Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
2000-09-08
2003-05-06
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S370010
Reexamination Certificate
active
06559451
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to manufacturing methods for two-dimensional image detectors capable of detecting images by means of X-rays and other kind of radiation and visible, infrared, and other kind of light and also relates to those two-dimensional image detectors.
BACKGROUND OF THE INVENTION
Conventionally known radiation two-dimensional image detectors (hereinafter, will be referred to simply as two-dimensional image detectors) include semiconductor sensors arranged in rows and columns with a switching element provided to each of the sensors. The semiconductor sensor generates electric charges (electron-hole pairs) upon detection of X-rays or other radiation (hereinafter, will be simply referred to as radiation). In the two-dimensional image detector, all the switching elements in a row are turned on to read electric charges from the semiconductor sensor in each column. The reading operation is performed for each column to detect a two-dimensional image.
The structure and principles of the two-dimensional image detector are explained in specific terms in publications including L. S. Jeromin, et al., “Application of a-Si Active-Matrix Technology in a X-Ray Detector Panel”, SID 97 DIGEST, pp. 91-94, 1997; and Japanese Laid-Open Patent Application No. 6-342098/1994 (Tokukaihei 6-342098; published on Dec. 13, 1994).
Now, the structure and principles of the conventional two-dimensional image detector will be discussed in reference to
FIGS. 17 and 18
. Whilst
FIG. 17
is a perspective view schematically showing a structure of the two-dimensional image detector,
FIG. 18
is a cross-sectional view showing a structure of a pixel shown in FIG.
17
.
The two-dimensional image detector includes an active matrix substrate
100
, a photoconductive film
112
, a dielectric layer
114
, an upper electrode
116
, a high voltage source
118
, and an amplifier
120
.
The active matrix substrate
100
is constituted by a glass substrate
102
, electrode wires (gate electrode line
104
a
and data electrode line
104
b
)
104
arranged in an XY matrix (arranged in rows and columns) on the glass substrate
102
, thin film transistors (hereinafter, will be referred to as TFTs)
106
connected to the electrode wires
104
, electric charge storage capacitances
108
connected to the TFTs
106
, etc.
The active matrix substrate
100
may be one of those used in manufacture of liquid crystal displays. An active matrix substrate used in an active matrix liquid crystal display (AMLCD) includes, among other components, TFTs
106
formed from amorphous silicon (a-Si) or polysilicon (p-Si), electrode wires
104
, and electric charge storage capacitances
108
, and can be used in the two-dimensional image detector with few modifications in design.
The photoconductive film
112
, the dielectric layer
114
, and the upper electrode
116
are formed so as to cover a substantial entirety of the active matrix substrate
100
.
The photoconductive film
112
is composed of a semiconductor material that produces electric charges (electrons-holes) when exposed to radiation. In the documents cited above, amorphous selenium (hereinafter, will be referred to as a-Se) is employed for use as the photoconductive film
112
, since the material has high dark resistance, exhibits satisfactory photoelectricity when exposed to radiation (X-rays), and is easy to form large films by vapor deposition. Specifically, a-Se is deposited 300 &mgr;m to 600 &mgr;m thick by vacuum vapor deposition to form the photoconductive film
112
.
Now, the operation principles of the two-dimensional image detector will be discussed.
When the photoconductive film
112
composed of a-Se is exposed to radiation, electric charges (electronsholes) develop in the photoconductive film
112
. As shown in
FIGS. 17 and 18
, the upper electrode
116
is electrically connected in series with Cs electrodes
108
a
in the electric charge storage capacitances
108
. Upon application of voltage across the upper electrode
116
and the Cs electrodes
108
a
, those electrons and holes developing in the photoconductive film
112
move toward the anodes and cathodes, building up electric charges in the electric charge storage capacitances
108
.
The electric charges thus accumulated in the electric charge storage capacitance
108
are sent to the amplifier
120
through the data electrode line
104
b
by changing the TFT
106
into an on-state by means of an input signal from the gate electrode line
104
a.
Since the electrode wires
104
(the gate electrode lines
104
a
and the data electrode lines
104
b
), the TFTs
106
, and the electric charge storage capacitances
108
are arranged to form an XY matrix as explained earlier, information on a two-dimensional radiation image is obtainable by sending an input signal sequentially to the gate electrode lines
104
a.
If the photoconductive film
112
exhibits photoconductivity to visible or infrared light, as well as in radiation, the two-dimensional image detector can function as a two-dimensional visible or infrared image detector. For example, an a-Se film mentioned above exhibits a satisfactory level of photoconductivity to visible light and avalanche effect on the application of a strong electric field. Studies are under way to develop supersensitive image sensors (two-dimensional image detectors) by means of the avalanche effect.
In manufacture of the two-dimensional image detector, the three processes A to C below are indispensable following the fabrication of active matrix elements (including the TFTs
106
and the electric charge storage capacitances
108
).
A. A-Se Film Deposition Process
In this process, an a-Se film is deposited by means of vacuum vapor deposition on the active matrix substrate
100
so as to cover at least areas in which the active matrix elements are formed.
B. Glass Cutting Process
In this process, a piece of mother glass is cut into the active matrix substrate
100
by a scribe or dicing technology.
Here, mother glass refers to the base material of the piece of glass on which active matrix elements are fabricated. Dividing a piece of mother glass into a designated dimensions will form active matrix substrates
100
.
Further, in this process, after active matrix substrates
100
are cut out, the edges along which the active matrix substrate
100
has been cut out are subjected to a chamfering process as necessary.
The glass cutting process is performed after the fabrication of matrix elements for the following reasons. First, the production line for active matrix substrates
100
includes dedicated machines exclusively used for a particular substrate size. Accordingly, the piece of mother glass, after having been subjected to the process to fabricate active matrix elements, needs to be of a size suitable to those dedicated machines. The piece of mother glass thus processed is then divided into smaller pieces of a required size for use as two-dimensional image detectors.
The second reason is that it is difficult in the fabrication process of active matrix elements to fabricate normal active matrix elements near the periphery of a glass substrate. This is chiefly due to the difficulty to satisfy suitable conditions for the fabrication of active matrix elements near the periphery of a glass substrate and the handling assembly directly contacting the periphery of the glass substrate. Therefore, the piece of mother glass needs to be of a size that actually forms the two-dimensional image detectors, plus the periphery. The unnecessary periphery is cut off after the fabrication of active matrix elements.
C. Mounting Process
In this process, various components and circuitry are mounted on the active matrix substrate
100
so as to obtain electric charges and other information from the active matrix substrate
100
.
However, regarding a two-dimensional image detector with an a-Se film deposited covering a substantial entirety of the active matrix substrate
100
, the following problems occur in its manufacturing process.
It is known that if pollutants in water
Hirasawa Shinya
Izumi Yoshihiro
Teranuma Osamu
Yoshimuta Toshinori
Hannaher Constantine
Lee Shun
Sharp Kabushiki Kaisha
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