Buffer layer for charge storage radiation detector

Details Buffer layer for charge storage radiation detector Buffer layer for charge storage radiation detector

2001-03-22

2003-09-09

Hannaher, Constantine (Department: 2878)

Radiant energy

Source with recording detector

Including a light beam read-out

C250S580000

Reexamination Certificate

active

06617604

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image recording medium that is capable of recording image information as an electrostatic latent image.
2. Description of the Related Art
For example, in medical X-ray photographing, for the purposes of a reduction in the radiation dose to which a subject is exposed, an enhancement in diagnosis performance, etc., there has been disclosed a system that uses an image recording medium employing a photoconductor sensitive to X-rays (e.g., a selenium (Se) plate, etc.,). In the system, an electrostatic latent image is recorded on the image recording medium by the use of X-rays and then the electrostatic latent image is read out (e.g., U.S. Pat. Nos. 4,176,275, 5,268,569, 5,354,982, 4,535,468, “23027 Method and Device for Recording and Transducing an Electromagnetic Energy Pattern,” in Research Disclosure, June 1983, Japanese Unexamined Patent Publication No. 9(1997)-5906, U.S. Pat. No. 4,961,209, “X-ray Imaging Using Amorphous Selenium,” in Med. Phys. 22(12), etc.).
The above-mentioned U.S. Pat. No. 4,535,468 discloses an image recording medium, in which (1) a 100~500-&mgr;m-thick photoconductive recording layer with amorphous selenium (&agr;-Se) as its main component, (2) a 0.01~10.0-&mgr;m-thick intervening layer (trap layer), which consists of AsS
4
, As
2
S
3
, As
2
Se
3
, etc., for storing, as a trap, a latent-image polarity charge generated within the photoconductive recording layer, (3) a 0.5~100-&mgr;m-thick photoconductive reading layer with amorphous selenium (&agr;-Se) as its main component, and (4) a 100-nm-thick reading-light transmitting electrode layer, consisting of Au or indium tin oxide (ITO), which allows reading electromagnetic waves (hereinafter also referred to as reading light) to pass through it, are stacked in the recited order on a 2-mm-thick recording-light transmitting electrode layer (conductive substrate), consisting of Al, which allows recording electromagnetic waves (hereinafter also referred to as recording light) to pass through it. Particularly, it is disclosed that the use of the reading-light transmitting electrode layer as a positive electrode is preferred because the satisfactory hole mobility of &agr;-Se can be utilized and that a blocking layer, consisting of an organic substance, is interposed between the reading-light transmitting electrode layer and the photoconductive reading layer in order to prevent S/N-ratio degradation due to the direct injection of electric charge through the electrode of the reading-light transmitting electrode layer. That is, this image recording medium is a multi-layer recording medium having both high dark resistance and excellent read response speed, and the image recording medium is constructed mainly of a layer having &agr;-Se as its main component.
For enhancing the S/N ratio of an image, and also for performing parallel reading (mainly in a horizontal scanning direction) to shorten the reading time, there are cases where the electrode of the reading-light transmitting electrode layer is replaced with a stripe electrode constructed of a large number of electrode elements (line electrode elements) disposed at intervals of a pixel pitch (e.g., Japanese Patent Application No. 10(1998)-232824 filed by the present applicant). However, in the stacked construction of the image recording medium described in above-mentioned U.S. Pat. No. 4,535,468, in the final fabrication step the reading-light transmitting electrode layer must be formed after formation of the photoconductive reading layer, so it is difficult to form the aforementioned stripe electrode. The reason for this is that photoetching is used for forming the electrode elements of the stripe electrode, but since a baking step is usually performed on photoresist at high temperature (e.g., 200° C.), &agr;-Se forming a previously formed photoconductive layer cannot endure such a high temperature and therefore the characteristics will be degraded. Furthermore, since an alkaline developing solution, which is employed in the step of developing the photoresist, contacts &agr;-Se and gives off harmful gases, steps becomes complicated for removing the harmful gases, resulting in an increased cost.
On the other hand, the present applicant has proposed, in the aforementioned Japanese Patent Application No. 10(1998)-232824, an image recording medium (electrostatic recording body) in which (1) a recording-light transmitting electrode layer which allows recording light to pass through it, (2) a 50~1000-&mgr;m-thick photoconductive recording layer with amorphous selenium (&agr;-Se) as its main component, (3) a charge transfer layer for forming a charge storage portion, which consists of &agr;-Se doped 10 to 200 ppm with an organic substance or Cl and stores a latent-image polarity charge generated in the photoconductive recording layer, at the interface between the charge transfer layer and the photoconductive recording layer, (4) a photoconductive reading layer with &agr;-Se as its main component, and (5) a reading-light transmitting electrode layer which allows reading light to pass through it, are disposed in the recited order. The aforementioned Japanese Patent Application No. 10(1998)-232824 does not disclose whether the image recording medium is fabricated in sequence from the recording-light transmitting electrode layer or conversely from the reading-light transmitting electrode layer. The image recording medium can be formed in either order. However, the aforementioned Japanese Patent Application No. 10(1998)-232824 has proposed that a conductive substance such as a film of NESA (SnO
2
) is provided as the reading-light transmitting electrode layer on a support body (transparent glass substrate) and has also proposed that the reading-light transmitting electrode layer is used as a positive electrode and that comb teeth are formed by the semiconductor fabrication technology in sufficiently narrow intervals of a fine pitch between comb teeth corresponding to a pixel pitch. That is, it has been proposed that the electrode of the reading-light transmitting electrode layer is constructed of a stripe electrode consisting of electrode elements disposed in the intervals of a pixel pitch. In this case, the stripe electrode is first formed on the transparent glass substrate by photoetching, etc. Then, the photoconductive reading layer, the photoconductive recording layer, the charge transfer layer, the photoconductive reading layer, and the recording-light transmitting electrode layer are formed in sequence. Although a specific numeral value for the pixel pitch has not been indicated, it would be obvious to those skilled in this field that the pixel pitch is 50 to 200 &mgr;m, because in the medical X-ray photographing, the image recording medium maintains high sharpness and makes a high S/N ratio possible.
In addition, the aforementioned Japanese Patent Application No. 10(1998)-232824, as with the aforementioned U.S. Pat. No. 4,535,468, has proposed that the S/N-ratio degradation due to the direct injection of the positive charge in the reading-light transmitting electrode layer can be prevented by providing a blocking layer of about 500 Å, which consists of an organic substance such as CeO
2
, between the reading-light transmitting electrode layer and the photoconductive reading layer.
On the other hand, the inventors of this application have made various investigations with respect to the image recording medium proposed in the aforementioned Japanese Patent Application No. 10(1998)-232824 and found the following facts:
(1) The method, which forms an ITO film of thickness 50 to 200 nm (i.e., the reading-light transmitting electrode layer) on the transparent glass substrate and then forms the stripe electrode by photoetching, is preferred because it can form a fine stripe pattern inexpensively;
(2) The photoconductive recording layer has high dark resistance, if it is constructed of an &agr;-Se layer having a thickness of 50 to 1000 &mgr;m;
(3) The charge transfer layer is excelle

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