KR20000038716A - Liquid crystal display - Google Patents

Abstract

PURPOSE: A liquid crystal display is provided to be used as a reflection LCD(liquid crystal display) when an outer light source is present and to be use a backlight when the light source is absent. CONSTITUTION: A liquid crystal display includes a first LCD layer and a second LCD layer. The first LCD layer includes an upper substrate(13), a liquid crystal layer(25) and a lower substrate(21). The upper substrate(13) includes a transparent electrode and a diffraction plate(13) applied on the outside. The second LCD layer includes an upper substrate, a liquid crystal layer, and a lower substrate. The upper substrate includes transparent electrodes formed on it. The liquid crystal with high reflection rate is applied to the lower substrate. The inner side of the second LCD layer includes transparent electrodes. On the outer side of the LCD layer is formed on the diffraction plates and the backlight(24).

Description

Liquid Crystal Display (DUAL MODE LCD)

The present invention relates to an LCD device, and more particularly to an LCD device that can switch the function of the component as needed.

The LCD uses a principle of transmitting or blocking light by injecting a liquid crystal between two substrates and applying a voltage to two electrodes formed on the inside of the substrate to adjust the arrangement of the liquid crystals present therebetween.

Early TN or STN LCDs with small screens were mostly reflective LCDs that used reflection of external light. On the other hand, LCDs used in high-definition large-screen color notebook computers or liquid crystal TVs use a backlit LCD that adopts its own light source called a back light on the back of the LCD.

Comparing these reflective LCDs and backlit LCDs, the reflective type uses a reflective film without a backlight, so the structure is simple, the cost of the backlight is reduced, and there is no power required for the backlight. There is an advantage to reduce.

On the other hand, in the case of a product that needs to provide a high quality image to the user by increasing the brightness of the screen while adopting a high-precision color type large screen, the backlight type is commercially available. In addition, there is a problem that the reflective LCD cannot be used by itself in a dark room or at night. To solve this problem of the reflective LCD, a method of installing a light source on the front surface is used. In the case of the front light, the front light is lost by reflecting a lot of light from the LCD panel surface and evenly shines the light toward the screen. There was a problem of difficulty. In addition, in the case of a backlit LCD, the backlight is always turned on when the product is used, and since the liquid crystal layer transmits external light, a brighter light source is needed to view the screen better.

An object of the present invention is to provide an LCD device that can operate as a reflective LCD using external light when there is an external light source and can use its own backlight in a dark environment without external light.

1 is a view showing a cross-sectional structure in an embodiment of the LCD device of the present invention.

2 is a view showing a state along the path of light when operating in the reflective mode in another embodiment of the LCD device of the present invention.

3 is a view showing a state along the path of light when operating in the transmission mode in another embodiment of the LCD device of the present invention.

※ Explanation of symbols for main parts of drawing

11: upper substrate 12: diffuser

13: upper polarizer 14: phase difference plate

15: color filter layer 16: upper transparent electrode layer

17: intermediate substrate 18: TFT forming layer

19: upper lower transparent electrode layer 20: lower upper transparent electrode layer

21: lower substrate 22: lower lower glass substrate

23: lower polarizer 24: back light

25: upper liquid crystal layer 26: lower liquid crystal layer

27: lower retarder

The LCD device according to the present invention for achieving the above object basically comprises a first substrate having a polarizing plate attached to the outer surface and a transparent electrode formed on the inner surface and a lower substrate on which a liquid crystal layer and a transparent electrode are formed on the inner surface. And a second LCD layer consisting of a transparent electrode on the inner surface and a lower electrode on which the polarizing plate and the backlight are attached on the inner surface of the liquid crystal layer comprising a layer and an upper substrate on which the transparent electrode is formed and a liquid crystal having high reflectance. It is done.

In this case, the lower substrate of the first LCD layer and the upper substrate of the second LCD layer may be replaced by one substrate having transparent electrodes formed on upper and lower surfaces thereof, respectively.

Of course, each basic LCD layer may include components such as a phase difference plate, a diffuser, and a color filter on the upper substrate of the first LCD layer in order to increase the function and range of use as a display device in a basic structure. Several attempts can be made to modify the material, arrangement and processing of elements such as electrodes, substrates, and the like.

As the liquid crystal constituting the liquid crystal layer, a nematic liquid crystal lamp, which is generally used for the first LCD layer, is used, and the second LCD layer is a liquid crystal such as cholesteric liquid crystal or PDLC (Polymer Dispersed Liquid Crystal). In mode, it is necessary to use a liquid crystal capable of increasing the reflectance. Looking at the operation principle, in the case of the cholesteric liquid crystal, a strong selective reflection is made when the arrangement of the liquid crystal matches or is adjacent to the wavelength of light passing by one pitch. Also, if a little polymer is added to the cholesteric liquid crystal, the liquid crystal array has a stable bi-stable state when the liquid crystal array has a planar structure and a conical state structure due to the influence of the polymer.

Therefore, the liquid crystal layer in which a little polymer is added to the cholesteric liquid crystal is transformed according to the applied voltage signal, so that the liquid crystal array has a strong reflection on incident light when the liquid crystal array is planar, and transmits incident light when the cone is conical. It can be used as a reflective film or a transmissive layer as needed.

Even in the case of using the PDLC, since the array of liquid crystals dispersed in the polymer transmits, scatters, or reflects incident light depending on the voltage applied to the LCD, the second LCD layer may be used as a transmission plate or a reflection plate.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a view showing a cross-sectional structure in an embodiment of the LCD device of the present invention.

First, the structure, the phase difference plate 14 for phase-changing the linearly polarized light from the diffuser 12 and the upper polarizing plate 13 to reduce the reflected light and secure the viewing angle on the upper surface of the upper substrate 11 of the first LCD layer; The upper polarizer 13 is attached in sequence, and the lower surface of the upper substrate 11 has a color filter layer 15 including a black matrix for increasing contrast of the screen, and an upper transparent electrode ITO. The layers 16 are formed in order.

In the intermediate substrate 17, the TFT forming layer 18 and the upper transparent electrode layer 19 insulated on the upper surface are formed in turn, and the lower transparent electrode layer 20 is formed on the lower surface.

The lower transparent electrode layer 22 is also formed on the upper surface of the lower substrate 21, and the lower polarizing plate 23 and the backlight 24 are sequentially attached to the lower surface. An upper liquid crystal layer 25 exists between the upper substrate 11 and the intermediate substrate 17, and a bi-stable state in which a polymer is partially added to the cholesteric liquid crystal between the intermediate substrate 17 and the lower substrate 21. There is a lower liquid crystal layer 26. In some cases, a separate lower retardation plate 27 may be provided between the lower surface of the lower substrate 21 and the lower polarizer 23.

2 and 3 are views showing the state of light on a path passing through each component when the second LCD layer is operated in the reflection mode and the transmission mode in the embodiment in which the separate retardation plate is installed on the lower substrate. Elements that do not change in phase of light are omitted.

When used in the reflection mode as shown in FIG. 2, the second LCD layer cholesteric liquid crystal takes a planar structure and operates as a reflector. The natural light incident from the outside has a form vibrating in all directions on the normal surface of the incident direction, but only components that vibrate in the left and right direction through the upper polarizer 13 are transmitted to become left and right vibration polarization. The left and right oscillating polarizations are circularly polarized in the counterclockwise direction through the phase difference plate 14, and the upper and lower sides of the upper liquid crystal layer 25 are vibrated up and down by changing their phase in a portion where no voltage is applied to the upper liquid crystal layer through the upper liquid crystal layer 25 Vibration is polarized. The vertically oscillated polarized light becomes the up and down oscillated polarized light reflected by the cholesteric liquid crystal layer, and changes its phase again as it passes through the upper liquid crystal layer to become the original counterclockwise circularly polarized light. The circularly polarized light passes through the retardation plate and is transmitted from the upper polarizing plate 13 which becomes the left and right vibration polarization and transmits only the left and right vibration components. Therefore, the part where no voltage is applied appears bright because of reflected light. In the part where voltage is applied to the upper liquid crystal layer, there is no change of phase when light passes through the liquid crystal layer, so that the incident light passes through the retardation plate is 180 ° C when the phase is reflected in the counterclockwise circularly polarized state. The reflected light in the liquid crystal layer becomes circularly polarized light rotating clockwise. The circularly polarized light becomes vertically oscillated polarized light while passing through the retardation plate, and the reflected light passing through the retardation plate is shielded in the upper polarizing plate that passes only the left and right polarization polarization. Therefore, since no reflected light passes through, the portion to which the voltage is applied appears dark.

When the cholesteric liquid crystal layer has a conical structure as shown in Fig. 3, this liquid crystal layer is used as a transmission membrane. In this case, since the external light is weak or blocked, only the light emitted from the backlight is considered.

First, the voltage applied to the upper liquid crystal layer will be described. The light incident from the backlight becomes left and right vibration polarization while passing through the lower polarizing plate 23, and circularly polarized light rotating through the lower retardation plate 27 clockwise. Here, the lower retardation plate 27 is a retardation plate that changes the phase of light by -90 °, unlike the upper retardation plate 14. Since the lower liquid crystal layer simply acts as a transmissive film, the circularly polarized light remains in the same state, passes through the lower liquid crystal layer, and the phase is changed by 90 ° in the upper liquid crystal layer to become left and right vibration polarization such as incident light. The left and right vibration polarization becomes counterclockwise circularly polarized light while passing through the upper phase difference plate 14 to pass through the upper polarizing plate. In this case, since there is light passing through the upper polarizing plate, the point where the voltage is not applied to the upper liquid crystal layer is bright as in the reflection mode of FIG. 2.

On the other hand, when a voltage is applied to the upper liquid crystal layer, both upper and lower liquid crystal layers function as transmissive films and are independent of phase change of light. Therefore, the light of the backlight having left and right vibration polarization while passing through the lower polarizing plate becomes clockwise circularly polarized light until it passes through the lower retardation plate 27 and reaches the upper retardation plate, and becomes vertical vibration polarization while passing through the upper retardation plate. Since the vertical vibration polarization does not pass through the upper polarizing plate 13, the portion where the voltage is applied to the upper liquid crystal layer appears dark.

As can be seen from the above, since the screen appears dark at the portion where the voltage is applied to the upper liquid crystal layer in both the reflection mode and the transmission mode, the user can see the same image regardless of the mode.

Therefore, according to the present invention, since there is no external light in the second LCD layer, the second LCD layer is used as a reflection type, and in the dark, the second LCD layer is used as a backlight type because it is used as a backlight type. Compared with the general reflection type, it can be used even in the absence of external light.

Although the present invention has been described in detail only with respect to the described embodiments, it will be apparent to those skilled in the art that various modifications and variations are possible within the technical scope of the present invention, and such modifications and modifications are within the scope of the appended claims.

Claims (3)

A first LCD layer including a top substrate having a polarizing plate attached to an outer surface and a transparent electrode formed on an inner surface thereof, a liquid crystal layer and a lower substrate formed on the inner surface of the transparent substrate; A second LCD layer including a top substrate on which a transparent electrode is formed, a liquid crystal layer formed of a liquid crystal having high reflectance, and a transparent electrode on an inner surface thereof, and a bottom substrate on which a polarizer and a backlight are attached to an outer surface thereof; An LCD device, which is made by overlapping one after another. The method of claim 1, The liquid crystal of the second LCD layer is an LCD device, characterized in that the liquid crystal array is formed in a stable Bi-stable state in both the planar structure and the conical structure by adding a polymer to the cholesteric liquid crystal. The method of claim 1, And the liquid crystal of the second LCD layer is PDLC (Polymer Dispersed Liquid Crystal).