Title of Invention

OPTICAL SWITCH FOR A DISPLAY DEVICE

Abstract

The present invention relates to an optical switch having at least one first fluid (5) and a second fluid (6) immiscible with each other within a space between a first transparent support plate, (3) a second support plate (4) and a wall (2), the second fluid being electro conductive or polar, characterized in that the optical switch comprises electrical switching means for reversibly switching the optical between a state wherein the continuous film of first fluid (5) covers the first support plate (3) and a state wherein a film of first fluid (5) adjoins the wall (2) and, on at least one of the support plates, a first electrode (7) only partly covering the total area of the optical switch. FIGURE 3

Full Text

Display device The invention relates to an optical switch having at least one first fluid and a second fluid inuniscible with each othra: within a space between a first transparent support plate and a second support plate, the second fluid being electroconductive or polar. In particular the invention relates to a display device comprising picture elements having at least one first fluid and a second fluid immiscible with each ofther within a space between a first transparent support plate and a second support plate, the second fluid being eledroconductrve or polar. Optical switches may be used in shutter applications, diaphragms, but also in switchable color filters in e.g. display applicatians, Display devices like TFT-LCDs are used in laptop computers and in organizers, but also find an increasingly wider ^plication in GSM telephones. Instead of LCDs, for example, (polymer) LED display devices are also being used. Apart from these display effects which are well established by now other display techniques are evolving like electrophoietic displays, which are suitable for paper white applications. The invention is based on a principle called electro-wetting. The invention provides new ways of using this principle. If for instance a (first) fluid is a (colored) oil and the second (the other) fluid is water (due to interfacial tensions) a two layer system is provided which comprises a water layer and an oil layer, However, if a voltage is applied between the water and an electrode on the first support plate the oil layer moves aside or breaks up due to electrostatic forces. Since parts of the water now penetrate die oil layer the picture element becomes partly transparent. If homogeneous (Indium Tin Oxide) electrodes are used to address the picture elements, smce this is the simplest way, the electric field is applied across the entire picture element Hence, in principle, there is no preferred direction for the (first) fluid (the oil) to move to. However, in practice there will always be a (small) inhomogeneity inside the picture element (insulator or oil thickness variation, slight irregularis in a pixel wall, etcetera) that will determine which way the (first) fluid (the oil) will move. As a result always the same motion occurs upon voltage application. However, the motion will vary from pixel to pixel. For several reasons, including grey-scale homogeneity and reducing the chance of oil mixing between adjacent pixels, the oil motion should be better controlled. To this end a display device according to the invention compnscG within each picture element a first electrode only partly covering the total area of the picture element Preferably the first electrode at least leaves clear a part of the picture element along an edge of the picture element When a voltage is applied, there will be an electric field at the places where the electrode is present Effectively this region will become more wettable for the second fluid (more hydrophilic in an oil-water system), On the other hand, at places where no electrode is present there will be no electric field, and thus this region will be less wettable for the second fluid (more hydrophobic). As a result, the oil will tend to move toward the least wettable region, In a particular embodiment a display device according to the invention comprises at least one furthier electrode at the remaining area of the picture element If driving means arc present to apply voltages to the first and further electrodes the oil motion can be enhanced. These and other aspects of the invaition are appaiatt firom and will be elucidated with reference to the embodiments described hereinafter. hi the drawings: Fig. 1 is a diagrammatic cross-section ofapart of a display device according to the invention. Fig. 2 is another diagrammatic cross-section of a part of a display device according to flie invention, while Figures 3 and 4 are plan views of a part of a display device accordmg to the invention and Figure 5 shows driving voltages The Figures are diagrammatic and not drawn to scale. Corresponding elements are generally denoted by the same reference numerals. Fig. 1 shows a diagrammatic cross-section of apart of a display device 1 according to the invention. Between two transparent substrates or support plates 3,4 a first fluid 5 and a second fluid 6 are provided, which are inuniscible with each other. The first fluid 5 is for instance an alkane like tetrsdecane or hexadecane or as in this example a (silicone) oil The second fluid 6 is elecuoconductive or polar, for instance water or a salt solution (e.g. a solution of KCl in a mixture of water and ethyl alcohol). In a first state, when no external voltage is applied (Fig. la) the fluids 5, 6 adjoin the first and second transparent support plates 3, 4 of e.g. glass or plastic. On liie first support plate 3 a (transparent) electrode 7, for example indium (tin) oxide is provided and an intermediate less wettable (lr?drophobic) layer S, in this example an amorphous fluoropolymer (AF1600). When a voltage is applied (voltage source 9) via interconnections 20,21 the layer 5 moves aside or breaks up into small droplets (Fig. lb, fragmented film). This occurs when the electrostatic energy gain is larger than the surface energy loss due to ibs creation of curved surfaces. As a very impratant aspect it was found that reversible switching between a contniuons film 5 covering the support plate 3 and a film adjoining the wall 2 is achieved by means of the electrical switching means (voltage source 9). Figure 2 shows an embodiment of a display device according to the invention, in which part of the electrode 7 has been left away (see also Figure 3). When a voltage is applied. There will be an electric field at the places where the electrode (ITO) is present. In this region the coating will become more wettable for the second fluid. On the other hand, at the lower left hand comer (Figure 3) where there is no electrode (ITO) present there will be no electric field, and Urns the coating will remain less wettable. As a result, the oil will tend to move toward the least wettable region; the lower left hand comer. As a result, always the same motion towards especially designed comers of display cells occurs upon voltage application. Voltages are applied by means of a driving unit 22. The size of the area of ITO that is removed should be chosen properly. When a large area is chosen, the remnant oil area will consequently be rather large, thereby reducing the brightness of the display. On the other hand, when the chosen area becomes too small, the oil motion will no longer have a preference to move into this comer. Preferably at least a part along the edge of the picture element comprising 5 % of the total area of the picture element is kept clear, while at most a part along the edge of the picture element comprising 50% (preferabty 10%) of the total area of the picture element is kept clear. In a matrix driven display device a matrix of switching elements e. g. fliin fihn transistors (TFT) may be chosen for applying the driving signals. "ITie tiiin film transistors preferably are located at the areas where no electrodes 7 are present If necessary this area {and also inter-pixel areas) may be covered by a black matrix to enhance contrast Figure 4 shows another embodiment in which a coiner of the picture element has been provide withi a further electrode 7'. Voltage pulses (see Figure 5) are provided to electrodes 7, T to accelerate the retraction of the oil film. First, a voltage pulse 15 is applied to electrode 7 to remove the oil from most of the active area. Electrode 7' is gromided and as a result, the oil will move into the corresponding comer of the picture element After the voltage on electrode 7 has beenemoved, a short voltage pulse 16 is applied to electrode 7'. As a result, the oil is removed from electrode 7' and redistributed over the rest of the picture element. When the voltage on electrode 7' is removed, the oil will also spread over this part of the picture element. The electrode configuration chosen here is merely an example. Other electrode configurations can be chosen, such as a circular geometiy. Such a circular geometry is used in e.g. shutter applications and diaphragms. The electrode on which the oil is collected should be as small as possible compared to the total size, while still being sufficiently large to determine the direction of motion The invention resides in each and every novel characteristic feature and each and every combination of characteristic features. Reference numerals in the claims do not hmit their protective scope. Use of the verb "to comprise" and ite conjugations does not exclude the presence of elements other than those stated in the claims. Use of the article "a" or "an" preceding an element does not exclude -the presence of a plurality of such elements. WE CLAIM: 1. An optical switch having at least one first fluid (5) and a second fluid (6) immiscible with each other within a space between a first transparent support plate, (3) a second support plate (4) and a wall (2), the second fiuid being electroconductive or polar, characterized in that the optical switch comprises electrical switching means for reversibly switching the optical between a state wherein the continuous film of first fluid (5) covers the first support plate (3) and a state wherein a film of first fluid (5) adjoins the wall (2) and, on at least one of the support plates, a first electrode (7) only partly covering the total area of the optical switch. 2. An optical switch as claimed in Claim 1 in which the first electrode leaves clear a part of the optical switch along an edge of the optical switch. 3. An optical switch as claimed in Claim 2 in which the first electrode leaves clear a part along one of the comers of a rectangular optical switch. 4. An optical switch as claimed in Claim 2 in which the first electrode leaves clear a part along the edge of the optical switch representing 5% or more of the total area of the optical switch. 5. An optical switch as claimed in Claim 2 in which the first electrode leaves clear apart along the edge of the optical switch representing 50 %or less of the total area of the optical switch. 6. An optical switch as claimed in Claim 5 in which the first electrode leaves clear a part along the edge of the optical switch representing 10% or less of the total area of the optical switch. 7. An optical switch as claimed in Claim 1 comprising at least one electrode (V) at the remaining area of the optical switch. 8. An optical switch as claimed in Claim 7 comprising driving means to apply voltages to the first and electrodes. 9. A display device comprising picture elements, a picture element having an optical switch as claimed in Claim 1 or 2. 10. A display device as claimed in Claim 9, in which switching devices are present at the part left clear by the first electrode. 11. A display device as claimed in Claim 10, in which the part left clear by the first electrode is covered by a black mask.

Documents:

3105-chenp-2005 correspondence-others.tif

3105-chenp-2005 abstract-duplicate.pdf

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3105-chenp-2005 abstract.pdf

3105-chenp-2005 claims-duplicate.pdf

3105-chenp-2005 claims.pdf

3105-chenp-2005 correspondence-po.pdf

3105-chenp-2005 descripition(completed)-duplicate.pdf

3105-chenp-2005 description(complete).pdf

3105-chenp-2005 drawings-duplicate.pdf

3105-chenp-2005 drawings.pdf

3105-chenp-2005 form-1.pdf

3105-chenp-2005 form-18.pdf

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3105-chenp-2005 form-3.pdf

3105-chenp-2005 form-5.pdf

3105-chenp-2005 pct search report.pdf

3105-chenp-2005 pct.pdf

3105-chenp-2005 petition.pdf