Radiant energy – Source with recording detector – Including a light beam read-out
Reexamination Certificate
2001-03-22
2003-07-08
Hannaher, Constantine (Department: 2878)
Radiant energy
Source with recording detector
Including a light beam read-out
C250S580000
Reexamination Certificate
active
06590224
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image storage medium capable of storing image data in the form of an electrostatic latent image, and a method of manufacturing the same.
2. Description of the Related Art
There have been known, in the field of medical X-ray radiology, for example, image recording mediums, on which an electrostatic latent image is recorded by the passing therethrough of X-rays, employing photoconductors sensitive to X-rays (such as selenium, etc.) in order to reduce the quantity of X-ray energy a subject is bombarded with, and to improved diagnostic performance; afterwards, systems for reading out such electrostatic latent images have been disclosed (as in for example: U.S. Pat. Nos. 4,176,275, 5,268,569, 5,354,982, 4,535,468, 4,961,209; “23027 Method and devise for recording and transducing an electromagnetic energy pattern”, Research Disclosure June 1983; Japanese Unexamined Patent Publication No. 9(1997)-5906; “X-ray imaging using amorphous selenium”, Med Phys. 22(12), etc.) More specifically, in U.S. Pat. No. 4,535,468, for example, an image storage medium comprising a relatively thick 2 mm Al, etc. electrode layer on the recording side, which serves as an electrically conductive substrate transparent to the radiation which is to serve as the electromagnetic energy (hereafter also referred to as recording light) to be recorded thereon, on which are formed a 100-500 &mgr;m thick recording photoconductive layer having a-Se (amorphous selenium) as a main component, a 0.1-10.0 &mgr;m thick middle storage portion (trap layer) formed of AsS
4
, As
2
S
3
, As
2
Se
3
, etc. for trapping the latent-image charge carriers generated within the recording-use photoconductive layer, a 0.5-100 &mgr;m thick readout photoconductive layer having of a-Se as a main component, and a 100 &mgr;m thick, readout-side electrode layer, which is transparent to the readout electromagnetic radiation (hereinafter also referred to as readout light) and is formed of Au or ITO (Indium Tin Oxide), superposed one on another in that order, is disclosed. Further, in particular, it is advantageous that the favorable hole mobility of the a-Se can be put to use in employing the readout side photoconductor as the positive electrode, and in order to prevent a deterioration of the S/N ratio upon direct injection of charges from the electrodes, an apparatus wherein a blocking layer formed of an organic material is disposed between the readout-side electrode layer and the readout photoconductive layer has been disclosed. That is, this image storage medium is a multi-layer recording medium, which has great dark resistance and readout responsiveness, and is comprised, overall, of a layer formed mainly of a-Se.
Here, to improve the image S/N ratio, because it has been proposed to shorten the readout time required to perform line readout (primarily in the main scanning direction), in which the electrodes of the readout photoconductive layer comprise many elements (straight line-shaped) aligned with the pixel pitch to form stripe-shaped electrodes (as in for example, Japanese Patent Application No. 10 (1998)-232824, by the same author as that of the current application). However, in the storage portion formation of the image storage medium disclosed in aforementioned U.S. Pat. No. 4,535,468, in the final manufacturing process thereof, the readout-use light side electrode layer must be formed after the readout-use photoconductive layer has been formed, making it difficult to form aforementioned stripe electrodes. To form these stripe electrodes, fine processing of the electrodes must be performed using the photo-etching technique employed in the manufacture of semiconductors. In this process, a high temperature (for example, 200° C.) is normally required for the process of baking the photo-resist etc., however, the a-Se of the already formed photoconductive layer is not capable of tolerating such high temperatures, and the characteristics thereof are thereby deteriorated.
In addition, if the alkaline developing agent used in the photo-resist developing processes is brought into contact with the a-Se, a harmful gas is produced, and complicated processes are necessary to circumvent the occurrence thereof, whereby prohibitively high costs are incurred.
On the one hand, the applicant of the current application has proposed, in Japanese Patent Application 10(1998)-232824, an image storage medium (static-electricity recording medium) comprising a recording-light side electrode layer, which is transparent to the radiation that is the recording light, formed of SnO
2
(Nesa film), a 50-1000 &mgr;m thick recording photoconductive layer formed mainly of a-Se, a charge transport layer formed of a-Se, etc. doped with 10-200 ppm of an organic material or chlorine (Cl), for forming at the interface with aforementioned recording photoconductive layer a storage portion that stores the latent-image charge emitted by the recording photoconductive layer, a readout-use photoconductive layer having a-Se as a main component thereof, and a readout-side electrode layer that is transparent to readout light, disposed in that order.
When manufacturing this image storage medium, no definite order in which the layers should be formed has been explicitly stated, and acceptable results have been obtained by forming the layers in the order starting with the recording-side electrode layer, or in the reverse order thereof. However, as the readout-side electrode layer, a Nesa film or other electrical conductor has been provided on a transparent glass support panel, which is used as the positive electrode and has highly fine “comb teeth at a pitch corresponding to the pitch of the pixels” and “formed using semiconductor production technology that forms the comb teeth having a sufficiently narrow interspace”. That is to say, the electrodes of the readout-light side electrode layer are provided as stripe electrodes arranged at intervals corresponding to the pitch of the pixels. In this case, at first, the stripe electrodes are formed on the transparent glass substrate by a photo-etching process, etc., after which the readout photoconductive layer through the recording-side electrode layer are formed in that order. Note that although a value for the pixel pitch has not been given directly, because in medical-use X-ray radiology a high S/N ratio is possible while maintaining image sharpness, the use of a pixel pitch of 50-200 &mgr;m is readily apparent to those skilled in the art.
In addition, in Japanese Patent Application 10 (1998)-232824, in the same way as described in aforementioned U.S. Pat. No. 4,535,468, by providing an approximately 500 A blocking layer formed of an inorganic material such as CeO
2
between the readout-light side electrode layer and the readout-use photoconductive layer, deterioration of the S/N ratio by the direct injection of positive charges into the readout-side electrode layer is prevented.
On the other had, afterwards, in further discussions the developers of the invention of the present application found the following points regarding the image storage medium of aforementioned Japanese Patent Application 10(1998)-232824:
1) When carrying out manufacture thereof, after forming a comparatively thin 50-200 nm thick film of ITO on the transparent glass layer, it has been possible to adequately form stable, highly fine stripe electrodes of the readout-side electrode layer.
2) Forming the recording photoconductive layer of a-Se at a thickness of 50-1000 &mgr;m provides for excellent dark resistance.
3) As the charge transport layer, a stacked layer type comprising a first hole transport layer composed of a thin layer of organic material 0.1-1.0 &mgr;m thick forming the condenser onto which electrons are placed, and a second, high-speed hole transport layer, formed of 5-30 &mgr;m thick “a-Se doped with 10-200 ppm of CL”, which has few hole traps, superposed one on the other, offers excellent readout responsiveness and after-image formation characteristics.
4) Formin
Fuji Photo Film Co. , Ltd.
Hannaher Constantine
Moran Timothy
Sughrue & Mion, PLLC
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