JP2001320037A - Conversion element, conversion device, photoelectric conversion device, and radiation imaging system - Google Patents

Abstract

(57) [Problem] To provide a converter in which an overlapping area between an electrode of a switch element and a gate electrode is reduced. SOLUTION: In a conversion element including a sensor for converting an incident electromagnetic wave into an electric signal and a transistor for reading out the electric signal converted by the sensor to a signal line, one main electrode of the transistor is connected to the other main electrode. The shape is such that it is surrounded by electrodes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conversion element including a sensor for converting an incident electromagnetic wave into an electric signal, a transistor for reading the electric signal converted by the sensor to a signal line, and a conversion device including the same. The present invention relates to a photoelectric conversion device and a radiation imaging system.

[0002]

2. Description of the Related Art Conventionally, a reduction optical system and a reading system using a CCD sensor have been used as a reading system of a facsimile, a digital copying machine, an X-ray imaging device, or the like. Hereinafter, "a
-Si ". With the development of the photoelectric conversion semiconductor material represented by (1), a so-called contact type sensor in which a photoelectric conversion element and a signal processing unit are formed on a large-sized substrate and read by an optical system of the same magnification as the medium to be read is remarkable.

In particular, since a-Si can be used not only as a photoelectric conversion material but also as a thin film field effect transistor, there is an advantage that a photoelectric conversion semiconductor layer and a semiconductor layer of a transistor can be formed simultaneously. are doing.

FIG. 7 is a circuit diagram of a photoelectric conversion device in which, for example, 3 × 3 pixels in which a photoelectric conversion semiconductor layer and a semiconductor layer of a transistor are simultaneously formed are arranged two-dimensionally. FIG.
In S11 to S33, G denotes a lower electrode side and D denotes an upper electrode side. C11 to C33 are storage capacitors, which are indicated in the equivalent circuit in this way because the photoelectric conversion elements of S11 to S33 function as capacitors.

Further, T11 to T33 are transfer transistors. Vs is a read power supply and Vg is a refresh power supply, which are connected to the D electrodes of all the photoelectric conversion elements S11 to S33 via switches SWs and SWg, respectively. The switch SWs is directly connected to the refresh control circuit RF via the inverter, and the switch SWg is controlled so that the switch SWg is turned on during the refresh period.

In this photoelectric conversion device, a total of nine pixels are divided into, for example, three blocks in a column direction, and outputs of three pixels per block are simultaneously transferred to a detection integrated circuit IC through signal lines SIG1 to SIG3. The output is sequentially converted and output by the detection integrated circuit IC (Vout). Each pixel is two-dimensionally arranged by arranging three pixels in one block in, for example, a row direction and arranging three blocks in a column direction in order.

Here, when the signal charge Q stored in the photoelectric conversion element S11 is transferred to SIG1 via the transistor T11 and is read by Amp via the switch M1, Cgs is connected to the gate of the transistor and the signal line. Assuming that the overlap capacitance is C _cross and the overlap capacitance between the Vg line and the signal line is CAmp, CAmp is Vo, which is the read capacitance of Amp.
ut may be expressed as Vout = Q / (ΣCgs + ΣC cross + CAmp). FIG. 7 shows the transistor T
11 and Cgs only between g2 and SIG1
_cross is shown, but in fact, other transistors T
Cgs also exist in 12 to T33, and control wirings g2 and g3
C _cross also exists between the signal line SIG1 and the signal lines SIG1 to SIG3.

FIG. 8 is a timing chart showing the operation of FIG. Next, the operation of the photoelectric conversion device of FIG. 7 will be described with reference to FIG. First, the shift register S
Control wirings g1 to g3, s1 to s2 by R1 and SR2
Is applied. Then, the transfer transistor T1
1 to T33 and switches M1 to M3 are turned on to conduct.

The G electrodes of all the photoelectric conversion elements S11 to S33 are at the GND potential (the input terminal of the integration detector Amp is GND).
D potential). At the same time, the refresh control circuit RF outputs Hi, the switches SWg are turned on, and the D electrodes of all the photoelectric conversion elements S11 to S33 become positive potential by the refresh power supply Vg.

Thus, all the photoelectric conversion elements S11 to S3
No. 3 enters the refresh mode and is refreshed.
Next, when the refresh control circuit RF outputs Lo and the switch SWs is turned on, all the photoelectric conversion elements S11
The D electrode in steps S33 to S33 is set to a higher positive potential by the reading power supply Vs.

Then, all the photoelectric conversion elements S11 to S33 enter the photoelectric conversion mode, and at the same time, the capacitors C11 to C33
Is initialized. In this state, Lo is applied to the control wires g1 to g3 and s1 to s2 by the shift registers SR1 and SR2. Then, the transfer transistors T11 to T33
Switches M1 to M3 are turned off, and all the photoelectric conversion elements S1
The G electrodes 1 to S33 are DC open, but the potential is held by the capacitors C11 to C33.

Thereafter, when light is emitted from a light source (not shown), the light is transmitted to each of the photoelectric conversion elements S11 to S33.
Incident on. The photocurrent flowing by this light is accumulated as electric charges in the respective capacitors C11 to C33, and is retained even after the end of X-ray incidence.

Next, a control pulse of Hi is applied to the control wiring g1 by the shift register SR1, and the control pulse is applied to the control wirings s1 to s3 of the shift register SR2 to switch M1 of the transfer transistors T11 to T33.
V1 to v3 are sequentially output through. Similarly,
Other optical signals are sequentially output under the control of the shift registers SR1 and SR2.

In this photoelectric conversion device, the D electrode of the photoelectric conversion element is commonly connected, and this common wiring is connected to the switch SWg.
And the switches SWs, the potential of the refresh power supply Vg and the potential of the read power supply Vs are controlled, so that all the photoelectric conversion elements can be simultaneously switched to the refresh mode and the photoelectric conversion mode. Therefore, an optical output can be obtained with one transistor per pixel without complicated control.

FIG. 9A is a schematic diagram of one pixel provided in the photoelectric conversion device of FIG. FIG. 9B is a cross-sectional view taken along a line AB in FIG. 9A. 9 (a), 9
As shown in (b), this pixel includes a sensor 8 and a transistor 9 on a glass substrate 7. The sensor 8 and the transistor 9 are simultaneously formed by an amorphous silicon thin film process.

The sensor 8 is of the MIS type. The sensor 8 and the transistor 9 sequentially form a lower metal layer 10, an insulating layer 11, a semiconductor layer 12, an n + thin film 13, an upper metal layer 14, and a protective layer (not shown) such as an amorphous silicon nitride film or polyimide on a glass substrate 7. The film is formed by patterning.

FIG. 10 is an equivalent circuit of the photoelectric conversion element of FIG. As shown in FIG. 10, the photoelectric conversion element performs a reading operation by generating charges in accordance with the amount of light incident on the sensor 8 and transferring the charges to a reading device (not shown) by the transistor 9.

[0018]

Here, in the photoelectric conversion device, the signal output of the photoelectric conversion element is increased as much as possible,
It is desired to improve the / N ratio. As a technique for increasing the signal output of the photoelectric conversion element, it is conceivable to reduce the stray capacitance of the signal line. The stray capacitance of a signal line is usually formed at an overlapping portion of a transistor electrode and a gate electrode.

The overlapping portion of the transistor electrode and the gate electrode corresponds to the transistor 9 of the pixel shown in FIG.
In other words, it is the portion of "C". Therefore, if the area of the “C” portion can be reduced, the stray capacitance of the signal line can be reduced.

Therefore, an object of the present invention is to provide a converter in which the overlapping area between the electrode of the switch element and the gate electrode is reduced.

[0021]

In order to solve the above problems, the present invention provides a sensor for converting an incident electromagnetic wave into an electric signal, and a transistor for reading the electric signal converted by the sensor to a signal line. In the conversion element provided, one main electrode of the transistor is shaped to be surrounded by the other main electrode.

Further, a conversion device according to the present invention includes a plurality of the conversion elements, and includes reading means for reading the electric signal from the conversion element, and processing means for processing the read electric signal.

Further, in the photoelectric conversion device of the present invention, a first electrode layer, an insulating layer, a photoelectric conversion semiconductor layer, a semiconductor layer for preventing injection of carriers of the first conductivity type, and a second electrode layer are laminated. A photoelectric conversion element and a carrier of a first conductivity type generated by signal light incident on the photoelectric conversion semiconductor layer are allowed to remain in the photoelectric conversion semiconductor layer, and a carrier of a second conductivity type different from the first conductivity type is transferred to the second conductive type. A photoelectric conversion means for applying an electric field to the photoelectric conversion element in a direction leading to the second electrode layer; and applying an electric field to the photoelectric conversion element to cause the carrier of the first conductivity type to move from the photoelectric conversion semiconductor layer to the second electrode. Refresh means for applying an electric field to the photoelectric conversion element in a direction leading to a layer; and the first conductivity type carrier or the second charge carrier accumulated in the photoelectric conversion semiconductor layer during a photoelectric conversion operation by the photoelectric conversion means. And a signal detecting portion for detecting said second conductivity type carrier guided to pole layer.

Further, the radiation imaging system according to the present invention is characterized in that the conversion device, signal processing means for processing a signal from the conversion device, recording means for recording a signal from the signal processing means, Display means for displaying a signal from the signal processing means, transmission processing means for transmitting the signal from the signal processing means, and a radiation source for generating the X-rays.

[0025]

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

(Embodiment 1) FIG. 1 is a schematic diagram showing a configuration of a photoelectric conversion element according to Embodiment 1 of the present invention. A sensor 8 and a transistor 9 are provided on a glass substrate 7. The sensor 8 and the transistor 9 are simultaneously formed by an amorphous silicon thin film process. The sensor 8 is M
It is of the IS type. The sensor 8 and the transistor 9 sequentially form a lower metal layer 10, an insulating layer 11, a semiconductor layer 12, an n ⁺ thin film 13, an upper metal layer 14, and a protective layer (not shown) such as an amorphous silicon nitride film or polyimide on a glass substrate 7. The film is formed by patterning.

In the photoelectric conversion element shown in FIG. 1, for example, the drain electrode (the other main electrode) has a U-shape, and the size of the drain electrode is the same as that of the drain electrode in FIG. Then, the source electrode (one main electrode) is arranged in the drain electrode.

When the transistor 9 has such a structure, the amount of charge transferred from the drain electrode to the source electrode can be the same, so that the source electrode can be shortened. Therefore, the overlapping area between the transistor electrode and the gate electrode can be reduced,
The stray capacitance of the signal line can be reduced.

Therefore, when the pixels are two-dimensionally arranged to manufacture a photoelectric conversion device, the overlap capacitance between the gate of the transistor and the signal line can be reduced to about half. Thus, the output signal Vout of the photoelectric conversion device, since the Vout = Q / (ΣCgs + ΣC cross + CAmp), compared to the conventional, it is possible to obtain an output of about two times.

As described above, in the present embodiment, the case where the shape of the drain electrode is a U-shape and the source electrode is disposed therein has been described as an example, but the drain electrode is formed so as to surround the source electrode. Whether its shape is three-dimensional like an arch or planar like a U-shape,
The overlap area between the electrode of the transistor and the gate electrode can be reduced.

(Embodiment 2) FIG. 2 is a circuit diagram of a photoelectric conversion device having a plurality of pixels shown in FIG. S11 to S33 are photoelectric conversion elements, in which the lower electrode side is denoted by G and the upper electrode side is denoted by D. C11 to C33 are storage capacitors;
This is shown in the equivalent circuit because the photoelectric conversion elements 11 to S33 function as capacitors.

T11 to T33 are transfer transistors. Vs is a read power supply and Vg is a refresh power supply, which are connected to the D electrodes of all the photoelectric conversion elements S11 to S33 via switches SWs and SWg, respectively. The switch SWs is directly connected to the refresh control circuit RF via the inverter, and the switch SWg is controlled so that the switch SWg is turned on during the refresh period.

This photoelectric conversion device divides a total of nine pixels into, for example, three blocks in the column direction, and simultaneously transfers outputs of three pixels per block to the detection integrated circuit IC through the signal lines SIG1 to SIG3. The output is sequentially converted and output by the detection integrated circuit IC (Vout). Each pixel is two-dimensionally arranged by arranging three pixels in one block in, for example, a row direction and arranging three blocks in a column direction in order.

The photoelectric conversion device shown in FIG.
The stray capacitance of 1~SIG3 [ΣCgs + ΣC _cross + CA
mp] is reset to a positive potential V _CRES , and a signal inversion processing circuit inverts the positive and negative potentials of the signal output Vout.

[0035] Here, for example, than the potential of the source electrode side of the sensor S11, when the potential of the drain electrode side set high V _CRES, for holes to move during the transfer, the conductance increases and therefore the resistance value decreases Since it is conceivable, the resistance value when the transistor is on is reduced. This is shown in FIG. FIG.
As shown in the figure, by increasing the potential on the signal line side,
Signal charges can be transferred in a short time.

(Embodiment 3) FIG. 4 is a circuit diagram of a photoelectric conversion system according to Embodiment 3 of the present invention. The photoelectric conversion system shown in FIG. Signal line S
IG1 has a capacitance between the electrodes (Cgs) of the switch element of 3
Capacitors for the number are added at the time of transfer, and are not shown as capacitance elements in FIG. Other signal lines SI
The same applies to G2 and SIG3.

A1 to A3 are signal lines SIG1 to SIG.
This is an operational amplifier for amplifying the signal charge of the IG3 and performing impedance conversion, and is illustrated only as a buffer amplifier constituting a voltage follower circuit in FIG.
Sn1 to Sn3 are transfer switches for reading the outputs of the operational amplifiers A1 to A3, that is, the outputs of the signal lines SIG1 to SIG3, and transferring the read signals to the capacitors CL1 to CL3.

The read capacitors CL1 to CL3 are read by read switches Sr1 to Sr3 via buffer amplifiers B1 to B3 constituting a voltage follower circuit. Further, the parallel signals of CL1 to CL3 are read switches Sr1 to Sr3 and read switches Sr
1 to Sr3 (SR
2), the signal is input to the operational amplifier 104 constituting the final-stage voltage follower circuit, and is digitized by the A / D conversion circuit unit 105.

RES1 to RES3 are connected to the signal line SIG.
A reset switch for resetting the signal components stored in the capacitors (3 Cgs for three) added to 1 to SIG3, and reset to a certain reset potential by a pulse from the CRES terminal (in FIG. reset)
Is done.

Reference numeral 106 denotes photoelectric conversion elements S11 to S3
3 is a power supply for applying a bias to the power supply 3. The readout circuit unit 107 includes buffer amplifiers A1 to A3, transfer switches Sn1 to Sn3, readout capacitors CL1 to CL
3, buffer amplifiers B1 to B3, readout switch S
r1 to Sr3, a shift register SR2, a final stage operational amplifier 104, and reset switches RES1 to RES3.

(Embodiment 4) FIGS. 5A and 5B
1A and 1B are a schematic configuration diagram and a schematic cross-sectional view of an X-ray imaging apparatus using a photoelectric conversion device equipped with a photoelectric conversion element described in Embodiment 1. First, the configuration of the X-ray imaging device will be described. The photoelectric conversion element and the transistor are a-S
A plurality of i-sensor substrates 6011 are formed. The shift register SR1 and the flexible circuit board 6010 on which the integrated circuit IC for detection is mounted are connected.

The opposite side of the flexible circuit board 6010
It is connected to circuit boards PCB1 and PCB2. a-S
A plurality of i-sensor substrates 6011 are bonded on a base 6012. A memory 6 in a processing circuit 6018 is provided below a base 6012 which constitutes a large-sized photoelectric conversion device.
A lead plate 6013 is mounted to protect 014 from X-rays.

On the a-Si sensor substrate 6011, a phosphor 6030 for converting X-rays into visible light, for example,
CsI is applied or pasted. X-rays are detected using the photoelectric conversion device described in FIG. In this embodiment, as shown in FIG. 5B, the whole is housed in a case 6020 made of carbon fiber.

FIG. 6 shows an example in which the photoelectric conversion device of FIG. 5 is applied to an X-ray diagnostic system.

X-ray 60 generated by X-ray tube 6050
Numeral 60 transmits through the chest 6062 of the patient or the subject 6061 and enters the photoelectric conversion device 6040 on which the phosphor is mounted. The incident X-ray includes information on the inside of the body of the patient 6061. The phosphor emits light in response to X-ray incidence, and photoelectrically converts the light to obtain electrical information. This information is converted to digital and converted to an image processor 607.
The image is processed by 0 and can be observed on the display 6080 in the control room.

This information can be transferred to a remote place by a transmission means such as a telephone line 6090, and can be displayed on a display 6081 such as a doctor's room in another place or stored in a storage means such as an optical disk. It is also possible to make a diagnosis. Also film processor 6
100 can also be recorded on the film 6110.

In this embodiment, the photoelectric conversion device is
The case of applying to an X-ray diagnostic system has been described,
The present invention can also be applied to a radiation imaging system such as a non-destructive inspection device using radiation other than X-rays such as α-rays, β-rays, and γ-rays. Further, the X-ray diagnostic system according to the present embodiment has been described as an example in which the X-ray is converted into light using a phosphor and the converted light is further converted into an electric signal. A material to be converted may be used.

[0048]

As described above, according to the present invention, one main electrode connecting the switch element and the signal line is surrounded by the other main electrode connecting the sensor and the switch element. With the shape, the overlapping area of one main electrode and the gate electrode is reduced, so that the stray capacitance of the signal line can be reduced. As a result, the output signal S /
The N ratio is improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of a photoelectric conversion element according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a photoelectric conversion device including a plurality of pixels of FIG.

FIG. 3 is a diagram illustrating a relationship between a potential difference between a source electrode and a drain electrode and a transistor on-resistance.

FIG. 4 is a circuit diagram of a photoelectric conversion system according to a third embodiment of the present invention.

FIG. 5 is a configuration diagram and a cross-sectional view of an X-ray imaging apparatus according to a fourth embodiment of the present invention.

FIG. 6 is a configuration diagram of an X-ray diagnostic system according to Embodiment 4 of the present invention.

FIG. 7 is a circuit diagram of a conventional photoelectric conversion device.

FIG. 8 is a timing chart showing the operation of FIG.

9 is a schematic view of one pixel provided in the photoelectric conversion device of FIG. 7;

FIG. 10 is an equivalent circuit of the photoelectric conversion element in FIG. 9;

[Explanation of symbols]

 S11 to S33 Photoelectric conversion element T11 to T33 Transistor C11 to C33 Capacitor SR1, SR2 Shift register IC Detection integrated circuit

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Noriyuki Kaibe 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 4M118 AA05 AB01 BA05 CA11 CA19 CB06 DD11 DD12 FB03 FB09 FB13 FB16 GA10 HA26 5F088 AA11 AB05 BA02 BA03 BB03 BB07 DA05 EA06 KA01 KA10 LA07

Claims (7)

[Claims] 1. A conversion element comprising: a sensor for converting an incident electromagnetic wave into an electric signal; and a transistor for reading an electric signal converted by the sensor to a signal line, wherein one main electrode of the transistor is connected to the other main electrode. A conversion element having a shape surrounded by a main electrode. 2. The conversion element according to claim 1, wherein the other main electrode has a U-shape or a U-shape so as to surround the one main electrode. . 3. The method according to claim 1, wherein the one and the other main electrodes have a comb shape, and the one main electrode and the other main electrode are arranged alternately. 3. The conversion element according to 2. 4. The conversion element according to claim 1, wherein a potential on the one main electrode side is higher than a potential on the other main electrode side. 5. A reading device comprising a plurality of the conversion elements according to claim 1, wherein the reading device reads the electric signal from the conversion device, and a processing device processes the read electric signal. A conversion device comprising: 6. A first electrode layer, an insulating layer, a photoelectric conversion semiconductor layer, a semiconductor layer for preventing injection of carriers of a first conductivity type,
And a photoelectric conversion element in which a second electrode layer is laminated, and a carrier of the first conductivity type generated by signal light incident on the photoelectric conversion semiconductor layer is retained in the photoelectric conversion semiconductor layer, and is different from the first conductivity type. A photoelectric conversion unit that applies an electric field to the photoelectric conversion element in a direction in which a carrier of the second conductivity type is guided to the second electrode layer; Refresh means for applying an electric field to the photoelectric conversion element in a direction leading from the conversion semiconductor layer to the second electrode layer; and the first conductivity type accumulated in the photoelectric conversion semiconductor layer during a photoelectric conversion operation by the photoelectric conversion means. And a signal detecting unit for detecting the second conductive type carrier guided to the second electrode layer. 7. The conversion device according to claim 5, a signal processing unit for processing a signal from the conversion device, a recording unit for recording a signal from the signal processing unit, and a signal processing unit. A radiation imaging system comprising: display means for displaying a signal of the type; transmission processing means for transmitting a signal from the signal processing means; and a radiation source for generating the X-ray. .