Patent Application
20070126963
This application is related to an application by CHIU-LIEN YANQ WEI-YI LING and CHIA-LUNG LIN entitled LIQUID CRYSTAL DISPLAY DEVICE, filed before the present application, and assigned to the same assignee as that of the present application.
The present invention relates to liquid crystal display (LCD) devices, and more particularly to a reflection/transmission type LCD device capable of providing a display both in a reflection mode and a transmission mode.
Conventionally, there have been three types of LCD devices commercially available: a reflection type LCD device utilizing ambient light, a transmission type LCD device utilizing backlight, and a semi-transmission type LCD device equipped with a half mirror and a backlight.
With a reflection type LCD device, a display becomes less visible in a dim environment. In contrast, with a transmission type LCD device, a display becomes hazy in strong ambient light (e.g., outdoor sunlight). Thus researchers sought to provide an LCD device capable of functioning in both modes so as to yield a satisfactory display in any environment. In due course, a semi-transmission type LCD device was disclosed in Japanese Laid-Open Publication No. 7-333598.
However, the above-mentioned semi-transmission type LCD device typically has the following problems.
The semi-transmission type LCD device uses a half mirror in place of a reflective plate used in a reflection type LCD device, and has a minute transmission region (e.g., minute holes in a metal thin film) in a reflection region, thereby providing a display by utilizing transmitted light as well as reflected light. Since reflected light and transmitted light used for a display pass through the same liquid crystal layer, an optical path of reflected light is twice as long as that of transmitted light. This causes a large difference in retardation of the liquid crystal layer with respect to reflected light and transmitted light. Thus, a satisfactory display may not be obtained. Furthermore, a display in a reflection mode and a display in a transmission mode are superimposed on each other, so that the respective displays cannot be separately optimized. This results in difficulty in providing a color display, and tends to cause a blurred display.
Accordingly, what is needed is an LCD device that can overcome the above-described deficiencies.
A transflective LCD device includes: a first substrate; a second substrate; a liquid crystal layer interposed between the substrates; a first polarizer disposed at a surface of the first substrate opposite to the liquid crystal layer; a second polarizer disposed at a surface of the second substrate opposite to the liquid crystal layer; a first retardation film disposed between the first polarizer and the first substrate; a second retardation film disposed between the first retardation film and the first polarizer; a third retardation film disposed between the second polarizer and the second substrate; a fourth retardation film disposed between the third retardation film and the second polarizer; and a first discotic molecular film disposed between the first retardation film and the first substrate.
Other objects, advantages, and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
The first and second alignment films 225 and 215 are homogeneous alignment films. A rubbing direction of the first alignment film 225 is parallel to that of the second alignment film 215. A pre-tilt angle of the liquid crystal molecules adjacent to the first and second alignment films 225 and 215 is in a range of 0° to 15°.
A first discotic molecular film 221, a first retardation film 222, a second retardation film 223, and a first polarizer 224 are disposed in that order on an outer surface of the first substrate 220. A third retardation film 212, a fourth retardation film 213, and a second polarizer 214 are disposed in that order on an outer surface of the second substrate 210.
An alignment direction of molecules in the first discotic molecular film 221 is parallel to that of the alignment films 225 and 215. A pre-tilt angle of the molecules in the first discotic molecular film 221 adjacent to the first substrate 220 is defined as θDLC1, and is in a range from 0° to 45°. A pre-tilt angle of molecules in the first discotic molecular film 221 adjacent to the first retardation film 222 is defined as θDLC2, and is in a range from 45° to 90°.
The first and third retardation films 222 and 212 are preferably quarter-wave plates. The second and fourth retardation films 223 and 213 are preferably half-wave plates. A slow axis of the second retardation film 223 maintains an angle θ1 relative to the polarizing axis of the first polarizer 224, and a slow axis of the first retardation film 222 maintains an angle 2θ1°±45° relative to the polarizing axis of the first polarizer 224. A slow axis of the fourth retardation film 213 maintains an angle θ2 relative to the polarizing axis of the second polarizer 214, and a slow axis of the third retardation film 212 maintains an angle 2θ2°±45° relative to the polarizing axis of the second polarizer 214.
The polarizing axis of the first polarizer 224 is perpendicular to that of the second polarizer 214. When θ1 is equal to θ2, the slow axis of the first retardation film 222 is perpendicular to that of the third retardation film 212, and the slow axis of the second retardation film 223 is perpendicular to that of the fourth retardation film 213.
A common electrode 226 is disposed on an inner surface of the first substrate 220. The common electrode 226 is made of a transparent conductive material, such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO).
A pixel electrode 216 and an insulating layer 219 are disposed on an inner surface of the second substrate 210. The pixel electrode 216 includes a reflection electrode 217 and a transmission electrode 218. The reflection electrode 217 is made of metal with a high reflective ratio, such as aluminum (Al) or an aluminum-neodymium (Al—Nd) alloy. The reflection electrode 217 is used for reflecting ambient light when the LCD device 200 operates in a reflection mode. The transmission electrode 218 is made of a transparent conductive material, such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO). The insulating layer 219 separates the reflection electrode 217 from the pixel electrode 216.
The LCD device 200 includes a plurality of pixel regions that span through the common electrode 226, the pixel electrode 216, and the liquid crystal layer 230 contained between the common and pixel electrodes 226, 216. Each of the pixel regions includes a reflection region (not labeled) corresponding to the reflection electrode 217, and a transmission region (not labeled) corresponding to a portion of the transmission electrode 218 not overlapped by the reflection electrode 217. The retardation value of the liquid crystal layer 230 in the transmission region is in the range from 130 nm˜350 nm, and the retardation value of the liquid crystal layer 230 in the reflection region is in the range from 65˜175 nm.
On the other hand, when a voltage is applied to the LCD device 200, the LCD device 200 is in an off-state (black state). Up to the point where ambient incident light reaches the liquid crystal layer 230, the ambient incident light undergoes transmission in substantially the same way as described above in relation to the LCD device 200 being in the on-state. Since an effective phase difference of the liquid crystal layer 230 is adjusted to be 0 by applying a voltage in order to obtain a black display, the circularly-polarized light incident on the liquid crystal layer 230 passes therethrough as circularly-polarized light. The circularly-polarized light exiting the liquid crystal layer 230 is reflected by the reflection electrode 217. The circularly-polarized light keeps its polarized state, and is incident on the liquid crystal layer 230 again. After passing through the liquid crystal layer 230, the circularly-polarized light is converted into linearly-polarized light by the first retardation film 222 (a quarter-wave plate). At this time, the polarizing direction of the linearly-polarized light is rotated by about 90° compared with that of a white display state. Then the linearly-polarized light passes through the second retardation film 223 (a half-wave plate), and is absorbed by the first polarizer 224. Thus the linearly-polarized light is not output from the LCD device 200 for displaying images.
The first, second, third, and fourth retardation films 222, 223, 212 and 213 can compensate the phase difference generated by the liquid crystal molecules that may not be completely perpendicular to the substrates 220 and 210 when voltage is provided thereto. This reduces the leakage of light when the LCD device 200 in an off-state, and increases a contrast of images displayed by the LCD device 200. Moreover, the first discotic molecular film 221 can compensate contrast and color-shift of the LCD device 200 according to different viewing angles, so as to improve a wide viewing angle performance of the LCD device 200.
An alignment direction of molecules in the second discotic molecular film 311 is parallel to that of first and second alignment films 325 and 315. A pre-tilt angle of the molecules in the second discotic molecular film 311 adjacent to the second substrate 310 is defined as θDLC1, and is in a range from 0° to 45°. A pre-tilt angle of the molecules in the second discotic molecular film 311 adjacent to the third retardation film 312 is defined as θDLC2, and is in a range from 45° to 90°.
It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set out in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200510102119.0 | Dec 2005 | CN | national |
