AN ELECTROWETTING OPTICAL ELEMENT

Abstract

An electrowetting optical element, a method of manufacturing and a display including the same. The element includes a containment space containing a polar liquid relative to a non-polar liquid, immiscible with each other, a first electrode layer stack defining a first enclosing surface of the space and including a substrate, a first electrode layer, and an insulating layer having a hydrophobic first interface layer with the space, a second electrode layer stack defining a second enclosing surface of the space and including a superstrate and a second electrode layer having a second interface layer with the space and one or more cell walls fixedly mounted on the second stack and extending toward the first stack, for defining sides of the space. An end face of the walls adjacent the first stack faces the first layer in a loose manner, the second stack includes a thin film transistor electrode layer, and the walls are composed of electrically insulating material.

Claims

1-9. (canceled)

10. An electrowetting optical element, comprising: a containment space for containing a polar liquid relative to a non-polar liquid, wherein the polar liquid and the non-polar liquid are immiscible with each other; a first electrode layer stack defining a first enclosing surface of the containment space, and comprising a substrate, a first electrode layer, and an insulating layer having a hydrophobic first interface layer with the containment space; a second electrode layer stack defining a second enclosing surface of the containment space, and comprising a superstrate and a second electrode layer having a second interface layer with the containment space; and one or more cell walls, fixedly mounted on the second electrode layer stack and extending towards the first electrode layer stack, defining sides of the containment space; wherein an end face of the one or more cell walls adjacent the first electrode layer stack faces the hydrophobic first interface layer in a loose manner; wherein the second electrode layer stack comprises a thin film transistor electrode layer; and wherein the one or more cell walls are comprised of an electrically insulating material.

11. The electrowetting optical element according to claim 10, wherein the electrically insulating material is comprised in an insulating surface layer of the one or more cell walls.

12. The electrowetting optical element according to claim 10, wherein the one or more cell walls are comprised of a monolithic insulating material.

13. The electrowetting optical element according to claim 10, wherein the one or more cell walls comprise a hydrophobic surface layer formed on the end face of the one or more cell walls adjacent the first electrode layer stack.

14. The electrowetting optical element according to claim 10, wherein a slit is provided between the end face of the one or more cell walls and the first electrode layer stack.

15. The electrowetting optical element according to claim 10, wherein the thin film transistor electrode layer comprises at least one transistor layout per containment space.

16. The electrowetting optical element according to claim 10, wherein the thin film transistor electrode layer comprises an indium tin oxide layer.

17. An electrowetting optical display comprising one or more electrowetting optical elements according to claim 10.

18. A method of manufacturing an electrowetting optical display, comprising the steps of: providing a first electrode layer stack comprising a substrate, a first electrode layer, and an insulating layer having a hydrophobic surface layer; providing a second electrode layer stack comprising a deposited thin film transistor layer; attaching cell walls to the second electrode layer stack to form a containment space defined at least by the second electrode layer stack and the cell walls; filling the containment space with a polar liquid and a non-polar liquid, wherein the polar liquid and the non-polar liquid are immiscible with each other; and covering the containment space with the first electrode layer stack.

Description

[0046] The invention will further be described with reference to the enclosed drawings wherein embodiments of the invention are illustrated, and wherein:

[0047] FIG. 1 shows in an illustrative manner, an electrowetting optical cell or pixel in accordance with an aspect of the invention;

[0048] FIG. 2 shows in an illustrative manner cross-sectional view of a cell of an electrowetting display with a three layered stack;

[0049] FIG. 3 shows in an illustrative manner an electrowetting optical cell or pixel with an active matrix TFT layer in accordance with an aspect of the invention.

[0050] FIG. 1 shows an electrowetting optical element or electrowetting element 10. In this figure only one single electrowetting optical element 10 is shown.

[0051] However, in a many electrowetting applications, such as digital traffic signs, message centers, full color billboards, wall scrapings, dynamic camouflage and other (outdoor) digital displays, the electrowetting display contains several of these elements 10.

[0052] Preferably, several cells form a tile which may be used to display a (single) character. A plurality of adjacent tiles may be contained in an electrowetting optical panel. The electronics to provide control and power to the device may be provided per panel, such that a panel can be operated separately. In most applications however the display may comprise several panels. The display, in case of multiple tiles and multiple panels, may comprise an optical wave guide to optically remove the visibility of the boundary of the element, i.e. the bezel or passive area of the individual electrowetting optical element.

[0053] The electrowetting element 10 of FIG. 1 consists of a containment space which is present between a two electrode layers 18, 20. The first electrode layer 18, seen from bottom to top, consists of a glass substrate 18. On top of the glass substrate is a transparent electrode(s) 16. The electrode is isolated from the other materials by an insulator layer 15 which covers the electrode(s) 16. The interface layer 14 is a layer with hydrophobic properties, such as a fluoropolymer. In order to improve the adhesion of the fluoropolymer to the insulator layer, the substrate may preferably also be provided with an adhesion promoting layer which is disposed between the fluoropolymer 14 and the insulator layer 15. Complete stack at the bottom of the pixel is also known as the substrate layer and defines a first enclosure surface of the containment space in which the two liquids 11, 12 are disposed.

[0054] The second stack is the superstrate or also known as the second electrode layer or second electrode layer stack. This second electrode layer defines a second enclosure surface of the containment space with the two liquids 11, 12. The second layer may also be constructed from a glass substrate 20 or also called superstrate. On top of the glass substrate a transparent electrode 21 is disposed, which is preferably formed of an electrically conducting material such as indium tin oxide (ITO) and preferably has a interface surface forming the interface with the containment space 25. As an alternative to ITO other transparent conducting materials may also be applicable. Also a conductive organic material known in the art having lower hydrophobic properties than the hydrophobic interface surface 14 of the first layer can be used.

[0055] The cell walls 13 are mounted on or attached to the second electrode layer stack 20 only and extend from this second electrode towards the first electrode interface layer 14. The cell walls 13 comprise small free end faces near the first interface layer 14. In between both a small slit may be present which is not shown in FIG. 1. This slit enables the non-polar liquid 12 to entrain the slits, and to form a small interface on the other side of the slit near the edge of the cell walls resulting from capillary action within the slit. An effect of the small capillary interface is that it greatly reduces the amount of light scattering caused by the cell walls 13 in the electrowetting optical cell from one electrode layer stack towards the other. The cell walls 13 thus form an effective barrier for the polar liquid 12 between the electrowetting cell and adjacent electrowetting cells to keep the non-polar liquid 12 from moving towards other cells. Although FIG. 1 may suggest a squire shaped pixel the electrowetting elements can have arbitrary shapes determined by the shape of the electrodes and cell walls, such that displays can be manufactured for specific purposes.

[0056] Together, the first and second electrode layer and the cell walls 13 allow the electrowetting element 10 to be powered on and off by applying an appropriate voltage 19 over the liquids. The superstrate layer 20 and substrate layer 18 may be formed by any suitable material but will often be formed by a transparent glass layer, and dependent on whether the electrowetting optical cell is of the transparent type or reflective type, the substrate layer may be formed by a non-transparent layer as well. Preferably, both the superstrate layer and substrate layer are formed from or flexible polymer material such as polyethersulfone (PES), polyimide (PI), polythiophene (PT), phenol novolac (PN), or polycarbonate (PC). Most preferably, the substrate and/or superstrate are formed from a polyethylene naphthalate or PEN. The PEN material is known to have very good barrier properties.

[0057] The layout of electrowetting element 40 with the thin film transistor is demonstrated in FIG. 3. The electrowetting element 40 is preferably comprised of a (flexible or rigid) thin film substrate transparent TFT and a thin film superstrate. The element is defined by the containment space in which the oil and water liquids are contained. This containment space has dimensions equal to the dimensions of the area formed by the two horizontal control lines 41, 44 and the two vertical control lines 43, 46. These control lines are preferably aligned with the cell walls such that no active area is lost. Since the cell walls of the electrowetting element extend between the two substrates, it is proposed to manufacture these walls from an electrically insulating material or provide them with such a coating or added layer. This way a voltage breakdown between the control lines, the transistor and the electrodes may be prevented or at least limited.

[0058] The pixel or cell can be activated through control of the horizontal and vertical control lines 41, 44, 43, 46. These vertical control lines may also be defined as source lines M 43 and the subsequent source line M+1 46. The horizontal control lines may also be defined as the gate line M 41 and the subsequent gate line M+1 44. In the intersection of the source line 41 and gate line 43 the switch element or active semiconductor, i.e. the transistor 42 is disposed. The transistor is connected to the source line 41, the gate line 43 and a transparent connection 45.

[0059] The pixel consists of a transparent electrode area 47 and an electrode-free area 48. The latter being located above or near the transistor 42. When the pixel is activated, the oil moves to the electrode-free area 48 such that the transistor will not decrease the transmissive area of the pixel.

[0060] As will be appreciated by the person skilled in the art, the present invention may be practiced otherwise than as specifically described herein. Obvious modifications to the embodiments disclosed, and specific design choices, will be apparent to the skilled reader. The scope of the invention is only defined by the appended claims.