Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1996-12-27
2001-10-30
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S187000, C349S106000, C349S138000
Reexamination Certificate
active
06310674
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to display device of various types including self-light emission type and non-self-light emission type, particularly a liquid crystal display device employing a liquid crystal as a display medium, and a process for producing the display device.
Heretofore, there has been generally used an electroconductive transparent film as a transparent electrode functioning as a display electrode of a display device, particularly a liquid crystal display device of a twisted nematic (TN)-type or a super twisted nematic (STN)-type, in view of several properties, such as a light transmittance, an electrical resistance and a mechanical strength.
As the electroconductive transparent film, a thin film of metal oxide, such as tin oxide or indium oxide, preferably indium oxide doped with tin (hereinbelow referred to as “indium-tin oxide (ITO)”) has been utilized.
Such an electroconductive transparent film, particularly an ITO film, has been known that has a high crystallinity and shows main peaks with respect to its crystal planes (Miller indices) (2, 2, 2) and (4, 0, 0) in X-ray diffractometry. The electroconductive transparent film is required to have a low sheet resistance and a high transparency as described above, thus resulting in a film produced by restricted processes and conditions. For this reason, there has been used a film having a high crystallinity (high-crystalline film) as the electroconductive transparent film. For example, in Japanese Laid-Open Patent Application (JP-A) 5-151827 (151827/1993), there has been proposed the use of a film of ITO having a large crystal particle size (at least 400 Å in <222> direction) from a viewpoint of surface roughening in order to improve its adhesiveness to a metal film disposed thereon.
However, such a high-crystalline transparent film (ITO film) has been accompanied with the following problems.
The high-crystalline transparent film has a large surface roughness, thus failing to provide a flat surface characteristic required for a display electrode. If the high-crystalline transparent film is used as a display electrode, the resultant display characteristic is insufficient. For instance, in where the high-crystalline transparent film has been used as a transparent electrode of a liquid crystal display device having a cell structure including a liquid crystal sandwiched between a pair of electrodes, an uneven surface of the transparent electrode has adversely affected some properties of the display device, such as an alignment control characteristic, particularly the property of providing uniform alignment state, to liquid crystal molecules.
More specifically, in the case of forming a ca. 100 nm-thick ITO film, when a high-crystalline ITO material is used, the resultant ITO film generally has a surface unevenness (surface roughness) of ca. 10-20 nm (100-200 Å) as a peak-to-peak (valley) value (i.e., a maximum difference in height) measured by using a scanning tunnel microscope (STM) although the resultant surface unevenness varies depending on film-forming processes and conditions. In case where such an ITO film is used as a display (transparent) electrode of the above-mentioned liquid crystal display device, an upper alignment control film (a film having an alignment control ability with respect to liquid crystal molecules) fails to exhibit a uniform property due to the above-mentioned uneven-surfaced ITO film, thus resulting in a film incapable of controlling an alignment state of the liquid crystal molecules uniformly in some cases. This problem is more noticeable when using a thinner alignment control film or when using a polymeric material for an alignment control film which has a high polymerization degree or a high rigidity which may not to readily produce a thin film formation.
Further, in case where, e.g., an organic film is formed on the above-mentioned uneven-surfaced ITO film and subjected to rubbing treatment to prepare an alignment control film, the resultant alignment control film causes not only an occurrence of film breakage but also failure of uniform rubbing in terms of micron-level rubbing over the entire surface of the alignment control film. Accordingly, such an alignment control film is liable to have ununiform properties and cause alignment defects or alignment irregularity of liquid crystal molecules.
Further, in the liquid crystal display device, at least one species of an insulating film for, e.g., preventing short circuit between oppositely disposed substrates is formed on an ITO film as a display electrode. In this case, if the high-crystalline ITO film is used, the insulating film has a nonuniform insulating performance due to surface unevenness of the ITO film, thus adversely affecting improvement in characteristics of the display device in some cases.
When the above-described ITO film is used as a display (transparent) electrode of a display device, the ITO film is generally patterned in a prescribed shape in accordance with, e.g., a pixel shape used.
In order to perform patterning of the ITO film, there has been generally practiced an etching treatment according to a photolithographic process after forming the ITO film by using, e.g., sputtering or vapor deposition. In this etching treatment, there have been generally used strong acids, such as hydrochloric acid-ferric chloride mixture liquid, hydrobromic acid and hydroiodic acid, as an etchant (etching liquid). Further, in order to prevent ununiform etching, an etchant comprising hydroiodic acid mixed with ferric chloride has been used. This etchant also falls under the category of strong acids.
In the etching treatment for providing a desired pattern to a transparent electrode by patterning of the ITO film, it is necessary to pay attention to an influence of the ITO film etching (patterning) on underlying layers. In this regard, e.g., in a production process of a color liquid crystal display device wherein a liquid crystal is disposed between a pair of glass substrates at least one of which is provided with a resinous color filter film and a resinous flattening (coating) layer disposed thereon, when a transparent electrode (ITO film) pattern is formed on the glass substrate having thereon the resinous layers (color filter film and the flattening layer) in the above-mentioned manner (etching with the strong acid-type etchant), chlorine ion and bromine ion contained in the etchant readily penetrate through the resinous layers to reach the surface of the glass substrate and form a salt with sodium (Na) ion thereat.
The above-mentioned strong acid-type etchant including hydrochloric acid-ferric chloride mixture liquid (pH=−1.52 to −1.22), hydrobromic acid (pH=1.58 to −1.28), hydroiodic acid (pH=−1.58 to −1.28 at 57 wt. % solution) and hydroiodic acid-ferric chloride (pH=−1.39 to −1.09 are reacted with a small amount of a metal component contained in the flattening layer to cause an occurrence of a peeling portion
32
and/or microcracks
33
with respect to a flattening layer
31
as shown in
FIG. 15
illustrating a schematic sectional view of a substrate provided with a color filter. Referring to
FIG. 15
, on a glass substrate
34
, a metal light-interrupting layer (called “black matrix”)
35
and a color filter layer (film)
30
are formed. On these layers
35
and
30
, the flattening layer
31
and a transparent electrode (ITO film)
36
are successively formed. In this type of a liquid crystal display device, patterning of the transparent electrode
36
is performed so as to correspond to a pattern of the color filter layer
30
to constitute display pixels.
Herein, each of the pH values of the above etchants is obtained as a value by subtracting 2 from a reference pH value measured by means of a pH meter by using an aqueous solution of a sample etchant (sample etchant:water=1:100 by weight) prepared by diluting the etchant with water.
As described above, under the influence of the etching treatme
Danjo Keishi
Masaki Yuichi
Suzuki Yoshiaki
Canon Kabushiki Kaisha
Sikes William L.
Ton Toan
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