Piezo-electrophoretic films and displays, and methods for manufacturing the same

Abstract

A low voltage piezo-electrophoretic display includes a low profile piezo-electrophoretic display. In some embodiments, the piezoelectric material of the piezo-electrophoretic film may be selectively patterned with an insulating material during manufacture. In some embodiments, the piezoelectric material of the piezo-electrophoretic film may be selectively patterned with slits, or partially coated with a conductive material on a surface opposite the electrodes. Such films have high contrast and can be used as security marks, security films or sensors. The membrane is typically flexible. Some of the films have a thickness of less than 100 [mu] m. Some of the films have a thickness less than 50 [mu] m. A display formed from the film does not require an external power source.

Description

(19) State Intellectual Property Office (12) Invention Patent Application (10) Application Publication Number (43) Application Publication Date (21) Application Number 202480083143.5 (22) Application Date 2024.12.26 (30) Priority Data 63 / 616721 2023.12.31 US (85) PCT International Application Entering National Phase Date 2026.06.29 (86) PCT International Application Application Data PCT / US2024 / 061985 2024.12.26 (87) PCT International Application Publication Data WO2025 / 144956 EN 2025.07.03 (71) Applicant Einker Company Address Massachusetts, USA (72) Inventor Y.B. Matus Gu Haiyan (74) Patent Agency Beijing Panhua Weiye Intellectual Property Agency Co., Ltd. 11280 Patent Attorney Guo Guangxun (51) Int.Cl. G02F 1 / 1676 (2006.01) (54) Invention Title: Piezoelectric Electrophoretic Film and Display and Method of Manufacturing Thereof (57) Abstract: This invention comprises a low-voltage piezoelectric electrophoretic display with a low profile. In some embodiments, the piezoelectric material of the piezoelectric electrophoretic film can be selectively patterned with an insulating material during manufacturing. In some embodiments, the piezoelectric material of the piezoelectric electrophoretic film can be selectively patterned with cuts or partially coated with a conductive material on the surface opposite the electrodes. Such films have high contrast and can be used as security markers, anti-counterfeiting films, or sensors. The films are typically flexible. Some films have a thickness of less than 100 μm. Some films have a thickness of less than 50 μm. The display formed from said film does not require an external power supply. Claims 2 pages, Description 16 pages, Drawings 8 pages, CN 122497909 A 2026.07.31 CN 1 22 49 79 09 A 1. A method for manufacturing a piezoelectric electrophoretic display including a first electrode and a second electrode, the method comprising: forming a microcell layer, wherein the microcell has a bottom, a wall, and a top opening; filling the microcell with an electrophoretic medium through the top opening; sealing the top opening of the filled microcell with a water-soluble polymer to form a sealing layer; bonding a second electrode to the sealing layer; treating a piezoelectric material film to form a piezoelectric layer, the piezoelectric layer including one or more voids in the piezoelectric material; bonding the piezoelectric layer to the microcell layer on a surface opposite to the sealing layer; and forming the first electrode by depositing a conductive material onto the piezoelectric layer, wherein the conductive material fills one or more voids in the piezoelectric material and coats the surface of the piezoelectric layer. 2. The method of claim 1, wherein the conductive material of the first electrode comprises poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT-PSS).3. The method of claim 1, wherein the conductive material of the first electrode filling one or more voids in the piezoelectric material is in contact with the microcell layer. 4. The method of claim 1, wherein the second electrode comprises a conductive material coupled to a substrate. 5. The method of claim 1, further comprising bonding the piezoelectric electrophoretic display to a target object, the target object comprising one of paper, banknotes, and circulating banknotes. 6. The method of claim 1, wherein the electrophoretic medium comprises a nonpolar fluid and charged pigment particles, the charged pigment particles moving toward or away from the piezoelectric layer when the piezoelectric layer is subjected to mechanical stress, wherein the nonpolar fluid and charged pigment particles are sealed within the microcell by a sealing layer. 7. The method of claim 1, wherein the piezoelectric layer is polarized by an electric field. 8. A method for manufacturing a piezoelectric electrophoretic display, the method comprising: processing a piezoelectric material film on a release film to form a piezoelectric layer, the piezoelectric layer including one or more voids in the piezoelectric material; forming a first electrode by depositing a conductive material onto the piezoelectric layer, wherein the conductive material fills one or more voids in the piezoelectric material and coats a surface of the piezoelectric layer; forming a microcell layer, wherein the microcell has a bottom, a wall, and a top opening; filling the microcell with an electrophoretic medium through the top opening; sealing the top opening of the filled microcell with a water-soluble polymer to form a sealing layer; bonding a second electrode to the sealing layer; removing the release film from the piezoelectric layer; and bonding the piezoelectric layer to the microcell layer on a surface opposite to the sealing layer. 9. The method of claim 8, wherein the conductive material of the first electrode comprises poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS). 10. The method of claim 8, wherein the conductive material of the first electrode filling one or more voids in the piezoelectric material is in contact with the microcell layer. 11. The method of claim 8, wherein the second electrode comprises a conductive material coupled to a substrate. 12. The method of claim 8, further comprising bonding a piezoelectric electrophoretic display to a target object, the target object comprising one of paper, banknotes, and circulating banknotes. 13. The method of claim 8, wherein the electrophoretic medium comprises a nonpolar fluid and charged pigment particles, wherein when the piezoelectric layer is subjected to mechanical stress, the charged pigment particles move toward or away from the piezoelectric layer, wherein the nonpolar fluid and charged pigment particles are sealed within the microcell by the sealing layer. 14. The method of claim 8, wherein the piezoelectric layer is polarized by an electric field.15. A method for manufacturing a piezoelectric electrophoretic display, the method comprising: bonding a first electrode to a piezoelectric layer comprising polyvinylidene fluoride (PVDF); forming one or more conductive segments on a surface of the piezoelectric layer opposite to the first electrode; forming a microcell layer, wherein the microcell has a bottom, a wall, and a top opening; filling the microcell through the top opening with an electrophoretic medium; sealing the top opening of the filled microcell with a water-soluble polymer to form a sealing layer; bonding a second electrode to the sealing layer; and bonding the piezoelectric layer and the one or more conductive segments to the microcell layer on the surface opposite to the sealing layer. 16. The method of claim 15, wherein the conductive material of the first electrode comprises poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS). 17. The method of claim 15, wherein the second electrode comprises a conductive material coupled to a substrate. 18. The method of claim 15, further comprising bonding the piezoelectric electrophoretic display to a target object, the target object comprising one of paper, banknotes, and circulating banknotes. 19. The method of claim 15, wherein the piezoelectric layer is polarized by an electric field. 20. The method of claim 15, wherein the thickness of the one or more conductive segments is about 50-100 nm. 21. The method of claim 15, wherein the one or more conductive segments comprise poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS). 22. The method of claim 15, wherein the electrophoretic medium comprises a nonpolar fluid and charged pigment particles, wherein the charged pigment particles move toward or away from the piezoelectric layer when the piezoelectric layer is subjected to mechanical stress, wherein the nonpolar fluid and charged pigment particles are sealed within the microcell by the sealing layer. Claims 2 / 2 Page 3 CN 122497909 A Piezoelectric Electrophoretic Film and Display and Method of Manufacturing the Same

[0001] Cross-Reference to Related Applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 616,721, filed December 31, 2023, the entire contents of which are incorporated herein by reference. Furthermore, the entire contents of any patent, published application, or other published work referenced herein are incorporated herein by reference in their entirety. Field of the Invention

[0003] The present invention relates to electrophoretic displays, and more particularly to thin piezoelectric electrophoretic displays with improved contrast and methods of manufacturing the same.

[0004] Background of the Invention

[0005] An electrophoretic display (EPD) is a non-emission device based on the electrophoresis of charged pigment particles dispersed in a solvent or solvent mixture. The display typically includes two electrodes placed opposite each other, which provide an electric field to drive the movement of the charged pigment particles. One of the electrodes is typically transparent.When a voltage difference is applied between two electrodes, (multiple) pigment particles migrate to one side or the other, resulting in the color of the pigment particles or the solvent (if colored) as seen from the viewing side. The electrophoretic fluid typically comprises a nonpolar solvent and one or more groups of charged particles. The particles may have different optical properties (color), different charges (positive or negative), different charge amounts (ζ-potential), and / or different absorption properties (broad light absorption, broad light reflection, or selective absorption or selective reflection). In the presence of multiple groups of particles with opposite charge polarities, the application of an electric field can cause one group of particles to appear on the viewing surface while other particles are driven away from the viewing surface.

[0006] Many electrophoretic displays are bistable, meaning that their optical state persists even after the activating electric field is removed. Bistableness is primarily due to an induced dipole charge layer formed around the charged pigment by the complex interactions between the pigment, charge control agent, and free polymer dispersed in the solvent. Bistable displays can persist for years in their last addressed optical state and then be switched again by applying a new driving field.

[0007] Driving an electrophoretic display requires a power source to provide an electric field between the electrodes. The power source is typically a battery that supplies power to the electrodes via a drive circuit. One or more electrodes may be incorporated into an active matrix backplane. The power source can also be, for example, a photovoltaic cell, a fuel cell, or a power source that operates using mains power (wall current). The power source can also be a piezoelectric element that generates charge through physical motion or thermal expansion, as described in U.S. Patent No. 5,930,026, which is incorporated herein by reference in its entirety. In all these examples, some type of drive circuit is required to provide an electrical path between the power source and the electrodes, and typically, the circuit includes control elements such as switches, transistors, etc. In most cases, the circuit is fairly conventional; however, it often adds volume and structural constraints to the final display (i.e., it is not flexible or non-twistable).

[0008] Furthermore, for many applications, it is desirable to reduce the overall thickness of the display. However, the thickness of the piezoelectric material layer is generally directly related to the voltage amplitude that the piezoelectric material can generate in response to mechanical stress. That is, reducing the thickness of the piezoelectric material also reduces the magnitude of the voltage generated by the piezoelectric material under stress (and vice versa). Therefore, in order to generate a sufficiently large voltage to induce adequate movement of the charged pigment particles required to achieve acceptable contrast, conventional piezoelectric electrophoretic displays typically incorporate layers of piezoelectric material that are too thick, making such displays unsuitable for applications requiring durability and which are essentially inconspicuous when incorporated into thin, low-profile end products such as paper or banknotes.

[0009] Furthermore, conventional piezoelectric electrophoretic displays are typically constructed using continuous layers of piezoelectric material that generate charge outside the desired area when subjected to mechanical stress.For example, if mechanical stress is applied to the area of ​​the piezoelectric layer (page 1 / 16 of the specification, CN 122497909 A), which is larger than the portion including the security seal or image, the piezoelectric material in the portion outside the security seal or image will generate charge, which will cause the charged pigment near those portions to move.

[0010] The above-described effect can produce a color gradient in the displayed image by bending a portion of the piezoelectric electrophoretic display. Therefore, the image may not have sharp edges due to the lateral overflow or diffusion of charge to the unbent portion of the piezoelectric electrophoretic display. These effects are similar to the blurring or crosstalk artifacts observed in electrophoretic displays with actively driven pixel arrays and can lead to blurring and other distracting visual artifacts, or make it difficult to reliably view the security seal or image.

[0011] Summary of the Invention

[0012] Therefore, for applications such as security tags, sensors, and indicators, there is a need for very simple, flexible, durable, and thin electrophoretic displays. There is also a need for piezoelectric electrophoretic displays that are thin and durable enough for such applications while also providing high contrast.

[0013] Therefore, in one aspect, the subject matter disclosed herein includes a method for manufacturing a piezoelectric electrophoretic display including a first electrode and a second electrode. The method includes forming a microcell layer. The microcell has a bottom, walls, and a top opening. The method further includes filling the microcell with an electrophoretic medium through the top opening and sealing the top opening of the filled microcell with a water-soluble polymer to form a sealing layer. The method further includes bonding a second electrode to the sealing layer. The method further includes treating a piezoelectric material film to form a piezoelectric layer including one or more voids in the piezoelectric material. The method further includes bonding the piezoelectric layer to the microcell layer on a surface opposite to the sealing layer and forming the first electrode by depositing a conductive material on the piezoelectric layer. The conductive material fills one or more voids in the piezoelectric material and coats the surface of the piezoelectric layer.

[0014] In some embodiments, the conductive material of the first electrode includes poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS). In some embodiments, the conductive material of the first electrode filling one or more voids in the piezoelectric material is in contact with the microcell layer. In some embodiments, the second electrode comprises a conductive material coupled to a substrate.

[0015] In some embodiments, the method further comprises bonding a piezoelectric electrophoretic display to a target object, the target object comprising one of paper, banknotes, and circulating banknotes.

[0016] In some embodiments, the electrophoretic medium comprises a nonpolar fluid and charged pigment particles, the charged pigment particles moving toward or away from the piezoelectric layer when subjected to mechanical stress, and the nonpolar fluid and charged pigment particles are sealed within the microcell by a sealing layer. In some embodiments, the method of claim 1, wherein the piezoelectric layer is polarized by an electric field.

[0017] On the other hand, the subject matter disclosed herein includes a method for manufacturing a piezoelectric electrophoretic display. The method includes treating a piezoelectric material film on a release film to form a piezoelectric layer comprising one or more voids in the piezoelectric material, and forming a first electrode by depositing a conductive material onto the piezoelectric layer. The conductive material fills one or more voids in the piezoelectric material and coats the surface of the piezoelectric layer. The method further includes forming a microcell layer, wherein the microcells have bottom, wall, and top openings, and filling the microcells with an electrophoretic medium through the top openings. The method further includes sealing the top openings of the filled microcells with a water-soluble polymer to form a sealing layer, and bonding a second electrode to the sealing layer. The method further includes removing the release film from the piezoelectric layer and bonding the piezoelectric layer to the microcell layer on a surface opposite the sealing layer.

[0018] In some embodiments, the conductive material of the first electrode filling one or more voids in the piezoelectric material is in contact with the microcell layer.

[0019] In some embodiments, the second electrode comprises a conductive material coupled to a substrate. In some embodiments, the conductive material of the first electrode comprises poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

[0020] In some embodiments, the method further includes bonding a piezoelectric electrophoretic display to a target object, the target object comprising one of paper, banknotes, and circulating banknotes. Specification 2 / 16 pages 5 CN 122497909 A

[0021] In some embodiments, the electrophoretic medium comprises a nonpolar fluid and charged pigment particles, the charged pigment particles moving toward or away from the piezoelectric layer when the piezoelectric layer is subjected to mechanical stress, and the nonpolar fluid and charged pigment particles are sealed in the microcell by a sealing layer. In some embodiments, the piezoelectric layer is polarized by an electric field.

[0022] On the other hand, the subject matter disclosed herein includes a method for manufacturing a piezoelectric electrophoretic display. The method includes bonding a first electrode to a piezoelectric layer comprising polyvinylidene fluoride (PVDF). The method further includes forming one or more conductive segments on the surface of the piezoelectric layer opposite the first electrode. The method further includes forming a microcell layer having openings at the bottom, walls, and top, filling the microcells with an electrophoretic medium through the top openings, and sealing the top openings of the filled microcells with a water-soluble polymer to form a sealing layer. The method also includes bonding a second electrode to the sealing layer and bonding a piezoelectric layer and one or more conductive segments to the microcell layer on an opposing surface of the sealing layer.

[0023] In some embodiments, the first electrode includes a conductive material coupled to a substrate.

[0024] In some embodiments, the conductive material of the second electrode includes poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

[0025] In some embodiments, the method further includes bonding a piezoelectric electrophoretic display to a target object, said target object including paper, banknotes, and circulating banknotes.In some embodiments, the piezoelectric layer is polarized by an electric field.

[0026] In some embodiments, the thickness of one or more conductive segments is about 50-100 nm. In some embodiments, one or more conductive segments comprise poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT-PSS).

[0027] In some embodiments, the electrophoretic medium comprises a nonpolar fluid and charged pigment particles, which move toward or away from the piezoelectric layer when subjected to mechanical stress, and the nonpolar fluid and charged pigment particles are sealed in the microcell by a sealing layer.

[0028] Brief Description of the Drawings

[0029] Further details of one or more embodiments of the subject matter described herein are set forth in the drawings and the following description. Other features, aspects, and advantages of the subject matter will become apparent from the description and drawings contained herein. The drawings are not necessarily drawn to scale, and in all drawings, elements of similar structures are generally labeled with similar reference numerals for illustrative purposes. However, the specific nature and function of elements in different embodiments may differ. Furthermore, the drawings are intended only for the convenience of describing the subject matter. The accompanying drawings do not illustrate every aspect of the described embodiments and do not limit the scope of this disclosure or the claims.

[0030] FIG1A is a schematic cross-sectional view of an exemplary conventional piezoelectric electrophoretic display.

[0031] FIG1B is a schematic cross-sectional view of another exemplary conventional piezoelectric electrophoretic display.

[0032] FIG2 is a schematic cross-sectional view of an exemplary conventional piezoelectric electrophoretic display under applied mechanical stress.

[0033] FIG3 shows an enlarged view of a partial cross-section of a piezoelectric electrophoretic display according to the subject matter disclosed herein.

[0034] FIG4 illustrates an exemplary equivalent circuit of the enlarged cross-section shown in FIG3.

[0035] FIG5 shows an enlarged view of a partial cross-section of a piezoelectric electrophoretic display according to the subject matter disclosed herein.

[0036] FIG6 illustrates an exemplary equivalent circuit of the enlarged cross-section shown in FIG5.

[0037] FIG7A shows a cross-section of a piezoelectric electrophoretic display according to the subject matter disclosed herein.

[0038] FIG7B shows a top view of a piezoelectric electrophoretic display with a first electrode not shown.

[0039] FIG. 7C shows a top view of a piezoelectric electrophoretic display with a first electrode not shown.

[0040] FIG. 8A shows a cross-section of a piezoelectric electrophoretic display formed according to the subject matter disclosed herein.

[0041] FIG. 8B shows a cross-section of a piezoelectric electrophoretic display according to the subject matter disclosed herein.

[0042] Detailed Description of the Invention 3 / 16 pages 6 CN 122497909 A

[0043] This document discloses low-profile piezoelectric electrophoretic films and display films including low-profile piezoelectric electrophoretic films. In some embodiments, the piezoelectric material of the piezoelectric electrophoretic film can be patterned with a high-voltage electric field after the piezoelectric electrophoretic film is manufactured.This feature allows end users to address the piezoelectric material during production using, for example, corona discharge. This could include, for example, barcodes or serial numbers, which are only visible when the piezoelectric electrophoretic membrane is operated. Other piezoelectric electrophoretic displays and membranes described herein include features that improve display contrast without increasing the overall thickness of the display. Such membranes can be used as security markers, anti-counterfeiting films, or sensors. The membranes are typically flexible. Some membranes are less than 100 μm thick. In some embodiments, the piezoelectric electrophoretic membrane is less than 50 μm and can be folded without breaking. Displays formed with this membrane do not require an external power source.

[0044] When applied to materials or displays, the term “electro-optic” herein takes on its conventional meaning in the field of imaging to refer to a material having a first display state and a second display state that differ in at least one optical property, which changes from its first display state to its second display state by applying an electric field to the material. Although the optical property is typically color perceptible to the human eye, it can be another optical property, such as transmittance, reflectivity, luminescence, or, in the case of a display intended for machine reading, pseudocolor, in the sense of a change in reflectivity at electromagnetic wavelengths outside the visible light range.

[0045] The terms “bistable” and “bistable” are used herein in their conventional sense to refer to a display comprising display elements having a first display state and a second display state that are different in at least one optical property, and such that after either given element is driven to present its first or second display state by an addressing pulse of finite duration, the state will persist for at least several times, for example, at least four times, the shortest duration of the addressing pulse required to change the state of the display element. U.S. Patent No. 7,170,670 shows that some particle-based electrophoretic displays capable of displaying grayscale are stable not only in their extreme black and white states but also in their intermediate gray states, and this is also true for some other types of electro-optical displays. This type of display is more accurately called "multistable" rather than bistable, but for convenience, the term "bistable" as used herein can be used to cover both bistable and multistable displays.

[0046] The term "gray state" is used herein in its conventional meaning in the field of imaging to refer to the intermediate state between two extreme optical states of a pixel, and does not necessarily mean a black-and-white transition between these two extreme states. For example, several E Ink patents and published applications mentioned below describe electrophoretic displays in which the extreme states are white and dark blue, making the intermediate "gray state" actually a light blue. In fact, as already mentioned, a change in optical state may not be a change in color at all.The terms “black” and “white” are used below to refer to the two extreme optical states of a display and should be understood to generally include extreme optical states that are not strictly black and white, such as the aforementioned white state and deep blue state. The term “monochrome” is used below to refer to a driving scheme that drives pixels only to their two extreme optical states without intermediate gray states.

[0047] The term “pixel” is used herein in its conventional meaning in the field of displays, referring to the smallest unit of a display capable of producing all the colors that the display itself can display. In a full-color display, each pixel is typically composed of multiple subpixels, each of which can display fewer than all the colors that the display itself can display. For example, in most conventional full-color displays, each pixel consists of a red subpixel, a green subpixel, a blue subpixel, and an optional white subpixel, each of which is capable of displaying a range of colors from black to the brightest version of its specified color.

[0048] Several types of electro-optical displays are known. One type of electro-optic display uses an electrochromic medium, such as an electrochromic film in the form of a nanochromic film, which comprises an electrode at least partially formed of a semiconductor metal oxide and a plurality of dye molecules reversibly capable of changing color attached to the electrode; 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. Patent Nos. 6, 4 / 16, 7 CN 122497909 A 301,038; 6,870,657; and 6,950,220; this type of medium is also typically bistable.

[0049] Another type of electro-optic 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 fabricated to be bistable.

[0050] One class of electro-optic displays that has been the subject of extensive research and development for many years is particle-based electrophoretic displays, 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 properties such as good brightness and contrast, wide viewing angle, bistable state, and low power consumption.

[0051] Electrophoretic displays typically include an electrophoretic material layer and at least two other layers disposed on opposite sides 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 of the display. For example, one electrode layer may be patterned as elongated row electrodes, and the other as elongated column electrodes extending perpendicularly to the row electrodes, with pixels defined by the intersections of the row and column electrodes. Alternatively and more commonly, one electrode layer has the form of a single continuous electrode, and the other electrode layer is patterned as a matrix of pixel electrodes, where each pixel electrode defines a pixel of the display. In another type of electro-optical display, intended for use with a stylus, printhead, or similar removable electrodes separate from the display, only one layer among the layers adjacent to the electrophoretic layer includes electrodes, and the layers on opposite sides of the electrophoretic layer are typically protective layers designed to prevent damage to the electrophoretic layer by the removable electrodes.

[0052] Numerous patents and applications assigned to or attributed to MIT and E Ink describe various techniques for encapsulating electrophoretic and other electro-optic media. Such encapsulated media comprise a plurality of vesicles, each vesicle itself containing an inner phase containing particles that are electrophoretically mobile in a fluid medium, and a vesicle wall surrounding the inner phase. Typically, the vesicle itself is held in a polymer binder to form a coherent layer located between two electrodes.The technologies described in these patents and applications include:

[0053] (a) electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patents 7,002,728 and 7,679,814;

[0054] (b) capsules, adhesives, and encapsulation methods; see, for example, U.S. Patents 6,922,276 and 7,411,719;

[0055] (c) films and subassemblies containing electro-optic materials; see, for example, U.S. Patents 6,982,178 and 7,839,564;

[0056] (d) backplanes, adhesive layers, and other auxiliary layers and methods used in displays; see, for example, U.S. Patents 7,116,318 and 7,535,624;

[0057] (e) color formation and color adjustment; see, for example, U.S. Patents 7,075,502 and 7,839,564;

[0058] (f) Methods for driving a display; see, for example, U.S. Patent Nos. 7,012,600 and 7,453,445;

[0059] (g) Applications of the display; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348;

[0060] (h) Non-electrophoretic displays, as described in U.S. Patent Nos. 6,241,921; 6,950,220; 7,420,549 and 8,319,759; and U.S. Patent Application Publication No. 2012 / 0293858;

[0061] (i) Microcell structures, wall materials, and methods for forming microcells; see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906; and

[0062] (j) Methods for filling and sealing microcells; see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088.

[0063] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby producing what is known as a polymer-dispersed electrophoretic display, wherein the electrophoretic medium comprises multiple discrete droplets of electrophoretic fluid and a continuous phase of polymeric material, and the droplets of discrete electrophoretic fluid in such a polymer-dispersed electrophoretic display can be considered as capsules or microcapsules, even if no discrete capsule membrane is 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 subclass of encapsulated electrophoretic media.

[0064] A related type of electrophoretic display is a microcell electrophoretic display, also known as MICROCUP®. In a microcell electrophoretic display, charged particles and fluids are not encapsulated in microcapsules but are retained in multiple cavities formed in a carrier medium (typically a polymer film).See, for example, U.S. Patents 6,672,921 and 6,788,449, the entire contents of which are incorporated herein by reference.

[0065] Although electrophoretic media are often opaque (e.g., because in many electrophoretic media, particles essentially block visible light from passing through the display) and operate in a reflective mode, many electrophoretic displays can be made to operate in a so-called “shutter mode,” in which one display state is substantially opaque and one display state is transparent. 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 electrophoretic displays, similar to electrophoretic displays but dependent on changes in electric field strength, can operate in a similar mode; see U.S. Patent 4,418,346. Other types of electro-optic displays may also be able to operate in a shutter mode. Electro-optic media operating in shutter mode can be used in multilayer structures for full-color displays; in such structures, at least one layer adjacent to the viewing surface of the display operates in shutter mode to expose or conceal a second layer further away from the viewing surface.

[0066] Encapsulated electrophoretic displays are generally not affected by the aggregation and sedimentation failure modes of conventional electrophoretic devices and offer further advantages such as the ability to print or coat the display on a wide variety of flexible and rigid substrates. (The use of the term “printing” is intended to include all forms of printing and coating, including but not limited to: volumetric coating, such as patch die coating, slot or extrusion coating, cascade coating, curtain coating; roll coating, such as doctor blade roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing; electrostatic printing; thermal transfer printing; inkjet printing; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques.) Therefore, the resulting display can be flexible. Furthermore, since the display medium can be printed using a variety of methods, the display can be manufactured at low cost.

[0067] The aforementioned U.S. Patent No. 6,982,178 describes a method for assembling a solid-state electro-optic display (including an encapsulated electrophoretic display) that is well-suited for mass production. Essentially, the patent describes a so-called "front panel laminate" ("FPL"), which sequentially comprises: a light-transmitting conductive layer; a solid electro-optic dielectric layer electrically in contact with the conductive layer; an adhesive layer; and a release sheet. Typically, the light-transmitting conductive layer is carried on a light-transmitting substrate, which is preferably flexible, meaning that the substrate can be manually wrapped around a roller with a diameter of (approximately) 10 inches (254 mm) without permanent deformation.The term "transparent" as used in this patent and herein means that the layer specified in this patent transmits sufficient light to allow an observer to observe changes in the display state of the electro-optic medium through the layer, changes in which would typically be viewed through the conductive layer and an adjacent substrate (if present); where the electro-optic medium exhibits a change in reflectivity at a non-visible wavelength, the term "transparent" should of course be interpreted as transmission at the corresponding non-visible wavelength. The substrate is typically a polymer film and typically has 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 is suitably a thin metal or metal oxide layer, such as aluminum or ITO, or it may be a conductive polymer. Poly(ethylene terephthalate) (PET) films coated with aluminum or ITO are commercially available, for example, from E.I. du Pont de Nemours & Company of Wilmington, Delaware, under the name "aluminized Mylar" ("Mylar" is a registered trademark), and such commercial materials can be used for front panel laminates with good results.

[0068] Assembly of an electro-optic display using such a front panel laminate can be achieved by removing the release liner from the front panel laminate and contacting the adhesive layer with the back panel under conditions that effectively adhere the adhesive layer to the back panel, thereby fixing the adhesive layer, electro-optic dielectric layer, and conductive layer to the back panel. This process is well-suited for mass production because the front panel laminate can be mass-produced, typically using roll-to-roll coating technology, and then cut into sheets of any size required for use with a specific back panel.

[0069] U.S. Patent No. 7,561,324 describes a so-called “dual release sheet,” which is essentially a simplified version of the front panel laminate of the aforementioned U.S. Patent No. 6,982,178. One form of dual release sheet includes a solid electro-optic dielectric layer sandwiched between two adhesive layers, wherein one or both adhesive layers are covered by the release sheet. Another form of dual release sheet includes a solid electro-optic dielectric layer sandwiched between two release sheets. Both forms of dual release sheets are intended for use in processes generally similar to those used for assembling electro-optic displays from the described front panel laminate, but involving two separate laminations; typically, in the first lamination, the dual release sheet is laminated to the front electrode to form a front sub-assembly, and then in the second lamination, the front sub-assembly is laminated to the back panel to form the final display, but the order of these two laminations can be reversed if desired.

[0070] The subject matter presented herein relates in particular to the design of piezoelectric electrophoretic films and display structures that do not require a power source (e.g., battery or wired power, photovoltaic power, etc.) to operate electrophoretic displays. This simplifies the assembly of such electrophoretic displays.In some embodiments, the piezoelectric material and the electrophoretic medium are directly laminated together. As mentioned above, the electrophoretic medium may be contained in microcells, microcapsules, or dispersed in a polymer matrix. In some embodiments, the piezoelectric material is polarized (i.e., written) with a high-voltage electric field after the piezoelectric electrophoretic film or piezoelectric electrophoretic display is generated.

[0071] Piezoelectricity is the response of the charge accumulated in a solid material to applied mechanical stress. Suitable materials for the subject matter disclosed herein may include polyvinylidene fluoride (PVDF), quartz (SiO2), berlinite (AlPO4), gallium orthophosphate (GaPO4), tourmaline, barium titanate (BaTiO3), lead zirconate titanate (PZT), zinc oxide (ZnO), aluminum nitride (AlN), lithium tantalate, lanthanum gallium silicate, potassium sodium tartrate, and any other known piezoelectric materials.

[0072] The piezoelectric electrophoretic films and piezoelectric electrophoretic displays described herein use piezoelectricity to drive charged pigments in the electrophoretic medium. Therefore, when the piezoelectric material coupled to the electrophoretic dielectric layer is manipulated or stressed (e.g., flexed, bent), the color change of the electrophoretic material at the surface can be observed. For example, a voltage can be generated by bending or introducing mechanical stress into a piece of piezoelectric material, and this voltage can be used to induce the movement of colored pigments in the electrophoretic material.

[0073] While many piezoelectric materials are crystalline, many flexible piezoelectric active polymers are known, such as polyvinylidene fluoride (PVDF) and its copolymers, polyamides, and parylene-C. Amorphous polymers, such as polyimide and polyvinylidene chloride (PVDC), belong to amorphous bulk polymers. The standard procedure for manufacturing piezoelectric active films such as polyvinylidene fluoride (PVDF) is to manufacture a polymer film and stretch it to generate stress and align dipoles. Stretching transforms the unpolarized α-phase region of PVDF into a polarized β-phase. For example, a strong electric field is then used to stimulate the polar regions of the β-phase. Other methods for aligning the β-phase, such as laser irradiation and strong magnetic fields, have been described in the literature. See, for example, U.S. Patent No. 9,831,417.

[0074] Piezoelectric material films such as PVDF can be melted and spin-coated onto a substrate to form a film. The film can optionally be thermally tempered or stretched prior to polarization. Suitable bulk PVDF is available from, for example, Sigma-Aldrich in bulk powder or film form. Pre-stretched piezoelectric active PVDF films are also available from, for example, PolyK Technologies (State College, PA). Such films can also have a metallized electrode coating on one side, which can also be used for piezoelectric electrophoretic films and displays, but it is difficult to use an electric field to polarize piezoelectric electrophoretic materials with a backing metal layer. Copolymers of PVDF, such as polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE), are also available from Sigma-Aldrich and PolyK.In some embodiments, films of PVDF and PVDF copolymers can be produced by preparing a concentrated solution of bulk PVDF in a compatible volatile solvent, such as dimethylformamide (DMF) (see page 7 / 16 of CN 122497909 A), and slit-coating the concentrated solution onto a suitable transfer substrate or release material, for example, using a roll-to-roll method. The PVDF-coated substrate is then heated to remove the DMF, producing a PVDF film (e.g., less than 20 μm, less than 10 μm, less than 5 μm). By carefully controlling the thermal cycling, the resulting film can be pre-conditioned to have a greater number of β-phase domains suitable for polarization.

[0075] The electrophoretic microunits discussed herein are generally formed from polymers such as acrylates, vinyl ethers, or epoxides, as described in detail in, for example, U.S. Patents Nos. 6,930,818, 7,052,571, 7,616,374, 8,361,356, and 8,830,561, the entire contents of which are incorporated herein by reference. In some embodiments, the electrophoretic microunit layer may be filled with an electrophoretic medium comprising two or more types of electrophoretic particles, which typically have different electrophoretic mobilities and optical properties. The electrophoretic medium may be sealed with a sealing layer 430, preferably a water-soluble sealing layer as described in U.S. Patents Nos. 7,560,004, 7,572,491, 9,759,978, or 10,087,344, the entire contents of which are incorporated herein by reference. In some embodiments, the electrophoretic microunit layer is formed on a release liner, filled with an electrophoretic medium and sealed with a sealing layer, and then the filled and sealed electrophoretic microunits are used as a substrate for producing a piezoelectric material film. The resulting structure is a thin piezoelectric electrophoretic film.

[0076] FIG1A is a schematic cross-sectional view of an exemplary conventional piezoelectric electrophoretic display 100a. As shown in Figure 1A, the piezoelectric electrophoretic display 100a includes a layered stacked assembly comprising a first electrode layer (e.g., electrode 181), a piezoelectric material layer (e.g., piezoelectric layer 160), an electrophoretic dielectric layer (e.g., electrophoretic layer 130), a sealing layer (e.g., sealing layer 140), and a second electrode layer (e.g., electrode 182).

[0077] Electrode layers 181 and 182 can be transparent or flexible. Suitable materials include commercially available ITO-coated PET, which can be used as a substrate for fabricating the electrode layers. In some embodiments, flexible and transparent conductive coatings comprising other transparent conductive oxides (TCOs) can be used, such as zinc oxide, zinc tin oxide, indium zinc oxide, aluminum zinc oxide, indium tin zirconium oxide, indium gallium oxide, indium gallium zinc oxide, or fluorinated variants of these oxides, such as fluorinated tin oxide. In some embodiments, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) is used because it has excellent bending properties and is optically transparent.Although the overall conductivity is not as high as, for example, PET / ITO, PEDOT:PSS is sufficient to provide the necessary electric field to drive the electrophoretic particles in the electrophoretic medium of electrophoretic layer 130.

[0078] Other materials include polymers, typically transparent polymers, doped with conductive materials such as carbon black, metal flakes, metal whiskers, carbon nanotubes, silicon nitride nanotubes, or graphene. In some cases, one or both of electrodes 181 and 182 are metal films, such as copper, silver, gold, or aluminum films or foils. Metal-coated polymer films are also suitable for use as electrode layers. The resistivity of the electrode layer can be 500 ohm-m or less, for example 100 ohm-m or less, for example 1 ohm-m or less, for example 0.1 ohm-m or less, for example 0.01 ohm-m or less. (For comparison, electrophoretic dielectric layers typically have a resistivity of approximately 107 to 108 ohm-m, while piezoelectric materials have a resistivity of 1011 to 1014 ohm-m.)

[0079] The piezoelectric material constituting the piezoelectric layer 160 can be any of the materials listed above; however, polymers such as PVDF and its copolymers are preferred because they can be made into very thin films. The electrophoretic dielectric of the electrophoretic layer 130 typically comprises one or more groups of charged particles that move through a nonpolar solvent in the presence of an electric field. The electrophoretic dielectric shown in FIG. 1A comprises microunits. However, the electrophoretic dielectric can be contained in other structures, such as microcapsules or dispersed droplets. The electrophoretic dielectric can also be contained in open grooves or holes that are sealed within a larger flexible container.

[0080] The sealing layer 140 of the microunits in the electrophoretic layer 130 can be coated with a conductive material, such as PEDOT or one of the materials described above, to form an electrode 182.

[0081] The sealing layer 140 may be a water-soluble sealing layer, which is applied to the open microcell structure of the electrophoretic layer 130 after the desired electrophoretic medium is filled. The sealing layer 140 may become conductive by containing a conductive material. The sealing layer 140 is typically light-transmitting or transparent. Specification 8 / 16 pages 11 CN 122497909 A

[0082] Although not shown in FIG. 1A, piezoelectric electrophoretic displays will often include at least one adhesive layer to bond the individual layers to each other when they are not formed directly on each other. As an example, ITO may be directly sputtered onto the piezoelectric layer 160 to form the electrode 181. The adhesive used may be formed from polymers such as acrylic or polyurethane.In some embodiments, at least one adhesive layer is formed from polyurethane, polyurea, polycarbonate, polyamide, polyester, polycaprolactone, polyvinyl alcohol, polyether, polyvinyl acetate derivatives such as poly(ethylene-co-vinyl acetate), polyvinyl fluoride, polyvinylidene fluoride, polyvinyl butyral, polyvinylpyrrolidone, poly(2-ethyl-2-oxazoline), acrylic or methacrylic acid copolymers, maleic anhydride copolymers, vinyl ether copolymers, styrene copolymers, diene copolymers, siloxane copolymers, cellulose derivatives, gum arabic, alginate, lecithin, amino acid-derived polymers, etc. The adhesive may further include one or more low-dielectric polymers or oligomers, ionic liquids, or conductive fillers such as carbon black, metal flakes, metal whiskers, carbon nanotubes, silicon nitride nanotubes, or graphene. Adhesives that include such charged and / or conductive materials are conductive adhesives. The polymers and oligomers used in the adhesive layer may have multiple functional groups for chain extension or crosslinking during or after lamination. The adhesive layer may have a resistivity value of approximately 106 ohm*cm to 108 ohm*cm, preferably less than 1012 ohm*cm.

[0083] Among the above polymers and oligomers, polyurethanes, polyureas, polycarbonates, polyesters, and polyamides, especially those containing functional groups, are particularly preferred because they have excellent adhesive and optical properties as well as high environmental resistance. Examples of functional groups may include, but are not limited to, -OH, -SH, -NCO, -NCS, -NHR, -NRCONHR, -NRCSNHR, vinyl or epoxides and their derivatives, including cyclic derivatives. The "R" in the above functional groups may be hydrogen or an alkyl, aryl, alkylaryl, or aralkyl group with up to 20 carbon atoms, which may optionally be substituted or interrupted by N, S, O, or a halogen. "R" is preferably hydrogen, methyl, ethyl, phenyl, hydroxymethyl, hydroxyethyl, hydroxybutyl, etc. Functionalized polyurethanes are particularly preferred, such as hydroxyl-terminated polyester polyurethanes or polyether polyurethanes, isocyanate-terminated polyester polyurethanes or polyether polyurethanes, or acrylate-terminated polyester polyurethanes or polyether polyurethanes.

[0084] In some embodiments, the piezoelectric electrophoretic film or display includes a release liner (not shown in FIG. 1A). For example, the release liner can be temporarily used to facilitate the processing of the piezoelectric electrophoretic film or display during imprinting, filling, cutting, etc. In other embodiments, the release liner can be used to deliver the final piezoelectric electrophoretic film or display to be adhered to the final product. In some cases, the release liner will protect the functional adhesive layer that will be used to manipulate the piezoelectric electrophoretic film or display before the piezoelectric electrophoretic film or display is placed in or on the final product. The release liner can be formed from a material selected from polyethylene terephthalate (PET), polycarbonate, polyethylene (PE), polypropylene (PP), paper, and laminates or overlays thereof.Release materials can also be metallized to facilitate quality control measurements and / or control static electricity during handling, transportation, and downstream integration into the product. In some embodiments, a siloxane release coating can be applied to the release material to improve its properties.

[0085] Although not shown in Figure 1A, the piezoelectric electrophoretic display may also include additional edge sealing and / or barrier materials to maintain a desired humidity level inside the piezoelectric electrophoretic display and to prevent leakage of, for example, nonpolar solvents or adhesives, as well as to prevent the ingress of water, dust, or gases. The barrier material can be any flexible material, typically a polymer with a negligible WVTR (water vapor transmission rate). Suitable materials include polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyimide, cycloolefins, and combinations thereof. If the piezoelectric electrophoretic membrane or piezoelectric electrophoretic display will be exposed to particularly harsh conditions, flexible glass such as WILLOW® glass (Corning, Inc.) can be used as the barrier layer. Edge seals may be metallized foils or other barrier foils adhered to the edges of the piezoelectric electrophoretic membrane or piezoelectric electrophoretic display. Edge seals may also be formed from dispersed sealants (thermally cured, chemically cured, and / or radiation cured), polyisobutylene, or acrylate-based sealants, which may be cross-linked. In some embodiments, edge seals may be sputtered ceramics, such as alumina or indium tin oxide (ITO), or advanced ceramics such as those available from the specification 9 / 16 pages 12 CN 122497909 A of Vitex Systems, Inc. (San Jose, CA).

[0086] FIG1B is a schematic cross-sectional view of another exemplary conventional piezoelectric electrophoretic display 100b. Piezoelectric electrophoretic display 100b is closely related to the piezoelectric electrophoretic display 100a of FIG1A, but has an alternative stack of layered components.

[0087] As shown in FIG1B, the piezoelectric electrophoretic display 100b includes a first electrode layer (e.g., electrode 181), an electrophoretic dielectric layer (e.g., electrophoretic layer 130), a sealing layer (e.g., sealing layer 140), a piezoelectric material layer (e.g., piezoelectric layer 160), and a second electrode layer (e.g., electrode 182).

[0088] Of course, it is also possible to fabricate the piezoelectric electrophoretic display using other arrangements of stacked layered components. For example, a piezoelectric electrophoretic display similar to piezoelectric electrophoretic display 100a can be configured such that the openings of the microcells of the electrophoretic layer 130 face the piezoelectric layer 160. As a further alternative, a piezoelectric electrophoretic display similar to piezoelectric electrophoretic display 100b can be configured such that the openings of the microcells of the electrophoretic layer 130 face away from the piezoelectric layer 160. Finally, as described above, the piezoelectric electrophoretic display can be constructed using an electrophoretic dielectric other than microcells such as microcapsules.

[0089] FIG2 is a schematic cross-sectional view of an exemplary conventional piezoelectric electrophoretic display 200 under applied mechanical stress. The piezoelectric electrophoretic display 200 has a stack similar to that of piezoelectric electrophoretic display 100a (FIG. 1A) and includes a first electrode layer (e.g., electrode 281), a piezoelectric material layer (e.g., piezoelectric layer 260), an electrophoretic dielectric layer and a sealing layer (depicted together in FIG. 2 as microcell layer 231), and a second electrode layer (e.g., electrode 282).

[0090] As depicted in FIG. 2, mechanical stress is applied to the piezoelectric electrophoretic display 200. In particular, bending force is applied to the middle portion of the piezoelectric electrophoretic display 200, represented by portion 290 in FIG. 2. The left portion of the piezoelectric electrophoretic display 200, represented by portion 291, and the right portion of the piezoelectric electrophoretic display 200, represented by portion 292, are not subjected to mechanical stress and remain unbent.

[0091] The force applied to the piezoelectric layer 260 causes charge separation within the piezoelectric material. As indicated by the "+" and "-" symbols, charge has been generated in portions 290 of the piezoelectric layer 260 in response to bending forces. Because the piezoelectric material generates a charge proportional to the magnitude of the mechanical stress applied per unit area, a higher charge concentration is generated near the middle of portion 290, and a more dispersed amount of charge is generated towards the edges of portions 290 adjacent to portions 291 and 292.

[0092] The layer stack of the piezoelectric electrophoretic display 200 provides a conductive path between electrodes 281 and 282 for the flow of charge generated by the piezoelectric layer 260. Therefore, a voltage can be generated across the layers of the piezoelectric electrophoretic display 200, and the electric field formed between electrodes 281 and 282 passes through the microcell layer 231, causing charged pigment particles within the microcells to move according to their charge polarity. This can be used to generate a security band with an image that remains neutral or hidden when no mechanical stress is applied to the display, but displays a security seal or image when the security band bends and charged ink particles move in the bent or stressed portion.

[0093] Due to the higher charge concentration near the middle of the aforementioned portion 290, the micro-units in the middle of portion 290 may be subjected to a stronger electric field. Therefore, charged pigment particles within those middle micro-units may move further and / or faster than charged pigment particles located at or near the edges of portions 290 adjacent to portions 291 and 292. Furthermore, because the layers of the electrophoretic display are continuous material layers, some of the charge generated in portion 290 flows through portions 291 and 292, potentially causing some movement of charged pigment particles in those portions. For example, if mechanical stress is applied to an area or portion of the piezoelectric layer 260 that is larger than the portion containing the security seal or image, the piezoelectric material in the portion outside the security seal or image will generate a charge, which will cause the charged pigment near those portions to move.

[0094] The above-described effects can lead to a transition gradient of charged pigment particles within the micro-unit layer 231. For example, an image displayed by bending a portion of the piezoelectric electrophoretic display 200 may lack sharp edges due to lateral charge overflow or diffusion to the unbent portion of the piezoelectric electrophoretic display 200. These effects are similar to the blurring or crosstalk artifacts observed in electrophoretic displays with actively driven pixel arrays.

[0095] The lower contrast provided by piezoelectric electrophoretic displays, such as conventional displays described above, may be unacceptable or undesirable for some applications. For example, some anti-counterfeiting applications require the display to be able to display images with sharp edges, so the fidelity of the image displayed by the security ribbon is not blurred.

[0096] FIG3 shows an enlarged view 300 of a partial cross-section of a piezoelectric electrophoretic display 301 according to the subject matter disclosed herein. The stacking of the piezoelectric electrophoretic display 301 is similar to that of the piezoelectric electrophoretic display 100b shown in FIG1B. However, for the purpose of describing the characteristics of the display, only a subset of the layers of the piezoelectric electrophoretic display 301 is shown: electrode 381, piezoelectric layer 360, electrophoretic dielectric layer (e.g., microcell 330), sealing layer 340, and second electrode 382. In magnified view 300, the electrophoretic dielectric layer and sealing layer 340 are represented by electrophoretic layer 331.

[0097] The piezoelectric layer 360 of the piezoelectric electrophoretic display 301 is not a continuous layer or film of piezoelectric material, but is instead dispersed with an electrically insulating material 361. The electrically insulating material 361 has a resistivity that prevents the rapid dissipation of charge generated by any adjacent piezoelectric electrophoretic material across the layers of the piezoelectric electrophoretic display 301. In some embodiments, the electrically insulating material 361 has a resistivity of approximately 108 ohm*cm. In some embodiments, the electrically insulating material 361 has a resistivity of approximately 102 ohm*cm to 1014 ohm*cm. Depending on the material used, the electrically insulating material 361 can act as a true insulator, but it can also act as a dielectric.

[0098] The electrical insulating material 361 may be formed from, for example, silicone resin, epoxy resin, or acrylic resin. In some embodiments, the electrical insulating material 361 is an insulating polymer material comprising polymethyl methacrylate as a major component. In some embodiments, the electrical insulating material 361 is made of polycarbonate, polyester, polystyrene, polyimide, epoxy resin, polyisocyanate, polyamide, polyvinyl alcohol, polybutadiene, polymethyl methacrylate, copolynylon, UV-curable acrylic resin, fluororesin, etc.

[0099] In some embodiments, the electrical insulating material 361 is formed from the unpolarized portion of the piezoelectric material of the piezoelectric layer 360.In some embodiments, the electrically insulating material 361 is formed of the same material as the piezoelectric material of the piezoelectric layer 360 (e.g., polyvinylidene fluoride or "PVDF"), but a portion of the electrically insulating material 361 is an α phase with a zero dipole moment chain, and is therefore essentially non-piezoelectric, while the charge-generating portion of the piezoelectric material is a β phase and has significant piezoelectric properties.

[0100] In some embodiments, the electrically insulating material 361 is formed of a piezoelectric material that is thicker than the charge-generating piezoelectric material of the piezoelectric layer 360. In this case, the two piezoelectric materials will generate different charges depending on their thickness.

[0101] As shown in FIG3, the piezoelectric layer 360 can be patterned alternately with the electrically insulating material 361. This allows images, shapes, and / or text to be embedded in the piezoelectric electrophoretic display 301. This can also increase the contrast of the piezoelectric electrophoretic display 301 because the potential generated near the charge-generating portion of the piezoelectric material is different from the potential generated near the electrically insulating material 361.

[0102] The enlarged view 300 includes a portion of an electrically insulating material 361 (denoted as insulating portion 362) and a portion of a charge-generating piezoelectric material of the piezoelectric layer 360 (denoted as charge-generating piezoelectric material 364). A first portion 332 of the electrophoretic layer 331 is located over the insulating portion 362, and a second portion 334 is located over the charge-generating piezoelectric material 364, as shown by dashed line 302. The first portion 332 and the second portion 334 each have a resistance based on the volume of the electrophoretic layer 331 they surround. In addition, the insulating portion 362 also has a resistance based on the volume and properties of the electrically insulating material 361 it surrounds. As indicated by the "+" and "-" symbols, for example, a voltage has been generated in the charge-generating piezoelectric material 364 of the piezoelectric layer 360 in response to bending or mechanical stress of the piezoelectric material.

[0103] FIG4 illustrates an exemplary equivalent circuit 400 of the enlarged cross-section shown in FIG3. The three nodes or points shown in Figure 3, 'A' at the piezoelectric material 364 that generates charge, 'B' at electrode 381, and 'C' at electrode 382, ​​correspond to the same points shown in the equivalent circuit 400 of Figure 4. Resistor R1 corresponds to the sum of the resistances of the first portion 332 of the electrophoretic layer 331 and the insulating portion 362 of the piezoelectric layer 360. Resistor R2 corresponds to the resistance of the second portion 334 of the electrophoretic layer 331.

[0104] The piezoelectric material 364 that generates charge in the piezoelectric layer 360 is represented as a battery, and the voltage VPZ is the voltage generated by the piezoelectric material 364 that generates charge across points A and C. Resistors R1 and R2 are represented in series because the presence of a voltage source under a portion of the electrophoretic layer 331 effectively divides the layer into independent portions with different electrical properties (as shown by dashed line 302).For example, when a voltage VPZ has been generated, the voltage potential at point A is higher than the voltage potential at point B or C. Using a conventional current flow example, current 401 flows from point A through resistor R1 to point B, and from point B through resistor R2 to point C. Thus, the voltage generated across resistor R1 is opposite in polarity to the voltage generated across resistor R2. In fact, the series connection across the separated portions of the electrophoretic layer generates two opposite voltages.

[0105] Therefore, manufacturing the piezoelectric electrophoretic display 300 as described above, with the piezoelectric layer 360 and the electrically insulating material 361 alternately patterned, provides advantages over conventional piezoelectric electrophoretic displays. For example, the electrically insulating material 361 can prevent the flow of large amounts of charge in its vicinity, thereby generating a smaller voltage potential across the piezoelectric electrophoretic display 300. This can improve the sharpness of the edges of lines and shapes that the piezoelectric electrophoretic display 300 can produce. Furthermore, the potential difference generated near the insulating portion 362 of the piezoelectric layer 360 and the charge-generating piezoelectric material 364 advantageously provides an improved means of driving pigment particles with opposite charges in opposite directions in the absence of individually addressable pixel electrode matrices. Thus, piezoelectric electrophoretic displays can be made thin enough for applications requiring durability and to be substantially inconspicuous when incorporated into thin, low-profile end products such as paper or banknotes, while still providing high contrast between the insulating portion 362 and the charge-generating piezoelectric material 364 of the piezoelectric layer 360 due to the aforementioned effects.

[0106] FIG5 shows an enlarged cross-sectional view 500 of a piezoelectric electrophoretic display 501 according to the subject matter disclosed herein. The stacking of the piezoelectric electrophoretic display 501 is similar to that of the piezoelectric electrophoretic display 100a shown in FIG1A. However, for the purpose of describing the characteristics of the display, only a subset of the layers of the piezoelectric electrophoretic display 501 is shown: the first electrode 581, the piezoelectric layer 560, the electrophoretic dielectric layer (e.g., microcell 530), the sealing layer 540, and the second electrode 582. In the magnified view 500, the electrophoretic dielectric layer and the sealing layer 540 are represented by the electrophoretic layer 531.

[0107] The piezoelectric layer 560 of the piezoelectric electrophoretic display 501 is not a continuous layer or film of piezoelectric material, but rather has one or more voids or cuts 562 scattered throughout, in which the piezoelectric material has been cut away or otherwise removed. In some embodiments, instead of removing material from the piezoelectric layer 560, the piezoelectric layer 560 is selectively deposited onto the microcell 530, such that gaps are left between portions of the piezoelectric material display cuts 562. The deposition of the piezoelectric material can be performed using one of many methods known in the art.

[0108] As shown in FIG5, when the electrode 581 is laminated on the piezoelectric layer 560, some parts of the electrode 581 contact the piezoelectric material of the piezoelectric layer 560, and other parts contact the micro-unit 530.Depending on the thickness of the piezoelectric material, bubbles or air gaps 565 may form at the edges of the piezoelectric material wherever the conductive material of electrode 581 transitions from different surface heights. Using a thinner piezoelectric material can prevent the formation of such air gaps 565.

[0109] Similar to the embodiment shown in FIG3, the piezoelectric layer 560 may be patterned with several gaps or cutouts 562 alternately. This allows images, shapes, and / or text to be embedded in the piezoelectric electrophoretic display 501. This can also increase the contrast of the piezoelectric electrophoretic display 501 because the potential generated near the piezoelectric material is different from the potential generated near the cutout 562, as described below.

[0110] The magnified view 500 includes a portion of the piezoelectric material of the piezoelectric layer 560 and a cutout 562. A first portion 532 of the electrophoretic layer 331 is located below the cutout 562, and a second portion 534 is located below the piezoelectric material of the piezoelectric layer 560, as shown by the dashed line 502. The first portion 532 and the second portion 534 each have a resistance based on the volume of the electrophoretic layer 531 they enclose. In this embodiment, since the cut 562 removes any material from the piezoelectric layer 560, there is no additional resistance. As shown in the specification 12 / 16 pages 15 CN 122497909 A, for example, a voltage is generated in the piezoelectric material of the piezoelectric layer 360 in response to bending or mechanical stress of the piezoelectric material.

[0111] FIG6 illustrates an exemplary equivalent circuit 600 with an enlarged cross-section shown in FIG5. The three nodes or points shown in FIG5, 'A' at piezoelectric layer 560, 'B' at electrode 582, and 'C' at electrode 581, correspond to the same points shown in the equivalent circuit 600 of FIG6. Resistor R1 corresponds to the resistance of the first portion 532 of the electrophoretic layer 531. Resistor R2 corresponds to the resistance of the second portion 534 of the electrophoretic layer 531.

[0112] The piezoelectric layer 560 is represented as a battery, and the voltage VPZ is the voltage generated by the piezoelectric material that generates charge across points A and C. Resistors R1 and R2 are represented in series because the presence of a voltage source beneath a portion of the electrophoretic layer 531 effectively divides the layer into independent portions with different electrical properties (as shown by dashed line 502). For example, when the voltage VPZ has been generated, the voltage potential at point A is higher than the voltage potential at point B or C. Using a conventional current flow paradigm, current 601 flows from point A through resistor R2 to point B, and from point B through resistor R1 to point C. Thus, the voltage generated across resistor R1 has the opposite polarity to the voltage generated across resistor R2. In fact, the series connection of the separated portions across the electrophoretic layer 531 generates two opposite voltages.

[0113] Therefore, manufacturing the piezoelectric electrophoretic display 500 as described above, in which the piezoelectric layer 560 is alternately patterned with one or more cutouts 562, provides advantages over conventional piezoelectric electrophoretic displays.For example, the potential difference generated near the piezoelectric material generating charge at the notch 562 and the piezoelectric layer 360 advantageously provides an improved means of driving pigment particles with opposite charges in opposite directions in the absence of individually addressable pixel electrode matrices. Thus, piezoelectric electrophoretic displays can be made thin enough for applications requiring durability and to be substantially inconspicuous when incorporated into thin, low-profile end products such as paper or banknotes, while still providing high contrast and improved sharpness of lines and shape edges that the piezoelectric electrophoretic display 500 can produce due to the aforementioned effects.

[0114] FIG7A shows a cross-section of a piezoelectric electrophoretic display 700 according to the subject matter disclosed herein. The stack of the piezoelectric electrophoretic display 700 is similar to that of the piezoelectric electrophoretic display 100a shown in FIG1A and includes a first electrode 781, a piezoelectric layer 760, an electrophoretic dielectric layer (e.g., microcell 730), a sealing layer 740, and a second electrode 782.

[0115] The piezoelectric layer 760 of the piezoelectric electrophoretic display 700 is not a continuous layer or film of piezoelectric material, but rather has one or more slits 763 distributed therebetween, where the piezoelectric material has been cut away or otherwise removed. This embodiment is similar to the piezoelectric electrophoretic display 501 shown in FIG. 5, but the slits 763 may be formed on the piezoelectric layer 760 before it is laminated or otherwise adhered to the microcell 730. For example, a piezoelectric material film may be pretreated to create one or more voids or slits 763. The pretreated piezoelectric material film may then be laminated to the microcell 730. Subsequently, the pretreated piezoelectric material film may be coated with a conductive material that fills the slits 763 and creates an electrode layer 781. Alternatively, the conductive material may be deposited on the pretreated piezoelectric material film on a release sheet before lamination to the microcell 730.

[0116] An exemplary process for manufacturing the piezoelectric electrophoretic display 700 will now be described. As shown in Figure 7A, the piezoelectric electrophoretic display 700 includes a first electrode (e.g., first electrode 781) and a second electrode (e.g., second electrode 782). The method includes forming a layer of microcells (e.g., microcell 730) having a bottom, walls, and a top opening. The method also includes filling the microcells with an electrophoretic medium through the top opening and sealing the top opening of the filled microcells with a water-soluble polymer to form a sealing layer (e.g., sealing layer 740). For example, as described above, the electrophoretic microcells can be formed from polymers such as acrylates, vinyl ethers, or epoxides.

[0117] In some embodiments, the electrophoretic microcell layer can be filled with an electrophoretic medium comprising two or more types of electrophoretic particles, which typically have different electrophoretic mobilities and optical properties. For example, the electrophoretic medium can include a nonpolar fluid and charged pigment particles that move toward or away from the piezoelectric layer (e.g., piezoelectric layer 760) when the piezoelectric layer is subjected to mechanical stress.The electrophoretic medium can be sealed with a sealing layer (e.g., sealing layer 740), preferably a water-soluble sealing layer as described above. Non-polar fluids and charged pigment particles are sealed within the microcell using the sealing layer.

[0118] A second electrode can be bonded to the sealing layer. For example, the sealing layer of the microcell can be coated with a conductive material, such as PEDOT or one of the aforementioned materials. In some embodiments, as described above, the second electrode comprises a conductive material coupled to a suitable substrate material.

[0119] Furthermore, as described above, the method can include processing a piezoelectric material film to form a piezoelectric layer (e.g., piezoelectric layer 760) that includes one or more voids (e.g., voids or cutouts 763) in the piezoelectric material. The method can then include bonding the piezoelectric layer to the microcell layer on a surface opposite the sealing layer. For example, a roll-to-roll process such as lamination can be used to bond the piezoelectric layer to the microcell layer. In some embodiments, the piezoelectric layer can be coupled to the microcell using an adhesive layer (not shown in FIG. 7A).

[0120] The first electrode can be formed by depositing a conductive material on the piezoelectric layer. The conductive material used to form the first electrode fills one or more voids in the piezoelectric material and coats the surface of the piezoelectric layer. Thus, the conductive material of the first electrode filling one or more voids in the piezoelectric material is in contact with the microcell layer because the voids penetrate the piezoelectric material.

[0121] The piezoelectric electrophoretic display can be bonded to a target object. For example, a piezoelectric electrophoretic display such as that shown in FIG. 7A can be processed and attached to a target object such as paper, banknotes, or circulating currency. In some embodiments, a hot stamping process is used to bond the piezoelectric electrophoretic display to the target object. In some embodiments, the piezoelectric layer is polarized by an electric field. In some embodiments, the electric field is provided by corona discharge.

[0122] As described above, an alternative method can be used to manufacture the piezoelectric electrophoretic display 700, wherein the piezoelectric layer is formed on a suitable release liner and processed as described above to include one or more voids in the piezoelectric material. Furthermore, the first electrode can be formed by depositing a conductive material onto the piezoelectric layer, with the conductive material filling one or more voids in the piezoelectric material and coating the surface of the piezoelectric layer. In an alternative embodiment of the method, a release liner is then removed from the piezoelectric layer, which is bonded to the microcell layer on the surface opposite the sealing layer. In some embodiments, a roll-to-roll process is used to bond the piezoelectric layer to the microcell layer.

[0123] FIG7B shows a top view of the piezoelectric electrophoretic display 700, where electrode 781 is not shown. In FIG7B, cutout 763b is formed as a slit extending completely from one edge of the piezoelectric layer 760 to the opposite edge. FIG7C shows a top view of the piezoelectric electrophoretic display 700, where electrode 781 is not shown.In Figure 7C, the notches 763c are formed as small holes or through-holes that can be dispersed throughout the piezoelectric layer 760.

[0124] Similar to the embodiment shown in Figure 5, the piezoelectric layer 760 can be patterned with several notches 763 alternately. This allows images, shapes, and / or text to be embedded in the piezoelectric electrophoretic display 700. This can also increase the contrast of the piezoelectric electrophoretic display 700 because the potential generated near the piezoelectric material is different from the potential generated near the notches 763, as described below. The embodiments described in conjunction with Figures 7A-7C show the same effects as the embodiment of Figure 5, but also prevent any problems that may occur, such as the formation of small holes and bubbles or air gaps due to the lamination process.

[0125] Figure 8A shows a cross-section 801a of a piezoelectric electrophoretic display formed according to the subject matter disclosed herein, showing an electrophoretic dielectric layer (e.g., microcell 830), a sealing layer 840, and a second electrode 882 bonded together. Figure 8A also shows a first electrode 881 applied to the piezoelectric layer 860. In this embodiment, a conductive segment 883 has been formed on the surface of a piezoelectric layer 860 opposite to the first electrode 881. For example, the conductive segment 883 may be formed from a thin layer of a conductive material such as PEDOT. In some embodiments, the thickness of the conductive segment 883 is about 50-100 nm.

[0126] As shown by the arrow in FIG8A, a structure including the first electrode 881, the piezoelectric layer 860 and the conductive segment 883 is applied to the surface of the microcell 830 to form the piezoelectric electrophoretic display 800 shown in FIG8B. For example, a roll-to-roll lamination process can be used to form the piezoelectric electrophoretic display 800.

[0127] An exemplary process for manufacturing the piezoelectric electrophoretic display 800 will now be described. The method includes bonding a first electrode (e.g., first electrode 881) to a piezoelectric layer comprising polyvinylidene fluoride (PVDF) (e.g., piezoelectric layer 860). For example, as described above, the first electrode can be formed of a conductive material deposited on a piezoelectric material film. Next, as described above, one or more conductive segments (e.g., conductive segment 883) can be formed on the surface of the piezoelectric layer opposite the first electrode. In some embodiments, the conductive segments are formed of a thin layer of a conductive material such as PEDOT and have a thickness of approximately 50-100 nm.

[0128] The method includes forming a layer of microcells (e.g., microcell 830) having a bottom, walls, and a top opening. The method also includes filling the microcells with an electrophoretic medium through the top openings and sealing the top openings of the filled microcells with a water-soluble polymer to form a sealing layer (e.g., sealing layer 840). For example, as described above, the electrophoretic microcells can be formed of polymers such as acrylates, vinyl ethers, or epoxides.

[0129] In some embodiments, the electrophoretic microcell layer may be filled with an electrophoretic medium comprising two or more types of electrophoretic particles, which typically have different electrophoretic mobilities and optical properties. For example, the electrophoretic medium may include a nonpolar fluid and charged pigment particles, which move toward or away from the piezoelectric layer (e.g., piezoelectric layer 860) when the piezoelectric layer is subjected to mechanical stress. The electrophoretic medium may be sealed with a sealing layer (e.g., sealing layer 840), preferably a water-soluble sealing layer as described above. The nonpolar fluid and charged pigment particles are sealed within the microcell with the sealing layer.

[0130] A second electrode (e.g., second electrode 882) may be bonded to the sealing layer. For example, the sealing layer of the microcell may be coated with a conductive material, such as PEDOT or one of the other conductive materials described above. In some embodiments, as described above, the second electrode comprises a conductive material coupled to a suitable substrate material. The method may then include bonding the piezoelectric layer to the microcell layer on a surface opposite the sealing layer. For example, a roll-to-roll process such as lamination may be used to bond the piezoelectric layer to the microcell layer. In some embodiments, the piezoelectric layer can be coupled to the microcells using an adhesive layer (not shown in FIG. 8B).

[0131] Thus, the piezoelectric layer having conductive segments (e.g., conductive segment 883) is bonded to the microcell layer such that the conductive segments are in contact with the microcell layer. Advantageously, the conductive segment 883 in the piezoelectric electrophoretic display 800 exhibits the same effect as in the piezoelectric electrophoretic displays 500 and 700, requiring no cutting or post-processing of the piezoelectric layer 860 once it is adhered to the microcell 830 (or alternatively formed on a release liner). For example, in response to the charge generated by the piezoelectric material when mechanical stress is applied, the conductive segment 883 is driven to the same potential as the first electrode 881. Thus, the conductive segment 883 effectively acts as a short circuit between the first electrode 881 and the surface of the microcell 830, thereby achieving the same beneficial effects as in the piezoelectric electrophoretic displays 500 and 700. Furthermore, the thickness of the conductive segment 883 is small enough to achieve the surface roughness level of the piezoelectric layer 860. Therefore, no special processing or fabrication is required to manufacture the piezoelectric electrophoretic display 800.

[0132] The piezoelectric electrophoretic display can be bonded to a target object. For example, a piezoelectric electrophoretic display such as the piezoelectric electrophoretic display 800 can be processed and attached to a target object such as paper, banknotes, or circulating currency. In some embodiments, a hot stamping process is used to bond the piezoelectric electrophoretic display to the target object. In some embodiments, the piezoelectric layer is polarized by an electric field. In some embodiments, the electric field is provided by corona discharge.

[0133] Those skilled in the art will understand that the methods described herein are exemplary and not limiting. Other methods or other sequences of method steps can be used to manufacture displays having the structure and features of the piezoelectric electrophoretic display described herein.

[0134] It will be apparent to those skilled in the art that various 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 entire preceding description should be interpreted as illustrative rather than restrictive.

[0135] This disclosure provides aspects and embodiments as set forth in the following clauses:

[0136] Clause 1: A method for manufacturing a piezoelectric electrophoretic display including a first electrode and a second electrode, the method comprising: forming a microcell layer, wherein the microcell has a bottom, a wall and a top opening; filling the microcell through the top opening with an electrophoretic medium; sealing the top opening of the filled microcell with a water-soluble polymer to form a sealing layer; bonding a second electrode to the sealing layer; treating a piezoelectric material film to form a piezoelectric layer, the piezoelectric layer including one or more voids in the piezoelectric material; bonding the piezoelectric layer to the microcell layer on a surface opposite to the sealing layer; and forming the first electrode by depositing a conductive material onto the piezoelectric layer, wherein the conductive material fills one or more voids in the piezoelectric material and coats the surface of the piezoelectric layer.

[0137] Clause 2: A method for manufacturing a piezoelectric electrophoretic display, the method comprising: processing a piezoelectric material film on a release film to form a piezoelectric layer, the piezoelectric layer including one or more voids in the piezoelectric material; forming a first electrode by depositing a conductive material onto the piezoelectric layer, wherein the conductive material fills one or more voids in the piezoelectric material and coats a surface of the piezoelectric layer; forming a microcell layer, wherein the microcell has a bottom, a wall, and a top opening; filling the microcell with an electrophoretic medium through the top opening; sealing the top opening of the filled microcell with a water-soluble polymer to form a sealing layer; bonding a second electrode to the sealing layer; removing the release film from the piezoelectric layer; and bonding the piezoelectric layer to the microcell layer on a surface opposite to the sealing layer.

[0138] Clause 3: A method for manufacturing a piezoelectric electrophoretic display, the method comprising: bonding a first electrode to a piezoelectric layer comprising polyvinylidene fluoride (PVDF); forming one or more conductive segments on a surface of the piezoelectric layer opposite to the first electrode; forming a microcell layer, wherein the microcell has a bottom, a wall, and a top opening; filling the microcell through the top opening with an electrophoretic medium; sealing the top opening of the filled microcell with a water-soluble polymer to form a sealing layer; bonding a second electrode to the sealing layer; and bonding the piezoelectric layer and one or more conductive segments to the microcell layer on the surface opposite to the sealing layer.

[0139] Clause 4: The method of any one of Clauses 1-3, wherein the conductive material of the first electrode comprises poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

[0140] Clause 5: The method of any one of Clauses 1-4, wherein the second electrode comprises a conductive material coupled to a substrate.

[0141] Clause 6: The method of any one of Clauses 1-5, further comprising bonding a piezoelectric electrophoretic display to a target object, said target object comprising one of paper, banknotes, and circulating banknotes.

[0142] Clause 7: The method of any one of Clauses 1-6, wherein said piezoelectric layer is polarized by an electric field.

[0143] Clause 8: The method of any one of Clauses 1-7, wherein said electrophoretic medium comprises a nonpolar fluid and charged pigment particles, said charged pigment particles moving toward or away from said piezoelectric layer when the piezoelectric layer is subjected to mechanical stress, said nonpolar fluid and charged pigment particles being sealed in microcells by a sealing layer.

[0144] Clause 9: The method of Clause 1 or 2, wherein the conductive material of the first electrode filling one or more voids in the piezoelectric material is in contact with the microcell layer. Instruction manual 16 / 16 pages 19 CN 122497909 A Figure 1A Figure 1B Instruction manual drawing 1 / 8 pages 20 CN 122497909 A Figure 2 Instruction manual drawing 2 / 8 pages 21 CN 122497909 A Figure 3 Instruction manual drawing 3 / 8 pages 22 CN 122497909 A Figure 4 Instruction manual drawing 4 / 8 pages 23 CN 122497909 A Figure 5 Instruction manual drawing 5 / 8 pages 24 CN 122497909 A Figure 6 Figure 7A Instruction manual drawing 6 / 8 pages 25 CN 122497909 A Figure 7B Figure 7C Instruction manual drawing 7 / 8 pages 26 CN 122497909 A Figure 8A Figure 8B Instruction manual drawing 8 / 8 pages 27 CN 122497909 A.

Claims

1. A method for manufacturing a piezoelectric electrophoretic display including a first electrode and a second electrode, the method comprising: A layer of micro-units is formed, wherein the micro-units have bottom, wall and top openings; The micro-units are filled with an electrophoretic medium through the top opening; The top opening of the filled micro-unit is sealed with a water-soluble polymer to form a sealing layer; The second electrode is bonded to the sealing layer; A piezoelectric material film is processed to form a piezoelectric layer, the piezoelectric layer comprising one or more voids in the piezoelectric material; The piezoelectric layer is bonded to the micro-unit layer on the surface opposite to the sealing layer; and A first electrode is formed by depositing a conductive material onto the piezoelectric layer, wherein the conductive material fills one or more voids in the piezoelectric material and coats the surface of the piezoelectric layer.

2. The method of claim 1, wherein the conductive material of the first electrode comprises poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

3. The method of claim 1, wherein the conductive material of the first electrode filling one or more voids in the piezoelectric material is in contact with the microcell layer.

4. The method of claim 1, wherein the second electrode comprises a conductive material coupled to the substrate.

5. The method of claim 1, further comprising attaching the piezoelectric electrophoretic display to a target object, the target object being one of paper, banknotes, and circulating banknotes.

6. The method of claim 1, wherein the electrophoretic medium comprises a nonpolar fluid and charged pigment particles, wherein the charged pigment particles move toward or away from the piezoelectric layer when the piezoelectric layer is subjected to mechanical stress, wherein the nonpolar fluid and charged pigment particles are sealed in the microcell by a sealing layer.

7. The method of claim 1, wherein the piezoelectric layer is polarized by an electric field.

8. A method for manufacturing a piezoelectric electrophoretic display, the method comprising: A piezoelectric material film on a release film is processed to form a piezoelectric layer, the piezoelectric layer comprising one or more voids in the piezoelectric material; A first electrode is formed by depositing a conductive material onto the piezoelectric layer, wherein the conductive material fills one or more voids in the piezoelectric material and coats the surface of the piezoelectric layer. A layer of micro-units is formed, wherein the micro-units have bottom, wall and top openings; The micro-units are filled with an electrophoretic medium through the top opening; The top opening of the filled micro-unit is sealed with a water-soluble polymer to form a sealing layer; The second electrode is bonded to the sealing layer; Remove the release film from the piezoelectric layer; and The piezoelectric layer is bonded to the microcell layer on the surface opposite to the sealing layer.

9. The method of claim 8, wherein the conductive material of the first electrode comprises poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

10. The method of claim 8, wherein the conductive material of the first electrode filling one or more voids in the piezoelectric material is in contact with the microcell layer.

11. The method of claim 8, wherein the second electrode comprises a conductive material coupled to the substrate.

12. The method of claim 8, further comprising incorporating a piezoelectric electrophoretic display to a target object, said target object comprising one of paper, banknotes, and circulating banknotes.

13. The method of claim 8, wherein the electrophoretic medium comprises a nonpolar fluid and charged pigment particles, wherein the charged pigment particles move toward or away from the piezoelectric layer when the piezoelectric layer is subjected to mechanical stress, wherein the nonpolar fluid and charged pigment particles are sealed in the microcell by the sealing layer.

14. The method of claim 8, wherein the piezoelectric layer is polarized by an electric field.

15. A method for manufacturing a piezoelectric electrophoretic display, the method comprising: The first electrode is bonded to a piezoelectric layer containing polyvinylidene fluoride (PVDF); One or more conductive segments are formed on the surface of the piezoelectric layer opposite to the first electrode; A layer of micro-units is formed, wherein the micro-units have bottom, wall and top openings; The micro-units are filled with an electrophoretic medium through the top opening; The top opening of the filled micro-unit is sealed with a water-soluble polymer to form a sealing layer; The second electrode is bonded to the sealing layer; and The piezoelectric layer and one or more conductive segments are bonded to a micro-unit layer on the opposite surface of the sealing layer.

16. The method of claim 15, wherein the conductive material of the first electrode comprises poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

17. The method of claim 15, wherein the second electrode comprises a conductive material coupled to the substrate.

18. The method of claim 15, further comprising attaching a piezoelectric electrophoretic display to a target object, said target object comprising one of paper, banknotes, and circulating banknotes.

19. The method of claim 15, wherein the piezoelectric layer is polarized by an electric field.

20. The method of claim 15, wherein the thickness of the one or more conductive segments is about 50-100 nm.

21. The method of claim 15, wherein the one or more conductive segments comprise poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT-PSS).

22. The method of claim 15, wherein the electrophoretic medium comprises a nonpolar fluid and charged pigment particles, wherein the charged pigment particles move toward or away from the piezoelectric layer when the piezoelectric layer is subjected to mechanical stress, wherein the nonpolar fluid and charged pigment particles are sealed in the microcell by the sealing layer.

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