JP2008191251A - Reflection-type display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection-type display device of high contrast, high reflectance and high definition. <P>SOLUTION: An array substrate 12 and a counter substrate 13 are disposed opposite to each other. An electrolyte layer 14 is interposed between a transparent structural body 23 of the array substrate 12 and an anode 33 of the counter substrate 13. High reflectance and high definition can be attained, by switching a colored state and a non-colored state of coloring bodies 24 by switching between a power turned-on state and a power turned-off state to control total reflection of incident light in the transparent structural body 23, when power is supplied and absorption of incident light in the transparent structural body 23, when no power is supplied. High contrast can be attained by increasing the optical distance by reflection in an inner part of the transparent structural body 23 to obtain a colored state, having high absorbance, when power is supplied. High reflectance is obtained by suppressing infiltration of reflection light in the internal part to suppress internal scattering. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a reflective display element using electrochromism.

  In recent years, liquid crystal display elements have been applied to various fields such as notebook personal computers, monitors, car navigation systems, mobile phones, and TVs.

  Among these, the reflective display element has advantages such as low power consumption, thinness and light weight because it does not require a backlight, and is applied to displays for portable devices. However, the conventional reflective display element has a display performance inferior in terms of brightness as compared with paper, printed matter, and the like. Liquid crystal display elements capable of reflective and transmissive display are also applied to displays for portable devices. However, since a backlight is used, if an attempt is made to obtain a sufficient driving time with a battery serving as a power source, the brightness of the backlight must be lowered, and sufficient brightness cannot be obtained.

  As means for solving these problems, there is a scattering type liquid crystal display element represented by polymer dispersed liquid crystal (PDLC). Using the scattering and reflection of incident light by the difference in refractive index between the randomly arranged liquid crystal and the isotropic layer without refractive index anisotropy, or the difference in refractive index between the molecules of the randomly arranged liquid crystal It is.

  When this scattering-type liquid crystal display element is used as a reflective type, no electric field is applied to the liquid crystal layer, and the refractive index of the liquid crystal layer is smaller than that of the isotropic layer in the direction in which light is incident, or refraction between molecules of the liquid crystal layer. When there is a similar difference in rate, incident light is reflected to make it bright, while an electric field is applied to the liquid crystal layer to make the refractive index of the isotropic layer and the liquid crystal layer equal to the direction in which the light is incident. Alternatively, the refractive index between the molecules of the liquid crystal layer is made equal, and the incident light is transmitted and absorbed by the light shielding layer disposed behind the element to obtain a dark state. However, the difference in refractive index cannot be obtained between the ordinary light refractive index and the average value of the extraordinary refractive index and the ordinary light refractive index of the liquid crystal molecules. There is only. For this reason, in order to obtain a sufficient reflectance, it is necessary to increase the thickness, and the driving voltage becomes extremely high. Therefore, power consumption becomes high and it becomes unsuitable for the display for portable devices.

  Further, when the scattering type liquid crystal display element is used as a transmission type, a dark state is obtained by scattering reflection. However, like the reflection type, it is necessary to increase the thickness to obtain sufficient contrast, and the driving voltage is extremely high. Become. Therefore, power consumption becomes high and it becomes unsuitable for the display for portable devices.

  On the other hand, a reflective display device using electrochromism has been proposed (see, for example, Patent Document 1). In this display device, coloring and decoloring of the color former formed on the observation side (front surface) substrate and the like are switched by electrochemical control, and display is performed (when colored). When the color is not displayed (decolored), the reflected light from the reflective layer formed on the back substrate is seen. That is, in order to obtain a clear display, sufficient absorbance of the reflective layer and the color developing layer with high reflectance is required.

Such a reflective display device has advantages such as low power consumption, high reflectivity, and memory properties compared to a liquid crystal display device, but the current configuration has scattering within the cell due to the distance between the front and back reflectors. As a result, the reflectance is lost. In addition, the distance may cause parallax and cause display deterioration in high-definition display. Further, in order to obtain sufficient absorbance, it is necessary to increase the thickness of the coloring layer. In this case, if the thickness of the coloring layer is not uniform, color unevenness may occur, and such a uniform thick film is formed. It is not easy.
JP 2005-266711 A

  As described above, the conventional reflective display device using electrochromism has a reflective layer formed on the counter substrate side, and display degradation during high-definition display due to parallax and scattering has been a problem. Moreover, in order to obtain a high reflectance and a high contrast, it is necessary to suppress the scattered light in the cell and to have sufficient absorbance of the coloring layer.

  The present invention has been made in view of these points, and an object thereof is to provide a reflective display element having high contrast, high reflectance, and high definition.

  The present invention provides a first substrate provided with a transparent structure having a translucent first conductive layer on one main surface side and having a color forming body showing electrochromism inside and having a continuous convex shape. And a second substrate having a second conductive layer and an anode on one main surface side and disposed opposite to the first substrate, and an electrolyte layer interposed between the transparent structure and the anode Is.

  Then, by switching between feeding and non-feeding, the colored body is switched between the colored state and the non-colored state, so that the total reflection of incident light during non-feeding in the transparent structure and the absorption by the transparent structure during feeding In addition, the optical distance is increased by reflection in the transparent structure, so that the absorbance at the time of power feeding is increased, and the invasion of reflected light into the interior is suppressed to suppress internal scattering.

  According to the present invention, it is possible to obtain a reflective display element with high contrast, high reflectance, and high definition.

  Hereinafter, the configuration of a reflective display element according to an embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the reflective display element 11 includes an array substrate 12 as a first substrate on the display surface side, a counter substrate 13 as a second substrate, and between the array substrate 12 and the counter substrate 13. And an electrolyte layer 14 sandwiched therebetween.

  The array substrate 12 includes a transparent substrate 21 made of, for example, transparent glass. A plurality of TFT elements, drain electrodes, common electrodes, signal lines, gate lines, and the like are formed on the inner surface of the transparent substrate 21 facing the counter substrate 13. Further, on the inner surface of the array substrate 12 facing the counter substrate 13, a transparent conductive layer 22, which is a coloring layer as a first conductive layer having translucency, such as an ITO film, is formed. A plurality of transparent structures 23 each projecting toward the counter substrate 13 are continuously formed on the substrate 22 in the substrate surface direction.

  In the transparent conductive layer 22, a plurality of electrodes 22a controlled by each TFT element are formed in a matrix, for example.

In addition, the transparent structure 23 is formed of, for example, a TiO ₂ film that is an insulating layer, and a cross-sectional shape having a pair of inclined surfaces 23a with the transparent conductive layer 22 side as a base is formed into a substantially isosceles triangle. The base angle θ of the transparent structure 23 is arcsin (ne / np) ≦ θ ≦ {180−arcsin (ne / np) where ne is the refractive index of the electrolyte layer 14 and np is the refractive index of the transparent structure 23. )} / 3.

  Furthermore, micropores (not shown) are formed inside the transparent structure 23, and the surface of the micropores is covered with a color former 24 that exhibits electrochromism.

  Between adjacent transparent structures 23, a V-groove-shaped recess 25 is formed that expands toward the array substrate 12.

  The refractive indexes in the visible light region of the transparent substrate 21, the transparent conductive layer 22, and the transparent structure 23 of the array substrate 12 have a magnitude relationship of transparent substrate 21 <transparent conductive layer 22 <transparent structure 23.

  An antireflection layer such as an antireflection film (not shown) is formed on the outer surface of the transparent substrate 21.

  A region facing the bottom side of each transparent structure 23 as viewed from the display surface side which is the outer surface of the array substrate 12 is formed as a pixel 26.

  The counter substrate 13 includes a substrate 31 made of, for example, stainless steel (SUS). A transparent conductive layer 32 as a second conductive layer having translucency such as an ITO film is formed on the inner surface of the substrate 31 facing the array substrate 12, and an anode 33 is formed on the transparent conductive layer 32. ing.

  Then, the counter substrate 13 and the array substrate 12 are bonded together at a predetermined position using an adhesive such as an epoxy-based thermosetting resin, and the electrolytic solution constituting the electrolytic solution layer 14 is filled through the injection port. The inlet is sealed with an ultraviolet curable resin or the like.

  In addition, for example, a 0.2 mM aqueous solution of lithium trifluoromethanesulfonate is used for the electrolytic solution layer 14 as an electrolytic solution.

  Next, the operation of the present embodiment will be described.

  First, a method for manufacturing the reflective display element 11 will be described.

  A TFT element, a drain electrode, a common electrode, a signal line, a gate line, and the like are formed by a normal TFT process in which film formation and patterning are repeated on the transparent substrate 21.

  Further, an ITO film is formed as the transparent conductive layer 22.

On the other hand, on the transparent conductive layer 22 of the transparent substrate 21, a TiO ₂ film having fine pores of 3 μm is formed as a transparent insulating film by a solution coating method, and further processed into a V-groove shape with a pitch of 6 μm by a cutting method. The array substrate 12 is provided with the structure 23 formed thereon. Then, the array substrate 12 is immersed in an aqueous solution of a viologen derivative, and is chemically adsorbed on the surface of the micropores of the transparent structure 23 to form a color former 24.

  Further, after forming the transparent conductive layer 32 on the stainless steel substrate 31 as the counter substrate 13, an antimony-doped tin oxide layer having fine holes is formed as the anode 33.

  The periphery of the array substrate 12 and the counter substrate 13 formed in this manner is bonded at a predetermined position at an interval of 20 μm using, for example, an adhesive made of an epoxy thermosetting resin.

  Next, a 0.2 mM aqueous solution of lithium trifluoromethanesulfonate as an electrolytic solution is filled between the array substrate 12 and the counter substrate 13, and the injection port is sealed with an ultraviolet curable resin to form the reflective display element 11.

  Next, the display principle of the reflective display element 11 will be described with reference to FIGS.

  As shown in FIGS. 2 and 3, incident light incident from the outside of the array substrate 12 enters the transparent substrate 21 of the array substrate 12, the transparent conductive layer 22, and the transparent structure 23 in this order, It reaches the interface with the electrolyte layer 14.

  The relationship between the incident angle and the refraction angle in each layer during this period is expressed as follows by the following Snell equation.

  n1 ・ sinθ1 ＝ n2 ・ sinθ2

  Here, n1 and n2 denote the refractive index of the incident layer and the refractive index of the refractive layer, and θ1 and θ2 denote the incident angle and the refractive angle.

  From this equation, when light enters the low refractive index layer from the high refractive index layer, the refraction angle becomes larger than the incident angle.

  Similarly, the light reaching the interface between the transparent structure 23 and the electrolyte layer 14 behaves according to Snell's formula, and the refractive index of the transparent structure 23 is the refractive index of the electrolyte layer 14 as shown in FIG. When the incident angle is sufficiently larger than that, total reflection occurs at the interface between the transparent structure 23 and the electrolyte layer 14, and light does not enter the electrolyte layer 14 from the transparent structure 23.

  The light totally reflected at the interface between one inclined surface 23a of the transparent structure 23 and the electrolyte layer 14 travels through the transparent structure 23, and again the other inclined surface 23a of the transparent structure 23 and the electrolyte layer. The incident light can be extracted with high efficiency toward the same surface as the incident light, that is, in the direction returning to the incident direction of the incident light.

  On the other hand, as shown in FIG. 3, when total reflection does not occur at the interface between the transparent structure 23 and the electrolyte layer 14 due to the difference in refractive index at the interface between the transparent structure 23 and the electrolyte layer 14, Fresnel's According to the equation, the reflectance depends on the refractive index difference at the interface between the transparent structure 23 and the electrolyte layer 14, and the reflectance is sufficiently smaller than the total reflection.

Incident angle θ1 = 0
R = (n1−n2) ² / (n1 + n2) ²

Incident angle θ1 ≠ 0
Rs = sin ² (θ2−θ1) / sin ² (θ2 + θ1)
Rp = tan ² (θ1−θ2) / tan ² (θ1 + θ2)

  Here, Rs, Rp, θ1, and θ2 represent the reflectance, incident angle, and refraction angle of s-polarized light and p-polarized light, respectively.

  Total reflection occurs even when the transparent structure 23 is flat, but it is usually limited to a large incident angle, and sufficient reflectivity is obtained at an angle near the display surface important for the reflective display element 11. I can't.

  In the reflective display element 11 of the present embodiment, as shown in FIG. 2, when no power is supplied, that is, when the power is off, the color body 24 in the transparent structure 23 is transparent, Since the refractive index difference at the interface with the electrolyte layer 14 is sufficiently large, the light that has entered the interface between the transparent structure 23 and the electrolyte layer 14 is totally reflected at the interface.

  The light totally reflected at the interface between one inclined surface 23a of the transparent structure 23 and the electrolyte layer 14 travels in the transparent structure 23, and again the other inclined surface 23a of the transparent structure 23 and the electrolyte layer 14 The incident light can be extracted with high efficiency toward the same plane as the incident light, that is, in the direction returning to the incident direction of the incident light. That is, white display is obtained by two total reflections.

  On the other hand, as shown in FIG. 3, when power is supplied, that is, when the power is on, the color former 24 in the transparent structure 23 is colored, and the light that has entered the transparent structure 23 is inclined on one side of the transparent structure 23. It is totally reflected at the interface between the surface 23a and the electrolyte layer 14 and further proceeds in the transparent structure 23, and is again flush with the incident light at the interface between the other inclined surface 23a of the transparent structure 23 and the electrolyte layer 14. This is totally reflected toward the side, that is, the direction returning to the incident direction of the incident light, but the total distance increases the optical distance that light passes through the transparent structure 23, and light is absorbed during this passage. . That is, black display is obtained by light absorption.

  In this way, the colored body 24 is switched between the colored state and the non-colored state (colorless state) by switching the power on and off, and the total reflection of the incident light in the transparent structure 23 in the power off state and the power source By controlling the absorption in the transparent structure 23 in the ON state, the reflective display element 11 with high reflectivity and high definition is obtained. At this time, by increasing the optical distance by reflection in the transparent structure 23, it is possible to obtain a colored state in which the absorbance in the power-on state is increased, thereby improving the difference in brightness between the colored state and the non-colored state. High contrast can be obtained. Furthermore, since the entrance of the reflected light into the reflective display element 11 can be suppressed, the scattering within the reflective display element 11 can be suppressed and the reflectance can be increased.

  The transparent structure 23 has an isosceles triangle cross-section, and its base angle θ is arcsin (ne / no when the refractive index of the electrolyte layer 14 is no and the refractive index of the transparent structure 23 is ne. ) ≦ θ ≦ {180−arcsin (ne / no)} / 3 so that the incident light is 2 at the interface between the inclined surface 23 a on both sides of the transparent structure 23 and the electrolyte layer 14. It is possible to define a range that can be taken out to the viewer side with high efficiency by performing total reflection once.

  Further, in the reflective display element 11, reflection due to a difference in refractive index between layers other than the interface between the transparent structure 23 and the electrolyte layer 14 also causes low contrast. In particular, since the refractive index difference at the interface between the air layer and the transparent substrate 21 of the array substrate 12 becomes the largest, high contrast can be obtained by providing an antireflection layer on the outer surface of the transparent substrate 21.

  Since the refractive index in the visible light region of the transparent substrate 21, the transparent conductive layer 22, and the transparent structure 23 of the array substrate 12 is the magnitude relationship of transparent substrate 21 <transparent conductive layer 22 <transparent structure 23, As shown in FIG. 4, even if the incident angle of the incident light on the array substrate 12 is small, the incident light is incident on the interface between the transparent conductive layer 22 and the transparent structure 23 at an incident angle close to perpendicular, that is, an incident angle close to zero. Therefore, incident light can be efficiently totally reflected at the interface between the transparent structure 23 and the electrolyte layer 14, and the viewing angle can be increased.

  In addition, regarding the relationship of the refractive index difference between the transparent structure 23 and the electrolyte layer 14, when the refractive index difference between the refractive index of the transparent structure 23 and the refractive index of the electrolyte layer 14 is large, a smaller incident Even when the angle is totally reflected, the viewing angle can be increased, and when the refractive index difference between the refractive index of the transparent structure 23 and the refractive index of the electrolyte layer 14 is small, the reflectance is low, and the high contrast and Become.

  In the above embodiment, for example, color display 24 colored in R, G, B, for example, is adsorbed and displayed in color for each specific area, or a color filter or the like is created on the array substrate 12 for color display. It is also possible to configure.

  Further, although stainless steel is used as the substrate 31 of the counter substrate 13, a transparent substrate can also be used, and a reflective layer that reflects light may be provided.

  Further, the convex shape of the transparent structure 23 is not limited to an isosceles triangle shape, and the same effect can be obtained even when it is a hemispherical shape.

  An ITO film that is a transparent electrode is used as the transparent conductive layer 22 of the array substrate 12, but the transparent structure 23 can also be used as the conductive layer. Further, although the transparent conductive layer 22 is disposed between the transparent substrate 21 and the transparent structure 23, it can also be formed on the surface of the transparent structure 23.

  Next, for Examples 1 to 3 of the reflective display element 11 and Comparative Example 1 and Comparative Example 2, the reflectance of the standard white plate and the contrast when displayed in black and white were measured, and the results of visual evaluation were obtained. As shown in FIG. In addition, an image with no edge blur at the time of still image display was considered good.

  Example 1 has the structure shown in the above embodiment, and a TFT element and a drain electrode, a common electrode, a signal line, a normal TFT process that repeats film formation and patterning on a transparent substrate 21 having a refractive index of 1.5. A gate line was created. Further, an ITO film was formed as a transparent conductive layer 22. The refractive index of the ITO film to be the transparent conductive layer 22 was 1.8.

On the other hand, a TiO ₂ film having fine pores of 3 μm is formed as a transparent insulating film on the transparent substrate 21 on which the transparent conductive layer 22 is formed by a solution coating method, and further processed into a V-groove shape with a pitch of 6 μm by a cutting method. Thus, an array substrate 12 was obtained. The refractive index of the TiO ₂ film having fine pores determined by the envelope method was 2.1. The array substrate 12 was immersed in an aqueous solution of a viologen derivative, and the color former 24 was chemically adsorbed on the surface of the micropores of the transparent structure 23.

  After forming the transparent conductive layer 32 on the substrate 31 made of stainless steel (SUS) as the counter substrate 13, an antimony-doped tin oxide layer having fine holes was formed as the anode 33.

  The array substrate 12 and the counter substrate 13 thus prepared were bonded around a predetermined position at an interval of 20 μm using an adhesive made of an epoxy thermosetting resin.

  Subsequently, a 0.2 mM aqueous solution of lithium trifluoromethanesulfonate is filled between the array substrate 12 and the counter substrate 13 as the electrolyte layer 14, and the injection port is sealed with an ultraviolet curable resin to form the reflective display element 11. Formed.

  Example 2 was produced in the same manner as Example 1 except that the convex shape of the transparent structure 23 of Example 1 was changed to a hemispherical shape.

  Example 3 was prepared in the same manner as Example 1 except that an antireflection film was attached as an antireflection layer on the outer surface of the transparent substrate 21 of the array substrate 12 of Example 1.

Comparative Example 1 was prepared in the same manner as in Example 1 except that the TiO ₂ particles of Example 1 were subjected to a color development treatment and a TiO ₂ reflective layer having fine holes was formed on the anode on the counter substrate side.

Comparative Example 2 was prepared in the same manner as in Example 1 except that the V-groove was formed of SiO ₂ having fine holes with a refractive index of 1.35 instead of TiO ₂ of Example 1.

  As a result, as shown in FIG. 5, Examples 1 to 3 had high reflectivity and contrast and good display quality in any case. On the other hand, Comparative Example 1 and Comparative Example 2 had low reflectance and contrast, and the display quality was poor.

It is sectional drawing of the reflection type display element which shows one embodiment of this invention. It is explanatory drawing which shows the behavior of the incident light at the time of power-off of a reflection type display element same as the above. It is explanatory drawing which shows the behavior of the incident light at the time of power-on of a reflection type display element same as the above. It is explanatory drawing which shows the behavior of incident light when the relationship of the refractive index of a reflection type display element is a transparent substrate <transparent conductive layer <transparent structure. It is a table | surface which shows the measurement result of the reflectance, contrast, and display quality about each Example and each comparative example.

Explanation of symbols

11 Reflective display element
12 Array substrate as first substrate
13 Counter substrate as second substrate
14 Electrolyte layer
21 Transparent substrate
22 Transparent conductive layer as the first conductive layer
23 Transparent structure
24 Chromogen
32 Transparent conductive layer as second conductive layer
33 Anode

Claims (4)

A first substrate provided with a transparent structure having a translucent first conductive layer on one main surface side and having a colored body showing electrochromism inside and having a continuous convex shape;
A second substrate having a second conductive layer and an anode on one main surface side and disposed opposite to the first substrate;
A reflective display element, comprising: an electrolyte layer interposed between the transparent structure and the anode. The transparent structure has an approximately isosceles triangle cross-section, the refractive index of the electrolyte layer is ne, the refractive index of the transparent structure is np, and the base angle of the transparent structure is θ. The reflective display element according to claim 1, wherein a relationship of ne / np) ≦ θ ≦ {180−arcsin (ne / np)} / 3 is satisfied. The reflection type display element according to claim 1, wherein an antireflection layer is provided on an outer surface of the first substrate. The first substrate includes a transparent substrate in which the first conductive layer and the transparent structure are sequentially formed on the side facing the second substrate, and the transparent substrate, the first conductive layer, and the visible light of the transparent structure are provided. The reflective display element according to any one of claims 1 to 3, wherein the refractive index in the region has a relationship of transparent substrate <first conductive layer <transparent structure.

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