Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-02-08
2003-10-28
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S129000
Reexamination Certificate
active
06639640
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD), and more particularly to improving image display of a LCD in which a source line is formed overlapping pixel electrodes.
2. Description of the Related Art
A vertical orientation type LCD comprising liquid crystal having negative anisotropy of dielectric constant and a vertical orientation film has been proposed in, for example, JPA H06-301036. An LCD of this type is described below.
FIG. 1A
is a plan view showing such a LCD, and
FIG. 1B
shows a cross-sectional view taken along line A-A′ of
FIG. 1A. A
gate line
51
is formed on a first substrate
50
, and a gate insulating film
52
is formed covering the gate line
51
. The gate line
51
comprises gate electrodes
51
a
within a portion of each pixel. Over these portions, poly-silicon film is provided in the form of discrete islands so as to cross over the gate electrodes
51
a
. The poly-silicon film is then doped with impurities to create, together with the gate electrodes
51
a
, thin film transistors (TFT)
54
. An interlayer insulating film
55
is formed over these components, and a data line
56
is superimposed on the interlayer insulating film
55
. Subsequently provided is a planarizing film
57
, and pixel electrodes
58
composed of ITO (indium tin oxide) are formed thereon. Each pixel electrode
58
is connected to a TFT
54
via a contact hole opened through the interlayer insulating film
55
and the planarizing film
57
. The data line
56
is formed overlapping under the pixel electrode
58
. The data line
56
is connected to the source regions of the TFTS
54
and supplies electric charges to the pixel electro des
58
when the gate electrodes
51
a
are turned on. Formed over the pixel electrodes
58
is a vertical orientation film
59
made of an organic material such as polyimide or of an inorganic silane material. Rubbing processing is not performed on the vertical orientation film
59
.
Provided on a second substrate
60
arranged opposing the first substrate
50
are color filters
66
in positions corresponding to the pixel electrodes
58
. Each color filter is colored either one of red (R), green (G), and blue (B), or alternatively, cyan, magenta, and yellow. Over the color filters
66
, a common electrode
61
composed of ITO or a similar material is formed extending in a region over a plurality of pixel electrodes
58
. A vertical orientation film
62
identical to the one disposed on the first substrate
50
is provided over the common electrode
61
. Orientation control windows
63
, i.e. regions where no electrode is present, are formed in the common electrode
61
. The orientation control windows
63
may have a shape of two letter Y's connected at their bottoms.
Liquid crystal
70
is sealed between the first and second substrates
50
,
60
. The orientation of liquid crystal molecules is controlled in accordance with the strength of electric field generated by a voltage applied between the pixel electrodes
58
and the common electrode
61
. On the outer side of the first substrate
50
and the second substrate
60
, polarizers (not shown) are arranged such that their polarization axes are perpendicular to one another. Linearly polarized light that travel between the polarizers is modulated while passing through the liquid crystal
70
controlled to different orientations in the respective display pixels. The light is thereby controlled to achieve desired transmittance.
The liquid crystal
70
has negative anisotropy of dielectric constant. That is, the liquid crystal
70
has the property to orient such that the longitudinal axes of its molecules become perpendicular to the direction of the electric field. The vertical orientation films
59
,
62
control the initial orientation of the liquid crystal
70
to the vertical direction. When no voltage is applied, the liquid crystal molecules are oriented vertically with respect to the plane of the vertical orientation films
59
,
62
. In this case, the linearly polarized light that has passed through one of the polarizers passes through the liquid crystal layer
70
, but is obstructed by the other polarizer. The resulting display is seen as black.
In the above-described arrangement, a voltage is applied between a pixel electrode
58
and the common electrode
61
to generate electric fields
64
,
65
which tilt the liquid crystal molecules. At end portions of the pixel electrode
58
, electric field
64
curves from the pixel electrode
58
towards the common electrode
61
. Similarly due to the absence of any electrodes, electric field
65
curves towards the pixel electrode
58
at edges of an orientation control window
63
. The curved electric fields control the orientation of the liquid crystal by tilting the molecules towards the inboard of the pixel electrode
58
and towards the orientation control window
63
.
In regions directly underneath orientation control windows
63
, no electric field is generated during voltage application because the common electrode
61
is absent. Liquid crystal molecules are therefore fixed in the initial orientation state, namely, the vertical direction. This allows regions of the liquid crystal on the respective sides of the orientation control window
63
to be oriented in opposing directions due to the continuous property of liquid crystal. As a result, a display with a broad viewing angle can be obtained.
The controller of the liquid crystal orientation is not limited to orientation control windows
63
. Alternatively, slope portions may be disposed in the vertical orientation films
59
,
62
on the sides contacting the liquid crystal
70
. Details concerning this point are found in Japanese Patent Application No. Hei 6-104044 (JPA H07-311383) filed by the present applicant.
The voltage application scheme of the LCD is next explained.
FIG. 2
is a timing chart showing voltages applied to gate lines
51
and data lines
56
, and voltages of pixel electrodes driven by those applied voltages. FIGS.
2
(
a
),
2
(
b
), and
2
(
c
) illustrate the voltages applied to mth gate line, m+1th gate line, and a data line, respectively. FIG.
2
(
d
) indicates the voltage of a pixel electrode controlled by the mth gate line and the data line. FIG.
2
(
e
) indicates the voltage of a pixel electrode controlled by the m+1th gate line and the data line. During one horizontal synchronization period (referred to hereinafter as 1H), a voltage is applied to the mth gate line to switch it on. When the mth gate line is switched on, TFTs of pixel electrodes in the associated row are accordingly turned on. During 1H, voltages according to an image to be displayed are applied to the respective data lines, and each of these voltages is retained by a pixel electrode in that row. In the next 1H, the mth gate electrodes are turned off while the m+1th gate electrodes are turned on. Accordingly, TFTs of pixel electrodes associated with the m+1th gate electrodes are turned on. Voltages in the data lines
56
are then retained by the pixel electrodes in this row. Similar procedures are repeated to apply voltages to each row of pixel electrodes
58
and to drive associated liquid crystal, thereby displaying an image. During these procedures, the direction of electric field is inverted for each adjacent rows to prevent degradation of liquid crystal. Specifically, the pixel electrodes in the row controlled by mth gate line may be applied with voltage V
high
(10V) higher than the potential Vc of the common electrode
63
(6V, for example) by a predetermined potential (4V, for example), while applying an inverted voltage V
low
(2V), i.e. a voltage lower than the potential Vc of the common electrode
63
by the predetermined potential, to the pixel electrodes of the adjacent row. When again applying a voltage to the pixel electrodes of the row associated with mth gate line, the inverted voltage of the previously applied voltage, namely, V
low
, is applied. Such a voltage application s
Maeda Kazuyuki
Matsuoka Hideki
Oima Susumu
Hogan & Hartson LLP
Parker Kenneth
Sanyo Electric Co,. Ltd.
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