Piezoelectric electrophoretic display

Abstract

A writing device includes a first electrode, a piezoelectric material layer; and an electrophoretic material layer located between the first electrode and the piezoelectric material layer, wherein stress on the piezoelectric material layer causes an optical change in the electrophoretic material layer.

Description

[0001] Citation of Related Applications

[0002] This application claims priority to U.S. Provisional Application No. 62 / 718,587, filed Aug. 14, 2018.

[0003] The entire disclosure of the above application is incorporated herein by reference. Technical Field

[0004] The subject matter disclosed herein relates to a piezoelectric electrophoretic display that can be activated or driven without being connected to a power source, and a method of operating such a device. Background Art

[0005] Non-emissive displays use a contrast difference to convey information, which is achieved by changing the reflectivity of light at different frequencies; thus, they are different from traditional emissive displays, which stimulate the eye by emitting light. One type of non-emissive display is an electrophoretic display, which utilizes the electrophoretic phenomenon to achieve contrast. Electrophoresis refers to the movement of charged particles in an applied electric field. When electrophoresis occurs in a liquid, the particle movement speed mainly depends on the viscous drag experienced by the particles, their charge, the dielectric properties of the liquid, and the magnitude of the applied electric field.

[0006] An electrophoretic display utilizes charged particles of one color (i.e., the light reflected by the particles) suspended in a dielectric liquid medium of a different color to be absorbed by the liquid. The suspension is contained in a cell located between (or partially defined by) a pair of oppositely disposed electrodes, one of which is transparent. When the electrodes are operated to apply a DC or pulsed field across the medium, the particles migrate towards the electrode of opposite sign. The result is a visually observable color change. In particular, when a sufficient number of particles reach the transparent electrode, their color dominates the display; however, if the particles are attracted to the other electrode, they are obscured by the color of the liquid medium, which then dominates. Summary of the Invention

[0007] In one aspect of the subject matter disclosed herein, a writing device includes a first electrode, a piezoelectric material layer, and an electrophoretic material layer located between the first electrode and the piezoelectric material layer, wherein stress on the piezoelectric material layer causes an optical change in the electrophoretic material layer. Brief Description of the Drawings

[0008] Figure 1 is a cross-sectional view of an exemplary writing device according to the subject matter disclosed herein;

[0009] Figure 2 is a cross-sectional view of another writing device according to the subject matter disclosed herein; and

[0010] Figure 3 is an embodiment of a writing board according to the subject matter disclosed herein. Detailed Description

[0011] As used herein, the term "electro-optic" as applied to a material or a display has its conventional meaning in the imaging art, and refers to a material having first and second display states, at least one optical property of which is different, and 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 a color perceptible to the human eye, it can be another optical property, such as light transmission, reflection, luminescence, or, in the case of a display for machine reading, a change in reflectivity of electromagnetic wavelengths outside the visible light range in the sense of a pseudo-color.

[0012] The terms "bistable" and "bistability" are used herein in their conventional meaning in the art, and refer to a display including a display element having first and second display states, at least one optical property of which is different, such that after driving any given element with an addressing pulse of a finite duration to present its first or second display state, after termination of the addressing pulse, the state will persist for a time that is at least several times (e.g., at least 4 times) the minimum duration of the addressing pulse required to change the state of the display element. As shown in U.S. Patent No. 7,170,670, some particle-based electrophoretic displays that support grayscale can be stable not only in their extreme black and white states, but also in their intermediate gray states, and so can some other types of electro-optic displays. Displays of this type are properly referred to as "multistable" rather than bistable, but for convenience, the term "bistable" may be used herein to cover both bistable and multistable displays.

[0013] The term "gray state" is used herein in its conventional meaning in the imaging art, and refers to a state intermediate between the two extreme optical states of a pixel, but does not necessarily imply a black-and-white transition between these two extreme states. For example, several patents and published applications of E Ink Corporation described hereinafter describe such electrophoretic displays in which the extreme states are white and dark blue, such that the intermediate "gray state" is actually light blue. In fact, as already mentioned, the change in the optical state may not be a color change at all. The terms "black" and "white" may be used hereinafter to refer to the two extreme optical states of the display, and should be understood to generally include extreme optical states that are not strictly black and white, such as the white and dark blue states mentioned above. The term "monochromatic" may be used hereinafter to denote a display or driving scheme that drives the pixel only to its two extreme optical states, without an intermediate gray state.

[0014] The term "pixel" is used herein in its conventional meaning in the display field, referring to the smallest unit of a display that can generate all the colors that the display itself can display. In a full-color display, typically, each pixel is composed of multiple sub-pixels, and each sub-pixel can display fewer colors than all the colors that the display itself can display. For example, in most conventional full-color displays, each pixel is composed of a red sub-pixel, a green sub-pixel, a blue sub-pixel, and optionally a white sub-pixel, and each sub-pixel is capable of displaying a color range from black to the brightest version of the designated color.

[0015] Several types of electro-optic displays are known. One type of electro-optic display is the rotating bichromal member type, as described, for example, in U.S. Patent Nos. 5,808,783, 5,777,782, 5,760,761, 6,054,071, 6,055,091, 6,097,531, 6,128,124, 6,137,467, and 6,147,791 (although this type of display is commonly referred to as a "rotating bichromal ball" display, the term "rotating bichromal member" is preferred to be more precise because in some of the above-mentioned patents, the rotating member is not spherical). This type of display uses many small bodies (usually spherical or cylindrical) and internal dipoles, and the bodies include two or more parts having different optical properties. These bodies are suspended within liquid-filled vesicles in a matrix, and the vesicles are filled with liquid such that the bodies are free to rotate. The appearance of the display is changed by applying an electric field to the display, thereby rotating the bodies to various positions and changing which part of the bodies is seen through the viewing surface. This type of electro-optic medium is typically bistable.

[0016] Another type of electro-optic display uses an electrochromic medium, such as an electrochromic medium in the form of a nanochromic film, which includes an electrode formed at least in part of a semiconductor metal oxide and a plurality of dye molecules attached to the electrode that can change color reversibly; 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. 6,301,038; 6,870,657; and 6,950,220. This type of medium is also typically bistable.

[0017] Another type of electro-optic display is the electrowetting display developed by Philips, which is described in Hayes, R. A. et al., "Video-Speed Electronic Paper Based on Electrowetting", Nature, 425, 383-385 (2003). Such an electrowetting display can be made bistable as shown in U.S. Patent No. 7,420,549.

[0018] One type of electro-optic display that has been the subject of intensive research and development for many years is the particle-based electrophoretic display, in which a plurality of charged particles move through a fluid under the influence of an electric field. Compared with liquid crystal displays, electrophoretic displays can have the properties of good brightness and contrast, wide viewing angles, bistable states, and low power consumption.

[0019] As described above, an electrophoretic medium requires the presence of a fluid. In most prior art electrophoretic media, the fluid is a liquid, but electrophoretic media can be made using a gaseous fluid; see, for example, Kitamura, T. et al., "Electronic toner movement for electronic paper-like display", IDW Japan , 2001, Paper HCS 1-1, and Yamaguchi, Y. et al., "Toner display using insulative particles charged triboelectrically", IDW Japan , 2001, Paper AMD4-4). See also U.S. Patent Nos. 7,321,459 and 7,236,291. When such a gas-based electrophoretic medium is used in a direction that allows particle sedimentation, such as in a sign where the medium is arranged in a vertical plane, this gas-based electrophoretic medium is prone to the same type of problems due to the same particle sedimentation as liquid-based electrophoretic media. In fact, the particle sedimentation problem in gas-based electrophoretic media is more severe than in liquid-based electrophoretic media because the lower viscosity of the gaseous suspension fluid allows electrophoretic particles to sediment faster compared to liquids.

[0020] Many patents and applications assigned to or in the names of the Massachusetts Institute of Technology (MIT) and E Ink Corporation describe various techniques for encapsulating electrophoretic and other electro-optic media. Such encapsulated media include many small capsules, each capsule itself including an inner phase and a capsule wall surrounding the inner phase, where the inner phase contains electrophoretically mobile particles in a fluid medium. Typically, the capsules themselves are held in a polymeric binder to form a coherent layer between two electrodes. The techniques described in these patents and applications include:

[0021] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814;

[0022] (b) Capsules, binders, and encapsulation processes; see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719;

[0023] (c) Films and subassemblies containing electro-optic materials; see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564;

[0024] (d) Backplanes, adhesive layers, and other auxiliary layers and methods for use in displays; see, for example, U.S. Patent Nos. 7,116,318 and 7,535,624;

[0025] (e) Color formation and color adjustment; see, for example, U.S. Patent Nos. 7,075,502 and 7,839,564;

[0026] (f) Methods for driving displays; see, for example, U.S. Patent Nos. 7,012,600 and 7,453,445;

[0027] (g) Applications of displays; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348;

[0028] (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;

[0029] (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

[0030] (j) Methods for filling and sealing microcells; see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088.

[0031] Many of the foregoing patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, resulting in so-called polymer dispersed electrophoretic displays, where the electrophoretic medium includes a plurality of discrete microdroplets of electrophoretic fluid and a continuous phase of polymeric material, and the discrete microdroplets of electrophoretic fluid within such polymer dispersed electrophoretic displays can be considered capsules or microcapsules even though no discrete capsule membrane is associated with each individual microdroplet; see, for example, the foregoing U.S. Patent No. 6,866,760. Thus, for the purposes of the present application, such polymer dispersed electrophoretic media are considered a subclass of encapsulated electrophoretic media.

[0032] A related type of electrophoretic display is the so-called "microcell electrophoretic display". In a microcell electrophoretic display, charged particles and fluid are not encapsulated within microcapsules, but rather are held within a plurality of cavities formed within a carrier medium (typically a polymeric film). See, for example, U.S. Patent Nos. 6,672,921 and 6,788,449, both assigned to Sipix Imaging, Inc.

[0033] Although electrophoretic media are generally opaque (because, for example, in many electrophoretic media, the particles substantially block visible light transmission through the display) and operate in a reflective mode, many electrophoretic displays can be made to operate in a so-called "shutter mode", in which one display state is substantially opaque and one display state is light transmissive. See, for example, U.S. Patent Nos. 5,872,552, 6,130,774, 6,144,361, 6,172,798, 6,271,823, 6,225,971, and 6,184,856. Dielectrophoretic displays, which are similar to electrophoretic displays but rely on changes in electric field strength, can operate in a similar mode; see U.S. Patent No. 4,418,346. Other types of electro-optic displays are also capable of operating in the shutter mode. Electro-optic media that operate in the shutter mode can be used in multilayer structures for full-color displays; in such structures, at least one layer adjacent to the viewing surface of the display operates in the shutter mode to expose or hide a second layer that is further from the viewing surface.

[0034] Encapsulated electrophoretic displays are generally not subject to the aggregation and sedimentation failure modes of conventional electrophoretic devices and offer additional benefits, such as the ability to print or coat the display on a variety of flexible and rigid substrates. (The use of the word "print" is intended to include all forms of printing and coating, including but not limited to: pre-metered coating such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating; roll coating such as rod bar coating, forward and reverse roll coating; gravure coating; dip coating; spraying; meniscus coating; spin coating; brush coating; air knife coating; screen printing processes; electrophotographic processes; thermal printing processes; ink jet printing processes; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques.) Accordingly, the resulting display can be flexible. Additionally, because the display medium can be printed using a variety of methods, the display itself can be manufactured inexpensively.

[0035] Other types of electro-optic materials can also be used in the present invention.

[0036] An electrophoretic display typically includes an electrophoretic material layer and at least two other layers disposed on opposite sides of the electrophoretic material, one of the two layers being an electrode layer. In most such displays, both layers are electrode layers, and one or both electrode layers are patterned to define the pixels of the display. For example, one electrode layer can be patterned as elongated row electrodes, and the other electrode layer can be patterned as elongated column electrodes extending perpendicular to the row electrodes, with the 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, while the other electrode layer is patterned as a matrix of pixel electrodes, each pixel electrode defining a pixel of the display. In another type of electrophoretic display designed to be used with a stylus, print head, or similar separable movable electrode relative to the display, only one of the layers adjacent to the electrophoretic layer includes an electrode, and the layer on the opposite side of the electrophoretic layer is typically a protective layer designed to prevent damage to the electrophoretic layer by the movable electrode.

[0037] In yet another embodiment, as described, for example, in U.S. Patent No. 6,704,133, an electrophoretic display can be constructed to have two continuous electrodes and an electrophoretic layer and an electrokinetic layer between the electrodes. Since the electrokinetic material changes resistivity upon absorption of photons, incident light can be used to change the state of the electrophoretic medium. Such a device is shown in Figure 1 As described in U.S. Patent No. 6,704,133, Figure 1The device works best when driven by a light source (such as an LCD display) located on the opposite side of the display from the viewing surface. In some embodiments, the device of U.S. Patent No. 6,704,133 includes a specific barrier layer between the front electrode and the electrophoretic material to reduce the "dark current" caused by incident light from the front of the display leaking through the reflective electro-optic medium.

[0038] The aforementioned U.S. Patent No. 6,982,178 describes a method of assembling a solid electro-optic display (including an encapsulated electrophoretic display) that is well-suited for mass production. Substantially, the patent describes a so-called "front plane laminate" ("FPL") that sequentially includes a light-transmissive conductive layer, a solid electro-optic dielectric layer in electrical contact with the conductive layer, an adhesive layer, and a release sheet. Generally, the light-transmissive conductive layer will be carried on a light-transmissive substrate, which is preferably flexible in the sense that the substrate can be manually wrapped around (e.g.) a 10-inch (254 mm) diameter roller without permanent deformation. The term "light-transmissive" is used in this patent and herein refers to a layer so designated that transmits sufficient light for an observer to view changes in the display state of the electro-optic medium through the layer, which will generally be through the conductive layer and an adjacent substrate (if present); in the case where the electro-optic medium displays a change in reflectivity at an invisible wavelength, the term "light-transmissive" should of course be interpreted as relating to the transmission of the relevant invisible wavelength. The substrate is typically a polymer film and will generally have a thickness in the range of about 1 to about 25 mils (25 to 634 microns), preferably about 2 to about 10 mils (51 to 254 microns). The conductive layer is conveniently a thin metal or metal oxide layer such as aluminum or ITO, or can be a conductive polymer. Poly(ethylene terephthalate) (PET) films coated with aluminum or ITO are commercially available, for example, "aluminized Mylar" (where "Mylar" is a registered trademark) from DuPont Company in Wilmington, Delaware, and such commercial materials can have good results in the front plane laminate.

[0039] The assembly of an electro-optic display using such a front plane laminate can be achieved by removing the release sheet from the front plane laminate and bringing the adhesive layer into contact with a backplane under conditions such that the adhesive layer effectively adheres to the backplane, thereby fixing the adhesive layer, the electro-optic dielectric layer, and the conductive layer to the backplane. This process is well-suited for mass production because the front plane laminate can typically be mass-produced using roll coating techniques and then cut into pieces of any size for a particular backplane.

[0040] U.S. Patent No. 7,561,324 describes a so-called "dual-release sheet", which is essentially a simplified version of the front planar laminate of the aforementioned U.S. Patent No. 6,982,178. One form of the dual-release sheet includes a solid electro-optic dielectric layer sandwiched between two adhesive layers, where one or both of the adhesive layers are covered by release sheets. Another form of the dual-release sheet includes a solid electro-optic dielectric layer sandwiched between two release sheets. Both forms of the dual-release sheet film are intended for use in a process generally similar to the process of assembling electro-optic displays from front planar laminates as already described, but involving two separate laminations; typically, in the first lamination, the dual-release sheet is laminated to the front electrode to form a front subassembly, and then in the second lamination, the front subassembly is laminated to the backplane to form the final display, but the order of these two laminations can be reversed if desired.

[0041] U.S. Patent No. 7,839,564 describes a so-called "inverted front planar laminate", which is a variant of the front planar laminate described in the aforementioned U.S. Patent No. 6,982,178. The inverted front planar laminate sequentially includes at least one of a light-transmissive protective layer and a light-transmissive conductive layer, an adhesive layer, a solid electro-optic dielectric layer, and a release sheet. The inverted front planar laminate is used to form an electro-optic display that has a laminated adhesive layer between the electro-optic layer and the front electrode or front substrate; a second, usually thinner, adhesive layer may or may not be present between the electro-optic layer and the backplane. Such an electro-optic display can combine good resolution with good low-temperature performance.

[0042] The photoelectrophoretic properties of certain pigments were recognized some time ago. For example, U.S. Patent No. 3,383,993 discloses a photoelectrophoretic imaging device that can be used to reproduce projected images on a medium (such as ITO), which is typically a transparent electrode. However, the photoelectrophoretic process described in the '993 patent and other related patents of Xerox Corporation is irreversible because the photoelectrophoretic process involves the migration of photoelectrophoretic particles to an "injecting electrode", where they will adhere to the electrode. Due to the lack of reversibility, as well as the cost and complexity of installation, this phenomenon has not been widely commercialized.

[0043] The subject matter presented herein relates to several designs of piezoelectrophoretic display structures that do not require a power source (such as a battery or a wired power source, etc.) to operate the electrophoretic display. Thus, the assembly of such an electrophoretic display is simplified.

[0044] Piezoelectricity is the electric charge that accumulates in solid materials in response to an applied mechanical stress. Suitable materials for the subject matter disclosed herein can include polyvinylidene fluoride (PVDF), quartz (SiO2), berlinite (AlPO4), single crystal gallium phosphate (GaPO4), tourmaline, barium titanate (BaTiO3), lead zirconate titanate (PZT), zinc oxide (ZnO), aluminum nitride (AlN), lithium tantalate, lanthanum gallium silicate, sodium potassium tartrate, and any other known piezoelectric material.

[0045] Many electrophoretic displays are bistable: their state persists even after the activating electric field has been removed. This is typically achieved through residual charge on the electrodes and van der Waals interactions between the particles and the walls of the electrophoretic cell. Driving an electrophoretic display requires a power source, such as a battery, to supply power to the display and / or its driving circuitry. The power source can be a driver IC to generate the electric field. The electric field may also need to be enhanced by a circuit. In any case, a physical connection via wires is required to attach the power source to the electrophoretic display and its driving circuitry.

[0046] An erasable drawing device is known. An erasable drawing device typically consists of a blackboard, a paper pad, or a whiteboard, and an erasable marking device (such as chalk, a pencil, or a dry-erase marker).

[0047] One drawback of such a drawing device is that the marking device may dissipate and need to be replaced. Another drawback is that the marking device may make marks on surfaces other than the screen of the drawing device, causing confusion. Another drawback is that even with the use of cleaning agents and vigorous erasing, the screen may not be completely erased.

[0048] Electronic drawing devices overcome some of the above problems. An electronic drawing device typically includes a touch screen and appropriate logic to cause the underlying electronic display to update its image in response to the movement of a stylus. The device includes, for example, a graphics input pad having a transparent capacitive pixel array that changes its capacitance in response to a conductive-tip stylus passing over the pad. The change in capacitance is sensed and used to address an LCD matrix. The drawback of this electronic drawing device is that it requires complex electronics and a large amount of power.

[0049] Magnetophoretic displays, which are commonly used as children's drawing toys, are another example of erasable drawing devices. In a magnetophoretic display, the stylus used to write on the display contains a magnet, and the contrast agent on the display contains a black iron material and white titanium dioxide. Magnetophoretic displays do not require a power source. However, magnetophoretic displays generally do not allow users to selectively erase parts of the drawing on the display unless the user has access to the front and back of the magnetophoretic medium. Typically, manufacturers of magnetophoretic displays only provide access to one surface only. The display is erased using a slider magnet embedded behind the magnetophoretic medium. Therefore, the display cannot be selectively erased.

[0050] Electrostatically addressed liquid crystal displays are another type of drawing device known in the art. However, liquid crystal drawing devices suffer from poor image persistence due to the dissipation of the surface static charge that maintains the image. Using higher voltages and additional resistive layers, the image persistence can be extended, but even then, a persistence of more than 30 minutes is considered the current highest level.

[0051] Electrophoretic displays are also used as drawing devices. In an electrophoretic drawing device, when an electric field is applied across the display medium, the electrophoretic particles in the display medium of the device migrate towards or away from the drawing surface of the device. For example, the drawing device can include a back electrode covered with an electrophoretic coating. To write, a positive voltage is applied to the back electrode, and the stylus in contact with the electrophoretic coating is set to ground. The stylus acts as a top electrode in a local area. A potential is generated between the stylus and the back electrode, which causes the migration of the electrophoretic particles and a color change in the device. The entire system can be covered with a dielectric or anisotropic top layer that protects the electrophoretic medium. Chiang et al., “A Stylus Writable Electrophoretic Display Device,” Society for Information Display 1979 Digest, describes an electrophoretic drawing device. Although this type of electrophoretic display can provide excellent contrast and brightness, as well as good electrical performance and image persistence, it still requires power to operate.

[0052] Some aspects of the subject matter presented herein utilize piezoelectricity to drive the pigments of electrophoretic materials to change the color of the electrophoretic materials when viewed from an observation surface. For example, by bending or applying stress to a piece of piezoelectric material, charges can be generated, and these charges can be used to cause the movement of the colored pigments of the electrophoretic materials. As used herein, the term “contrast ratio” (CR) for an electro-optical display (e.g., an electrophoretic display) is defined as the ratio of the luminance of the brightest color (white) to the luminance of the darkest color (black) that the display is capable of producing. Generally, a high contrast ratio, i.e., CR, is a desirable aspect of a display.

[0053] As described above, in some embodiments, a piezoelectric material can be used to generate charge to power a writable device having electrophoretic material. The writable device can operate without a power source and be powered only by the charge generated by the piezoelectric material. In practice, a user can write on the device using a stylus (conductive or non-conductive) or any pointed object, and can also erase the writing without being coupled to a power source.

[0054] Figure 1 An exemplary embodiment of a writable device in accordance with the subject matter disclosed herein is shown. As Figure 1 shown, device 100 can include an electro-optic dielectric layer 106 (e.g., an electrophoretic material layer) located between a first electrode 104 and a piezoelectric material layer 108. The electrophoretic material layer can include micro-units or micro-capsules having electrophoretic particles, or any other electrophoretic material commonly used in the art. In some embodiments, the top electrode 104 can be a layer of a light-transmissive conductive material, where the term "light-transmissive" is used herein to describe that layer 104 is capable of transmitting sufficient light such that an observer can observe a change in the display state of the electro-optic dielectric through that layer 104, which will typically be observed through the conductive layer and an adjacent substrate (if present); in the case where the electro-optic dielectric exhibits a change in reflectivity at an invisible wavelength, the term "light-transmissive" should of course be interpreted as relating to the transmission of the relevant invisible wavelength. It should be understood that there should be no continuous conductor between the electrophoretic material 106 and the piezoelectric material 108. The absence of a conductor between these two layers can improve the CR of the writing device.

[0055] In addition, in some embodiments, there can be a second electrode 110 located on the opposite side of the piezoelectric material 108 from the electrophoretic material 106. The second electrode 110 can be separated from the piezoelectric material 108 by a gap or spacer 102, preferably, the gap 102 is narrow. In practice, a stylus 112 can be used to apply stress to the piezoelectric material 108. The stylus 112 can be pressed against the first electrode 104 as if the stylus 112 were being used to write on the first electrode 104. This pressing force can cause the electrophoretic material 106 and the piezoelectric material 108 to bend accordingly. Desirably, this bending can cause the piezoelectric material 108 to contact the second electrode 110 across the gap 102. In this way, when the piezoelectric material 106 is subjected to such stress caused by writing on the first electrode 104 by the stylus 112, the piezoelectric material 106 thus generates charge. In some embodiments, when the piezoelectric material 106 contacts the second electrode 110, a conduction path can be formed that allows the generated charge to cause the movement of colored pigments within the electrophoretic material 106, where the movement of the pigments can cause an optical state change in the electrophoretic material 106 (e.g., at the location where the stylus 112 writes, the electrophoretic material 106 can change from white to black). And Figure 1Similar to the embodiments shown, it should be understood that where writing is expected, there is no continuous conductor between the piezoelectric material and the electrophoretic material. The absence of a continuous conductor can contribute to better CR of the writing device.

[0056] In some embodiments, instead of the gap 102, the piezoelectric film 108 can be positioned on top of the second electrode 110 without lamination. In this way, the piezoelectric film 108 is in slight contact with the second electrode 110. And when the stylus 112 performs a writing operation on the first electrode 104, the stylus 112 can apply a force to the EPD film 106 and the piezoelectric film 108 and cause both films to bend in the vertical direction. Such bending and the applied force can create a closer contact between the piezoelectric film 108 and the second electrode 110, and cause a change in resistance between the piezoelectric film 108 and the second electrode 110. In use, this change in resistance and the charge generated by the piezoelectric film 110 can cause visible lines (such as black lines) to appear separately where the stylus has written.

[0057] In practice, the size of the stylus 112 may affect the clarity and / or contrast of the writing on the electrophoretic material 106. For example, compared with a stylus having a larger-sized tip, a smaller or thinner-tipped stylus 106 can produce clear and / or legible handwriting. This may be due to the fact that when writing on the first electrode 104, the smaller-tipped stylus creates pressure or stress on the underlying electrophoretic film 106 and piezoelectric film 108, which also creates a relatively small contact surface area with the second electrode 110. Compared with a stylus having a larger tip, due to this relatively small contact surface area (compared with a stylus having a larger-sized tip), the electric field generated by the charge from the piezoelectric film can be located in a smaller area, which increases the magnitude of the generated electric field, and thus produces clearer handwriting with improved CR. In some other embodiments, the thickness of the electrophoretic layer and the overall thickness of the writing device 100 may also affect the clarity and / or CR of the writing. This may be due to the fact that the thicker the device, the greater the curvature generated due to writing, and thus the larger the contact surface area, which reduces the localization of the generated electric field. It should be understood that the stylus 112 used here does not need to be made of a conductive material.

[0058] Similarly, the writing device 100 can be bent (e.g., compressed) or written in the direction from the second electrode 110 towards the first electrode 104. In this way, the electrophoretic film 106 is bent or compressed from the opposite direction as described above, where alternatively, the electrophoretic film 106 is bent or compressed towards the first electrode layer 104. Thus, the charge generated by the electrophoretic film 106 will flow in the opposite direction as described above and also generate an opposite electric field. Therefore, the color pigments of the electrophoretic material 106 will move in the opposite direction as described above and produce different optical changes. For example, writing on the second electrode 110 can produce a different color of writing on the first electrode 104 compared to writing on the first electrode 104. If writing on the first electrode 104 produces a black line on the first electrode 104, then writing on the second electrode 110 will produce a non-black line, e.g., a white line. In some embodiments, the writing on the first electrode 104 can be erased by generating stress on the second electrode 110. For example, the writing produced on the first electrode 104 can be black. Generating stress (e.g., writing) at approximately the same position on the second electrode 110 can produce white writing on the first electrode 104, thus effectively erasing or masking the black writing. It should be understood that the second electrode 110 preferably should have a resistance less than 10 13 ohms. A resistivity exceeding this limit may cause the second electrode 110 to not conduct electricity sufficiently for the device 100 to operate properly.

[0059] In some embodiments, the electrophoretic material 106 for the device 100 can be an electrophoretic material designed for low-voltage applications. Such materials can include microcells that are shallower than the usual cell depth or height. Examples of electrophoretic media or displays based on microcells can be found in U.S. Patent Nos. 7,072,095 and 9,279,906, the entire contents of which are incorporated herein. In some embodiments, if a regular or standard microcell has a cell depth or height of 60, the low-voltage material can have a cell height or depth of 40 microns or less. In some other embodiments, the height or depth of the microcell can be less than 20 microns. In some embodiments, for shallow microcells, the fluid sealed inside the microcell can also have a different chemical composition. For example, the electrophoretic material 106 can have an inner phase with a viscosity of 1 Pa*S and a particle concentration of 39%. Shown in Table 1 below are examples of electrophoretic materials that can be utilized.

[0060]

[0061] Table 1. Electrophoretic Materials for Low-Voltage Applications

[0062] In some other embodiments, a conductive stylus 202 can be used to write directly on the piezoelectric material, such as Figure 2As shown. In this configuration, the writing device 200 may have only the first electrode 204. The electrophoretic material 206 may be located between the first electrode 204 and the piezoelectric film material 208. However, in this case, a conductive stylus 202 is used to write directly on the piezoelectric material. The compression on the piezoelectric material 208 caused by the stylus 202 generates charges, which can be used to change the optical state of the electrophoretic material 206. It should be noted that the stylus 202 used herein is preferably made of a conductive material.

[0063] Figure 3 An embodiment is shown in which Figure 1 and 2 the configuration shown can be integrated into a large writing device 300. In some embodiments, the entire device may include a writing unit 302 that includes multiple rows of mechanical styli, and writing can be completed on the writing unit 302. Depending on the application, the writing unit 302 may have the same size as or be smaller than the display unit 304. The writing device may also include an erasing unit 306 in the form of a roller, where a continuous rolling action can erase the entire board. In some embodiments, the material for erasing needs to have a lower resistivity of <10 13 Ohm / sq and elastic properties. Non-limiting examples of such materials are silicone rubber, natural latex rubber, thermoplastic elastomer (TPE), thermoplastic vulcanizate (TPE-v), thermoplastic polyurethane (TPU), and ethylene-vinyl acetate copolymer (EVA), each having additives such as carbon, copper, nickel, or silver flakes.

[0064] In some embodiments, the resistivity of the writing stylus may be similar to that of the eraser or erasing device described above.

[0065] It will be apparent to those skilled in the art that many changes and modifications can be made to the specific embodiments of the present invention described above without departing from the scope of the invention. Accordingly, the entire foregoing description is to be construed in an illustrative rather than a restrictive sense.

Claims

1. A writing device, comprising: A first electrode; A piezoelectric material layer; An electrophoretic material layer located between the first electrode and the piezoelectric material layer, wherein stress on the piezoelectric material layer causes an optical change in the electrophoretic material layer; A second electrode located on a side of the piezoelectric material opposite to the first electrode; And A gap located between the piezoelectric material layer and the second electrode.

2. The device according to claim 1, wherein, The electrophoretic material layer is micro-unit based.

3. The device according to claim 1, wherein, The electrophoretic material layer is microcapsule based.

4. The device according to claim 1, further comprising a stylus.

5. The device according to claim 4, wherein, The stylus is non-conductive.

6. The device according to claim 4, wherein, The stylus is conductive.

7. The device according to claim 1, wherein The resistivity of the second electrode is less than 10 13 Ohm / sq.

8. The device according to claim 2, wherein The height of the micro-units is less than 20 micrometers.

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