JP2005091514A - Electrochromic display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrochromic display device which facilitates writing and erasure of pixels and whose rewriting time is short. <P>SOLUTION: This electrochromic display device has each pixel equipped with two switching means and two rewriting means, and uses a TFT 21 as a switching means A and a TFT 22 as a switching means B. Further, a TFT 23 is used as a rewriting means C and a TFT 24 is used as a rewriting means D. Two independent gate lines 25 and 26 are wired; and the TFT 21 is connected to the gate line 25 and the TFT 22 is connected to the gate line 26. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrochromic display device that displays an image using an electrochromic phenomenon.

  Electronic paper as a new display medium that combines the characteristics of paper, such as no need for information holding energy, reliable storage, easy-to-read, easy reading, and the ability to rewrite information. Recently, it has attracted more and more attention.

  Various display principles in this electronic paper are known. For example, a capsule that is called a microcapsule type electrophoretic display method, in which black and white particles that are charged positively and negatively are moved between electrodes. Also called the twist ball display method, which controls the orientation of spherical particles painted in white and black. These are all displayed using physical phenomena.

On the other hand, there is also known one that displays using a chemical phenomenon. Among them, those utilizing an electrochromic phenomenon in which a voltage is applied between electrodes to cause coloring or erasure by an oxidation-reduction reaction are known. This is described in Patent Document 1, for example.
JP 2002-258327 A

  As shown in Patent Document 1, a drive circuit for driving each pixel of the electrochromic display device is the same as the drive circuit in the liquid crystal display device. In other words, one TFT is used for each pixel, the gate electrode of the TFT is connected to the gate line, the source electrode is connected to the source line, and the drain electrode is connected to the pixel electrode. I have control. If this liquid crystal type drive circuit is used as it is in an electrochromic display device, it depends on the current capability of the source driver and TFT, and therefore it takes a long time to accumulate the amount of charge necessary for the oxidation-reduction reaction in the pixel electrode. Resulting in. Although it is conceivable to increase the size of the TFT and pass a large current, there is a limit to the size of the TFT that can be formed in one pixel, and using a high-performance driver leads to an increase in cost.

  It is also conceivable to use a drive circuit that is generally used in an organic EL display device as disclosed in JP-A-2002-108252. This is because each pixel has a TFT connected to the gate line and the source line, a gate electrode connected to the drain electrode of the TFT, a source electrode connected to the power supply line, and a drain electrode connected to the pixel electrode. It is the composition which has. In this organic EL type drive circuit, since there is only one power supply line, charges can be stored in the pixel electrodes, but charges cannot be reduced. That is, the display state can be changed from white display to black display, but the display state cannot be changed from black display to white display.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electrochromic display device that can easily write to and erase pixels and has a short rewrite time.

  In order to solve the above problems, an electrochromic display device of the present invention includes an electrochromic device including a pixel electrode, a counter electrode, and a plurality of pixels each including an electrochromic layer and an electrolytic layer formed between the pixel electrode and the counter electrode. In the display device, the pixel is provided with independent erasing means and writing means.

  In addition, the pixel includes two switching means and two rewriting means.

  According to the present invention, since the erasing means and the writing means are provided independently for each pixel, writing / erasing can be performed separately. In addition, since the power supply lines are provided to each other, charge can be supplied to the pixel electrode in a short time.

  Further, according to the present invention, since two rewriting means are provided for each pixel, writing and erasing can be performed separately, and charge can be supplied to the pixel electrode in a short time.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a configuration of a pixel portion in an electrochromic display device. In FIG. 1, a drive circuit for supplying a current to the pixel electrode is omitted.

  The electrochromic display device includes an array side substrate 10, a color filter side substrate 50, and an electrolytic layer 80 sandwiched between the substrates.

  In the array-side substrate 10, a plurality of pixel electrodes 12 are arranged in a matrix on a glass substrate 11, and an electrochromic layer 13 is laminated on the surface of the pixel electrodes 12. The pixel electrode 12 is formed of a metal that acts as a reflective electrode, and each electrochromic layer 13 has a shape corresponding to the pixel electrode 12 and is separated from the adjacent pixel electrode 13.

  The electrochromic layer 13 can be used as long as it is made of a substance that shows coloring or decoloring by an electrochemical oxidation or reduction reaction and is usually used in an electrochromic display device. For example, tungsten oxide, titanium oxide, molybdenum oxide, iridium oxide, nickel oxide, vanadium oxide, tin nitride, indium nitride, polythiophene, polypyrrole, metal phthalocyanine, viologen, and the like can be given. Moreover, you may use the thing of a nanoparticle thin film form as described in international publication 97/35227 etc. By using a nanoparticle thin film, the oxidation-reduction reaction can be accelerated, the display response can be speeded up, and the contrast can be improved. Also in this embodiment, this nanoparticle thin film is used, and in this embodiment, specifically, a nanoparticle thin film made of SnO2 doped with Sb is used.

  Around the pixel electrode 12, an adjacent pixel electrode 12 and a short circuit preventing means for preventing the adjacent electrochromic layers 13 from being short-circuited are provided. Specifically, the partition wall 14 is formed so as to surround the pixel electrode 15. The partition wall 14 is formed of an organic insulating material such as a novolac resin. The height of the partition wall 14 is substantially the same as the height of the surface of the electrochromic layer 13. If high-definition display is to be performed, the size of each pixel is reduced, and the interval between adjacent pixels is also reduced, so that there is a high possibility that a short circuit between adjacent pixel electrodes 12 will occur.

  However, by providing the short-circuit prevention means in this way, it is possible to prevent short-circuiting between the adjacent pixel electrodes 12, and the electrochromic layer 13 formed on the pixel electrode 12 is short-circuited with the adjacent electrochromic layer 13. This can also be prevented, and is suitable for high definition.

  In the color fill substrate 50, color filters 52 are formed on a glass substrate 51 corresponding to the respective pixels. Each color filter 52 is partitioned by a light shielding film 53. A counter electrode 54 made of a transparent electrode is formed on each color filter 52, and an electrochromic layer 55 is laminated on the counter electrode 54.

  The counter electrode 54 is a solid electrode formed on the entire surface of the glass substrate 51, and the electrochromic layer 55 is also formed on the entire surface in the same manner as the counter electrode 54. The electrochromic layer 54 is formed using a nanoparticle thin film similar to the array-side substrate 10. Specifically, a nanoparticle thin film made of TiO 2 is used, and after the nanoparticle thin film is formed on the counter electrode 54, the nanoparticle thin film is sintered and the oxidized or reduced compound is adsorbed. Forming.

An electrolytic layer 80 exists between the electrochromic layer 13 of the array side substrate 10 and the electrochromic layer 55 of the color filter side substrate 50. The electrolytic layer 80 plays a role of carrying charges by ions contained in the solvent. The electrolytic layer 80 may be any material that is generally used in electrochromic display devices, and there are no particular limitations on the constituent materials and the formation method. For example, a liquid electrolytic layer gel-based electrolytic layer or a solid electrolytic layer may be used.

  As the liquid electrolytic layer, a solution obtained by dissolving an electrolyte in a solvent can be used. Specific examples of the solvent include water, propylene carbonate, ethylene carbonate, and γ-butyrolactone. Specific examples of the electrolyte include sulfuric acid and hydrochloric acid. Examples of the alkali include sodium hydroxide, potassium hydroxide and lithium hydroxide. Examples of the salts include inorganic ion salts such as alkali (earth) metal salts such as lithium perchlorate, sodium perchlorate, and silver perchlorate, quaternary ammonium salts, and cyclic quaternary ammonium salts.

  Specific examples of the gel-based electrolytic layer include those obtained by mixing a polymer such as polyacrylonitrile or polyacrylamide with acetonitrile, ethylene carbonate, propylene carbonate or a mixture thereof.

  Specific examples of the solid electrolytic layer include those having a salt such as a sulfonimide salt, an alkyl imidazolium salt, or a tetracyanoquinodimethane salt in a polymer side chain such as polyethylene oxide.

  The layer thickness of the electrolytic layer 80 is between about 5 μm and about 50 μm, preferably between about 7 μm and about 30 μm. If the layer thickness of the electrolytic layer 80 becomes too large, when the observer observes the display device, the display state of the adjacent pixels may be recognized through one pixel. On the other hand, if the thickness of the electrolytic layer 80 becomes too narrow, the role of the electrolytic layer 80 becomes insufficient, and there is a high possibility that a short circuit will occur between the electrochromic layers 13 and 55 due to foreign matter. Considering these, the above-mentioned layer thickness is appropriate.

  In the electrochromic display device having such a configuration, when a voltage is applied between the pixel electrode 12 and the counter electrode 54, an oxidation-reduction reaction occurs in the electrochromic layers 13 and 55, and various displays can be performed.

  Next, a circuit configuration for supplying current to the pixel electrode 12 in the present embodiment will be described. FIG. 2 is a circuit diagram schematically showing a drive circuit provided for each pixel. Each pixel includes two switching means for supplying or stopping current to the pixel electrode 12 and two rewriting means.

  Specifically, an n-type TFT 21 is used as the switching means A, and an n-type TFT 22 is used as the switching means B. An n-type TFT 23 is used as the rewriting means C, and an n-type TFT 24 is used as the rewriting means D. Each pixel is provided with two independent gate lines 25 and 26, the gate electrode of the switching TFT 21 is connected to the gate line 25, and the gate electrode of the TFT 22 is connected to the gate line 26. Each pixel is provided with a source line 27, and the source electrode of the TFT 21 and the source electrode of the TFT 22 are connected to the source line 27.

  The drain electrode of the TFT 21 and the gate electrode of the rewrite TFT 23 are connected to each other, and the drain electrode of the TFT 22 and the gate electrode of the rewrite TFT 24 are connected to each other. Each pixel is provided with two independent power supply lines Vss and Vdd, the source electrode of the TFT 23 is connected to the power supply line Vss, and the source electrode of the TFT 24 is connected to the power supply line Vdd. The drain electrode of the TFT 23 and the drain electrode of the TFT 24 are connected to the pixel electrode 12 with each other.

  When scanning signals are sequentially supplied to the gate lines and the gate lines 25 are scanned, the TFTs 21 are turned on. The state of the TFT 23 is changed by the data signal supplied from the source line 27, and the current from the power supply line Vss is controlled. When the gate line 26 is scanned, the TFT 22 is turned on, the state of the TFT 24 is changed by the data signal supplied from the source line 27, and the current from the power supply line Vdd is controlled. A storage capacitor 28 is formed between the power supply line Vss and the gate electrode side of the TFT 23, and a storage capacitor 29 is formed between the power supply line Vdd and the gate electrode side of the TFT 24. Can be held.

  At this time, for example, when + 5V is supplied to the power supply line Vss and + 8V is supplied to the power supply line Vdd, the display state in the electrochromic display device is changed from the erased state, that is, the black display by the power supply from the power supply line Vss. It changes to white display. Conversely, the display state changes from the white state to the black state by the power supply from the power supply line Vdd. As described above, each pixel is provided with independent erasing means and writing means.

  Next, a description will be given with reference to a timing chart shown in FIG. In this embodiment, the number of gradations is four, complete writing (erasing) is not performed with only one frame, and complete writing (erasing) is performed using a maximum of three frames as a writable (erasable) period. ing.

  (A) has shown the case where a display state is changed from black display to white display using an erasure | elimination means. First, when the gate line 25 is scanned in the first frame, a signal is supplied from the source line 27 to supply current to the pixel electrode 12 that is 33% lighter than black, and the TFT 23 is controlled by this signal. As a result, the current from the power supply line Vss is adjusted, and the display state of the pixel changes from black display to gray display (from gray to 33% lightened gray). When the gate line 26 is scanned in the first frame, a signal for performing writing is not supplied from the source line 27. When the gate line 25 is scanned in the second frame, a signal is supplied from the source line 27 to supply current to the pixel electrode 12 that is 33% lighter than the previous gray, and the TFT 23 is controlled by this signal. As a result, the current from the power supply line Vss is adjusted, and the display state of the pixel changes from gray display in the first frame to gray display with 33% lightening (from black to 66% lightening). Also at this time, when the gate line 26 is scanned, a signal for performing writing is not supplied from the source line 27. By doing so, the display state changes from black display to white display in the third frame. It is not always necessary to control the color to be lightened at equal intervals such as 33%.

  (B) shows a case where a gray display which is 66% lighter than the black display is performed using the erasing means. In this case, the target gray display state is realized by performing the same process as that up to the second frame in the case of (a).

  (C) shows a case where the display state is changed from white display to black display using the writing means. First, when the gate line 25 is scanned in the first frame, a signal for erasing is not supplied from the source line 27. When the gate line 26 is scanned, a signal for supplying current to the pixel electrode 12 to supply a current that is 33% darker than white from the source line 27 flows, and the TFT 24 is controlled by this signal to supply power. The current from the line Vdd is adjusted, and the display state of the pixel changes from white display to gray display (gray that is 33% darker than white). Even in the second frame, when the gate line 25 is scanned, a signal for performing writing is not supplied from the source line 27. When the gate line 26 is scanned, the source line 27 changes from gray to 33. %, A signal for supplying current that is dark gray to the pixel electrode 12 flows, the TFT 24 is controlled by this signal, the current from the power supply line Vdd is adjusted, and the display state of the pixel is in the first frame. The gray display changes from 33% dark gray display (white to 66% dark gray). By doing so, the display state changes from white display to black display in the third frame.

  (D) shows a case in which a gray display that is 66% darker than the white display is performed using the writing means. In this case, the target gray display state is realized by performing the same process as that up to the second frame in the case of (c).

  In the case of an electrochromic display device, since it has a so-called display memory property, if the display of the corresponding pixel is the same as the previous selection, it is possible to reduce power consumption by keeping the display as it is. (It is shown as a memory state in FIG. 3). Accordingly, in the case of (a), white display is continued from the fourth frame onward, and therefore no signal is supplied from the source line 27 to change the display state when the gate lines 25 and 26 are scanned. Such signal supply from the source line 27 can be realized, for example, by comparing with the previous frame using a frame memory mounted on the display device and performing signal generation processing based on the comparison result.

  In this embodiment, complete writing (erasing) is performed using three frames. However, writing (erasing) may be completed in only one frame, but in this case, the gate lines 25 and 26 are connected. Since it is necessary to simultaneously scan and supply a current corresponding to writing (erasing) to the pixel electrode 12 and power consumption increases, the erasing means or writing is divided into several frames as in this embodiment. It is preferred to drive only one of the means.

It is a section schematic diagram of a pixel of an embodiment of the present invention. It is a circuit diagram of each pixel of the present invention. It is a timing chart of an embodiment of the present invention.

Explanation of symbols

10 Array side substrate 11, 51 Glass substrate 12 Pixel electrode 13, 55 Electrochromic layer 25, 26 Gate line 27 Source line 54 Counter electrode 80 Electrolytic layer Vss, Vdd Power supply line

Claims (7)

In an electrochromic display device comprising a pixel electrode, a counter electrode, and a plurality of pixels composed of an electrochromic layer and an electrolytic layer formed between the pixel electrode and the counter electrode,
The electrochromic display device, wherein the pixel is provided with independent erasing means and writing means.   2. The electrochromic display device according to claim 1, wherein a current supply line is connected to each of the erasing unit and the writing unit.   3. The electrochromic display device according to claim 2, wherein a gate line is connected to each of the erasing unit and the writing unit. In an electrochromic display device comprising a pixel electrode, a counter electrode, and a plurality of pixels composed of an electrochromic layer and an electrolytic layer formed between the pixel electrode and the counter electrode,
The electrochromic display device, wherein the pixel includes two switching means and two rewriting means.   The electrochromic display device according to claim 4, wherein a gate line is connected to each of the switching means.   5. The electrochromic display device according to claim 4, wherein a current supply line is connected to each of the rewriting means. In an electrochromic display device comprising a pixel electrode, a counter electrode, and a plurality of pixels composed of an electrochromic layer and an electrolytic layer formed between the pixel electrode and the counter electrode,
The pixel includes two independent gate lines, two switching TFTs connected to the gate line via the gate electrode, a source line connected to the source electrode of the switching TFT, and the switching There are provided two rewriting TFTs that are respectively connected via the drain electrode and the gate electrode of the TFT, and two power supply lines that are respectively connected to the source electrodes of the rewriting TFT. An electrochromic display device, wherein an electrode is connected to the pixel electrode.

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