Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2000-03-07
2004-08-31
Choadhury, Tanifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S038000
Reexamination Certificate
active
06784949
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to active matrix substrates for use in, for example, liquid crystal display devices and flat-panel-type image sensors, and methods of manufacturing such substrates, and further relates to image sensors incorporating such active matrix substrates.
BACKGROUND OF THE INVENTION
An active matrix substrate for use in, for example, a liquid crystal display device is primarily constituted by electrode wires that are signal lines and scanning lines disposed in a matrix, pixel electrodes each provided for a pixel that is encircled by the signal lines and the scanning lines, and switching elements.
Each of the switching elements, if it is of a double terminal type, is connected to one of the pixel electrodes as well as to either one of the signal lines or one of the scanning lines, and if it is of a triple terminal type, is connected to one of the pixel electrodes, one of the signal lines, and one of the scanning lines. AS the scanning line receives a predetermined voltage signal, the switching element is turned on, causing the image signal (electric potential) applied to the signal line to be transmitted to the pixel electrode. Well-known examples of switching elements for selectively driving pixel electrodes typically include TFT (Thin Film Transistor) elements of a triple terminal type and MIM (metal-insulating film-metal) elements of a double terminal type.
As shown in FIG.
9
through
FIG. 11
, in an active matrix substrate constituting a part of a liquid crystal display device that includes TFT elements (hereinafter, will be referred to simply as TFTs) as switching elements, the pixel is primarily constituted by electrode wires that are two signal lines
101
and two scanning lines
102
disposed in a matrix, a pixel electrode
103
provided for a pixel area that is encircled by the signal lines
101
and the scanning lines
102
, and a TFT
104
.
Note that
FIG. 10
is a cross-sectional view taken along line F-F′ in FIG.
9
and that
FIG. 11
is a cross-sectional view taken along line G—G′ in FIG.
9
.
The TFT
104
has a gate electrode
106
connected to one of the scanning lines
102
, a source electrode
107
connected to one of the signal lines
101
, and a drain electrode
108
connected to the pixel electrode
103
and also to one of two terminals (transparent electrode layer
112
) of a pixel capacitor (storage capacitor)
105
a
which will be discussed later. As a scanning signal is coupled to the scanning line
102
, it drives the TFT
104
, causing an image signal (video signal) coupled to the signal line
101
to be transmitted through a source electrode
107
and a drain electrode
108
and applied to the pixel electrode
103
.
In the foregoing active matrix substrate, as shown in
FIG. 11
, the pixel capacitor
105
a
for storing the image signal applied to the pixel electrode
103
is constituted by a gate insulation film
110
, as well as a pixel capacitor electrode (storage capacitor electrode)
105
and a transparent electrode layer
112
that are disposed opposing each other across a gate insulation film
110
. The pixel capacitor electrode
105
doubles as a pixel capacitor common wire (storage capacitor common wire) that commonly connects a plurality of the pixel capacitors
105
a
together that are located parallel to the scanning lines
102
, and is coupled to an opposite electrode on an opposite substrate (not shown) when incorporated in a liquid crystal cell.
FIG.
12
(
a
) through FIG.
12
(
h
) and FIG.
13
(
a
) through FIG.
13
(
h
) illustrate a manufacturing process of the active matrix substrate, where gate electrodes
106
and pixel capacitor electrodes
105
are formed on an insulating transparent substrate
109
, and subsequently, a gate insulation film
110
, a semiconductor layer
111
, a n
+
-Si layer (corresponding to source electrodes
107
and drain electrodes
108
), a transparent conductive layer
112
, a metal layer
113
, a protection film
114
, an interlayer insulation film
115
, and a transparent conductive layer constituting pixel electrodes
103
are deposited and patterned in this order. The transparent conductive layer
112
and the metal layer
113
connected to the source electrodes
107
of the TFTs
104
constitute signal lines
101
.
In the active matrix substrate, the pixel electrode
103
is connected to the drain electrode
108
of the TFT
104
through a contact hole
116
formed through the interlayer insulation film
115
. Meanwhile, the pixel electrode
103
(see
FIG. 9
) is separated from the signal lines
101
and the scanning lines
102
by the interlayer insulation film
115
, permitting the pixel electrode
103
to overlap the signal lines
101
and the scanning lines
102
(see FIG.
9
and FIG.
10
). It is known that this structure allows improvements on the aperture ratio and prevents insufficient alignment (disclination) from occurring in the liquid crystal, which would otherwise be caused by the shielding of the electric field generated by the signal lines
101
and the scanning lines
102
.
Another typical, simpler method omits the step of forming the interlayer insulation film
115
and the pixel electrodes
103
which is provided on the film
115
; the transparent conductive layer
112
is provided as pixel electrodes, and a large aperture for a pixel is formed in the protection film
114
which is deposited on the transparent conductive layer
112
. This structure does not give as high an aperture ratio as the foregoing structure, but enables the active matrix substrate to be fabricated by a fewer steps and provides an advantage in terms of manufacturing costs.
The active matrix substrate prepared as above can find a wide range of applications which includes liquid crystal display devices. A specific example is a photosensor, serving as a photodiode, constituted by a semiconductor-layer-deposited element formed on the pixel electrode
103
so as to provide a PIN connection and a shot key connection; the pixel capacitor (storage capacitor)
105
a
of each pixel stores data in the form of electric potential as the diode increases its conductivity where it is irradiated with light while applying a predetermined d.c. voltage to the other terminal of the diode.
Another example is a sensor for sequentially reading electric charges that are generated by an conversion layer provided in place of the photodiode so as to directly convert light, x-ray, etc. to electric charges and then stored in the pixel capacitor
105
a
using a high voltage. An embodiment is disclosed, for example, in Japanese Laid-Open Patent Application No. 4-212458/1992 (Tokukaihei 4-212458; published on Aug. 4, 1992) where each pixel stores in its pixel capacitor
105
a
those electric charges generated by the conversion layer as data in the form of electric charges (as data in the form of electric potential) in accordance with the characteristics of an object. Similarly to a liquid crystal display device, by sequentially scanning the scanning lines
102
, for example, the data stored in a pixel selected through the scanning lines
102
is read and transmitted through an active element (corresponding to the TFT
104
) to a data line (corresponding to the signal line
101
). At the other end of the data line, there is provided a circuit, such as an OP amplifier, for recovering a signal from the data; a set of image data is thus obtained from the object by the sensor.
The active matrix substrate, which is a precursor to the sensor in the foregoing example with no photodiode and no light-to-electricity conversion layer, can be manufactured at low costs without new investments in manufacturing tools and facilities, because the manufacturing process for liquid crystal display devices is applicable to sensors only by adjusting the dimensions of the pixel capacitor
105
a
and the time constants of the active element so as to obtain optimal results when used in a sensor.
For example, there is a demand for liquid crystal display devices used as computer display elements (monit
Izumi Yoshihiro
Nagata Hisashi
Shimada Takayuki
Choadhury Tanifur R.
Duong Thoi V.
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