Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
2000-12-28
2003-05-27
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S580000
Reexamination Certificate
active
06570161
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention-relates to an X-ray detecting device, and more particularly to a liquid crystal display (LCD) X-ray detecting device that is capable of preventing a short between a lower electrode of a capacitor and a data line. Also, the present invention is directed to a method and apparatus for fabricating the X-ray detecting device.
2. Description of the Related Art
Diagnostic X-ray sensor imaging systems, which irradiate X-rays rather than visible light onto an object to photograph an image, are widely used in areas such as medical fields. An X-ray sensor requires a device for detecting the X-ray.
Recently, studies have been conducted where an active matrix liquid crystal display (LCD) is used in the X-ray detecting device. The active matrix LCD uses a thin film transistor (TFT) as a switching device.
Such an X-ray detecting device as described above includes a photo sensitive layer for detecting an X-ray and a thin film transistor substrate for switching and outputting the detected X-ray from the photo sensitive layer. The sensitive layer is formed from selenium, as described in Korean Patent Application No. 1999-36717 (Korean Patent No. 10-0299537) which filed with the Korean Industrial Property Office by the applicant on Aug. 31, 1999. The thin film transistor substrate includes pixel electrodes arranged in a pixel unit, and thin film transistors, each of which is connected to a charging capacitor, a gate line and a data line. The photo sensitive layer produces an electron-hole pair when an X-ray is incident thereto and separates the electron-hole pair when a high voltage of several is applied to the upper electrode. The pixel electrode charges the charging capacitor with holes produced by detection of an X-ray of the photo sensitive layer. The thin film transistor produces a gate signal inputted over the gate line to apply a voltage stored in the charging capacitor to the data line. Pixel signals supplied to the data line are applied, via a data reproducer, to a display device.
FIG. 1
is a sectional view showing a thin film transistor substrate of a conventional X-ray detecting device. The TFT substrate of conventional X-ray detecting device includes a TFT including a gate electrode
13
, a gate insulating layer
15
, an active layer
17
, an ohmic contact layer
19
, a source electrode
21
and a drain electrode
23
all on a transparent substrate
11
. The conventional TFT substrate also includes a storage capacitor Cst including lower and upper electrodes
29
and
33
and a dielectric layer
31
. The TFT substrate further includes a protective layer
35
formed on the TFT and the storage capacitor Cst, and a pixel electrode
37
connected electrically to the upper electrode
33
of the storage capacitor Cst through a contact hole which is formed on the protective layer
35
.
The conventional device is arranged at an intersection between a gate line (not shown) and a data line
25
. The gate line is connected to the gate electrode
13
and the data line
25
is connected to the source electrode
21
. The gate electrode
13
and the insulating layer
15
, which cover the gate electrode
13
, are formed on the transparent substrate
11
. The gate electrode
13
is made from a conductive metal such as aluminum (Al) or copper (Cu) and the gate insulating layer
15
is made from silicon nitride or silicon oxide.
The active layer
17
is formed on the gate insulating layer
15
to overlap with the gate electrode
13
, and the ohmic contact layer
19
is formed on the active layer
17
excluding a center portion of the active layer
17
. The active layer
17
is made from amorphous silicon or polycrystalline silicon, and the ohmic contact layer
19
is also made from amorphous silicon or polycrystalline silicon. The active layer
17
is not doped, but the ohmic contact layer
19
is doped with either an n-type or p-type impurities at high concentrations.
The source and drain electrodes
21
and
23
are formed on the ohmic contact layer
19
and spaced apart from each other. The source and drain electrodes
21
and
23
are made from molybdenum (Mo), chromium (Cr), titanium (Ti), tantalum (Ta), or from molybdenum alloys such as MoW, MoTa or MoNb, and make an ohmic contact with the ohmic contact layer
19
. The source electrode
21
is connected to the data line
25
.
The lower electrode
29
of the storage capacitor Cst is formed on the gate-insulating layer
15
and overlaps with a ground line
27
. The ground line
27
is formed from the same material as the source and drain electrodes
21
and
23
, and is formed by the same process that forms the source and drain electrodes
21
and
23
.
The dielectric layer
31
covers the TFT including the lower electrode
29
. The upper electrode
33
is formed on the dielectric layer
31
above the lower electrode
29
. The dielectric layer
31
is made from silicon nitride or silicon oxide. The lower and upper electrodes
29
and
33
are made from indium tin oxide (ITO), tin oxide (TO) or indium zinc oxide (IZO).
FIGS. 2A
to
2
E show a process of fabricating a structure having the upper electrode
33
of the storage capacitor Cst on the TFT substrate of the conventional X-ray detecting device shown in FIG.
1
. Referring to
FIG. 2A
, a metal, such as aluminum (Al) or copper (Cu), is deposited on the transparent substrate
11
by the sputtering technique to form a thin metal film. The thin metal film is patterned to form the gate electrode
13
, connected to the gate line (not shown), by photolithography including wet etching.
Referring to
FIG. 2B
, the gate insulating film
15
, the active layer
17
and the ohmic contact layer
19
are sequentially formed on the transparent substrate
11
by the chemical vapor deposition (CVD) technique and cover the gate electrode
13
. The gate insulating film
15
is formed by depositing an insulation material such as silicon oxide or silicon nitride.
Also, as mentioned above, the active layer
17
is made from amorphous silicon or polycrystalline silicon, and the ohmic contact layer
19
is also made from amorphous silicon or polycrystalline silicon. The active layer
17
is not doped, but the ohmic contact layer
19
is doped with either n or p-type impurities at high concentrations.
The ohmic contact layer
19
and the active layer
17
are patterned by photolithography including anisotropic etching so that a desired portion corresponding to the gate electrode
13
remains.
Referring to
FIG. 2C
, a metal such as molybdenum (Mo), chromium (Cr), titanium (Ti), tantalum (Ta), or from molybdenum alloys such as MoW, MoTa or MoNb, is deposited on the gate insulating film
15
by the CVD or sputtering technique to cover the ohmic contact layer
19
. The metal or the metal alloy so deposited makes an ohmic contact with the ohmic contact layer
19
.
Then, the source and drain electrodes
21
and
23
are formed by patterning the metal or the metal alloy by photolithography so that portions corresponding to each side of the active layer
17
remain. At this time, the data line
25
and the ground line
27
are also formed, both of which are perpendicular to the gate line (not shown).
The data line
25
and the ground line
27
are made from the same material as the source and drain electrodes
21
and
23
. Further, the ground line
27
is connected to the source electrode
21
(connection not shown).
When the source and drain electrodes
21
and
23
are formed, a portion of the ohmic contact layer
19
between the source and drain electrodes
21
and
23
is patterned to expose the active layer
17
. A portion of the active layer
17
above the gate electrode
13
and between the source and drain electrodes
21
and
23
becomes a channel.
Referring to
FIG. 2D
, a transparent conductive material such as ITO, TO or IZO is deposited on the gate insulating layer
15
covering the data line
25
and the ground line
27
. Then the transparent conductive material is selectively removed by photolithography including wet etching to form the lo
Lim Byoung Ho
You Myung Ho
Birch & Stewart Kolasch & Birch, LLP
Gabor Otilia
Hannaher Constantine
LG Philips LCD Co., Ltd.
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