Solid state radiation detector

Radiant energy – Source with recording detector – Including a light beam read-out

Reexamination Certificate

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Details

C250S580000

Reexamination Certificate

active

06707059

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid state radiation detector with a storage portion for storing a quantity of electric charge proportional to a quantity of radiation irradiated or quantity of light emitted by excitation of the radiation, as latent image charge.
2. Description of the Related Art
Today, in the field of radiation photography with the object of medical analysis, etc., a wide variety of radiation image information recording-reading units have been proposed and put to practical use. The recording-reading unit uses a solid state radiation detector or static storage medium (also stated as simply a detector), which temporarily stores electric charge obtained by detecting radiation, as latent image charge in its charge storage portion and also converts the stored latent image charge to an electrical signal representing radiation image information and outputs the converted signal.
Various types have been proposed as solid state radiation detectors that are used in the recording-reading unit. For instance, there is an optical reading type which employs the process of reading out a stored electric charge from the detector. In this type of detector, the stored electric charge is read out by irradiating reading light (e.g., electromagnetic waves for reading) to the detector.
The applicant of this application has proposed, in Japanese Patent Application Nos. 10 (1998)-271374, 11 (1999)-87922, and 11 (1999)-89553 published as Japanese Unexamined Patent Publication Nos. 2000-162726. 2000-284056, and 2000-284057, respectively, a solid state radiation detector of an optical reading type in which high-speed reading responsivity is compatible with efficient fetching of signal charge from the detector. The detector is constructed of (1) a first electrode layer (conductive layer) which has permeability with respect to recording radiation, or light emitted by excitation of the radiation (hereinafter referred to as recording radiation, etc.), (2) a recording photoconductive layer which exhibits electric conduction when irradiated with the recording light, etc., (3) a charge transfer layer which operates as substantially an insulator with respect to an electric charge of the same polarity as electric charge on the first electrode layer and also operates as substantially an electric conductor with respect to an electric charge of the opposite polarity, (4) a reading photoconductive layer which exhibits electric conduction when irradiated with reading light (electromagnetic waves for reading), and (5) a second electrode layer (conductive layer) which has permeability with respect to the reading light, which are stacked in the recited order. In this type of detector, signal charge (latent image charge) carrying image information is stored in a charge storage portion formed in the interface between the recording photoconductive layer and the charge transfer layer.
Particularly, in the above-mentioned Japanese Patent Application Nos. 11 (1999)-87922 and 11 (1999)-89553, there is proposed a detector where the electrode (light irradiating electrode) of a second conductive layer having permeability with respect to reading light is constructed with a stripe electrode consisting of a large number of main line electrodes. Also, a great number of secondary line electrodes, for outputting an electric signal which has a level proportional to a quantity of latent image charge stored in the charge storage portion, are provided within the second conductive layer so that the main and secondary line electrodes are alternately arranged in parallel to one another.
Thus, by providing the charge fetching electrode which consists of secondary line electrodes, within the second electrode layer, an additional capacitor is formed between the charge storage portion and the secondary line electrodes, and a transfer charge of the opposite polarity from the latent image charge stored in the charge storage portion by recording can be transferred to the secondary line electrodes by charge rearrangement at the time of reading. This can make smaller the quantity of the aforementioned transfer charge distributed to the capacitor formed between the main line electrodes and the charge storage portion through the reading photoconductive layer, compared with the case where the secondary line electrodes are not provided. As a result, the quantity of signal charge that can be fetched from the detector is made larger and therefore the fetch efficiency is enhanced. In addition, high-speed reading responsivity is compatible with efficient fetching of signal charge.
However, in the case where the-transmission factor of each main line electrode of the stripe electrode with respect to the reading light is small, or the case where the transmission factor of each secondary line electrode of the charge fetching electrode with respect to the reading light is great, even if the secondary line electrodes are provided within the second electrode layer, there is a possibility that a quantity of signal charge that can be fetched from the detector will become smaller. In addition, the quantity of signal charge that can be fetched from the detector varies depending on the area of the main or secondary line electrodes.
SUMMARY OF THE INVENTION
The present invention has been made in view of the aforementioned drawbacks found in the prior art. Accordingly, it is the primary object of the present invention to provide a solid state radiation detector which is capable of reliably making larger a quantity of signal charge that can be fetched therefrom.
The inventors of this application, in the detectors disclosed in the aforementioned [publication] Japanese Patent Application No. 11 (1999)-87922, particularly the detector where the main line electrodes and the secondary line electrodes are provided in the secondary electrode layer so that the main and secondary line electrodes are alternately arranged in parallel to one another, have made various investigations and experiments with respect to the relationship between the transmission factors and areas of the main and secondary line electrodes with respect to reading light and the magnitude of a quantity of signal charge that can be fetched from the detector, and have found the following relationship therebetween.
(1) The quantity of signal charge that can be fetched from the detector becomes larger, if the total quantity (quantity of light transmitted) R
1
of the reading light incident on the reading photoconductive layer through the main line electrodes forming the stripe electrode for light irradiation is larger and also the total quantity R
2
of the reading light incident on the reading photoconductive layer through the secondary line electrodes is smaller, that is, if the ratio R
1
/R
2
of the total light quantity R
1
of the former to the total light quantity R
2
of the latter is greater.
Note that in the case where the distance between the main line electrode, for light irradiation and the secondary line electrode is not negligible with respect to the electrode width, there is a need to take this distance between electrodes into consideration. However, the space between electrodes is normally set small and filled with a material which intercepts the reading light. Therefore, the influence of the space on the quantity of signal charge is considered practically negligible.
(2) The total quantity of the reading light incident on the reading photoconductive layer through the electrodes is proportional to the product of the areas of the electrodes and the transmission factor with respect to the reading light, if the irradiation intensity of the reading light is the same. Since the length of the main line electrode for light irradiation is essentially the same as that of the secondary line electrode, the total quantity of the reading light incident on the reading photoconductive layer through the electrodes is considered practically proportional to the product of the widths of the electrodes and the transmission factor. That is,

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