ELECTROFLUIDIC CHROMATOPHORE (EFC) DISPLAY APPARATUS
A display apparatus is described that includes a plurality of electrofluidic chromatophore (EFC) pixel cells. Each pixel cell comprises a fluid holder for holding a polar fluid and a non-polar fluid having differing display properties, the fluid holder comprising a reservoir with a geometry having a small visible area projected in the direction of a viewer onto the polar fluid, and a channel with a geometry having a large visible area projected in the direction of a viewer onto the polar fluid. The channel is connected to the reservoir so as to enable free movement of the polar fluid and non-polar fluid between the channel and the reservoir. At least part of a surface of the channel comprises a wetting property responsive to a supply voltage over the pixel cell and defining (i) a stable region wherein the supply voltage stabilizes polar fluid in the channel; (ii) a fill region that controls filling of polar fluid in the channel and (iii) a retract region that controls retracting of polar fluid in the channel. At least two pixel cell terminals are configured to supply the supply voltage to at least part of the surface of the channel comprising the wetting property for supply voltage controlled channel movement of polar fluid. The display further comprises a driver operative to provide controlled column voltages and any of a predefined row select or non-select voltage. A circuit board comprises a row electrode and a column electrode each directly connecting the driver to the pixel cell terminals for supplying the supply voltage to the pixel cell terminals as a voltage difference between the row and column electrodes in a passive matrix configuration.
1 . A display apparatus comprising:
a plurality of electrofluidic chromatophore (EFC) pixel cells, each pixel cell comprising:
a fluid holder for holding a polar fluid and a non-polar fluid having differing display properties, the fluid holder comprising
a reservoir with a geometry having a small visible area projected in the direction of a viewer, and
a channel with a geometry having a large visible area projected in the direction of a viewer, the channel being connected to the reservoir so as to enable free movement of the polar fluid and non-polar fluid between the channel and the reservoir, at least part of a surface of the channel comprising a wetting property responsive to a supply voltage over the pixel cell and defining (i) a stable region wherein the supply voltage stabilizes the amount of polar fluid in the channel; (ii) a fill region that controls the flow of polar fluid into the channel and (iii) a retract region that controls the flow of polar fluid into the reservoir;
at least two pixel cell terminals being configured to supply the supply voltage to at least part of the surface of the fluid holder comprising the wetting property for supply voltage controlled movement of polar fluid; the display further comprising
a driver operative to provide controlled column voltages and any of a predefined row select or non-select voltage via respective column and row electrodes; and
a circuit board comprising the row and column electrodes each directly connecting the driver to the pixel cell terminals for supplying the supply voltage to the pixel cell terminals as a voltage difference between the row and column electrodes in a passive matrix configuration.
2 . The display apparatus according to claim 1 , wherein the driver is configured to provide a row select condition, and a row non-select condition, wherein, in the row select condition, depending on a column voltage polarity, the supply voltage at least ranges in the fill or the retract region; and wherein the column voltage range is chosen such that in the row non-select condition the supply voltage only ranges in the stable region.
3 . The display apparatus according to claim 2 , wherein the driver is configured to provide, in the row select condition, the supply voltage ranging in the stable region to provide a stable condition.
4 . The display apparatus according to claim 1 , wherein a further pixel cell terminal is electrically connected to a further electrode directly connected to the driver to provide a bias supply voltage.
5 . The display apparatus according to claim 4 , wherein the further electrode is a common terminal connected to an electrode that is common for all or a group of pixel cells in the display.
6 . The display apparatus according to claim 1 , wherein the wetting property defines a stable voltage range having a lower stable voltage and a higher stable voltage differing in a range of 0.5-2.5 V.
7 . The display apparatus according to claim 1 , wherein the wetting property defines a width of the stable region that is at least larger or equal to half the width of the retract region.
8 . The display apparatus according to claim 1 , wherein the channel comprises wetting barriers.
9 . The display apparatus according to claim 1 , wherein the driver is configured to periodically invert the row and column polarities relative to each other to invert the polarity of the supply voltage, so as to obtain an average supply voltage being essentially zero with no directional build-up of charges in the pixel cells.
10 . The display apparatus according to claim 1 , wherein the wetting property is expressed as a rate of change in the transmission and/or reflection of the pixel cell for a predefined wavelength.
11 . The display apparatus according to claim 1 , wherein the polar fluid is conductive, wherein the row electrode is coupled to a contact electrode contacting the conductive polar fluid.
12 . The display apparatus according to claim 1 , wherein the polar fluid is conductive and wherein the row electrode is coupled to a channel electrode
13 . The display apparatus according to claim 1 , wherein the polar fluid is conductive and the column voltage terminal is coupled only to a channel electrode on a side facing away from a direction of the viewer.
14 . A method of driving a display apparatus comprising a plurality of electrofluidic chromatophore (EFC) pixel cells, each pixel cell comprising a fluid holder for holding a polar fluid and a non-polar fluid having differing display properties, the fluid holder comprising a reservoir with a geometry having a small visible area projected in the direction of a viewer onto the polar fluid, and a channel with a geometry having a large visible area projected in the direction of a viewer onto the polar fluid, the channel being connected to the reservoir so as to enable free movement of the polar fluid and non-polar fluid between the channel and the reservoir, at least part of a surface of the channel comprising a wetting property responsive to a supply voltage over the pixel cell and defining (i) a stable region wherein the supply voltage stabilizes the amount of polar fluid in the channel; (ii) a fill region that controls the flow of polar fluid into the channel and (iii) a retract region that controls the flow of polar fluid into the reservoir; wherein at least two pixel cell terminals are configured to supply the supply voltage to at least part of the surface of the channel comprising the wetting property for supply voltage controlled movement of polar fluid; comprising
providing controlled column voltages and any of a predefined row select or non-select voltage via a circuit board comprising respective row and column electrodes each directly connecting the driver to the pixel cell terminals for supplying the supply voltage to the pixel cell terminals as a voltage difference between the row and column electrodes in a passive matrix configuration.
15 . The method according to claim 14 wherein, in a row select condition, depending on a row select and/or column voltage polarity, the supply voltage at least ranges in the fill or the retract region; and wherein the column voltage range is chosen such that in a row non-select condition, the supply voltage only ranges in the stable region.