Apparatus and method for detecting radiation

An apparatus and method for detecting radiation, which can improve the resolution of a radiation image and contribute to the simplification of the manufacture of the apparatus, are provided. The apparatus includes an upper electrode layer transmitting radiation; a first photoconductive layer becoming photoconductive upon exposure to the radiation and thus generating charges therein; a charge trapping layer trapping therein the charges generated in the first photoconductive layer and serving as a floating electrode; a second photoconductive layer becoming photoconductive upon exposure to rear light for reading out a radiation image; a lower transparent electrode layer charged with the charges trapped in the charge trapping layer; a rear light emission unit applying the rear light to the second photoconductive layer via the lower transparent electrode layer in units of pixels; and a data processing unit reading out a signal corresponding to the charges trapped in the charge trapping layer from the lower transparent electrode layer and generating a radiation image based on the read-out signal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2010-0095571, filed on Sep. 30, 2010, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes.

BACKGROUND

The following description relates to an apparatus and method for detecting radiation, which can detect radiation such as X-rays and can thus generate image data

2. Description of the Related Art

Digital radiation detection apparatuses are devices that obtain information on the inside of the human body through X-ray irradiation without a requirement of films, detect electric image signals from the obtained information with the use of image detection sensors and generate a digital image based on the electrical image signals. Digital radiation detection apparatuses are largely classified into direct-type and indirect-type digital radiation detection apparatuses. Direct-type digital radiation detection apparatuses directly detect electric signals generated by irradiating the human body using amorphous selenium (a-Se) and thin film transistors (TFTs). Indirect-type digital radiation detection apparatuses use light receptors such as charge-coupled deices (CCDs) or photodiodes and thus obtain radiation images from light emitted by phosphors (such as CsI) that convert radiation into visible light. Indirect-type digital radiation detection apparatuses have a relatively low resolution, compared to direct-type digital radiation detection apparatuses.

Conventional radiation detection apparatuses using TFTs are likely to result in a considerable amount of noise. The greater the size of radiation detection apparatuses, the greater the amount of noise generated, and the lower the detective quantum efficiency. In addition, since a TFT is required for each pixel in a panel, radiation detection apparatuses are generally difficult and costly to manufacture on a large scale.

SUMMARY

The following description relates to an apparatus and method for detecting radiation, which can improve the resolution of radiation images and can contribute to the simplification of the manufacture of the apparatus.

In one general aspect, there is provided an apparatus for detecting radiation, the apparatus including an upper electrode layer transmitting radiation; a first photoconductive layer becoming photoconductive upon exposure to the radiation and thus generating charges therein; a charge trapping layer trapping therein the charges generated in the first photoconductive layer and serving as a floating electrode; a second photoconductive layer becoming photoconductive upon exposure to rear light for reading out a radiation image; a lower transparent electrode layer charged with the charges trapped in the charge trapping layer; and a rear light emission unit applying the rear light to the second photoconductive layer via the lower transparent electrode layer in units of pixels.

In another general aspect, there is provided a method of detecting radiation, which is performed by an apparatus for detecting radiation, including an upper electrode layer transmitting radiation, a first photoconductive layer becoming photoconductive upon exposure to the radiation and thus generating charges therein, a charge trapping layer trapping therein the charges generated in the first photoconductive layer and serving as a floating electrode, a second photoconductive layer becoming photoconductive upon exposure to rear light for reading out a radiation image, a lower transparent electrode layer charged with the charges trapped in the charge trapping layer, and a rear light emission unit applying the rear light to the second photoconductive layer via the lower transparent electrode layer in units of pixels, the method including generating pairs of positive and negative charges in the first photoconductive layer upon exposure to radiation when applying a high voltage to the upper electrode layer; separating the positive and negative charges from each other and moving the positive and negative charges toward the upper electrode layer and the charge trapping layer, respectively; trapping the positive or negative charges in the charge trapping layer; connecting the upper electrode layer to a ground source and generating pairs of positive and negative charges in the second photoconductive layer upon exposure to the rear light; and reading out a signal corresponding to the charges trapped in the charge trapping layer from the lower transparent electrode layer, the charges trapped in the charge trapping layer originating from the second photoconductive layer.

DETAILED DESCRIPTION

FIG. 1is a cross-sectional view of an exemplary apparatus10for detecting radiation. Referring toFIG. 1, the apparatus10may include an upper electrode layer101, a first photoconductive layer102, a charge trapping layer103, a second photoconductive layer104, a lower transparent electrode layer105and a data processing unit200. The upper electrode layer101may transmit radiation incident thereupon from an external source to the first photoconductive layer102. Examples of the radiation include, but are not limited to X-rays, alpha rays and gamma rays.

The first photoconductive layer102may become photoconductive upon exposure to the radiation transmitted thereto by the upper electrode layer101. That is, the first photoconductive layer102may generate pairs of positive and negative charges (i.e., holes and electrons) upon exposure to radiation. The amount of charges generated by the first photoconductive layer102may be proportional to the intensity of radiation transmitted to the first photoconductive layer102. The amount of radiation that reaches the first photoconductive layer102may vary according to the composition of an object (such as the human body), if any, placed on the upper electrode layer101. The first photoconductive layer102may be formed of amorphous selenium (a-Se), As2Se3or an asbestos (As)-contained a-Se compound.

The charge trapping layer103may trap therein the positive and negative charges generated in the first photoconductive layer102, and may thus serve as a floating electrode.

More specifically, the charge trapping layer103may block the charges collected from the first photoconductive layer102and accumulated between the first photoconductive layer102and the charge trapping layer103. The charge trapping layer103may include a metal layer, a dielectric layer or the combination thereof.

The second photoconductive layer104may become photoconductive upon exposure to rear light for reading out a radiation image. The second photoconductive layer104may generate pairs of positive and negative charges upon exposure to rear light. The amount of positive and negative charges generated in the second photoconductive layer104may be proportional to the intensity of rear light transmitted to the second photoconductive layer104. The second photoconductive layer124may be formed of a-Se, As2Se3or an As-contained a-Se compound.

The term ‘rear light,’ as used herein, indicates light irradiated from an opposite side of the apparatus10with respect to the direction of radiation. Examples of a rear light source include, but are not limited to, various light source systems capable of applying light in units of pixels, such as a liquid crystal display (LCD), a plasma display panel (PDP), a light-emitting diode (LED), a field emission display (FED), and a laser light source.

The lower transparent electrode layer105may be charged with the charges trapped in the charge trapping layer103. The lower transparent electrode layer105may be formed of a transparent material and may thus be able to transmit rear light therethrough to the second photoconductive layer104. More specifically, the lower transparent electrode layer105may be formed of a transparent material such as indium tin oxide (ITO) or indium zinc oxide (IZO). Once pairs of positive and negative charges are generated in the second photoconductive layer104, the lower transparent electrode layer105may be charged with the opposite polarity to that of the charges trapped in the charge trapping layer103.

The data processing unit200may read out a signal corresponding to the charges in the lower transparent electrode layer105and may thus generate a radiation image.FIG. 1illustrates the structure of a portion of the apparatus10corresponding to a pixel. Thus, the data processing unit200may perform the reading out of the signal in units of pixels or rows or columns of pixels in a pixel array in the apparatus10and may thus obtain a whole radiation image.

FIG. 2is a circuit diagram for explaining the operation of the first and second photoconductive layers102and104, which are stacked with the charge trapping layer103interposed therebetween. Referring toFIG. 2, when radiation is transmitted to the first photoconductive layer102by the upper electrode layer101, pairs of positive and negative charges may be generated in the first photoconductive layer102. An electric field may be generated in the upper electrode layer101in response to a high voltage of, for example, 4 kV, applied to the upper electrode layer101. Then, the positive and negative charges in the first photoconductive layer102may move toward opposite directions. As a result, positive or negative charges may be trapped in the charge trapping layer103. More specifically, if a negative voltage is applied to the upper electrode layer101, the positive charges in the first photoconductive layer102may move toward the upper electrode layer101, whereas the negative charges in the photoconductive layer102may move toward the charge trapping layer103.

Referring toFIG. 2, the first and second photoconductive layers102and104, which are stacked with the charge trapping layer103interposed therebetween, may serve as capacitors connected in series. The relationship between capacitance C and energy W may be defined by the following equation:

W=12⁢CV2.
Since a charge quantity Q1of the first photoconductive layer102is the same as a charge quantity Q2of the second photoconductive layer104,

12⁢C1⁢V12=12⁢C2⁢V22
where C1and C2respectively indicate the capacitances of the first and second photoconductive layers102and104, and V1and V2respectively indicate the voltages of the first and second photoconductive layers102and104. In addition, since

12⁢ɛo⁢AE12⁢d1=12⁢ɛo⁢AE22⁢d2
where d1and d2respectively indicate the thicknesses of the first and second photoconductive layers102and104and E1and E2respectively indicate the electric fields applied to the first and second photoconductive layers102and104. The thickness d1of the first photoconductive layer102may be much greater than the thickness d2of the second photoconductive layer104. For example, the thickness d1of the first photoconductive layer102may be about 500 μm, and the thickness d2of the second photoconductive layer104may be about 7-12 μm. Thus, the magnitude of the electric field E2applied to the second photoconductive layer104may be greater than the magnitude of the electric field E1applied to the first photoconductive layer102. During an image recording operation, a high voltage may be applied to the upper electrode layer101, whereas, during a radiation image read-out operation, a ground voltage may be applied to the upper electrode layer101. Therefore, most of the electric field generated in the apparatus10may be applied to the second photoconductive layer104.

Referring toFIG. 2, the charges (regardless of whether positive or negative) generated in the first photoconductive layer102may be blocked by an energy barrier between the charge trapping layer103and the first photoconductive layer102. Even when blocked by the charge trapping layer103, electrons can jump over the energy barrier if the energy barrier becomes low due to, for example, a variation in the electric field or temperature outside the charge trapping layer103. However, since the electric field applied to the first photoconductive layer102is much weaker than the electric field applied to the second photoconductive layer104, there is no sufficient external energy for the charges generated in the first photoconductive layer102to jump over the energy barrier. Thus, the charges generated in the first photoconductive layer102can be effectively blocked by the charge trapping layer103.

If rear light is applied to the second photoconductive layer104when the negative charges are blocked by the charge trapping layer103, pairs of positive and negative charges may be generated in the second photoconductive layer104. In this case, the positive charges in the second photoconductive layer104may move toward the charge trapping layer103, and thus, the surface of the charge trapping layer103may be electrically neutralized. The negative charges in the second photoconductive layer104may move toward the lower transparent electrode layer105and may thus be subjected to a radiation image read-out operation. In short, the negative charges trapped in the charge trapping layer103may be read out, and image processing may be performed on the read-out negative charges, thereby obtaining a radiation image.

The energy band at the interface between the charge trapping layer103and the first photoconductive layer102may depend on the difference between the work function of a conductive material of the charge trapping layer103and the work function of the first photoconductive layer102, and may be adjusted according to the physical properties of the charge trapping layer103and the first photoconductive layer102such as thickness and specific resistance.

In order to properly trap charges in the charge trapping layer upon exposure to radiation, the charge trapping layer103may be formed as a metal layer, a dielectric layer or the combination thereof. More specifically, the charge trapping layer103may be formed as a metal layer by using silver (Ag), copper (Cu), gold (Au), aluminum (Al), calcium (Ca), tungsten (W), zinc (Zn), nickel (Ni), iron (Fe), platinum (Pt), tin (Sn), lead (Pb), manganese (Mn), constantan, mercury (Hg), nichrome, carbon (C), germanium (Ge), silicon (Si), glass, quartz, polyethylene terephtalate (PET), or Teflon. Alternatively, the charge trapping layer123may be formed as a dielectric layer by using an organic dielectric material such as benzocyclobutene (BCB), parylene, a-C:H(F), polyimide (PI), polyarylene ether, or fluorinated amorphous carbon, an inorganic dielectric material such as SiO2, Si3N4, polysilsequioxane, or methyl silane, or a porous dielectric material such as xetogel/aerogel or polycaprolactone (PCL). By forming the charge trapping layer103as a metal layer, a dielectric layer or the combination thereof, it is possible to simplify the fabrication of the charge trapping layer103, effectively trap the charges generated in the first photoconductive layer102in the charge trapping layer103and reduce the time and cost required to manufacture the apparatus10, compared to the case when the charge trapping layer103is formed of doped semiconductor. Thus, it is possible to improve the resolution of a radiation image and simplify the manufacture of the apparatus10.

FIG. 3is a cross-sectional view of another exemplary apparatus20for detecting radiation, which uses a plasma display panel (PDP). Referring toFIG. 3, the apparatus20may include an upper electrode layer101, a first photoconductive layer102, a charge trapping layer103, a second photoconductive layer104, a lower transparent electrode layer105, an intermediate substrate106and a PDP110. The PDP110, the lower transparent electrode layer105, the second photoconductive layer104, the charge trapping layer103, the first photoconductive layer102, and the upper electrode layer101may be sequentially stacked. The intermediate substrate106may support the upper electrode layer101, the first photoconductive layer102, the charge trapping layer103, the second photoconductive layer104and the lower transparent electrode layer105, and may be formed of, for example, glass.

The upper electrode layer101, the first photoconductive layer102, the charge trapping layer103, the second photoconductive layer104, and the lower transparent electrode layer105are the same as their respective counterparts shown inFIG. 1, and thus, detailed descriptions thereof will be omitted.

The PDP110may provide plasma light as rear light. The PDP110may include a first substrate111, a plurality of barrier ribs112, a gas layer113, a plurality of phosphor layers114, an insulating layer115, a plurality of electrodes116and a second substrate117.

The first and second substrates111and112may face each other.

The barrier ribs112may define a cell structure between the first and second substrates111and112. More specifically, the barrier ribs112may be formed between the first substrate111and the insulating layer115and may thus form a sealed cell structure. The barrier ribs112may define a plurality of pixels of the PDP110. The barrier ribs112may prevent crosstalk between the pixels. The barrier ribs112may be formed in various shapes such as 2-, 6-, and 8-directional shapes according to the shape of pixels. The barrier ribs112may determine the resolution of the PDP110. The barrier ribs112may be formed using the same method used to manufacture a typical PDP. The area and height of the barrier ribs112can be appropriately adjusted in order to increase the reaction area of each pixel for radiation.

The gas layer113may be disposed in an inner chamber within the cell structure formed by each of the barrier ribs112, and may generate a plasma discharge. Plasma light generated by the gas layer113may be provided to the lower transparent electrode layer105.

The phosphor layers114may reflect plasma light generated by the gas layer113and may thus enable high-intensity plasma light to be provided to the lower transparent electrode layer105. The phosphor layers114may be formed between the insulating layer115and the barrier ribs112. The phosphor layers114may be optional.

The insulating layer115may be formed on the second substrate117as a dielectric layer. The insulating layer115may prevent the electrodes116, which are arranged in units of pixels, from being short-circuited and may also prevent a leakage current. The electrodes116may transmit power for generating plasma to the gas layer113.

FIGS. 4A through 4Eare cross-sectional views for explaining the operation of another exemplary apparatus20for detecting radiation, which includes a metal layer103-1as a charge trapping layer. The apparatus30may be the same as the apparatus20shown inFIG. 3except that it includes the metal layer103-1formed of a metal. InFIGS. 4A through 4E, the plus sign ‘+’ indicates a positive charge, and the negative sign ‘−’ indicates a negative charge.

Referring toFIG. 4A, when radiation such as X-rays is applied to the apparatus30, the radiation may be transmitted to a first photoconductive layer102through an upper electrode layer101, and pairs of positive and negative charges may be generated in the first photoconductive layer102. When a high voltage HV is applied to the upper electrode layer101, the positive and negative charges may be separated from each other and may move toward opposite directions. More specifically, if a negative voltage is applied to the first photoconductive layer102, the positive charges in the first photoconductive layer102may move toward the upper electrode layer101, and the negative charges in the first photoconductive layer102may move toward the metal layer103-1.

The negative charges moving toward the metal layer103-1may be trapped in the metal layer103-1. That is, the negative charges generated in the first photoconductive layer102may move toward the metal layer103-1and may thus accumulate at the interface between the first photoconductive layer102and the metal layer103-1. The negative charges accumulated between the first photoconductive layer102and the metal layer103-1can be blocked by a weak electric field applied to the first photoconductive layer102, as described above with reference toFIG. 2. Since the amount of radiation transmitted through an object (such as the human body), if any, placed on the apparatus30varies according to the composition and shape of the object, the amount of positive and negative charges generated in the first photoconductive layer102and the amount of negative charges trapped in the metal layer103-1may also vary according to the composition and shape of the object. Therefore, the amount of negative charges trapped in the metal layer103-1may correspond to a radiation image recorded by the apparatus30.

Once negative charges are trapped in the metal layer103-1, a second photoconductive layer104can serve as a capacitor. As a result, referring toFIG. 4B, a lower transparent electrode layer105may be charged with positive charges. More specifically, the lower transparent electrode layer105may be charged with a number of positive charges corresponding to the number of negative charges trapped in the metal layer103-1.

A radiation image read-out operation will hereinafter be described in detail. If a first row of pixels in the pixel array of a PDP110is turned on, plasma light may be emitted from the first row of pixels. The plasma light may transmit through the lower transparent electrode layer105, and may thus reach the second photoconductive layer104.

Due to the plasma light, pairs of positive and negative charges may be generated in the second photoconductive layer104, and particularly, in a portion of the second photoconductive layer104corresponding to the first row of pixels. Referring toFIG. 4C, the positive charges in the second photoconductive layer104may be electrically attracted to the negative charges trapped in the metal layer103-1, and the negative charges in the second photoconductive layer104may be electrically attracted to the positive charges in the lower transparent electrode layer105. As a result, the positive and negative charges in the second photoconductive layer104may be separated from each other.

Thereafter, referring toFIG. 4D, due to the positive charges in the lower transparent electrode layer105, the negative charges generated by the second photoconductive layer104may be read out from the first row of pixels by a data processing unit200. Then, the read-out negative charges may be subjected to image processing performed by the data processing unit200.

The positive charges generated in the second photoconductive layer104may move toward the metal layer103-1due to the negative charges trapped in the metal layer103-1, and thus, the metal layer103-1may be electrically neutralized.

Thereafter, referring toFIG. 4E, the first row of pixels may be turned off, and a second row of pixels may be turned on. Then, the second row of pixels may emit plasma light. Due to the plasma light, pairs of positive and negative charges may be generated in a portion of the second photoconductive layer104corresponding to the second row of pixels. The positive and negative charges generated in the second photoconductive layer104may be electrically attracted to the metal layer103-1and the lower transparent electrode layer105, respectively, and may thus be separated from each other. Due to the positive charges in the lower transparent electrode layer105, negative charges may be read out from the portion of the second photoconductive layer104corresponding to the second row of pixels by the data processing unit200. Then, the read-out negative charges may be subjected to image processing performed by the data processing unit200.

Thereafter, the same operation as that performed on the first and second rows of pixels may also be performed on a third row of pixels. As a result, negative charges may be read out from a portion of the second photoconductive layer104corresponding to the third row of pixels by the data processing unit200. Then, the read-out negative charges may be subjected to image processing performed by the data processing unit200.

By performing the above-mentioned operation on all rows of pixels in the PDP110, it is possible to obtain a radiation image of an object, if any, placed on the apparatus30.

FIGS. 5A through 5Dare cross-sectional views for explaining the operation of another exemplary apparatus40for detecting radiation, which includes a dielectric layer103-2as a charge trapping layer. The apparatus40is the same as the apparatus20shown inFIG. 3except that it includes the dielectric material103-2as a charge trapping layer.

Referring toFIG. 5A, when radiation such as X-rays is applied to the apparatus40, the radiation may be transmitted to a first photoconductive layer102through an upper electrode layer101, and pairs of positive and negative charges may be generated in the first photoconductive layer102. When a high voltage HV is applied to the upper electrode layer101, the positive and negative charges may be separated from each other and may move toward opposite directions. More specifically, if a negative voltage is applied to the first photoconductive layer102, the positive charges in the first photoconductive layer102may move toward the upper electrode layer101, and the negative charges in the first photoconductive layer102may move toward the dielectric layer103-2.

Due to the movement of the negative charges toward the dielectric layer103-2, the dielectric layer103-2may be polarized, and dipoles may be generated in the dielectric layer103-2. The dipoles in the dielectric layer103-2may be arranged in a manner shown inFIG. 5B.

Due to the pattern of the arrangement of the dipoles in the dielectric layer103-2, a lower transparent electrode layer105may be charged with positive charges, and particularly, as many positive charges as there are dipoles in the dielectric layer103-2.

An image read-out operation will hereinafter be described in detail.

The upper electrode layer101may be connected to a ground source. Then, if a first row of pixels in a PDP110is turned on, plasma light may be emitted from the first row of pixels. The plasma light may transmit through the lower transparent electrode layer105and may thus reach a second photoconductive layer104.

Referring toFIG. 5C, pairs of positive and negative charges may be generated in the second photoconductive layer104, and particularly, in a portion of the second photoconductive layer104corresponding to the first row of pixels, upon exposure to the plasma light emitted from the first row of pixels. The positive and negative charges generated in the second photoconductive layer104may be electrically attracted to the dielectric layer103-2and the lower transparent electrode layer105, respectively, and may thus be separated from each other.

Referring toFIG. 5D, due to the positive charges in the lower transparent electrode layer105, negative charges may be read out from the portion of the second photoconductive layer104corresponding to the first row of pixels by the data processing unit200. Then, the read-out negative charges may be subjected to image processing performed by the data processing unit200. The positive charges generated in the second photoconductive layer104may move toward the dielectric layer103-2due to the dipoles in the dielectric layer103-2.

Thereafter, the first row of pixels may be turned off, and a second row of pixels may be turned on. Then, the second row of pixels may emit plasma light. Due to the plasma light, pairs of positive and negative charges may be generated in a portion of the second photoconductive layer104corresponding to the second row of pixels. The positive and negative charges generated in the second photoconductive layer104may be electrically attracted to the metal layer103-1and the lower transparent electrode layer105, respectively, and may thus be separated from each other. Due to the positive charges in the lower transparent electrode layer105, negative charges may be read out from the portion of the second photoconductive layer104corresponding to the second row of pixels by the data processing unit200. Then, the read-out negative charges may be subjected to image processing performed by the data processing unit200.

Thereafter, the same operation as that performed on the first and second rows of pixels may also be performed on a third row of pixels. As a result, negative charges may be read out from a portion of the second photoconductive layer104corresponding to the third row of pixels by the data processing unit200. Then, the read-out negative charges may be subjected to image processing performed by the data processing unit200.

By performing the above-mentioned operation on all rows of pixels in the PDP110, it is possible to obtain a radiation image of an object, if any, placed on the apparatus40.

FIGS. 6A through 6Dare cross-sectional views for explaining the operation of another exemplary apparatus50for detecting radiation, which includes both a metal layer103-2and a dielectric layer103-2that serve together as a charge trapping layer. The apparatus50is the same as the apparatus20shown inFIG. 3except that it includes the metal layer103-1and the dielectric material103-2as a charge trapping layer.

Referring toFIG. 6A, when radiation such as X-rays is applied to the apparatus50, the radiation may be transmitted to a first photoconductive layer102through an upper electrode layer101, and pairs of positive and negative charges may be generated in the first photoconductive layer102. When a high voltage HV is applied to the upper electrode layer101, the positive and negative charges may be separated from each other and may move toward opposite directions. More specifically, if a negative voltage is applied to the first photoconductive layer102, the positive charges in the first photoconductive layer102may move toward the upper electrode layer101, and the negative charges in the first photoconductive layer102may move toward the dielectric layer103-2.

Due to the movement of the negative charges toward the dielectric layer103-2, the dielectric layer103-2may be polarized, and dipoles may be generated in the dielectric layer103-2. The dipoles in the dielectric layer103-2may be arranged in a manner shown inFIG. 6B.

Due to the pattern of the arrangement of the dipoles in the dielectric layer103-2, the metal layer103-1may be charged with positive charges. A lower transparent electrode layer105may be charged with negative charges due to the positive charges in the metal layer103-1. More specifically, the lower transparent electrode layer105may be charged with as many negative charges as there are dipoles in the dielectric layer103-2.

A radiation image read-out operation will hereinafter be described in detail.

The upper electrode layer101may be connected to a ground source. Then, if a first row of pixels in a PDP110is turned on, plasma light may be emitted from the first row of pixels. The plasma light may transmit through the lower transparent electrode layer105and may thus reach a second photoconductive layer104.

Referring toFIG. 6C, pairs of positive and negative charges may be generated in the second photoconductive layer104, and particularly, in a portion of the second photoconductive layer104corresponding to the first row of pixels, upon exposure to the plasma light emitted from the first row of pixels. The positive and negative charges generated in the second photoconductive layer104may be electrically attracted to the metal layer103-1and the lower transparent electrode layer105, respectively, and may thus be separated from each other.

Referring toFIG. 6D, due to the negative charges in the lower transparent electrode layer105, positive charges may be read out from the portion of the second photoconductive layer104corresponding to the first row of pixels by the data processing unit200. Then, the read-out positive charges may be subjected to image processing performed by the data processing unit200.

Thereafter, the first row of pixels may be turned off, and a second row of pixels may be turned on. Then, the second row of pixels may emit plasma light. Due to the plasma light, pairs of positive and negative charges may be generated in a portion of the second photoconductive layer104corresponding to the second row of pixels. The positive and negative charges generated in the second photoconductive layer104may be electrically attracted to the metal layer103-1and the lower transparent electrode layer105, respectively, and may thus be separated from each other. Due to the negative charges in the lower transparent electrode layer105, positive charges may be read out from the portion of the second photoconductive layer104corresponding to the second row of pixels by the data processing unit200. Then, the read-out positive charges may be subjected to image processing performed by the data processing unit200.

Thereafter, the same operation as that performed on the first and second rows of pixels may also be performed on a third row of pixels. As a result, positive charges may be read out from a portion of the second photoconductive layer104corresponding to the third row of pixels by the data processing unit200. Then, the read-out positive charges may be subjected to image processing performed by the data processing unit200.

By performing the above-mentioned operation on all rows of pixels in the PDP110, it is possible to obtain a radiation image of an object, if any, placed on the apparatus50.

FIG. 7is a flowchart of an exemplary method of detecting radiation. Referring toFIG. 7, a high voltage may be applied to the upper electrode layer101(710), and radiation may be applied onto the upper electrode layer101(720). Pairs of positive and negative charges may be generated in the first photoconductive layer102(730). The positive and negative charges may be separated from each other and may move toward the upper electrode layer101and the charge trapping layer103, respectively. As a result, either the positive or negative charges may accumulate in the charge trapping layer103(740). More specifically, if a negative voltage is applied to the upper electrode layer101, negative charges may be trapped in the charge trapping layer103, and thus, the lower transparent electrode layer105may be charged with the opposite polarity to that of the charges trapped in the charge trapping layer103.

The application of a high voltage to the upper electrode layer may be terminated, and the upper electrode layer101may be connected to a ground source (750). Thereafter, if rear light such as plasma light is applied (760), pairs of positive and negative charges may be generated in the second photoconductive layer104(770).

Thereafter, a signal corresponding to the charges trapped in the charge trapping layer103may be read out from the lower transparent electrode layer105due to the positive or negative charges in the second photoconductive layer104(780). Thereafter, a radiation image may be generated based on the read-out signal (790).

More specifically, if the charge trapping layer103includes a dielectric layer, the charge trapping layer103may be polarized due to the positive or negative charges in the first photoconductive layer102, and thus, dipoles may be generated and arranged in the charge trapping layer103. Due to the pattern of the arrangement of the dipoles in the charge trapping layer103, the lower transparent electrode layer105may be charged, and thus, the positive or negative charges in the second photoconductive layer104may be attracted to the lower transparent electrode layer105. In this manner, a signal reflecting the arrangement of the dipoles in the charge trapping layer103can be read out from the lower transparent electrode layer105.

Alternatively, if the charge trapping layer103includes a dielectric layer and a metal layer and the dielectric layer and the metal layer contact the first photoconductive layer102and the second photoconductive layer104, respectively, the dielectric layer may be polarized due to the positive or negative charges trapped in the charge trapping layer103, and thus, dipoles may be generated and arranged uniformly in the dielectric layer. The metal layer may be charged according to the pattern of the arrangement of the dipoles in the dielectric layer.

As a result, the lower transparent electrode layer105may be charged with the opposite polarity to that of the charges in the metal layer, e.g., positive charges. During a radiation image read-out operation, positive charges generated in the second photoconductive layer104upon exposure to rear light may be attracted to the lower transparent electrode layer105, and thus, a signal reflecting the arrangement of the dipoles in the dielectric layer or corresponding to the charges in the metal layer may be read out from the lower transparent electrode layer105.

As described above, it is possible to provide an apparatus and method for detecting radiation, which can improve the resolution of a radiation image and can contribute to the simplification of the manufacture of the apparatus.