Bi-Stable Electrowetting Optical Element and Driving Method Therefor

• US 20070263306A1
• Filed: 06/14/2005
• Published: 11/15/2007
• Est. Priority Date: 06/23/2004
• Status: Active Grant

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Hayes, Robert, Feenstra, Bokke, Massard, Romaric
• Granted Patent: US 7,548,363 B2
• Time in Patent Office: Days
• US Class Current: 359/886
• CPC Class Codes: G02B 26/005 based on electrowetting
• CPC Class Codes: G09F 9/372 the positions of the elements being controlled by the application of an electric field

Abstract

The present invention relates to an optical element, used e.g. in an electrowetting display device comprising a number of pixels, arranged in an array. Each optical element comprises a cell filled with a polar conductive fluid (5), such as a water solution, and a non-polar fluid (6), such as an oil. The cell further comprises first and second planar electrodes (7, 10), covered with first and second hydrophobic layers (8, 11). By applying a voltage between on one hand the first fluid and on the second hand alternately the first or second electrodes (7, 10), the oil (6) is forced to migrate between the first and second hydrophobic layers (8, 11). Thus a bi-stable, energy efficient optical element is provided.

Claims

1. Optical element, comprising a closed cell, containing a first fluid (5) and a second fluid (6), wherein the first fluid (5) is conductive and the second fluid (6) is coloured and immiscible with the first fluid (5), a first electrode (7), covered with a first hydrophobic, insulating layer (8) and located at a first wall (2) in the cell, the voltage between the first electrode (7) and the first fluid (5) being controllable in order to control the area of the first hydrophobic layer (8) that contacts the first fluid (5), and thereby the amount of light that is transmitted through the cell in a direction perpendicular to the first wall (2), wherein the cell comprises a second electrode (10) covered by a second hydrophobic, insulating layer (11), and the optical element comprises means for applying a voltage between the first fluid (5) and, alternately, the first electrode (7) or the second electrode (11).

2. Optical element according to claim 1, wherein the first electrode (7) is planar and parallel with the first wall (2), and wherein the second electrode (11) extends substantially perpendicular to the first electrode (7).

3. Optical element according to claim 2, wherein the second electrode (11) extends adjacent to a second wall (3) of the cell, which is perpendicular to the first wall (2).

4. Optical element according to claim 3, wherein the second electrode (11) extends adjacent to more than one wall of the cell, each of said more than one wall being perpendicular to the first wall (2).

5. Optical element according to claim 4, wherein the second electrode extends adjacent to all walls of the cell that are perpendicular to the first wall (2).

6. Optical element according to claim 1, wherein there is a continuous gap (14) between the first hydrophobic layer (8) and the second hydrophobic layer (11).

7. Optical element according to claim 1, comprising at least one hydrophobic material bridge (15, 16) between the first hydrophobic layer (8) and the second hydrophobic layer (11).

8. Optical element according to claim 1, wherein the optical element forms part of a switchable diaphragm, a shutter or a colour filter.

9. Display device, comprising a plurality of picture elements, each picture element comprising an optical element as claimed in claim 1.

10. A method for providing driving signals to an optical element, comprising a closed cell, containing a first fluid and a second fluid, wherein the first fluid is conductive and the second fluid is coloured and immiscible with the first fluid, a first electrode, covered with a first hydrophobic, insulating layer and located at a wall in the cell, the voltage between the electrode and the first fluid being controllable in order to control the area of the first hydrophobic layer that contacts the first fluid, and thereby the amount of light that is transmitted through the cell, wherein each cell comprises a second electrode covered by a second hydrophobic, insulating layer, the method comprising the steps of:

applying a voltage between the first fluid and the first electrode in order to obtain a first cell transmittance, and

applying a voltage between the first fluid and the second electrode in order to obtain a second cell transmittance.