JP2007011127A - Display element and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display element and an electrophoretic display device that can obtain stable driving characteristics. <P>SOLUTION: An interface member 8c which connects and covers a pair of electrodes 6 and 7 is arranged on the interface between the pair of electrodes 6 and 7 and a fluid dispersion consisting of a dispersant and a plurality of charged particles, and the resistance between the electrodes through the interface member 8c is made smaller than the resistance through the fluid dispersion to suppress accumulation (residual DC) in interface members 8a, 8b, and 8c and cancel accumulated electric charges. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a display element and a display device, and more particularly to a configuration for obtaining stable driving characteristics.

  In recent years, with the remarkable progress of digital technology, the amount of information that can be handled by individuals has increased dramatically. Along with this, the development of displays as information output means has been actively carried out, and technical innovations have continued to display with high usability such as high definition, low power consumption, light weight, and thinness.

  In particular, in recent years, there has been a demand for an “easy-to-read” high-definition display having display quality equivalent to that of printed materials, which is an indispensable technology for next-generation products such as electronic paper and electronic books.

  By the way, one of the technologies for embodying such electronic paper, electronic book, and the like is one that uses an electrophoretic phenomenon, and there is a particle movement type display device as a display device that uses such an electrophoretic phenomenon. As an example, Harold D.C. An electrophoretic display device proposed by Lee et al. Is known (for example, see Patent Document 1).

  Here, this electrophoretic display device has a dispersion liquid composed of a dispersion medium mixed with colored charged electrophoretic particles and a colorant sandwiched between a pair of substrates, and by contrasting the colored charged electrophoresis particles and the colored dispersion medium. An electrophoretic display element for displaying an image is provided. However, in such an electrophoretic display element, the life and contrast are deteriorated due to mixing of a colorant such as a dye in the dispersion medium. was there.

  Therefore, in order to solve such a problem, the colored charged electrophoretic particles are dispersed in a transparent dispersion medium and a colored layer is disposed on the substrate. By contrasting the colored charged electrophoretic particles and the colored layer disposed on the substrate, An electrophoretic display device including an electrophoretic display element that displays an image without coloring a dispersion medium has been proposed (see, for example, Patent Documents 2 and 3).

US Pat. No. 3,612,758 JP-A-11-202804 JP 11-357369 A

  By the way, in an electrophoretic display device (particle movement type display device) provided with such a conventional electrophoretic display element (particle movement type display device), at the time of rewriting the display, it is colored charged that is charged positively or negatively. In order to move the electrophoretic particles by an electric field, a DC voltage is applied to the electrophoretic display element. Here, when such display rewriting is repeated many times, as a result, a DC voltage is applied to the electrophoretic display element for a long time.

  When a DC voltage is applied to the electrophoretic display element for a long time in this way, a space charge distribution is formed by electrons, ions, etc. in the insulating layer or the dispersion medium, and the DC component remains in the electrophoretic display element. It becomes like this.

  If writing according to only the gradation value indicated by the image data is performed with the DC component remaining in this manner, a desired gradation value display may not be obtained. This is because the residual DC component causes a difference between the applied voltage at the time of writing and the effective voltage applied to the electrophoretic display element. Note that a phenomenon in which a desired gradation value display cannot be obtained due to such a residual DC component is called burn-in.

  Further, in the electrophoretic display element, the dispersion of the physical properties of the dispersion medium and the temperature change thereof cause the resistance value of the dispersion to fluctuate, thereby causing a problem of driving instability.

  Therefore, the present invention has been made in view of such a current situation, and provides an electrophoretic display element (display element) and an electrophoretic display apparatus (display apparatus) capable of obtaining stable driving characteristics. It is the purpose.

  The present invention includes a substrate, a partition wall disposed on the substrate, a dispersion liquid that is partitioned on the substrate by the partition wall and a plurality of charged particles, and a surface facing the dispersion liquid. A first electrode disposed on the substrate and a second electrode facing the dispersion and disposed along the partition wall, and the charging is performed by a voltage applied between the first electrode and the second electrode. A display element that performs display by changing the distribution of particles, wherein an interface member that covers and covers the first electrode and the second electrode at an interface between the first electrode and the second electrode and the dispersion liquid The resistance through the interface member between the first electrode and the second electrode is smaller than the resistance through the dispersion between the first electrode and the second electrode. Is.

  As in the present invention, an interface member that connects and covers the electrodes is disposed at the interface between the pair of electrodes and the dispersion liquid so that the resistance through the interface member between the electrodes is smaller than the resistance through the dispersion liquid. As a result, charge accumulation (residual DC) on the interface member can be suppressed, and the accumulated charge can be canceled, and stable drive characteristics can be obtained.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an electrophoretic display element (display element) provided in an electrophoretic display apparatus (display apparatus) according to an embodiment of the present invention.

  As shown in FIG. 1, the electrophoretic display element includes a first substrate 2 on the observer side and a second substrate 1 on the opposite side, which are a pair of substrates arranged with a predetermined gap therebetween, and these substrates. The partition wall 3 is a partition member for keeping the gap between 1 and 2 constant, the transparent dispersion medium 4 filled in the space surrounded by the substrates 1 and 2 and the partition wall 3, and the dispersion medium 4. In addition, a colored charged electrophoretic particle 5 as an example of a charged particle that is a plurality of fine particles and a particle dispersion composed of an additive are provided.

  This electrophoretic display element has pixels arranged in a matrix on a substrate, and the partition wall 3 also has a function of preventing the movement of the colored charged electrophoretic particles 5 between adjacent pixels.

  Further, the first electrode 6 is applied on the second substrate 1, and a voltage different from that of the first electrode 6 is applied to the inside and the side surface of the partition 3 in the present embodiment, almost the same as the partition 3. Two electrodes 7 are formed. By forming an electric field for controlling the spatial distribution of the colored charged electrophoretic particles 5 by the first and second electrodes 6 and 7, the colored charged electrophoretic particles 5 are connected to the first electrode 6 and the first electrode 6. It can be moved in the horizontal direction between the two electrodes 7. The first electrode 6 and the second electrode 7 are insulated by an insulating member 9.

  In FIG. 1, other display element components (for example, an electric signal applying means for applying an electric signal between the electrodes and a thin film transistor TFT disposed in each space) are omitted.

  By the way, the electrophoretic display element according to the present embodiment reflects the distribution state of the colored charged electrophoretic particles 5 in the display state. For example, the colored charged electrophoretic particles 5 are positively charged to black particles and the first electrode. Assuming that 6 is colored white and the second electrode 7 is grounded to 0 V, when −10 V is applied to the first electrode 6, as shown in FIG. The migrating particles 5 move on the first electrode. As a result, the first electrode 6 is covered with the black colored charged electrophoretic particles 5, and when this state is observed from the first substrate 2 side, this pixel looks black to the observer.

  When +10 V is applied to the first electrode 6, the black colored charged electrophoretic particles 5 move to the side walls of the partition as shown in FIG. As a result, the white first electrode 6 is exposed. When the pixel in this state is observed from the first substrate 2 side, the pixel looks white to the observer. The gradation display can be performed by changing the amount of the colored charged electrophoretic particles 5 to be moved by changing the magnitude of the voltage applied to the first electrode 6 and the application time.

  By the way, in FIG. 1, 8 is an interface member formed in the interface which contact | connects the liquid layer comprised by the particle dispersion liquid of the 1st electrode 6, the 2nd electrode 7, and the insulating member 9, This interface member 8 is It has a volume resistivity smaller than the volume resistivity of the liquid layer.

Here, the interface member 8 is a light transmissive material, such as an organic film such as polysilane, polysiloxane, or polyacetylene, or a composite or copolymer thereof, or a carbon-containing film, indium-tin oxide (ITO). An inorganic film such as silicon, a semiconductor film such as silicon, or a conductive filler (filler), for example, a metal powder, carbon particles, or the like can be used in an epoxy resin, a polypropylene resin, or the like. Further, the interface member 8 may be a laminated film of these films. In the present embodiment, the interface member 8 preferably has a volume resistivity of 10 ⁶ Ωcm to 10 ¹² Ωcm and a film thickness of 1 nm to 200 nm.

  In the present embodiment, the first substrate 2 and the second substrate 1 are made of a polymer film such as polyethylene terephthalate (PET), polyethersulfone (PES), polycarbonate (PC), or an inorganic material such as glass or quartz. Can be used.

  The first electrode 6 and the second electrode 7 are made of a conductive material such as aluminum (Al), titanium (Ti), copper (Cu), silver (Ag), or indium-tin oxide (ITO). be able to. Furthermore, an acrylic resin can be used for the insulating member 9 that insulates the first electrode 6 and the second electrode 7.

  Moreover, non-polar solvents, such as isoparaffin, silicone oil, toluene, xylene, can be used for a dispersion medium. Further, as the colored charged electrophoretic particles to be colored, it is preferable to use a material that is colored and exhibits good charging characteristics in a dispersion medium. For example, various inorganic pigments, organic pigments, carbon black, or resins containing them. Can be used.

In addition, although there is no restriction | limiting in particular in the particle size of the colored electrophoretic particle 5, Usually, it is good to use a thing of about 0.1 micrometer-10 micrometers. In addition, a charge control agent for controlling and stabilizing the charging of the colored charged electrophoretic particles 5 may be added to the dispersion medium and the colored charged electrophoretic particles described above. Here, the volume resistivity of the liquid layer obtained by mixing the colored electrophoretic particles 5 and the charge control agent in the dispersion medium is generally about 10 ¹¹ Ωcm to 10 ¹⁴ Ωcm.

  By the way, the interface member 8 having a volume resistivity smaller than that of the liquid layer includes a first interface member (not shown) formed at the interface with the liquid layer of the first electrode 6 indicated by symbol A in FIG. A second interface member (not shown) formed at the interface with the liquid layer 7 and a liquid layer of the insulating member 9 located between the electrodes of the first electrode 6 and the second electrode 7 shown in FIG. It is comprised integrally by the 3rd interface member not shown formed in the interface. That is, in the present embodiment, the low resistance interface member 8 composed of the first interface member, the second interface member, and the third interface member is formed so as to be connected between the electrodes while being in contact with the liquid layer.

  FIG. 3 shows a simple equivalent circuit of the electrophoretic display device having such a configuration. For convenience of explanation, the interface member 8 is drawn with a film thickness that is larger than necessary.

Here, the liquid layer and each layer of the interface member 8 can be generally described by a parallel circuit of a capacitance component and a resistance component. In FIG. 3, C _V1 is the capacity of the first interface member 8a on the first electrode, R _V1 is the resistance of the first interface member 8a on the first electrode, C _L is the capacity of the liquid layer, and _RL is the liquid resistance of the _{layer, C V2} is the capacitance of the second interface member 8b on the second _{electrode, R V2} is the resistance of the second interface member 8b on the second _electrode, the _{C BL} represents the capacitance of an electric double layer.

  Then, as in the present embodiment, the low-resistance interface member 8 is formed so as to be in contact with the liquid layer so as to be connected between the two electrodes, whereby the third interface member 8c causes the electric charge to contact the liquid layer. Thus, an electrically conductive path for conducting is formed. Hereinafter, this electric conduction path is referred to as a short path.

Here, when this short path is expressed as an equivalent circuit, the short path resistance (R _sp ) is arranged in parallel with the resistance (R _L ) of the liquid layer, as shown in FIG. Become. In addition, the low-resistance interface member 8 (first and second interface members 8a and 8b) is arranged on the electrode, and the interface member 8 (third interface member 8c) performs a short path in parallel with the liquid layer. As a result, the charge accumulation (residual DC) on the interface member 8 is suppressed. Even when charges are accumulated in the interface member 8, the residual DC time constant can be shortened by canceling the charges through a short path.

When the volume resistance of the interface member 8 is large and the short path resistance (R _sp ) is greater than the resistance (R _L ) of the liquid layer, the charge accumulated at the interface between the liquid layer and the interface member 8 is discharged through the liquid layer. There is only. The time constant at this time is C _L R _L.

Conversely, when the interface member 8 is formed of a material whose short path resistance (R _sp ) is smaller than the resistance (R _L ) of the liquid layer, the charge is discharged through the interface member with a short time constant C _L R _sp . . In addition, when a new voltage is applied for each frame and the position of the migrating particles changes, the charge due to the voltage of the previous frame needs to disappear before the voltage application of the next frame. It is shorter than one frame time. That is,
1F (one frame period)> C _L R _sp
Therefore , the absolute value of the upper limit of the short path resistance (R _sp ) is determined from this.

The conditions regarding the resistance value also differ depending on the film thickness of the interface member, the dimension of the liquid layer, and the shape of the first electrode / second electrode. However, if the volume resistivity of the interface member and the liquid layer is appropriately selected, it can be made to satisfy the above condition (R _sp <R _L ).

On the other hand, the resistance value of the liquid layer is affected by variations in the physical properties of the dispersion medium and changes in temperature, but as shown in FIG. 3B, the short path resistance (R _sp ) is the resistance of the liquid layer (R _L ), the effective resistance of the liquid layer can be uniquely controlled by the short path resistance (R _sp ). Thereby, even if the resistance (R _L ) of the liquid layer is fluctuated due to variations in the physical properties of the dispersion medium or changes in temperature, stable driving characteristics can be realized.

  Thus, by making the resistance through the interface member 8 (the first interface member 8a, the second interface member 8b, and the third interface member 8c) smaller than the resistance through the liquid layer, it is in parallel with the dispersion liquid. A conductive path can be formed, and charge accumulation (residual DC) in the interface member 8 is suppressed. In addition, since the accumulated charge is canceled through the short path, the residual DC time constant can be shortened. As a result, it is possible to perform stable driving without changing the desired gradation display level.

Further, by configuring in this way, the effective resistance (R _L ) of the liquid layer can be uniquely controlled by the short path resistance (R _sp ), and the physical property value of the liquid layer (dispersion) can be controlled. Even if the resistance (R _L ) of the liquid layer is fluctuated due to variations or temperature changes, stable driving characteristics can be realized.

  In the above description, in FIG. 1, the interface member 8 including the first interface member 8a, the second interface member 8b, and the third interface member 8c is formed as an integral film. The first interface member 8a, the second interface member 8b, and the third interface member 8c are separately provided as long as they have a volume resistivity smaller than the volume resistivity of the liquid layer. You may form with another material.

  Further, in the above description, when changing the display state, the colored charged electrophoretic particles 5 are displaced on the substrate by the electrophoretic force. As a method for displacing the colored charged electrophoretic particles 5, for example, dielectric Electrophoretic force, electrohydrodynamic flow of a dispersion medium, or the like may be used.

  In the description so far, the colored charged electrophoretic particles 5 are black and the electrode surface of the first electrode 6 is white. However, the present invention is not limited to this. For example, the electrode surface of the first electrode 6 is appropriately set. Color display is also possible by coloring red, green, blue, etc.

  Next, the present invention will be described in detail using examples.

  In this embodiment, a matrix panel having the configuration shown in FIG. 1 as an electrophoretic display element, in which 600 × 1800 pixels having a rectangular planar shape and a pixel size of 40 μm wide × 120 μm long are arranged.

In addition, a 1.1 mm thick glass substrate is used as the first substrate, and a thin transistor (not shown) and other wiring and IC (not shown) necessary for driving are formed on the first substrate. Thereafter, a Si ₃ N ₄ film is formed as an insulating layer on the entire surface of the substrate. Thereafter, Al is formed and patterned to form the first electrode. At the time of forming the Al film, the thin film transistor and the first electrode are brought into conduction through a contact hole formed in advance.

  Next, a second electrode that also serves as a partition is formed with a height of 15 μm and a width of 5 μm by electroplating. The first electrode and the second electrode are formed so as to be insulated by an acrylic resin having a height of 1 μm.

Next, an indium-tin oxide (ITO) film is formed as an integrated film having a thickness of 5 nm so as to cover the surfaces of the first electrode and the second electrode. At this time, the film formation conditions are set so that the volume resistivity is 5.0 × 10 ¹⁰ Ωcm, and the volume resistivity of the formed film is measured by an impedance analyzer SI1260 (manufactured by Solartron, UK). The resistance value using the first electrode and the second electrode as terminals is 1.6 × 10 ¹³ Ω.

  Next, each pixel is filled with a dispersion composed of colored charged electrophoretic particles, a dispersion medium, and a charge control agent. The colored charged electrophoretic particles use a polystyrene-polymethyl methacrylate copolymer resin containing carbon black having a particle size of about 1 to 2 μm. Further, isoparaffin (trade name: Isopar, manufactured by Exxon) is used as the dispersion medium, and the charged charged electrophoretic particles are made positively charged by containing a charge control agent.

At this time, the dispersion is prepared so that the volume resistivity is 2.2 × 10 ¹² Ωcm. Thereafter, the volume resistivity of the dispersion (liquid layer) obtained by mixing the colored charged electrophoretic particles and the charge control agent in the dispersion medium is measured with an impedance analyzer SI1260 (manufactured by Solartron, UK). When there is no indium-tin oxide film, the resistance of the dispersion liquid having the first electrode and the second electrode as terminals is 1.9 × 10 ¹⁹ Ω. Therefore, in the present embodiment, the relationship of R _sp < _RL is established.

  Finally, the second substrate is disposed and sealed to complete the electrophoretic display element.

  Next, the electrophoretic display element thus manufactured is connected to a drive driver (not shown) to perform a display operation. In this embodiment, the second electrode is set to 0 V as a common electrode for all pixels, and black and white rewrite is performed by applying ± 10 V to the first electrode through the thin film transistor. In the case of gradation display, voltage modulation is performed such as + 2V, + 4V, + 6V, and + 8V.

  Then, display rewriting by the above driving method is repeated in a temperature range from 0 ° C. to 60 ° C. As a result, stable drive characteristics can be realized without causing a burn-in problem that the desired gradation optical level fluctuates.

  Next, a comparative example of the present invention will be described.

  First, the first comparative example will be described. FIG. 4 is a diagram showing a schematic configuration of the electrophoretic display element according to this comparative example. In FIG. 4, reference numeral 81 denotes an interface member having a volume resistivity larger than the volume resistivity of the liquid layer. Reference numeral 82 denotes an insulating film constituting an insulating member formed on the first substrate 1.

  FIG. 5 is a simple equivalent circuit of FIG. Here, generally, in the electrophoretic display element, no charge is exchanged between the liquid layer and the electrodes 6 and 7. That is, the migrating particles that have moved onto the electrode form an electric double layer, while the electric charge flowing from the electrodes 6 and 7 accumulates in the interface member 81 in contact with the liquid layer, causing residual DC. End up.

  Next, a second comparative example of the present invention will be described. FIG. 6 is a diagram showing a schematic configuration of the electrophoretic display element according to this comparative example. In FIG. 6, reference numeral 83 denotes a low-resistance interface member having a volume resistivity smaller than the volume resistivity of the liquid layer.

  Here, in this comparative example, the interface member 83 is formed only on the surfaces of the first electrode 6 and the second electrode 7, that is, the region A in FIG. 2 described above, and the insulating member 9 located between the two electrodes. 2 is not formed at the interface in contact with the liquid layer, that is, the region B in FIG. That is, the two interface members 83 are disconnected without being connected between the two electrodes.

In such a configuration, electric charges cannot be conducted between the electrodes so as to be in contact with the liquid layer, and a short path (R _sp ) parallel to the conduction path (R _L ) of the liquid layer is not formed. R _sp can be considered substantially infinite, R _sp > R _L. 6 is produced when the interface member 8 and the insulating member 9 have poor wettability and the interface member is coated with a spin coater or the like.

1 is a diagram showing a schematic configuration of an electrophoretic display element provided in an electrophoretic display device which is an example of a particle mobile display element provided in a particle mobile display device according to an embodiment of the present invention. Sectional drawing which shows arrangement | positioning of the interface member of the said electrophoretic display element. The figure which shows the equivalent circuit of the said electrophoretic display element. The figure which shows schematic structure of the electrophoretic display element which concerns on the 1st comparative example of this invention. The figure which shows the equivalent circuit of the electrophoretic display element which concerns on the 1st comparative example of this invention. The figure which shows schematic structure of the electrophoretic display element which concerns on the 2nd comparative example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 2nd board | substrate 2 1st board | substrate 3 Partition 4 Dispersion medium 5 Colored charged electrophoretic particle 6 1st electrode 7 2nd electrode 8 Interface member 8a 1st interface member 8b 2nd interface member 8c 3rd interface member 9 Insulating member A of electrode Interface B in contact with liquid layer Interface in contact with liquid layer of insulating member

Claims (2)

A substrate, a partition wall disposed on the substrate, a dispersion liquid comprising a dispersion medium and a plurality of charged particles disposed on the substrate by the partition wall, and the substrate facing the dispersion liquid A first electrode disposed above and a second electrode facing the dispersion and disposed along the partition wall, and the distribution of the charged particles is determined by a voltage applied between the first electrode and the second electrode. A display element that changes the display,
An interface member for connecting and covering the first electrode and the second electrode is disposed at the interface between the first electrode and the second electrode and the dispersion;
A display element, wherein resistance through the interface member between the first electrode and the second electrode is smaller than resistance through the dispersion between the first electrode and the second electrode. A display device comprising the display element according to claim 1.

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