Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-05-14
2004-10-19
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S042000, C349S096000, C349S112000, C349S114000, C349S117000, C257S059000, C257S072000
Reexamination Certificate
active
06806934
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 based upon the source of illumination. Reflective type displays are illuminated by ambient light that enters the display from the front and the peripheral side. A reflective surface, such as an aluminum or silver reflector placed in or behind the reflective display, reflects the 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, the ambient light from the front and the peripheral side is not always enough to illuminate the reflective displays, and, thus, the application of the reflective displays will be limited.
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 available and backlighting only when necessary. This dual function of reflection and transmission leads to the designation, “transflective”. Transflective LCDs are a dual mode display device. These devices operate either with the available ambient light in a reflective mode or with an internal backlight in a transmissive mode.
FIG. 15
illustrates a conventional transflective LCD. In the reflective mode, the ambient light
10
passes through the outside polarizer
20
, and then passes into the LCD cell
30
. Generally, the LCD cell
30
consists of two opposing glass substrates
32
,
34
with a liquid crystal layer
36
sandwiched therebetween. Typically, the substrate
34
is provided with a plurality of pixel regions arranged as a matrix with a switching element such as TFT and a pixel electrode (not shown) formed at every pixel region. The substrate
32
is provided with color filters for displaying colors and a common electrode (not shown). While the liquid crystal layer having positive dielectric anisotropy is possible, for the sake of simplicity, it will be assumed that the liquid crystal layer has the more popular negative dielectric anisotropy. Thus, when the switching element is in the “on” state, the liquid crystal layer has no effect upon the light passing through it. When the switching element is “off”, the light passing though the liquid crystal layer will be altered in some way, depending upon the nature of the light and the type of LCD. The light
10
passing through the LCD cell
30
proceeds through the inside polarizer
40
to the transflective film
50
serving as a reflector of ambient light and a transmitter of light from the backlight. At the transflective film
50
, a portion of the light is reflected. The reflected light
10
then returns through the inside polarizer
40
, through the LCD cell
30
and finally through the outside polarizer
40
to a viewer.
Since the transflective film
50
is placed outside the LCD cell
30
, reflections from the interface between the liquid crystal layer
36
and the glass substrate
34
as well as the transflective film
50
will form a multiple image, which can cause serious problem depending on the thickness of the glass and adversely affect the display resolution. Furthermore, in the reflective mode, the light passes through the polarizers
20
and
40
twice; however, in the transmission mode, the light passes through the polarizers
20
and
40
only once. Apparently, the conventional transflective LCD is not efficient in the reflective mode. The efficiency is important because the size, weight and battery life of portable instrumentation are heavily dependent upon the efficiency of the instrumentation's display.
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 an object of the present invention to provide transflective LCDs which are more efficient and have low power consumption in the reflective mode.
To achieve the above listed and other objects, the present invention provides a liquid crystal display (LCD) characterized by having a dielectric multilayer formed inside an LCD cell so as to overcome, or at least reduce the above-mentioned problems of the prior art. The dielectric multilayer is composed of multiple layers of transparent dielectric materials with different refractive index. The LCD cell is sandwiched between two polarizers and comprises a first substrate and a second substrate being located facing each other with a liquid crystal layer therebetween. When the light traveling through the dielectric multilayer encounters material with different refractive index, a great part of the light is reflected while the other part is transmitted. The dielectric multilayer may be disposed between the first substrate and the liquid crystal layer or between the second substrate and the liquid crystal layer such that the light only passes through one of the polarizers in the reflective mode thereby increasing efficiency while meeting the need for low power consumption.
In a general aspect of the present invention, the first substrate is provided with a plurality of gate lines formed parallel to one another, a plurality of data lines formed parallel to one another vertically to the gate lines, a plurality of switching elements and pixel electrodes, and a passivation layer formed on the switching elements and pixel electrodes. 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 data lines, and the pixel electrodes are formed in the pixel regions. The passivation layer has a plurality of contact holes. The second substrate is provided with a light-shielding matrix, a plurality of color filters and a common electrode. A first polarizer, a retardation film, and a second polarizer on the retardation film are disposed outside of the LCD cell. A backlight is disposed behind the LCD cell.
According to a preferred embodiment of the present invention, the dielectric multilayer is directly formed on one surface of the first substrate, the gate lines are formed on the dielectric multilayer, and the light source is disposed behind the other surface of the first substrate. In this embodiment, the LCD cell may include an overcoat layer formed on the passivation layer. The overcoat layer has a plurality of contact holes to expose the contact holes of the passivation layer. The pixel electrodes are formed on the overcoat layer and electrically connected to the switching elements through the contact holes of the passivation layer and the contact holes of the overcoat layer.
According to another preferred embodiment of the present invention, the dielectric multilayer is formed on the gate lines as an insulating layer.
According to still another preferred embodiment of the present invention, the dielectric multilayer is formed between the switching elements and the pixel electrodes as a passivation layer. The dielectric multilayer has a plurality of contact holes, and the pixel electrodes are electrically connected to the switching elements through the contact holes of the dielectric multilaye
Furuhashi Hiroyuki
Wei Chung Kuang
Wu Chao Wen
Chi Mei Optoelectronics Corp.
Chowdhury Tarifur R.
LandOfFree
Transflective liquid crystal display having dielectric... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transflective liquid crystal display having dielectric..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transflective liquid crystal display having dielectric... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3331015