Piezoelectric electrophoresis display

Abstract

Providing piezoelectric electrophoretic displays. [Solution] An electro-optical display is provided herein, the electro-optical display having a layer of electrophoretic material, a first conductive layer, and a piezoelectric material positioned between the layer of electrophoretic material and the first conductive layer, wherein the piezoelectric material overlaps with a portion of the layer of electrophoretic material, and a portion of the first conductive layer overlaps with the rest of the electrophoretic material. In one embodiment, the electro-optical display further comprises a second conductive material positioned adjacent to the layer of electrophoretic material and on the opposite side from the piezoelectric material.

Description

[Technical Field]

[0001] (Reference to related applications) This application relates to and claims priority from U.S. Provisional Application No. 62 / 673,092, filed on 17 May 2018. This application also relates to U.S. Provisional Application No. 62 / 727,033, filed on 5 September 2018.

[0002] The entire disclosure of the aforementioned application is incorporated herein by reference. (Subject of the invention)

[0003] The subject matter disclosed herein relates to piezoelectric electrophoretic displays that can be activated or driven without being connected to a power source, and methods for manufacturing them. [Background technology]

[0004] Non-emissive displays transmit information using contrast differences, which is achieved by varying the reflectivity of light at different frequencies. Therefore, they differ from conventional emissive displays that stimulate the eye by emitting light. One type of non-emissive display is the electrophoretic display, which achieves contrast by utilizing the phenomenon of electrophoresis. Electrophoresis refers to the movement of charged particles in an applied electric field. When electrophoresis occurs in a liquid, particles move with a velocity that is primarily determined by the viscous resistance experienced by the particles, their charge, the dielectric properties of the liquid, and the magnitude of the applied field.

[0005] Electrophoretic displays utilize charged particles of one color suspended in a dielectric liquid medium of different colors (i.e., light reflected by the particles is absorbed by the liquid). The suspension is housed in a cell located between (or partially defined by) a pair of opposing electrodes, one of which is transparent. When the electrodes are activated and a DC or pulsed field is applied across the medium, the particles move towards the electrode of the opposite sign. The result is a visually observable color change. In particular, when a sufficient number of particles reach the transparent electrode, their color dominates the display. However, if the particles are attracted to the other electrode, they are obscured by the color of the liquid medium, which then dominates instead.

[0006] Many electrophoretic displays are bistable. Their state persists even after the activated electric field is removed. This is generally achieved through residual charge on the electrodes and van der Waals interactions between the particles and the walls of the electrophoretic cell. Driving an electrophoretic display requires a power source, such as a battery, to provide power to the display and / or its drive circuit. The power source may be a driver IC for generating the electric field. The electric field may also need to be amplified by the circuit. In either case, a physical connection via wires is required to connect the power source to the electrophoretic display and its drive circuit. [Overview of the project] [Means for solving the problem]

[0007] According to one aspect of the subject matter disclosed herein, an electro-optical display may include a layer of electrophoretic material, a first conductive layer, and a piezoelectric material positioned between the layer of electrophoretic material and the first conductive layer, wherein the piezoelectric material overlaps with a portion of the layer of electrophoretic material, and a portion of the first conductive layer overlaps with the remainder of the electrophoretic material. For example, this application provides the following items. (Item 1) An electro-optical display, wherein the electro-optical display is A layer of electrophoretic material, A first conductive layer and A piezoelectric material positioned between the electrophoretic material layer and the first conductive layer. Equipped with, An electro-optical display in which the piezoelectric material overlaps with a portion of the layer of the electrophoretic material, and a portion of the first conductive layer overlaps with the rest of the electrophoretic material. (Item 2) The electro-optical display according to item 1, further comprising a second conductive material adjacent to the layer of electrophoretic material and positioned on the opposite side from the piezoelectric material. (Item 3) An electro-optical display, wherein the electro-optical display is A layer of electrophoretic material, Semiconductive materials and, A piezoelectric material stacked on the aforementioned semiconducting material and Equipped with, An electro-optical display in which the piezoelectric material and the semiconducting material are positioned adjacent to the electrophoretic material. (Item 4) The electro-optical display according to item 3, further comprising a first conductive layer overlapping the piezoelectric material and the electrophoretic material. (Item 5) The electro-optical display according to item 4, further comprising a second layer of semiconductive material between the second conductive layer and the piezoelectric material and the electrophoretic material. (Item 6) The electro-optical display according to item 1, further comprising a second conductive layer overlapping the semiconducting material and the electrophoretic material. (Item 7) An electro-optical display, wherein the electro-optical display is A layer of electrophoretic material, The first layer of piezoelectric material, The second layer of piezoelectric material and Equipped with, The first and second layers of the piezoelectric material are positioned side by side, overlap with the layer of the electrophoretic material, and the first and second layers of the piezoelectric material have opposite polarization directions, an electro-optical display. (Item 8) A method of producing a display, the method comprising: producing a layer of electrophoretic display material having a first portion and a second portion, the first portion having a plurality of microcells and the second portion being substantially flat; providing a piezoelectric material; aligning the piezoelectric material with the second portion of the electrophoretic display material such that the piezoelectric material substantially overlaps the second portion; A method comprising. (Item 9) The method according to item 8, wherein the first and second portions of the electrophoretic material are produced using a single photolithography step. (Item 10) The method according to item 8, further comprising installing the electrophoretic display material and the piezoelectric material on a substrate. (Item 11) The method according to item 10, wherein the substrate is flexible. (Item 12) The method according to item 10, further comprising providing a conductive electrode on the substrate. (Item 13) The method according to item 12, further comprising providing a barrier layer between the conductive electrode and the substrate. (Item 14) The method according to item 8, further comprising providing a layer of release liner after the step of producing the layer of the electrophoretic display. <H (Item 15) The method according to item 14, wherein the release liner has a height substantially the same as that of the plurality of microcells.

Brief Description of the Drawings

[0008] [Figure 1]Figure 1 is a cross-sectional view of an exemplary electrophoretic display according to the subject disclosed herein.

[0009] [Figure 2A] Figure 2A is another cross-sectional view of the display shown in Figure 1.

[0010] [Figure 2B] Figure 2B is an equivalent circuit model of the display shown in Figures 1 and 2A.

[0011] [Figure 3-1] Figure 3A is a cross-sectional view of another exemplary display according to the subject disclosed herein. Figure 3B is a cross-sectional view of the display illustrated in Figure 3A along line C1. Figure 3C is a cross-sectional view of the display illustrated in Figure 3A along line C2.

[0012] [Figure 3-2] Figure 3D illustrates yet another embodiment of the display according to the subject matter presented herein.

[0013] [Figure 4] Figure 4 is a cross-sectional view of yet another exemplary display of the subject disclosed herein.

[0014] [Figure 5] Figure 5 is a cross-sectional view of another exemplary display according to the subject matter disclosed herein.

[0015] [Figure 6] Figure 6 illustrates one embodiment of a piezoelectric electrophoretic display with a jigsaw pattern, according to the subject matter disclosed herein.

[0016] [Figure 7] Figure 7 illustrates yet another embodiment of a piezoelectric electrophoretic display having a certain pattern, according to the subject matter disclosed herein.

[0017] [Figure 8] Figure 8 illustrates a piezoelectric electrophoretic display used as part of a foreign currency bill for anti-counterfeiting purposes, according to the subject matter disclosed herein.

[0018] [Figure 9] Figure 9 illustrates a cross-section of yet another embodiment of a piezoelectric display according to the subject matter disclosed herein.

[0019] [Figure 10] Figure 10 is a cross-sectional view of a piezoelectric display having a barrier layer according to the subject disclosed herein.

[0020] [Figure 11A] Figure 11A is a top view of the microcell layer.

[0021] [Figure 11B] Figure 11B is a cross-sectional view of the microcell layer shown in Figure 10A.

[0022] [Figure 12A] Figures 12A and 12B illustrate another embodiment of an electrophoretic display according to the subject matter disclosed herein. [Figure 12B] Figures 12A and 12B illustrate another embodiment of an electrophoretic display according to the subject matter disclosed herein.

[0023] [Figure 13A] Figures 13A and 13B illustrate yet another embodiment of an electrophoretic display according to the subject matter disclosed herein. [Figure 13B] Figures 13A and 13B illustrate yet another embodiment of an electrophoretic display according to the subject matter disclosed herein.

[0024] [Figure 14A]Figure 14A illustrates an additional embodiment of an electrophoretic display with a printed image or shape, according to the subject matter disclosed herein.

[0025] [Figure 14B] Figures 14B-14E illustrate the display of Figure 14A in use, according to the subject matter disclosed herein. [Figure 14C] Figures 14B-14E illustrate the display of Figure 14A in use, according to the subject matter disclosed herein. [Figure 14D] Figures 14B-14E illustrate the display of Figure 14A in use, according to the subject matter disclosed herein. [Figure 14E] Figures 14B-14E illustrate the display of Figure 14A in use, according to the subject matter disclosed herein.

[0026] [Figure 15A] Figure 15A illustrates yet another embodiment of an electrophoretic display with a printed image or shape, according to the subject matter disclosed herein.

[0027] [Figure 15B] Figures 15B-15C illustrate the display of Figure 15A in use, according to the subject matter disclosed herein. [Figure 15C] Figures 15B-15C illustrate the display of Figure 15A in use, according to the subject matter disclosed herein. [Modes for carrying out the invention]

[0028] The term “electro-optics” is used herein in its conventional sense in the field of imaging technology, as applied to materials or displays, to refer to a material having first and second display states in which at least one optical property differs, and which can be changed from its first to its second display state by the application of an electric field to the material. The optical property is typically color perceptible to the human eye, but may be other optical properties such as optical transmittance, reflectance, luminescence, or, in the case of displays intended for machine reading, pseudocolor in the sense of changes in the reflection of electromagnetic wavelengths outside the visible range.

[0029] The terms “bistable” and “bistable” are used herein to refer to a display having a display element having a first and second display state having at least one different optical property, where a given element is driven by a finite-duration address pulse to show either the first or second display state, and after the address pulse has finished, that state lasts for at least several times, e.g., at least four times, the minimum duration of the address pulse required to change the state of the display element. U.S. Patent No. 7,170,670 shows that several grayscale-enabled particle-based electrophoretic displays are stable not only in their extreme black and white states but also in their intermediate gray states, and that the same is true for several other types of electro-optic displays. While this type of display is appropriately called “multistable” rather than bistable, for convenience the term “bistable” may be used herein to refer to both bistable and multistable displays.

[0030] The term “gray state” is used herein in its conventional sense in the field of imaging technology, referring to a state intermediate between two extreme optical states of pixels, and not necessarily meaning a transition between these two extreme states of black and white. For example, several patents and published applications relating to electrophoretic inks referenced below describe electrophoretic displays in which the extreme states are white and dark blue, and the intermediate “gray state” is actually light blue. In fact, as already stated, a change in optical state may not be a change in color at all. The terms “black” and “white” may also be used below to refer to two extreme optical states of a display, and should be understood to usually include extreme optical states that are not strictly black and white, such as the aforementioned white and dark blue states. The term “monochromatic” may hereafter be used to refer to a display or driving scheme that drives pixels to only its two extreme optical states without an intervening gray state.

[0031] The term "pixel" is used herein in its conventional sense to mean the smallest unit of a display capable of producing all the colors that the display itself can produce. In a full-color display, typically each pixel consists of several subpixels, each of which can display less than all the colors that the display itself can produce. For example, in most conventional full-color displays, each pixel consists of a red subpixel, a green subpixel, a blue subpixel, and optionally, a white subpixel, each of which is capable of displaying a range of colors from black to the brightest version of its defined color.

[0032] Several types of electro-optical displays are known. One type of electro-optical display is the rotating dicolor member type, as described, for example, in U.S. Patents 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 (this type of display is often referred to as a “rotating dicolor ball” display, but in some of the aforementioned patents the rotating member is not spherical, so the term “rotating dicolor member” is preferred as it is more accurate). Such displays use a number of small bodies (typically spherical or cylindrical) having two or more segments with different optical properties and an internal dipole. These bodies are suspended in vacuoles filled with liquid within a matrix, and the vacuoles are filled with liquid so that the bodies can rotate freely. The appearance of the display is changed by applying an electric field to the display, and thus rotating the bodies to various positions, thereby changing the divisions of the bodies seen through the viewing surface. This type of electro-optical medium is typically bistable.

[0033] Another type of electro-optical display uses an electrochromic medium in the form of a nanochromic film comprising an electrode formed at least partially from a semiconductor metal oxide and a plurality of dyeing molecules adhering to the electrode and capable of reversing the color change. See, for example, O'Regan, B., et al, Nature 1991, 353, 737, and Wood, D., Information Display, 18(3), 24 (March 2002). See also Bach, U., et al, Adv. Mater., 2002, 14(11), 845. This type of nanochromic film is also described, for example, in U.S. Patents 6,301,038, 6,870,657, and 6,950,220. This type of medium is also typically bistability.

[0034] Another type of electro-optical display is the electrowetting display, developed by Philips and described in Hayes, RA, et al., "Video-Speed ​​Electronic Paper Based on Electrowetting," Nature, 425, 383-385 (2003). U.S. Patent No. 7,420,549 shows that such an electrowetting display can be made bistably constructed.

[0035] One type of electro-optical display that has been the subject of research and development interest for many years is a 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, electrophoretic displays can have attributes such as good brightness and contrast, wide viewing angle, state bistable, and low power consumption.

[0036] As mentioned above, electrophoretic media require the presence of a fluid. In most conventional electrophoretic media, this fluid is a liquid, but electrophoretic media can be produced using a gaseous fluid (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. Such gas-based electrophoretic media are considered susceptible to the same types of problems as liquid-based electrophoretic media for particle sedimentation when used in orientations that allow for such sedimentation, such as in signs where the medium is positioned vertically. In fact, particle sedimentation is considered a more serious problem in gas-based electrophoretic media than in liquid-based electrophoretic media, due to the lower viscosity of gaseous suspension fluids compared to the viscosity of fluids that allow for faster sedimentation of electrophoretic particles.

[0037] Numerous patents and applications, assigned to or filed in the names of the Massachusetts Institute of Technology (MIT) and E Ink Corporation, describe various techniques used in encapsulated electrophoretic and other electro-optical media. Such encapsulated media comprise numerous small capsules, each containing an internal phase in a fluid medium containing particles that are themselves mobile by electrophoresis, and a capsule wall surrounding the internal phase. Typically, the capsules themselves are held within a polymer adhesive, forming a tightly bonded layer positioned between two electrodes. Techniques described in these patents and applications include: (a) Electrophoretic particles, fluids, and fluid additives (see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814) (b) Capsules, binders, and encapsulation processes (see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719) (c) Films and subassemblies containing electro-optical materials (see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564) (d) Backplanes, adhesive layers, and other auxiliary layers, and methods used for display (see, for example, U.S. Patents No. 7,116,318 and 7,535,624) (e) Color formation and color adjustment (see, for example, U.S. Patent Nos. 7,075,502 and 7,839,564) (f) A method for driving the display (see, for example, U.S. Patent Nos. 7,012,600 and 7,453,445) (g) Application of the display (see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348) (h) Non-electrophoretic displays (see U.S. Patents No. 6,241,921, 6,950,220, 7,420,549, and 8,319,759, and U.S. Patent Application Publication No. 2012 / 0293858) (i) Microcell structures, wall materials, and methods for forming microcells (see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906) (j) Methods for filling and sealing microcells (see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088)

[0038] Many of the aforementioned patents and applications recognize that the walls surrounding separate microcapsules within an encapsulated electrophoretic medium can be replaced with a continuous phase, thus producing a so-called polymer-dispersed electrophoretic display, in which the electrophoretic medium comprises a plurality of separate droplets of electrophoretic fluid and a continuous phase of polymer material, and that the separate droplets of electrophoretic fluid within such a polymer-dispersed electrophoretic display can be considered capsules or microcapsules even if separate capsule membranes are not associated with each individual droplet. See, for example, U.S. Patent No. 6,866,760 mentioned above. Therefore, for the purposes of this application, such polymer-dispersed electrophoretic media are considered a variant of encapsulated electrophoretic media.

[0039] A 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 instead are held within a carrier medium, typically a polymer film, in multiple cavities formed within it. See, for example, U.S. Patent Nos. 6,672,921 and 6,788,449 (both assigned to Sipix Imaging, Inc.).

[0040] In many cases, electrophoretic media are opaque (because, for example, in many electrophoretic media, the particles substantially block the transmission of visible light through the display) and operate in reflective mode. However, many electrophoretic displays can be manufactured to operate in a so-called "shutter" mode, where one display state is substantially opaque and the other is light-transmitting. See, for example, U.S. Patents 5,872,552, 6,130,774, 6,144,361, 6,172,798, 6,271,823, 6,225,971, and 6,184,856. Dielectric displays are similar to electrophoretic displays but depend on variations in electric field strength and can operate in similar modes. See, for example, U.S. Patent 4,418,346. Other types of electro-optical displays may also be capable of operating in shutter mode. An electro-optical medium operating in shutter mode can be used in a multilayer structure for a full-color display, in which at least one layer adjacent to the screen of the display operates in shutter mode to expose or hide a second layer that is further away from the screen.

[0041] Encapsulated electrophoretic displays typically avoid the clustering and sedimentation failure modes of conventional electrophoretic equipment and offer further advantages such as the ability to print or coat displays on a variety of flexible and rigid substrates. (The use of the term "printing" is intended to include, but is not limited to, all forms of printing and coating, including, pre-metering coatings such as patch-die coatings, slot or extrusion coatings, slide or cascade coatings, curtain coatings, etc.; roll coatings such as knife-over roll coatings, forward and reverse roll coatings, etc.; gravure coatings, immersion coatings, spray coatings, meniscus coatings, spin coatings, brush coatings, air knife coatings; silkscreen printing processes; electrostatic printing processes; thermal printing processes; inkjet printing processes; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques.) Thus, the resulting displays can be flexible. Furthermore, since the display medium can be printed using a variety of methods, the displays themselves can be manufactured inexpensively.

[0042] Other types of electro-optical materials may also be used in this invention.

[0043] Electrophoretic displays typically comprise a layer of electrophoretic material and at least two other layers positioned on either side of the electrophoretic material (one of which is an electrode layer). In most such displays, both layers are electrode layers, and one or both of the electrode layers are patterned to define pixels on the display. For example, one electrode layer may be patterned into elongated row electrodes, and the other into elongated column electrodes extending perpendicular to the row electrodes, with pixels defined by the intersections of the row and column electrodes. Alternatively, and more commonly, one electrode layer may have the form of a single continuous electrode, and the other electrode layer may be patterned into a matrix of pixel electrodes, each of which defines one pixel on the display. In another type of electrophoretic display intended for use with a stylus, print head, or similar movable electrode separate from the display, only one of the layers adjacent to the electrophoretic layer contains the electrode, and the layer opposite the electrophoretic layer is typically a protective layer intended to prevent the movable electrode from damaging the electrophoretic layer.

[0044] In yet another embodiment, as described in U.S. Patent No. 6,704,133, an electrophoretic display may be constructed of two continuous electrodes and an electrophoretic layer and a photoelectrophoretic layer between the electrodes. Since the photoelectrophoretic material changes its resistivity in response to the absorption of photons, incident light can be used to alter the state of the electrophoretic medium. Such a device is illustrated in Figure 1. As described in U.S. Patent No. 6,704,133, the device of Figure 1 functions best when driven by a light-emitting source, such as an LCD display, located on the opposite side of the viewing surface of the display. In some embodiments, the device of U.S. Patent No. 6,704,133 incorporates a special barrier layer between the front electrode and the photoelectrophoretic material to reduce the “dark current” generated by incident light from the front of the display, which leaks across the reflective electro-optic medium.

[0045] U.S. Patent No. 6,982,178, mentioned above, describes a method for assembling solid-state electro-optic displays (including encapsulated electrophoretic displays) that are highly suitable for mass production. Essentially, this patent describes a so-called “front-plane laminate” (“FPL”) comprising, in order, a light-transmitting conductive layer, a layer of solid-state electro-optic medium in electrical contact with the conductive layer, an adhesive layer, and a release sheet. Typically, the light-transmitting conductive layer is supported on a light-transmitting substrate, which is preferably flexible in the sense that the substrate can be hand-wrapped around a drum of, for example, 10 inches (254 mm) in diameter without permanent deformation. In this application and herein, the term “light-transmitting” is used to mean that a layer designated as such transmits enough light to allow an observer looking through the layer to observe changes in the display state of the electro-optic medium, and is typically seen through the conductive layer and adjacent substrates (if any), and the term “light-transmitting” should, of course, be interpreted with respect to the transmission of relevant invisible wavelengths when the electro-optic medium display changes in reflectivity at invisible wavelengths. The substrate is typically a polymer film and will usually have a thickness in the range of about 1 to about 25 mils (25 to 634 μm), preferably about 2 to about 10 mils (51 to 254 μm). The conductive layer may conveniently be, for example, a thin metal or metal oxide layer of aluminum or ITO, or a conductive polymer. Poly(ethylene terephthalate) (PET) films coated with aluminum or ITO are commercially available, for example, as "Aluminum-Coated Mylar" ("Mylar" is a registered trademark) from EI du Pont de Nemours & Company (Wilmington DE), and such commercial materials may be used with good results in front-plane lamination.

[0046] The assembly of an electro-optical display using such a front-plane laminate can be achieved by removing the release liner from the front-plane laminate and bringing the adhesive layer into contact with the backplane under conditions effective for bonding the adhesive layer to the backplane, thereby fixing the adhesive layer, the electro-optical medium layer, and the conductive layer to the backplane. This process is very suitable for mass production because the front-plane laminate is typically mass-produced using a roll-to-roll coating technique and can then be cut into pieces of any size required for use with a particular backplane.

[0047] U.S. Patent No. 7,561,324 describes a so-called “double release sheet,” which is essentially a simplified variation of the front-plane laminate described in U.S. Patent No. 6,982,178. One form of the double release sheet comprises a layer of solid electro-optic medium sandwiched between two adhesive layers, one or both of which are covered by the release sheet. Another form of the double release sheet comprises a layer of 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 the front-plane laminate already described, but involving two distinct laminations, typically in the first lamination, the double release sheet is laminated onto the front-plane electrodes to form the front-plane assembly, and then in the second lamination, the front-plane assembly is laminated onto the back-plane to form the final display, although the order of these two laminations may be reversed as desired.

[0048] U.S. Patent No. 7,839,564 describes a so-called “inverted front-plane laminate,” which is a variation of the front-plane laminate described in U.S. Patent No. 6,982,178. This inverted front-plane laminate comprises, in order, at least one of a light-transmitting protective layer and a light-transmitting conductive layer, an adhesive layer, a solid-state electro-optic medium layer, 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, with or without a second typically thin layer of adhesive between the electro-optic layer and the backplane. Such an electro-optic display can combine good resolution with good low-temperature performance.

[0049] The photoelectrophoretic properties of certain pigments have been recognized for some time. For example, U.S. Patent No. 3,383,993 discloses a photoelectrophoretic imaging apparatus that can be used to reproduce images projected onto a transparent electrode, typically ITO, on a medium. However, the photoelectrophoretic process described in Patent No. 993 and other related patents by Xerox Corporation is not reversible. This is because the photoelectrophoretic process involves the movement of photoelectrophoretic particles to an "injection electrode," where they become attached to the electrode. Due to the lack of reversibility and the cost and complexity of setup, this phenomenon has not been widely commercialized.

[0050] The subject matter presented herein relates to several piezoelectric electrophoretic display structural designs that do not require a power source (e.g., a battery or wired power source) for the electrophoretic display to operate. The assembly of such electrophoretic displays is therefore simplified.

[0051] Pneumatic charge is an electric charge that accumulates in a solid material in response to applied mechanical stress. Suitable materials for the subject disclosed herein include polyvinylidene fluoride (PVDF), quartz (SiO2), berinite (AlPO4), gallium phosphate (GaPO4), tourmaline, barium titanate (BaTiO3), lead zirconate titanate (PZT), zinc oxide (ZnO), aluminum nitride (AlN), lithium tantalate, gallium silicate lanthanum, potassium sodium tartrate, and any other known piezoelectric material.

[0052] Some aspects of the subject presented herein involve using voltage to drive the pigments of electrophoretic materials and change the color of the electrophoretic material when viewed from a viewing surface. For example, a voltage can be generated by bending a piezoelectric material or by introducing stress into it, and this voltage can be used to cause the migration of the color pigments of the electrophoretic material. As used herein, the term “contrast ratio” (CR) in relation to electro-optical displays (e.g., electrophoretic displays) is defined as the ratio of the brightness of the brightest color (white) to the brightness of the darkest color (black) that the display is capable of producing. Typically, a high contrast ratio, i.e., CR, is a desired aspect of a display.

[0053] Figure 1 illustrates a cross-sectional view of an exemplary electro-optical display 100, according to the subject matter disclosed herein, which drives an electrophoretic material (EPD) film 104 using a piezoelectric material 102. In this embodiment, the piezoelectric film 102 may be laminated onto a portion of the EPD film 104, and a conductive adhesive material (e.g., copper tape) may be used to coat the piezoelectric film 102 and the remainder of the EPD film 104, as shown in Figures 1 and 2A. In some embodiments, the conductive adhesive material may function as an electrode 2 108 and be attached to a substrate (not shown). In another embodiment, the electrode 2 108 may function as a pixel electrode, modulating the potential across the EPD film 104 to display a color or image (e.g., by changing the gray tone of the EPD film 104). Furthermore, opposite to the electrode 2 108, an electrode 1 106 may overlap with the EPD film layer 104. In yet another embodiment, the EPD film 104 may be fabricated first on the electrode 1 106. For example, electrode 1 106 may be initially patterned to include a microcell structure, and an electrophoretic fluid with electrophoretic particles may be embossed into the microcell structure to form an EPD film layer. Further details in this regard will be illustrated in Figures 9 and 11A-B below. In this configuration, the EPD film 104 and electrode 1 106 may be an integrated structure. In one other embodiment, electrode 1 Both electrode 106 and electrode 2 108 may be transparent, or one of electrode 1 106 or electrode 2 108 may be transparent so that the display 100 can be viewed from either direction.

[0054] In practice, the CR of the electro-optical display 100 may vary depending on the ratio of the surface area A1 110 (i.e., the portion of the EPD film 104 that overlaps with, is covered with, or is in direct contact with, the piezoelectric material 102) to the area A2 112 (i.e., the portion of the EPD film 104 that overlaps with or is covered by the electrode 2 108), as shown in Figure 1. Experimental results of the CR are shown in Table 1 below. [Table 1]

[0055] As shown in Figure 1, displays such as those illustrated in Figure 1 can improve their CR by overlapping the electrode 2 108 (i.e., conductive adhesive material) and reducing the overall surface area (e.g., A2) of the EPD film 104 on it. The CR was improved from 2 when the ratio of the piezoelectric film 102 (e.g., A1) to the electrode 2 108 (e.g., A2) of the EPD film 104 was 1:2 to 7 when the ratio was 2:1. In some embodiments, to further improve the CR, the width of either electrode 1 106 or electrode 2 108 can be reduced so that any applied physical stress can be applied vertically to the longer side of electrode 2 108.

[0056] Figure 2B illustrates an exemplary equivalent circuit of the display 100 shown in Figure 1, according to the subject matter disclosed herein. The portion of the EPD film 104 in contact with the piezoelectric film 102 may have an electrical resistance R1, and the portion covered by the electrode 2 108 may have an electrical resistance R2. In practice, the voltage generated by the piezoelectric film 104 can be divided between R1 and R2, which are arranged in series. In some embodiments, an adhesive layer may be present between the piezoelectric film 102 and the EPD film layer 104, and the adhesive layer is approximately 10 8 Ohm * cm, preferably 10 12 Ohm * It may have a resistivity value of less than cm.

[0057] In another embodiment according to the subject matter disclosed herein, as shown in FIGS. 1 and 2A, instead of having a piezoelectric film directly laminated on or overlapping with the EPD film, as shown in FIG. 3A, the piezoelectric film 302 is laminated on a semiconductive or high-resistance layer 304, and then the semiconductive or high-resistance layer 304 can be laminated on the electrode 1 layer 306. In this configuration, the semiconductive or high-resistance layer 304 replaces a portion of the EPD film 308 above the piezoelectric film 302, thereby not only reducing the overall thickness of the display but also preventing the rapid dissipation of charges across the piezoelectric film 302. Thus, the charges locally generated (by the piezoelectric film 302) can be effectively and efficiently applied to the EPD film 308, which results in an improvement in the display CR. The comparison of the resistivity level of the semiconductive layer 304 and the resulting CR is illustrated in Table 2 below. As shown, an optimal CR ratio of 12 can be achieved when the semiconductive layer 304 has a resistivity of 10 8 ohm * cm.

Table 2

[0058] Furthermore, the display CR can be optimized by adjusting the resistance value of the semiconductive layer 304. For example, in a resistance range of about 10 8 (ohm * cm), a display CR of 12 can be achieved. In another embodiment, the resistance of the electrode 1 layer 306 can be about 450 ohm / sq, the resistance of the electrode 2 layer 310 can be 0.003 ohm / sq, the EPD film 308 can have a resistance of about 10 7 ~10 8 oh, and the piezoelectric material 302 can have a resistance of 10 13 ~10 14 ohm.

[0059] Figures 3B and 3C are cross-sectional views of the display illustrated in Figure 3A. Figure 3B shows a cross-section of the display along line C1, and Figure 3C shows a cross-section of the display along line C2. In practice, only the EPD portion 308 of the display may be visible to the user, while the piezoelectric film portion may be hidden. As also illustrated in Figures 3B and 3C, the electrode 2 layer 310 may be separated. As a result, the gray tone variation in the EPD film layer 308 will also appear separated. Alternatively, if electrode 2 310 is a single continuous sheet, the gray tone variation in the EPD film layer 308 will also be continuous. It should be understood that both electrode 1 306 and electrode 2 310 may be transparent, and all layers (e.g., layers 302, 304, 310, etc.) may be transparent so that the display can be viewed from any orientation or direction.

[0060] In another embodiment, Figure 3D illustrates a cross-sectional view of another display 312 according to the subject matter presented herein. This display 312 differs from the display illustrated in Figure 3A in that only a portion of the piezoelectric film layer 318 overlaps with the electrode 1 316 layer. In this configuration, the piezoelectric film layer 318 can avoid being positioned in a neutral plane so that a better image can be generated from the piezoelectric film 318. In addition, the piezoelectric film layer 318 may be a metallized piezoelectric film and may be covered by a metal layer 320. In some embodiments, a first semiconducting layer 314 may be positioned between the metal layer 320 and the electrode 1 layer 316. Another second semiconducting layer 322 may also be positioned between the piezoelectric film layer 318 and the electrode 2 layer 324. Electrode 1 316 and electrode 2 It should be understood that all layers presented herein, including the 324 layers, may be transparent so that this display can be viewed from any direction or orientation.

[0061] In yet another embodiment, the configuration is similar to those illustrated in Figures 1 and 2A, but as shown in Figure 4, a semiconducting layer 402 may be placed between the electrode 2 layer 404 and the piezoelectric film layer 406 and EPD film layer 408. This semiconducting layer 402 can insulate the piezoelectric film layer 406 and EPD film layer 408 from electrode 2 404. Similarly, the display illustrated in Figure 3A may be modified to include an additional semiconducting layer to insulate the piezoelectric film and EPD film from electrode 2. Of the various configurations, the display illustrated in Figure 4 demonstrated 18 best CR performance. In any case, the display configurations herein enable the construction of piezoelectric-driven devices with a thickness of less than 50 μm, also significantly simplifying the device structure and making the display more sensitive to smaller applied physical stresses.

[0062] Figure 5 illustrates another display design 500. This display 500 is similar to the one shown in Figure 3A, except that an additional semiconducting layer 502 is placed between the piezoelectric layer 504 and the two electrode layers 506. A comparison of the CR ratios between the various designs is shown in Table 3 below. [Table 3]

[0063] It should be understood that all layers shown in Figures 4 and 5, including electrode 1 and electrode 2 layers, can be transparent so that these displays can be viewed from any direction or orientation.

[0064] Referring to the display configuration illustrated in Figure 1-5, it should be noted that the conductive path is completed between electrodes 1 and 2 and the piezoelectric material layer and EPD film layer, and no other conductors or electrodes are required between electrodes 1 and 2. This reduces the overall thickness of the device and effectively improves the CR ratio of the display.

[0065] Figures 6 and 7 illustrate embodiments of piezoelectric electrophoretic displays that can be configured to display various patterns, such as a jigsaw pattern in Figure 6 and a star pattern in Figure 7. In Figure 6, the display 600 may include a design of multiple electrodes 602 for transporting charge to electrophoretic display media 604 and 606. In the embodiment illustrated in Figure 6, the display medium 604 is red and the display medium 606 is black. It should be understood that other colors can also be conveniently employed. In this configuration, the electrodes 602 in the upper part of the display may be connected to the black-colored display medium 606, and the electrodes 602 in the lower part may be connected to the red-colored display medium 604. When a force is applied to the display 600 during use, the display media 606 and 604 may display both black and red. This particular configuration illustrated in Figure 6 can be printed using conductive material, which can greatly simplify the manufacturing process.

[0066] In one other embodiment, the piezoelectric electrophoretic display according to the subject matter disclosed herein may be combined with another device, such as a foreign currency bill as shown in Figure 8. In this embodiment, the display may be attached to one end of the bill, and when physical stress is applied, the display may switch between one or more shades of gray. In this manner, a user can easily distinguish between a genuine bill and a counterfeit. As described above, the electrodes for the display may be separate, and the resulting shades of gray may appear separately. Alternatively, the electrodes for the display may be a continuous sheet, and the resulting shades of gray may vary in a continuous manner.

[0067] (Manufacturing method)

[0068] Figure 9 illustrates a cross-sectional view of yet another embodiment of the piezoelectric display 910 according to the subject matter presented herein. As shown in Figure 9, the EPD layer 900 partially extends directly beneath the piezoelectric material 902, substantially overlapping with the piezoelectric material 902 and ensuring a secure connection thereto. In this embodiment, the EPD layer 900 has one portion 906 having microcells and another substantially flat portion 904 which may be configured to establish a connection with the piezoelectric material 902. In this configuration, the piezoelectric material 902 is positioned to overlap the substantially flat portion 904 and ensure a good connection with the EPD layer 900. This configuration advantageously allows for the establishment of a robust connection between the piezoelectric material 902 and the EPD layer 900. For example, this configuration results in a robust connection between the piezoelectric material 902 and the EPD layer 900 that can withstand repeated bending or applied stress on the display device 910. In addition, an adhesive layer 908 may be placed between the piezoelectric material layer 902 and the conductor 912. In another embodiment, the piezoelectric material 902 may be circular in shape and surround the EPD material 900. Furthermore, as shown in Figure 9, the piezoelectric material 902 and the EPD layer 900 may be sandwiched between two layers of conductor or conductive material, and all the layers and materials described above may be positioned on a substrate that can be flexible. The substrate is preferably less than 10 microns thick to thin the overall device. In some embodiments, ITO / PET may be used as the substrate as described herein. In some other embodiments, flexible and transparent conductive coatings such as PEDOT:PSS, graphene, carbon nanotubes, or silver nanowires may be used. In yet another embodiment, as shown in Figure 10, a barrier layer may be sputtered onto the substrate layer (e.g., PET) before coating the conductive layer to provide a barrier to the ink solvent. In some cases, this barrier layer may be SiOx. Since the substrate in this case is thin, the barrier layer may also be coated on the other side of the substrate. In addition, other optical layers may be printed on the substrate for decorative purposes. In some embodiments, the carrier film may be discarded after the display has been assembled.Furthermore, the remaining portion of the display without a carrier film can be integrated with other structures. It should be understood that all layers presented herein, including electrode 1 and electrode 2 layers, can be transparent so that the display can be viewed from any direction or orientation.

[0069] Figure 11A illustrates a top view of the EPD layer 900 in Figure 9. As shown, the EPD layer 900 can be manufactured only on a portion of the layer 900 by a patterned microcell structure, leaving the rest of the layer substantially flat. In this method, a substantially flat portion 1102 without microcells (i.e., a separate portion 1102 is designated to have a microcell structure) can be used to create a connection with the piezoelectric layer, as shown in Figure 9. This manufacturing method offers several advantages. Firstly, manufacturing the EPD layer in this method, where the contact portion (i.e., the substantially flat portion) and the microcell portion 1102 are manufactured simultaneously, is easier compared to alternative methods in which the two portions are manufactured separately. Secondly, since the substantially flat contact portion 1100 and the microcell portion 1102 are manufactured together, they are structurally more robust, which leads to a better connection between the EPD layer and the piezoelectric layer and a more durable display device. Figure 11B illustrates a cross-sectional view of an EPD layer as shown in Figure 11A. The EPD layer may include a first portion 1104 with microcell patterning and a flat portion 1106 without microcells. In practice, the substantially flat portion 1106 and the microcell portion 1104 may be patterned in the same photolithography step. In some embodiments, once the pattern is defined, after the embossing step, fragments of a release liner may be laminated onto the substantially flat portion, and the thickness of the release liner may be the same as the microcell height. The surface energy of the release liner is preferably sufficiently high so that the seal layer does not dewet on top of the release liner, and in some embodiments, the surface energy may be adjusted to a specific level depending on the application. The release liner may, in this case, contain polyvinyl alcohol or other water-soluble polymers. Furthermore, after the sanding and sealing steps, the release liner may be removed along with the ink and the seal layer on top of it, exposing the flat area directly underneath. In practice, removing the release liner will remove the seal layer / material and ink from the substantially flat portion of the EPD layer. This process can ensure a substantially clean separation of the ink and seal material from the microcell portion 1104.Pieces of non-metallic piezoelectric film can be laminated on a flat surface. The total thickness of the piezoelectric film and adhesive layer may be similar to the total thickness of the seal layer and microcells. In addition, pieces of the adhesive layer can be laminated on a release liner and on a full display panel. In-line or offline chamber humidification steps may be used to ensure good optical performance of the display. In practice, after the pattern is defined in Figures 11A and 11B, the structure can be cut along line A'A' to produce a display.

[0070] In some embodiments, a method for producing a display as described above may include producing a layer of electrophoretic display material having a first portion 1102 and a second portion 1100, wherein the first portion 1102 has a plurality of microcells and the second portion 1100 is substantially flat. The method may further include providing a piezoelectric material and aligning the piezoelectric material with a second portion of the electrophoretic display material such that the piezoelectric material substantially overlaps with the second portion. In some embodiments, the first 1102 and second 1100 portions of the electrophoretic material are produced using a single photolithography step. The method may further include placing the electrophoretic display material and the piezoelectric material on a substrate, the substrate may be flexible. In some embodiments, the method may further include providing conductive electrodes on the substrate and providing a barrier layer between the conductive electrodes and the substrate. In some embodiments, after the step of producing a layer of electrophoretic display, the method may further include providing a layer of exfoliation liner, the exfoliation liner having substantially the same height as that of the multiple microcells.

[0071] Furthermore, another second electrode may be printed on the top of the substrate, as shown in Figure 6. To connect the second electrode to the EPD material, conductive ink may be used to pattern conductive traces or lines. In some embodiments, the pattern may consist of two parts. The first part may be printed as small stripes, and the second part may be a two-pixel pattern. Each pixel may be connected to one or two small stripes using conductive ink. These patterns can then be aligned and laminated on the FPL described above, together with the piezoelectric film on top of the small stripes.

[0072] Figures 12A and 12B illustrate another embodiment of an electrophoretic display 1200 utilizing a piezoelectric material. As shown, a piezoelectric material layer 1202 can be stacked with a display medium layer 1204 (e.g., an electrophoretic medium layer) to form a display. Two electrodes, namely electrode 1 1206 and electrode 2 1208, can be positioned on the two sides as shown in Figures 12A and 12B, to narrow the EPD layer 1204 and the piezoelectric material layer 1202 and complete a conductive path for charge. In some embodiments, electrode 2 1208 may be a metal on a piezoelectric film or a laminated conductive adhesive on a piezoelectric film. In this configuration, no other connections are required to drive the electrophoretic display material 1204.

[0073] When a force is applied to the piezoelectric material layer 1202 during use, charge separation occurs within the piezoelectric material 1202. Charges on the interface between the electrophoretic display medium layer 1204 and the piezoelectric material layer 1202 induce charges in the EPD film, allowing the electric field to pass through the EPD and move the particles. Figure 12B illustrates the charge distribution.

[0074] In yet another embodiment, to achieve an even better contrast ratio, piezoelectric films with opposite polarization directions may be positioned in a side-by-side configuration, as shown in Figures 13A and 13B. When in use, PZ1 and PZ2 can produce opposite voltages under applied force, and Figure 13B shows one embodiment of the charge distribution when force is applied. It should be understood that all layers presented in Figures 12A–13B of this specification, including electrode 1 and electrode 2 layers, may be transparent so that the display can be viewed from any direction or orientation.

[0075] The embodiments shown in Figures 12A-13B not only reduce the overall device thickness to less than 50 micrometers, but also significantly improve the CR (Critical Value). Furthermore, they simplify the device structure and make the display device more sensitive to small strain changes.

[0076] (Latent image)

[0077] In some embodiments, displays similar to or based on the configurations illustrated in Figure 12A or Figure 1 may be modified to display latent images. A display device 1400 similar to that presented in Figure 12A, but with an image or shape laminated or printed on either electrode 1 1406 or electrode 2 1408, is illustrated in Figure 14A. It should be understood that the configuration presented in Figure 14A is for illustrative purposes only, and other configurations can be readily employed to achieve the same effect. In practice, all layers of the display 1400 (even the adhesive layer and electrode 1 and 2 layers) may be transparent so that the display can be viewed from any direction or orientation (e.g., layers 1402, 1404, 1406, 1408, etc.).

[0078] In some embodiments, an image or shape is printed or laminated on a white background and on either electrode 1 1406 or electrode 2 1408 so that it can be seen from the opposite side. When in use, when the EPD layer 1404 is white, the printed image or shape is hidden (i.e., see Figure 14B), and when force is applied and the EPD 1404 switches to another color, the printed image or shape can be revealed (i.e., see Figure 14C).

[0079] In yet another embodiment, a dark-colored image or shape is produced on either electrode 1406 or electrode 21408 without a background and can be viewed from the opposite side. In this configuration, if the display 1400 is positioned on a black background, as shown in Figure 14D, the printed image or shape will remain hidden no matter how much the EPD 1404 is bent. Alternatively, if the display 1400 is positioned on a white or lightly colored background, the printed image or shape will appear and become more apparent when the EPD 1404 switches to a darker color, as shown in Figure 14E.

[0080] In yet another embodiment, as shown in Figure 15A, the image or shape may be produced outside of electrodes 1 1502, 1504 or either EPD display 1 1506 or EPD display 2 1508. The two EPD displays 1506, 1508 may be joined together using a transparent adhesive material. When force is applied (e.g., by bending), both EPD displays 1 1506 and 2 1508 may change color. If EPD display 2 1508 darkens and EPD display 1 1506 darkens, the printed image or shape will not appear, as shown in Figure 15C. Alternatively, if EPD display 2 1508 darkens and EPD display 1 1506 darkens, the printed image or shape will appear, as shown in Figure 15B.

[0081] Referring to the display configuration illustrated in Figure 9-14A, it should be noted that a conductive path is completed between electrodes 1 and 2 and the piezoelectric material layer and EPD film layer, and no other conductors or electrodes are required between electrodes 1 and 2. In the case of the display illustrated in Figure 15, no additional conductors or electrodes are required for each of the stacked displays 1506 and 1508. This reduces the overall thickness of the device and effectively improves the CR ratio of the display.

[0082] It will be apparent to those skilled in the art that numerous changes and modifications can be made to the specific embodiments of the invention described above without departing from the scope of the invention. Therefore, the entirety of the foregoing description should be interpreted as illustrative rather than restrictive.

Claims

[Claim 1] Apparatus, system, or method.

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