JP2009123423A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly sensitive imaging device in which a superior imaging signal can be obtained by suppressing occurrence of image failure phenomenon such as a false signal, a ripple phenomenon, and an inversion phenomenon or the like. <P>SOLUTION: On a conductive face 1a of a light-transmissive substrate 1, a light-conductive part 2 is formed. The light-transmissive substrate 1 and a glass tube 4 are sealed by an indium ring 3 in a state that a conductive film 1A and the indium ring 3 are electrically connected so that an internal space of the glass tube 4 is held in vacuum. A shielding ring 10 is pinched by the photo-conductive part 2 and a meshed electrode 9, and a non-forming region in which the light-conductive part 2 is not formed among the conductive film 1A of the light-transmitting substrate 1, and the indium ring 3 are covered by this shielding ring 10. Due to this, the entry of a floating electrons into the conductive film 1A and the indium ring 3 can be suppressed so that the image signal of high quality image can be obtained without accompanying the image failure phenomena such as the false signal, the ripple phenomenon, and the inversion phenomenon or the like. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging device suitable for use by applying a high voltage to a target electrode.

  The image pickup tube includes a target unit composed of a target electrode on a conductive surface and a photoconductive unit including a photoconductive film, and a scanning electron beam generating unit that generates an electron beam for reading a signal. By applying a positive voltage from, the light (including ultraviolet rays, infrared rays, visible rays, and X-rays, which are collectively referred to as light) incident on the photoconductive film is absorbed and converted into charges, and the converted charges Is a device that takes out the accumulated charges as an electric signal directly by an electron beam. The target unit and the scanning electron beam generating unit are held by the housing so as to face each other through a vacuum.

  In a conventional imaging tube such as a vidicon or sachicon, the charge generated by the photoconductive film is read out through an indium ring electrically connected to the conductive surface of the target portion. However, in this case, since the indium ring has the same potential as that of the conductive surface, secondary electrons generated in the imaging tube, a return electron beam that is surplus electrons at the time of scanning, or reflected by the electrode wall and scattered. Electrons straying in the tube such as electrons (hereinafter referred to as stray electrons) are attracted to the indium ring.

  In particular, an image pickup tube (for example, see Non-Patent Document 1) that realizes high sensitivity by utilizing the avalanche multiplication phenomenon of charges in the photoconductive film, and a photoconductive film for increasing the amount of incident X-ray absorption. In an imaging tube with an increased thickness, it is necessary to operate with a higher target voltage (voltage applied to the target electrode). As a result, stray electrons attach to the indium ring and secondary electrons are emitted more rapidly by entering the indium ring, and the reflected image is reflected on the reconstructed image (the return electron beam is reflected by the electrode in the tube and re-enters the target portion). Corresponds to a ripple signal (particularly a phenomenon in which an abnormal pattern changing in a ripple pattern occurs in the peripheral part of the reproduced image), a reverse phenomenon (particularly the peripheral part of the reproduced image) An image defect phenomenon such as an abnormal decrease in the level of the video signal or a phenomenon in which the polarity of the signal is reversed is likely to occur.

  In order to prevent stray electrons from being attracted to the indium ring as a countermeasure against such an image defect phenomenon, a method of providing an electrode insulated from the target portion in a non-scanning region of the target portion has been proposed ( For example, see Patent Document 1). However, in this method, it is necessary to newly install a mechanism for applying a voltage from the outside to an electrode insulated from the target unit, and there is a problem that the configuration of the imaging device and the imaging apparatus becomes complicated.

Therefore, in order to operate by applying a high voltage to the target portion while preventing the image defect phenomenon without newly installing such a voltage application mechanism, a metallic pin is made to penetrate through the substrate, A method has been proposed in which the charge generated by the photoconductive film is read to the outside through this metallic pin, and the indium ring is electrically insulated from the target electrode and held at the ground potential (the same potential as the electron beam source). (For example, refer to Patent Document 2).
Proceedings of the annual conference of the Institute of Television Engineers of Japan, 15-16 pages, 1989 JP-A-4-230941 Japanese Patent Laid-Open No. 5-343016

  By the way, in the imaging tube described in Patent Document 2, charges generated by the photoconductive film can be read out to the outside without causing an image defect phenomenon even when operated by applying a high voltage to the target electrode.

  However, the installation of metal pins that penetrate the substrate requires a sufficient vacuum-tightness of the imaging tube and a reliable contact between the metal pins and the target electrode. There was a problem that a process was necessary.

  In particular, a substrate having a conductive surface such as a beryllium (Be) thin plate, a crystalline silicon (Si) thin plate, or a boron nitride (BN) thin plate that easily transmits X-rays or γ-rays is used for an X-ray imaging device. In particular, when a signal pin is implanted on a conductive substrate, it is necessary to electrically insulate the substrate from the signal pin, which causes a problem that the manufacturing process is further complicated.

  Therefore, the present invention comprises means for reading out signal charges through an indium ring electrically connected to a conductive surface on a substrate, and even if a high voltage is applied to the target portion, it is possible to generate a false signal or ripple phenomenon. In addition, an object of the present invention is to provide an imaging device that realizes high sensitivity and obtains good image quality by suppressing the occurrence of an image defect phenomenon such as a reversal phenomenon.

  An imaging device according to one aspect of the present invention includes a light-transmitting substrate having a conductive surface, a photoconductive portion formed on the conductive surface, and an electron beam that emits an electron beam for scanning the surface of the photoconductive portion. A source, a signal readout electrode that is electrically connected to the conductive surface and reads an imaging signal obtained by scanning the electron beam or selecting the electron beam source, the photoconductive portion, and the electron beam source In an imaging device comprising a housing that forms a vacuum space in which electrons travel, at least a part of the conductive surface on which the photoconductive portion is not formed or at least a part of the signal readout electrode Shielding means for shielding from stray electrons in the vacuum space is included.

  The shielding means is disposed so as not to overlap with an effective scanning region where the photoconductive portion is scanned by the electron beam when viewed from the electron beam source.

  The shielding means may be an insulator made of any one of ceramic, glass, sapphire, or resin.

  The shielding means preferably has a surface secondary electron emission ratio of 1 or less.

  A porous thin film made of antimony trisulfide, arsenic triselenide, or cadmium telluride may be formed on the surface of the shielding means to make the secondary electron emission ratio 1 or less.

  The photoconductive portion may include a photoconductive film composed of an amorphous semiconductor layer containing selenium as a main material.

  According to the present invention, it is possible to provide an imaging device that is easy to manufacture and has high resolution and high sensitivity characteristics while suppressing the occurrence of image defect phenomena such as false signals, ripples, and inversions. can get.

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

[Embodiment 1]
1A and 1B are diagrams conceptually illustrating the configuration of an imaging device according to Embodiment 1, in which FIG. 1A is a side cross-sectional view, and FIG. 1B is a diagram illustrating the imaging device in a cross-section taken along line AA in FIG. It is.

  A conductive film 1A is formed on one surface of the translucent substrate 1 shown in FIG. 1A, and a photoconductive portion 2 is further formed on the conductive surface 1a of the conductive film 1A. Note that the conductive film 1A does not necessarily have to be formed on the entire surface of one side, and in that case, the photoconductive portion 2 covers the translucent substrate 1 in the peripheral portion of the conductive film 1A so as to cover the conductive film 1A. You may form as follows. The translucent substrate 1 is sealed by an indium ring 3 and attached to the glass tube 4 in a state where the conductive film 1A and the indium ring 3 are electrically connected. The glass tube 4 is a tubular member having an opening to which the indium ring 3 is attached. The glass tube 4 is sealed (sealed) with the translucent substrate 1 by the indium ring 3, whereby the internal space is maintained in a vacuum.

  FIG. 2 is a diagram showing in detail the configuration of the light-transmitting substrate 1 and the photoconductive portion 2 of the imaging device of Embodiment 1, (a) is a plan view showing in detail the configuration of FIG. 1 (b), (B) is a figure which shows an imaging device by the BB arrow cross section of (a). The translucent substrate 1 is a disk-shaped substrate made of translucent glass having a diameter of 25 mm. A conductive film 1A made of a light-transmitting conductive film (ITO) having a rectangular shape having lead portions 1B on both sides and a film thickness of 30 nm is formed on one surface of the substrate 1 by a sputter deposition method. The rectangular portion has a size including the scanning region 2C. The conductive film 1A may have a circular shape with a diameter of 25 mm, for example, but a rectangular shape is more preferable because the capacitance of the target electrode can be reduced.

  The photoconductive portion 2 includes a hole injection blocking enhancement layer 2a, a photoconductive film 2b, and an electron beam landing layer 2c.

The hole injection blocking enhancement layer 2a is made of cerium oxide (CeO ₂ ) having a diameter of 20 mm and a film thickness of 10 to 30 nm, and is formed by a vacuum deposition method. The photoconductive film 2b is formed on the hole injection blocking enhancement layer 2a as an amorphous semiconductor layer made of selenium (Se) having a diameter of 20 mm and a thickness of 2 to 50 μm as a main material by a vacuum deposition method. The electron beam landing layer 2c is deposited as an antimony trisulfide (Sb ₂ S ₃ ) layer having a diameter of 20 mm and a film thickness of 0.1 μm, for example, in an argon (Ar) gas atmosphere at a pressure of 0.1 to 0.4 Torr. Is done. In this case, the electron beam landing layer 2c also functions as an electron injection blocking layer and plays a role of making the photoconductive portion 2 a low dark current type.

  Inside the glass tube 4, an electron beam source 5, a first grid electrode 6, a second grid electrode 7, a third grid electrode 8, and a mesh electrode 9 are disposed from the back to the opening. Further, a shielding ring 10 is disposed between the mesh electrode 9 and the photoconductive portion 2 as a blocking means for blocking stray electron entry. The shielding ring 10 is an annular insulating member that is fitted to the inner peripheral surface of the glass tube 4, and is held between the photoconductive portion 2 and the mesh electrode 9. The function of the shielding ring 10 will be described later. The glass tube 4 is a housing that forms a vacuum space in which electrons travel between the photoconductive portion 2 and the electron beam source 5.

  The indium ring 3 is connected to a positive terminal of a power source 11 for applying a positive voltage to a target electrode composed of the conductive film 1A, and a reading unit 12 for reading an imaging signal. 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. A voltage applied to the target electrode is referred to as a target voltage.

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

  The electron beam source 5 contains a cathode material, and an electron cloud is excited and generated by heating the cathode material with a heater. The first grid electrode 6, the second grid electrode 7, the third grid electrode 8, and the mesh electrode 9 are electrodes for extracting and accelerating electrons in the direction of the photoconductive portion 2. These accelerating electrons are deflected and focused by the focusing coil and the deflection coil, and are passed through the mesh electrode 9 to form a scanning electron beam that is uniform in the in-plane direction.

  Here, the voltage applied to each electrode is as follows: heater of electron beam source: about 6V, first grid electrode 6: about 20V, second grid electrode 7: about 300V, third grid electrode 8: about 600V, mesh electrode 9: About 800V.

  An electron beam adheres to the surface of the region scanned with the electron beam on the scanning surface 2A of the photoconductive portion 2 until it becomes substantially the same potential as the electron beam source 5 during the scanning period, and surplus electrons become return beam electrons. Will be reflected in the tube. As a result, a target voltage is applied between the scanning surface 2A and the conductive surface 1a of the photoconductive portion 2, and a strong deceleration electric field is generated in the gap between the scanning surface 2A and the mesh electrode 9 immediately after the end of scanning. When light is incident during the non-scanning period, electron-hole pairs are generated in the photoconductive film 2b by the absorbed light, and the holes travel along the electric field in the photoconductive portion 2 to the scanning surface 2A. Since it recombines with the adhering electrons, the surface potential of the scanning surface 2A changes in the positive direction. In the next electron beam scanning, the scanning electron beam adheres until the surface potential of the scanning surface 2A that has risen in the positive direction is restored, and a change in current flowing in the closed circuit at that time is detected from the signal reading unit 12 as an imaging signal. As taken out.

  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 an electron beam deflected and focused by the deflection coil and the focusing coil.

  The shield ring 10 has an opening 10A larger than the scanning region 2C, and is disposed so that the opening 10A does not overlap the scanning region 2C when viewed from the electron beam source 5. For example, a glass member having an outer diameter of 20 mm, an inner diameter of 17 mm, and a thickness of 2.5 mm is sandwiched between the photoconductive portion 2 and the mesh electrode 9.

  Note that the opening 3A of the indium ring 3 is larger than the opening 10A of the shielding ring 10 and is located on the radially outer side. That is, the indium ring 3 is disposed so as not to overlap with the scanning region 2 </ b> C of the photoconductive portion 2.

  As shown in FIGS. 1A and 1B, a non-formation region where the photoconductive portion 2 is not formed in the conductive film 1 </ b> A of the translucent substrate 1 and the indium ring 3 are covered with an insulating shielding ring 10. Is called.

  According to the imaging device of the present embodiment, since the conductive film 1A and the indium ring 3 are shielded from stray electrons existing in the vacuum space in the glass tube 4 by having the shielding ring 10, the conductive film 1A and indium Intrusion of stray electrons into the ring 3 can be suppressed. As a result, even if a high voltage of 1000 V to 5000 V is applied to the conductive film 1A as a target voltage, for example, an image defect phenomenon such as a false signal, a ripple phenomenon, or an inversion phenomenon Therefore, it is possible to obtain a high-quality image pickup signal without accompanying.

  Moreover, it can manufacture easily, without requiring complicated manufacturing processes, such as planting a metal pin in the translucent board | substrate 1 like a prior art.

  The shielding ring 10 is an electrical insulator so that electrons do not stay, and is naturally electrically insulated from the translucent substrate 1 and the indium ring 3. Moreover, the material is not limited to glass, For example, any of ceramic, sapphire, or resin may be sufficient.

  Further, the opening 10A of the shielding ring 10 may be any shape that does not interfere with the trajectory of the electron beam 5A, and is not limited to a circle but may be an ellipse or a rectangle.

  Moreover, although the case where the shielding ring 10 is used as a member for shielding the conductive film 1A and the indium ring 3 from stray electrons has been described above, the shielding member is not limited to a ring (ring shape). Alternatively, it may be divided in the inner peripheral direction of the glass tube 4 or may have a cutout like a C shape, and the photoconductive portion 2 is not formed on the conductive surface 1a of the conductive film 1A. The surface and / or at least a part of the inner peripheral surface of the indium ring 3 or both of them can be formed in any shape that shields stray electrons in the vacuum space.

Further, it is desirable that the surface of the shielding ring 10 be processed so that the secondary electron emission ratio is 1 or less. For example, the surface is roughened, or the surface is composed of antimony trisulfide (Sb ₂ S ₃ ), arsenic triselenide (As ₂ Se ₃ ), or porous cadmium telluride (CdTe). You may give the process etc. which form a thin film.

  In the above description, the imaging device using the photoconductive film 2b including the amorphous semiconductor layer mainly composed of selenium (Se) in the photoconductive portion 2 has been described. Regardless of the type, it can be applied to an imaging device having various types of photoconductive films. In particular, in an imaging device using an amorphous semiconductor layer mainly composed of selenium (Se) as described above for the photoconductive film 2b, a high voltage that causes charge avalanche multiplication within the photoconductive film is targeted. By applying it to the electrodes, it is possible to suppress the image defect phenomenon and realize extremely high quality image quality with ultra-high sensitivity, high resolution, and low afterimage, but other types of photoconductive films were used. Also in the imaging device, it is possible to suppress the image defect phenomenon and realize an extremely high quality image quality.

  Note that the voltage applied to each electrode to drive the imaging device of the present embodiment is not limited to the above values.

  The translucent substrate 1 is not limited to a glass substrate, and may be a translucent resin substrate or an optical fiber plate. Further, when a thin plate such as beryllium (Be), crystalline silicon (Si), or boron nitride (BN) having a high X-ray transmittance is used as the translucent substrate 1, the shielding member (shielding ring 10 described above) is used. ) Can be applied to an X-ray imaging device. In this case, even if the thickness of the photoconductive film 2b is increased and the target voltage is increased in order to increase the absorption amount of incident X-rays, the image defect phenomenon can be significantly suppressed.

  In the above description, a generally used magnetic field focusing / deflection image pickup tube has been described. However, a method of reading an accumulated charge by accelerating an electron beam in a vacuum and landing it on a photoconductive portion. Any other type of imaging device may be used as long as it is a device.

[Embodiment 2]
FIG. 3 is a side sectional view schematically showing a configuration of the imaging device of the second embodiment. 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 25 mm as the translucent substrate 1 is provided with an electron emission source array 20 as an electron beam source. Is different from the imaging device of the first embodiment. Hereinafter, the same reference numerals are used for the same or equivalent components as those of the imaging device of Embodiment 1, and the description thereof is omitted.

  The imaging device of Embodiment 2 is suitable for an X-ray imaging device. 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. For this reason, the conductive surface 1 a becomes one surface of the translucent substrate 1. The photoconductive portion 2 is the same as the photoconductive portion 2 of the first embodiment, and is formed on the conductive surface 1a.

The glass tube 4 is cup-shaped, and a ceramic shielding ring 21 having an outer diameter of 20 mm, an inner diameter of 17 mm, and a height of 10 mm is disposed inside as a shielding means for shielding stray electrons from entering. A secondary electron emission suppression layer made of antimony trisulfide (Sb ₂ S ₃ ) having a thickness of 100 nm is deposited on the surface of the shielding ring 21 in an argon (Ar) gas atmosphere at a pressure of 0.1 to 0.4 Torr. ing. A metal vacuum chamber may be used instead of the cup-shaped glass tube 4.

  The electron emission source array 20 is a flat electron beam source in which micro cathodes are arranged in a matrix. By controlling the voltage value applied to the scanning line and the selection line, an electron beam can be emitted from the desired cathode to the photoconductive portion 2. Since the electron emission source array 20 can select the cathode and emit an electron beam, the first grid electrode 6, the second grid electrode 7, the third grid electrode 8, the deflection, as in the imaging device of the first embodiment. A coil and a focusing coil are not provided.

  The shield ring 21 is disposed in contact with the scanning surface 2A of the photoconductive portion 2 so that the opening does not interfere with the scanning region 2C when viewed from the electron emission source array 20. As shown in FIG. 3, the transparent substrate 1 and the glass tube 4 are sealed via the indium ring 3 with the shielding ring 21 sandwiched between the photoconductive portion 2 and the bottom portion in the glass tube 4. .

  According to the imaging device of the present embodiment, by having the shielding ring 21, the conductive surface 1a and the indium ring 3 are shielded from stray electrons existing in the vacuum space in the glass tube 4, so Similar to the imaging device, stray electrons can be prevented from entering the conductive translucent substrate 1 and the indium ring 3. As a result, for example, a high voltage of 1000 V to 5000 V is used as the target voltage. Even when applied to one conductive surface 1a, it is possible to obtain a high-quality image pickup signal without causing an image defect phenomenon such as a false signal, a ripple phenomenon, or an inversion phenomenon.

  Moreover, it can manufacture easily, without requiring complicated manufacturing processes, such as planting a metal pin in the translucent board | substrate 1, like the past.

As described above, when the imaging device obtained in Embodiments 1 and 2 is mounted on a television camera and a voltage is applied to the photoconductive portion 2 such that the electric field strength of the photoconductive film 2b is about 1 × 10 ⁸ V / m. In any television camera using any imaging device, no image defect phenomenon was observed. In particular, in an imaging device having a photoconductive film 2b made of an amorphous semiconductor whose main material is selenium (Se) with a thickness of 50 μm, a target voltage of 5000 V or more is applied to cause avalanche multiplication. However, no image defect phenomenon was observed.

  Thus, the imaging devices of Embodiments 1 and 2 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). It is a figure which shows the structure of the translucent board | substrate 1 and the photoconductive part 2 of the imaging device of Embodiment 1 in detail, (a) is a top view which shows the structure of FIG.1 (b) in detail, (b) is It is a figure which shows an imaging device in the BB arrow cross section of (a). 4 is a side sectional view schematically showing a configuration of an imaging device according to a second embodiment. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Translucent board | substrate 1A Conductive film 1a Conductive surface 1B Lead part 2 Photoconductive part 2a Hole injection prevention reinforcement | strengthening layer 2b Photoconductive film 2c Electron beam landing layer 2A Scanning surface 2B Light incident surface 2C Scanning area 3 Indium ring 3A Opening part 4 Glass tube 5 Electron beam source 6 First grid electrode 7 Second grid electrode 8 Third grid electrode 9 Mesh electrode 10, 21 Shielding ring 10 A Opening 11 Power supply 12 Reading unit 20 Electron emission source array

Claims (6)

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 electrode electrically connected to the conductive surface and for reading out an imaging signal obtained by scanning the electron beam or selecting the electron beam source;
In an imaging device comprising: a housing that forms a vacuum space in which electrons travel between the photoconductive portion and the electron beam source,
An imaging device comprising: a non-formed surface on which the photoconductive portion is not formed in the conductive surface; or a shielding unit that shields at least a part of the signal readout electrode from stray electrons in the vacuum space.   The imaging device according to claim 1, wherein the shielding unit is disposed so as not to overlap with an effective scanning region in which the photoconductive portion is scanned by the electron beam as viewed from the electron beam source.   The imaging device according to claim 1, wherein the shielding unit is an insulator made of any one of ceramic, glass, sapphire, or resin.   The imaging device according to claim 1, wherein the shielding means has a secondary electron emission ratio of 1 or less on a surface.   The imaging device according to any one of claims 1 to 4, wherein a porous thin film made of antimony trisulfide, arsenic triselenide, or cadmium telluride is formed on the surface of the shielding means. .   The imaging device according to claim 1, wherein the photoconductive portion includes a photoconductive film including an amorphous semiconductor layer containing selenium as a main material.

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