Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-05-24
2004-06-08
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S114000, C349S149000
Reexamination Certificate
active
06747723
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to reflective and transflective liquid crystal devices which use silver alloys and the like to reflect light, to a method for making the same, and to electronic apparatuses using the liquid crystal devices as display sections.
2. Description of the Related Art
As is well known, liquid crystal devices do not emit light but performs display by controlling the polarization state of light. Thus, it is necessary that the configuration be such that light is incident on a panel of the liquid crystal device, and in this regard, they are quite different from other display devices, such as electroluminescent devices and plasma display devices.
Incidentally, the liquid crystal devices are classified into two types, that is, a transmissive type having a light source provided behind a panel such that the light passing through the panel can be observed by a viewer, and a reflective type in which a light source is arranged at the front side of the panel (or is not arranged) and the light incident from the front face is reflected by the panel and can be observed by a viewer.
In the transmissive type, the light emitted from the light source provided at the rear side of the panel is introduced to the entire panel through a light guide plate. Then, the light passes through a polarizer, a back substrate, an electrode, a liquid crystal, another electrode, a viewer-side substrate, and another polarizer and is observed by the viewer.
On the other hand, in the reflective type, the light incident on the panel passes through a polarizer, a viewer-side substrate, an electrode, a liquid crystal, and another electrode, is reflected by a reflective film, and passes through the path in the reverse direction, and is observed by a viewer.
As described above, the reflective type needs two paths including an incident path and a reflected path and large optical losses occur in both paths. Compared to the transmissive type, the amount of light from the surrounding environment (external light) is less than that of a light source disposed at the rear side of the panel. Since only a small amount of light is observed by the viewer, the display becomes dim. However, the reflective type also has noticeable advantages, such as high outdoor visibility under sunlight and an ability to display without a light source, compared with the transmissive type. Thus, the reflective liquid crystal display devices are widely used in display sections of portable electronic apparatuses and the like.
The reflective type, however, has a notable disadvantage in that the viewer cannot see the display when insufficient natural illumination is provided from the environment. In recent years, a transflective type has appeared in which a backlight is provided at the rear face of a panel, and a reflective film not only reflects the light incident from the viewer's side but also transmits some of the light from the rear face. This transflective type functions both as a transmissive type by switching on the backlight to ensure visibility of the display when there is insufficient external light and as a reflective type by switching off the backlight in order to reduce power consumption when there is sufficient external light. This means, the transmissive type or the reflective type is selected depending on the intensity of the external light to ensure visibility of the display and to reduce power consumption.
In the reflective type and the transflective type, aluminum has been generally used as a material for the reflective film. However, in recent years, the use of elemental silver or a silver alloy primarily composed of silver (hereinafter referred to as merely “silver alloy”) has been investigated to improve reflectance for achieving bright display.
It is not desirable that one electrode used for applying a voltage to the liquid crystal is also used as a reflective layer to simplify the configuration. When this electrode is formed of the silver alloy and the other electrode is formed of a transparent conductive material such as indium tin oxide (ITO) which meets the transparency requirement, irregularity of polarization occurs by sandwiching the liquid crystal with different metals. Furthermore, in a configuration in which only an alignment film is present between the liquid crystal and the silver alloy, impurities in the silver alloy are dissolved into the liquid crystal through the alignment film, and may cause deterioration of the liquid crystal itself.
Thus, the electrode on the substrate provided with the reflective layer cannot be formed of the silver alloy and must be formed of the same transparent conductive material which is used as the electrode of the other substrate. Accordingly, the substrate provided with the reflective layer must use at least two metals, that is, the silver alloy used as the reflective layer and the transparent conductive material as the electrode.
Incidentally, the silver alloy exhibits high conductivity, in addition to high reflectance, and the use thereof as a lead layer of the substrate is being investigated. When the silver alloy used as the reflective layer is also used as the lead layer, the silver alloy must be put into contact with the transparent conductive material used as the electrode for electrical connection therebetween.
Since the silver alloy exhibits poor adhesiveness to other materials, the alloy is damaged by mechanical friction and moisture penetrating from the interface causes corrosion, separation, and the like. As a result, it is difficult to complete a highly reliable liquid crystal display device.
Accordingly, the object of the present invention is to provide a liquid crystal device having high reliability when a silver alloy is used as both a reflective layer and a lead layer, a method for making the same, and an electronic apparatus.
SUMMARY OF THE INVENTION
A liquid crystal device according to an aspect of the present invention comprises a first substrate and a second substrate opposing each other and a liquid crystal enclosed in a gap between the first substrate and the second substrate, and the liquid crystal device further comprises an underlying film provided on the first substrate, a reflective conductive film which is formed on the underlying film and which contains silver, and a metal oxide film which is deposited on the reflective conductive film and which is patterned so that the edge portion of the metal oxide film comes into contact with the underlying film. According to this configuration, the reflective conductive film is covered by the metal oxide film and the metal oxide film is patterned so that the edge portion thereof comes into contact with the underlying film; hence, the surface of the reflective conductive film is not exposed after the metal oxide film is formed. Thus, the reliability of the reflective conductive film containing silver is improved.
Preferably, the underlying film comprises a metal oxide. The reflective conductive film is thereby sandwiched by the two metal oxides. Since the metal oxides have high adhesiveness, moisture barely penetrates into the reflective conductive film through the interface between the underlying film containing the metal oxide and the metal oxide film deposited on the reflective conductive film.
Incidentally, the reflectance vs. wavelength relationship of the reflective conductive film containing silver is not so flat as that of aluminum (Al) which is generally used, and tends to decrease at the shorter wavelength end (see to FIG.
7
). As a result, the light reflected by the reflective conductive film less contains the blue light component and thus is yellowish. Thus, a reflective layer reflecting blue light is preferably provided on the upper face of the reflective conductive film. As a result of such a configuration, large amounts of blue light components are reflected by the reflective layer before the blue light component is reflected by the reflective conductive film, preventing that all light reflected by the reflective l
Hanakawa Manabu
Hinata Shoji
Chowdhury Tarifur R.
Harness & Dickey & Pierce P.L.C.
Schechter Andrew
Seiko Epson Corporation
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