JP2009294447A - Transparent electrode substrate of dot matrix display device, liquid crystal display element and reflective display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To materialize a new structure of a transparent strip electrode, which reduces reddish black phenomenon and sufficiently reduces the surface resistance of the transparent strip electrode so as to drive the display device. <P>SOLUTION: The display device is equipped with transparent substrates 11, 13, and a plurality of transparent strip electrodes 14, 15 arranged in parallel to one another on the transparent substrates, the transparent strip electrode 14 being formed of a single conductive material and partially different in thickness. The transparent strip electrode preferably is thin on a portion of a display section, and is thick on other portions thereof. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present embodiment relates to a transparent electrode substrate used in a dot matrix display device, a liquid crystal display element using the same, and a reflective display element in which the transparent electrode substrate is laminated, and in particular, realizes a reflective display element with improved color tone of black display. The present invention relates to a transparent electrode substrate.

  A dot matrix type display element (panel) such as a liquid crystal display element is widely used as a monitor for a television receiver or a computer system. The dot matrix type display element includes a passive type and an active type. The disclosed technology relates to a passive dot matrix display element. The passive dot matrix display element includes a plurality of first strip electrodes (scan lines) arranged in parallel and a plurality of second strip electrodes (segment lines) arranged to intersect the scan lines perpendicularly. ), And pixels are formed at intersections of the plurality of scan lines and the plurality of segment lines. Writing of an image to be displayed is performed by sequentially applying scan pulses to the scan lines and outputting data for one line to a plurality of segment lines in synchronization with the application of the scan pulses. There are various types of dot matrix type display elements such as CRT, PDP, EL, and liquid crystal display elements, and liquid crystal display elements are particularly widely used.

  In recent years, electronic paper has been actively developed at companies and universities as rewritable display devices that can retain display contents even when the power is turned off. Electronic paper has an ultra-low power consumption that enables memory display even when the power is turned off, a reflective display that is gentle on the eyes and that does not get tired even when viewed, and a flexible and thin display body that is flexible like paper. Aiming at research. Applications of electronic paper include electronic books, electronic newspapers, and electronic posters.

  Various display methods such as an electrophoretic method, an electronic powder fluid method, a twist ball method, a liquid crystal display, and an organic EL display have been proposed as display methods for electronic paper. The electrophoresis method is a method in which charged particles are moved by a liquid. The electronic powder fluid system is a system in which charged toner is moved in a gas. The twist ball method is a method of rotating charged particles that are color-coded in two colors. An organic EL display element (organic electroluminescence display device) is a self-luminous display having a structure in which a plurality of thin films made of an organic material are sandwiched between a cathode and an anode. Since the organic EL display element does not have a memory property, it may not be included in the classification of electronic paper. A liquid crystal display device is a non-self-luminous display having a structure in which a liquid crystal layer is sandwiched between a pixel electrode and a counter electrode.

  Electronic paper using liquid crystal displays is being researched and developed using bistable, selective-reflection cholesteric liquid crystals that utilize interference reflection of the liquid crystal layer. Cholesteric liquid crystals are sometimes referred to as chiral nematic liquid crystals. By adding a relatively large amount (several tens of percent) of chiral additives (chiral materials) to nematic liquid crystals, the nematic liquid crystal molecules are spirally cholesteric. It is a liquid crystal that forms a phase. Here, bistability is a property in which liquid crystal exhibits stability in two different alignment states, and cholesteric liquid crystal maintains two stable states, a planar state and a focal conic state, for a long time after electric field removal. It has the property. In the cholesteric liquid crystal, incident light is reflected and reflected in the planar state, and the incident light is transmitted in the focal conic state. For this reason, in a liquid crystal panel using cholesteric liquid crystal as a liquid crystal layer, light polarization can be displayed by selective reflection of incident light in the liquid crystal layer, so that a polarizing plate is not necessary. Cholesteric liquid crystal has excellent characteristics such as semi-permanent display retention (memory property), vivid color display, high contrast, and high resolution.

  As described above, various electronic papers have been developed, and there are various definitions of electronic paper.In the following description, a flexible passive liquid crystal display element using cholesteric liquid crystal will be described as an example. It is not limited to this.

  Patent Document 1 describes the configuration of a cholesteric liquid crystal display device. In this application, the description of Patent Document 1 is referred to, and description of the configuration and operation of the cholesteric liquid crystal display device is omitted.

  FIG. 1 is a diagram showing a basic configuration of a cholesteric liquid crystal display element for color display. As illustrated, the cholesteric liquid crystal display element for color display includes three stacked liquid crystal display panels 10B, 10G, and 10R, and a light absorbing layer 17 provided on the back surface. A color filter may be provided between the liquid crystal display panels 10B, 10G, and 10R. The liquid crystal display panels 10B, 10G, and 10R have similar configurations, but have different wavelength reflection characteristics. Specifically, since the liquid crystal display panel 10B mainly reflects light near 480 nm, it displays blue, the liquid crystal display panel 10G mainly reflects light near 550 nm, and thus displays green, and the liquid crystal display panel 10R mainly displays 630 nm. It displays red because it reflects nearby light. Each of the liquid crystal display panels 10B, 10G, and 10R includes upper transparent substrates 11B, 11G, and 11R, liquid crystal layers 12B, 12G, and 12R, lower transparent substrates 13B, 13G, and 13R, upper electrodes 14B, 14G, and 14R, and a lower side, respectively. It has electrodes 15B, 15G, and 15R. In addition, a sealing material and a spacer for sealing the liquid crystal are provided, but the illustration is omitted. In the display device, driving circuits for driving the upper electrode and the lower electrode are provided.

  2 is a diagram showing in more detail the configuration of one liquid crystal panel constituting the cholesteric liquid crystal display element for color display in FIG. 1, wherein (A) is a sectional view and (B) is a top view. is there.

  The upper substrate 11 and the lower substrate 13 are bonded together at a predetermined interval so that the upper electrode 14 and the lower electrode 15 formed thereon face each other. In order to bond the upper substrate 11 and the lower substrate 13 at a predetermined interval, particles having a predetermined diameter called a spacer are scattered on the bonding surface, but the illustration is omitted here. A cholesteric liquid crystal is filled between the upper substrate 11 and the lower substrate 13 to form the liquid crystal layer 12. The upper electrode 14 and the lower electrode 15 have a plurality of transparent strip electrodes arranged in parallel, and are arranged so that the plurality of strip electrodes cross each other, and a pixel is formed at the intersecting portion. The transparent strip electrodes 14 and 15 are generally formed of an inorganic transparent electrode material such as ITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide). The upper substrate 11 and the lower substrate 13 are also formed of a glass substrate, but in the case of a flexible panel, PET (polyethylene terephthalate), PES (polyethersulfone), PSF, PC (polycarbonate), It is formed of a film such as PEN (polyethylene).

  The plurality of strip electrodes 14 and 15 are drawn out to one side of the film, and the electrode terminals 18 and 19 provided thereon are connected to a flexible circuit board (FPC) on which a driver circuit is mounted. In FIG. 2A, the FPC 21 connected to the strip electrode 15 of the lower substrate 13 is shown. The wiring pattern 22 of the FPC 21 is connected to the electrode terminal 19 by a connection layer 23 using ACF (Anisotropic Conductive Film) or the like. A seal member 16 is provided around the bonded portion to seal the liquid crystal.

  In the case of a color liquid crystal display device, three panels having different reflection wavelengths are laminated, and a light absorption layer 17 is formed on the back surface of the panel arranged on the lowermost side. When a voltage is applied between the strip electrodes 14 and 15, the alignment of the liquid crystal changes, and a specific wavelength band is bistable and transmitted. In the state of transmitting light, the transmitted light is absorbed by the light absorption layer on the back surface, so that black display is obtained.

  FIG. 3 is a diagram showing an example of the reflection wavelength characteristic of a color display element in which the cholesteric liquid crystal panel (display element) of FIG. 1 is laminated. In FIG. 3, the solid line indicates the characteristic in the planar state (white display), and the broken line indicates the characteristic in the focal conic state (black display). As shown in FIG. 3, in the black display, the reflection of the red wavelength is large, resulting in a black display with a red color. This is the so-called “red floating” phenomenon. The cause of the “red floating” phenomenon will be described below.

  FIG. 4 is a diagram showing the transmission wavelength characteristics of a single substrate when the thickness of the transparent electrode used in the above panel is 130 nm and 26 nm. When the solid line is 130 nm, the broken line is The case of 26 nm is shown. As shown in FIG. 4, it can be seen that when the thickness of the transparent electrode is 130 nm, the transmittance becomes maximum near 550 nm. The refractive index of the upper and lower substrates is 1.6 to 1.65 when the substrate material is PC or PES, and about 1.5 when glass is used, and the refractive index of the electrode material is about 2 when ITO or IZO is used. 0 and reflection at the interface occurs. When the thickness of the strip electrode is 130 nm, it acts as an antireflection film for a wavelength of 520 nm, and reduces the reflectance of light near 520 nm and increases the transmittance. When the thickness is 26 nm, it does not function as an antireflection film in the visible range, so the wavelength characteristic does not have a peak, and the transmittance increases as the wavelength becomes longer.

  On the other hand, since the surface resistance of the strip electrode decreases almost in inverse proportion to the thickness of the electrode, the thicker one is preferable for driving, but if it is too thick, the reflection in blue and green increases, and the light absorption in the electrode material increases. This is not preferable from the viewpoint of manufacturing efficiency. Therefore, the optimum electrode thickness is generally around 130 nm. However, when the thickness of the electrode is 130 nm, the antireflection function decreases for wavelengths other than green, so the reflectance does not decrease and the transmittance does not increase. This is the reason why the transmittance in the green wavelength band is high in FIG.

  However, when the thickness of the electrode is 130 nm, reflections of wavelengths other than green (near 550 nm) are relatively reflected in each layer of the strip electrode of the color display element in which three panels are laminated as shown in FIG. growing. As shown in FIG. 1, all the light incident in the black display is transmitted in the order of the blue panel 10B, the green panel 10G, and the red panel 10R because the panel is in the transmission state (focal conic state). Since two electrode layers are provided, interface reflection at the electrode is performed six times. Furthermore, incident light is scattered to some extent in each liquid crystal layer, and light that travels toward the back surface (light absorption layer 17) of the scattered light is subjected to interface reflection at the electrodes in the same manner as described above. Thus, in black display, the number of interface reflections on the electrode is large, and the reflected light of red and blue is relatively larger than that of green. Although not shown in FIG. 1, a blue cut filter is generally provided between the blue panel 10B and the green panel 10G, and a green cut filter is generally provided between the green panel 10G and the red panel 10R. Since the red panel 10R is provided on the back side, the red cut filter is not provided. For this reason, the blue color is reduced because the blue color of the interface reflected light at the electrode is cut. For this reason, red reflection in black display is increased, and a “red floating” phenomenon occurs. As described above, since the number of interface reflections on the red electrode is large and the reflectance is high, the black display is displayed with a very reddish appearance.

  One method of preventing “red float” is to extremely reduce the thickness of the electrode to about 26 nm. In this case, the transmittance near 550 nm is lowered and the brightness is slightly lowered, but the red transmittance is relatively increased, that is, the red reflection is relatively decreased, and the “red floating” phenomenon is eliminated. However, there arises a problem that the surface resistance of the belt-like electrode becomes large and cannot be driven.

International Publication WO2007 / 110949A1 Japanese Patent Application Laid-Open No. 60-088986 JP 2007-128879 A JP 2006-012785 A

  In order to solve the above problem, it is conceivable to reduce the refractive index difference from the substrate by reducing the refractive index of the material forming the electrode. When the refractive index difference between the substrate and the electrode is reduced, the interface reflectance is reduced. Therefore, it is conceivable to form the electrode with an organic conductive material having a small difference in refractive index from the substrate that is put into practical use in a touch panel or the like, but the organic conductive material that can be used has low transmittance and high surface resistance. Cannot be used for strip electrodes.

  In addition, in order to reduce the surface resistance, a method of providing a metal auxiliary wiring such as copper is also performed, but there is a problem that the brightness of display is lowered because the metal material does not transmit light. In addition, since the auxiliary wiring needs to be formed in a separate process from the transparent electrode, there is a problem that the manufacturing cost increases.

  Patent Documents 2 to 4 describe a configuration in which the transparent electrode has a two-layer structure, and the thickness of one layer is reduced to reduce the synthetic surface resistance. There is a problem that the cost increases.

  This embodiment realizes a new structure of a transparent strip electrode that has a small “red float” and is sufficiently small that the surface resistance of the transparent strip electrode can be driven.

  In order to achieve the above object, according to the present embodiment, the transparent strip electrode is formed of a single conductive material, and the thickness is partially varied.

  The transparent strip electrode is thin at a part of the display part and thick at the other part.

  In a liquid crystal display device manufactured using a substrate having a transparent strip electrode having such a structure, and a reflective display device for color display in which such liquid crystal display devices are stacked, the “red floating” phenomenon is reduced. The

  According to the present embodiment, a part of the transparent belt-like electrode, particularly a part of the display unit, is thin, so there is no difference in the reflected wavelength characteristics in the visible range, and the “red floating” phenomenon does not occur. Moreover, since the thickness is only a part, the surface resistance of the transparent strip electrode can be made small enough to be driven. Furthermore, although the transparent belt-like electrode is partially different in thickness, since it is made of the same material, it can be manufactured with a few additional steps and the increase in manufacturing cost is small.

  Hereinafter, an embodiment will be described by taking the cholesteric liquid crystal display element for color display of FIG. 1 in which three panels are laminated as an example.

  FIGS. 5A and 5B are diagrams showing a configuration of one liquid crystal display element (panel) constituting the cholesteric liquid crystal display element for color display, where FIG. 5A is a cross-sectional view and FIG. 5B is a top view. As apparent from comparison with FIG. 2, the liquid crystal display element (panel) of the embodiment has a configuration similar to that of the conventional example, but the thickness of the transparent strip electrodes 14 and 15 is partially different. It is different from the conventional example.

  As shown in FIG. 5, the lower belt-like electrode is composed of a thin portion 15b within the display range and a thick portion 15a corresponding to the lead-out wiring portion of the electrode outside the display range. The thick portion 15a and the thin portion 15b are made of ITO or IZO. The thick portion 15a is, for example, 150 nm thick, the surface resistance is 20Ω / □, and the thin portion 15b is, for example, 30 nm thick, and the surface resistance is 150Ω / □. Similarly, the upper band-shaped electrode is also composed of a thin portion 14b within the display range and a thick portion 14a corresponding to the lead-out wiring portion of the electrode outside the display range, and is made of ITO or IZO having a thickness of 30 nm and 150 nm, respectively. Made.

  FIG. 6 is a diagram illustrating a manufacturing process of the transparent electrode substrate of the embodiment. As shown in FIG. 6A, a resist coating process A for depositing an ITO or IZO electrode layer 32 on the surface of a PC film (substrate) 31 and coating a resist layer 33 thereon is performed. As shown in (2) of FIG. 6, an exposure process A for exposing a portion between the strip electrodes is performed. As shown in FIG. 6 (3), when the development process A for developing the resist layer 33 is performed, the resist layer corresponding to the portion between the strip electrodes is removed, and a portion 34 without resist is formed. As shown in FIG. 6 (4), the etching process A is performed, and the electrode layer 32 corresponding to the portion 34 without the resist is removed. As shown in FIG. 6 (5), the stripping process A of the resist layer 33 is performed, and the strip electrode 32 is formed.

  As shown in FIG. 6 (6), a resist coating process B for coating a resist layer 35 on the strip electrode 32 is performed. As shown in (7) of FIG. 6, an exposure process B for exposing the thinned portion 32b of the strip electrode is performed. As shown in (8) of FIG. 6, when the development process B for developing the resist layer 33 is performed, the resist layer in the thinned portion 32b of the strip electrode is removed. As shown in FIG. 6 (9), the etching process B is performed, and the electrode layer 32b corresponding to the portion without the resist is thinned to a thickness of 30 nm. As shown in (10) of FIG. 6, when the stripping process B of the resist layer 35 is performed, a thick strip electrode 32a and a thin strip electrode 32b are formed.

  Since other processes such as the formation of the sealing material, the dispersion of the spacers, the assembly, and the injection of the liquid crystal are the same as those in the conventional example, the description is omitted.

  A color display element obtained by laminating three panels of blue (B), green (G), and red (R), which are manufactured by laminating a substrate having a strip electrode having a thick part and a thin part as described above, FIG. 7 shows the reflection wavelength characteristics during display and black display. Compared with the reflection wavelength characteristic of the conventional example of FIG. 3, the red (long wavelength) reflection in black display was reduced, and “red floating” was eliminated. In addition, the reflectance in white display hardly decreased, and the brightness of the display was maintained.

  In the embodiment, the resistance of the transparent strip electrode increases from 25 kΩ to 125 kΩ and the lead-out wiring portion decreases from 5 kΩ to 3 kΩ in the embodiment as compared with the conventional example having a thickness of 130 nm over the entire electrode. As a result, the overall resistance is 128 kΩ in the embodiment, which is larger than the conventional example, which was 30 kΩ, but is at a level that can sufficiently drive the display element. Further, since the resistance of the lead-out wiring portion has become considerably small, it is possible to reduce the area by reducing the electrode width of the lead-out wiring portion in design. Further, as described with reference to FIG. 6, there is one kind of electrode material, and the cost increase is small compared to the auxiliary electrode made of metal.

  FIG. 8 is a diagram illustrating a modification of the manufacturing process of the transparent electrode substrate of the embodiment. (1) to (4) are the same as in FIG. Even after the etching process A is completed, the resist layer 33 is not peeled off, and as shown in FIG. 8 (5), an exposure process B is performed in which the thinned portion 32b of the strip electrode is exposed in the unexposed resist layer. . As shown in (6) of FIG. 8, when the development process B for developing the resist layer is performed, the resist layer in the thinned portion 32b of the strip electrode is removed. As shown in (7) of FIG. 8, the etching process B is performed, and the electrode layer 32b is thinned to a thickness of 30 nm. At this time, an etching process method in which the substrate 31 is not etched is used. As shown in (8) of FIG. 8, when stripping process B of resist layer 35 is performed, thick strip electrode 32a and thin strip electrode 32b are formed.

  In the manufacturing process of FIG. 8, since the resist layer applied first is exposed twice and used, two steps can be omitted compared to the example of FIG. As a result, in the process shown in FIG. 8, only three steps are added as compared to the case of forming a strip-shaped electrode having a constant film thickness in the conventional example, and considering that it is a single material, the cost increase is Very small.

  FIG. 9 is a diagram showing a modification of the shape of the transparent strip electrode. FIG. 9A shows an example in which only a portion 34b is thinned without thinning all the display portions of the electrodes. Accordingly, part of the lead-out wiring portion and the display portion has a thick portion 34a. For example, if the area of the thinned portion is about 50% of the display portion, the red floating can be reduced in half of the display, so that “red floating” can be halved as a whole. In this case, the electrical resistance of the electrode was changed from 5 kΩ to 3 kΩ at the lead-out wiring portion, from 25 kΩ to 50 kΩ at the display portion, and as a whole 53 kΩ. This resistance is sufficiently small to sufficiently display about 300 mm and 150 dpi.

  Pixels are formed at the intersections of the upper strip electrode and the lower strip electrode, and the gap between the strip electrodes is outside the pixel. FIG. 9B shows an example in which the electrode portion 34b corresponding to the pixel portion is thinned and a thick electrode portion 34a is provided so as to surround the pixel. There is an electrode gap of 20 to 30 μm between the pixels, and even if this portion is a thick transparent electrode, the brightness does not decrease. Thereby, the electrical resistance of the electrode can be further reduced.

  Although the embodiment has been described above, it goes without saying that various modifications other than the described configuration are possible. For example, the shape of the portion where the thickness of the electrode is reduced can be variously modified, and the types of the electrode thickness are not limited to two.

  As described above, in the present embodiment, by thinning a part of the electrode, “red floating” is reduced, and an electrode having an electrical resistance that has no practical problem is obtained. In addition, the brightness is substantially maintained, and the cost increase is small because it is formed of a single electrode material. Moreover, although the liquid crystal display element using a cholesteric liquid crystal was demonstrated as an example, it is also applicable to the display element using another liquid crystal. Furthermore, as described in the embodiment, this technique is particularly effective for a multilayer reflective display element, but it goes without saying that the effect is not limited to the multilayer type but can be obtained by a single layer type.

FIG. 1 is a diagram showing a basic configuration of a cholesteric liquid crystal display element for color display. FIG. 2 is a diagram showing in more detail the configuration of one liquid crystal panel constituting a conventional cholesteric liquid crystal display element for color display. FIG. 3 is a diagram showing the reflection wavelength characteristics during white display and black display in the conventional example. FIG. 4 is a diagram showing the transmittance wavelength characteristic of the transparent electrode substrate. FIG. 5 is a diagram showing in more detail the configuration of one liquid crystal panel constituting the cholesteric liquid crystal display element for color display of the embodiment. FIG. 6 is a diagram illustrating a manufacturing process of the transparent electrode substrate of the embodiment. FIG. 7 is a diagram showing reflection wavelength characteristics at the time of white display and black display in the display element configured by the transparent electrode substrate of the embodiment. FIG. 8 is a diagram illustrating a modification of the manufacturing process of the transparent electrode substrate of the embodiment. FIG. 9 is a diagram illustrating a modification of the shape of the transparent electrode substrate in the embodiment.

Explanation of symbols

11 Upper substrate (film)
12 Liquid crystal layer 13 Lower substrate (film)
14 Upper electrode 15 Lower electrode 16 Seal member 17 Light absorption layer 14a, 15a Thick electrode portion 14b, 15b Thin electrode portion

Claims (5)

A substrate,
A plurality of strip electrodes arranged in parallel on the substrate,
The strip-shaped electrode is formed of a single conductive material and partially has a different thickness.   The display device according to claim 1, wherein the strip electrode is thin at a part of the display unit and thick at the other part.   The display device according to claim 1, wherein the strip electrode is formed of an oxide of indium, tin, or zinc. A pair of the substrates are arranged facing each other at a predetermined interval,
The display device according to claim 1, wherein a liquid crystal is disposed between the substrates.   The display element according to claim 1, wherein a lead wiring is connected to a thick portion of the strip electrode.

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