Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-02-23
2002-04-02
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S111000, C430S007000
Reexamination Certificate
active
06366332
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a display apparatus, particularly a color display apparatus, and a process for producing the display apparatus. More specifically, the present invention relates to a display apparatus including an electrode plate provided with a masking member improved in various properties (particularly optical properties) and productivity, and a process for production of the display apparatus.
Heretofore, a color display apparatus using a CRT (cathode-ray tube) has generally been used.
In recent years, however, various color liquid crystal apparatus have attracted considerable attention as a color display apparatus replacing the above CRT display apparatus.
FIG. 1
shows an example of such color liquid crystal apparatus.
Referring to
FIG. 1
, a liquid crystal display apparatus
1
includes a liquid crystal panel P and a backlight unit B.
The liquid crystal panel P includes a pair of glass substrates disposed opposite to and in parallel with each other and comprising a first (upper) glass substrate
3
and a second glass (lower) substrate
2
. The second (lower) glass substrate
2
is provided with color filters (i.e., color filter segments)
5
of primary colors (red (R), green (G) and blue (B)) disposed with prescribed spacings at which a masking (light-interrupting) film
6
comprising a metal such as chromium (Cr) is disposed. The color filters
5
and the masking film
6
are covered with a protective film
7
on which a multiplicity of stripe-shaped (transparent) electrodes
9
are formed to prepare a second electrode plate. On the other hand, the first (upper) glass substrate
3
is also provided with a multiplicity of stripe-shaped (transparent) electrodes
10
disposed perpendicular to the stripe-shaped electrodes
9
to prepare a first electrode plate. These first and second glass substrates
3
and
2
(electrode plates) are applied to each other via a liquid crystal layer
11
.
The color filters
5
may be formed by using processes including a dyeing process, a pigment-dispersion process and a combination of a sputtering process and a photolithographic process. The masking film
6
may be formed through a sputtering process and a subsequent photolithographic process.
On the back side of the liquid crystal panel P, a backlight unit (illumination means) for illuminating the liquid crystal panel P is disposed so as to face the first glass substrate
3
as shown in FIG.
1
.
When the liquid crystal panel P is driven, liquid crystal molecules of the liquid crystal layer
11
are caused to effect switching for each pixel. Further, when the backlight unit B is driven (actuated), the liquid crystal panel P is illuminated with light issued from the backlight unit B (hereinbelow, referred to as “backlight or illuminating light”), whereby transmitted light fluxes of the backlight (illuminating light) provide various information as color display images depending on combinations thereof with the color filter segments through which the backlight passes. Between the spacings of the color filter segments of the color filter
5
, the masking film
6
is disposed as mentioned above, whereby it is possible to prevent mixing of the primary colors to improve a contrast.
However, the above liquid crystal apparatus was accompanied with a problem such that light issued from a viewer side indicated as “A” in
FIG. 1
(hereinbelow, referred to as “external light” illuminating the panel in a direction opposite to that of the backlight) was reflected by the masking film
6
to lower a display quality of the liquid crystal panel P.
In order to solve the problem, the use of a masking film
16
or
26
(as shown in
FIG. 2A
or
2
B) having a lamination structure comprising two or three layers has been proposed in, e.g., Japanese Laid-Open Patent Application (JP-A) 2-144525 and 61-235819. Referring to
FIG. 2A
, the masking film
16
includes a first layer
16
a
consisting of a metal (chromium) film disposed on the second substrate
2
and a second layer
16
b
consisting of a metal oxide (chromium oxide) film disposed on the first layer
16
a.
Similarly, referring to
FIG. 2B
, the masking film
26
has a lamination structure including a second layer
26
b
consisting of a metal (chromium) film disposed between first and third layers
26
a
and
26
c
each consisting of a metal oxide (chromium oxide) film. These masking films
16
and
26
are designed to retain a good display quality by the metal oxide film(s) (the first and third layers
16
a,
26
a
and
26
c
) effective in decreasing a degree of the reflection of the external light and to ensure a sufficient light-interrupting property.
These masking films
16
and
26
are generally formed through a sputtering process. In the sputtering process, in case where a batch-type sputtering apparatus, it is necessary to adopt different sputtering conditions for forming the metal film and the metal oxide film. For this purpose, there has been used several methods including: (i) one wherein a mixture gas of Ar and O
2
(as an ambient gas) and a metal target (chromium in the above case) are used for forming a metal oxide film (e.g., the first layers
16
a
and
26
a
shown in
FIGS. 2A
an
2
B) and then the ambient gas is replaced by an Ar gas while using the metal target as it is for forming a metal film (e.g., the second layers
16
b
and
26
b
shown in FIGS.
2
A and
2
B), and (ii) one wherein an ambient gas of Ar and a metal oxide target are used for forming a metal oxide film (e.g., the first layers
16
a
and
26
a
) and then the metal oxide target is replaced by a metal target without changing the ambient Ar gas for forming a metal film (e.g., the second layers
16
b
and
26
b
).
Further, as a method not using a batch process, it is possible to apply a method using a continuous-type (or load lock-type) sputtering apparatus wherein a substrate is transferred from a first chamber charged with a mixture gas of Ar and O
2
for forming a metal oxide film (e.g., the first layers
16
a
and
26
a
) to a second chamber partitioned with a gate valve by the first chamber and charged with an Ar gas for forming a metal film (e.g., the second layers
16
b
and
26
b
).
The thus formed metal oxide and metal films constituting a lamination structure are then subjected to patterning through a photolithographic process to form a patterned masking film having the lamination structure.
However, the above-described masking films
16
and
26
prepared in the above manner were accompanied with several problems due to their lamination structures.
More specifically, it was difficult to design a lamination structure capable of keeping a balance of a decreased degree of the external light reflection (i.e., a decreased reflectance) and an improvement in light-interrupting property in the case of the masking films including the above-described combinations of the metal oxide film and the metal film. Further, in the conventional lamination structure of the masking film as described above, the metal oxide film and the metal film showed different etching degrees at the time of patterning by the photolithographic process, thus causing uneven (stepwise) side surfaces or a stepwise difference in width with respect to the metal and metal oxide films (i.e., a wider metal oxide film and a narrower metal film) to deteriorate a display quality of the liquid crystal panel P. In the case of using a sputtering target of a metal oxide, there arises a problem with respect to mass production, such as a slow sputtering rate and a crack in (or breakage of) the target. Further, in case where the continuous-type sputtering apparatus is used, the apparatus is accompanied with problems, such as an expensive apparatus and complicated film-forming steps, thus resulting in an increase in production cost.
In order to lower a degree of the external light reflection, it is necessary to appropriately control an oxygen content of a metal oxide film used so as to provide the metal oxide film with an extinction coefficient within an approp
Kameyama Makoto
Sawamura Mitsuharu
Suzuki Hiroyuki
Yoshikawa Toshiaki
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Ton Toan
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