Radiation image sensing apparatus and its driving method

This invention has as its object to realize a radiation image sensing apparatus which can adjust (AEC-controls) the amount of incoming light or dose without requiring high-speed driving. Since a second photoelectric conversion element (108) which is used to detect the total dose of radiation that enters a conversion unit is formed independently of pixels having first conversion elements (101) that are formed in the conversion unit on a single substrate, the need for reading out the outputs from the first conversion elements (101) at high speed for the purpose of adjustment of the dose of incoming radiation can be obviated, and another sensor used to adjust the dose need not be added, thus simplifying the structure of a radiation image sensing apparatus.

FIELD OF THE INVENTION

The present invention relates to a radiation image sensing apparatus and its driving method and, more particularly, to a technique which is suitable for a device that forms an image by radiation, and a device that outputs image information corresponding to incoming radiation.

BACKGROUND OF THE INVENTION

In recent years, a demand for “digitization of X-ray image information” has increasingly arisen in the medical field. If such digitization is achieved, a doctor can examine X-ray image information of a patient at an optimal angle in real time, and the obtained X-ray image information can be recorded and managed using a medium such as a magnetooptical disk or the like. Using a facsimile or other communication methods, X-ray image information of a patient can e sent to any hospitals on the globe within a short period of time.

In nondestructive inspection represented by inspection of the interior of an object such as the skeleton of a building or the like, installation of various devices required for X-ray image sensing, and image sensing of a required portion cannot be done so frequently.

Therefore, in such field, a demand for providing X-ray image information of a desired portion in real time is increasing. Hence, an X-ray image sensing apparatus which uses a CCD solid-state image sensing element or amorphous silicon sensor in place of a film has been proposed recently.

An example of a radiation image sensing apparatus that we proposed previously will be explained below.

FIG. 11is a circuit diagram showing the arrangement of a two-dimensional (2D) area sensor.FIGS. 12A and 12Bare respectively a plan view and sectional view of respective building components corresponding one pixel of the 2D area sensor;FIG. 12Ais a plan view andFIG. 12Bis a sectional view.

The radiation image sensing apparatus shown inFIG. 11comprises a 2D matrix of a total of 16 pixels1103, i.e., 4 cells in the vertical direction×4 cells in the horizontal direction. Each pixel1103comprises a set of a sensor element1101, and a transfer transistor1102connected to the element1101.

The sensor elements1101are connected to a bias means1104, and the gates of the transfer transistors1102are connected to a shift register1105via gate lines. Output signals of the transfer transistors1102are transferred to an amplifier/multiplexer/A/D converter1106via signal output lines, and are processed in turn. A reset means1107is connected to the signal output lines of the transfer transistors1102.

A portion bounded by the broken line inFIG. 11is formed on a single, large-area insulating substrate1108.FIG. 12Ais a plan view of a portion corresponding to one pixel.

As shown inFIG. 12A, a photoelectric conversion element1101, TFT (thin film transistor)1102, and a signal line SIG are formed.FIG. 12Bis a sectional view taken along a broken line A–B inFIG. 12A.

According to the layer structure shown inFIG. 12B, the photoelectric conversion element1101, TFT1102, and signal line SIG are simultaneously stacked and formed on an insulating substrate1. These components are formed by only stacking a common lower metal layer2, silicon nitride layer (SiN)7, i-layer4, n-layer5, and upper metal layer6in turn on the insulating substrate1, and etching these layers. After that, a P-layer23, I-layer24, and N-layer25are formed as the photoelectric conversion element1101, and an upper electrode layer26of ITO or the like is formed on the element1101.

Also, a passivation silicon nitride film (SiN)8and a phosphor12which is made up of CsI, Gd2O2S, or the like and wavelength-converts radiation into visible light, are formed on the upper portion of a pixel. When X-rays13that contain image information enter the radiation image sensing apparatus, they are converted by the phosphor12into image information light14, which enters the photoelectric conversion element1101.

An X-ray automatic exposure controller (AEC) that automatically controls the exposure of X-rays emitted by an X-ray source in the radiation image sensing apparatus will be explained below.

In general, in the radiation image sensing apparatus having a 2D sensor matrix, the amount of incoming light must be adjusted (undergo AEC control). This control can be classified into the following two processes.

(1) An AEC control sensor is arranged independently of the radiation image sensing apparatus.

(2) All or some sensor elements in the radiation image sensing apparatus are read at high speed, and are used as an AEC control signal.

Conventionally, a plurality of low-profile AEC control sensors with an X-ray attenuation ratio of around 5% are arranged on the front surface of a 2D sensor that converts an incoming X-ray pattern into a 2D image, and X-ray radiation is stopped by the outputs from these AEC control sensors, thus obtaining an X-ray dose suited to image formation. As an AEC control sensor used in this case, a sensor that directly extracts a charge using an ion chamber, or a sensor which externally extracts phosphor light via a fiber, and converts the extracted light into a charge using a photomultiplier, is used.

However, when the AEC control sensors are independently provided to the radiation image sensing apparatus having the 2D sensor matrix so as to adjust (AEC control) the amount of incoming light or dose, the layout of the AEC control sensors poses a problem. That is, information required for AEC control is present at the central portion of an object, and in order to lay out the AEC control sensors without disturbing image sensing of the image sensing sensor, another optical means or AEC control sensors which have a very low optical attenuation ratio are required.

When all pixels are used, AEC control can be done in a sensor with a relatively small number of pixels. However, in a sensor with 2,000×2,000 pixels or more, a high-speed driving circuit is required, resulting in an increase in cost of the overall apparatus.

Since high-speed driving is required, it becomes difficult for the sensor of the radiation image sensing apparatus to assure a sufficiently long charge accumulation time, charge transfer time, and capacitor reset time, and the like, resulting in poor image quality of a sensed image.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the aforementioned problems, and has as its object to provide a radiation image sensing apparatus and its driving method, which can adjust (AEC control) the amount of incoming light or dose without requiring high-speed driving.

A radiation image sensing apparatus of the present invention is directed to a radiation flat panel detector sensing apparatus which has a conversion unit that comprises a plurality of pixels having first conversion elements, and switch elements connected to the first conversion elements on a substrate, and which outputs image information in accordance with a intensity of radiation that enters the conversion unit, comprising a second conversion element which is formed on the substrate to detect a total intensity of radiation that enters the conversion unit and/or start/stop of a irradiation of radiation, and a processing circuit unit which is connected to the second conversion element and processes a detected signal.

A method of driving a radiation image sensing apparatus of the present invention is directed to a method of driving a radiation image sensing apparatus, which has a conversion unit that comprises a plurality of pixels having first conversion elements, and switch elements connected to the first conversion elements on a substrate, a second conversion element which is formed on the substrate to detect a total intensity of radiation that enters the conversion unit, and a processing circuit unit which is connected to the second conversion element, comprising the step of making the processing circuit unit detect the total intensity and/or start/stop of a irradiation of radiation and controlling the intensity of radiation that enters the conversion unit, in accordance with an output from the second conversion element.

A radiation image sensing apparatus of the present invention is directed to a radiation image sensing apparatus for outputting image information corresponding to incoming radiation, comprising a substrate, conversion means which comprises, on the substrate, a plurality of pixels each of which has a first conversion element that converts the incoming radiation into an electrical signal, and a switch element connected to the first conversion element, and total intensity detection means which comprises a second conversion element that is formed on the substrate and converts the incoming radiation into an electrical signal, and a processing circuit that is connected to the second conversion element and detects a total dose of radiation that enters the conversion means, wherein radiation detection of the second conversion element is disabled at a timing at which image information is output in accordance with the dose of radiation that enters the first conversion elements.

According to an aspect of the radiation image sensing apparatus of the present invention, the second conversion element has a TFT structure, and the processing circuit unit disables radiation detection of the second conversion elements by setting source and drain electrodes of the second conversion element at a ground potential or another identical potential.

According to an aspect of the radiation image sensing apparatus of the present invention, the processing circuit unit extracts an electrical signal from the second conversion element as a current.

According to an aspect of the radiation image sensing apparatus of the present invention, the processing circuit unit includes addition means for adding a charge output from the second conversion element, integral means for integrating the charge added by the addition means, comparison means for comparing an integral value obtained by the integral means with a threshold value which is set in advance, and radiation interception means for, when the comparison means determines that the integral value is larger than the threshold value, stopping radiation with which the conversion means is irradiated.

According to an aspect of the radiation image sensing apparatus of the present invention, the second conversion element is formed at a plurality of positions on the substrate, and the processing circuit unit detects the intensity of radiation by selecting the second conversion element at an optimal position from the plurality of second conversion elements.

According to an aspect of the radiation image sensing apparatus of the present invention, each of the first conversion elements is formed to have a MIS semiconductor structure.

A method of driving a radiation image sensing apparatus of the present invention is directed to a method of driving a radiation image sensing apparatus for outputting image information corresponding to incoming radiation, which apparatus includes a substrate, conversion means which comprises, on the substrate, a plurality of pixels each of which has a first conversion element that converts the incoming radiation into an electrical signal, and a switch element connected to the first conversion element, and total dose detection means which comprises a second conversion element that is formed on the substrate and converts the incoming radiation into an electrical signal, and a processing circuit that is connected to the second conversion element and detects a total dose of radiation that enters the conversion means, the method comprising the step of disabling radiation detection of the second conversion element at a timing at which image information is output in accordance with the dose of radiation that enters the first conversion elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of a radiation image sensing apparatus and its driving method according to the present invention will be described hereinafter with reference to the accompanying drawings.

The first embodiment of the present invention will be described below with reference toFIG. 1.

FIG. 1is a circuit diagram of a radiation image sensing apparatus of this embodiment. As shown inFIG. 1, the radiation image sensing apparatus of this embodiment comprises a 2D matrix of a total of 16 pixels103, i.e., 4 cells in the vertical direction×4 cells in the horizontal direction. Each pixel103comprises a first photoelectric conversion element101, and a transistor102, which is connected to the element101and serves as a transfer switch element.

The first photoelectric conversion elements101are connected to a first bias means104, and the gates of the transistors102are connected to a shift register105via gate lines G1to G4for respective rows. Output signals of the transistors102are transferred to an amplifier/multiplexer/A/D converter106via signal lines S1to S4for respective columns, and undergo signal processes in turn. A reset means107is connected to the signal lines S1to S4of the transistors102for respective columns.

Furthermore, an elongated second photoelectric conversion element108, hatched inFIG. 1, is arranged. The second photoelectric conversion element108has a shape different from those of the first photoelectric conversion elements101used to sense a normal image.

The first photoelectric conversion elements101correspond to gray element portions inFIG. 1, which are arranged at equal pitches p in a 4×4 2D matrix, and are connected to the first bias means104.

Charges generated by the first photoelectric conversion elements101corresponding to a row selected by the shift register105are read out via the transistors102, are transferred to the amplifier/multiplexer/A/D converter106, are selectively amplified by the amplifier (AMP), and are then converted by the A/D converter.

After the charges are read out, the reset means107executes a charge reset operation. Note that this operation is not necessary depending on the structure of the radiation image sensing apparatus.

The second photoelectric conversion element108is arranged in an elongated shape among the pixels103and between the signal lines (S2and S3) in the column direction. Since the second photoelectric conversion element108is flush with the first photoelectric conversion elements101, first photoelectric conversion elements101′ which neighbor the second photoelectric conversion element108have an area smaller than those of other first photoelectric conversion elements101.

The second photoelectric conversion element108is connected to a second bias means109. Upon reading out a charge, the second photoelectric conversion element108can always output a charge according to the amount of incoming light without being selected by the shift register105. For this purpose, the second photoelectric conversion element108is always applied with a constant potential. A charge detected by the second photoelectric conversion element108is amplified by a second amplifier (AMP)110, and the total dose of radiation is detected by adding the output from the second amplifier110.

According to this embodiment, since an AEC control sensor (second photoelectric conversion element108) is formed in a photoelectric conversion substrate111, it need not be independently arranged, a radiation detection apparatus can be made compact, and the circuit arrangement can be simplified. Since the AEC control sensor has an arrangement independent from a sensor (first photoelectric conversion elements) used to acquire image information, and a processing circuit unit is independently arranged, the need for reading out a charge by high-speed driving can be obviated, thus preventing deterioration of the image quality of a sensed image.

Since the AEC control sensor (second photoelectric conversion element108) is laid out to run across a plurality of pixels in a direction perpendicular to driving lines in the row direction, i.e., in a direction parallel to the signal lines S1to S4in the column direction, so as not to form any intersections with the signal lines S1to S4in the column direction, an extra capacitance can be prevented from being parasitic on the signal lines S1to S4, thus allowing to read out output signals with a high S/N ratio. Since the AEC control sensor is laid out to run across a plurality of pixels in a direction parallel to the signal lines, the radiation dose can be detected on the average of a broader region.

The second embodiment of the present invention will be described below with reference toFIG. 2andFIGS. 3A and 3B.

FIG. 2is a circuit diagram of a radiation image sensing apparatus of this embodiment.FIGS. 3A and 3Bare respectively a plan view and sectional view of building components corresponding to one pixel of the radiation image sensing apparatus;FIG. 3Ais a plan view, andFIG. 3Bis a sectional view taken along a broken line A–B inFIG. 3A.

In this embodiment, each first photoelectric conversion element201has a PIN structure. Each switch element202is formed by a TFT (thin film transistor). The gates of the switch elements202are connected to a shift register208via gate lines G1to G3. Output signals from the switch elements202are externally output via signal lines S1to S3.

A second photoelectric conversion element204, which has an elongated shape compared to the first photoelectric conversion elements201used to read out a normal image, is laid out in a photoelectric conversion circuit unit203formed on a substrate to run across a plurality of pixels in the signal line direction of normal pixels. Especially, in this embodiment, the second photoelectric conversion element204is formed in a combtooth shape.

Since the second photoelectric conversion element204is flush with the first photoelectric conversion elements201, first photoelectric conversion element201′ which neighbor the second photoelectric conversion element204have an area smaller than those of other first photoelectric conversion elements201. This decrement of the area can be compensated for by image correction executed after a charge is read out.

The second photoelectric conversion element204is connected to a second bias power supply (Bias2) independently of a first bias power supply205used to acquire image information, and always outputs a charge in accordance with the amount of incoming light. Hence, the element204is always applied with a bias. A charge output from the element204is amplified by an amplifier (AMP2)207.

FIGS. 3A and 3Bare respectively a plan view and sectional view of building components corresponding to one pixel of the radiation image sensing apparatus, and the second photoelectric conversion element204;FIG. 3Ais a plan view andFIG. 3Bis a sectional view.

Note that the second photoelectric conversion element204as an AEC control sensor has a layer structure in which a lower metal layer2of the TFT202is removed. A formation method of this layer structure will be described below.

A 50-nm thick Cr film is deposited on a glass substrate1of an insulating material by, e.g., sputtering to form a lower metal layer2, which is patterned by photolithography to remove an unnecessary area by etching. As a result, the gate electrode of the TFT202is formed.

Then, a 200-nm thick silicon nitride film (SiN)7, 500-nm thick i-layer4, and 50-nm n-layer5are respectively deposited by CVD in a single vacuum environment. In the TFT202, the silicon nitride film (SiN)7serves as a gate insulating film, the i-layer4serves as a semiconductor layer, and the n-layer5serves as an ohmic contact layer. Also, in the second photoelectric conversion element204, the silicon nitride film (SiN)7serves as a lower insulating layer, the i-layer4serves as a photoelectric conversion semiconductor layer, and the n-layer5serves as an ohmic contact layer.

After these layers are deposited, a 1,000-nm thick Al film is deposited by, e.g., sputtering.

Furthermore, the resultant structure is patterned by photolithography to remove an unnecessary area by etching. With this process, an upper metal layer6, which serves as the source and drain electrodes as main electrodes of the TFT202, and a signal line SIG, is formed. Also, in the second photoelectric conversion element204, an upper electrode30is formed.

After that, a P-layer23, I-layer24, and N-layer25are formed as the first photoelectric conversion element201′, and an upper electrode layer26of ITO or the like is formed on the resultant structure.

Furthermore, the n-layer5in only a channel portion of the TFT202is removed by etching, and unnecessary layers are then removed by etching to isolate elements.

With the aforementioned fabrication process, the first photoelectric conversion element201′, TFT202, and second photoelectric conversion element204are fabricated. The process for one pixel has been described, but other pixels are formed at the same time.

In order to improve durability, a passivation film8of, e.g., a silicon nitride film (SiN) or the like is formed on the respective elements to cover them, and a phosphor12, which is made up of CsI, Gd2O2S, or the like and serves as a waveform converter, is further formed.

In this embodiment, since the second photoelectric conversion element204as the AEC control sensor need only detect the total dose of incoming radiation, it is always applied with a bias during irradiation. For this reason, the second photoelectric conversion element204can be fabricated as a structure obtained by removing the lower metal layer2of the TFT2, thus simplifying the fabrication process and achieving a cost reduction.

The third embodiment of the present invention will be described below with reference toFIG. 4andFIGS. 5A and 5B.

FIG. 4is a circuit diagram of a radiation image sensing apparatus of this embodiment.FIGS. 5A and 5Bare respectively a plan view and sectional view of building components corresponding to one pixel of the radiation image sensing apparatus;FIG. 5Ais a plan view andFIG. 5Bis a sectional view. In this embodiment, a first photoelectric conversion element401has an MIS structure, and a switch element402comprises a TFT.

In this embodiment as well, first photoelectric conversion elements401′ which neighbor a second photoelectric conversion element403have an area smaller than those of other first photoelectric conversion element401.

The second photoelectric conversion element403is connected to a second bias power supply (Bias2)206, need not be selected by a shift register208upon reading out a charge, and is always applied with a bias so as to output a charge in accordance with the amount of incoming light all the time. A charge generated by the second photoelectric conversion element403is amplified by an amplifier (AMP2)207.

FIGS. 5A and 5Bare respectively a plan view and sectional view of one pixel which includes the second photoelectric conversion element403, and its neighboring first photoelectric conversion element401′;FIG. 5Ais a plan view andFIG. 5Bis a sectional view. A formation method of the structure shown inFIGS. 5A and 5Bwill be described below.

A 50-nm thick Cr film is deposited on a glass substrate1of an insulating material by, e.g., sputtering to form a lower metal layer2, which is patterned by photolithography to remove an unnecessary area by etching. In this case, the lower electrode layer2on a prospective formation region of the second photoelectric conversion element403is removed. As a result, the lower electrode of the photoelectric conversion element401′, the gate electrode of the TFT402, and the lower electrode of a capacitor407are formed.

Then, a 200-nm thick silicon nitride film (SiN)7, 500-nm thick i-layer4, and 50-nm n-layer5are respectively deposited by CVD in a single vacuum environment. In the photoelectric conversion element401′, the silicon nitride film (SiN)7serves as a lower insulating film, the i-layer4serves as a photoelectric conversion semiconductor layer, and the n-layer5serves as a hole injection blocking layer. Also, in the TFT402, the silicon nitride film (SiN)7serves as a gate insulating film, the i-layer4serves as a semiconductor layer, and the n-layer5serves as an ohmic contact layer. Furthermore, in the capacitor407, the silicon nitride film (SiN)7, i-layer4, and n-layer5serve as interlayers. Moreover, in the second photoelectric conversion element403, the silicon nitride film (SiN)7serves as a lower insulating film, the i-layer4serves as a photoelectric conversion semiconductor layer, and the n-layer5serves as an ohmic contact layer.

Also, these layers are used as cross-part insulating layers of a signal line SIG.

The thicknesses of the respective layers are not limited to such specific values, and are optimally designed depending on the voltage, current, charge, amount of incoming light, and the like used for a 2D area sensor. However, at least the silicon nitride layer (SiN)7must have a thickness of 50 nm or more so as to block electrons and holes and to serve as a gate insulating film of the TFT402.

After these layers are deposited, a 1,000-nm thick Al film is deposited by, e.g., sputtering. Furthermore, the resultant structure is patterned by photolithography to remove an unnecessary area by etching. With this process, the upper electrode of the photoelectric conversion element401′, the source and drain electrodes as main electrodes of the TFT402, the upper electrode of the capacitor407, the signal line SIG, and an upper electrode30of the second photoelectric conversion element402are formed. Note that an ITO film or the like may be formed only on the upper electrodes of the first and second photoelectric conversion elements401′ and403depending on element characteristics.

Furthermore, the n-layer5in only a channel portion of the TFT402is removed by etching, and unnecessary portions of the silicon nitride layer (SiN)7, i-layer4, and n-layer5are then removed by etching to isolate elements.

With the aforementioned fabrication process, the first photoelectric conversion element401′, TFT402, second photoelectric conversion element403, and capacitor407are formed. The process for one pixel has been described, but other pixels are formed at the same time.

In order to improve durability, a passivation film8of, e.g., a silicon nitride film (SiN) or the like is formed on the respective elements to cover them, and a phosphor12, which is made up of CsI, Gd2O2S, or the like and serves as a waveform converter, is further formed.

Note that the second photoelectric conversion element403as an AEC control sensor has a layer structure obtained by removing the lower metal layer2of the first photoelectric conversion element401′, TFT402, and capacitor407, as described above.

In this way, since the AEC control sensor (second photoelectric conversion element403) need only detect the total dose of incoming radiation, it can be fabricated together with the layer structure of the first photoelectric conversion element401′, switch element402, and the like, thus achieving a simple fabrication process of the AEC control sensor and a cost reduction.

The fourth embodiment of the present invention will be described below with reference toFIG. 6.

FIG. 6is a system block diagram of a radiation image sensing apparatus of this embodiment. X-rays generated by an X-ray generator6are converted into visible light by a phosphor unit (not shown), and radiation having image information strikes a 2D sensor602.

Simultaneously with incidence on the 2D sensor602, the converted visible light hits first, second, and third photoelectric converters603,604, and605of a second photoelectric conversion element, which is formed on a sensor substrate and serves as an AEC control sensor.

The photoelectric converters603,604, and605of the second photoelectric conversion elements as the AEC control sensor are arranged at different positions on the sensor substrate. For example, groups L, R, and C of stripe-shaped AEC control sensors (second photoelectric conversion elements) shown inFIG. 13may be used.

Charges generated by the photoelectric converters603,604, and605of the second photoelectric conversion element in response to incoming light are extracted from the photoelectric converters603,604, and605, and are added for respective groups by adders606to608. As an addition method, simple addition, and a method of adding charges by weighting them in correspondence with the positions of six stripes, as shown inFIG. 13, may be used. The charges added by the adders606to608are integrated by integrators609to611, and the integral outputs are input to a selector612.

The selector612controls whether to selectively use the integral outputs of three channels as the integrators609to611or to add them to use the sum. This control depends on a portion to be sensed. For example, a larger one of the outputs of groups L and R is selected upon sensing a chest front image, and the output of group C is solely used upon sensing an abdomen or chest side image.

The output selected by the selector612is compared with a threshold value which is set in advance in a comparator614by a threshold value setting unit613. If the selected output is larger than the threshold value, an X-ray intercept unit615is driven to stop radiation from the X-ray generator601. When X-ray radiation is stopped, the integral process of the 2D sensor602ends, and data from the 2D sensor602is transferred to and stored in a memory616after A/D conversion. The data stored in the memory616is read out or the like under the control of a system controller618which is connected via a system bus617.

Using the output from the second photoelectric conversion element, X-ray radiation stop control can be implemented. Also, the integral process of the 2D sensor602can be finished earlier so as to limit unnecessary offset charges accumulated on the 2D sensor602.

Since data is fetched in synchronism with X-ray radiation stop control, a sensed image can be displayed earlier.

The fifth embodiment of the present invention will be described below with reference toFIG. 7.

FIG. 7is a circuit diagram of a radiation image sensing apparatus of this embodiment. Note that the same reference numerals denote the same building components as those described inFIG. 1of the first embodiment, and differences from the first embodiment will be described below.

In this embodiment, a second photoelectric conversion element701as an AEC control sensor has a size for four pixels (from one edge pixel to another edge pixel).

In this manner, the width in a direction parallel to signal lines S1to S4is smaller than the pitch of pixels103, and the length is around four times of the pitch of the pixels103since it amounts to four pixels, Since the light-receiving area of the second photoelectric conversion element701as the AEC control sensor is increased by increasing the width in the direction parallel to the signal lines S1to S4, a photocurrent generated by the second photoelectric conversion element701as the AEC control sensor can be increased, thus improving the sensitivity of the AEC control sensor (second photoelectric conversion element701).

The sixth embodiment of the present invention will be described below with reference toFIG. 8.

FIG. 8is a circuit diagram of a radiation image sensing apparatus of this embodiment. Note that the same reference numerals denote the same building components as those described inFIG. 1of the first embodiment, and differences from the first embodiment will be described below.

In this embodiment, first photoelectric conversion elements, which are arranged in a given column, and do not neighbor a second photoelectric conversion element801as an AEC controls sensor, have the same size as that of a normal pixel.

With this structure, the number of pixels, in which the outputs from the first photoelectric conversion elements must be corrected since they have smaller areas, can be reduced.

The seventh embodiment of the present invention will be described below with reference toFIG. 9.

FIG. 9is a circuit diagram of a radiation image sensing apparatus of this embodiment. Note that the same reference numerals denote the same building components as those described inFIG. 1of the first embodiment, and differences from the first embodiment will be described below.

In this embodiment, a second photoelectric conversion element901has the same length or width as that of a first photoelectric conversion element forming region, and first photoelectric conversion elements have the same size in all pixels.

Since the first photoelectric conversion elements have the same size in all pixels, the need for output correction due to different element sizes of the first photoelectric conversion elements can be obviated.

The eighth embodiment of the present invention will be described below with reference toFIG. 10.

FIG. 10is a circuit diagram of a radiation image sensing apparatus of this embodiment. Note that the same reference numerals denote the same building components as those described inFIG. 1of the first embodiment, and differences from the first embodiment will be described below.

In this embodiment, a second photoelectric conversion element for AEC control is locally formed in a first photoelectric conversion element forming region, and the first photoelectric conversion elements have the same size in all pixels.

Since the first photoelectric conversion elements have the same size in all pixels, the need for output correction due to different element sizes of the first photoelectric conversion elements can be obviated.

The ninth embodiment of the present invention will be described below with reference toFIG. 14andFIGS. 15A and 15B.

FIG. 14is a circuit diagram of a radiation image sensing apparatus of this embodiment.FIGS. 15A and 15Bare respectively a plan view and sectional view of building components corresponding to one pixel of the radiation image sensing apparatus;FIG. 15Ais a plan view andFIG. 15Bis a sectional view.

In this embodiment, a first photoelectric conversion element901has an MIS structure, and a switch element902comprises a TFT. In the radiation image sensing apparatus, the first photoelectric conversion element901, the switch element902, and a capacitor904form one pixel. A second photoelectric conversion element903has a TFT structure, and its gate (lower metal) is applied with a bias to be a given potential.

In this embodiment as well, first photoelectric conversion elements901′ which neighbor a second photoelectric conversion element903have an area smaller than those of other first photoelectric conversion element901.

The source or drain electrode of the second photoelectric conversion element903is connected to a second bias power supply (Bias2)206, need not be selected by a shift register208upon reading out a charge, and is always applied with a bias to output a charge in accordance with the amount of incoming light. The gate electrode is set at a given potential, i.e., is applied with a negative bias inFIG. 14. A charge generated by the second photoelectric conversion element903is amplified by an amplifier (AMP2)207.

FIGS. 15A and 15Bare respectively a plan view and sectional view of one pixel which includes the second photoelectric conversion element903, and its neighboring first photoelectric conversion element901′;FIG. 15Ais a plan view andFIG. 15Bis a sectional view. The same formation method as that described in the third embodiment can be used to form a structure that leaves the gate (lower electrode) of the second photoelectric conversion element.

In order to improve durability, a passivation film8of, e.g., a silicon nitride film (SiN) or the like is formed on the respective elements to cover them, and a phosphor12, which is made up of CsI, Gd2O2S, or the like and serves as a waveform converter, is further formed.

In this embodiment, the second photoelectric conversion element903has the same layer structure as that of the TFT that serves as the switch element902to simply the fabrication process. Also, the second photoelectric conversion element903with stable characteristics can be obtained.

Processing circuits that apply a bias to the source/drain, a bias to the gate, amplify a signal, and so forth in association with the second photoelectric conversion element903are preferably formed near a side close to the forming region of the second photoelectric conversion element903, thus allowing easy wiring layout.

The 10th embodiment of the present invention will be described below with reference toFIG. 1.

FIG. 1is a circuit diagram of a radiation image sensing apparatus of this embodiment. As shown inFIG. 1, the radiation image sensing apparatus of this embodiment comprises a 2D matrix of a total of 16 pixels103, i.e., 4 cells in the vertical direction×4 cells in the horizontal direction. Each pixel103comprises a first photoelectric conversion element101, and a transistor102, which is connected to the element101and serves as a transfer switch element.

The first photoelectric conversion elements101are connected to a first bias means104, and the gates of the transistors102are connected to a shift register105via gate lines G1to G4for respective rows. Output signals of the transistors102are transferred to an amplifier/multiplexer/A/D converter106via signal lines S1to S4for respective columns, and undergo signal processes in turn. A reset means107is connected to the signal lines S1to S4of the transistors102for respective columns.

Furthermore, an elongated second photoelectric conversion element108, hatched inFIG. 1, is arranged. The second photoelectric conversion element108has a shape different from those of the first photoelectric conversion elements101used to sense a normal image.

The first photoelectric conversion elements101correspond to gray element portions inFIG. 1, which are arranged at equal pitches p in a 4×4 2D matrix, and are connected to the first bias means104.

Charges generated by the first photoelectric conversion elements101corresponding to a row selected by the shift register105are read out via the transistors102, are transferred to the amplifier/multiplexer/A/D converter106, are selectively amplified by the amplifier (AMP), and are then converted by the A/D converter.

After the charges are read out, the reset means107executes a charge reset operation. Note that this operation is not necessary depending on the structure of the radiation image sensing apparatus.

The second photoelectric conversion element108is arranged in an elongated shape among the pixels103and between the signal lines (S2and S3) in the column direction. Since the second photoelectric conversion element108is flush with the first photoelectric conversion elements101, first photoelectric conversion elements101′ which neighbor the second photoelectric conversion element108have an area smaller than those of other first photoelectric conversion elements101.

The second photoelectric conversion element108is connected to a second bias means109. Upon reading out a charge, the second photoelectric conversion element108can always output a charge according to the amount of incoming light without being selected by the shift register105. For this purpose, the second photoelectric conversion element108is always applied with a constant potential. In this case, since the second photoelectric conversion element108is formed independently of pixels, a charge can be read out from it without using the shift register. A charge detected by the second photoelectric conversion element108is amplified by a second amplifier (AMP)110, and a total dose of radiation is detected by adding the output from the second amplifier110.

According to this embodiment, since an AEC control sensor (second photoelectric conversion element108) is formed in a photoelectric conversion substrate111, it need not be independently arranged, a radiation detection apparatus can be made compact, and the circuit arrangement can be simplified. Since the AEC control sensor has an arrangement independent from a sensor (first photoelectric conversion elements) used to acquire image information, and independent processing circuit units are arranged, the need for reading out a charge by high-speed driving can be obviated, thus preventing deterioration of the image quality of a sensed image.

Since the AEC control sensor (second photoelectric conversion element108) is laid out to run across a plurality of pixels in a direction perpendicular to driving lines in the row direction, i.e., in a direction parallel to the signal lines S1to S4in the column direction, so as not to form any intersections with the signal lines S1to S4in the column direction, an extra capacitance can be prevented from being parasitic on the signal lines S1to S4, thus allowing to read out output signals with a high S/N ratio. Since the AEC control sensor is laid out to run across a plurality of pixels in a direction parallel to the signal lines, the radiation dose can be detected on the average of a broader region.

The 11th embodiment of the present invention will be described below with reference toFIG. 16.

FIG. 16shows a driving circuit unit and processing circuit unit when the second photoelectric conversion element903shown inFIG. 14is a TFT sensor. As shown inFIG. 16, the radiation image sensing apparatus of this embodiment comprises a TFT second photoelectric conversion element S100, operational amplifier OP100, power supply M100, and feedback resistor R100.

As a driving method of the radiation image sensing apparatus, a bias is applied across the source and drain electrodes of the TFT second photoelectric conversion element S100to fix the gate electrode at a given potential.

Subsequently, when signal light enters in this state, a photocurrent is generated, and a positive signal charge (hole) flows into the feedback resistor R100. Hence, this photocurrent can be read at the output terminal of the operational amplifier OP100. At this time, by connecting the power supply M100to the non-inverting input terminal of the operational amplifier OP100, the potential of the source electrode of the TFT second photoelectric conversion element S100can be set to be equal to that of the power supply M100.

The 12th embodiment of the present invention will be described below with reference toFIG. 17.

FIG. 17shows a driving circuit unit and processing circuit unit when the second photoelectric conversion element903shown inFIG. 14is a TFT sensor, as another aspect of the 10th embodiment. As shown inFIG. 17, the radiation image sensing apparatus of this embodiment comprises a TFT second photoelectric conversion element S200, operational amplifier OP200, power supply M200, switch SW200, and feedback resistor R200.

As a driving method of the radiation image sensing apparatus, a bias is applied across the source and drain electrodes of the TFT second photoelectric conversion element S200to fix the gate electrode at a given potential.

Subsequently, when signal light enters in this state, a photocurrent is generated, and a positive signal charge (hole) flows into the feedback resistor R200. Hence, the total charge amount of accumulated positive signal charges (holes) can be read at the output terminal of the operational amplifier OP200. At this time, the switch SW200is open. Also, by connecting the power supply M200to the non-inverting input terminal of the operational amplifier OP200, the potential of the source electrode of the TFT second photoelectric conversion element S200can be set to be equal to that of the power supply M200.

After the total charge amount of accumulated positive signal charges (holes) is read at the output terminal of the operational amplifier OP200, the switch SW200is closed to reset the accumulated total charge.

The 13th embodiment of the present invention will be described below with reference toFIG. 18.

FIG. 18shows a driving circuit unit and processing circuit unit when the second photoelectric conversion element903shown inFIG. 14is a TFT sensor, as still another aspect of the 10th embodiment. As shown inFIG. 18, the radiation image sensing apparatus of this embodiment comprises a TFT second photoelectric conversion element S300, operational amplifier OP300, power supply M300, switch SW300, and feedback resistors R300and R310.

As a driving method of the radiation image sensing apparatus, a bias is applied across the source and drain electrodes of the TFT second photoelectric conversion element S300to fix the gate electrode at a given potential.

Subsequently, when signal light enters in this state, a photocurrent is generated, and positive signal charges (holes) are accumulated on a cumulative capacitor C300. Hence, since the potential of the total charge amount of accumulated positive signal charges (holes) can be amplified at a gain of ((R300+R310)/R310), the amplified potential can be read at the output terminal of the operational amplifier OP300. At this time, the switch SW300is open.

After the amplified potential is read at the output terminal of the operational amplifier OP300, the switch SW300is closed to reset the accumulated total charge, and the source electrode of the TFT second photoelectric conversion element S300is fixed at a given potential of the power supply M300.

The 14th embodiment of the present invention will be described below with reference toFIG. 19.

FIG. 19shows a driving circuit unit and processing circuit unit when the second photoelectric conversion element S200shown inFIG. 17is an MIS sensor. As shown inFIG. 19, the radiation image sensing apparatus of this embodiment comprises a TFT second photoelectric conversion element S400, operational amplifier OP400, power supply M400, transistor T400, switch SW400, and feedback capacitor C400.

As a driving method of the radiation image sensing apparatus, a bias is applied across the upper and lower electrodes of the MIS second photoelectric conversion element S400.

Subsequently, when signal light enters in this state, a photocurrent is generated, and a positive signal charge (hole) flows into the feedback capacitor C400. Hence, the total charge amount of accumulated positive signal charges (holes) can be read at the output terminal of the operational amplifier OP400. At this time, the switch SW400is open. Also, by connecting the power supply M400to the non-inverting input terminal of the operational amplifier OP400, the potential of the source electrode of the MIS second photoelectric conversion element S400can be set to be equal to that of the power supply M400.

After the total charge amount of accumulated positive signal charges (holes) is read at the output terminal of the operational amplifier OP400, the switch SW400is closed to reset (refresh) a photocharge accumulated on the MIS second photoelectric conversion element S400.

FIG. 1is a circuit diagram of a radiation image sensing apparatus of this embodiment.

As shown inFIG. 1, the radiation image sensing apparatus of this embodiment comprises a conversion means formed by arranging, two-dimensionally (in a matrix), a large number of pixels103, each of which comprises a first photoelectric conversion element101, and a transistor102, which is connected to the element101and serves as a transfer switch element, on a glass substrate, and a total dose detection means which has a second photoelectric conversion element108, and a second amplifier (AMP)110that is connected to the element108and detects the total dose of radiation that enters the conversion means. In this embodiment,FIG. 1illustrates a total of 16 pixels, i.e., 4 cells in the vertical direction×4 cells in the horizontal direction, for the sake of simplicity.

The first photoelectric conversion elements101are connected to a first bias means104, and the gates of the transistors102are connected to a shift register105via gate lines G1to G4for respective rows. Output signals of the transistors102are transferred to an amplifier/multiplexer/A/D converter106via signal lines S1to S4for respective columns, and undergo signal processes in turn. A reset means107is connected to the signal lines S1to S4of the transistors102for respective columns.

Furthermore, the elongated second photoelectric conversion element108, hatched inFIG. 1, is arranged. The second photoelectric conversion element108has a shape different from those of the first photoelectric conversion elements101used to sense a normal image.

The first photoelectric conversion elements101correspond to gray element portions inFIG. 1, which are arranged at equal pitches p in a 4×4 2D matrix, and are connected to the first bias means104.

Charges generated by the first photoelectric conversion elements101corresponding to a row selected by the shift register105are read out via the transistors102, are transferred to the amplifier/multiplexer/A/D converter106, are selectively amplified by the amplifier (AMP), and are then converted by the A/D converter.

After the charges are read out, the reset means107executes a charge reset operation. Note that this operation is not necessary depending on the structure of the radiation image sensing apparatus.

The second photoelectric conversion element108is arranged in an elongated shape among the pixels103and between the signal lines (S2and S3) in the column direction. Since the second photoelectric conversion element108is flush with the first photoelectric conversion elements101to have the same layer structure, first photoelectric conversion elements101′ which neighbor the second photoelectric conversion element108have an area smaller than those of other first photoelectric conversion elements101.

The second photoelectric conversion element108is connected to a second bias means109. Upon reading out a charge, the second photoelectric conversion element108can always output a charge according to the amount of incoming light without being selected by the shift register105. For this purpose, the second photoelectric conversion element108is always applied with a constant potential. A charge detected by the second photoelectric conversion element108is amplified by the second amplifier (AMP)110, and a total dose of radiation is detected by adding the output from the second amplifier110.

According to this embodiment, since an AEC control sensor (second photoelectric conversion element108) is formed in a photoelectric conversion substrate111, it need not be independently arranged, a radiation detection apparatus can be made compact, and the circuit arrangement can be simplified. Since the AEC control sensor has an arrangement independent from a sensor (first photoelectric conversion elements) used to acquire image information, and a processing circuit unit is independently arranged, the need for reading out a charge by high-speed driving can be obviated, thus preventing deterioration of the image quality of a sensed image.

Since the AEC control sensor (second photoelectric conversion element108) is laid out to run across a plurality of pixels in a direction parallel to the signal lines S1to S4in the column direction so as not to form any intersections with the signal lines S1to S4in the column direction, an extra capacitance can be prevented from being parasitic on the signal lines S1to S4, thus allowing to read out output signals with a high S/N ratio.

The driving operation and signal process of the second photoelectric conversion element will be described below.

FIG. 20shows a processing circuit unit when the second photoelectric conversion element shown inFIG. 1is a TFT sensor.

Reference numeral S100denotes a TFT second photoelectric conversion element; D, a drain electrode; S, a source electrode; and G, a gate electrode. Reference numeral110denotes the second amplifier (AMP: operational amplifier) inFIG. 1; M100, a power supply; and R100, a feedback resistor.

As an actual driving method, a bias is applied across the source and drain electrodes of the TFT second photoelectric conversion element S100to fix the gate electrode at a given potential.

When signal light enters in this state, a photocurrent is generated, and a positive signal charge (hole) flows into the feedback resistor R100. Hence, the photocurrent can be read at the output terminal of the second amplifier110. At this time, by connecting the power supply M100to the non-inverting input terminal of the second amplifier110, the potential of the source electrode of the TFT second photoelectric conversion element S100can be set to be equal to that of the power supply M100.

The second photoelectric conversion element S100is set OFF at the output timing of image information read by the first photoelectric conversion elements101by fixing the potentials of the respective electrodes of the second photoelectric conversion element S100at a ground (GND) potential or a constant potential, so as not to influence signals of the first photoelectric conversion elements101, which are formed around the element S100.

In this way, the influence on the operation for outputting signals read by the first photoelectric conversion elements101as image information can be eliminated.

Also, by reading the output from the AEC sensor (photoelectric conversion element S100) as a current using the second amplifier110, not only an X-ray dose suited to image formation can be obtained by stopping X-ray radiation based on the output from the photoelectric conversion element S100, but also the stop timing of generated X-rays can be obtained.

The 16th embodiment of the present invention will be described below.

FIG. 21is a circuit diagram of a radiation image sensing apparatus of this embodiment.FIG. 22is a timing chart of the radiation image sensing apparatus of this embodiment.FIGS. 15A and 15Bare respectively a plan view and sectional view of building components corresponding to one pixel of the radiation image sensing apparatus;FIG. 15Ais a plan view andFIG. 15Bis a sectional view taken along a broken line A-B inFIG. 15A.

Referring toFIG. 21, reference numerals S11to S33denote photoelectric conversion elements; C11to C33, cumulative capacitors; and T11to T33, transfer TFTs. Reference symbol Vs denotes a read power supply; and Vg, a refresh power supply. These power supplies Vs and Vg are respectively connected to all the photoelectric conversion elements S11to S33via switches SWs and SWg. The switches SWs is connected to a refresh control circuit RF via an inverter, and the switch SWg is directly connected to it. These switches are controlled by the refresh control circuit RF, so that the switch SWg is turned on during a refresh period, and the switch SWs is turned on during the remaining period. One pixel is formed by one photoelectric conversion element, capacitor, and TFT, and its signal output is connected to a detection integrated circuit IC via a signal line SIG. In a 2D area sensor of this embodiment, a total of nine pixels are divided into three blocks, and the outputs from three pixels per block are simultaneously transferred, and are sequentially converted and output by the detection integrated circuit via the signal line. By arranging three pixels per block in the horizontal direction, and arranging three blocks in turn in the vertical direction, the pixels are arranged two-dimensionally.

A second photoelectric conversion element is arranged between the photoelectric conversion elements S11and S21, and photoelectric conversion elements S12and S22. The second photoelectric conversion element has an elongated, combtooth shape, which is different from the shapes of the first photoelectric conversion elements S11to S22used to sense a normal image.

Note that the second photoelectric conversion element inFIG. 21is a TFT sensor.

The drain electrode of the second photoelectric conversion element inFIG. 21is connected to a bias power supply (Bias2), and its source electrode is connected to an amplifier (AMP2), which amplifies and outputs a charge generated in accordance with the amount of incoming light of radiation.

At this time, since the gate electrode potential is fixed to be negative with respect to the source electrode potential, a larger ratio between the photocurrent and dark current can be obtained. The larger ratio between the photocurrent and dark current can improve the performance of the second photoelectric conversion element.

FIGS. 15A and 15Bare respectively a plan view and sectional view of the photoelectric conversion elements S12and S22.

InFIGS. 15A and 15B, reference numeral S0denotes the second photoelectric conversion element for an AEC sensor. The second photoelectric conversion element has the same layer structure as the photoelectric conversion element (S11), capacitor (C11), and TFT (T1-1).

In this way, since the second photoelectric conversion element is used as an AEC sensor, the AEC sensor can be formed at low cost, and a low-cost image sensing apparatus can be provided.

A portion bounded by the broken line inFIG. 21is formed on a single, large-area insulating substrate. Reference numeral S11denotes a photoelectric conversion element; T11, a TFT; C11, a capacitor; and SIG, a signal line. In this embodiment, the capacitor C11and photoelectric conversion element S11are not specially isolated, and the capacitor C11is formed by increasing the area of the electrode of the photoelectric conversion element S11.

A passivation silicon nitride film (SiN)8and a phosphor12of CsI, Gd2O2S, or the like are formed on the upper portion of a pixel. When X-rays13that contain image information enter from the upper surface of the structure, they are converted by the phosphor12into image information light14, which enters the photoelectric conversion element.

The formation method of respective elements will be described in turn usingFIGS. 15A and 15B.

A 50-nm thick Cr film is deposited on a glass substrate1of an insulating material by, e.g., sputtering to form a lower metal layer2, which is patterned by photolithography to remove an unnecessary area by etching. As a result, the lower electrode of the photoelectric conversion element S11, the gate electrode of the TFT T11, and the lower electrode of the capacitor C11are formed. Then, a 200-nm/500-nm/50-nm thick SiN (7)/i (4)/n (5) layers are respectively deposited by CVD in a single vacuum environment. These layers serve as an insulating layer/photoelectric conversion semiconductor layer/hole injection blocking layer of the photoelectric conversion element S11, a gate insulating film/semiconductor layer/ohmic contact layer of the TFT T11, and an interlayer of the capacitor C11. Also, these layers are used as cross-part insulating layers of the signal line. The thicknesses of the respective layers are not limited to such specific values, and are optimally designed depending on the voltage, current, charge, amount of incoming light, and the like used for a 2D area sensor. However, at least the SiN layer must have a thickness of 50 nm or more so as to block electrons and holes and to serve as a gate insulating film of the TFT.

After these layers are deposited, a 1,000-nm thick Al film is deposited by, e.g., sputtering. Furthermore, the resultant structure is patterned by photolithography to remove an unnecessary area by etching. With this process, the upper electrode of the photoelectric conversion element S11, the source and drain electrodes as main electrodes of the TFT T11, the upper electrode of the capacitor C11, and the signal line SIG are formed.

Furthermore, the n-layer in only a channel portion of the TFT T11is etched by RIE, and unnecessary portions of the SiN (7)/i (4)/n (5) layers are then removed by etching to isolate elements. In this manner, the photoelectric conversion element S11, TFT T11, and capacitor C11are formed. The process for one pixel has been described, but other pixels are formed at the same time.

In order to improve durability, a passivation film8of, e.g., a silicon nitride film (SiN) or the like is formed on the respective elements to cover them, and a phosphor12of CsI, Gd2O2S, or the like is further formed.

As described above, in this embodiment, the photoelectric conversion element, TFT, capacitor, and signal line SIG can be formed by only the common lower metal layer2, the SiN (7)/i (4)/n (5) layers, and the upper metal layer6, which are deposited at the same time, and etching of respective layers. The photoelectric conversion element S11has only one injection element layer, and can be formed in a single vacuum environment. Furthermore, the gate insulating film/i-layer interface, which is important in terms of the characteristics of the TFT, can be formed in a single vacuum environment. Moreover, since the interlayer of the capacitor C11includes an insulating layer that suffers less leakage due to heat, a capacitor with satisfactory characteristics can be formed.

The operation of the radiation image sensing apparatus of this embodiment will be described below using the timing chart shown inFIG. 22.

A doctor or operator sets a patient to be examined, i.e., an object (not shown) at a position between an X-ray source (not shown) and 2D area sensor (not shown) and poses the object to be able to observe a portion to be examined. At the same time, the doctor or operator inputs conditions at a control panel (not shown) so as to obtain an optimal image sensing output in consideration of the symptom, physical attribute, and age of the patient obtained by doctor's questions or the like in advance, and information to be acquired. This signal is sent to an AE controller (not shown) as an electrical signal. At the same time, a condition memory circuit (not shown) stores the input condition.

In this state, when the doctor or operator presses an image sensing exposure start button (not shown), an image sensing mode starts. A system control circuit (not shown) controls the 2D area sensor (not shown) to execute a refresh operation. Shift registers SR1and SR2apply Hi signals to control lines g1to g3, and s1and s2. In response to these signals, the transfer TFTs T11to T33, and switches M1to M3are enabled (turned on), and the D electrodes of all the photoelectric conversion elements S11to S33are set at GND potential (since the input terminal of an integral detector Amp is designed to be GND potential).

At the same time, the refresh control circuit RF outputs a Hi signal to turn on the switch SWg, and the G electrodes of all the photoelectric conversion elements S11to S33are set at a positive potential by the refresh power supply Vg. Then, all the photoelectric conversion elements S11to S33are set in a refresh mode, and are refreshed.

Subsequently, the refresh control circuit RF outputs a Lo signal to turn on the switch SWs, and the G electrode of all the photoelectric conversion elements S11to S33are set at a negative potential by the read power supply Vs. Then, all the photoelectric conversion elements S11to S33are set in a photoelectric conversion modes and the capacitors C11to C33are reset at the same time. In this state, the shift registers SR1and SR2apply Lo signals onto the control lines g1to g3, and s1and s2. The transfer TFTs T11to T33and switches M1to M3are turned off, and the electrodes of all the photoelectric conversion elements S11to S33are opened in a DC manner but their potentials are held by the capacitors C11to C33. However, since no X-rays enter all the photoelectric conversion elements S11to S33at this time, no photocurrents flow. In this way, the refresh operation ends.

During the refresh operation of the first photoelectric conversion elements, the potentials of the respective electrodes (source, drain, and gate) of a second photoelectric conversion element S100shown inFIG. 21andFIGS. 15A and 15Bare fixed at GND or s given potential. As a result, the first photoelectric conversion elements of all the pixels are refreshed uniformly.

The respective electrodes (source, drain, and gate) of the second photoelectric conversion element S100shown inFIGS. 20 and 21are then set at potentials that allow photoelectric conversion. More specifically, the source electrode potential is set at around 3 V, the drain electrode potential is set at around 10 V, and the gate electrode potential is set at around 0 V.

In this state, when X-rays are generated, are transmitted through the object, and enter the phosphor, they are converted into light, and that light enters the first photoelectric conversion elements S11to S33and the second photoelectric conversion element S100.

When the total amount of light that has entered the second photoelectric conversion element S100reaches a given threshold value, a signal that stops X-ray radiation is output, thus ending X-ray radiation. With this process, since the second photoelectric conversion element S100ends its role, the potentials of the respective electrodes (source, drain, and gate) of the second photoelectric conversion element S100shown inFIGS. 20 and 21are fixed at GND or a given potential. Thus, the influence on the subsequent operation for outputting signals read by the first photoelectric conversion elements S11to S33as image information can be eliminated.

An actual operation will be described below with reference to the timing chart inFIG. 22.

Photocurrents, which flow in the first photoelectric conversion elements S11to S33in response to a given amount of light, are accumulated as charges in the capacitors C11to C33, and are held after completion of X-ray radiation. The 2D area sensor then executes a read operation. When the shift register SR1applies a Hi control pulse to the control line g1, and the shift register SR2applies control pulses to the control lines s1to s3, signals v1to v3are sequentially output via the transfer TFTs T11to T13and switches M1to M3. Likewise, other light signals are output under the control of the shift registers SR1and SR2. In this manner, 2D information of the inner structure of a human body or the like is obtained as signals v1to v9. Note that signals v2, v5, and v8, which are output from the control line s2via the switch M2, have smaller outputs than other signals since the areas of the first photoelectric conversion elements S12, S22, and S32are smaller than other elements. However, these signals are finally compensated for later.

Since the first photoelectric conversion elements are driven in the same manner as in the prior art shown inFIG. 11and do not require high-speed driving, a high-performance image sensing apparatus, which is free from any drop of image quality of a sensed image, can be consequently provided.

Also, since the size of the AEC control sensor can be reduced without using another commercially available AEC control sensor, a compact image sensing apparatus can be provided. Since the first and second photoelectric conversion elements can be formed to have the same layer structure using same thin films, a low-cost image sensing apparatus can be provided.

According to the present invention, since a second conversion element used to detect the total dose of radiation that enters a conversion unit is arranged on a single substrate independently of pixels having first conversion elements, which are arranged in the conversion unit that outputs image information, the need for reading out outputs from the first conversion elements at high speed for the purpose of input dose adjustment can be obviated, and no sensor for adjusting the dose is required, thus simplifying the structure of the radiation image sensing apparatus.

Furthermore, since the second conversion element is formed to have a TFT structure, and radiation detection of the second conversion element is disabled at the timing at which the first conversion elements output image information in accordance with the dose of radiation that has entered the first conversion elements in the conversion unit, i.e., since the potentials of the respective electrodes (source, drain, and gate) of the second photoelectric conversion element are fixed at GND or a given potential, the influence on the subsequent operation for outputting signals read by the first photoelectric conversion elements as image information can be eliminated.

Moreover, since the output from the second conversion element is read as a current using a processing circuit unit (operational amplifier), not only X-ray radiation is stopped in response to the output from the second conversion element to obtain an X-ray dose suited to image formation, but also the stop timing of generated X-rays can be obtained.

In this embodiment, a second conversion element, which is arranged independently of first conversion elements that detect signals used to read an image, is used as a sensor for detecting start/stop of a irradiation of radiation (to be referred to as an X-ray monitor hereinafter). This X-ray monitor, for example, is used deciding the timing that starts read-out of the sensor. In this case, a differential circuit in a read circuit is connected to the second conversion element to differentiate the detected signal, thereby detecting incidence and/or stop of radiation. Alternatively, a circuit shown inFIG. 18can be used. The second conversion element may be either of TFT or MIS type. Note that the MIS type is of capacitance type that stores carriers in an insulating layer, and corresponds to a sensor disclosed in, e.g., U.S. Pat. No. 6,075,256.

Also, both a conversion element used to detect the total dose of radiation, which has been explained until the 16th embodiment, and an X-ray monitor conversion element can be formed on the substrate, or an element which has both functions may be formed in place of forming the two elements. In this case, a current read circuit shown inFIG. 18can be used as the arrangement of a read circuit.

(Other Embodiments of Present Invention)

The present invention may be applied to either a system constituted by a plurality of devices, or an apparatus consisting of a single equipment.

The scope of the present invention includes a case wherein the functions of the embodiments are implemented by supplying, from a storage medium or via a communication medium such as the Internet or the like, a program code of software that implements the functions of the embodiments to a computer (or a CPU or MPU) in a system or apparatus, which is connected to various devices to make these devices implement the functions of the aforementioned embodiments, and making the computer of the system or apparatus control the devices in accordance with the stored program.

In this case, the program code itself of software implements the functions of the embodiments, and the program code itself, and means for supplying the program code to the computer (e.g., a storage medium which stores the program code) constitutes the present invention. As the storage medium for storing such program code, for example, a flexible disk, hard disk, optical disk, magnetooptical disk, CD-ROM, magnetic tape, nonvolatile memory card, ROM, and the like may be used.

The program code is included in the embodiments of the present invention not only when the functions of the above embodiments are implemented by executing the supplied program code by the computer, but also when the functions of the embodiments are implemented by collaboration of the program and an OS (operating system) or another application software running on the computer.

Furthermore, the present invention includes a case wherein the functions of the above embodiments are implemented by some or all of actual processing operations executed by a CPU or the like arranged in a function extension board or a function extension unit, which is inserted in or connected to the computer, after the supplied program code is written in a memory of the extension board or unit.

According to the present invention, since a second conversion element used to detect the total dose of radiation that enters a conversion unit is arranged on a single substrate independently of pixels having first conversion elements, which are arranged in the conversion unit that outputs image information, the need for reading out outputs from the first conversion elements at high speed for the purpose of input dose adjustment can be obviated, and no sensor for adjusting the dose is required, thus simplifying the structure of the radiation image sensing apparatus.