JP2009300529A - Electrophoretic display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophoretic display for suppressing increase in power consumption. <P>SOLUTION: Since a floating electrode corresponding to each pixel electrode is provided between adjacent pixel electrodes, a distance between the adjacent pixel electrodes can be made larger. The influence of a potential difference generated between the adjacent pixel electrodes is lessened by making the distance between the adjacent pixel electrodes larger, and the occurrence of leakage current is suppressed. Thereby, the increase of power consumption is suppressed. In addition, the floating electrode is induced in potential of the pixel electrodes, and since the potential generates in itself, display is performed even in a region provided by the floating electrode. Thereby, the display is secured even between the pixel electrodes so as to display in higher contrast. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophoretic display device.

  As an active matrix electrophoretic display device, one having a switching transistor and a memory circuit in a pixel is known (see Patent Document 1). The display device described in Patent Document 1 has a configuration in which microcapsules containing charged particles are bonded to a substrate on which switching transistors and pixel electrodes are formed. This electrophoretic display device displays an image by controlling charged particles by an electric field generated between a pixel electrode sandwiching microcapsules and a common electrode.

  The pixel circuit of such an electrophoretic display device is preferably laid out so that the circuit area is small in order to realize higher definition display. Therefore, it is desirable that the number of wirings required in the pixel circuit is as small as possible. For example, a configuration in which one capacitor is provided for one transistor is mainly used for a pixel circuit of a liquid crystal device which is a kind of display device. This circuit has a circuit structure including a selection transistor connected to a scanning line and a data line, and a capacitor connected to a ground line or a scanning line of an adjacent pixel. Wiring necessary in the pixel circuit is only wiring for connecting the transistor and the capacitor, and wiring with the ground line and wiring area between the pixel circuit elements are rarely problematic.

The pixel circuit of the electrophoretic display device includes a latch circuit as a memory circuit, and two transmission gates controlled to transmit an external signal to the pixel electrode according to data stored in the latch circuit. Is also known. According to this circuit configuration, the state of the display can be changed to all black, all white, and a reverse image while holding image data in the latch circuit. There is no need to operate the driver circuit except when a new image is displayed, and a more flexible display method is possible.
JP 2005-114822 A

  However, in the electrophoretic display device having the above-described configuration, when different gradations are displayed on adjacent pixels, a large potential difference is generated between adjacent pixel electrodes, a leakage current is generated between the pixels, and power consumption is increased. There was a problem that.

  In view of the circumstances as described above, an object of the present invention is to provide an electrophoretic display device capable of suppressing an increase in power consumption.

  In order to achieve the above object, an electrophoretic display device according to the present invention is an electrophoretic display device in which an electrophoretic layer is sandwiched between a first substrate and a second substrate, and is provided on the first substrate. And a plurality of pixel electrodes provided between the adjacent pixel electrodes of the first substrate, and floating electrodes provided corresponding to the adjacent pixel electrodes, respectively.

  According to the present invention, since the floating electrodes provided corresponding to the adjacent pixel electrodes are provided between the adjacent pixel electrodes, the distance between the adjacent pixel electrodes can be increased accordingly. By increasing the distance between adjacent pixel electrodes, the influence of a potential difference generated between the adjacent pixel electrodes can be reduced, and the generation of leakage current can be suppressed. Thereby, an increase in power consumption can be suppressed. In addition, since the floating electrode is induced by the potential of the pixel electrode and potential can be generated in itself, display is also performed in the region where the floating electrode is provided. As a result, display can be ensured even between the pixel electrodes, and display with higher contrast becomes possible.

In the electrophoretic display device, the floating electrode is provided in a region surrounding the pixel electrode in a plan view.
According to the present invention, since the floating electrode is provided in a region surrounding the pixel electrode in a plan view, a distance can be secured for the entire area around the pixel electrode in the plan view. Thereby, generation | occurrence | production of leak current can be suppressed more reliably. In addition, since display by the floating electrode is performed in a region surrounding the pixel electrode, display of the outline of the pixel can be ensured, and high-contrast display is possible.

The electrophoretic display device further includes a selection transistor provided on the first substrate, and a latch circuit provided on the first substrate and connected between the selection transistor and the pixel electrode. Features.
According to the present invention, in the configuration in which the latch circuit is provided, the generation of leakage current can be suppressed and the increase in power consumption can be suppressed. In particular, in a configuration in which a latch circuit is provided, a large potential difference tends to be easily generated between adjacent pixel electrodes. Therefore, it can be said that the effect obtained by the present invention is great.

The electrophoretic display device includes: a selection transistor provided on the first substrate and connected to the pixel electrode; and a capacitance element provided on the first substrate and connected to the selection transistor and the pixel electrode. It is further provided with the feature.
According to the present invention, it is possible to suppress generation of leakage current and suppress increase in power consumption even in a configuration in which a capacitive element is provided.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the present embodiment, an electrophoretic display device driven by an active matrix method will be described as an example. In the following drawings, in order to make each configuration easy to understand, the actual structure and the scale and number of each structure are different.

  FIG. 1 is a plan view showing a schematic configuration of an electrophoretic display device 1 according to the present embodiment. The electrophoretic display device 1 includes a display unit 3 in which a plurality of pixels 20 are arranged, a scanning line driving circuit 60, and a data line driving circuit 70.

  The display unit 3 includes a plurality of scanning lines 40 (Y1, Y2,..., Ym) extending from the scanning line driving circuit 60 and a plurality of data lines 50 (X1, X2,..., Xn) extending from the data line driving circuit 70. And are formed. The pixels 20 are arranged corresponding to the intersections of the scanning lines 40 and the data lines 50, and each pixel 20 is connected to the scanning lines 40 and the data lines 50.

  Although not shown, in addition to the scanning line driving circuit 60 and the data line driving circuit 70, a common power supply modulation circuit and a controller are arranged around the display unit 3. The controller comprehensively controls the circuits based on image data and synchronization signals supplied from the host device.

  In addition to the scanning line 40 and the data line 50, each pixel 20 is connected with a high potential power line, a low potential power line, a first control line, and a second control line from a common power modulation circuit. Under the control of the controller, the common power supply modulation circuit generates various signals to be supplied to each of the wirings, and electrically connects and disconnects (high impedance) the wirings.

FIG. 2 is a diagram illustrating a circuit configuration of the pixel 20.
As shown in the figure, the pixel 20 includes a pixel switching element 24, a latch circuit (memory circuit) 25, a pixel electrode 21, a common electrode 22, and an electrophoretic element 23.

  The pixel switching element 24 is a field effect N-type transistor. The scanning line 40 is connected to the gate terminal of the pixel switching element 24, the data line 50 is connected to the source terminal, and the input terminal N1 of the latch circuit 25 is connected to the drain terminal.

  The latch circuit 25 includes a transfer inverter 25a and a feedback inverter 25b, and is a circuit corresponding to an SRAM (Static Random Access Memory) cell.

  The output terminal of the transfer inverter 25a is connected to the input terminal of the feedback inverter 25b, and the output terminal of the feedback inverter 25b is connected to the input terminal of the transfer inverter 25a. That is, the transfer inverter 25a and the feedback inverter 25b have a loop structure in which the other output terminal is connected to each other's input terminal. The input terminal of the transfer inverter 25a (the output terminal of the feedback inverter 25b) is the input terminal N1 of the latch circuit 25, and the output terminal of the transfer inverter 25a (the input terminal of the feedback inverter 25b) is the output terminal of the latch circuit 25. N2. The high potential power supply terminal PH of the latch circuit 25 is connected to the high potential power supply line 78, and the low potential power supply terminal PL is connected to the low potential power supply line 77.

  The transfer inverter 25 a has an N-type transistor 31 and a P-type transistor 32. The gate terminals of the N-type transistor 31 and the P-type transistor 32 are connected to the input terminal N 1 of the latch circuit 25. The source terminal of the N-type transistor 31 is connected to the low potential power line 77, and the drain terminal is connected to the output terminal N2. The source terminal of the P-type transistor 32 is connected to the high potential power supply line 78, and the drain terminal is connected to the output terminal N2.

  The feedback inverter 25 b includes an N-type transistor 33 and a P-type transistor 34. The gate terminals of the N-type transistor 33 and the P-type transistor 34 are connected to the output terminal N2 of the latch circuit 25 (the drain terminals of the N-type transistor 31 and the P-type transistor 32). The source terminal of the N-type transistor 33 is connected to the low-potential power line 77, and the drain terminal is connected to the input terminal N1. The source terminal of the P-type transistor 34 is connected to the high potential power supply line 78, and the drain terminal is connected to the input terminal N1. The output terminal N2 is connected to the pixel electrode 21 via the wiring 35.

  In the pixel 20 having the above configuration, when a low level is input to the latch circuit 25, the input terminal N1 is at a low level and the output terminal N2 is at a high level. Accordingly, a high level is input to the pixel electrode 21 connected to the output terminal N2. On the other hand, when a high level is input to the latch circuit 25, the input terminal N1 is at a high level and the output terminal N2 is at a low level. Therefore, a low level is input to the pixel electrode 21 connected to the output terminal N2. Thus, the potential based on the image data input to the latch circuit 25 is input to the pixel electrode 21 through the wiring 35.

  FIG. 3 is a partial cross-sectional view of the electrophoretic display device 1 in the display unit 3. The electrophoretic display device 1 has a configuration in which an electrophoretic element 23 formed by arranging a plurality of microcapsules 80 is sandwiched between an element substrate 28 and a counter substrate 29.

  In the display unit 3, a plurality of pixel electrodes 21 are arrayed on the electrophoretic element 23 side of the element substrate 28, and the electrophoretic elements 23 are bonded to the pixel electrodes 21 through an adhesive layer 30. A common electrode 22 having a planar shape facing the plurality of pixel electrodes 21 is formed on the counter substrate 29 on the electrophoretic element 23 side, and the electrophoretic element 23 is provided on the common electrode 22.

  The element substrate 28 is a substrate made of glass, plastic, or the like, and is not necessarily transparent because it is disposed on the side opposite to the image display surface. Although not shown, the scanning line 40, the data line 50, the pixel switching element 24, the latch circuit 25, and the like shown in FIGS. 1 and 2 are formed between the pixel electrode 21 and the element substrate 28. Yes.

  The counter substrate 29 is a substrate made of glass, plastic, or the like, and is a transparent substrate because it is disposed on the image display side. The common electrode 22 formed on the counter substrate 29 is formed using a transparent conductive material such as MgAg (magnesium silver), ITO (indium tin oxide), IZO (indium zinc oxide) or the like.

  The electrophoretic element 23 is generally formed in advance on the counter substrate 29 side and is handled as an electrophoretic sheet including the adhesive layer 30. A protective release paper is attached to the adhesive layer 30 side.

  In the manufacturing process, the display unit 3 is formed by attaching the electrophoretic sheet from which the release paper is peeled off to the separately manufactured element substrate 28 on which the pixel electrode 21 and the circuit are formed. Yes. For this reason, the adhesive layer 30 exists only on the pixel electrode 21 side.

  FIG. 4 is a schematic cross-sectional view of the microcapsule 80. The microcapsule 80 has a particle size of about 50 μm, for example, and encloses therein a dispersion medium 81, a plurality of white particles (electrophoretic particles) 82, and a plurality of black particles (electrophoretic particles) 83. It is a spherical body. As shown in FIG. 3, the microcapsule 80 is sandwiched between the common electrode 22 and the pixel electrode 21, and one or a plurality of microcapsules 80 are arranged in one pixel 20.

  The outer shell (wall film) of the microcapsule 80 is formed using a transparent polymer resin such as acrylic resin such as polymethyl methacrylate or polyethyl methacrylate, urea resin, or gum arabic.

  The dispersion medium 81 is a liquid that disperses the white particles 82 and the black particles 83 in the microcapsules 80. Examples of the dispersion medium 81 include water, alcohol solvents (methanol, ethanol, isopropanol, butanol, octanol, methyl cellosolve, etc.), esters (ethyl acetate, butyl acetate, etc.), ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.) ), Aliphatic hydrocarbons (pentane, hexane, octane, etc.), alicyclic hydrocarbons (cyclohexane, methylcyclohexane, etc.), aromatic hydrocarbons (benzene, toluene, benzenes having a long-chain alkyl group ( Xylene, hexylbenzene, hebutylbenzene, octylbenzene, nonylbenzene, decylbenzene, undecylbenzene, dodecylbenzene, tridecylbenzene, tetradecylbenzene)), halogenated hydrocarbons (methylene chloride, chloroform, tetrachloride) Element, and 1,2-dichloroethane), can be exemplified a carboxylate, it may be other oils. These substances can be used alone or as a mixture, and a surfactant or the like may be further blended.

  The white particles 82 are particles (polymer or colloid) made of a white pigment such as titanium dioxide, zinc white, and antimony trioxide, and are used, for example, by being negatively charged. The black particles 83 are particles (polymer or colloid) made of a black pigment such as aniline black or carbon black, and are used by being charged positively, for example.

  These pigments include electrolytes, surfactants, metal soaps, resins, rubbers, oils, varnishes, compound charge control agents, titanium-based coupling agents, aluminum-based coupling agents, silanes as necessary. A dispersant such as a system coupling agent, a lubricant, a stabilizer, and the like can be added.

FIG. 5 is a plan view showing a configuration on the element substrate 28 side of the electrophoretic display device 1 according to the present embodiment. In the figure, a configuration of a plurality of pixels, for example, three pixels 20 is shown.
As shown in the figure, each pixel 20 is provided with a floating electrode 26 corresponding to the pixel electrode 21.

  The floating electrode 26 is not connected to the pixel electrode 21, other wirings, or electrodes at all, and is an electrically floating (floating) electrode. The floating electrode 26 is provided in a region surrounding the pixel electrode 21 in plan view. Specifically, the floating electrode 26 is provided in an annular region along the outline of the pixel electrode 21 formed in a rectangular shape in plan view. A gap is provided between the floating electrode 26 and the pixel electrode 21 so as not to contact each other.

  In the present embodiment, floating electrodes 26 are provided for the pixel electrodes 21 of all the pixels 20. Therefore, two floating electrodes 26 are disposed between two adjacent pixel electrodes 21. In FIG. 5, only the three pixel electrodes 21 adjacent in the horizontal direction in the figure are illustrated, but actually the pixel electrodes 21 arranged in the vertical and horizontal directions have the same configuration.

  FIG. 6 is a cross-sectional view showing a state when a voltage is applied to adjacent pixel electrodes 21 in the electrophoretic display device 1. In the figure, two pixel electrodes 21 are shown by way of example.

  As shown in FIG. 6, for example, when a high level voltage H is applied to the pixel electrode 21A on the left side in the figure and a low level voltage L is applied to the pixel electrode 21B on the right side in the figure, the pixel electrode 21A and the pixel electrode 21B A potential difference is generated between the two. On the other hand, two floating electrodes 26A and 26B are disposed between the pixel electrode 21A and the pixel electrode 21B, and the distance between the pixel electrode 21A and the pixel electrode 21B is secured accordingly. . For this reason, a leak current is unlikely to occur between the pixel electrodes 21A and 21B.

  The floating electrode 26A is induced by the pixel electrode 21A to which the high level voltage H is applied, and becomes a potential close to the high level voltage H. Therefore, for example, when the voltage COM of the common electrode 22 is at a low level, an electric field is generated between the pixel electrode 21A and the common electrode 22, and an electric field is also generated between the floating electrode 26A and the common electrode 22. . This electric field moves not only the electrophoretic element in the region overlapping the pixel electrode 21A in plan view but also the electrophoretic element in the region overlapping the floating electrode 26A in plan view. Thus, display can be performed as a part of the pixel 20 in the region where the floating electrode 26A is provided in addition to the region where the pixel electrode 21A is provided.

  The floating electrode 26B is induced by the pixel electrode 21B to which the low level voltage L is applied, and becomes a potential close to the low level voltage L. Therefore, for example, when the voltage COM of the common electrode 22 is at a high level, an electric field is generated between the pixel electrode 21B and the common electrode 22, and an electric field is also generated between the floating electrode 26B and the common electrode 22. . This electric field moves not only the electrophoretic element in the region overlapping the pixel electrode 21B in plan view but also the electrophoretic element in the region overlapping the floating electrode 26B in plan view. Thus, display can be performed as a part of the pixel 20 in the region where the floating electrode 26B is provided in addition to the region where the pixel electrode 21B is provided.

  Thus, according to this embodiment, since the floating electrode 26 corresponding to each pixel electrode 21 is provided between the adjacent pixel electrodes 21, the distance between the adjacent pixel electrodes 21 is increased accordingly. be able to. By increasing the distance between the adjacent pixel electrodes 21, the influence of the potential difference generated between the adjacent pixel electrodes 21 can be reduced, and the occurrence of leakage current can be suppressed. Thereby, an increase in power consumption can be suppressed.

  In addition, since the floating electrode 26 is induced by the potential of the pixel electrode 21 and a potential can be generated in itself, display is performed also in the region where the floating electrode 26 is provided. Thereby, since display can be performed also between the pixel electrodes 21, display with higher contrast becomes possible.

  When the floating electrode 26 is provided in a region surrounding the pixel electrode 21 in plan view as in the present embodiment, distances can be secured in all directions around the pixel electrode 21 in plan view. Thereby, generation | occurrence | production of leak current can be suppressed more reliably. Further, since the display by the floating electrode 26 is performed in the region surrounding the pixel electrode 21, display of the outline of the pixel 20 can be ensured, and display with high contrast is possible.

  In addition, in the configuration in which the latch circuit 25 is provided as in the present embodiment, the generation of leakage current can be suppressed and the increase in power consumption can be suppressed. In particular, in a configuration in which the latch circuit 25 is provided, it can be said that the effect obtained by the present invention is great because a large potential difference tends to occur between adjacent pixel electrodes 21.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. The electrophoretic display device 101 according to this embodiment has a configuration in which a transfer gate as a potential control switch circuit is provided in the pixel 20 shown in FIGS. 2 and 5 of the first embodiment. Therefore, in the drawings referred to below, the same reference numerals are given to the same components as those of the pixel 20 in FIGS. 2 and 5, and detailed description thereof will be omitted.

FIG. 7 is a diagram illustrating a circuit configuration of the pixel 120 of the electrophoretic display device 101, and corresponds to FIG. 2 in the first embodiment.
As shown in the figure, the pixel 120 includes a selection transistor 24, a latch circuit (memory circuit) 25, transmission gates TG1 and TG2 which are potential control switch circuits, a pixel electrode 21, a common electrode 22, An electrophoretic element 23 and a floating electrode 26 are provided. Since the configuration of the selection transistor 24 and the latch circuit 25 is the same as that of the first embodiment, description thereof is omitted here.

  Further, as in the first embodiment, a floating electrode 26 corresponding to the pixel electrode 21 is provided. The configuration of the floating electrode 26 is also the same as that of the first embodiment, and a description thereof will be omitted.

  The transmission gate TG1 includes a field effect type P-type transistor T11 and a field effect type N-type transistor T12. The source terminal of the P-type transistor T11 and the source terminal of the N-type transistor T12 are connected, and these are connected to the first control line S1. The drain terminal of the P-type transistor T11 and the drain terminal of the N-type transistor T12 are connected, and these are connected to the pixel electrode 21. The gate terminal of the P-type transistor T11 is connected to the input terminal N1 of the latch circuit 25, and the gate terminal of the N-type transistor T12 is connected to the output terminal N2 of the latch circuit 25.

  The transmission gate TG2 includes a field effect type P-type transistor T21 and a field effect type N-type transistor T22. The source terminal of the P-type transistor T21 and the source terminal of the N-type transistor T22 are connected, and these are connected to the second control line S2. The drain terminal of the P-type transistor T21 and the drain terminal of the N-type transistor T22 are connected, and these are connected to the pixel electrode 21 via the wiring 35.

  The gate terminal of the P-type transistor T21 is connected to the output terminal N2 of the latch circuit 25 together with the gate terminal of the N-type transistor T12 of the transmission gate TG1, and the gate terminal of the N-type transistor T22 is connected to the transmission gate TG1. The gate terminal of the P-type transistor T11 is connected to the input terminal N1 of the latch circuit 25.

  In the pixel 120 having the above-described configuration, when low-level image data is input from the data line 50 to the latch circuit 25 via the pixel switching element 24, the input terminal N1 of the latch circuit 25 receives the low level and the output terminal N2 High level is output. Accordingly, only the P-type transistor T11 and the N-type transistor T12 constituting the transmission gate TG1 are turned on. Accordingly, the pixel electrode 21 is electrically connected to the first control line S1 via the wiring 35.

  On the other hand, when high level image data is input from the data line 50 to the latch circuit 25 via the pixel switching element 24, a high level is output from the input terminal N1 and a low level is output from the output terminal N2. Accordingly, only the P-type transistor T21 and the N-type transistor T22 constituting the transmission gate TG2 are turned on. Accordingly, the pixel electrode 21 is electrically connected to the second control line S2 via the wiring 35.

  As in the present embodiment, the configuration in which the transmission gates TG1 and TG2 are provided can suppress the occurrence of leakage current and suppress the increase in power consumption, as in the above embodiment.

The technical scope of the present invention is not limited to the above-described embodiment, and appropriate modifications can be made without departing from the spirit of the present invention.
In the above embodiment, the floating electrodes 26 are provided in all the pixels 20. However, the present invention is not limited to this. For example, the floating electrodes 26 are provided only in the pixel electrodes 21 of some of the pixels 20. It does not matter.

  Further, in the configuration of the first embodiment, the present invention can be applied to a configuration in which a capacitor element 125 is provided instead of the latch circuit 25 as shown in FIG. In FIG. 8, the capacitor element 125 has a configuration in which one terminal is connected between the pixel switching element 24 and the pixel electrode 21 and the other terminal is grounded.

1 is a schematic configuration diagram of an electrophoretic display device according to a first embodiment of the present invention. FIG. 3 is a circuit configuration diagram of a pixel of the electrophoretic display device according to the embodiment. 1 is a partial cross-sectional view of an electrophoretic display device according to an embodiment. FIG. 3 is a cross-sectional configuration diagram of a microcapsule of the electrophoretic display device according to the embodiment. FIG. 3 is a plan view showing a configuration of one pixel of the electrophoretic display device according to the embodiment. FIG. 6 is a plan view showing the operation of the electrophoretic display device according to the embodiment. The top view which shows the structure of the electrophoretic display device which concerns on 2nd Embodiment of this invention. FIG. 3 is a diagram illustrating a partial configuration of an electrophoretic display device according to the invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrophoretic display device 3 ... Display part 20, 120 ... Pixel 21, 21A, 21B ... Pixel electrode 22 ... Common electrode 23 ... Electrophoretic element 24 ... Pixel switching element 25 ... Latch circuit 26, 26A, 26B ... Floating electrode 125 ... Capacitance element

Claims (4)

An electrophoretic display device comprising an electrophoretic layer sandwiched between a first substrate and a second substrate,
A plurality of pixel electrodes provided on the first substrate;
An electrophoretic display device comprising: a floating electrode provided corresponding to each of the adjacent pixel electrodes between the adjacent pixel electrodes of the first substrate. The electrophoretic display device according to claim 1, wherein the floating electrode is provided in a region surrounding the pixel electrode in a plan view. A selection transistor provided on the first substrate;
The electrophoretic display device according to claim 1, further comprising: a latch circuit provided on the first substrate and connected between the selection transistor and the pixel electrode. A select transistor provided on the first substrate and connected to the pixel electrode;
The electrophoretic display device according to claim 1, further comprising: a capacitor provided on the first substrate and connected to the selection transistor and the pixel electrode.

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