JP5111276B2 - Imaging device - Google Patents

Description

  The present invention relates to a photoconductive imaging device capable of obtaining a high-quality image with high sensitivity and high resolution and high S / N.

  It is known that when a high electric field is applied to a photoconductive layer composed of a selenium-based amorphous semiconductor, an avalanche multiplication phenomenon occurs inside. A photoconductive high-sensitivity imaging tube using this phenomenon is proposed. (For example, refer nonpatent literature 1).

In order to cause such an avalanche multiplication phenomenon, it is necessary to apply a high electric field of 5 × 10 ⁷ V / m or more to the photoconductive layer. For example, a cerium oxide thin film is interposed between the positive electrode and the selenium-based amorphous semiconductor (photoconductive layer) as a technique for preventing the injection of electric charges (holes) into the conductive layer and suppressing dark current. A method of providing as a hole injection blocking layer is known.
Proceedings of the annual conference of the Institute of Television Engineers of Japan, 33-34, 1989

  However, even if a cerium oxide thin film is provided as a hole injection blocking layer as described above, depending on the film quality of the hole injection blocking layer and the strength of the applied electric field, a selenium-based amorphous semiconductor (photoconductive In some cases, the injection of charge into the layer) cannot be effectively suppressed, and a dark current resulting from the charge injection that has passed through the hole injection blocking layer may occur.

  In general, in a high-sensitivity imaging tube using the avalanche multiplication phenomenon, a higher multiplication factor (sensitivity) can be obtained as the electric field strength applied to the photoconductive layer is increased, but the electric field strength is too high. The dark current resulting from the charge injection also causes avalanche multiplication, which may cause degradation of image quality such as S / N.

  For this reason, there is a limit to the intensity of the electric field that can be applied to the photoconductive layer, and there is a problem that the maximum value of the multiplication factor of the high-sensitivity image pickup tube is limited by the limit of the electric field intensity.

  Therefore, the present invention uses a photoconductive layer in which an avalanche multiplication phenomenon occurs due to application of a high electric field, and a hole injection blocking layer made of cerium oxide with an enhanced degree of blocking hole injection into the photoconductive layer. Thus, an object of the present invention is to provide a photoconductive imaging device that can obtain a high-quality image with high sensitivity and high resolution and high S / N.

An imaging device according to one aspect of the present invention includes a translucent substrate having a conductive surface, a photoconductive portion formed on the conductive surface, an electron beam source that emits a scanning electron beam to the photoconductive portion, and A signal reading unit electrically connected to the photoconductive unit and for reading an imaging signal obtained by scanning the electron beam, wherein the photoconductive unit is directed from the conductive surface toward the electron beam source. The hole injection blocking layer includes a hole injection blocking layer, a photoconductive layer, and an electron beam landing layer, which are sequentially stacked, and the hole injection blocking layer is made of cerium oxide having a density of 6.5 g / cm ³ or more.

  The photoconductive layer may include a photoconductive film formed of an amorphous semiconductor layer mainly composed of selenium.

  In addition, a voltage that causes an avalanche multiplication phenomenon in the photoconductive portion may be applied to the photoconductive portion.

  According to the present invention, a photoconductive layer in which an avalanche multiplication phenomenon is caused by application of a high electric field, and a hole injection blocking layer made of cerium oxide with an enhanced degree of blocking hole injection into the photoconductive layer are used. Thus, it is possible to provide a peculiar effect that it is possible to provide a photoconductive imaging device capable of obtaining a high-quality image with high sensitivity and high resolution and high S / N.

  Embodiments to which the imaging device of the present invention is applied will be described below.

[Embodiment 1]
1A and 1B are diagrams illustrating a configuration of an imaging device according to Embodiment 1, in which FIG. 1A is a side cross-sectional view, and FIG.

  A conductive film 1A is formed on one surface of the translucent substrate 1 shown in FIG. 1A, and a photoconductive portion 2 is formed on the conductive film 1A. This translucent substrate 1 is sealed by an indium ring 3 and attached to a glass tube 4.

  The glass tube 4 is a glass tubular member sealed at one end, and an electron beam source 5, a first grid electrode 6, and a second electrode are formed inside the glass tube 4 from the back to the opening. A grid electrode 7, a third grid electrode 8, and a mesh electrode 9 are provided.

  Moreover, the translucent board | substrate 1 is equipped with metal pins 1B. The metal pin 1 </ b> B is fitted into a through hole that penetrates the translucent substrate 1. The metal pin 1B is electrically connected to the conductive film 1A, and a positive polarity terminal of a power source 11 for applying a voltage to the photoconductive portion 2 and a reading portion 12 for reading an imaging signal are connected. . At that time, the other negative terminal of the power source 11 is connected to the electron beam source 5 and installed so as to form a closed circuit via the scanning electron beam.

  Further, a deflection coil and a focusing coil (not shown) are disposed outside the glass tube 4 to deflect and focus the electrons (electron beam 5A) accelerated in the third grid electrode 8.

"Configuration of each part"
The translucent substrate 1 is a transparent substrate that transmits the reflected light obtained from the subject and guides it to the photoconductive portion 2, and is composed of, for example, a disc-shaped substrate made of translucent glass and having a diameter of 18 mm. . A conductive film 1A having a diameter of 14 mm and a thickness of 30 nm mainly composed of indium oxide is formed on one surface of the translucent substrate 1 by a sputter deposition method.

  The photoconductive portion 2 is a thin-film photoconductive portion that serves as a target of the electron beam 5A emitted from the electron beam source 5 and causes an avalanche multiplication phenomenon inside when a high electric field is applied. The photoconductive portion 2 has a circular shape in plan view, and has a scanning surface 2A that is scanned by the electron beam 5A, and an incident surface 2B through which light enters from the upper direction in the drawing through the translucent substrate 1 and the conductive film 1A. . The incident surface 2B is a boundary surface between the photoconductive portion 2 and the conductive film 1A. A voltage applied from the power source 11 to the photoconductive portion 2 is referred to as a target voltage.

  As shown in FIG. 1B, the photoconductive portion 2 has a scanning region 2C at the center of the scanning surface 2A facing the electron beam source 5. The scanning region 2C is a region where scanning for taking out an imaging signal is performed by the electron beam 5A deflected and focused by the deflection coil and the focusing coil. The metal pin 1B is disposed at a position outside the scanning region 2C in plan view. The detailed configuration of the photoconductive portion 2 will be described later with reference to FIG.

  The indium ring 3 is an indium ring member for sealing (sealing) between the translucent substrate 1 and the glass tube 4.

  The glass tube 4 is a glass tubular member that has an opening to which the indium ring 3 is attached at one end and is sealed at the other end. The glass tube 4 transmits light by the indium ring 3 in order to realize scanning with an electron beam. By sealing (sealing) with the conductive substrate 1, the internal space is maintained in a vacuum.

  The electron beam source 5 is an electron emission source disposed at an end in the glass tube 4 and is an apparatus that excites an electron cloud by heating a cathode material with a heater.

  The first grid electrode 6, the second grid electrode 7, and the third grid electrode 8 are electrodes for extracting and accelerating electrons excited by the electron beam source 5 as electron beams 5A in the direction of the mesh electrode 9.

  The mesh electrode 9 is an electrode that generates a decelerating electric field for reducing the velocity of electrons that collide with the photoconductive portion 2 that is a target of the scanning electron beam 5A.

  Here, the voltage applied to each electrode is, for example, the heater of the electron beam source 5: about 6V, the first grid electrode 6: about 20V, the second grid electrode 7: about 300V, and the third grid electrode 8: about 600V. Mesh electrode 9: about 800V.

  Further, a target voltage of 100 to 5000 V is applied to the light incident surface 2B of the photoconductive portion 2 from the power supply 11 through the conductive film 1A according to the thickness of the photoconductive portion 2.

  The surface potential of the scanning region 2C becomes the same potential as that of the electron beam source 5 immediately after the end of scanning, and the same voltage as the target voltage is applied between the incident surface 2B of the photoconductive portion 2 and the scanning surface 2A. Thereafter, when light is incident, electron-hole pairs are generated in the photoconductive portion 2 by the absorbed light, and the holes travel to the scanning surface 2A along the electric field in the photoconductive portion 2, and the scanning surface 2A. The surface potential changes in the positive direction. The surface potential of the scanning surface 2A that has risen in the positive direction returns to the same potential as that of the electron beam source 5 again by the next electron beam scanning. .

  Electrons generated from the electron beam source 5 are extracted by the first grid electrode 6, emitted as the electron beam 5 </ b> A by the second grid electrode 7, deflected and focused by an external magnetic field, and accelerated by the third grid electrode 8. The The accelerated electrons are decelerated when passing through the mesh electrode 9 and reach the surface of the photoconductive portion 2 at a substantially zero speed. Thereby, it can suppress that an electron collides with the photoconductive part 2 at high speed, and discharge | release of the secondary electron by collision is suppressed.

"Configuration of photoconductive part 2"
FIG. 2 is a cross-sectional view showing in detail the configuration of the photoconductive portion 2 of the imaging device of the first embodiment.

  The photoconductive portion 2 is a stacked body of a hole injection blocking layer 2a, a photoconductive layer 2b, and an electron beam landing layer 2c, and is stacked on the surface of the conductive film 1A of the translucent substrate 1.

The hole injection blocking layer 2a is a layer for blocking the injection of charges (holes) from the conductive film 1A to the photoconductive layer 2b, and is formed to suppress dark current, cerium oxide (CeO ₂ ). It is a thin film layer. The hole injection blocking layer 2a is formed on the surface of the conductive film 1A by a vacuum deposition method.

  The photoconductive layer 2b is an amorphous semiconductor layer containing selenium (Se) as a main material, and is a semiconductor layer that causes an avalanche multiplication phenomenon when a high voltage is applied. This photoconductive layer 2b is formed on the surface of the hole injection blocking layer 2a by vacuum deposition.

  The electron beam landing layer 2 c is a layer that is emitted from the electron beam source 5 and accelerated by the first grid electrode 6, the second grid electrode 7, and the third grid electrode 8, and reaches the electrons decelerated by the mesh electrode 9. is there.

“Production Method of Photoconductive Section 2”
Such a photoconductive portion 2 is manufactured as follows. First, a hole injection blocking layer 2a made of cerium oxide having a diameter of 14 mm and a film thickness of 10 nm is formed on the conductive film 1A by vacuum deposition. At this time, if the temperature of the translucent substrate 1 is maintained at 220 ° C. using a heating mechanism provided in the vacuum deposition apparatus, the density of cerium oxide constituting the hole injection blocking layer 2a is 6.7-6. About 8 g / cm ³ .

Next, a photoconductive layer 2b made of an amorphous semiconductor mainly composed of selenium (Se) having a diameter of 14 mm and a film thickness of 2 to 50 μm is formed on the hole injection blocking layer 2a by vacuum deposition. Further, antimony trisulfide (Sb ₂ S ₃ ) is deposited in an argon (Ar) gas atmosphere at a pressure of 0.1 to 0.4 Torr to form an electron beam landing layer 2c having a diameter of 14 mm and a film thickness of 0.1 μm. The photoconductive portion 2 is obtained as described above.

  By sealing the translucent substrate 1 with the photoconductive portion 2 formed in this way and the glass tube 4 containing the electron beam source 5, mesh electrode 9 and the like with the indium ring 3, and vacuum-sealing the inside. The imaging device of Embodiment 1 is obtained.

  FIG. 3 is a diagram illustrating imaging signal current characteristics and dark current characteristics in the imaging device of the first embodiment. These are characteristics obtained by an imaging device in which the thickness of the photoconductive layer 2b is 4 μm, and the temperature of the translucent substrate 1 when forming the hole injection blocking layer 2a is in addition to the above-mentioned 220 ° C. , 40 ° C, 100 ° C, and 150 ° C. The horizontal axis represents the target voltage applied from the power supply 11 to the photoconductive portion 2.

  When the density of the hole injection blocking layer 2a of the imaging device manufactured by changing the substrate temperature in this manner was measured, the results shown in Table 1 were obtained.

また、図４は、表１の結果を特性として示す図である。この測定結果では、透光性基板１の温度を１００℃以上とした場合に、正孔注入阻止層２ａの酸化セリウムの密度は、６．５ｇ／ｃｍ^３以上の値が得られた。なお、設定温度が２５℃の撮像デバイスは、室温で作製したものであり、従来の撮像デバイスに相当するものである。

FIG. 4 is a diagram showing the results of Table 1 as characteristics. In this measurement result, when the temperature of the translucent substrate 1 was set to 100 ° C. or higher, the density of cerium oxide in the hole injection blocking layer 2a was 6.5 g / cm ³ or higher. Note that an imaging device having a set temperature of 25 ° C. is manufactured at room temperature and corresponds to a conventional imaging device.

  As shown in the characteristic diagram of FIG. 3, the imaging signal current characteristics obtained substantially the same characteristics at all temperatures.

  On the other hand, the dark current decreased as the production temperature of the hole injection blocking layer 2a increased to 40 ° C, 100 ° C, 150 ° C, and 220 ° C. When the imaging device at 25 ° C. is used as a reference, it is about 20% lower at 40 ° C., about 50% at 100 ° C., about 1/3 at 150 ° C., and about 1/200 at 220 ° C. Decreased to 4.

  As described above, the dark current value decreased because the density of cerium oxide constituting the hole injection blocking layer 2a increased as the production temperature increased as shown in Table 1, and the production temperature. This is considered to be because the amount of oxygen defects in cerium oxide decreased as the value of cerium oxide increased, the defect level in cerium oxide decreased, and the energy barrier with conductive film 1A increased.

From these results, when the density of cerium oxide constituting the hole injection blocking layer 2a is set to 6.5 g / cm ³ or more, the dark current value becomes very low, and the hole injection blocking layer 2a is manufactured. It is found that when the temperature of the translucent substrate 1 is set to 100 ° C. or higher, a photoconductive imaging device capable of obtaining a high-quality image with high sensitivity and high resolution and high S / N can be provided. It was. In particular, it was found that when the temperature of the translucent substrate 1 is 220 ° C., an imaging device in which the dark current is reduced to about ¼ that of the conventional imaging device can be manufactured.

  As described above, according to the first embodiment, when the hole injection blocking layer 2a is formed, the translucent substrate 1 is heated to greatly reduce the dark current, thereby achieving high sensitivity / high resolution and high S / N. It is possible to provide a photoconductive imaging device capable of obtaining a high-quality image.

In the above, the imaging device using the photoconductive layer made of an amorphous semiconductor mainly composed of selenium (Se) has been described. However, the present invention does not place any restrictions on the material of the photoconductive layer, Needless to say, the present invention can also be applied to an imaging device using a photoconductive layer made of Si, PbO, CdS, CdSe, CdTe, Sb ₂ S ₃ or the like.

Moreover, although cerium oxide was formed by the vacuum evaporation method above, other methods may be used as long as cerium oxide having a density of 6.5 g / cm ³ or more can be obtained.

  The translucent substrate 1 is not limited to a glass substrate, and may be a translucent resin substrate or an optical fiber plate. Further, if a thin plate such as beryllium (Be), crystalline silicon (Si), or boron nitride (BN) having a high X-ray transmittance is used, the dark current of the X-ray imaging device can be reduced. .

  In the above description, the image pickup tube that is generally widely used has been described. However, any device that accelerates an electron beam in a vacuum and lands on a photoconductive layer to read out accumulated charges can be used. It may be an imaging device of the form.

[Embodiment 2]
FIG. 5 is a diagram illustrating a cross-sectional structure of the imaging device according to the second embodiment. The imaging device of the second embodiment is suitable for an imaging device for X-ray images, and is mainly different from the imaging device of the first embodiment in that an electron emission source array 20 as an electron beam source is provided. The electron emission source array 20 includes a plurality of minute cathodes arranged in a matrix, and an arbitrary cathode can be selected to emit an electron beam. Therefore, unlike the imaging device of the first embodiment, the first grid electrode 6, the second grid electrode 7, the third grid electrode 8, the deflection coil, and the focusing coil are not provided.

  In the second embodiment, the glass tube 4 has a cup shape. The electron emission source array 20 is disposed on the bottom surface of the glass tube 4.

  Other configurations are basically the same as those of the imaging device according to the first embodiment. Therefore, the same or equivalent components are denoted by the same reference numerals, and description thereof is omitted.

  In the imaging device of the second embodiment, a thin plate-like conductive substrate made of beryllium (Be) having a thickness of 0.5 mm and a diameter of 18 mm is used as the translucent substrate 1. Since the thin plate-like translucent substrate 1 made of beryllium (Be) has conductivity, it is not necessary to form the conductive film 1A on one surface as in the first embodiment.

  The photoconductive portion 2 is formed on one surface of the translucent substrate 1 as in the first embodiment. The translucent substrate 1 is sealed with a glass tube 4 through an indium ring 3.

  Moreover, as mentioned above, the glass tube 4 of Embodiment 2 is cup-shaped. An electron emission source array 20 is disposed on the bottom surface inside the cup-shaped glass tube 4, and a mesh electrode 9 is disposed in the vicinity of the opening 4A.

  The electron emission source array 20 is a flat electron beam source in which a plurality of minute cathodes are arranged in a matrix. By controlling the voltage value applied to the scanning line and the selection line, the electron beam 20A can be emitted from the desired cathode to the photoconductive portion 2.

  The translucent substrate 1 having the photoconductive portion 2 formed on the surface as described above and the glass tube 4 containing the electron emission source array 20 and the mesh electrode 9 are sealed using the indium ring 3, and the inside is sealed. By performing vacuum sealing, the imaging device of Embodiment 2 can be manufactured.

  The relationship between the voltage applied to the photoconductive portion 2 and the imaging signal current and dark current of the imaging device depends on the structure and film thickness of the photoconductive portion 2. For this reason, the imaging device of the second embodiment using the same photoconductive portion 2 including the hole injection blocking layer 2a and the photoconductive layer 2b as in the first embodiment is the same as the imaging device of the first embodiment. In addition, the dark current can be reduced as compared with the imaging device according to the prior art.

  In the above description, the glass tube 4 has a cup shape. However, instead of the cup-shaped glass tube 4, a metal vacuum chamber having the same shape may be used.

  The imaging devices of Embodiments 1 and 2 described above are most suitable for television cameras that require high image quality, particularly high-definition cameras, and if applied to image analysis systems in the industrial, medical, physics and chemistry fields, Effects such as signal processing with a high S / N are obtained.

  Although the imaging device of the exemplary embodiment of the present invention has been described above, the present invention is not limited to the specifically disclosed embodiment, and does not depart from the scope of the claims. Various modifications and changes are possible.

It is a figure which shows the structure of the imaging device of Embodiment 1, (a) is a sectional side view, (b) is a figure which shows an imaging device by the AA arrow cross section of (a). 2 is a cross-sectional view showing in detail the configuration of a photoconductive portion 2 of the imaging device of Embodiment 1. FIG. 3 is a diagram illustrating imaging signal current characteristics and dark current characteristics in the imaging device of Embodiment 1. FIG. It is a figure which shows the result of Table 1 as a characteristic. 6 is a diagram illustrating a cross-sectional structure of an imaging device according to Embodiment 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Translucent substrate 1A Conductive film 1B Metallic pin 2 Photoconductive part 2a Hole injection blocking layer 2A Scanning surface 2b Photoconductive layer 2B Incident surface 2c Electron beam landing layer 2C Scanning region 3 Indium ring 4 Glass tube 4A Opening 5 Electron beam source 5A, 20A Electron beam 6 First grid electrode 7 Second grid electrode 8 Third grid electrode 9 Mesh electrode 11 Power supply 12 Reading unit 20 Electron emission source array

Claims (3)

A translucent substrate having a conductive surface;
A photoconductive portion formed on the conductive surface;
An electron beam source for emitting a scanning electron beam to the photoconductive portion;
A signal readout unit electrically connected to the photoconductive unit and for reading out an imaging signal obtained by scanning the electron beam;
The photoconductive portion includes a hole injection blocking layer, a photoconductive layer, and an electron beam landing layer, which are sequentially stacked in a direction from the conductive surface toward the electron beam source, and the hole injection blocking layer has a density of Is an imaging device composed of cerium oxide of 6.5 g / cm ³ or more.   The imaging device according to claim 1, wherein the photoconductive layer includes a photoconductive film including an amorphous semiconductor layer mainly containing selenium.   The imaging device according to claim 1, wherein a voltage that causes an avalanche multiplication phenomenon in the photoconductive portion is applied to the photoconductive portion.

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