JPH114821A - X-ray diagnostic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a high definition image (an animation) without impairing an advantage of a direct converting method to prevent elemental rupture by a voltage increase in picture element electric potential by providing an active element which is connected to picture element capacity to accumulate detecting electric charge corresponding to a carrier and releases partial electric charge of the detecting electric charge to source electric potential. SOLUTION: An electrode 100 and a picture element electrode 104 are arranged so as to vertically sandwich a photoconductor 101 to generate a carrier by X-ray irradiation, and the following circuit constitution is formed to read signal electric charge on the picture element electrode 104. A high withstand voltage transistor Tr10 to which signal capacity 105 is connected in parallel is connected to this picture element electrode 104, and a second Tr106 is connected. The signal electric charge is distributed to the picture element capacity 104 and the signal capacity 105 of the photoconductor 101 by X-ray irradiation, and when picture element electric potential (at a point A) increases, gate voltage is impressed on a gate line 110 of a Tr10, and is put in an ON condition. Therefore, a part of electric charge is released, and the impression of breakdown voltage on a Tr106 and the signal capacity 105 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct conversion type X
The present invention relates to the structure of a line diagnostic device.

[0002]

2. Description of the Related Art Conventionally, an X-ray diagnostic apparatus is a useful apparatus capable of non-destructively examining a specimen, and it has been desired to obtain a moving image with high definition. Furthermore, in order to avoid an increase in the size and weight of the apparatus, a flat detector of the diagnostic apparatus is required. In order to achieve these requirements, an active matrix type flat detector has been proposed. Such a plane detector includes an indirect conversion method and a direct conversion method. The direct conversion method can obtain a higher definition image than the indirect conversion method. This direct conversion method is, for example, EIDuPont
USP5319206, DLLee et al. SPIE vol.2432 p.23
7 1995, which will be described with reference to FIGS. 13 (a) and 13 (b). First, the X-ray X incident on the photoconductor 301 is
An electron-hole pair 309 is generated, and the generated charge is transferred to the signal capacitor 305 and the electrode 300 facing the pixel electrode 304.
And the volume formed by X-ray incident charges are collected by the integrator through the drains D1 to D4 when the gate G of the transistor is opened by a signal from the gate signal Gl. In the direct conversion method, the photoconductor 301
Since all the information incident on the pixel electrode is collected as electron-hole pairs 309, it is possible to realize a high-definition image by refining the shape of the pixel electrode. Where 308
Is a power supply, and the insulating film 302 is a film for preventing the destruction of a circuit caused by an abnormal rise in the potential of the pixel electrode 304 because a large amount of electron-hole pairs 309 generated when the amount of X-rays is large are simultaneously generated. is there. The capacitance formed by the insulating film 302 becomes a protection capacitance 312 on an equivalent circuit. The newly provided protection capacitor 312 has an effect of alleviating a potential rise due to charges corresponding to the electron-hole pairs generated by X-ray irradiation. Therefore, destruction of the transistor 306 and the signal capacitor 305 can be prevented.

[0003] However, this conventional method has a drawback that it cannot handle moving images. This is especially shown in Figure 13 (b)
This will be described using the equivalent circuit of FIG. The charge generated by the X-rays is distributed to the protection capacitor 312, the capacitance of the photoconductor pixel electrode 304, and the signal capacitance 305. By opening the gate G of the transistor 306, charges of the signal capacitor 305 and the photoconductor capacitor 304 can be read using the data line D. The signal capacity 305 and the capacity 304 of the photoconductor can be initialized by the charge reading operation. At this time, in order to initialize the charge of the protection capacitor 312, a time corresponding to a time constant depending on the internal resistance of the photoconductor 301 and the resistance of the transistor 306 is required. Therefore, this method has a problem that, even if high definition can be achieved, a moving image which is a problem peculiar to the direct method cannot be obtained.

[0004]

In the conventional system using the direct conversion system, a moving image cannot be obtained even if a high-definition image can be obtained. An object of the present invention is to provide an X-ray diagnostic apparatus capable of obtaining a high-definition image as a moving image without impairing the advantage of a direct conversion method for preventing element destruction due to a rise in pixel potential in the X-ray diagnostic apparatus. Aim.

[0005]

According to a first aspect of the present invention, there is provided an X-ray diagnostic apparatus, comprising: a photoconductor having two opposing main surfaces and generating carriers by X-ray irradiation; A pixel electrode formed on one main surface side of the conductor to receive the carrier, a signal capacitor connected between the pixel electrode and a power supply potential to receive the carrier and accumulate detected charges corresponding to the carrier; An X-ray diagnostic apparatus having a first transistor connected to a capacitor and detecting the charge as a pixel potential, comprising: an active element connected to the pixel capacitor and releasing a part of the detected charge to the power supply potential. It is characterized by the following.

According to a second aspect of the present invention, in the first aspect, the active element is a second transistor having a higher withstand voltage than the first transistor, and an offset region between the source / drain electrode and the gate electrode. And the amount of the partial charge is controlled by a set distance between the source electrode and the drain electrode from the gate electrode in the offset region.

According to a third aspect of the present invention, there is provided an X-ray diagnostic apparatus, wherein a plurality of X-ray receiving elements are two-dimensionally arranged, and a plurality of pixel capacitors are formed in a pair with the X-ray receiving elements and accumulate charges generated from the X-ray receiving elements. A first transistor which is formed as a pair for each pixel capacitor and which extracts a charge stored in the pixel capacitor as a detection signal from a drain in accordance with a timing at which a source is connected to the pixel capacitor and a gate is opened; In a direct conversion type X-ray diagnostic apparatus including a plurality of protective capacitors connected between a source of each transistor and a power supply potential, the terminal connected between a terminal for storing the electric charge of the pixel capacitance and a power supply potential has the terminal An active element for releasing a part of the charge to the power supply potential when the potential exceeds a certain potential is provided. The X-ray diagnostic apparatus according to claim 4 is
According to a third aspect, the active element is a second transistor having a source and a drain connected to both ends of the protection capacitor.

According to a fifth aspect of the present invention, in the third aspect, the gate electrodes of the second transistor are commonly connected. Here, the power supply potential includes not only ± power supply potential but also GND.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to an active element such as a high breakdown voltage transistor (especially a thin film transistor (TFT)) for preventing an abnormal increase in pixel potential due to X-ray irradiation.
The main point is to provide a charge storage circuit configuration and a circuit configuration for initialization using the same. This will be described in detail with reference to the following examples.

(Embodiment 1) An embodiment of the present invention will be described with reference to FIG. FIG. 1A is a sectional structural view of an embodiment of the present invention, and FIG. 1B is an equivalent circuit diagram of one pixel. The electrode 100 and the pixel electrode (the pixel electrode 104 is formed by the two electrodes so as to sandwich the photoconductor 101 from above and below.
Since the electric charge used is the electric charge accumulated in the pixel electrode 104, the same number is assigned to the pixel capacitance and the pixel electrode.)
4 are formed. The following circuit configuration for reading a signal charge is formed for the pixel electrode 104. The first transistor 10 is connected in parallel with the signal capacitor 105. Further, a second transistor 106 is connected to the pixel electrode. D, D1, D2, etc. indicate signal lines or connections to signal lines. Here, in the present invention, it is important that the first transistor 10 is of a high withstand voltage type. Here, the first transistor 10 is hereinafter referred to as a high breakdown voltage transistor.

The principle of operation of this embodiment will be described with reference to FIG. 1B, which is an equivalent circuit for one pixel. The pixel capacitance 104 and the signal capacitance 10 of the photoconductor 101 are irradiated by X-ray irradiation.
5, the signal charges are distributed. As a result, the pixel potential (point A) increases. At this time, the high voltage transistor 10
A gate voltage of an appropriate constant potential is applied to the gate line 110b to turn it on, and the second transistor 10
6. Operate so as to release a part of the accumulated charges so that the breakdown voltage is not applied to the signal capacitor 105. In addition, when reading the charge in the signal capacitor 105, the initialization is easy because the unnecessary charge is not stored anywhere. Therefore, an X-ray diagnostic apparatus capable of outputting a moving image can be provided, since it is possible to avoid a circuit breakdown of the transistor 106 or the like due to a rise in pixel potential, which is a problem in the direct conversion method, and to realize initialization in a sufficiently short time. Can be.

Here, the reason why the high breakdown voltage transistor 10 is required will be described with reference to FIG. FIG. 2 shows a comparison between a voltage-current characteristic 20 of a normal transistor and a voltage-current characteristic 21 of a high breakdown voltage transistor. The high breakdown voltage transistor has a drain current I in a region where the drain voltage Vd is small.
d hardly flows. However, a certain drain voltage Vdo
, And a large drain current Id is observed. The high breakdown voltage transistor described in FIG. 1 needs to have characteristics as shown in FIG. Therefore, the drain voltage Vdo is changed to the signal capacitance 1 described in FIG.
By setting it to 05 or less than or equal to the withstand voltage of the pixel capacitor 104, it is possible to fulfill the role described in FIG.

Next, it will be described that the drain voltage Vdo can be arbitrarily set by describing the cross-sectional structure of the X-ray diagnostic apparatus of the present invention using the structure of the high breakdown voltage transistor. FIG. 3 shows a cross-sectional structure of one pixel of the X-ray diagnostic apparatus of the present embodiment.
The electrode 100 and the pixel electrode 104 are arranged at both ends of the photoconductor 101. Further, a signal capacitor 105 having a pair of a pixel electrode 104 and an electrode 112 is formed, and a transistor 106 for reading a signal charge and a high withstand voltage transistor 1 are provided on both sides thereof.
0 is formed. The signal charge reading transistor 106 has a gate electrode 107 formed on a substrate 115, an electrode 114 serving also as a drain electrode of the high breakdown voltage transistor 10 and a source electrode of the signal charge reading transistor 106, and a drain electrode 109 sandwiching the semiconductor 108. It has a staggered structure. The high breakdown voltage transistor 10 also has an inverted stagger structure. The gate electrode of the high voltage transistor 10 is 111 and is connected to a gate line of a different system from the gate electrode of the transistor 106 for reading signal charges. Transistor 10 for signal reading
6 is symmetrical, whereas the high breakdown voltage transistor 10
Is an offset region Lo between the gate electrode 111 and the contact portion.
The feature is that ff is formed. Offset area Lo
ff means the contact layer 113 from the end of the gate electrode 111.
And the distance from the semiconductor layer 108 to the contact B. The setting of the drain voltage Vdo described with reference to FIG. 2 can be arbitrarily set by the offset length Loff. In this embodiment, the offset region Loff is set to the drain electrode 114 which is likely to have a high potential, but the same effect can be expected even if it is set to the source electrode 119 side. The same effect can be expected regardless of the source or drain side. Next, the manufacturing process will be specifically described with reference to FIG. First, the electrode patterns 107, 111, and 112 are formed on the insulating substrate 115 by, for example, a sputtering method, whole-surface resist coating and mask patterning, and etching. As the insulating substrate 115, a transparent insulating substrate such as a glass substrate may be used. The electrode patterns 107 and 111 are also gate electrodes of the transistor, and 112 is an electrode of a signal capacitor described later. In this sense, the electrodes 107, 111, 112
Is desired to have low resistance, and Mo, Ta, W, Al, C
u or an alloy containing at least one of these metals may be used. The thickness of the electrodes 107, 111, 112 is 50 nm to 30
0 nm is desirable from the viewpoint of realizing the above-described low resistance and improving the coverage of the first insulating film described later. Patterned electrodes 107, 111, 11
On the second insulating film 116, a first insulating film 116, a semiconductor layer 108, and a second insulating film 117 are deposited. In forming these films, for example, a film using a chemical vapor deposition method (PECVD) by plasma excitation is used in consideration of film deposition on a large area. PECVD
Using a silicon oxide film as the first insulating film 116,
A silicon nitride film, a silicon oxynitride film, or a stacked film thereof is deposited, hydrogenated amorphous silicon is deposited as the semiconductor layer 108, and a silicon oxide film, a silicon nitride film, or a silicon oxide film is formed as a second insulating film. A nitride film or a stacked film of these may be deposited. The semiconductor layer 108
Polycrystalline silicon, microcrystalline silicon, or the like may be used. The thickness of the first insulating film 116 is the same as that of the electrodes 107, 111, and 1 described above.
12 and 100 n so that a sufficiently large electric field can be applied to the semiconductor 108 in order to maintain a good coverage for the transistor to be formed and to obtain a sufficient on / off ratio of the transistor to be formed.
m to 400 nm, the film thickness of the semiconductor layer 108 is 20 nm to 300 nm in order to ensure a sufficient volume velocity per unit time, and the on / off ratio of the transistor is sufficient. The film thickness of the second insulating film 117 is In order to obtain a sufficient margin when etching the contact layer 113 to form an electrode, the thickness may be 100 nm to 400 nm (FIG. 4A).

Next, the second insulating film 117 is patterned, and a contact layer 118 is deposited. Contact layer 1
As No. 18, n + type amorphous silicon doped with P or the like was used. In addition, n + type polycrystalline silicon, microcrystalline silicon, or the like can be used. Contact layer 118
May have a thickness of 20 nm to 300 nm. Second insulating film 11
Reference numeral 7 denotes a pattern for determining the channel length of the transistor. In particular, in the high breakdown voltage transistor 10 shown in FIG. 3, the pattern also determines the offset length Loff. The offset length Loff is a value to be determined by the pixel potential that increases according to the X-ray detection efficiency. In the manufacturing process, the offset length Loff is also determined from the restriction on the pattern alignment accuracy. In this sense, it is desirable that the offset length Loff is not less than 2 μm in order to make the withstand voltage of the obtained high withstand voltage transistor sufficient and to avoid a short circuit between the patterns (FIG. 4B).

Thereafter, source / drain electrode layers 114 are deposited. Al, as the source / drain electrode layer 114,
A favorable source / drain electrode layer 114 can be formed by using Mo, an alloy thereof, or a laminated film. The thickness of the source / drain electrode layer 114 may be 300 nm to 1 μm in order to obtain a sufficiently low-resistance wiring (FIG. 4).
(C)).

Further, by patterning the source / drain electrode layer 114 and patterning the contact layer 113 using the patterned source / drain electrode layer 114 as a mask, the source / drain electrodes 109, 114, 1
19 are formed (FIG. 4D).

Further, an interlayer insulating film 219 is deposited on each completed transistor, and etching is performed so that the source / drain electrodes 114 are exposed in order to form a signal capacitance between the transistor 105 and the electrode 105. The above-described PECVD may be used as the interlayer insulating film 219, and a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a stacked film thereof may be used. If the film thickness is 300 nm to 1 μm, it is good in terms of insulation properties and stability of characteristics (FIG. 5A).

Next, the pixel electrode 10 is filled so as to fill this hole.
4 is formed. A transparent conductive film such as Indi
um Tin Oxide may be used, or a metal thin film such as Al may be used. The thickness of the pixel electrode 104 may be 100 nm to 500 nm. Further, a photoconductor 101 for detecting X-rays is deposited on the pixel electrode 104, and the electrode 100 is formed so as to face the pixel electrode 104. As the photoconductor 101, amorphous selenium or amorphous silicon may be used.
A thickness of 0 μm to 1 mm is good in terms of X-ray conversion efficiency. The electrode 100 may be made of Al or the like, and may have a thickness of about 100 nm (FIG. 5B).

In this manner, the X-ray detector is formed on the pixel electrode 104, and the signal capacitor 105, the signal charge reading transistor 106, and the high voltage transistor 10 can be obtained.

FIG. 6A shows an equivalent circuit in which detectors for one pixel shown in FIG. 1 are two-dimensionally arranged. The fact that a two-dimensional X-ray diagnostic diagram can be obtained will be described with reference to FIG. It is assumed that the signal charge Q11 is accumulated in the signal capacitor 105 connected to the gate line G1 and the data line D1 by X-ray irradiation. The signal charge Q11 is large and the signal capacity 1
When the breakdown voltage reaches the breakdown voltage 05 and the breakdown voltage of the charge reading transistor 106, the high voltage transistor 10 discharges along the path (a). Next, when reading Q11, a voltage is applied to the gate line G1 and the transistor 106 is opened, so that the charge Q11 passes through the path (b).
To the read amplifier 600 or the charge integrator. Thus, a pixel signal corresponding to the pixel potential dropped from the breakdown voltage can be detected. At this time, the charges of all the pixels connected to the gate line G1, for example, Q
12, Q13... Are similarly read. After such a sufficient time has passed, the voltage of the gate line G1 is turned off, and then the gate line G2 is turned on. Similarly, charges, Q21, Q22, Q23. After selecting all the gate lines, a two-dimensional image can be obtained. The gate electrodes of the high breakdown voltage transistors 10 arranged in the row direction in the detector have g1, g2, g3,.
As shown in FIG. 6A, a common potential is applied through the gate line to prevent a high voltage from being applied to the signal capacitance. Here, the method of applying the gate voltage of the first transistor 106 and the gate voltage of the high withstand voltage transistor 105 are different from each other, but they may be used at the same potential as the source electrode of the first transistor 106. That is, as shown in FIG. 6B, the gate potential and the drain potential of the high breakdown voltage transistor are short-circuited. By doing so, the number of wirings can be significantly reduced, which is advantageous not only in yield but also in power for switching the high breakdown voltage transistor 10. With this potential and the offset length Loff described with reference to FIG. 6A, a destructive voltage increase of the pixel potential can be prevented, and the charge of the signal capacitor 105 can be instantaneously initialized. Further, the resolution of the obtained two-dimensional image depends only on the pixel area. In this sense, according to the configuration of the present invention, it has become possible to obtain a high-definition moving image that could not be obtained conventionally.

According to the configuration of the above embodiment, in a direct conversion type X-ray diagnostic apparatus for directly detecting an electron-hole pair generated by X-ray irradiation, the signal capacity for accumulating signal charges of X-ray irradiation is reduced. By providing a high-voltage transistor in parallel to prevent electrical destruction of the signal capacitance, the signal charge reading transistor, and the X-ray detector, the signal capacitance can be initialized by reading the signal charge. Can be. As a result, it has become possible to obtain a high-definition moving image by the direct conversion method. In addition, the X-ray diagnostic system can realize high-definition moving images that could not be obtained by the conventional method only by changing the pattern without using a complicated wiring configuration and without changing the manufacturing process of the conventional detector at all. can do.

(Embodiment 2) Embodiment 2 will be described with reference to FIGS. 7 and 8.
Will be described. The difference from the first embodiment is the structure of the transistor and the like, and the other points are the same. Therefore, the description will be focused on this transistor. FIG. 7 is an equivalent circuit illustrating the second embodiment. A signal reading transistor 706 is connected to the gate line G and the data line D. The signal reading transistor 706 has a signal capacitor 705 and an X-ray detector 711.
And the detection unit capacitance 704 are connected. Signal capacity 705
Are connected to the source and drain of the high voltage transistor 710, and the source electrode is dropped to the ground potential.

The signal charge reading transistor 706 is a high breakdown voltage transistor having an offset structure like the high breakdown voltage transistor 710, and the offset region of the signal charge reading transistor 706 is provided on the signal capacitor 705 side. The circuit configuration is as follows.

FIG. 8 shows a sectional structure of one pixel corresponding to FIG. An offset (offset amount Loff) of the signal charge reading transistor 706 around the signal capacitance 705
1) and the offset (offset amount Loff2) of the high breakdown voltage transistor 710 are formed so as to face each other. Electrode 80
7 is connected to the gate line G of FIG. 7, the electrode 809 is connected to the data line D of FIG. 7, and the pixel electrode 804 and the electrode 812 are connected to the signal capacitor 7 of FIG.
05. The electrode 800 sandwiches the photoconductor 801
The X-ray detection unit 711 and the detection unit capacitance 704 in FIG.

The manufacturing process is the same as that of the first embodiment, except that the structure of the signal charge reading transistor 706 has an offset Loff1 as shown in FIG. It can be realized only by changing the pattern.

In the second embodiment, the pixel electrode and the data line of the signal charge reading transistor 706 generated at the time of X-ray detection are different from the case where the signal charge reading transistor 706 is a normal transistor shown in the first embodiment. Withstand voltage against the potential difference is improved. The signal charge reading transistor 706 has a role of quickly transferring the charge of the signal capacitor 705 to the data line D. Therefore, not only must the withstand voltage with respect to the pixel potential be increased, but also a sufficient drain current must be obtained. For this reason, the offset length Loff1 of the signal reading transistor 806 is determined.
1011 is the offset length L of the high voltage transistor 810
It is desirable that the relationship of Loff1 <Loff2 be established between off2 1012. This embodiment has the same effect as the first embodiment, and also has the effect that the high potential generated at the point A can prevent the signal charge reading transistor 706 from being destroyed. Therefore,
It is important that the point A side of the signal reading transistor 706 is offset.

(Embodiment 3) This embodiment is different from Embodiment 1 in the structure of two transistors, and the other points are the same as Embodiment 1. Third Embodiment A third embodiment will be described with reference to FIG. FIG. 9 shows a sectional structure of one pixel. Example 2
As shown in the figure, two transistors are connected around the signal capacitor 905. One of the two transistors is the signal charge reading transistor 906, and the other is the high withstand voltage transistor 910 described in the first and second embodiments. Transistor 906 for signal reading
Each of the high voltage transistor 910 and the high breakdown voltage transistor 910 has an offset structure, and the offset region is formed on the signal capacitance side.
Further, the feature is that the two semiconductor layers 908 are not separated from each other. In other respects, parts similar to those of the first embodiment are indicated in the 900s with the same last two digits. By having such a structure, in addition to having the same effect as the first embodiment, the insulation resistance of the signal capacitor 905 is increased, and when the charge generated by the X-ray irradiation is accumulated in the pixel and the pixel potential increases, Destruction can be prevented. The manufacturing process is not different from the first and second embodiments, and can be easily realized by changing the patterning shape of the semiconductor layer 908. According to this embodiment, the same effects as those of the first embodiment can be obtained. In addition, the area occupied by the transistors can be reduced by shortening the distance between the two or more transistors 906 and 910 so as not to perform element isolation. This makes it possible to achieve high definition of the X-ray diagnostic apparatus.

(Embodiment 4) An embodiment relating to the structure of the transistor having the offset shown in Embodiments 1, 2, and 3 will be described. The other points other than the transistor structure are the same as those in the first embodiment, and the description will be omitted.

When a transistor having an offset is applied to an X-ray diagnostic apparatus, its role is to read a signal charge and initialize the charge of a signal capacitor. FIG. 10 shows an embodiment of a transistor structure for making the two compatible. An offset length Loff is formed in a transistor including a gate electrode 1007, a gate insulating film 1016, a semiconductor layer 1008, a second insulating film 1020, a contact layer 1013, and a source / drain electrode 1009 over an insulating substrate 1015. Also, the second insulating film 102
A length Lov is formed on 0 so as to cover the source / drain electrodes 1009.

Here, the offset length is the distance from the end of the gate electrode to the point where the semiconductor layer 1008 is in contact with the contact layer 1013 or the end of the second insulating film. Lov is the distance from the end of the electrode pattern of the source / drain electrode to the end of the second insulating film. In the transistor structure described above, a transistor is characterized in that the relationship between the offset lengths Loff and Lov is Loff <Lov.

The operational characteristics of the transistor shown in FIG. 10 will be described. Carriers flowing through the transistor are generated by the potential of the gate electrode 1007. Gate electrode 1007
In the offset region out of the range, the carrier amount is not adjusted by the gate electrode 1007, and reaches the drain electrode 1208 according to only the potential of the end of the gate electrode 1007 and the potential of the drain electrode 1208. It is hard to flow. Parasitic capacitance occurs between the drain electrode 1208 and the gate electrode 1007, and in this sense, it is suitable for using the high breakdown voltage transistor 10 shown in FIG.

However, in order to quickly suppress the pixel potential to be equal to or lower than the breakdown voltage when the pixel potential rises, it is necessary for carriers to flow better when the pixel potential rises. Drain electrode 1 in the offset region of the transistor shown in FIG.
If 208 is the same as the pixel electrode potential, the pixel potential can be suppressed to a breakdown voltage or less without increasing the voltage resistance and the leak current.

The drain electrode 1 is formed on the second insulating film 1020.
Reference numeral 208 denotes the semiconductor layer 100 with the second insulating film 1020 interposed therebetween.
8 and a MOS structure. Accordingly, when the pixel electrode potential is connected to the drain electrode 1208 and the pixel electrode potential rises above, the drain electrode 1208 forms a channel in the semiconductor layer 1008 immediately below, and extra charge can be released. As the excess charge is released, the potential of the pixel electrode, that is, the potential of the drain electrode 1208 also decreases, and the channel closes.

As described above, by setting the drain electrode shape of the offset region to Lov> Loff, the two roles of the potential control of the high breakdown voltage transistor and the charge retention of the signal capacitance can be realized more efficiently. According to this embodiment, in addition to the effect similar to that of the first embodiment, the on-state current of the transistor which has been turned on can be increased, and the electric charge at the point A in FIG. 1B can be efficiently released. It has another effect that it can be done.

(Embodiment 5) An embodiment relating to the structure of the transistor having an offset shown in Embodiments 1, 2, and 3 will be described.

FIG. 11 shows a cross-sectional structure of the transistor structure of the fifth embodiment. The other points other than the transistor structure are the same as those in the first embodiment, and the description will be omitted. A light-shielding film 1302 is formed over an insulating substrate 1301, and a gate electrode 1304 is formed with an interlayer insulating film 1303 interposed therebetween. The gate insulating film 1305, the semiconductor layer 1306, the second
Transistor structure having an insulating film 1307, a contact layer 1308, and source / drain electrodes 1309.

In the above-described transistor structure, the second
The pattern of the insulating film 1307 plays an important role. No.
The pattern of the second insulating film 1307 determines the channel length and offset length of the transistor. In this sense, the second
It can be said that the insulating film 1307 is a pattern that determines transistor characteristics.

When such transistors are two-dimensionally arranged in a large area like an X-ray diagnostic apparatus, it is important to make the transistor characteristics uniform within an effective area. FIG.
Provides a method for forming a second insulating film in a self-aligned manner to improve the uniformity of characteristics. A feature is that the light-shielding film 1302 and the gate electrode 1304 on the insulating substrate 1301 have an overlapping region.

A method for forming the second insulating film 1307 in a self-aligned manner will be described with reference to FIG. Insulating substrate 140
1, a light-shielding film 1402 is formed by patterning,
A gate electrode 1404 is formed with an interlayer insulating film 1403 interposed. Next, a gate insulating film 1405, a semiconductor layer 1406, and a second insulating film 1407, which are films included in the transistor, are sequentially deposited. To pattern the second insulating film 1408, a photoresist 1408 is applied. When patterning the photoresist 1408,
Using a normal mask exposure, a photoresist 1408 for patterning the second insulating film 1407 in a self-aligned manner is exposed from the back side of the insulating substrate 1401 using the light shielding film 1402 and the gate electrode 1404 as a mask. By adopting such a method, this embodiment can provide the same effect as that of the first embodiment, and the second insulating film 1407 can be misaligned by a self-aligned method as shown in FIG. Without, it will be formed. Therefore, it is possible to ensure uniformity of transistor characteristics for controlling one pixel of the X-ray diagnostic apparatus that requires a two-dimensional image.

[0040]

According to the above configuration, an X-ray diagnostic apparatus capable of obtaining a high-definition image and a moving image without deteriorating the advantage of the direct conversion method for preventing element destruction due to an increase in pixel potential in the X-ray diagnostic apparatus. Can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an X-ray diagnostic apparatus according to a first embodiment of the present invention, and an equivalent circuit diagram of one pixel.

FIG. 2 illustrates a first embodiment of the present invention.

FIG. 3 is a sectional view of a pixel according to the first embodiment of the present invention.

FIG. 4 is a sectional view in the order of the manufacturing process according to the first embodiment of the present invention.

FIG. 5 is a sectional view in the order of the manufacturing process according to the first embodiment of the present invention.

FIG. 6 is an operation explanatory diagram when pixels of the first embodiment of the present invention are two-dimensionally arranged;

FIG. 7 is an equivalent circuit diagram of Embodiment 2 of the present invention.

FIG. 8 is a cross-sectional view illustrating a pixel structure according to a second embodiment of the present invention.

FIG. 9 is a cross-sectional view illustrating a pixel structure according to a third embodiment of the present invention.

FIG. 10 is a cross-sectional view and operation principle explanatory diagram of a fourth embodiment of the present invention.

FIG. 11 is a sectional view of a pixel according to a fifth embodiment of the present invention.

FIG. 12 illustrates a fifth embodiment of the present invention.

FIG. 13 shows an example of a conventional direct conversion type X-ray diagnostic apparatus.

[Explanation of symbols]

 Reference Signs List 10 first transistor 100 electrode 101 photoconductor 104 pixel electrode 105 signal capacity 106 second transistor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI // G01N 23/04 H01L 27/14 C

Claims (5)

[Claims] 1. A photoconductor having two opposing main surfaces to generate carriers by X-ray irradiation, a pixel electrode formed on one main surface side of the photoconductor to receive the carriers, An X-ray having a signal capacitor connected between an electrode and a power supply potential for receiving the carrier and accumulating a detected charge corresponding to the carrier, and a first transistor connected to the signal capacitor and detecting the charge as a pixel potential; An X-ray diagnostic apparatus, comprising: an active element connected to the pixel capacitor for releasing a part of the detected charge to the power supply potential. 2. The active element is a second transistor having a higher breakdown voltage than a first transistor, and has an offset region between a source / drain electrode and a gate electrode. Source·
2. The X-ray diagnostic apparatus according to claim 1, wherein the amount of the partial charge is controlled by a set distance between the drain electrodes. 3. A plurality of X-ray light receiving elements arranged two-dimensionally, a plurality of pixel capacitances formed as a pair with the X-ray light reception elements, and a plurality of pixel capacitances for accumulating charges generated from the X-ray light reception elements. And extracting a charge stored in the pixel capacitor from the drain as a detection signal in accordance with a timing at which a source is connected to the pixel capacitor and a gate is opened.
And a plurality of protective capacitors connected between a source of each of the first transistors and a power supply potential, a terminal for storing the charge of the pixel capacitor and a power supply. An X-ray diagnostic apparatus comprising: an active element that is connected between potentials and that releases a part of the charge to the power supply potential when the terminal exceeds a certain potential. 4. The X-ray diagnostic apparatus according to claim 3, wherein the active element is a second transistor having a source and a drain connected to both ends of the protection capacitor. 5. The X-ray diagnostic apparatus according to claim 3, wherein the gate electrodes of the second transistor are connected in common.