This Application claims priority of Taiwan Patent Application No. 100144312, filed on Dec. 2, 2011, the entirety of which is incorporated by reference herein.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and in particular, to a liquid crystal display device having a high-transmittance characteristic without gray-level inversion.
2. Description of the Related Art
The transmittance of a liquid crystal (LC) display device can be modified due to different polarizations or diffractions of an incident light by changing the arrangements of liquid crystal molecules, so that the LC display can produce images. The conventional twisted nematic (TN) device has good transmittance performance. However, the conventional TN device has a very narrow viewing-angle, which is limited by the structure and optical characteristics of the liquid crystal molecules. Therefore, it is a challenge for the LC display to have both a wide-viewing-angle and high utilization of light characteristics.
A vertical alignment (VA) type wide-viewing-angle LC display has been developed to solve the aforementioned problems. The VA type LC display comprises a patterned vertical alignment (PVA) type LC display, a multi-domain vertical alignment (MVA) type LC display, and etc. The PVA type LC display achieves the goal of wide-viewing-angle characteristics by applying a fringing-field effect thereto and optical compensation films. The MVA type LC display widens the viewing-angle and improves transmittance of the LC display by dividing a pixel area into multi domains and tilting liquid crystals respectively in the multi domains in several different directions using protrusion features or specific indium tin oxide (ITO) patterns.
The conventional VA type LC display, however, suffers from a gray-level inversion problem. The LC display theoretically has higher brightness at higher gray-levels (from gray-level of 0 (black) to gray-level of 255 (white)). But the LC display may have higher brightness at relatively lower gray-levels at certain large angles. In other words, when the LC display has a black and white reversal phenomenon, the gray-level inversion problem occurs. The gray-level inversion problem results in an unacceptable imaging quality for the LC display.
Thus, a novel liquid crystal display device with improved high-transmittance characteristics without gray-level inversion is desired.
A liquid crystal display is provided. An exemplary embodiment of a liquid crystal display device comprises a first substrate having a pixel unit. A second substrate is disposed opposite to the first substrate, having an opposite electrode. A first polarizer is disposed under the first substrate. A second polarizer is disposed under the second substrate, wherein a polarization axis of the second polarizer is vertical to that of the first polarizer. A liquid crystal (LC) layer with chiral dopants is disposed between the first and second substrates, wherein a parameter of the LC rotations (d/p ratio) of the LC layer with chiral dopants is between 0.2 and 0.3, and a parameter of the optical phase retardation factor R of the LC layer with chiral dopants is larger than 0.6 and less than 0.95, wherein
wherein d is a thickness of the LC layer with chiral dopants, p is a pitch of chiral dopants, Δn is a birefringence coefficient of the LC layer with chiral dopants, and λ is a wavelength of an incident light.
Another exemplary embodiment of a liquid crystal display device comprises a first substrate having a pixel unit. A second substrate is disposed opposite to the first substrate, having an opposite electrode. A first polarizer is disposed under the first substrate. A second polarizer is disposed under the second substrate, wherein a polarization axis of the second polarizer is vertical to that of the first polarizer. A liquid crystal (LC) layer with chiral dopants is disposed between the first and second substrates, wherein a parameter of the optical path difference (Δnd) of the LC layer with chiral dopants is between 330 and 600, and a parameter of the LC rotations (d/p ratio) of the LC layer with chiral dopants is between 0.2 and 0.3, wherein Δn is a birefringence coefficient of the LC layer with chiral dopants, d is a thickness of the LC layer with chiral dopants, and p is a pitch of chiral dopants.
A detailed description is given in the following embodiments with reference to the accompanying drawings.
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
a is a side view showing one exemplary embodiment of vertical alignment type liquid crystal molecules of one exemplary embodiment of a liquid crystal display device of the invention without an applied electronic field.
b is a side view showing one exemplary embodiment of vertical alignment type liquid crystal molecules of one exemplary embodiment of a liquid crystal display device of the invention with an applied electronic field.
a is a transmittance diagram showing a liquid crystal display device formed by a liquid crystal material without chiral dopants.
b is a transmittance diagram showing a liquid crystal display device formed by a liquid crystal material with chiral dopants.
a to 5c are transmittance-voltage curve diagrams corresponding to different parameters of the LC rotations (d/p ratio) of a vertical alignment type liquid crystal display at zero-degree, 45-degree and 90-degree viewing-angles.
a and 8b are gray-level inversion value distribution diagrams corresponding to different parameters of the optical phase retardation factor R and LC rotations (d/p ratio) of one exemplary embodiment of a liquid crystal (LC) display device of the invention, which comprises an LC layer with chiral dopants, at 45-degree and 90-degree viewing-angles, respectively.
The following description is of a mode for carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. Wherever possible, the same reference numbers are used in the drawings and the descriptions to refer the same or like parts.
The present invention will be described with respect to particular embodiments and with reference to certain drawings, but the invention is not limited thereto and is only limited by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual dimensions to practice the invention.
Embodiments provide a liquid crystal (LC) display device with improved transmittance characteristics in a display region without gray-level inversion. An LC material with chiral dopants is used as an LC layer of one embodiment of an LC display device of the invention.
The second substrate 208 may serve as a color filter (CF) substrate, comprising a base 204, an opposite electrode 206 and color filters (not shown). Additionally, black matrixes (not shown) may be disposed between the color filters.
The LC display device 500 further comprises a first polarizer 218 and a second polarizer 210. The first polarizer 218 is disposed under the first substrate 214, and the second polarizer is disposed above the second substrate 208. In one embodiment, a polarization axis of the second polarizer 210 is vertical to that of the first polarizer 218. In one embodiment, the LC display device 500 further comprises a first compensation film 222 disposed between the first substrate 214 and the first polarizer 218, and a second disposed between the second substrate 208 and the second polarizer 210.
As shown in
a is a side view of showing one exemplary embodiment of liquid crystal molecules 203 of the LC layer 202 of the liquid crystal display device 500 of the invention without an electronic field applied between the first substrate 214 and the second substrate 208. Directions of arrows on the first polarizer 218 and the second polarizer 210 illustrate directions of the polarization axis of the first substrate 214 and the second substrate 208, respectively.
Please refer to
Please refer to
In order to find the preferred parameters of the optical phase retardation factor R, LC rotations (d/p ratio) and optical path difference (66 nd) of a vertical alignment (VA) liquid crystal (LC) display, which comprises an LC layer with chiral dopants, to improve the transmittance of the liquid crystal display device without gray-level inversion, the numerical simulation method is used to analyze and calculate the transmittance distribution corresponding to different parameters of the optical path difference (66 nd) and LC rotations (d/p ratio) of a display region of a liquid crystal (LC) display device, which comprises an LC layer with chiral dopants. When an incident light penetrates an LC layer having the birefringence characteristic, a parameter of the optical phase retardation factor R is represented as
wherein λ is a wavelength of an incident light.
Please refer to
0.6<R<0.95 equation (1)
0.2≦d/p ≦0.3 equation (2)
When the parameter of the optical phase retardation factor R of the LC layer with chiral dopants of the LC display device 500, which is operated by an incident light having a wavelength between 380 nm and 780 nm, satisfies equation (1), the value of the optical path difference (66 nd) is between 228 nm and 741 nm. In one embodiment, the parameter of the optical path difference (66 nd) of the LC display device 500, which comprises an LC layer with chiral dopants, may preferably satisfy equation (3). When the parameters of the LC rotations (d/p ratio) and optical path difference (Δnd) of the LC display device 500, which comprises the LC layer 202 with chiral dopants, respectively satisfy equation (2) and equation (3), the gray-level inversion (delta T) value of the LC display device 500 at a 45-degree viewing-angle is not larger than 0.02 (corresponding to a region surrounded by a dotted line of
330≦Δnd≦600 equation (3)
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
Number | Date | Country | Kind |
---|---|---|---|
100144312 | Dec 2011 | TW | national |