EP-4736155-A1 - MULTI-PARTICLE ELECTROPHORETIC DISPLAY HAVING LOW-FLASH IMAGE UPDATES

EP4736155A1EP 4736155 A1EP4736155 A1EP 4736155A1EP-4736155-A1

Abstract

Electrophoretic displays with multi-particle electrophoretic media and improved methods for driving such multi-particle electrophoretic media, especially using active matrix backplanes and controllers. The driving methods use faster gate updates with differential gaps between set of gate updates for a given pixel. The methods are generalizable to any electrophoretic display using push-pull waveforms, and are particularly well-suited for newer multi-particle electrophoretic displays capable of producing four or more colors at each pixel. Using such methods, electrophoretic displays will appear less "flashy" than addressing with conventional row-by-row constant-frame-spacing updating.

Inventors

HUITEMA, HJALMAR EDZER AYCO
TELFER, STEPHEN J.

Assignees

E Ink Corporation

Dates

Publication Date: 20260506
Application Date: 20240625

Claims (16)

1. An electrophoretic display comprising: a light-transmissive electrode; an active matrix backplane comprising a plurality of pixel electrodes, each pixel electrode being coupled to a thin-film transistor comprising a gate line and a source line, and each pixel electrode being coupled to a storage capacitor; an electrophoretic medium disposed between the light-transmissive electrode and the active matrix backplane, wherein the electrophoretic medium includes at least three different types of charged pigment particles; a controller coupled to a plurality of gate lines of the plurality of pixel electrodes and to a plurality of source lines of the plurality of pixel electrodes, the controller being configured to address the pixel electrodes in a row-by-row fashion; the controller further being configured to update an image on the electrophoretic display by performing the following steps: address a first row of pixel electrodes by providing a first gate voltage at a first time; address a second row of pixel electrodes by providing a second gate voltage at a second time; address the first row of pixel electrodes by providing a third gate voltage at a third time; address the second row of pixel electrodes by providing a fourth gate voltage at a fourth time; and address the first row of pixel electrodes by providing a fifth gate voltage at a fifth time, wherein the first, second, third, fourth, and fifth times are not the same, and a time elapsed between the first time and the third time is shorter than a time elapsed between the third time and the fifth time.
2. The electrophoretic display of claim 1, wherein the time elapsed between the third time and the fifth time is at least twice as long as the time elapsed between the first time and the third time.
3. The electrophoretic display of claim 1, wherein the time elapsed between the first time and the third time is less than 20 milliseconds, optionally less than 10 milliseconds, optionally around 6 milliseconds or shorter.
4. The electrophoretic display of claim 1, wherein the controller simultaneously provides a first source voltage to a pixel of the first row of pixel electrodes at the first time and a second source voltage to the pixel of the first row of pixel electrodes at the third time, and the polarity of the first source voltage and the polarity of the second source voltage are opposite.
5. The electrophoretic display of claim 4, wherein the magnitude of the first source voltage and the magnitude of the second source voltage are different.
6. The electrophoretic display of claim 4, wherein the magnitudes of the first source voltage and the magnitude of the second source voltage are between -15 V and +15V, or between -24V and +24V.
7. The electrophoretic display of claim 4, wherein the controller simultaneously provides a third source voltage to the pixel of the first row of pixel electrodes at the fifth time.
8. The electrophoretic display of claim 7, wherein the first source voltage and the third source voltage have the same polarity and magnitude.
9. The electrophoretic display of claim 1, wherein a portion of electrophoretic medium above a pixel electrode in the first row of pixel electrodes and a portion of the electrophoretic medium above a pixel electrode in the second row of pixel electrodes undergo a same color transition when the controller updates the image.
10. The electrophoretic display of claim 1, wherein the controller performs the additional following steps: address a third row of pixel electrodes by providing a sixth gate voltage at a sixth time; and address the third row of pixel electrodes by providing a seventh gate voltage at a seventh time, wherein the first, second, third, fourth, fifth, sixth, and seventh times are not equal, and the time elapsed between the first time and the third time is the same as the time elapsed between the sixth time and the seventh time.
11. The electrophoretic display of claim 1, wherein there are n rows of pixel electrodes in the active matrix backplane, and the first row of pixel electrodes and the second row of pixel electrodes are separated by nil rows of pixel electrodes.
12. The electrophoretic display of claim 11, wherein the controller provides at least two separate gate voltages to each and every thin-film transistor of the active matrix backplane between the first time and the fifth time.
13. The electrophoretic display of any of the proceeding claims wherein the electrophoretic medium includes a reflective white particle and at least one subtractive color particle or a reflective white particle and at least one reflective color particle.
14. The electrophoretic display of any of the proceeding claims wherein the electrophoretic medium includes a fourth type of electrophoretic particle.
15. The electrophoretic display of claim 14, wherein two of the types of particles are negatively charged and two of the types of particles are positively charged, or wherein one of the types of particles is negatively charged and three of the types of particles are positively charged, or wherein three of the types of particles are negatively charged and one of the types of particles is positively charged.
16. The electrophoretic display of any of the proceeding claims wherein the electrophoretic medium is encapsulated in microcapsules or microcells.

Description

MULTI-PARTICLE ELECTROPHORETIC DISPLAY HAVING LOW- FLASH IMAGE UPDATES RELATED APPLICATIONS [Para 1] This application claims priority to U.S. Provisional Application No. 63/523,541, filed June 27, 2023. All patents and publications disclosed herein are incorporated by reference in their entireties. BACKGROUND [Para 2] An electrophoretic display (EPD) changes color by modifying the position of one or more charged colored particles with respect to a light-transmissive viewing surface. Such electrophoretic displays are typically referred to as “electronic paper” or “ePaper” because the resulting display has high contrast and is sunlight-readable, much like ink on paper. Electrophoretic displays have enjoyed widespread adoption in eReaders because the electrophoretic displays provide a book-like reading experience, use little power, and allow a user to carry a library of hundreds of books in a lightweight handheld device. Such devices are increasingly being adapted to display of out-of-home (OOH) digital content, such as shelf labels, outdoor advertisement and transportation signage. [Para 3] For many years, electrophoretic displays included only two types of charged color particles, black and white. (To be sure, “color” as used herein includes black and white.) The white particles are often of the light scattering type, and comprise, e.g., titanium dioxide, while the black particle are absorptive across the visible spectrum, and may comprise carbon black, or an absorptive metal oxide, such as copper chromite. In the simplest sense, a black and white electrophoretic display only requires a light-transmissive electrode at the viewing surface, a back electrode, and an electrophoretic medium including oppositely charged white and black particles. When a voltage of one polarity is provided, the white particles move to the viewing surface, and when a voltage of the opposite polarity is provided the black particles move to the viewing surface. If the back electrode includes controllable regions (pixels) - either segmented electrodes or an active matrix of pixel electrodes controlled by transistors - a pattern can be made to appear electronically at the viewing surface. The pattern can be, for example, the text to a book. [Para 4] More recently, a variety of color option have become commercially available for electrophoretic displays, including three-color displays (black, white, red; black white, yellow), and four color displays (black, white, red, yellow). Similar to the operation of black and white electrophoretic displays, electrophoretic displays with three or four reflective pigments operate similar to the simple black and white displays because the desired color particle is driven to the viewing surface. The driving schemes are far more complicated than only black and white, but in the end, the optical function of the particles is the same. [Para 5] Advanced Color electronic Paper (ACeP™) also includes four particles, but the cyan, yellow, and magenta particles are subtractive rather than reflective, thereby allowing thousands of colors to be produced at each pixel. The color process is functionally equivalent to the printing methods that have long been used in offset printing and ink-jet printers. A given color is produced by using the correct ratio of cyan, yellow, and magenta on a bright white paper background. In the instance of ACeP, the relative positions of the cyan, yellow, magenta and white particles with respect to the viewing surface will determine the color at each pixel. While this type of electrophoretic display allows for thousands of colors at each pixel, it is critical to carefully control the position of each of the (50 to 500 nanometer-sized) pigments within a working space of about 10 to 20 micrometers in thickness. Obviously, variations in the position of the pigments will result in incorrect colors being displayed at a given pixel. Accordingly, exquisite voltage control is required for such a system. More details of this system are available in the following U.S. Patents, all of which are incorporated by reference in their entireties: U.S. Patent Nos. 9,361,836, 9,921,451, 10,276,109, 10,353,266, 10,467,984, 10,593,272, and 10,657,869. [Para 6] As described in the aforementioned patents, the waveforms (i.e., electric fields provided across the electrophoretic medium as a function of time) typically require substantial swings in voltage polarity in a short time. Because of this, in some instances, the colored electrophoretic display “flashes,” “flickers,” or “looks flashy” when switching between color images. This shortcoming is particularly pronounced when a full-color eReader is quickly switched (i.e., in less than 1 second) between full-color images. A solution to diminish the flashing in multi-particle electrophoretic displays, such as ACEP displays, is presented below. [Para 7] This invention relates to color electrophoretic displays, especially, but not exclusively, to electrophoret