Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-05-17
2004-12-14
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S106000, C349S043000
Reexamination Certificate
active
06831718
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to Liquid Crystal Display (LCD) and in particular to LCDs of the transflective type.
2. Description of the Related Art
LCDs can be classified according to the source of illumination. Reflective displays are illuminated by ambient light that enters the display from the front. A reflective surface, such as an aluminum or silver reflector placed in or behind the reflective display, returns light to illuminate the reflective display. Although reflective displays meet the need for low power consumption, the displays often appear rather dark and are therefore difficult to read. In addition, there are many conditions where there is insufficient ambient light, the purely reflective display is thus limited in usefulness.
In applications where the intensity of ambient light is insufficient for viewing, supplemental lighting, such as a backlight assembly, is used to illuminate the display. Although supplemental lighting can illuminate a display regardless of ambient lighting conditions, it is an expensive drain on battery life. Thus, the batteries on portable computers, for example, must typically be recharged after 2 to 4 hours of continuous backlight use. In applications where the intensity of ambient light is very strong, e.g., under an outdoor burning sun, the transmissive image illuminated only by the backlight assembly is insufficient for viewing because of poor contrast.
In an attempt to overcome the above described drawbacks of reflective and transmissive displays, some electronic displays have been designed to use ambient light when it is available and backlighting only when it is necessary. This dual function of reflection and transmission leads to the designation, “transflective”. Transflective LCDs are dual mode display devices. These devices operate either with the available ambient light in a reflective mode or with an internal backlight in a transmissive mode.
FIG. 1
illustrates a conventional transflective LCD
100
which comprises two opposing glass substrates
32
and
34
with a liquid crystal layer
36
sandwiched therebetween. Two polarizers
20
and
40
are formed on the outer surfaces of the two substrates
32
and
34
. A retardation film
22
is formed between the substrate
32
and the polarizer
20
, and a retardation film
24
is formed between the substrate
34
and the polarizer
40
. Typically, the substrate
34
is provided with a plurality of pixel regions arranged in a matrix each with a TFT, a reflection electrode
37
(as an ambient light reflector) and a transmission electrode
38
(as a back light transmitter) which is formed at a location corresponding to the opening of the reflection electrode
37
. The substrate
32
is provided with color filter elements
33
for displaying colors and a common electrode
35
. While the liquid crystal layer having negative dielectric anisotropy is possible, the liquid crystal layer has the more popular positive dielectric anisotropy. Thus, when the switching element is in the “on” state or in the “off” state, the light passing through the liquid crystal layer will be altered in some way, depending upon the nature of the light and the type of LCD.
In the reflective mode, the light passes through the color filter element
33
twice; however, in the transmissive mode, the light passes through the color filter element
33
only once. Therefore, each pixel region of the conventional LCD
100
is provided an extra color filter layer
33
a
on the color filter element
33
of the substrate
32
. This arrangement can effectively prevent degraded color saturation in the transmissive mode. However, since the extra color filter layer
33
a
and transmission electrode
38
are formed on the two different substrates
32
and
34
, the two glass substrate
32
and
34
must be precisely aligned during assembly such that the extra color filter layer
33
a
can be precisely formed on the region of the color filter element
33
corresponding to the transmission electrode
38
. Therefore, the manufacturing process of the conventional LCD
100
may not be easily controlled and requires precise design. Accordingly, there exists a need in the art for a transflective liquid crystal display which overcomes, or at least reduces the above-mentioned problems of the prior art.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a transflective LCD which has good color saturation in the transmissive mode and can be easily manufactured.
The liquid crystal display (LCD) according to the present invention primarily comprises a first substrate, a second substrate and a liquid crystal layer formed between the inner surfaces of the first and the second substrates. The first substrate is provided with a plurality of pixel regions arranged in a matrix each with a switching element (e.g., TFT), a reflection electrode (as an ambient light reflector) and a transmission electrode (as a backlight transmitter). The LCDs according to the present invention are characterized by having an extra color filter layer provided in each of the pixel regions of the first substrate for improving the color saturation in the transmissive mode.
In a general aspect of the present invention, the first substrate is provided with a plurality of gate lines formed parallel to one another, and a plurality of data lines formed parallel to one another and vertically to the gate lines. The gate lines and the data lines are arranged to form a matrix of pixel regions with each of the pixel regions bounded by two adjacent gate lines and two adjacent data lines. The switching elements are formed at intersections of the gate lines and the data lines. A passivation layer is formed on the switching elements and the data lines. The passivation layer has a plurality of contact holes. An overcoat layer is formed on the passivation layer with an uneven surface closest to the liquid crystal layer (i.e., the side of the overcoat layer adjacent to the liquid crystal layer has an uneven surface) and the overcoat layer has a plurality of cavities to expose the contact holes of the passivation layer. Preferably, two polarizers are provided on the outer surfaces of the first and second substrates. A first retardation film is provided between the first substrate and the polarizer and a second retardation film is provided between the second substrate and the polarizer.
According to one embodiment of the present invention, the reflection electrode is formed on the overcoat layer such that the surface of the reflection electrode is uneven. The reflection electrode has at least one opening corresponding to the cavity of the overcoat layer, and the transmission electrode is disposed at a location corresponding to the opening of the reflection electrode. The transmission electrode and the reflection electrode are electrically connected to each other and at least one of them is electrically connected to the switching element. It is noted that the color filter layer is formed in the cavities of the overcoat layer. In this embodiment, the second substrate is provided with color filter elements for displaying colors. In the transmissive mode, light will pass through the color filter layer in the cavities and the color filter element on the second substrate, and then arrive a viewer thereby obtaining better color saturation. It will be understood that the transmission electrode is preferably disposed between the color filter layer and the liquid crystal layer. Alternatively, the transmission electrode may be also disposed under the color filter layer. In any pixel region, the color filter element of the second substrate and the corresponding color filter layer of the first substrate have the same color.
According to another embodiment of the present invention, the overcoat layer is made of a color filter material. The reflection electrode is formed on the overcoat layer such that the surface of the reflection electrode is uneven. The reflection electrode has at least one opening formed at a location
Kuo Chen Lung
Wei Chung Kuang
Chi Mei Optoelectronics Corp.
Ton Toan
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