)
• PET poly (ethylene terephthalate) films coated with aluminum or ITO are available commercially, for example as "aluminized Mylar” ("Mylar” is a Registered Trade Mark) from E.I. du Pont de Nemours & Company, Wilmington DE, and such commercial materials may be used with good results in the front plane laminate.
• a processes for forming electro-optic displays using the front plane laminates may include the use of a thermal lamination process to attach the FPL or double release film to the backplane.
• the backplane may be of the direct drive segmented variety with one or more patterned conductive traces, or may be of the non-linear circuit variety (e.g. active matrix).
• U.S. Patent No. 7,561,324 describes a so-called "double release sheet" which is essentially a simplified version of the front plane laminate of the aforementioned U.S. Patent No. 6,982,178.
• One form of the double release sheet comprises a layer of a solid electro optic medium sandwiched between two adhesive layers, one or both of the adhesive layers being covered by a release sheet.
• Another form of the double release sheet comprises a layer of a solid electro-optic medium sandwiched between two release sheets.
• Both forms of the double release film are intended for use in a process generally similar to the process for assembling an electro-optic display from a front plane laminate already described, but involving two separate laminations; typically, in a first lamination the double release sheet is laminated to a front electrode to form a front sub-assembly, and then in a second lamination the front sub-assembly is laminated to a backplane to form the final display, although the order of these two laminations could be reversed if desired.
• U. S. Patent No. 7,839,564 describes a so-called "inverted front plane laminate", which is a variant of the front plane laminate described in the aforementioned U.S. Patent No. 6,982, 178.
• This inverted front plane laminate comprises, in order, at least one of a light- transmissive protective layer and a light-transmissive electrically-conductive layer; an adhesive layer; a layer of a solid electro-optic medium; and a release sheet.
• This inverted front plane laminate is used to form an electro-optic display having a layer of lamination adhesive between the electro-optic layer and the front electrode or front substrate; a second, typically thin layer of adhesive may or may not be present between the electro-optic layer and a backplane.
• Such electro-optic displays can combine good resolution with good low temperature performance.
• While displays of the invention are intended to display images for long periods of time with little to no energy input, the looped displays, described above, can be used to refresh content on the same time scale as emissive displays, e.g., large format LED displays.
• Displays of the invention can display two different images in less than one hour, e.g., in less than 10 minutes, e.g., in less than five minutes, e.g., in less than two minutes.
• the refresh periods can be staggered, depending upon the use of the display. For example, a transportation schedule may be refreshed every five minutes with an advertisement that lasts for 30 seconds, whereupon the transportation schedule is returned for another five minute period.
• one way of enabling the use of DC-imbalanced waveforms is discharging the display module after an active update.
• discharging involves short- circuiting the display’s imaging film to drain away residual charges that builds-up on the imaging film (e.g., a layer of electrophoretic material) due to the DC imbalance drive.
• the use of update Post Drive Discharging (uPDD or UPD to be referred to herein) has successfully demonstrated the reduction in the build-up of residual charges (as measured by the remnant voltage) and the corresponding module polarization that would have resulted in permanent degradation of the imaging film due to electrochemistry.
• Such polarization occurs in various ways.
• a first (for convenience, denoted “Type I”) polarization an ionic double layer is created across or adjacent a material interface.
• a positive potential at an indium-tin-oxide (“GGO”) electrode may produce a corresponding polarized layer of negative ions in an adjacent laminating adhesive.
• GGO indium-tin-oxide
• the decay rate of such a polarization layer is associated with the recombination of separated ions in the lamination adhesive layer.
• the geometry of such a polarization layer is determined by the shape of the interface, but may be planar in nature.
• nodules, crystals or other kinds of material heterogeneity within a single material can result in regions in which ions can move or less quickly than the surrounding material.
• the differing rate of ionic migration can result in differing degrees of charge polarization within the bulk of the medium, and polarization may thus occur within a single display component.
• Such a polarization may be substantially localized in nature or dispersed throughout the layer.
• polarization may occur at any interface that represents a barrier to charge transport of any particular type of ion.
• One example of such an interface in a microcavity electrophoretic display is the boundary between the electrophoretic suspension including the suspending medium and particles (the “internal phase”) and the surrounding medium including walls, adhesives and binders (the “external phase”).
• the internal phase is a hydrophobic liquid whereas the external phase is a polymer, such as gelatin. Ions that are present in the internal phase may be insoluble and non-diffusible in the external phase and vice versa.
• Polarization may occur during a drive pulse. Each image update is an event that may affect remnant voltage.
• a positive waveform voltage can create a remnant voltage across an electro-optic medium that is of the same or opposite polarity (or nearly zero) depending on the specific electro-optic display.
• an electrophoretic display operates by motion of charged particles, which inherently causes a polarization of the electro-optic layer, in a sense a preferred electrophoretic display is not one in which no remnant voltages are always present in the display, but rather one in which the remnant voltages do not cause objectionable electro-optic behavior.
• the remnant impulse will be minimized and the remnant voltage will decrease below 1 V, and preferably below 0.2 V, within 1 second, and preferably within 50 ms, so that that by introducing a minimal pause between image updates, the electrophoretic display may affect all transitions between optical states without concern for remnant voltage effects.
• electrophoretic displays operating at video rates or at voltages below +/-15 V these ideal values should be correspondingly reduced. Similar considerations apply to other types of electro-optic display.
• remnant voltage as a phenomenon is at least substantially a result of ionic polarization occurring within the display material components, either at interfaces or within the materials themselves. Such polarizations are especially problematic when they persist on a meso time scale of roughly 50 ms to about an hour or longer.
• Remnant voltage can present itself as image ghosting or visual artifacts in a variety of ways, with a degree of severity that can vary with the elapsed times between image updates. Remnant voltage can also create a DC imbalance and reduce ultimate display lifetime. The effects of remnant voltage therefore may be deleterious to the quality of the electrophoretic or other electro-optic device and it is desirable to minimize both the remnant voltage itself, and the sensitivity of the optical states of the device to the influence of the remnant voltage.
• a post-drive or post-update discharging may be performed using a readily available thin-film-transistor (TFT) backplane 100 for an EPD and the EPD’s controller circuitry, as illustrated in Figure 1.
• TFT thin-film-transistor
• each display pixel may include a thin film transistor UPD (e.g., TFT (upd) ) 102 that can be configured to provide a certain degree of electrical conduction such that the display’s top plane 106 and source (or data) line VS are held at the same voltage potential for some time (e.g., ground).
• TFT thin film transistor
• the TFT (upd) 102 is designed to function as the pixel controlling transistor for providing or transmitting driving waveforms to the pixel’s pixel electrode 104.
• the TFT (upd) 102 is usually configured to operate in a conduction state (i.e., the “ON” state) for a very short amount of time in comparison to the non-conduction state (i.e., the “OFF” state), for example, in the ratio of more than 1:1000 of “ON” time over “OFF” time. While the use of uPDD will change this ratio to about 1 :2 or 1 : 50 depending on the uPDD configurations, which leads to positive bias stress after long terms of usage, in some cases the usage will amount to stress normally caused by tens of thousands of image updates or more. Positive bias stress is known to cause threshold voltage shifts in amorphous silicon TFTs that is permanent.
• a shift in threshold voltage can result in behavior changes to the affected TFT and the TFT backplane, which in turn results in optical shifts in the optical performances of the EPD.
• the optical shift due to uPDD has been observed and is illustrated in Figures 2A and 2B.
• display gray-tone ( Figure 2A) and ghosting shift ( Figure 2B) values can increase significantly in a two year period after tens of thousands update cycles.
• TFT (upd) 102 With using only a single TFT such as the TFT (upd) 102 illustrated in Figure 1, normal image updates and uPDDs are both achieved through the same TFT (i.e., TFT (upd) ).
• an additional TFT may be added to each pixel and used solely for the uPDD discharging scheme. While the overall discharging scheme remains the same, the pixel TFT (e.g., TFT (upd) 102 of Figure 1) that is used for normal display operation will be used only for active display updates, just like in standard active-matrix driving of EPDs that do not incorporate the discharging.
• This configuration ensures that the performance of the pixel TFT used for normal display operation is stable and unaffected by the discharging. While the additional TFT used for discharging may experience threshold voltage shift due to positive bias stress but this will not cause optical shifts in the EPD, and this will not affect the discharging operation as long as the TFT is turned on during discharging (i.e., as long as the potential threshold voltage shift is account for by the discharging scheme).
• Such configuration can allow for stable display operation without optical response shifts while at the same time allowing for DC-imbalanced waveforms as enabled by post-drive discharging.
• a display pixel 300 may include an active component dedicated for draining the remnant voltage or excessive charges from the electrophoretic film 314.
• This active component may be a transistor of any kind (e.g., TFT, CMOS etc.) or any other component that may be activated or turned on by an application of an electrical (e.g., voltage) or optical energy, devices such as a diode or a photo detector/diode, or any electrically/optically activated switch in general.
• a TFT e.g., an n-type TFT
• a designated transistor TFT(dis) 304 may be used for the purpose of discharging the charges of the remnant voltage within the electrophoretic imaging film 314.
• the gate of the TFT (upd) 302 is connected to the select lines (e.g., Vg(upd) 308) from the gate driver outputs, while the gate of the TFT(dis) 304 is connected to a discharge select line such as the Vg(dis) 306, where this select line may be used to turn on and off the TFT (dis) 304 at its gate (e.g., by supply a voltage to the transistor’ s gate through the select line to affect the gate-source or gate-drain potential).
• select lines e.g., Vg(upd) 308
• Vg(upd) 306 a discharge select line
• this select line may be used to turn on and off the TFT (dis) 304 at its gate (e.g., by supply a voltage to the transistor’ s gate through the select line to affect the gate-source or gate-drain potential).
• all the pixel discharge select lines for multiple pixels may be connected together to a single display output such as to turn on all the pixel discharge TFT (e.g., TFT (diS) 304) transistors of all the display pixels of a display at the same time for simultaneous discharging of the whole display.
• the source lines of the TFT( upd) 302 and the TFT( dis) 304 may be both connected to the data lines Vs 310.
• the TFT (dis) 304 may be turned off for all the pixels while the TFT (upd) 302 is used for active updating of the display.
• the TFT (dis) 304 can be turned on while the TFT (upd) 302 may be turned off.
• either or both the TFT (upd) 302 and TFT (dis) 304 may be an n- type transistor.
• the source of the TFT (upd) 302 may be electrically coupled to the source line Vs 310, and the drain of the TFT (upd) 302 may be coupled to the pixel electrode 312 of the display pixel 300.
• the TFT (dis) 304 transistor is an n-type transistor, its source may be coupled to the source line Vs 310, while its drain may be coupled to the pixel electrode 312.
• charges from the electrophoretic film 314 may be drained or discharged through the TFT (dis) 304 and/or the source line Vs 310.
• FIG. 4 illustrates another embodiment of a display pixel 400 in accordance with the subject matter presented herein.
• a discharge TFT (dis) 402 may be electrically coupled to an EPD’s top plane 404 (e.g., connected to the EPD’s common electrode) and the Vcom 406 voltage line as shown in Figure 4 (e.g., the discharge TFT’s 402 drain is directly coupled to the EPD’s top plane 404, while its source is coupled to pixel’s pixel electrode 408).
• the discharging of the display module does not occur through the source drivers (e.g., Vs 410) but instead is done directly through the top plane connection.
• the TFT (dis) 402 may be activated through the select line Vg (dis) 412, while the transistor TFT (upd) 414 may be activated by through the select line Vg (upd) 416, where the two select lines (i.e., Vg( dis) 412 and Vg( upd) 416) may be optionally not electrically coupled.
• Figure 5 illustrates an exemplary voltage sequence that may be applicable to either of the two proposed pixel designs presented in Figures 3 and 4. This voltage sequence ignores potential RC time constraints that may appear when switching from one voltage to another or that may be introduced during power down for example.
• Vg(upd) is connected to the select line, as in standard active-matrix driving, switching between a high and a low voltage to turn on and off the TFT. During the active update, Vcom may be held constant at a voltage that is typically equal to the kickback voltage of TFT (upd) .
• Vs is connected to the data line that provides the data signal to refresh the pixel with the desired waveform.
• Vg(dis) is connected to a low voltage in order to keep TFT(dis) turned off.
• Vg(upd) is turned off, and Vcom and Vs are held at OV.
• Vg(dis) is turned on in order to short-circuit the electrophoretic imaging film through TFT(dis).
• the voltage sequence shown in Figure 5 is an exemplary illustration of the discharging scheme using the new TFT pixel design.
• This new TFT pixel design is flexible enough to accommodate more complicated implementations of the discharging scheme. The main idea is that the discharging happens by turning on a dedicated TFT while leaving the pixel TFT used for normal display operation out of the discharging operation.
• TFT( upd) and TFT(dis) are both N-type TFTs. These transistors could also be both P-type TFT or N-type and P-type each.
• Figure 6 One of the example based on the circuit in Figure 3 is shown in Figure 6, where both the TFT( upd) 604 and TFT(dis) 602 are P-type TFTs.
• FIG. 7 shows another possible implementation of the subject matter presented herein where a resistor Rdis 702 is placed in parallel with the storage capacitor Cs 704 of the pixel. As shown, resistor Rdis 702 is also coupled to both the pixel electrode 706 and the common electrode 708. The purpose of this resistor is to provide a pathway to discharge the remnant voltage from the electrophoretic imaging film at the end of a driving period. The benefit of this pixel design is that it does not require adding an extra line Vgdis to control the second TFT.
• Rdis 702 now has a fixed resistance value, the resistance value of Rdis 702 needs to be designed appropriately.
• the RC constant associated with the addition of Rdis 702 to the pixel circuit, including the pixel electrode and the storage capacitor needs to be larger than the driving frame time in order to achieve the required pixel voltage holding characteristics during the frame time. This RC constant also needs to be low enough to provide sufficient discharging at the end of the driving period.
• the Rdis 702 may also be replaced with a field switchable shunt resistor using amorphous silicon or any other technologies that provide an appropriate resistance in parallel with the electrophoretic imaging film for discharging without preventing normal driving operation.
• the subject matter presented herein also enables some additional usage modes that could be beneficial as described below.
• FIG. 8 shows an exemplary voltage sequence applicable only to the circuitry presented in Figure 3 where the TFT upd 302 and TFTdis 304 have dedicated gate lines.
• the TFT upd 302 and the TFTdis 304 are both turned on during the active update stage, while the TFTdis 304 may or may not be turned on at the end of the update for discharging.
• the TFTdis 304 could provide extra current for faster pixel charging that could enable for example higher frame rate driving.
• the TFTdis 304 in proposed pixel designs can also be used as a global update transistor. By turning on TFTdis 304 and turning off TFT upd 302, we could prevent long term positive bias on TFT upd 302 when the global update is performed.
• Figure 9 illustrates another embodiment of the subject matter disclosed herein. Similar to the setup presented in Figure 7, a display apparatus 900 may use a resistor Rd 902 connected across the FPL 904 layer to discharge remnant charges and/or remnant voltages, thereby spare the pixel TFT 906 the additional stress and device degradation induced by having to be turned on to discharge the remnant charges.
• a resistor Rd 902 may be placed in parallel with the storage capacitor Cs 908 to create a pathway for draining the remnant charges.
• the storage capacitor Cs 908 itself may be configured to be “leaky” and provides a pathway for draining the remnant charges.
• the term leaky is defined herein as the dielectric resistance of the capacitor (e.g., Cs 908) has decreased to the point where the capacitor can ohmically conduct sufficient current to allow the remnant charges to be drained or discharged.
• the resistance value of the resistor Rd or the dielectric resistance value of the capacitor may be chosen to be between 1/3 and 3 times the resistance of the FPL 904 layer or
• Figure lOd illustrates that each frame consists of holding a FPL voltage VFPL at a desired level for 1ms followed by floating (i.e., no current is applied to the circuit) for 9ms to simulate the active matrix drive scheme.
• the front plane laminate or FPL layer as described herein may include a light-transmissive electrically-conductive layer; a layer of a solid electro-optic medium in electrical contact with the electrically-conductive layer; an adhesive layer; and a release sheet.
• this FPL layer may include another light transmissive electrically-conductive layer instead of the release sheet.
• Figure 11a illustrates measured FPL voltages during the driving phase and Figure lib illustrates display lightness during the driving phase;
• Figure 11c illustrates the measured FPL voltages during the floating phase and
• Figure lid illustrates the lightness during the floating phase;
• Figure lie illustrates the measured FPL voltages at the end of the floating phase (i.e., remnant charges) for four different Rd values and the two different test waveforms.
• the storage capacitor capacitance is usually chosen such that it is sufficient to maintain the FPL voltage during frame time (Cs * R FPL » frame time)
• the resistance value of Rd is preferably not too small compared to the FPL resistance value R EPL to prevent a rapid discharge of the FPL voltage during frame time, which can cause loss of ink speed during the driving phase.
• the resistance value of Rd cannot be too large compared to that of R EPL neither, otherwise the benefit of having this passive discharging pathway is diminished.
• the resistance value of Rd or the storage capacitor’s ohmic resistance may be chosen to be
• the Rd or the storage capacitor’s ohmic resistance value may be set to be approximately the same as the REPL value.
• the storage capacitor’s ohmic resistance may be configured to be between 90% to 110% of the REPL value; or the storage capacitor’s ohmic resistance may be configured to be between 80% to 120% of the REPL value; or the storage capacitor’s ohmic resistance may be configured to be between 70% to 130% of the REPL value; or the storage capacitor’s ohmic resistance may be configured to be between 50% to 150% of the REPL value; or the storage capacitor’s ohmic resistance may be configured to be approximately between one third to three times of the RFPL value.
• this configuration allows for the discharging of the remnant voltages while eliminate the need to end the waveform with a grounding frame.
• this configuration also reduces optical kickback and allows the white state to be more white (see Figure lid) and thereby achieve a better contrast ratio.
• a display pixel 1200 may include a pixel TFT 1202 positioned on a glass substrate 1206 and adjacent to a storage capacitor 1204. Where this TFT 1202 may include a source 1206, a drain 1210 and a gate 1212. The storage capacitor 1204 may he connected to the drain 1210 of the TFT 1202 through a pixel electrode 1214 (e.g., ITO).
• a pixel electrode 1214 e.g., ITO
• this storage capacitor 1204 may be, for example, doped with dopants to sufficiently reduce its dielectric resistance to allow the remnant charges to be discharged.
• an additional capacitor may be added to a display pixel and configured to be leaky to create a pathway for discharging remnant voltages.
• a discharge capacitor 1302 may be positioned in parallel to a storage capacitor 1304, and this discharge capacitor 1302 may be configured to be leaky such that it can ohmically conduct sufficient current to allow the remnant charges to be discharged.
• this discharge capacitor 1400 may be positioned on the same substrate 1402 and adjacent to a storage capacitor 1404 and pixel TFT 1406,
• the TFT 1406 can have a source 1408, a drain 1410 and a gate 1412, where the drain 1410 may be electrically coupled to the discharge capacitor 1400 and the storage capacitor 1404 through a pixel electrode 1414.

Landscapes

• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• General Physics & Mathematics (AREA)
• Nonlinear Science (AREA)
• Computer Hardware Design (AREA)
• Theoretical Computer Science (AREA)
• Optics & Photonics (AREA)
• Electrochromic Elements, Electrophoresis, Or Variable Reflection Or Absorption Elements (AREA)
• Liquid Crystal Display Device Control (AREA)
• Control Of Indicators Other Than Cathode Ray Tubes (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=85087193

Family Applications (1)

Country Status (5)

Family Cites Families (7)

• 2022
  • 2022-07-26 CN CN202280052308.3A patent/CN117716418A/zh active Pending
  • 2022-07-26 EP EP22850164.9A patent/EP4377947A1/de active Pending
  • 2022-07-26 KR KR1020247001983A patent/KR20240022641A/ko unknown
  • 2022-07-26 WO PCT/US2022/038280 patent/WO2023009480A1/en active Application Filing
  • 2022-07-27 TW TW111128136A patent/TWI815577B/zh active

Also Published As

Similar Documents

Legal Events