Liquid crystal cells – elements and systems – Liquid crystal system – Liquid crystal writing tablet
Reexamination Certificate
2001-09-17
2004-08-03
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Liquid crystal writing tablet
C349S014000, C349S122000, C349S117000, C349S149000, C349S074000, C345S104000, C345S175000
Reexamination Certificate
active
06771327
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a liquid crystal display device comprising an input panel for detecting input information, made up of a pair of transparent substrates with an electrode provided on respective inner surfaces thereof, facing each other, and disposed on the visible side of a liquid crystal display panel made up by filling a gap between a pair of substrates with liquid crystal, and in particular, to a reflective or transflective liquid crystal display device.
2. Description of the Related Art
Many matrix type liquid crystal display panels have recently been put to use for a display of various information terminals, instruments, personal computers, and so forth. In particular, for portable information equipment, there have been in widespread use reflective liquid crystal display devices capable of effecting display by making use of ambient light in order to realize lower power consumption or transflective liquid crystal display devices capable of effecting reflective display when the surroundings are bright and effecting transmissive display by lighting up an auxiliary light source incorporated therein when the surroundings are dark.
With the portable information equipment, while reduction in weight and thickness is important from the viewpoint of portability, use of a liquid crystal display panel having a large area is preferable from the viewpoint of visibility. For this reason, it has been in practice to reconcile miniaturization of a liquid crystal display device with enlargement of a display area thereof by installing an input panel as an input device on a display surface (display region) of the liquid crystal display panel such that display can be recognized through the input panel.
As the input panel for use in this case, there is available, for example, a touch panel of a resistive membrane type, made up of an upper substrate and a lower substrate, both transparent, with an upper electrode and a lower electrode provided on the inner surfaces of the respective substrates, facing each other, in such a way as to be deformable by applying pressure to either the upper substrate or the lower substrate (mainly the upper substrate), so that the upper substrate is caused to come into contact with the lower substrate as a result of such deformation, thereby enabling position coordinates of pressed parts of the upper substrate or the lower substrate to be read.
Although the touch panel of this type has been in widespread use because it is convenient to use, and has excellent recognizability while its fabrication cost is low, it has had a problem of causing deterioration in visibility of the liquid crystal display panel when it is disposed so as to overlay the display region of the liquid crystal display panel.
Cited as the reasons for such a problem are occurrence of absorption of light by respective light transmitting members, reflection due to the difference in refractive index between the light transmitting members in contact with each other, and occurrence of coloring caused by absorption or interference because the disposition of the touch panel on the visible side (the viewer's side) of the liquid crystal display panel will have the same effect as that in the case where a plurality of light transmitting members are disposed on the visible side of the liquid crystal display panel. Accordingly, there will arise problems that, as compared with the case of employing the liquid crystal display panel alone, display becomes darker, a contrast ratio deteriorates, coloring occurs, and a quantity of incident light decreases due to reflection of light by the touch panel.
Among the methods of solving these problems, there are available a method of reducing reflection by inserting an optical member, capable of reducing the difference in refractive index, between respective constituent members, a method of reducing a quantity of absorbed light by reducing the thickness of the respective constituent members, or a method of selecting constituent members having a low absorption ratio for use, and a method of reducing the number of the constituent members.
Further, there is another method of preventing reflection of light by the touch panel by disposing a polarizer on the visible side of the touch panel, and disposing a quarter-wave (lambda: &lgr;) plate on the rear face side of the polarizer, however, in this case, there is the need for disposing one more sheet of polarizer between the liquid crystal display panel and the touch panel, and consequently, it follows that light is transmitted through two sheets of the polarizers twice when effecting reflective display, so that there will be an increase in absorption of light, resulting in darker display.
Besides the above, as a construction for preventing reflection of light, there is available a construction wherein a filling medium having a refractive index, equivalent to the mean between the refractive index of the upper electrode as well as the lower electrode, made up of a transparent and electrically conductive film, and the refractive index of air, is sealed between the upper substrate and the lower substrate of the touch panel, however, even with such a construction as described, reflection occurs between the lower substrate of the touch panel and a first substrate of the liquid crystal display panel, so that reduction in reflection of light has been found insufficient.
Further, particularly, in the case of a liquid crystal display panel using supertwisted nematic (STN) liquid crystal, and a reflective or transflective liquid crystal display panel having three-terminal thin film transistors (TFTs) or two-terminal thin film diodes (TFDs), and using twisted nematic (TN) liquid crystal or parallel alignment liquid crystal, there is the need for a reflector or a transflective reflector, and a polarizer as well as a retardation film on the viewer's side of the former. With the use of these constituent members, bright display and dark display are effected.
Accordingly, if a constituent member for preventing reflection of light from the touch panel is additionally laminated on top of such a liquid crystal display panel as described above, this will create problems such as an increase in the number of the constituent members thereof, an increase in quantity of light absorbed, and an increase in the weight as well as thickness of the liquid crystal display device, resulting in an increase in the cost of the device. Thus, improvement in these respects has been highly desired.
Furthermore, although there is another method of employing a film substrate for the upper substrate or lower substrate of the input panel, this has caused a problem that the display contents of the liquid crystal display panel is distorted or unevenness in reflective intensity is increased due to swelling (distortion) of the film substrate.
In order to solve the problem described, it is conceivable to adopt a constitution wherein the first substrate of the liquid crystal display panel doubles as the lower substrate of the input panel. In this case, however, during the process of fabricating a first electrode to be installed on the side of the first substrate of the liquid crystal display panel, facing a liquid crystal layer, or during the process of fabricating the liquid crystal display panel, there is involved the risk that a change occurs to a resistance value of the transparent and electrically conductive film of the input panel, depending on a temperature at which the process as described is carried out, and deterioration in unevenness or damage occurs to the transparent and electrically conductive film, so that the constitution described is not suitable for fabrication of a high quality liquid crystal display device.
SUMMARY OF THE INVENTION
In order to solve various problems described in the foregoing, it is an object of the invention to prevent deterioration of visibility of the liquid crystal display panel due to the effect of the input panel, and to realize reduction in the number of constituent m
Chowdhury Tarifur R.
Citizen Watch Co. Ltd.
Westerman Hattori Daniels & Adrian LLP
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