Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2003-01-21
2004-09-14
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S054000, C349S192000
Reexamination Certificate
active
06791634
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device.
2. Description of the Related Art
Liquid crystal display devices are space-saving, easily portable, and lightweight display devices with low power dissipation, and are extensively used today as displays for notebook computers, TV sets with a reduced thickness and cell phones. Among other things, a super twisted nematic (STN) mode liquid crystal display device has found applications in a broad variety of electronic appliances including cell phones. This is because an STN mode liquid crystal display device has a relatively simple structure and is less expensive.
FIG. 13
is a perspective view schematically illustrating the structure of a conventional STN mode liquid crystal display device. As shown in
FIG. 13
, the STN mode liquid crystal display device includes two substrates
100
and
102
that face each other and a liquid crystal layer
104
interposed between these substrates
100
and
102
. On one surface of one substrate
100
, multiple striped common lines
106
are provided so as to face the liquid crystal layer
104
. On one surface of the other substrate
102
, multiple striped segment lines
108
are provided so as to face the liquid crystal layer
104
, too. The direction in which the segment lines
108
extend is perpendicular to the direction in which the common lines
106
extend. In this STN mode liquid crystal display device, when a voltage is created between one common line
106
and one segment line
108
, a portion of the liquid crystal layer
104
, located at the intersection between these lines
106
and
108
, is driven by the voltage applied thereto. These common and segment lines
106
and
108
also function as pixel electrodes and are made of a transparent conductive film such as an ITO film.
However, this STN mode liquid crystal display device has no active components as switching elements. Accordingly, the voltage to be applied to the liquid crystal layer is inconstant (i.e., the voltage applied cannot be retained constantly enough). For that reason, a liquid crystal display device of this type cannot fully satisfy various requirements including multi-gray-scale display (in 4,096 or 6,500 colors, for example), high resolution and high contrast ratio.
Thus, a modified STN mode liquid crystal display device, in which active components are provided for respective pixels, was proposed. In a liquid crystal display device of this newly proposed type, a data signal is supplied to one of striped data electrodes on a counter substrate, and a reference signal voltage (i.e., a common voltage) is applied to a pixel electrode that is connected to its associated switching element. This type of liquid crystal display device will be referred to herein as a “data-to-counter-electrode” type liquid crystal display device. A liquid crystal display device of this type is disclosed in U.S. Pat. No. 4,694,287, for example. Hereinafter, the data-to-counter-electrode type liquid crystal display device disclosed in the United States patent identified above will be described with reference to FIG.
14
.
As shown in
FIG. 14
, multiple three-terminal switching elements (i.e., TFTs)
112
and pixel electrodes
114
are arranged in columns and rows (i.e., in matrix), and multiple gate lines
116
and multiple reference signal lines
118
are arranged in the row direction, on one surface of one substrate
110
so as to face a liquid crystal layer. The three terminals of each TFT
112
are connected to its associated pixel electrode
114
, gate line
116
and reference signal line
118
, respectively. In response to a gate signal that has been supplied to the gate electrode of a TFT
112
through its associated gate line
116
, the TFT
112
is turned ON. Then, a reference signal voltage (i.e., common voltage) is applied through its associated reference signal line
118
to its associated pixel electrode
114
by way of the TFT
112
in ON state.
On the surface of the counter substrate
120
, multiple striped data electrodes
122
are provided so as to face the liquid crystal layer and cross the gate lines
116
and reference signal lines
118
substantially at right angles when this device is viewed from above. A data (or video) signal is supplied to each of these data electrodes
122
. A portion
124
of each data electrode
122
that faces its associated pixel electrode
114
also functions as a counter electrode.
Generally speaking, very precise processing on the order of several microns is required to fabricate a liquid crystal display device. Thus, if dust is deposited on, or a tiny scratch is done on, a liquid crystal display device being fabricated, then current leakage or disconnection is likely caused in the final product. Recently, a liquid crystal display device needs to increase the number of colors to display or its resolution and minimize the non-display area around its periphery. Accordingly, it is often necessary to pattern a conductive film into a desired shape on a color filter layer, an overcoat resin or a stepped portion. The interconnects of a liquid crystal display device also need to decrease their widths. Under the circumstances such as these, the current leakage, disconnection and other defects happen more and more often, which is a major factor of unwanted decrease in production yield.
To overcome these problems, Japanese Laid-Open Publication No. 3-85525, for example, discloses an active-matrix-addressed liquid crystal display device including a spare line to repair a disconnection.
In the liquid crystal display device disclosed in the publication identified above, the spare line to repair a disconnected source or gate line is provided on an active-matrix substrate. That is to say, the spare line and the line to be repaired are located on the same substrate.
In the data-to-counter-electrode type liquid crystal display device shown in
FIG. 14
, the striped data electrodes
122
are formed on the counter substrate
120
by patterning a transparent conductive film such as an ITO film. Defects such as disconnection of one of these data electrodes
122
often happen on the counter substrate
120
. Thus, to repair such a disconnected data electrode
122
, a spare line may be provided as in the active-matrix-addressed liquid crystal display device described above for the substrate
120
including the data electrodes
122
.
Hereinafter, such a liquid crystal display device will be described with reference to
FIGS. 15A through 15C
and
FIGS. 16A and 16B
.
FIGS. 15A and 15B
are plan views of the two substrates
120
and
110
, respectively.
FIG. 15C
is transparent plan view of the liquid crystal display device.
FIGS. 16A and 16B
are partial cross-sectional views of the liquid crystal display device shown in
FIG. 15C
as taken on the planes XVIa—XVIa and XVIb—XVIb, respectively. Each of the components of this liquid crystal display device, having substantially the same function as the counterpart shown in
FIG. 14
, will be identified by the same reference numeral and the description thereof will be omitted herein.
In this liquid crystal display device, a spare line
124
to repair any defective data electrode
122
is provided on the substrate
120
on which the data electrodes
122
are located as shown in FIG.
15
A. The substrate
120
including the data electrodes
122
and spare line
124
will be referred to herein as a “first substrate” for convenience sake. In this structure, if any of the data electrodes
122
has been disconnected, then a gray-scale signal (i.e., data signal) that should have been supplied to the disconnected data electrode
122
is input through the input terminal
132
of the spare line
124
.
In the data-to-counter-electrode type liquid crystal display device shown in
FIGS. 15A through 15C
, the input terminals
122
A of the data electrodes
122
and the input terminal
132
of the spare line
124
are provided on the first substrate
120
. On the other hand, a driver circuit (such as a driver IC)
128
to supply sig
Fujiwara Koji
Ichioka Hideki
Inoue Naoto
Tanaka Keiichi
Yamamoto Tomohiko
Chowdhury Tarifur R.
Nixon & Vanderhye P.C.
Schechter Andrew
Sharp Kabushiki Kaisha
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