JP2001108748A - Radiographic image picking-up device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiographic image picking-up device having linearity in sensor sensititvity used favorably for medical care and non-destructive inspection. SOLUTION: This device is provided with plural input picture elements of which the each is provided with a charge conversion means 121 for converting an incident radiation into a charge, a charge accumulating means 122 for accumulating the converted charge, a control means 123 arranged between the means 121, 122 to control an electric field applied to the charge conversion means 121, and a reading-out means 124 for reading out the charge accumulated in the charge accumulating means 122 or a reading-out means for reading out a signal based on a potential due to the charge accumulated in the means 122, an output line connected to the plural picture elements to output the charge read out from the input picture elements, and a switching means for resetting the charge accumulating means 122.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation imaging apparatus and, more particularly, to a radiation imaging apparatus which can be suitably used for converting a radiation image such as an X-ray transmitted through a subject such as a human body into an electronic image. .

[0002]

2. Description of the Related Art An image intensifier (II) for converting X-rays into light, a television camera, and a television, as an X-ray imaging apparatus for converting X-rays, which is one type of radiation, into electric signals. There is a method of obtaining an X-ray image by combining devices (II-TV system). This method is
The X-ray input surface size of the image intensifier becomes the imageable size. The input surface size is about 16 inches.

[0003] The X-ray image converted into light is formed once at an image intensifier output unit. This output image is
Images are taken by a television camera via an optical system and output as electrical images. In this method, an X-ray image can be observed in real time.

[0004]

However, in this method, the resolution is not sufficient, and there is room for improvement. In addition, compared to film, the photographing device is large, and has an improvement in handling, such as a limited installation place and limited movement.

(Purpose) An object of the present invention is to provide a radiation imaging apparatus which can be suitably used for the X-ray imaging apparatus.

Another object of the present invention is to provide a radiation imaging apparatus having excellent sensitivity to incident radiation.

Another object of the present invention is to provide a radiation imaging apparatus capable of preventing carrier overflow via a switch even when an excessive input is made.

It is a further object of the present invention to provide a radiation imaging apparatus capable of performing stable electrical conversion of image information with little afterimage.

Another object of the present invention is to provide a radiation imaging apparatus capable of achieving higher sensitivity.

[0010]

According to the present invention, there is provided a charge converting means for converting incident radiation into electric charge, a charge accumulating means for accumulating the converted electric charge, and a charge converting means. An input pixel provided between the charge storage means and a control means for controlling an electric field applied to the charge conversion means; and a reading means for reading a signal based on the charge stored in the charge storage means. A radiation imaging apparatus comprising: a plurality of the output pixels; an output line connected to the plurality of input pixels for outputting charges read from the input pixels; and switch means for resetting the charge storage means.

Further, the present invention is provided with a charge conversion means for converting incident radiation into charges, a charge storage means for storing the converted charges, and a charge conversion means provided between the charge conversion means and the charge storage means. In addition, the present invention is a radiation imaging apparatus comprising: a control unit that controls an electric field applied to the charge conversion unit; and a reading unit that reads out a signal based on a potential based on charges accumulated in the charge accumulation unit.

In the present invention, radiation is not limited to X-rays, but may include electromagnetic waves such as α, β, and γ-rays. Of course, X-rays are the most common.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic sectional view of an X-ray sensor according to the present invention.

In FIG. 1, reference numeral 100 denotes an X-ray sensing unit which generates electrons and holes by X-ray irradiation. One of the generated carriers is stored and read out as a signal having image information. Reference numeral 200 denotes an electric carrier reading unit, on which the transistor 2 and the like are formed on the insulating substrate 1.

The X-ray sensing unit 100 includes GaAs, G
ap ⁺ layer 10 made of a semiconductor such as aP, Ge, or Si;
a pin diode composed of an n − (or i) layer 20 and an n ⁺ layer 30, and a depletion layer extending from an interface between the p ⁺ layer 10 and the n − layer 20; a metal layer 31 formed on the n ⁺ layer 30; 3
2. It is composed of metal layers 11 and 12 formed below the p ⁺ layer 10. The metal layer 12 is a barrier metal. In the drawings, reference numerals 40 and 50 are protective films. The X-ray sensing unit 100 can be formed on the above-described semiconductor single crystal substrate.

The reading section 200 has a transistor 2 on an insulating substrate 1 which forms a circuit. Transistor 2
Are a gate 101, a source, a drain 102, an active layer 1
03, a metal wiring 110 connected to the source and drain. The transistor 2 is covered with a protective film 113. As a semiconductor material constituting a thin film transistor,
Non-single-crystal materials such as amorphous silicon, polysilicon, and microcrystal silicon are preferably used. Since these can be manufactured on a large glass substrate at a low temperature of 400 ° C. or lower, they are most suitable for a radiation imaging apparatus having a large sensor surface using a large substrate. 111 is an Al layer, and 112 is a metal layer. Although not shown in FIG. 1, the reading unit 200 also has a capacitance.

The metal layer 112 of the read section 200 and the metal layer 11 of the X-ray sensing section 100 are connected by a bump metal 13.

The transistor 2 corresponds to the transistor 124 in FIG. 2 showing a schematic equivalent circuit diagram.

FIG. 23A shows the read portion 20.
FIG. 23B is a schematic plan view illustrating another example of 0.
FIG. 24 is a schematic sectional view taken along line XX ′ of FIG. Further, regarding the member numbers shown in FIG.
This will be described with reference to FIG.

FIG. 2 is a schematic equivalent circuit for explaining an example of the X-ray imaging apparatus according to the present invention.

In FIG. 2, a unit cell as an input pixel includes an X-ray sensor cell 121 as a charge conversion unit, a storage capacitor 122 as a charge storage unit, and an electric field for transferring a signal from the X-ray sensor cell 121 to the storage capacitor 122. The first transistor 123, the storage capacitor 1
And a second transistor 124 serving as a reading unit for reading a signal from the reference signal 22. As shown in FIG. 2, the unit cells are arranged vertically and horizontally at desired intervals, that is, arranged in a matrix. First transistor 12
Reference numeral 3 denotes control means for controlling the electric field applied to the X-ray sensor cell 121.

The X-ray sensor cell 121 is connected to the other end not connected to the first transistor.
The other end of the storage capacitor 122 is connected to sensor potential fixing means for giving a desired potential, and the other end of the storage capacitor 122 not connected to the first and second transistors 123 and 124 is connected to the other end of the storage capacitor 122. Is connected to the storage potential fixing means for fixing the potential of the storage device.

The second transistor 124 of each unit cell is selected for each row by a horizontal scanning circuit (scanning means such as a shift register) 120, and the storage capacity 1 of each unit cell is selected.
A signal is read from 22 to an output line 125, and the signal is input to an output circuit 130 via an amplifier 140 connected to the output line 125, and is sequentially output by the output circuit 130 for each column. Each output line 125 is set to the potential V _V by the output line reset transistor 150. The output circuit 130, for example, a storage capacitor provided for each output line (not shown), becomes from a transistor for connecting the storage capacitor and the common output line (not shown), from the scanning circuit (not shown) phi _H1, phi _H2, ... are sequentially inputted transistor is turned on to the output circuit 130, the signal for each column from the storage capacitors is output is read to the common output line.

FIG. 23A and FIG. 23B will be described.

On an insulating substrate 1 such as a glass substrate, layers of a lower electrode 231, an insulating film (silicon nitride film) 232, high-resistance amorphous silicon 233, n ⁺ amorphous silicon 234, and an upper electrode 235 are formed in this order. . Thin film transistors 123 and 124 and storage capacitor 122
Are manufactured with the same laminated film configuration as shown. Because of the same laminated film configuration, the manufacturing process can be shortened, the manufacturing cost is low, and the manufacturing yield is improved.

The metal layer 112 serves as one of the main electrodes of the transistor 123. The X-ray sensing unit 100 is electrically connected to the metal layer 112. Here, an example in which the sensing unit is separated for each pixel is shown.

Since the thin film transistor circuit portion made of a non-single crystal material formed on the insulating substrate 1 is formed of a thin film, it can be easily formed on a large insulating substrate. The circuit portion is formed of a thin film transistor because the thin film transistor has a thin active layer (usually 0.5 μm or less) and thus has a low probability of absorbing radiation. This is preferable in that the problem of material damage due to radiation hardly occurs, and since radiation is hardly absorbed in the readout circuit, noise is hardly generated and noise characteristics are excellent.

By forming the radiation X-ray sensing unit 100 and the readout circuit unit in a laminated structure, the X-ray sensing unit has an aperture ratio of 100%. or,
By forming only the readout circuit on the insulating substrate,
Since there is no need to divide the area for the X-ray incident area,
A sufficient gate width of the thin film transistor can be obtained, and high-speed operation of the thin film transistor can be achieved. 30 FPS depending on the characteristics of the semiconductor to be formed and the number of pixels
(30 image readings per second: frames / second) to 6
Reading of 0FPS information can also be sufficiently achieved.

FIG. 3A is an equivalent circuit of a unit cell, and FIGS. 3B to 3D are schematic potential diagrams for explaining the operation of the unit cell of the X-ray imaging apparatus. is there. 3B to 3D, the horizontal axis indicates a location on the unit cell, and the vertical axis indicates a potential at each location.

FIG. 3B is a potential diagram showing a sensor reset state. When the second transistor 124 and the output line reset transistor 150 shown in FIG. 2 are turned on, the potential of the storage capacitor 122 becomes the reset voltage V _V as shown in FIG. When a constant voltage _VA is applied to the gate of the transistor 123, the transistor 12
3 is always V _A -V _T (V _T is the threshold voltage of the transistor 123) and has a potential of.

FIG. 3C is a potential diagram showing a signal accumulation state. With the transistor 124 turned off,
When X-rays are irradiated on the sensor cell 121, the sensor cell 1
In 21, carriers are generated, and the carriers are stored in the storage capacitor 122 via the transistor 123, and the potential of the storage capacitor 122 changes from the potential V _V.

FIG. 3D is a potential diagram showing a read state. When the transistor 124 is turned on with the output line reset transistor 150 turned off, the electric charge stored in the storage capacitor 122 is read out to the output line 125.

In principle, the above-described operations of sensor reset, signal accumulation and reading are repeated.

FIG. 4 is a timing chart for explaining an example of driving of the X-ray imaging apparatus.

Voltage applied to gate of transistor 123
At a constant voltage (voltage V_A). Reset of output line 125
Reset (reset potential V_V), Φ_VRTo V_RAs the output line
Performed by turning on the reset transistor 150
Then, the horizontal scanning circuit 120 outputs φ _V1Pulse to the storage volume
Read out to each output line 125 to the signal accumulated in the quantity 122
And each horizontal scan is φ_H2, Φ_H2... by doing
Output from the power circuit 130 (V_out) Is done.

The absorption of X-rays by the semiconductor material of the X-ray sensor shown in FIG. 1 is determined by three mechanisms: photoelectric effect, Compton, and electron pair creation. FIG. 5 shows Si and G
The example of e is shown.

For applications such as medical and analytical purposes, 0.1
Since MeV or less is often used, absorption is mainly determined by the photoelectric effect.

As for X-ray absorption, a material having a higher atomic number has a higher absorption coefficient. Considering detection by a pn junction in a semiconductor, if the band gap is smaller than 1 eV, the dark current increases even when used at room temperature, and the noise characteristics are deteriorated. Therefore, a material having a band gap of 1 eV or more and having a small dark current at the pn junction and a large X-ray absorption is desirable.
GaAs, GaP, and the like have a larger band gap than Si, and are preferable as the radiation detection material.

As shown in FIG. 5, Si has a relatively small X-ray absorption coefficient. In view of this, Si may be used for low energy.

FIG. 6 shows the energy required to generate carriers by radiation of a semiconductor material. The horizontal axis shows the semiconductor energy gap, and the vertical axis shows the energy required for generation. Regarding the energy required for carrier generation, a smaller energy is preferable because a larger number of carriers are generated.

GaAs and CdTe are about 5 eV. Therefore, for example, 10,000 carrier pairs can be generated from 50 keV X-rays. GaAs, Cd
Te is desirable as an X-ray detection material because it has a large band gap, a small ε (eV), and a large X-ray absorption.

Furthermore, GaAs is desirable as a material to be used because of its high crystal perfection and small dark current. GaAs
s has an X-ray absorption characteristic very similar to that of Ge. In view of the above characteristics, it can be suitably used for medical applications or the like in which the irradiated X-ray dose is limited. The mass productivity of GaAs is as good as that of Si at present, and is very economically favorable.

In the X-ray sensor shown in FIG. 1, the portions where the X-rays are detected (X-ray sensing section 100), ie, the n ⁺ layer 30 and the p ⁺ layer 10, are dead zones for radiation (here, X-rays). Conversion of X-rays to carriers is effectively performed in the depletion layer.

FIG. 7 shows the applied voltage and the thickness of the depletion layer, using the resistivity of n ⁺ or p in Si as a parameter. It is preferable that the resistivity is high at 100 Ω · cm or more, and the applied voltage is 10 V or more, preferably 100 V or more. 1000V to make the depletion layer close to 1mm
The applied voltage is also required as described above. In GaAs, 107Ω
Since a wafer having a resistance of not less than 1 cm can be manufactured, a thick depletion layer can be obtained at a lower voltage than that of Si, and the sensitivity can be increased. GaAs has the same X-ray absorption characteristics as Ge, and is therefore suitable as a direct X-ray material.

In FIG. 2, the terminal 1000 has 10
A voltage of 00 V or more is applied. In GaAs, the voltage is lower.

Transistor (thin film transistor: TF
T) 123, by constantly applying a constant voltage _VA ,
The other electrode of the sensor cell 121 is always VA-VT
It has become. Therefore, a constant voltage is always applied to the sensor cell 121, and the thickness of the depletion layer does not change and stable operation is possible.

FIG. 8 is a diagram showing the X-ray absorption characteristics of TiBr, CsI, and Se.

FIG. 24 shows an example in which a single crystal semiconductor is used as a high-resistance X-ray detector. The material of the single crystal high resistance portion 20 ′ has high resistance (> 10 ^7).
GaAs is particularly preferable because of its small dark current (band gap to 1.5 eV), large-diameter wafers (6 inch φ), and the like. 10 'indicates an n + layer.

FIG. 9 is a sectional view of an X-ray sensor according to another embodiment of the present invention.

In the present embodiment, by providing a p region 500 (which serves as a guard region) having a lower concentration than p + around the p + layer 10, a high voltage is applied to the X-ray detector.
The steep electric field in the periphery is alleviated to improve the breakdown voltage of the pn junction.

FIG. 10 is a sectional view of an X-ray sensor according to still another embodiment of the present invention.

In this embodiment, the upper n + region 30 is separated, which is effective in improving the resolution. 33
Is an insulating film for separating the n + region 30.

FIG. 11 is a sectional view of an X-ray sensor according to still another embodiment of the present invention.

FIG. 11 shows an example in which the lower substrate is a single crystal substrate. By using the single crystal substrate 114, the peripheral circuit can be incorporated into the lower substrate, which further enhances the functions and the high-speed reading. In a single crystal substrate 114 as a semiconductor substrate, a source and a drain 10 as n-type regions are provided.
2 is formed, and a gate electrode is formed over the p region 116 with an insulating layer interposed therebetween, so that the transistor 115 is formed.

FIG. 12 is an equivalent circuit showing another embodiment of the X-ray imaging apparatus according to the present invention. In the present embodiment, the reset transistor 126 is connected to the sensor cell 121. The introduction of the reset transistor (reset thin film transistor) 126 can improve the afterimage of the sensor.
By setting the voltage VRS slightly higher than VA-VT, an X-ray sensor with improved afterimage is obtained. Note that the reset transistor 126 serves as a potential fixing means for fixing the potential of the sensor cell 121 for a certain period.

FIG. 22 shows a timing chart of the X-ray imaging apparatus.

.., ΦV2,..., ΦV1, φV2,. φR1, φR2
When the voltage VB is applied to the gate of the reset transistor 126 without completely turning it off when
When a strong input X-ray enters the sensor unit and a large charge Q _Lange is stored in the storage capacitor 122 (capacitance value C ₁ ), V
_Lange = Q _Lange / C ₁ is not greater than V _B -V _TH. This prevents an excessive voltage from being applied to the switch transistor 124. Excessive voltage is
For example, Vma of the transistor 124 shown in FIG.
x and a voltage equal to or higher than Vmax
When the charges are accumulated in (122), carriers flow out to the output side of the transistor 124, which greatly affects an image. C
In a CD or the like, it is possible to eliminate an effect on an image which is called blooming.

FIG. 13 is a diagram showing an example in which a reset switch 127 for resetting a storage capacitor is provided for each storage capacitor.

Assuming that the operation of the switch transistor 127 is the same as that of the transistor 126 of the sensor shown in FIG. 12, if the voltage of VB is given in the off state, the storage capacitor 122 (capacity value C1) becomes VB-VTH It is possible to prevent the voltage from becoming higher than the above. By preventing overflow of carriers in the storage capacitor 122 from the read transistor 124, the characteristics of the vertical image could be improved.

When the amount of X-rays is sufficiently small, the off-state voltage may be a complete off-potential.

With this function, it is possible to provide a protection function when an excessive X-ray input is made. The switch transistor 127 can have two functions of a reset switch and a protection circuit for preventing carrier overflow.

FIG. 14 is a diagram showing an embodiment in which transistors 126 and 127 are provided at the same time.

[0064] V _B is, or slightly higher than V _A large, and to the same extent _{((V A -V TH126) ≒} (V B -V TH128)),
Maximum charge storage of the _{sensor, Q max = (V A -V} TH126 -Vv) is C _1.

By changing V _A , V _B , and V _R , Q
_max can be easily changed. And source-gate breakdown voltage (V _S -G _max) or the source of the switching transistor 124 - than smaller withstand voltage between the drain (V _S -D _max), by setting the V _B, the voltage of the switching transistor Destruction protection is also possible.

FIG. 15 shows that each cell has a source follower, that is, each cell has an amplifier, so that signal amplification can be performed and sensitivity can be improved. Each cell has a transistor 128 for selection and a transistor 129 serving as an amplifier, and constitutes a source follower.

FIGS. 16, 17 and 18 show the unit cells of the configurations of FIGS. 12, 13 and 14, respectively, as shown in FIG.
The source follower is provided. 16 and 18
Thus, afterimages are improved by providing the reset transistors 126 respectively.

FIG. 19 shows the removal of fixed pattern noise.
Therefore, in this embodiment, two output systems are provided. FIG.
At φVR, the cell and capacitor are turned on.
After resetting the quantity C, the cell
The noise (N) is transferred to the storage capacitor via the transistor 131.
C_NTo accumulate. After that, the signal (S) is stored in the cell.
After that, a signal (S + N) containing a noise component is
Read through the transistor 132 and read the storage capacitance C_STo
accumulate. Then, the storage capacity C_N, C_STigers from both
Turn on the transistors 135 and 136 to include noise and noise components.
And the noise component is read out by the subtraction amplifier 137.
Subtract the noise component (N) from the signal (S + N) containing
The signal (S) is output (Vout). 133, 134
Is the storage capacity C_N, C_SReset transistor
You. Before resetting the cell, _NAnd C_sIs to φHR
To turn on and reset transistors 135 and 136
Keep it.

Next, an example of another X-ray imaging apparatus according to the present invention will be described.

FIG. 25 is a schematic sectional view of an X-ray sensor according to the present invention.

In FIG. 25, members having the same reference numerals as those in FIG. 1 are the same as those described in FIG. 1, and therefore, detailed description thereof will be omitted. The X-ray sensor shown in FIG. 25 generates an electron-hole pair from the X-ray radiated to the sensing unit 100, accumulates one of the carriers, and carries the image information, as described in FIG. Read as a signal.

As described above, the X-ray sensing unit 100 is formed using a semiconductor such as GaAs, GaP, or Si, and includes an n ⁺ layer 310, a p ⁻ layer (i layer) 320, and a p ⁺ layer 3.
30. In these layers, the depletion layer is composed of n ⁺ layer 310 and p ^+
- forming a pin diode extending from the interface of the layer 320. The metal layers 31 and 32 are formed on the p ⁺ layer 330, that is, on the X-ray incident side, and formed below the n ⁺ layer 310, that is, on the side opposite to the X-ray incident side, here, on the readout unit 200 side. It has metal layers 11 and 12. The metal layer 12 is a barrier metal as described above. X-ray sensing unit 100
Can be formed using a single crystal semiconductor substrate as described above.

As shown, the present embodiment differs from the embodiments shown in FIGS. 1 and 2 in that the connection direction of the diode of the X-ray sensing unit 100 is different.

The reading section 200 has an n-type thin film transistor 220 constituting a circuit on the insulating substrate 1. The n-type thin film transistor 2 has a gate 221, an n + source, an n + drain 222, and a semiconductor active layer having a low impurity concentration. 223, a metal wiring 230 connected to the source and the drain.
The thin film transistor 220 is covered with the protective film 113. As described above, as the semiconductor material of the thin film transistor, a non-single-crystal material such as amorphous silicon, polysilicon, or microcrystal silicon is preferably used. Similar to FIG. 1, although not shown in FIG. 25, the reading unit 200 has a capacitance serving as a storage capacitor.

FIG. 26 shows a schematic equivalent circuit of an X-ray imaging apparatus having the X-ray sensor shown in FIG. The same members as those shown in FIG. 2 are the same as those shown in FIG.

In FIG. 26, the unit cells are an X-ray sensor cell 121, a storage capacitor 122, and an X-ray sensor cell 121.
A first n-type thin film transistor (TFT) 123 for transferring a signal from the storage capacitor 122 to a storage capacitor 122, and a second n-type thin film transistor (TF) for reading a signal from the storage capacitor 122
T) 124.

In FIG. 26, the polarity of the X-ray sensor cell 121 shown as a diode differs from the equivalent circuit diagram shown in FIG.

Horizontal scanning circuit (shift register, etc.) 12
0, the second thin film transistor 124 of each unit cell is selected for each row, a signal is read from the storage capacitor 122 of each unit cell to the output line 125, and this signal is output to the amplifier connected to the output line 125. Output circuit 1 via 140
30 and output by the output circuit 130 sequentially for each column. Connecting an amplifier (140: amplifier) to each signal line requires a radiation imaging device on a large circuit board (for example, a size of 20 cm × 20 cm or 43 cm × 43 cm) formed on a glass substrate. Is smaller than the capacitance value of the charge storage capacitor (generally about 0.5 to 3 pF), the parasitic capacitance value including the capacitance between the wiring cross portion of the output line and the source connected to the gate of the thin film transistor and the output line is several times smaller. Since it is large from about 10 pF to about 100 pF, it is effective to obtain a sufficient signal-to-noise ratio. Each storage capacity 122
And each output line 125 is connected to the output line reset transistor 15.
By 0, the potential is set to the potential Vv via the transistor 124. The output circuit 130 includes, for example, a sampling storage capacitor 160 provided for each output line, and a transistor 170 connecting the sampling storage capacitor to a common output line.
Having. (Refer to the schematic circuit diagram of FIG. 35.) In this output circuit 30, electric signals from the output lines are sequentially accumulated in a sampling accumulation capacitor 160 by a transfer pulse φT, and φH1, φH2,. .. Are sequentially input to the transistor 180 in the circuit, and the transistor 180 is sequentially turned on, and the signal is read out from the sampling storage capacitor 160 to the buffer amplifier 190 connected to the common output line for each column and output ( V _OUT ).

FIG. 27 is an example of a timing chart for driving the X-ray imaging apparatus shown in FIG.

The voltage applied to the gate of the transistor 123 is a constant voltage (voltage VA). For resetting of the storage capacitor 122 and the output line 125, the .phi.V _R as V _R, and on the output line reset transistor 150 connected to the reset potential Vv, simultaneously turns on the .phi.V ₁ (reset mode). Thereafter, .phi.V _R, turn off the .phi.V _1, X-ray sensor cell 121 enters a storage mode. Next, a pulse is applied to φV ₁ by the horizontal scanning circuit 120, and the signal stored in the storage capacitor 122 is read out to each output line 125 (readout mode). Thereafter, charges are collectively transferred to a sampling storage capacitor (not shown) by a transfer pulse, and then each horizontal scan is performed as φH1, φH2,..., So that an output (Vout) is sequentially output from the sampling storage capacitor. After the stored charge is transferred to the output line 125, the operation returns to the reset mode again.

The above-described cycle is similarly performed for each horizontal line, and information is sequentially read.

In the reading mode, φVi (i = 1,
In a state in which the transistor 124 serving as the reading means is turned off (φVi is in an off state) immediately before (2, 3...) Is turned on,
Than to the state of turning on the transistor 150 is a reset means (? V _R the ON state), it may be further subjected to reset only the output line. In this case, the other operations may be performed in the same manner as shown in FIG. By this operation, when strong radiation enters the imaging region of some imaging devices, charge leaks from the storage capacitor to the output line via the switch 124 and affects the other cell reading (CC).
A phenomenon called blooming in D etc.) can be prevented.

In the X-ray sensor shown in FIG. 25, portions of the p ⁺ layer 330 and the n ⁺ layer 310 where X-rays are detected are dead zones of radiation. Conversion of X-rays to carriers is effectively performed in the depletion layer.

By constantly applying a constant voltage VA to the thin film transistor 123, the other electrode of the sensor cell 121 is always at VA-VT. Therefore, a constant voltage is always applied to the sensor cell 121, and the thickness of the depletion layer does not change and stable operation is possible.

FIG. 28 is a schematic sectional view showing an example of another X-ray sensor of the present invention. As shown in the figure, the present example is an X-ray sensing unit 1 of the X-ray sensor shown in FIG.
00 are different polarities, p-type or i-type.
An example is shown in which a single crystal semiconductor of a type is used as a high-resistance X-ray detection unit. Single crystal high resistance portion (here, p ^- region) 320
Material having high resistance (> 10 ⁷ Ωc)
m), a small dark current (a band gap of 1.5 eV), a large-diameter wafer (6 inch φ), and the like are preferably used. 310 is n ⁺
Layer 330 is the p ⁺ region.

FIG. 29 is a schematic sectional view showing an example of another X-ray sensor according to the present invention.

This example is based on the X-ray sensor shown in FIG.
This is an example in which the polarity of the X-ray sensing unit 100 is different, and shows an example in which a p ^- type or i-type single crystal semiconductor (p ^- region in the figure) is used as a high-resistance X-ray detection unit. Here, the periphery of the n ⁺ layer 310, the n ⁺ lower concentrations n
By providing the region 3500 (which becomes a guard region), when a high voltage is applied to the X-ray detector, a steep peripheral electric field is relaxed, and the withstand voltage of the pn junction is improved.

FIG. 30 is a schematic sectional view showing another example of the X-ray sensor according to the present invention.

This example is based on the X-ray sensor shown in FIG.
This is an example in which the polarity of the X-ray sensing unit 100 is different, and shows an example in which a p ⁻ -type or i-type single crystal semiconductor (p ⁻ region 320 in the figure) is used as the high-resistance X-ray detection unit. Here, the upper p ⁺ region 330 is separated, which is effective in improving the resolution. 33 is an insulating film separating the p ⁺ region 30.

In FIG. 30, p ⁻ region 320 is changed to n ^{− of the} opposite conductivity type.
Then, the depletion layer spreads from the surface side, and the sensitivity and the resolution are stabilized because the depletion layer surely exists in the place where the X-rays are largely incident. However, the depletion layer is required to extend between p ⁺ and n ^{+ and} the entire thickness of the n ⁻ region.

FIG. 31 is a schematic sectional view of an X-ray sensor according to still another embodiment of the present invention.

FIG. 31 shows an example in which the lower substrate of the X-ray sensor shown in FIG. 28 is a single-crystal substrate. The X-ray sensor shown in FIG. This is an example. Here, by using the single crystal substrate 114, the peripheral circuit can be incorporated into the lower substrate,
It is even more effective for advanced functions and high-speed reading.
The transistor 115 is formed by forming a gate electrode over the p region 116.

FIG. 32 is a schematic sectional view for explaining an example of another X-ray sensor. Figure 32 provides an X-ray sensor shown in FIG. 31, n ⁺ all around the region 310, n ⁺ lower n-type region 31 having an impurity density than region 310
1 is provided. With such a configuration, p
By reducing the electric field around the n ⁺ region 310 at the n junction, p
It is possible to improve the breakdown voltage of the n-junction and reduce the dark current in the depletion layer region.

FIG. 33 shows an X-ray imaging apparatus according to the present invention.
FIG. 9 is a schematic equivalent circuit diagram for explaining another example. In this example, an example is shown in which the polarity of the sensor cell 121 in the schematic equivalent circuit diagram shown in FIG. 12 is reversed.

FIG. 34 is a timing chart for explaining an example of driving the X-ray imaging apparatus.

ΦR ₁ , φR ₂ ..., ΦV ₁ , φV ₂ ,.
Each in synchronization with the V _R, transistor 124,12
6, 130 are driven to reset the sensor cell (sensor unit) 121. .phi.R _1, when the off-.phi.R ₂ is not completely turned off reset transistor 126, the previously applied voltage of V _B to the gate of the reset transistor 126 enters a strong input X-ray to the sensor unit, the storage Capacity 122
When a large charge Q _Lange is accumulated in (capacitance value C ₁ ), V _Lange = Q _Lange / C ₁ does not become larger than V _B −V _TH . Thus, an excessive voltage is not applied to the transistor 124. Excessive voltage and is a voltage greater than Vmax of the thin film transistor 124 illustrated in example FIG. 3 (C), the the V _max or voltage is stored in the storage capacitors (C) 122, a carrier on the output side of the transistor 124 Flows out, and the image is greatly affected.
As described above, by controlling the driving of the transistor 126, it is possible to eliminate an influence on an image which is called blooming in a CCD or the like.

Of course, even when the polarity of the X-ray sensing unit 100 is changed, the polarity of the X-ray sensing unit can be reversed in the schematic equivalent circuit diagrams as shown in FIGS. Needless to say, these circuits can be similarly applied.

FIG. 35 shows an embodiment of the output circuit.
After the output from each line is simultaneously transferred to the capacitor 160 via the amplifier 140 by the transfer pulse φT by the transistor 170, a pulse is sequentially output from the shift register 195 to the transistor 180, and V is output through the amplifier 190.
out is output. The transfer pulses in FIGS. 27 and 34 indicate φT.

FIG. 20 shows an example in which a large-screen radiation imaging apparatus is manufactured by combining a plurality of X-ray sensing units 100 on a substrate 200 on which a readout circuit and the like are formed on an insulating substrate. It is a typical perspective view which shows. In the figure, reference numerals 1500 and 1600 denote a driving circuit and an output circuit, respectively, which are installed on the reading section 200 which is a circuit board section. By using a glass substrate as the substrate 1 of the reading unit 200, the size of the imaging device can be increased.

FIG. 21 is a schematic diagram showing an example of a medical diagnostic device using the imaging apparatus of the present invention.

In FIG. 21, reference numeral 1001 denotes an X-ray tube serving as an X-ray generation source; 1002, an X-ray shutter for controlling opening and closing of X-ray passage; 1003, an irradiation tube or a movable diaphragm;
Denotes a subject, 1005 denotes a radiation detector using the present invention, 1
Reference numeral 006 denotes a data processing device that performs data processing on a signal from the radiation detector 1005. 1007 is a computer, based on a signal from the data processing device 1006,
An X-ray image or the like is displayed on a display 1009 such as a CRT or the like, and an X-ray tube 1 is transmitted through a camera controller 1010, an X-ray controller 1011, and a capacitor type high voltage generator 1012.
001 is controlled to control the amount of X-ray generation.

[0102]

According to the present invention described above, the following effects can be obtained. (1) By keeping the applied electric field of the radiation detector to which a high voltage is applied, the linearity of the reading sensitivity of the sensor can be maintained. In the pn junction structure X-ray detector,
Since the thickness of the depletion layer can be kept constant at a constant applied voltage, the quantum efficiency can be kept constant at a high level. The neutral region becomes a detection dead zone. In the conductivity modulation type as well, by keeping the electric field constant, the charge generation rate can be kept constant and the directness can be kept constant. (2) When the radiation is excessively input, it is possible to prevent a carrier overflow through a switch of the sensor. (3) Afterimages can be reduced. (4) High sensitivity can be achieved. (5) By laminating the readout circuit and the radiation detector on the insulating substrate, it is possible to obtain a high aperture ratio, and a thin film transistor capable of supporting a moving image with low noise and high S / N.
A highly reliable radiation imaging apparatus can be obtained. (6) By using a non-single-crystal semiconductor thin film transistor on an insulating substrate, a large-area radiation imaging apparatus based on the insulating substrate can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an X-ray sensor showing an example of a radiation imaging apparatus according to the present invention.

FIG. 2 is a schematic equivalent circuit diagram illustrating an example of a radiation imaging apparatus according to the present invention.

FIGS. 3 (A), 3 (B), 3 (C) and 3
FIG. 3D is a schematic equivalent circuit diagram showing an example of a unit cell of the radiation imaging apparatus (FIG. 3A) and a potential diagram showing an example of its operation (FIGS. 3B, 3C and 3C). 3
(D)).

FIG. 4 is a timing chart illustrating an example of an operation of the radiation imaging apparatus.

FIG. 5 is a characteristic diagram showing an example of X-ray energies and absorption ratios of Si and Ge.

FIG. 6 is a characteristic diagram showing an example of energy required for generating carriers by radiation of a semiconductor material.

FIG. 7 is a characteristic diagram showing an example of a relationship between an applied voltage and a thickness of a depletion layer, using a resistivity of an n ⁺ type region or a p type region in Si as a parameter.

FIG. 8 is a diagram showing an example of the X-ray absorption characteristics of TiBr, CsI, and Se.

FIG. 9 is a schematic sectional view of an X-ray sensor showing one example of the radiation imaging apparatus of the present invention.

FIG. 10 is a schematic sectional view of an X-ray sensor showing one example of the radiation imaging apparatus of the present invention.

FIG. 11 is a schematic sectional view of an X-ray sensor showing one example of the radiation imaging apparatus of the present invention.

FIG. 12 is a schematic equivalent sectional view showing an example of the radiation imaging apparatus of the present invention.

FIG. 13 is an equivalent circuit diagram showing an example of a unit cell according to the present invention.

FIG. 14 is an equivalent circuit diagram illustrating an example of a unit cell according to the present invention.

FIG. 15 is a schematic equivalent circuit diagram illustrating an example of a radiation imaging apparatus according to the present invention.

FIG. 16 is an equivalent circuit diagram illustrating an example of a unit cell according to the present invention.

FIG. 17 is an equivalent circuit diagram illustrating an example of a unit cell according to the present invention.

FIG. 18 is an equivalent circuit diagram showing an example of a unit cell according to the present invention.

FIG. 19 is a schematic equivalent circuit diagram showing an example of the radiation imaging apparatus of the present invention.

FIG. 20 is a schematic perspective view showing one configuration example of an X-ray imaging apparatus.

FIG. 21 is a schematic configuration diagram showing an example of a non-destructive inspection device represented by a medical diagnostic device using the radiation imaging apparatus of the present invention.

FIG. 22 is a timing chart illustrating an example of the operation of the radiation imaging apparatus.

FIG. 23A is a schematic plan view illustrating a configuration example of a radiation imaging apparatus, and FIG.
It is a typical sectional view in XX 'of (A).

FIG. 24 is a schematic cross-sectional view showing a case where a single-crystal semiconductor is used as a high-resistance X-ray detector.

FIG. 25 is a schematic sectional view of an X-ray sensor showing one example of the radiation imaging apparatus of the present invention.

FIG. 26 is a schematic equivalent circuit diagram illustrating an example of a radiation imaging apparatus according to the present invention.

FIG. 27 is a timing chart showing an example of the operation of the radiation imaging apparatus.

FIG. 28 is a schematic sectional view of an X-ray sensor showing one example of the radiation imaging apparatus of the present invention.

FIG. 29 is a schematic sectional view of an X-ray sensor showing one example of the radiation imaging apparatus of the present invention.

FIG. 30 is a schematic sectional view of an X-ray sensor showing one example of the radiation imaging apparatus of the present invention.

FIG. 31 is a schematic sectional view of an X-ray sensor showing an example of the radiation imaging apparatus of the present invention.

FIG. 32 is a schematic sectional view of an X-ray sensor showing one example of the radiation imaging apparatus of the present invention.

FIG. 33 is a schematic equivalent circuit diagram showing an example of the radiation imaging apparatus of the present invention.

FIG. 34 is a timing chart showing an example of the operation of the radiation imaging apparatus.

FIG. 35 is a schematic circuit diagram illustrating an example of an output circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Transistor 10 P + layer 20 i layer 30 n + layer 31, 32 Metal layer 11, 12 Metal layer 13 Bump metal 40, 50 Protective film 101 Gate 102 Source and drain 103 Active layer 110 Metal wiring 111 Al layer 112 Gold layer 113 Protective film 120 Horizontal scanning circuit 121 X-ray sensor cell 122 Storage capacitor 123 First transistor 124 Second transistor 125 Output line 130 Output circuit 140 Amplifier 150 Output line reset transistor 100 X-ray sensing unit 200 Reading unit

Claims (27)

[Claims] A charge conversion unit configured to convert incident radiation into a charge; a charge storage unit configured to store the converted charge; and the charge unit provided between the charge conversion unit and the charge storage unit. A plurality of input pixels having control means for controlling an electric field applied to the conversion means and reading means for reading out a signal based on the electric charge accumulated in the electric charge accumulating means, outputting the electric charge read from the input pixel; , An output line connected to a plurality of the input pixels, and switch means for resetting the charge storage means. 2. The radiation imaging apparatus according to claim 1, wherein the signal based on the charge is a signal based on a potential due to the charge. 3. The radiation imaging apparatus according to claim 1, further comprising a sensor potential fixing unit for setting a potential of one terminal of the charge conversion unit to a desired potential. 4. The radiation imaging apparatus according to claim 1, wherein said switch means is connected to a storage potential fixing means for setting a potential of one terminal of said charge storage means to a desired potential. 5. The radiation imaging apparatus according to claim 3, wherein said switch means is connected to a storage potential fixing means for setting a potential of one terminal of said charge storage means to a desired potential. 6. The switch means has one end connected to the output line side and the other end connected to an accumulation potential fixing means for setting a potential of one terminal of the charge accumulation means to a desired potential. The radiation imaging apparatus according to claim 1. 7. The switch means has one end connected to the output line side and the other end connected to an accumulation potential fixing means for setting a potential of one terminal of the charge accumulation means to a desired potential. The radiation imaging apparatus according to claim 3. 8. The radiation imaging apparatus according to claim 1, wherein the charge conversion unit has a pn structure. 9. The radiation imaging apparatus according to claim 8, wherein a guard region for alleviating an electric field is provided around one of the conductive semiconductor regions constituting the pn structure. 10. The radiation imaging apparatus according to claim 1, wherein said charge conversion means is a conduction modulation type element. 11. The radiation imaging apparatus according to claim 1, wherein the input pixels are arranged in a two-dimensional matrix. 12. The radiation imaging apparatus according to claim 1, wherein at least the control unit, the charge storage unit, and the readout unit are formed on a same insulating substrate. 13. The radiation imaging apparatus according to claim 12, wherein the charge conversion unit is stacked on the insulating substrate. 14. A means for storing a signal containing an image information component and a noise component, a means for storing a noise component, and a means for subtracting the noise component from the signal containing the image information component and the noise component. The radiation imaging apparatus according to claim 1 having. 15. The radiation imaging apparatus according to claim 8, wherein the pn structure of the charge conversion means is formed on a semiconductor single crystal substrate. 16. The semiconductor device according to claim 1, wherein said semiconductor substrate has a band gap of 1.
16. An energy band gap of eV or more.
A radiation imaging apparatus according to claim 1. 17. A sensor potential fixing means for setting a potential of one terminal of the charge conversion means to a desired potential,
2. The radiation imaging apparatus according to claim 1, wherein the sensor potential fixing unit applies a constant potential when the sensor is off, and when the potential of the charge storage unit is an excessive potential, the potential fixing unit operates as a sweeping unit that sweeps out an excessive charge. . 18. A storage potential fixing means for setting a potential of one terminal of the charge storage means to a desired potential, wherein the storage potential fixing means applies a constant potential when the charge storage means is turned off. 2. The radiation imaging apparatus according to claim 1, wherein when the potential is excessive, the potential fixing unit operates as a sweeping unit that sweeps out excessive charges. 3. 19. A sensor potential fixing means for setting a potential of one terminal of the charge conversion means to a desired potential, and a storage potential fixing for setting a potential of one terminal of the charge storage means to a desired potential. 2. The radiation imaging apparatus according to claim 1, further comprising: means for operating, wherein one of the potential fixing means operates as a sweeping means. 20. The method according to claim 20, wherein the charge conversion means is a single crystal GaAs
A radiation imaging apparatus having: 21. The semiconductor device according to claim 8, wherein the entirety of the one conductive semiconductor region forming the pn junction has the same conductive semiconductor region lower than the impurity concentration of the one conductive semiconductor region for electric field relaxation. Radiation imaging device 22. At least the control means and the readout means are n-type thin film transistors, and a terminal of an n region of the pn junction is electrically connected to a source or a drain of the n-type thin film transistor of the control means. The terminal of the p region of the junction is connected to the bias means,
9. The radiation imaging apparatus according to claim 8, wherein the pn junction is reverse-biased and a depletion layer sufficient for radiation detection is formed in the semiconductor substrate. 23. A reset mode in which at least the switch means and the readout means are turned on at the same time to reset the charge storage means, the switch means and the readout means are turned off, and the charge generated by the charge conversion means by incident radiation. 2. The radiation imaging apparatus according to claim 1, further comprising: an accumulation mode in which the charge accumulation unit accumulates the signal; and a read mode in which the read unit is turned on, the switch unit is turned off, and the signal charge is output from the charge accumulation unit to an output line. . 24. The radiation imaging apparatus according to claim 23, further comprising an output line reset mode in which a switch unit is turned on, a read unit is turned off, and only an output line is reset between the accumulation mode and the read mode. 25. The radiation imaging apparatus according to claim 1, wherein at least the reading unit and the control unit are thin film transistors, and the thin film transistors include a non-single-crystal semiconductor. 26. At least one of the control unit, the charge storage unit, and the readout unit having the same layer configuration of a lower electrode, an insulating film, a high-resistance semiconductor film, a low-resistance semiconductor film, and an upper electrode on one surface of the insulating substrate. The radiation imaging apparatus according to claim 1, wherein 27. The semiconductor device according to claim 1, wherein a plurality of semiconductor substrates forming the charge conversion means are arranged on at least the insulating substrate on which the control means, the charge storage means, and the read means are formed. Radiation imaging device.