Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2003-09-23
2004-11-23
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S102000, C349S114000, C349S117000, C349S180000
Reexamination Certificate
active
06822709
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a transflective display device, and more particularly to a transflective liquid crystal display (LCD) device with an optical supplement structure for improving viewing angle, increasing light recycling rate and reducing thickness thereof.
2. Description of the Related Art
Liquid crystal display (LCD) devices are usually classified as transmissive type or reflective type according to the difference in their display light source. The transmissive type LCD device uses a back light module, in which the light is incident to an LC layer and is absorbed or passes through the LC layer, thus the disadvantages of faded color and reduced contrast ratio occur under a natural light source or an artificial exterior light source. Conversely, the reflective type LCD device relies on ambient incident light from an exterior light source, and offers superior performance and high contrast under outdoor sunlight. Also, because of its low power consumption, the reflective type LCD devices are primarily employed in portable display products. The quality of reflective type LCD devices, however, suffers when the exterior light source is obscured, and it is comparatively difficult to achieve high resolution for a full color display. Accordingly, transflective LCD devices have been developed to compensate for the previously mentioned disadvantages and combine the advantages of reflective and transmissive LCD devices. The transflective LCD device can use well known active driving processes, such as amorphous silicon thin film transistors (a-Si TFTs) or low temperature polysilicon (LTPS) TFTs, and is applicable to low power products.
FIG. 1
is a cross-section of a conventional transflective LCD device. A transflective LCD device
10
comprises an upper substrate
12
, a lower substrate
14
and an LC layer
16
interposed therebetween. Adjacent to the inner surface of the upper substrate
12
, opposing the LC layer
16
, lies a color filter and a common electrode layer
18
. On the outer surface of the upper substrate
12
, a first quarter-wave plate (QWP)
20
I, a first half-wave plate (HWP)
22
I and a first polarizer
24
I are successively formed. The first HWP
22
I has an optical retardation of &lgr;/2, and the first QWP
20
I has an optical retardation of &lgr;/4, in which “&lgr;” indicates a wavelength of the incident light.
On the inner surface of the lower substrate
14
, opposing the LC layer
16
, a transparent electrode layer
26
, a passivation layer
28
and a reflective electrode layer
30
are successively formed, in which the transparent electrode layer
26
and the reflective electrode layer
30
act together as a pixel electrode. Also, an opening
29
is formed to penetrate the central portions of the reflective electrode layer
30
and the passivation layer
28
, thus the exposed portion of the transparent electrode layer
26
serves as a transmissive area T of the pixel electrode, and the overlapped portion between the reflective electrode layer
30
and the transparent electrode layer
26
serves as a reflective area R of the pixel electrode. On the outer surface of the lower substrate
14
, a second QWP
20
II, a second HWP
22
II and a second polarizer
24
II are successively formed. The second HWP
22
II has an optical retardation of &lgr;2, and the second QWP
20
II has an optical retardation of &lgr;4. Additionally, a backlight device
32
is arranged adjacent to the second polarizer
24
II.
Operation of the transflective LCD device
10
is described in the following. First, in reflective mode, external incident light is reflected from the reflective electrode layer
30
(the reflective area R of the pixel electrode), and is directed toward the upper substrate
12
. At this point, when electrical signals are applied to the reflective electrode layer
30
by a switching element (such as a TFT device), the arrangement of LC molecules in the LC layer
16
varies and thus the reflected light is colored by the color filter, thereby displaying a color image. Second, in the transmissive mode, the light emitted from the backlight device
32
passes through the opening
29
(the transmissive area T of the pixel electrode). At this point, when the electrical signals are applied to the transparent electrode layer
26
by the switching element, the arrangement of LC molecules in the LC layer
16
varies and thus the light passing through the LCD device
10
is colored by the color filter, thereby forming a color image.
The object of forming the retardation films including the first QWP
20
I, the second QWP
20
II, the first HWP
22
I and the second HWP
22
II on both substrates
12
and
14
is to expand the optical compensation effect through the broad-wavelength light band. Also, in one pixel area, the LC layer
16
has a first cell gap over the reflective area R and a second cell gap over the transmissive area T, thus the phase retardation in the transmissive area T is twice the phase retardation in the reflective area R. The difference in the phase retardation between the reflective area R and the transmissive area T, nevertheless, impedes the retardation films to achieve the accurate optical compensation. Accordingly, based on the dual cell gaps design, reducing the cell thickness of the transflective LCD device
10
and reducing the thickness of each retardation film are considered. Moreover, the first QWP
20
I and the second QWP
20
II limit the viewing angle within the transmissive area T, thus a novel structure to solve the problem of narrowed viewing angle is called for.
The light recycling effect between the backlight device
32
and the reflective area R is concerned with the optical structure including the QWPs
20
I and
20
II and HWPs
22
I and
22
II.
FIG. 2
is a cross-section illustrating the light recycling effect between the backlight device
32
and the reflective area R. When a first incident light
33
emitted from the backlight device
32
passes through the second polarizer
24
II, the second HWP
22
II and the second QWP
20
II, the first incident light
33
is weakened and becomes a second incident light
34
. When directed toward the upper substrate
12
, the second incident light
34
is reflected from the reflective electrode layer
30
to form a first reflective light
35
. After passing the second QWP
20
II, the second HWP
22
II and the second polarizer
24
II, the first reflected light
35
is further weakened and becomes a second reflected light
36
. Accordingly, the incident light and the reflected ight completely pass through the second QWP
20
II and the second HWP
22
II twice, and are mostly absorbed and weakened causing the second reflected light
36
to be extremely weak and incapable of being recycled. Thus, the light recycling rate is too low to provide adequate illumination, and a greater power is required to increase the light intensity of the backlight device
32
in order to improve the luminescent property of the transflective LCD device
10
.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a transflective display device with an optical supplement structure to achieve a smaller size, a thinner profile, and a lower cost.
Another object of the present invention is to provide a transflective display device with an optical supplement structure to achieve superior display performance at a wide viewing angle.
Another object of the present invention is to provide a transflective display device with an optical supplement structure to increase the light recycling rate.
Another object of the present invention is to provide a transflective display device with an optical supplement structure to achieve greater brightness and higher resolution.
According to the object of the invention, a transflective LCD device has an upper substrate, a lower substrate and a liquid crystal layer interposed therebetween. A reflective electrode layer is formed overlying the inner surface of the lower substrate to serve as a reflective area of a pixel
Chang Wei-Chih
Chuang Li-Sen
Duong Tai
Quintero Law Office
Ton Toan
Toppoly Optoelectronics Corp.
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