JP3968482B2 - Reflective display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reflective display device that performs display using external light such as natural light. More specifically, the present invention relates to an illumination structure that is used supplementarily when external light is scarce.
[0002]
[Prior art]
A display device using liquid crystal as an electro-optical material has a flat panel structure, and is characterized by being thin and light and having low power consumption. Liquid crystal display devices are often used for display of portable devices, for example, taking advantage of these characteristics. Unlike a self-luminous display such as an LED, a liquid crystal display (LCD) is a passive device that displays an image by transmitting and blocking external light in response to a voltage. Therefore, some kind of lighting structure is required. From the viewpoint of the illumination structure, the display device is divided into a transmission type and a reflection type. In the transmissive type, a backlight is arranged on the back of the display device, and an image is observed from the front. The reflection type uses external light as it is as an illumination light source.
[0003]
[Problems to be solved by the invention]
In a transmissive display device, a panel holding a liquid crystal as an electro-optical material is created between a pair of transparent substrates, and a light source for illumination (backlight) is arranged on the back side, while an image is displayed from the front side of the backlight. Observe. In the case of the transmissive type, a backlight is essential, and for example, a cold cathode tube or the like is used. For this reason, since the backlight consumes most of the power when viewed as the entire display, it is not suitable for a display of a portable device. On the other hand, in the reflection type, a reflection plate is disposed on the back surface of the panel, and external light such as natural light is incident from the front, and an image is observed from the front using the reflected light. Unlike the transmissive type, a light source for back lighting is not used, so the reflective type requires relatively low power consumption and is suitable for a display of a portable device. However, the reflective display device cannot observe an image in an environment with poor outside light such as at night, which is a problem to be solved.
[0004]
[Means for Solving the Problems]
In order to solve the above-described problems of the prior art, the following measures were taken. That is, the reflective display device according to the present invention includes a panel, a light guide plate, and a light source as a basic configuration. The panel includes a transparent first substrate positioned on the incident side of external light, a second substrate positioned on the reflective side bonded to the first substrate via a predetermined gap, an electro-optic material held in the gap, and An electrode is formed on at least one of the first substrate and the second substrate and applies a voltage to the electro-optic material. The light guide plate is made of a transparent material and is disposed outside the first substrate, and overlaps the in-screen area and the out-screen area of the panel. A light source is disposed at the end of the light guide plate and generates illumination light as necessary. As a feature, the light guide plate normally transmits external light, enters the first substrate, and emits external light reflected from the second substrate. The illumination light incident on the light guide plate is guided into the light guide plate, enters the first substrate, and emits the illumination light reflected from the second substrate. The light guide plate has a flat portion divided into strips and an inclined portion positioned between the flat portions, and each of the illumination lights guided forward from the light source through the inside of the light guide plate The light reflected from the inclined portion is incident on the in-screen region of the panel, and the illumination light reflected from the in-screen region of the panel is emitted from each flat portion. As a further feature, the panel is provided with a specular reflection layer in a region outside the screen, and the light guide plate has an attenuation means at a position in the region outside the screen between the light source and the region in the screen. In the illumination light emitted from the light source, the component having a relatively large incident angle is substantially attenuated in the off-screen region, and the component having a relatively small incident angle is guided toward the front in-screen region. Preferably, the attenuation means is a light diffusion layer formed on the surface of the light guide plate. Alternatively, the attenuation means may be a light absorption layer formed on the surface of the light guide plate.
[0006]
According to the present invention, the light guide plate is disposed on the surface of the reflective panel, and the light source is disposed at the end thereof. In a dark environment, the light source is turned on and illumination light is incident on the panel side through the light guide plate to project an image. In a bright environment, the light source is turned off, and images are projected directly using outside light through a transparent light guide plate. The light guide plate is basically transparent and does not hinder any image observation even in a bright environment. Thus, according to the present invention, the light source only needs to be turned on when necessary, and the power consumption of the entire display can be greatly reduced, which is suitable for a display of a portable device. In addition to the basic operations described above, the present invention has been devised in order to improve the image quality particularly in a dark environment. That is, the light guide plate has an attenuation means at the position of the off-screen region between the light source and the in-screen region of the panel, and the component with a relatively large incident angle is included in the illumination light emitted from the light source. The light is substantially attenuated and the component having a relatively small incident angle is guided toward the front in-screen region, thereby enabling uniform night illumination without unevenness.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing a conceptual configuration of a reflective display device according to the present invention. As shown in the figure, the reflective display device includes a panel 0, a light guide plate 30, and a light source 40 as a basic configuration. The panel 0 is held in the gap between the transparent first substrate 1 located on the incident side of the external light, the second substrate 2 located on the reflection side and bonded to the first substrate 1 via a predetermined gap. The electro-optical material 3 and at least one of the first substrate 1 and the second substrate 2 are provided with electrodes for applying a voltage to the electro-optical material 3. The light guide plate 30 is made of an injection-molded product made of a transparent material such as acrylic resin, and is disposed outside the first substrate 1. The light source 40 is disposed at the end of the light guide plate 30 and generates illumination light as necessary. The light source 40 is formed of a cold cathode tube, for example, and is called a so-called edge light. In order to improve the illumination efficiency of the edge light, a reflecting mirror 41 is disposed behind the cylindrical light source 40. In such a configuration, the light guide plate 30 normally transmits external light, enters the first substrate 1, and emits external light reflected from the second substrate 2, while guiding the illumination light as necessary. Illumination light incident on the substrate 1 and reflected from the second substrate 2 is emitted. Although not shown, a reflective layer is provided on the second substrate 2 side.
[0008]
The light guide plate 30 has flat portions 31 divided into strips and inclined portions 32 positioned between the flat portions 31, and the illumination light guided forward from the light source 40 is reflected by the inclined portions 32. Then, the light enters the in-screen area of the panel 0 and the illumination light reflected from the in-screen area of the panel is emitted from each flat portion 31. As a characteristic matter, the light guide plate 30 has an attenuating means 33 at a position in an outside screen area between the light source 40 and the in-screen area. The attenuating means 33 is composed of, for example, a light diffusing layer or a light absorbing layer, and a component having a relatively large incident angle in the illumination light emitted from the light source 40 is substantially attenuated in the off-screen region, and a component having a relatively small incident angle. The light is guided toward the front screen area. With this configuration, the panel 0 can be illuminated uniformly over the entire area in the screen.
[0009]
FIG. 2 is a schematic diagram for explaining the function of the light guide plate 30. A light guide plate not provided with attenuation means is shown. Illumination light PH (oblique light indicated by a dotted line) emitted from the light source and having a large incident angle is guided forward while being reflected by the flat portion 31 of the light guide plate 30. On the other hand, illumination light PL (parallel light shown by a solid line) having a small incident angle is totally reflected by the 45 ° inclined portion 32 and emitted in a direction perpendicular to the light guide plate 30. The illumination light PL emitted vertically is used for illumination of the reflective liquid crystal panel.
[0010]
FIG. 3 shows a use state in which the light guide plate shown in FIG. As described above, the panel 0 is generally divided into an in-screen area constituting an effective screen and a peripheral area outside the screen. Peripheral circuits and the like are formed in the area outside the screen, and a mirror reflection layer 9a is generally disposed. On the other hand, a scattering reflection layer 9 is disposed in the screen area. Illumination light PL having a small incident angle emitted from the light source travels in the same manner as the single unit shown in FIG. However, the illumination light PH having a large incident angle has its reflection angle changed by the scattering reflection layer 9 in the screen area of the panel 0, and cannot travel forward in the light guide plate 30 as in a single unit. The light is emitted toward the inner region. Therefore, the illuminance of the panel 0 is bright on the light source side and dark on the front side.
[0011]
FIG. 4 shows a state in which the light guide plate 30 provided with attenuation means in the area outside the screen is used for the panel 0 according to the present invention. In this example, a light diffusion layer 33a is provided as an attenuation means. Instead, a light absorption layer may be used. The illumination light PH having a large incident angle emitted from the light source is first incident on the flat portion 31 in the area outside the screen. As described above, the light diffusion layer 33a is formed in the flat portion 31 as an attenuation means in a band shape. Here, the illumination light PH is diffused and the angle suddenly increases with respect to the horizontal direction of the light guide plate 30, and is eventually confined in the area outside the screen. When a light absorption layer is provided instead of the light diffusion layer 33a, the illumination light PH having a large incident angle emitted from the light source is absorbed here, and therefore is not guided toward the in-screen region. Therefore, it is the illumination light PL having a small incident angle that is guided to the in-screen area beyond the out-of-screen area, and thereby the in-screen area can be illuminated uniformly.
[0012]
When a light guide plate that does not include attenuation means is used, the difference in luminance between the light source side and the front side becomes more significant as the width dimension of the flat portion 31 increases. For example, the 45 ° inclined portion 32 has a fixed width of 6 μm, and the flat portion 31 has a width of 70 μm and 252 μm. In the light guide plate with the flat portion 31 having a width of 70 μm, uniform illumination could be achieved over the entire area in the screen without providing any attenuation means. However, the light guide plate in which the width of the flat portion 31 is 252 μm has doubled the luminance on the light source side on the front side. In the case where the light guide plate in which the flat portion 31 has a width of 252 μm is provided with an attenuating means including a light diffusion layer having a width of 5 mm, illumination with no luminance difference could be performed over the entire area in the screen.
[0013]
FIG. 5 is a schematic partial cross-sectional view showing an embodiment of a reflective display device according to the present invention. The present embodiment basically has a flat structure in which the light guide plate 130 and the panel are overlapped. The light guide plate 130 is formed with attenuation means (not shown) in addition to the flat portion 131 and the inclined portion 132. The panel has an active matrix type configuration. The upper substrate 101 is positioned on the incident side in contact with the light guide plate 130 and is made of a transparent base material such as glass. On the other hand, the lower substrate 102 is located on the reflection side, and it is not always necessary to use a transparent material. A guest-host liquid crystal layer 103 is held in the gap between the pair of substrates 101 and 102. This guest-host liquid crystal layer 103 is mainly composed of nematic liquid crystal 104 having negative dielectric anisotropy, and contains a dichroic dye 105 at a predetermined ratio. However, the present invention is not limited to guest-host liquid crystal, and liquid crystal in other display modes can be used. A counter electrode 106 and an alignment film 107 are formed on the surface of the upper substrate 101. Further, a color filter 150 is also formed. The alignment film 107 is made of, for example, a polyimide film, and the guest-host liquid crystal layer 103 is vertically aligned. At least a switching element made of a thin film transistor 108, a scattering reflection layer 109, and a pixel electrode 111 are formed on the lower substrate 102. The scattering reflection layer 109 is flattened by a flattening layer 114, and the pixel electrode 111 is patterned thereon. Therefore, a sufficient electric field can be applied to the guest-host liquid crystal layer 103 between the pixel electrode 111 and the counter electrode 106. The pixel electrode 111 is electrically connected to the thin film transistor 108 through a contact hole 112 opened in the planarization layer 114.
[0014]
As described above, the planarization layer 114 is interposed to fill the unevenness of the scattering reflection layer 109 and the thin film transistor 108, and the pixel electrode 111 is connected to the thin film transistor 108 through the contact hole 112. The scattering reflection layer 109 is subdivided corresponding to each pixel electrode 111. The individual subdivided portions are connected to the same potential as the corresponding pixel electrode 111. The scattering reflection layer 109 is used to improve the image quality by preventing the specular reflection of incident light. An alignment film 115 is formed so as to cover the surface of the pixel electrode 111 and is in contact with the guest-host liquid crystal layer 103 to control the alignment. In the present embodiment, the alignment film 115 and the alignment film 107 facing each other vertically align the guest-host liquid crystal layer 103.
[0015]
The thin film transistor 108 has a bottom gate structure, and has a stacked structure in which a gate electrode 116, a gate insulating film 117, and a semiconductor thin film 118 are stacked in this order from the bottom. The semiconductor thin film 118 is made of, for example, polycrystalline silicon, and a channel region aligned with the gate electrode 116 is protected from above by a stopper 119. The bottom-gate thin film transistor 108 having such a structure is covered with an interlayer insulating film 120. A pair of contact holes are opened in the interlayer insulating film 120, and the source electrode 121 and the drain electrode 122 are electrically connected to the thin film transistor 108 through these contact holes. These electrodes 121 and 122 are formed by patterning, for example, aluminum. The drain electrode 122 is at the same potential as the scattering reflection layer 109. The pixel electrode 111 is electrically connected to the drain electrode 122 through the contact hole 112 described above. On the other hand, a signal voltage is supplied to the source electrode 121.
[0016]
FIG. 6 is a schematic plan view of the active matrix display device shown in FIG. As shown in the figure, the display device 200 includes a pixel array unit 204 included in the in-screen area 203, peripheral circuits included in the off-screen area, and a plurality of input terminals 205 for supplying signals to the outside. Yes.
[0017]
The pixel array unit 204 has pixels arranged in a matrix. Each pixel includes a pixel electrode PXL and a switching thin film transistor Tr. In addition, gate lines X arranged in rows and signal lines Y arranged in columns are provided. The gate electrode of each thin film transistor Tr is connected to the corresponding gate line X, the source electrode is connected to the corresponding signal line Y, and the drain electrode is connected to the corresponding pixel electrode PXL.
[0018]
The peripheral circuit section has vertical drive means for selectively driving each row of pixels in response to a signal supplied from the input terminal 205, and horizontal drive means for selectively driving selected pixels in column order. In this example, the vertical drive means is composed of a pair of vertical drive circuits 206 and 207 arranged on the left and right sides of the in-screen area 203, and selectively drives each row of pixels from both sides. The first vertical drive circuit 206 is connected to the left end side of the gate line X, while the second vertical drive circuit 207 is connected to the right end side of the gate line X. Both vertical drive circuits 206 and 207 sequentially output gate pulses at the same timing, and open and close the thin film transistors Tr for each row to perform the above-described pixel selective drive. On the other hand, the horizontal driving means comprises a single horizontal driving circuit 208 and is connected to one end of the signal line Y. The horizontal drive circuit 208 distributes the video signal supplied from the outside via the input terminal 5 to each signal line Y, and writes and drives the selected pixels in a column order. The vertical driving circuits 206 and 207 and the horizontal driving circuit 208 described above are arranged in the outside area of the screen, while the pixel array unit 204 is arranged in the in-screen area 203.
[0019]
FIG. 7 shows a state in which a light guide plate and a light source are set on the reflective display device shown in FIG. As shown in the figure, a light source 240 is disposed at the end of the reflective display device 200. The display device 200 is divided into a central screen area 203 and a peripheral external screen area 213. As described above, peripheral circuits are integrated in the outside-screen region 213, and basically has a specular reflection structure. On the other hand, pixel electrodes and thin film transistors for switching them are integrated in the in-screen region 203, which basically has a scattering reflection structure. Although the light guide plate is not shown, a light guide plate that is not provided with attenuation means is used for convenience of explanation.
[0020]
FIG. 8 is a schematic graph showing the brightness distribution of the screen of the display device shown in FIG. The horizontal axis shows the vertical position of the screen, and the vertical axis shows the brightness. On the graph, x0 corresponds to the edge of the outside-screen area 213 shown in FIG. 7, and x1 corresponds to the boundary between the inside-screen area 203 and the outside-screen area 213. As is apparent from the graph of FIG. 8, when no attenuation means is provided on the light guide plate, an extremely bright area Z is generated at the end of the in-screen area 203 close to the light source 240. This significantly impairs the appearance of the in-screen area 203. The phenomenon shown in FIG. 8 corresponds to the state schematically shown in FIG. As shown in FIG. 3, since a large amount of illumination light is emitted to the outside in a portion of the in-screen region close to the out-of-screen region, only this portion becomes particularly bright. Therefore, as shown in FIG. 4, unnecessary illumination light that may leak into the screen is confined in the off-screen region by providing, for example, a light diffusion layer as an attenuation means in the off-screen region.
[0021]
The structure of the light guide plate according to the present invention can be applied not only to the reflection type display device described above but also to the backlight of the transmission type display device. An example of this application is shown in FIG. As shown in the figure, the transmissive display device includes a panel 300, a light guide plate 330, and a light source 340 as a basic configuration. The panel 300 includes a transparent first substrate 301 located on the front side, a transparent second substrate 302 located on the back side bonded to the first substrate 301 via a predetermined gap, and an electro-optic held in the gap. It includes a material and an electrode that is formed on at least one of the first substrate 301 and the second substrate 302 and applies a voltage to the electro-optic material. In this example, the electro-optic material is a TN mode nematic liquid crystal, and a pair of polarizing plates 370 and 380 are arranged on both sides of the panel 300 in this relation. The light guide plate 330 is disposed outside the second substrate 302 and overlaps the in-screen area and the out-screen area of the panel 300. A light diffusion plate 360 is interposed between the light guide plate 330 and the panel 300. The light source 340 is disposed at the end of the light guide plate 330 and generates illumination light. The light source 340 is accommodated in the reflecting mirror 341. The light guide plate 330 has strip-shaped inclined portions 332 arranged at a predetermined interval. The illumination light guided forward from the light source 340 is reflected by the inclined portions 332 and the screen of the panel 300 is viewed from the back side. Incident into the inner region. In order to assist the incidence of the illumination light, a light reflection plate 390 is provided. As a feature, the light guide plate 330 has an attenuation means 333 at a position in an outside area between the light source 340 and the in-screen area, and a component having a relatively large incident angle in the illumination light emitted from the light source 340. Is substantially attenuated in the area outside the screen, and a component having a relatively small incident angle is guided toward the area in the front screen. This makes it possible to uniformly illuminate the screen area of the transmissive display device from the back. The attenuation means 333 is composed of a light diffusion layer formed on at least one surface of the light guide plate 330, for example. Alternatively, the attenuation means 333 may be a light absorbing layer formed on at least one surface of the light guide plate 330.
[0022]
【The invention's effect】
As described above, according to the present invention, the light guide plate is disposed on the reflective panel, and the light source for auxiliary illumination is disposed at the end of the light guide plate. The light guide plate normally transmits external light, enters the panel, and emits external light reflected from the panel, while guiding the illumination light as necessary, enters the panel, and emits illumination light reflected from the panel. . In a dark environment, the light source is turned on so that an image can be observed even with a reflective panel. On the other hand, in a bright environment with abundant outside light, the light source is turned off to save power. The light guide plate has a flat portion divided into strips and an inclined portion positioned between the flat portions, and the illumination light guided forward from the light source is reflected by each inclined portion to be within the screen of the panel. While entering the area, the illumination light reflected from the in-screen area of the panel is emitted from each flat portion. The light guide plate has an attenuation means at the position of the off-screen region between the light source and the in-screen region, and the component having a relatively large incident angle in the illumination light emitted from the light source is substantially in the off-screen region. Uniform illumination of the in-screen region is realized by guiding the attenuated component having a relatively small incident angle toward the front in-screen region. By using the light guide plate having such a configuration for the backlighting of the transmissive display device, uniform backlighting in the in-screen region can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a basic concept of a reflective display device according to the present invention.
FIG. 2 is a schematic diagram illustrating a reference example of a light guide plate.
FIG. 3 is a reference example showing a use state of a light guide plate.
FIG. 4 is a schematic diagram for explaining a usage state and functions of a light guide plate according to the present invention.
FIG. 5 is a schematic partial sectional view showing an embodiment of a reflective display device according to the present invention.
FIG. 6 is a schematic plan view of a reflective display device.
7 is a schematic plan view showing a reference example in which a light guide plate and a light source are incorporated in the reflective display device shown in FIG. 6;
8 is a graph showing the brightness distribution of the screen of the display device shown in FIG.
FIG. 9 is a cross-sectional view showing an embodiment of a transmissive display device according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 0 ... Panel, 1 ... 1st board | substrate, 2 ... 2nd board | substrate, 3 ... Electro-optical substance, 30 ... Light guide plate, 31 ... Flat part, 32 ... Inclination part 33 ... Attenuating means, 40 ... Light source

Claims (3)

A transparent first substrate positioned on the incident side of external light, a second substrate bonded to the first substrate via a predetermined gap and positioned on the reflecting side, an electro-optic material held in the gap, and the first A panel having an electrode formed on at least one of the first substrate and the second substrate and applying a voltage to the electro-optic material;
A light guide plate disposed on the outside of the first substrate and overlapping an in-screen region and an out-of-screen region of the panel; and a light source disposed at an end of the light guide plate to generate illumination light as required.
The light guide plate normally transmits external light, enters the first substrate, and emits external light reflected from the second substrate, and, if necessary, illumination that enters the end portion of the light guide plate from the light source. A reflective display device that guides light into the light guide plate, enters the first substrate, and emits illumination light reflected from the second substrate,
The light guide plate has a flat portion divided into strips and an inclined portion located between the flat portions, and each of the illumination lights guided forward from the light source through the inside of the light guide plate While being reflected by the inclined portion and entering the in-screen area of the panel, the illumination light reflected from the in-screen area of the panel is emitted from each flat portion,
The panel is provided with a specular reflection layer in an area outside the screen,
The light guide plate has an attenuating means at a position of the off-screen region between the light source and the on-screen region, and a component having a relatively large incident angle is included in the illumination light emitted from the light source. A reflection type display device characterized by guiding a component that is substantially attenuated at a relatively small incident angle toward the front screen area.   2. The reflection type display device according to claim 1, wherein the attenuation means is a light diffusion layer formed on the surface of the light guide plate.   2. The reflection type display device according to claim 1, wherein the attenuating means is a light absorption layer formed on the surface of the light guide plate.

Images