Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-03-15
2003-08-19
Chawdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S106000, C349S110000, C349S111000, C349S112000, C349S114000, C349S122000
Reexamination Certificate
active
06608660
ABSTRACT:
TECHNICAL FIELD
The present invention relates to liquid crystal display devices in which a reflector and coloring layers are provided on a surface of a substrate at a liquid crystal layer side, electronic apparatuses provided with the liquid crystal display devices, and substrates for use in the liquid crystal display devices.
BACKGROUND ART
Hitherto, due to low power consumption characteristics, reflective liquid crystal display devices have been used for mobile information terminals and the like. In particular, concomitant with the recent increase in the communication of image information, movement towards color reflective liquid crystal display devices is in progress.
In liquid crystal display devices, by providing a reflector on an exterior surface or an interior surface of a liquid crystal layer, a reflective liquid crystal display device can be constructed. However, it is believed that the reflector is preferably provided on the interior surface of the liquid crystal layer since decrease in display quality, such as double images by parallax and color blurring, can be avoided. For example, in active matrix liquid crystal display devices, when pixel electrodes are also used as a reflector by providing reflective properties to the pixel electrodes formed at a substrate provided with switching elements, a reflective color liquid crystal display device can be realized in which decrease in display quality can be avoided.
Recently, in order to ensure visibility in dark environments, there is a proposal in which a transflective liquid crystal display device capable of performing both reflective display and transmissive display is constructed by forming a reflector which not only reflects light but also transmits light. According to the transflective liquid crystal display device as described above, reflective display is performed in normal conditions in which power consumption is low, and when necessary, transmissive display is performed in dark environments, whereby visibility can be ensured.
However, in an arrangement in which pixel electrodes are also used as a reflector, aluminum generally used as a reflector is exposed in manufacturing steps. Since aluminum has poor corrosion resistance, as is well known, in the arrangement described above, damage will be done to the aluminum, and hence, reflective properties as a reflector and electrical properties as electrodes may be degraded in some cases.
For example, among manufacturing processes for liquid crystal display devices, a process for forming an alignment film includes a step of coating a solution primarily composed of a polyimide resin or a polyamic acid dissolved in a polar solvent, such as N-methyl pyrrolidone (1-methyl-2-pyrrolidinone) or &ggr;-butyrolactone (4-hydroxy butyric acid &ggr;-lactone) and a following step of heating to 150 to 250° C. Accordingly, the probability of damaging the aluminum is high.
In addition, when the other electrodes opposing the reflective electrodes are formed of ITO (Indium Tin Oxide), a difference in polarity is generated between the aluminum electrode and the ITO electrode with the liquid crystal layer provided therebetween, and hence, long term reliability of the liquid crystal display device and display quality thereof are both degraded. These phenomena described above also occur when an aluminum alloy containing other atoms is used, even though the degree thereof may be different to some extent.
In the transflective liquid crystal display device described above, when transmissive display is performed, the contrast ratio is significantly decreased by light leakage from areas other than pixels, and hence, high quality display cannot be performed. In order to prevent a decrease in the contrast ratio due to light leakage, a shading layer may be additionally provided on a substrate opposing a substrate provided with a reflector, i.e., a substrate closer to an observer.
As a shading film, chromium or a black resin material is usually used. Among the materials mentioned above, chromium has high shading properties and can be formed to a thickness of 200 nm or less; however, since chromium is a metal material, the surface reflectance thereof is high. For example, the reflectance of monolayer chromium is high, such as approximately 60%, and the reflectance of low reflectance two-layer chromium is approximately 7%. Accordingly, when chromium is used for a shading film, since light incident from the observer side reflects at the surface of the shading film, there is a problem in that the contrast ratio in reflective display is decreased.
On the other hand, since a black resin material has a low reflectance, surface reflectance can be suppressed; however, since the shading properties of the black resin material is poor, in order to maintain an optical density of 2 or more which is required for transmissive display, the black resin material must be formed to be thick. Consequently, there are problems in that the flatness of the substrate is degraded, and since patterned width cannot be small, the opening area ratio is decreased as a result.
SUMMARY OF THE INVENTION
In consideration of the situation described above, the present invention is completed, and an object thereof is to provide a liquid crystal display device having superior reflective properties and high display quality, an electronic apparatus, and a substrate for use in the liquid crystal display device.
To these ends, the liquid crystal display device according to a first invention having a liquid crystal layer provided between a first transparent electrode formed at a first substrate side and a second transparent electrode formed at a second substrate side, comprises a reflector formed on a surface of the second substrate at the liquid crystal layer side so as to reflect at least light incident from the first substrate side, a shading film formed above the surface at the second substrate at the liquid crystal layer side so as to have an opening area corresponding to an intersection area at which the first transparent electrode and the second transparent electrode intersect each other, and a coloring layer formed above the surface of the second substrate at the liquid crystal layer side so as to cover the shading film.
According to the first invention, since the liquid crystal layer is provided between the first and the second transparent electrodes composed of the same type of material, the display quality and the long-term reliability of the liquid crystal display device are not degraded. In addition, on the reflector, since the shading film and the coloring layer are formed, so that the reflector is not to be exposed. Accordingly, in a manufacturing process of the liquid crystal display device, since the reflector will not be exposed to chemical reagents, gases, liquid crystal, and the like, damage done to the reflector can be avoided. Furthermore, since the coloring layer is formed so as to cover the shading film, the surface reflection at the shading film can be suppressed, and in addition, an optical density required for the shading film can be less. In particular, since light passes through the shading film twice in reflective display, even if the optical density is less, sufficient shading properties in practical use can be obtained when reflective display is primarily performed.
In the first invention, in the opening areas in the shading film, the reflector is preferably provided with first openings at which light passes therethrough. In the structure mentioned above, since the reflector will not function as an electrode, that is, since liquid crystal layer even at the first openings in the reflector is driven by the second transparent electrode, transmissive display can be performed by light passing through the openings. In transmissive display, since light is not determined by the opening areas in the shading film but is determined by the first openings provided in the reflector, an optical density required for the shading film can be determined only in consideration of reflective display.
In the first invention, the struct
Okamoto Eiji
Seki Takumi
Takizawa Keiji
Chawdhury Tarifur R.
Seiko Epson Corporation
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