Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-03-14
2003-07-22
Ngo, Julie (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S129000, C349S130000, C349S143000, C349S144000
Reexamination Certificate
active
06597423
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) and in particular to improvement of display quality of a vertically aligned LCD having an alignment control window.
2. Description of the Related Art
A vertically aligned LCD having an alignment control window is proposed, for example, in Japanese Patent Laid-open No. Hei 6-301036, in which alignment direction of liquid crystal is controlled. The vertically aligned LCD has liquid crystal having negative dielectric constant anisotropy and a vertically aligned film. In the following, an LCD of this type will be described.
FIG. 6A
is a plan view showing an LCD having an alignment control window, and
FIG. 6B
is a cross sectional view of the LCD along the line A-A′ in
FIG. 6A. A
gate line
51
is formed on a first substrate (TFT substrate)
50
, and covered by a gate insulating film
52
. On the insulating film
52
there is formed a thin film transistor (TFT)
53
comprising a polysilicon film. A part of the gate line
51
constitutes a gate electrode for the TFT
53
. Covering the above, an interlayer insulating film
54
is formed, on which a pixel electrode
55
, comprising indium tin oxide (ITO), is formed being connected to the TFT
53
via a contact hole formed on the interlayer insulating film
54
. On the pixel electrode
55
there is formed a vertically aligned film
56
, comprising an organic material, such as polyimide, or an inorganic material, such as silane material. The interlayer insulating film
54
consists of two layers, including an interlayer insulating film
54
a
having a data line
57
formed thereon. The data line
57
, connected to a source region of the TFT
53
, supplies charges to the pixel electrode
55
when the gate line
51
is turned on. Note that the data line
57
is formed below the pixel electrode
55
in order to prevent the liquid crystal from being caused to slant directly by the voltage applied to the data line
57
.
A second substrate
60
is located as it is opposing the first substrate
50
, having a color filter
61
formed thereon at a position corresponding to the pixel electrode
55
. Further, a common electrode
63
, comprising ITO or the like, is formed via the insulating film
62
on the second substrate
60
, opposing the plurality of pixel electrodes
55
. Similar to the first substrate
50
side, a vertically aligned film
64
is formed on the common electrode
63
. The common electrode
63
has an alignment control window
65
formed thereon at a position corresponding to the pixel electrode
55
. An alignment control window
65
, or an opening on the common electrode in absence of an electrode, has a shape resembling, for example, a “Y” and a inverted “Y” connected together, specifically, having branching upper and lower ends.
Liquid crystal
70
is enclosed between the first and second substrates
50
,
60
. Direction, or alignment, of the liquid crystal molecules is controlled according to the strength of an electric field formed by the voltage applied to between the pixel electrode
55
and the common electrode
63
. Polarizers (not shown) are respectively provided on the outside of the first and second substrates
50
,
60
, with the polarizing axes thereof being vertical. A straight polarization (light) proceeding from one polarizer to the other is modulated while passing through the liquid crystal
70
, to thus achieve a desired transmittance, the liquid crystal
70
being controlled for every display pixel to have an alignment corresponding to the applied voltage to the pixel electrode.
The liquid crystal
70
has negative dielectric constant anisotropy, and slants, by nature, relative to the direction of an electric field. The liquid crystal
70
is controlled to have vertical initial alignment by vertically aligned films
56
,
64
. In this case, with no voltage applied, the liquid crystal molecules are aligned vertically with respect to the vertically aligned films
56
,
64
. Therefore, the straight polarization having gone through the polarization panel on one side, proceeds through the liquid crystal layer
70
to reach and be shielded by the polarization panel on the other side, as a result of which a black is display is shown. When a voltage is applied to between the pixel electrode
55
and the common electrode
63
in the above structure, electric fields
66
,
67
are generated, whereby the liquid crystal molecules are caused to slant. In particular, around the edges of each pixel electrode
55
, the caused electric field
66
is vertical directing from the pixel electrode
55
toward the common electrode
63
. Similarly, around the edges of each alignment control window
65
, the caused electric field
67
is vertical directing toward the pixel electrode
55
due to the absence of an electrode. As the liquid crystal molecules are controlled to be aligned vertically with respect to this vertical electric fields, the molecules are resultantly forced to slant directing toward the inner side of each pixel electrode
55
, i.e., the alignment control window
65
. As a result, the straight polarization having penetrated the polarizer on one side is subjected to birefringence in the liquid crystal layer
70
to be thereby converted into elliptically polarized light before passing through the polarizer on the other side. With the above, a nearly white color is displayed.
The pixel electrode
55
is supplied with a voltage via the TFT, when the gate line
51
and the data line
57
are both turned on to drive the liquid crystal immediately thereabove. Application of appropriate voltages to the respective pixel electrodes
55
could achieve LCD display. That is, an area with a pixel electrode
55
formed thereon constitutes a pixel.
In a part immediately below the alignment control window
65
, an electric field is not caused despite voltage application due to the lack of common electrode
63
, and liquid crystal molecules in that part therefore remain in the initial state, or fixed directing in a vertical direction. As a result of the above, liquid crystal molecules on both sides of the alignment control window
65
have opposite alignments due to continuity of liquid crystal, and this contributes to ensuring a wider viewing angle.
An LCD voltage application method will next be described.
FIG. 7
is a timing chart for voltages to be applied to the gate lines
51
and the data line
57
, and for a voltage of a pixel electrode driven thereby. (a), (b), and (c) show voltages to be applied to the first gate line
51
, the second gate line
51
, and the data line
57
, respectively, the second gate line
51
being positioned next to the first gate line
51
. (d) and (e) show voltages of the pixel electrode
55
to be controlled by the first gate line
51
and the data line
57
, and of the pixel electrode
55
to be controlled by the second gate line
51
and the data line
57
.
A voltage is applied to the first gate line
51
during one horizontal synchronization period (hereinafter denoted as
1
H), so that the gate line
51
is turned on to thereby turn on the TFTs
53
of the associated arrayed pixel electrode
55
on the first horizontal line. In addition, voltages corresponding to a display image are continuously applied to the respective data lines
57
during a period
1
H, so that the arrayed pixel electrodes
55
with turned-on TFTs can retain their voltages. During the next period
1
H, the first gate line
51
is turned off, while the second gate line
51
is turned on. Accordingly, the TFTs of the pixel electrodes
55
corresponding to the second gate line
52
are turned on, and the pixel electrodes
55
connected to the TFTs on the second horizontal line can retain their voltages supplied from the data line
57
. Subsequently, a voltage is supplied to pixel electrodes
55
in each row for every period
1
H to thereby drive associated liquid crystal for image display. Here, an electric field is caused in an opposite direction for every pixel electrode row in order to prevent dete
Nishikawa Ryuji
Oima Susumu
Hogan & Hartson LLP
Ngo Julie
Sanyo Electric Co,. Ltd.
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