WO2008084898A1

WO2008084898A1 - Reflection-type display system

Info

Publication number: WO2008084898A1
Application number: PCT/KR2007/000989
Authority: WO
Inventors: Hyun Ha Hwang; Seung Gon Kang
Original assignee: IMAGELAB CO Ltd
Current assignee: IMAGELAB CO Ltd
Priority date: 2007-01-11
Filing date: 2007-02-27
Publication date: 2008-07-17
Anticipated expiration: 2009-07-11
Also published as: KR20080066255A

Abstract

Provided is a reflective display device. The reflective display device includes lower and upper substrate, a plurality of pixel electrodes, a color filter, a plurality of light source electrodes, a light source, a common electrode, and a plurality of microcapsules. The color filter is disposed at the bottom surface of the upper substrate and has a plurality of color pixels. The light source electrodes are disposed between adjacent color pixels of the color filter. The light source is coupled to the bottom surface of the color filter and radiates light to the lower substrate. The common electrode is disposed at the bottom surface of the color filter, and a plurality of microcapsules are disposed between the common electrode and the pixel electrode. Each of the microcapsules includes white particles having a positive charge, black particles having a negative charge, and dielectric liquid.

Description

REFLECTION-TYPE DISPLAY SYSTEM

Technical Field

[1] The present invention relates to a display device, and more particularly, to a reflective display device receiving light radiated from an external light source and reflecting the received light using an internal reflector for displaying images to a user.

Background Art

[2] In general, liquid crystal display (LCD) devices are categorized into a transmissive type and a reflective type by a way of using light.

[3] The transmissive LCD device includes a liquid crystal display (LCD) panel formed of two glass plates with liquid crystal interposed therebetween, and a back light unit for providing light to the LCD panel. Due to the back light unit, the transmissive LCD devices have a problem of excessive power consumption. Also, it is difficult to make the transmissive LCD devices thinner and lighter because of the thickness and the volume of the backlight unit. Due to the drawbacks of the transmissive LCD devices, the reflective LCD devices without the backlight unit have been widely used.

[4] When the ambient light does not provide sufficient light intensity, the reflective LCD device cannot display information thereon. In order to overcome such a problem of the reflective LCD device, a front light unit (FLU) for providing a light source has been introduced.

[5] Fig. 1 is a schematic diagram illustrating a reflective LCD device having a front light unit according to the related art.

[6] As shown in Fig. 1, the reflective LCD device includes a reflective liquid crystal panel 10 and a front light unit 20 disposed on the reflective liquid crystal panel 10 for providing light to the liquid crystal panel 10. A diffusing reflective electrode 11 is formed at the bottom of the reflective liquid crystal panel 10 for reflecting an ambient light and a supplementary light to the display side of the liquid crystal panel 10.

[7] The front light unit 20 includes a light source 30 for emitting light, a light guide plate

40 for uniformly outputting the light in a direction to a whole display area of a liquid crystal panel, a reflective mirror 50 for reflecting the light from the light source 30 to the light guide plate 40, and an antireflective coating 60 for preventing the light from being leaked from the light guide plate 40.

[8] The light guide plate 40 has an upper surface formed in a prism pattern, thereby changing the propagation path of light that enters with a predetermined angle inclined to be vertical from the display surface. Then, the light guide plate 40 guides the light to propagate to the reflective liquid crystal panel 10 in a vertical direction from the reflective liquid crystal panel 10. Then, the reflective liquid crystal panel 10 reflects the light to the upper surface of the light guide plate 40, thereby providing the information to a user's eyes.

[9] However, the conventional reflective liquid crystal display device has a problem of deteriorating an image quality due to the front light unit 20 disposed on the entire area of the reflective liquid crystal panel 10.

[10] That is, the optical interference between the prism pattern of the light guide plate 40 and the liquid crystal panel 10 generates Moire. The reflected light from the uppermost surface of the light guide plate 40 lowers the contrast ratio, and the transmittance ratio of the light guide plate 40 degrades the brightness.

[11] Due to the prism pattern formed on the upper surface of the light guide plate 40, it is more likely to produce inferiority caused by scratch or dust while assembling parts of the reflective display device.

[12] Furthermore, the conventional reflective LCD device has a limitation to reduce the overall thickness thereof due to the thickness of the light guide plate 40. Disclosure of Invention Technical Problem

[13] It is, therefore, an object of the present invention to provide a reflective display device for not deteriorating an image quality, not generating inferiority due to dust and scratch, and reducing a thickness thereof. Technical Solution

[14] In accordance with one aspect of the present invention, there is a reflective display device including: a lower substrate and an upper substrate, which are separated to each other at a predetermined distance; a plurality of pixel electrodes disposed on the lower substrate; a color filter disposed at the bottom surface of the upper substrate and having a plurality of color pixels; a plurality of light source electrodes disposed between adjacent color pixels of the color filter; a light source coupled to the bottom surface of the color filter for emitting a light in a direction to the lower substrate; a common electrode disposed at the bottom surface of the color filter; and a plurality of microcapsules disposed between the common electrode and the pixel electrode, and each of which includes white particles having a positive charge, black particles having a negative charge, and dielectric liquid.

[15] A passivation layer may be disposed between the lower substrate and the pixel electrode and between the upper substrate and the light source electrodes to prevent humidity and oxygen from being penetrated.

[16] The passivation layer may be made of at least one selected from the group consisting of acryl, polyimide, silicon oxide (SiO ), and silicon nitride (SiNx). [17] The light source electrode may play a role of a black matrix.

[18] The light source may be a white organic light emitting diode (OLED).

[19] The light source may be smaller than the light source electrode.

Advantageous Effects

[20] A reflective display device according to a certain embodiment of the present invention has following advantageous effects.

[21] At first, the reflective display device according to a certain embodiment of the present invention is able to display information without distortions by including a light source integrally formed at the bottom surface of an upper substrate for generating light in a direction to a lower substrate, and microcapsules for reflecting light radiated from the light source. Therefore, the reflective display device according to the present invention provides superior image quality even when the ambient light is weak or dark.

[22] Secondly, the reflective display device according to a certain embodiment of the present invention includes the light source integrally formed at the bottom surface of the upper substrate. Therefore, the overall thickness of the reflective display device becomes thinner, and the assembly process of the reflective display device becomes easier.

Brief Description of the Drawings

[23] The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which: [24] Fig. 1 is a schematic diagram illustrating a reflective LCD device having a front light unit according to the related art; [25] Fig. 2 is a cross-sectional view of a reflective display device according to an embodiment of the present invention; and [26] Fig. 3 is a cross-sectional view of a reflective display device for describing an operating state when the voltage is applied to the microcapsule shown in Fig. 2.

Mode for the Invention [27] Other objects and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter. [28] Fig. 2 is a cross-sectional view of a reflective display device according to an embodiment of the present invention. [29] Referring to Fig. 2, the reflective display device according to an embodiment of the present invention includes a lower substrate 100, an upper substrate 200, a pixel electrode 300, a color filter 900, a plurality of light source electrodes 400, a plurality of light sources 500, a common electrode 600, and microcapsules 700. [30] The upper substrate 200 and the lower substrate 100 are separated from each other at a predetermined distance. [31] Each of the upper and lower substrates 200 and 100 is a substrate having a flat top and bottom surface. The upper and lower substrates 300 may be formed of one of a transparent material or an opaque material. [32] That is, it is preferable that the lower and upper substrates 100 and 200 are formed of one of glass and plastic. [33] A plurality of the pixel electrodes 300 are formed on the top surface of the upper substrate 100 and receive a driving voltage. [34] The color filter 900 is a filter disposed on the bottom surface of the upper substrate

200. [35] The color filter 900 includes a plurality of Red pixels R, green pixels G, and blue pixels B. [36] The plurality of the light source electrodes 400 supplies the driving voltage to the light source 500 to radiate light from the light source 500. [37] It is preferable that a light source electrode 400 is disposed between every two adjacent color pixels in the color filter 900. [38] It is preferable that the light source electrode 400 is a black matrix in order to emit light only in a direction to the lower substrate 100 not to emit the light in a direction to the upper substrate 200 when the light source 500 emits light. [39] Herein, the light source 400 can be formed as a block matrix by depositing chrome

(Cr) and chrome oxide (CrO ) through a sputtering process and patterning the depositing result through a photolighography process.

[40] Since the light source electrodes 400 having the black matrix characteristics are disposed between every two adjacent color pixels of the color filter 900 in the present embodiment, the light passes only through the opening end of each color pixel of the color filter 900. Also, the light source electrodes 400 having the black matrix characteristics prevent the light from being transmitted to a space between the color pixels, or a region not allowed controlling the color, such as regions of a switching element and a wire. Therefore, the contrast ratio becomes improved.

[41] The light sources 500 are an element emitting light using a driving voltage applied to the light source electrode 400.

[42] The light sources 500 are coupled to the bottom of the light source electrodes 400 and radiate the light in a direction to the lower substrate 100 when a driving voltage is supplied to the light source electrodes 400.

[43] It is preferable that a white organic light emitting diode (OLED) is used as the light source 500, which can be operated with a low driving voltage.

[44] It is also preferable that the light source 500 is formed to be smaller than the light source electrode 400 in order not to emit the light in a direction to the upper substrate

200, and the light sources 500 are a bottom emission type. [45] Furthermore, a passivation layer 800 is formed between the lower substrate 100 and the pixel electrode 300, and between the upper substrate 200 and the light source electrodes 400 in order to prevent humidity or oxygen from being penetrated, thereby extending the life time of the light source 500. [46] It is preferable that the passivation layer 800 is formed of one selected from the group consisting of a high polymer such as acryl and polyimide, and ceramic such as silicon oxide (SiO 2 ) and silicon nitride (SiN).

[47] The common electrode 600 is a transparent electrode disposed at the bottom of the color filter 800 and receives the driving voltage. [48] The common electrode 600 is connected to the light source electrodes 400 and receives the driving voltage of elements on the upper substrate 300 and the driving voltage from the light source 500 at the same time. [49] The plurality of microcapsules 700 are a capsule disposed between the common electrode 600 and the pixel electrode 300. [50] Each of the microcapsules 700 includes a transparent dielectric fluid 710, white particles 720 each having a positive charge, and black particles 730 each having a negative charge. [51] As shown in Fig. 3, in each of the microcapsules 700, the locations of the white particles 720 having the positive charge and the locations of the black particles 730 having the negative charge are decided according to the electric potential supplied to the common electrode 600 and the pixel electrode 300. [52] That is, when the common electrode 600 is applied as a positive electrode and the pixel electrode 300 is applied as a negative electrode, the black particles 730 move to the common electrode 500 and the white particles 720 move to the pixel electrode 300. [53] On the contrary, when the common electrode 600 is applied as a negative electrode and the pixel electrode 300 is applied as a positive electrode, the black particles 730 move to the pixel electrode 300 and the white particles 720 move to the common electrode 600. [54] If the particles moving to the common electrode 600 are the black particles 730, the microcapsules 700 reflect the light emitted from the light source 500 and the reflected light is displayed in black color at the outside. If the particles moving to the common electrode 600 are the white particles 720, the microcapsules 700 reflect the light emitted from the light source t00 and the reflected light is displayed in white color at the outside. [55] And, the light reflected from the white particles 720 of the microcapsule 700 can be transformed in various colors by the color filter 900 and displayed in various colors at the outside.

[56] The operation of the reflective display device according to an embodiment of the present invention will be described with reference to Figs. 2 and 3.

[57] When the driving voltage is applied to the common electrode 600 and the pixel electrode 300, the light source 500 radiates light through the light source electrode 400 and the light is propagated to the pixel electrode 300.

[58] Furthermore, the locations of the white particles 720 having the positive charge and the black particles 730 having the negative charge change according to the electric potential applied to the common electrode 600 and the pixel electrode 300.

[59] When the common electrode 600 is applied as the negative electrode, the white particles 720 having the positive charge move to the common electrode 600 and the light radiated from the light source 500 is reflected by the white particles 720. Therefore, the light is displayed in the white color or transformed in red, green, and blue color by the color filter 900.

[60] On the contrary, if the common electrode 600 is applied as the positive electrode, the black particles 730 having the negative charge move to the common electrode 600, and the light radiated from the light source 500 is reflected by the black particle 730 and displayed in the black color at the outside. Therefore, it allows an overall display shape to be recognized.

[61] In the reflective display device according to the present embodiment, the light source

500 is integrally disposed on the flat bottom of the upper substrate 200. Therefore, the light generated from the light source 500 is reflected by the microcapsules 700 and displayed without distortion. Therefore, the reflective display device according to the present embodiment can provide superior image quality even when the ambient light is weak or dark.

[62] Furthermore, the light source 500 is integrally disposed on the bottom of the upper substrate 200. Therefore, the overall thickness of the reflective display device becomes thinner, and the assembly process of the reflective display device becomes easier.

[63] While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.

Claims

[ 1 ] A reflective display device comprising : a lower substrate and an upper substrate, which are separated to each other at a predetermined distance; a plurality of pixel electrodes disposed on the lower substrate; a color filter disposed at the bottom surface of the upper substrate and having a plurality of color pixels; a plurality of light source electrodes disposed between adjacent color pixels of the color filter; a light source coupled to the bottom surface of the color filter for emitting a light in a direction to the lower substrate; a common electrode disposed at the bottom surface of the color filter; and a plurality of microcapsules disposed between the common electrode and the pixel electrode, and each of which includes white particles having a positive charge, black particles having a negative charge, and dielectric liquid.

[2] The reflective display device of claim 1, wherein a passivation layer is disposed between the lower substrate and the pixel electrode and between the upper substrate and the light source electrodes to prevent humidity and oxygen from being penetrated.

[3] The reflective display device according to claim 2, wherein the passivation layer is made of at least one selected from the group consisting of acryl, polyimide, silicon oxide (SiO 2 ), and silicon nitride (SiNx).

[4] The reflective display device according to claim 4, wherein the light source electrode plays a role of a black matrix. [5] The reflective display device of claim 1, wherein the light source is a white organic light emitting diode (OLED). [6] The reflective display device of anyone of claims 1 to 5, wherein the light source is smaller than the light source electrode.