Reflective display device

The reflective display device includes: a cell having: a display surface; a rear surface; side surfaces; and an interior space; a partition in a shape having radial extension dividing the rear surface into N regions; N rear electrodes respectively provided for the N regions on the rear surface; first side electrodes disposed on a display surface side and second side electrodes disposed on a rear surface side; N display-side electrodes separated by a separator zone in a shape having radial extension; a dielectric layer covering the N rear electrodes; polar liquid portions of N colors respectively disposed in N portions in the interior space; and polarity fluid placed within the interior space. A center of the partition matches with a center of the separator zone. A direction of the radial extension of the partition is different from that of the separator zone.

BACKGROUND

1. Field of the Invention

The present disclosure relates to a reflective display device.

2. Description of the Related Art

In recent years, reflective display devices using electrowetting have been gaining attention as a reflective display device for electronic paper.

For example, “Nature” 425, 383-385 (2003) discloses a reflective display device in which colored non-polar liquid (color oil) and transparent and colorless polar liquid (water) are filled within a cell having, on a bottom surface of the cell, a white substrate, transparent electrodes disposed on the white substrate, and an insulating film having a water-repellent front surface and disposed on the transparent electrode. When no voltage is applied, the color oil spreads over an entire surface of the water repellent film and a color of the oil is displayed. When a voltage is applied between the electrodes and the polar liquid, a contact angle of water with the water repellent film is reduced, and a front surface of the water repellent film apparently becomes hydrophilic. This causes a white color of the substrate to be displayed as the water spreads over the bottom surface and the color oil moves to corners. In this manner, displayed colors may he switched by applying a voltage, and high reflectance and contrast may be achieved in a monochrome operation.

Unfortunately, in color display, as it is usually required to use color filters, a loss increases, and, a reflective area for each color decreases in inverse proportion to a number of colors as the different colors are arranged in parallel. Therefore, reflectance and contrast in a polychrome operation are reduced to a large extent as the number of colors increases. In addition, with such a configuration, it is usually difficult to perform a bistable operation required for passive matrix driving.

Unexamined. Japanese Patent Publication No. 2011-65182 discloses a reflective display device having a color shifting pixel configuration and capable of performing a bistable operation. This reflective display device includes an equilateral triangular display surface having triangular sub-pixels of four colors of red (R), green (G), blue (B), and black (K), and K is disposed in center, and R, G, and B are arranged around K. Each sub-pixel is provided with a separate electrode, and an entire pixel is covered by an insulating film having a water repellent surface. The entire pixel is provided with transparent polar water and non-polar black oil. When no voltage is applied, the non-polar black oil spreads over the entire pixel to display black. When a voltage is applied to the R, G, and B sub-pixels, it is possible to achieve display of white (actually, gray). When a voltage is applied to the electrodes at a peripheral portion, R, G, and B are achieved as the colors of the pixel to which the voltage is applied. Further, when a voltage is applied to two of the electrodes excluding one for black, colors of cyan (C), magenta (M), and yellow (Y) are displayed.

Unexamined Japanese Patent Publication No. 2011-65182 also discloses a reflective display device that realizes a bistable operation allowing passive matrix driving. This structure includes a lower substrate, an electrode disposed on the lower substrate, a dielectric layer disposed over the electrode, an upper substrate, a transparent electrode disposed on the upper substrate, and a dielectric layer disposed over the transparent electrode. The upper substrate and the lower substrate are disposed such that the dielectric layers of the both substrates face toward each other, and colored oil and an aqueous layer that is colored by a different color are disposed between the two substrates. When no voltage is applied, the reflective display device displays the color of the aqueous layer. When a voltage is applied between the electrode of the lower substrate and the aqueous layer, the oil turns into small droplets due to charge formation between the aqueous layer and the oil, and makes the dielectric layer of a front surface wet as a driving voltage is cancelled. This achieves a second stable state. Unexamined. Japanese Patent Publication No. 2011-65182 discloses that the electrode disposed on the upper substrate may be disposed on a side wall.

Further, international Publication No. WO2012/039471 discloses a reflective display device capable of performing color display with high contrast. This reflective display device is provided, with a cell configured by a pair of substrates, and layers made of a hydrophilic material are respectively provided for upper and lower surfaces within the cell. Hydrophobic liquid is filled within the cell.

In “Proceedings of the International Symposium on Electronic Paper”, pp 1-6 (2012), a reflective display device capable of performing a bistable operation and having a different structure is disclosed. This reflective display device includes electrodes at a display position as a pixel, and a standby position of droplets, and realizes the bistable operation of moving polar droplets among non-polar droplets by switching the electrodes to which a voltage is applied.

SUMMARY

One non-limiting and exemplary embodiment of the present disclosure provides a reflective display device capable of performing color display with higher reflectance than that in a conventional configuration.

A reflective display device according to one exemplary embodiment disclosed in the present disclosure includes: a cell having: a display surface; a rear surface facing the display surface; side surfaces positioned between the display surface and the rear surface; and an interior space defined by the display surface, the rear surface, and the side surfaces; a partition in contact with the rear surface and the side surfaces, the partition having height smaller than a gap between the display surface and the rear surface and being in a shape having radial extension dividing the rear surface into N regions; N rear electrodes respectively provided for the N regions on the rear surface; first side electrodes disposed on a display surface side and second side electrodes disposed on a rear surface side, each of the first side electrodes and each of the second side electrodes are provided for each of N regions of the side surfaces respectively adjacent to the N regions of the rear surface; N display-side electrodes transparent to visible light, the display-side electrodes being disposed on the display surface and separated by a separator zone in a shape having radial extension; a dielectric layer covering the N rear electrodes, the N display-side electrodes, and the first side electrodes and the second side electrodes in the N regions of the side surfaces; polar liquid portions of N colors respectively disposed in N portions in the interior space divided by the partition; and polarity fluid placed within the interior space. When viewed from the display surface side, a center of the partition in the shape having the radial extension and a center of the separator zone in the shape having the radial extension match with each other, and a direction of the radial extension of the partition is different from a direction of the radial extension of the separator zone.

According to the reflective display device disclosed in the present disclosure, it is possible to realize a reflective display device capable of performing color display with high reflectance in one pixel.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Close examination by the inventor of the present disclosure shows that a reflective display device capable of performing conventional color display is able to display eight colors by changing a portion of four sub-pixels to which a voltage is to be applied. However, when R, G, and B are displayed, a reflective area for each color is only 25% at a maximum.

On the other hand, when C, M, and Y are displayed based on two types of additive color mixing, a reflective area for each color is 50% at a maximum, and when white is displayed based on RGB additive color mixing, a reflective area is 75% at a maximum. However, as the color mixing is performed based on a lateral arrangement, these colors have broad spectra and are grayish and dull. Therefore, a color reproduction range in a color solid scale including brightness is very small.

Further, there is a case in which a reflective display device capable of performing the conventional color display is not able to sufficiently realize a bistable operation.

In view of the above conventional problems, the inventor of the present disclosure inventor has conceived of a reflective display device capable of performing color display with higher reflectance than that in a conventional configuration. Outlines of a reflective display device according to exemplary embodiments disclosed in the present disclosure are as follow.

A reflective display device according to one exemplary embodiment disclosed in the present disclosure includes: a cell having: a display surface; a rear surface facing the display surface; side surfaces positioned between the display surface and the rear surface; and an interior space defined by the display surface, the rear surface, and the side surfaces; a partition in contact with the rear surface and the side surfaces, the partition having height smaller than a gap between the display surface and the rear surface and being in a shape having radial extension dividing the rear surface into N regions; N rear electrodes respectively provided for the N regions on the rear surface; first side electrodes disposed on a display surface side and second side electrodes disposed on a rear surface side, each of the first side electrodes and each of the second side electrodes are provided for each of N regions of the side surfaces respectively adjacent to the N regions of the rear surface; N display-side electrodes transparent to visible light, the display-side electrodes being disposed on the display surface and separated by a separator zone in a shape having radial extension; a dielectric layer covering the N rear electrodes, the N display-side electrodes, and the first side electrodes and the second side electrodes in the N regions of the side surfaces; polar liquid portions of N colors respectively disposed in N portions in the interior space divided by the partition; and polarity fluid placed within the interior space. When viewed from the display surface side, a center of the partition in the shape having the radial extension and a center of the separator zone in the shape having the radial extension match with each other, and a direction of the radial extension of the partition is different from a direction of the radial extension of the separator zone.

When viewed along a direction perpendicular to the display surface, the partition may be rotated by 180°/N with respect to the separator zone.

The N may be 4 or 8.

On a front surface of the dielectric layer, regions around the rear electrodes and around the display-side electrodes may have higher wetting properties as compared to other regions.

A front surface of each of the display-side electrodes may he provided with bumps of a size of not less than 1 μm and not more than 20 μm.

Hereinafter, exemplary embodiments according to the present invention will be described with reference to the drawings.

First Exemplary Embodiment

FIG. 1schematically shows a cross-section of a reflective display device according to one exemplary embodiment. Reflective display device11in this exemplary embodiment is provided with cell.150. Cell150is a display unit that constitutes 1 pixel. Cell150includes display surface152, rear surface151facing display surface152, side surfaces153positioned between display surface152and rear surface151, and interior space155defined by display surface152, rear surface151, and side surfaces153.

FIG. 2Ais a plan view illustrating rear surface151viewed from display surface152side. Further, side surfaces153adjacent to rear surface151are shown developed in the same plane as rear surface151.FIG. 1. Shows the cross-section taken along line A-A′ inFIG. 2A. InFIG. 2A, cell150includes four side surfaces153and cell150has a rectangular shape. A size of interior space155of cell150may he designed according to applications of reflective display device11. The example of of interior space155of cell150has 1 mm×1 mm×1 mm (x, y, and z directions inFIG. 1). Further, in a case a plurality of cells150are arranged (two-dimensionally in the x direction and the y direction inFIG. 1), a shape of display surface152may be triangular, quadrilateral, or hexagonal, such that no gap is produced between a plurality of cells150. In this case, a number of the side surfaces varies depending on the shape of display surface152. The reflective display device according to this exemplary embodiment is able to realize color display by 1 pixel. The color display used herein refers to an ability of displaying white, black, and at least one different color.

In this exemplary embodiment, cell150is constituted by display-side substrate102, partition wall103, and rear substrate101. Display-side substrate102is made of a material transparent with respect to visible light such that light may enter cell155through display surface152, and the light reflected on cell155may be emitted through display surface152. Examples of the material include glass and resin. Partition wall103and rear substrate101are also made of glass, resin, or the like.

Referring toFIG. 1andFIG. 2A, reflective display device11is provided with partition111. Partition111is in a shape having radial extension, and is in contact with rear surface151and side surfaces153. Partition111divides rear surface151into N regions. Here, N is an integer no smaller than 3, and N is 4 in this exemplary embodiment. In principle, there is no upper limit to N. However, when N increases, an amount of polar liquid provided in cell155in order to display the colors decreases. Practically, it is possible to perform color display with preferable brightness when N is around a number no smaller than 4 and no greater than 10.

Referring toFIG. 1andFIG. 2A, the shape having radial extension is configured by lines connecting a center and four corners of a square. In other words, partition plates are radially arranged at intervals of 90° around the center. Height h of partition111is smaller than gap H between rear surface151and display surface152. Gap H is height of the cell, and for example, H is 0.5 mm. With this, interior space155is divided into N portions155bon rear surface151divided by partition111and portion155apositioned above portions155band communicated with N portions155b.Portion155afaces an entire surface of display surface152. Width of partition111is approximately 0.1 mm, for example.

Reflective display device11is provided with rear electrodes, display-side electrodes, first side electrodes, and second side electrodes, in order to cause polar liquid portions112a-112dcolored to respective display colors by electrowetting and non-polar fluid113to move between portions155band portion155awithin interior space155described above.

In the N regions of rear surface151, N rear electrodes, specifically, rear electrodes104a,104b,104c,and104dare disposed. In this exemplary embodiment, rear electrodes104a,104b,104c,and104dare triangular. In the following description, rear electrodes104a,104b,104c,and104dare referred to as rear electrodes104a-104dwhen specifying the four rear elect

A first electrode and a second electrode are disposed on each of side surfaces153respectively in contact with the N regions of rear surface151. Specifically, side surface153adjacent to the region provided with rear electrode104ais provided with first side electrode106aon a rear surface151side and second side electrode107aon the display surface152side. Similarly, at a part of side surface153adjacent to the region provided with rear electrode104b,first side electrode106bon the rear surface151side and second side electrode107bon the display surface152side are provided. Further, at a part of side surface153adjacent to the region provided with rear electrode104c,first side electrode106con the rear surface151side and second side electrode107con the display surface152side are provided. Moreover, at a part of side surface153adjacent to the region provided with rear electrode104d,first side electrode106don the rear surface151side and second side electrode107don the display surface152side are provided.

N display-side electrodes are disposed on display surface152. Specifically, as illustrated inFIG. 2B, display surface152is separated by separator zone110in a shape having radial extension, and display-side electrodes109a,109b,109c,and109dare disposed in the separated regions, respectively. In order to facilitate understanding,FIG. 2Bshows the display-side electrodes on display surface152when viewed above reflective display device11. Separator zone110in the shape having radial extension divides display surface152in a square shape into four smaller squares. Display-side electrodes109a,109b,109c,and109d(hereinafter referred to as display-side electrodes109a-109d) are transparent with respect to visible light. Width of separator zone110is approximately 0.1 mm, for example.

FIG. 2Cshows separator zone110in the shape having radial extension provided for display surface152and a positional relation with partition111in the shape having radial extension on the rear surface viewed from display surface152. As illustrated inFIG. 2C, a center of separator zone110in the shape having radial extension and a center of partition111in the shape having radial extension on the rear surface substantially match with each other, and a direction of the radial extension of partition111is different from that of separator zone110. More specifically, when viewed perpendicularly to display surface152, the radial extension of partition111is rotated by 180°/N with respect to the radial extension of separator zone110. In this exemplary embodiment, N is 4, and therefore the radial extension of partition111is rotated by 45° with respect to the radial extension of separator zone110. A difference between the directions of the radial extension of partition111and the radial extension of separator zone110may not be 180°/N in a strict sense, and may be in a range of (180°/N)±5°, for example. With this, when the display-side electrodes and the rear electrodes are viewed from the display surface side, each of the rear electrodes overlaps with two of the display-side electrodes. Thus, when the polar liquid portion is moved from the rear surface151side to the display surface152side via side surfaces153, the polar liquid portion is first allowed to be brought into contact with the two display-side electrodes on display surface152, and therefore it is possible to reduce steps of spreading the polar liquid portion over an entire surface of display surface152. As illustrated inFIG. 2C, partition111includes center111aand a plurality of partition plates111b-111ein a planar view, partition plates111b-111eextend from center111atoward outside of cell110. Each of partition plates111b-111ehas a normal line that is parallel to display-side surface102or rear substrate101. In other words, partition plates111b-111eare perpendicular to display-side surface102or rear substrate101.

Display-side electrodes109a-109dare made of a transparent electrically-conducting material such as ITO or ZnO. It is sufficient that rear electrodes104a-104d,first side electrodes106a-106d,and second side electrodes107a-107dhave electron conductivity, and these electrodes may be made of a metallic material such as Cr, Pt, Au, Cu, or Al, or a conductive oxide such as ITO. As an influence given by rear electrodes104a-104d,first side electrodes106a-106d,and second side electrodes107a-107dto colors to be displayed in reflective display device11is small, the material for these electrodes may be selected from various materials considering mechanical strength and conductivity of the electrodes.

Reflective display device11is further provided with dielectric layer108that covers the rear electrodes, the display-side electrodes, and the first and the second side electrodes. In this exemplary embodiment, dielectric layer108also covers a surface of partition111. A surface of dielectric layer108is water repellent. For dielectric layer108, a material having a low wetting property to the polar liquid portions colored to display colors, and a high wetting property to non-polar fluid is used. A compound containing fluorine in its chemical structure has low polarity as a material due to strong covalent bonding between carbon and fluorine, and wetting property to a polar solvent is low. At the same time, this compound has high chemical stability, and may be advantageously utilized as dielectric layer108.

By applying a voltage to the electrodes, interface energy between solid substances in contact with polar liquid portions112a-112ddecreases by an amount of electrostatic energy of capacitors provided between the electrodes and respective polar liquid portions112a-112d,and a contact angle between polar liquid portions112a-112dand dielectric layer108is reduced. This is known as electrowetting. With this, apparently, a wetting property of the surface of dielectric layer108changes, and wetting properties to polar liquid portions112a-112dincrease at portions to which the voltage has been applied.

In view of the above,the movement of polar liquid portions112a-112dbased on electrowetting is more advantageous as an electrostatic capacitance of dielectric layer108is larger. Accordingly, the material or thickness of dielectric layer108may be selected or designed so that the electrostatic capacitance increases, such as forming dielectric layer108using a material having high relative permittivity, or reducing the thickness of a film. As adhesiveness of a fluorine-based compound with a substrate is poor in general, dielectric layer108may be configured as a stacked body in order to improve this point. For example, dielectric layer108may be configured by providing a layer including various inorganic compounds at the interface with the substrate and then providing a resin layer containing fluorine above this layer, in order to improve adhesiveness between the substrate and the electrodes and to increase the relative permittivity of an entire dielectric film. In this exemplary embodiment, water repellent film114made of Teflon (registered trademark) AF is provided over dielectric layer108made of silicon dioxide.

In interior space155of cell150, polar liquid portions112a-112dand non-polar fluid113are arranged. For polar liquid portion112a-112dand for non-polar fluid113, the materials that are not mixed with each other are selected materials.

Polar liquid portions112a-112dare partitioned by partition111, respectively disposed within four portions in the interior space in which rear electrodes104a-104dare positioned. Polar liquid portions112a-112dare respectively colored to four different colors. For example, polar liquid portions112a-112drespectively represent black (K), green (G), red (R), and blue (B). Amounts of polar liquid portions112a-112dare selected within a range that is equal to or smaller than the respective portions in interior space155divided by partition111, and that an entirety of display surface152may be covered.

Examples of polar liquid portions112a-112dinclude liquid having high polarity such as water, amide, glycol, polyalcohol, amino alcohol, or glycerin. Further, organic ambient temperature molten salt called ionic liquid may be used as polar liquid portions112a-112d,since the ionic liquid is a polar solvent and its vapor pressure is small and susceptible to evaporation. In order to display the above described colors, polar liquid portions112a-112dcontain colorant or pigment dissolved therein, corresponding to the colors to be displayed. A number of the colorant or pigment is not limited to one kind, and two or more kinds of colorant or pigment may be dissolved in polar liquid portions112a-112d.

Non-polar fluid113is liquid, for example. As the liquid, oil that is carbon tetrachloride based or hydrocarbon based may be used. In its chemical structure, silicone oil has low polarity and low solubility parameters to many kind of liquid, and thus may be used in this exemplary embodiment in various combinations with polar liquid portions112a-112d.Here, non-polar fluid113is colored to white.

Reflective display device11may be manufactured using manufacturing techniques for liquid crystal display apparatuses and semiconductor devices.

For example, partition wall103and partition111are first provided on rear substrate101using a method such as screen printing. Alternatively, partition wall103, partition111, and interior space155may be provided by etching rear substrate101using a method such as sandblasting. Then, rear electrodes104a-104d,first side electrodes106a-106d,and second side electrodes107a-107dare provided on rear substrate101and partition wall103using a semiconductor manufacturing technology. Thereafter, dielectric layer108and water repellent film114are provided so as to cover these electrodes.

Further, display-side electrodes109a-109dare provided on display-side substrate102. Then, dielectric layer108and water repellent film114are provided so as to cover display-side electrodes109a-109dusing a technique such as thin-film formation or application.

Thereafter, polar liquid portions112a-112dand non-polar fluid113are filled into interior space155, and display-side substrate102is joined with partition wall103, and thus reflective display device11is completed. While lines for applying a voltage to the electrodes are not shown inFIG. 1, such lines may also be provided when providing the electrodes described above.

Next, an operation of reflective display device11will be described with reference toFIG. 1throughFIG. 4. Further, Table 1 shows a state of an electrode to which a voltage is applied and a corresponding polar liquid portion. In the following description, an example in which polar liquid portion112a(black) positioned above rear electrode104ais moved to display black will be described. Other colors may also be displayed by applying voltages to the corresponding electrodes.

When a voltage is not applied to any of the electrodes, as illustrated inFIG. 1, non-polar fluid113is positioned on the display surface152side and polar liquid portions112a-112dare positioned on the rear surface151side. Therefore, light that enters display surface152from outside is emitted from display surface152after diffused reflection within non-polar fluid113. Thus, reflective display device11displays white.

As illustrated inFIG. 3A, for example, when positive voltage V is applied to first side electrode106aand a reference voltage is applied to rear electrode104a,a negative charge is induced at a position facing a position at which a positive charge produced at rear electrode104aand a positive charge is induced at a position facing a position at which a negative charge produced at first side electrode106awithin polar liquid portion112a.Accordingly, polar liquid portion112ais disposed symmetrically across rear electrode104aand first side electrode106asuch that electrostatic energy due to the two capacitors is minimized and stabilized.

Next, as shown inFIG. 3B, voltage V is applied to second side electrode107a,and a reference voltage is applied to first side electrode106a.With this, the charges within inks are also redistributed according to a voltage change at the electrodes, polar liquid portion112amoves to a position so as to be disposed across first side electrode106aand second side electrode107aas an energetically stable position.

Further, as illustrated inFIG. 4A, when voltage V is applied to display-side electrodes109aand109cand a reference voltage is applied to second side electrode107a,polar liquid portion112amoves to the display surface152side, and polar liquid portion112amoves to a position so as to be disposed across display-side electrodes109aand109cand second side electrode107a.

Moreover, as illustrated inFIG. 4B, when voltage V is applied to display-side electrodes109band109dand a reference voltage is applied to display-side electrodes109band109d,polar liquid portion112amoves to the display surface152side, and polar liquid portion112amoves to a position so as to be disposed across display-side electrodes109a-109dand second side electrode107a.With this, polar liquid portion112amoves to the display surface152side, and reflective display device11is able to display black.

In order to resume white display from black display, it is possible to move polar liquid portion112aback to the position at which rear electrode104ais positioned by applying voltages to the electrodes in an inversed order of the order described above. In particular, when a volume of the polar liquid is reduced down to several microliters or smaller, an influence of a gravity force reduces and a change in Coulomb's force due to charges is dominant. Accordingly, it is possible to realize movement of the polar liquid on side surfaces153and on display surface152that is similar to the movement on a normal plane.

As described above, the rest of polar liquid portions112b-112dmay also be moved to the display surface152side by applying voltages to the corresponding electrodes in the order described above.

As described bed above, according to this exemplary embodiment, each of the plurality of colored polar liquid portions may be disposed over an entire display surface. Accordingly, when the polar liquid portions of red, blue, green, and black are prepared, for example, it is possible to display red, blue, green, black, and white with reflectance close to 100%.

Further, a state in which a polar liquid portion is positioned on the display surface side and a color of this polar liquid portions is displayed, and a state in which non-polar fluid is positioned on the display surface side and white is displayed are a bistable state, and a capacitance due to a charge pair between the electrodes and the polar liquid portions may be maintained even if application of the voltage is stopped. Accordingly, it is possible to maintain display of the color in the corresponding state.

Moreover, according to this exemplary embodiment, the radial extension of partition111is rotated by 180°/N with respect to the radial extension of separator zone110. Accordingly, when the polar liquid portion is moved from the rear surface side to the display surface side via the side surface, the polar liquid portion is first allowed to be brought into contact with the two display-side electrodes on the display surface. With this, it is possible to display the color stably with a reduced number of steps. By contrast, when the display-side electrodes are arranged in the same pattern as rear electrodes104a-104b,it may possibly become difficult to move the polar liquid portion reliably in the above described steps. For example, when the display-side electrodes are provided as display-side electrodes104a′-104d′ that are arranged in the same pattern as rear electrodes104a-104b,in a state corresponding to the state illustrated inFIG. 4Ain the above steps, a voltage is applied to only display-side electrode104a′ among the display-side electrodes. As a charge within the polar liquid portion induced by application of a voltage to the electrode controls a position of the polar liquid portion, it is difficult to reliably spread the polar liquid portion disposed symmetrically across display-side electrode104a′ and second side electrode107aover an entire surface of display surface152only by a voltage applied next. Further in order to move the polar liquid portion reliably, it is then necessary to apply a voltage between display-side electrode104a′ and display-side electrode104d′ (or104c′), and to finally apply a voltage between display-side electrodes104a′ and104d′and display-side electrode104c′ and104b′. In other words, the number of steps for applying voltages increases.

Second Exemplary Embodiment

A reflective display device according to this exemplary embodiment is different from the reflective display device of the first exemplary embodiment in that the number N of the interior spaces divided by the partition is 8.

A cross-sectional structure of the reflective display device according to this exemplary embodiment is the same as that illustrated inFIG. 1, and therefore differences in the structure will be mainly described.

FIG. 5Ais a plan view of rear surface151viewed from the display surface152side of reflective display device12. Further, side surfaces153adjacent to rear surface151are shown developed in the same plane as rear surface151. The cross-section taken along line A-A′ inFIG. 5Acorresponds toFIG. 1. Partition111′ is in a shape having radial extension, and divides rear surface151into 8 regions. Rear electrodes104a-104hare disposed in the respective regions.

In this exemplary embodiment, non-polar fluid113may be white or transparent. Further, non-polar fluid113may be a gaseous body.

Polar liquid portions112a-112hare arranged on rear electrodes104a-104h. Polar liquid portions112a-112hare respectively colored to different colors. For example, polar liquid portion112ais colored to black (K), polar liquid portion112bis colored to green (G), polar liquid portion112cis colored to red (R), and polar liquid portion112dis colored to blue (B). Further, polar liquid portion112eis colored to cyan (C), polar liquid portion112fis colored to magenta (M), polar liquid portion112gis colored to yellow (Y), and polar liquid121his colored to white (W).

FIG. 5Bshows display-side electrodes109a-109hdisposed on display surface152. Display surface152is separated by separator zone110′ in a shape having radial extension, and display-side electrodes109a-109hare disposed in the separated regions, respectively.

Similarly to the first exemplary embodiment, as illustrated inFIG. 5(c), a center of separator zone110′ in the shape having radial extension and a center of partition111′ in the shape having radial extension on the rear surface substantially match with each other, and a direction of the radial extension of partition111′ is different from that of separator zone110. More specifically, the radial extension of partition111′ is rotated by 180°/N=22.5° with respect to the radial extension of separator zone110′.

Referring toFIG. 5A, first side electrodes106a,106f,and106f,and second side electrodes107a,107f,and107fare disposed on left side surface153. First side electrodes106b,106e,and106g,and second side electrodes107b,107e,and107gare disposed on right side surface153. Further, first side electrodes106d,106f,and106e,and second side electrodes107d,107f,and.107eare disposed on upper side surface153. First side electrodes106c,106h,and106g,and second side electrodes107c,107h,and107gare disposed on lower side surface153. The first side electrodes and second side electrodes107that are provided side by side for adjacent side surfaces153are denoted by the same reference numerals. For example, first side electrode106fof upper side surface153is disposed adjacent to first side electrode106fof left side surface153. The two side electrodes provided side by side for adjacent side surfaces153may be electrically connected with or separated from each other. Further, these two side electrodes may be provided monolithically. The same voltage is applied to these two side electrodes provided side by side for adjacent side surfaces153when the polar liquid portions are moved.

Reflective display device12operates in the same manner as reflective display device11in the first exemplary embodiment. When a voltage is not applied to the electrodes, all of polar liquid portions112a-112hare positioned on the rear surface side, and the color of non-polar fluid113filled in the ink is displayed. Further, when non-polar fluid113is transparent, gray is displayed, which is a color resulted from color mixing of the 8 colors (RGBCMYWK).

Next, an operation of reflective display device12will he described with reference toFIG. 3,FIG. 4, andFIG. 5, taking the example of movement of black polar liquid portion112aas in the first exemplary embodiment. Table 2 shows a state of an electrode to which a voltage is applied and a corresponding polar liquid portion.

As illustrated inFIG. 3A, for example, when positive voltage V is applied to first side electrodes106aand a reference voltage is applied to rear electrodes104a,polar liquid portion112ais disposed symmetrically across rear electrode104aand first side electrode106a.

Next, as shown inFIG. 3B, voltage V is applied to second side electrode107a,and a reference voltage is applied to first side electrode106a.With this, the charges within inks are also redistributed according to a voltage change at the electrodes, polar liquid portion112amoves to a position so as to be disposed across first side electrode106aand second side electrode107aas an energetically stable position.

Further, as illustrated inFIG. 4A, when voltage V is applied, to display-side electrodes109aand109hand a reference voltage is applied to second side electrode107a,polar liquid portion112amoves to the display surface152side, and polar liquid portion112amoves to a position so as to be disposed across display-side electrodes109aand109hand second side electrode107a.

Moreover, as illustrated in FIG,4B, when voltage V is applied to display-side electrodes109d,109e,109b,and109gand a reference voltage is applied to display-side electrodes109f,109a,109h,and109c,polar liquid portion112amoves to the display surface152side, and polar liquid portion112amoves to a position so as to be disposed across display-side electrodes109d,109e,109b,and109gand display-side electrodes109f,109a,109h,and109c.With this, polar liquid portion112amoves to the display surface152side, and reflective display device12is able to display black.

In order to resume white display from black display, it is possible to move polar liquid portion112aback to the position at which rear electrode104ais positioned by applying voltages to the electrodes in an inversed order of the order described above. In the same manner, green polar liquid portion112b,red polar liquid portion112c,and blue polar liquid portion112dmay also be moved to the display surface152side to display green, red, or blue over an entire surface of display surface152.

As described above, the same voltage is applied to the two first side electrodes or the two second side electrodes having the same reference numeral when polar liquid portions112e,112f,112g,and112hat rear electrodes104e,104f,104g,and104hare moved.

For example, when magenta polar liquid portion112fis moved, polar liquid portion112fmay be moved to the display surface152side by applying a voltage in order as shown in Table 3, and magenta may be displayed over an entire surface of display surface152.

According to the reflective display device of this exemplary embodiment, 8 colors of R, G, C, M, Y, W, and K, and gray, in addition, may be displayed, and it is possible to display each of the colors with reflectance close to 100%. Thus, it. is possible to set a color solid having a large volume representing color reproducibility, and to realize high color reproducibility. Further, it is possible to achieve sufficiently high reflectance even when the number of the colors for the polar liquid portions is reduced.

Third Exemplary Embodiment

FIG. 6Ashows a cross-section structure of reflective display device13of this exemplary embodiment. Reflective display device13has higher wetting properties or hydrophilic properties in regions115b,115c,and115daround the display-side electrodes, and regions115aand115earound the rear electrodes on a front surface of the dielectric layer. With this, even when an electrostatic attractive force due to charges between the electrodes and the polar liquid, portions is lost due to a voltage not being applied for an extended period of time, it is possible to maintain a state in which the polar liquid portions are positioned on the rear surface side or a state in which the polar liquid, portions are positioned on the display surface side by a chemical affinity between hydrophilic regions and the polar liquid portions.

As illustrated inFIG. 6B, the hydrophilic regions may he provided, for example, such that non-formation regions116bare provided at portions of a front surface of water repellent film116aprovided over a front surface of a hydrophilic dielectric layer. Further, as illustrated inFIG. 6C, water repellent film117ain stripes may be provided on front surface117bof the dielectric layer. In either case, long-term stability of display increases if an area ratio of the hydrophilic regions with respect to the water repellent is larger. However, this increases a voltage to be applied to move the polar liquid portion.

When a still image is displayed in a display apparatus configured by the reflective display device, as a time period in which the still image is displayed is long, power consumed by the display apparatus in the operation does not increase much even if a driving voltage somewhat increases. Further, by appropriately determining the area ratio of the hydrophilic region with respect to the water repellent region, it is possible to improve long-term stability when displaying a still image and to reduce a voltage when displaying a moving image.

Fourth Exemplary Embodiment

FIG. 7Ashows a cross-section structure of reflective display device14according to this exemplary embodiment. Reflective display device14is different form reflective display device11of the first exemplary embodiment in that cloudy body118is provided over the display-side electrodes. Cloudy body118is in a shape having random bumps of a size approximately from 1 μm to 20 μm. The bumps of this size cause entered light to be scattered by Mie scattering. Cloudy body118may be provided, for example, by imprinting glass or curing droplets of inks in dots. When monolithically provided over the display-side electrodes, cloudy body118may also be provided by sol-gel processing or electro-deposition of wide-gap semiconductor such as ZnO.

Over cloudy body118, water repellent film119is provided, which is in contact with air120. In this exemplary embodiment, a gaseous body is used as non-polar fluid113. White light that enters display surface152is subjected to total reflection on cloudy body118by Mie scattering, and is reflected with high reflectance over 50%.FIG. 7Bshows a state in which black polar liquid. portion112ais moved according to the steps described in the first exemplary embodiment to be disposed on the front surface side. By bringing polar liquid portion112ainto contact with cloudy body118, the entered light does not totally reflect on a front surface of cloudy body118and is transmitted to polar liquid portion112a.Then, polar liquid portion112aabsorbs the entered light. With this, reflective display device14displays black. This effect is large when a difference between a refractive index of polar liquid portion112aand a refractive index of the cloudy body is small. For example, when the cloudy body is glass and polar liquid portion112ais water-based, a contrast W/K may be around 10:1. Further, when the cloudy body is configured by wide-gap semiconductor (refractive index>2), reflecting brightness of 70% or above in contact with air may be obtained. By using polar liquid portion112ahaving a high refractive index close to this value, it is possible to realize a reflective display device with high reflectance and high contrast.

Moreover, according to this exemplary embodiment, it is possible to perform color display without using oil, as the non-polar fluid. Therefore, it is possible to reduce long-term color degradation, as color elements such as colorant or pigment may not move each other via the oil. Thus, it is possible to realize a highly reliable reflective display device having a simpler configuration.

It should be appreciated that the shape of the cell is quadrilateral when viewed, from the display surface side in the first exemplary embodiment to the fourth exemplary embodiment, but may be in another shape. Alternatively, the patterns of the display-side electrodes and the rear electrodes may be opposite.

The reflective display device disclosed in the present disclosure may be suitably used for various types of display apparatuses, and useful for color electronic paper such as electronic magazines and electronic books. In addition, the reflective display device disclosed, in the present disclosure may be applicable to large-sized signage such as electronic advertising display and electronic mural painting.