US3371239A - Electron discharge device with storage target electrode - Google Patents

Electron discharge device with storage target electrode Download PDF

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Publication number
US3371239A
US3371239A US115551A US11555161A US3371239A US 3371239 A US3371239 A US 3371239A US 115551 A US115551 A US 115551A US 11555161 A US11555161 A US 11555161A US 3371239 A US3371239 A US 3371239A
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United States
Prior art keywords
target
layer
aluminum oxide
target electrode
storage target
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Expired - Lifetime
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US115551A
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English (en)
Inventor
Robert A Shaffer
Jr Leo G Bonney
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Westinghouse Electric Corp
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Westinghouse Electric Corp
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Priority to NL279364D priority Critical patent/NL279364A/xx
Application filed by Westinghouse Electric Corp filed Critical Westinghouse Electric Corp
Priority to US115551A priority patent/US3371239A/en
Priority to GB14925/62A priority patent/GB947959A/en
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Publication of US3371239A publication Critical patent/US3371239A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
    • H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
    • H01J29/36—Photoelectric screens; Charge-storage screens
    • H01J29/39—Charge-storage screens
    • H01J29/41—Charge-storage screens using secondary emission, e.g. for supericonoscope
    • H01J29/413—Charge-storage screens using secondary emission, e.g. for supericonoscope for writing and reading of charge pattern on opposite sides of the target, e.g. for superorthicon

Definitions

  • This invention relates generally to electron discharge devices, such as pickup tubes, having storage target electrodes.
  • the invention is particularly applicable to image orthicons.
  • an electron image containing scene information is impressed upon one side of a storage target electrode forming a charge image and the other side is scanned by a uniform electron beam which discharges the charge image. Electrons of the uniform beam not needed to neutralize the charge on the target are captured to provide the output signal from the device.
  • the target is made of glass having a conductance such that the electrons deposited on the target by the scanning beam leak through and neutralize the positive charge on the opposite side in the of a second that elapses between scans.
  • Such targets exhibit what is known as a burn effect whereby after a certain period of useful life electrons fromthe scanning beam are unable to be conducted through the target Within the necessary time and hence the charge thereon is not neutralized.
  • the generally accepted explanation of this phenomenon is that conduction through the glass target is by migrating ions, usually of sodium. The part of the target near the surface on which the electron image is deposited becomes deficient in the ions with age. Thus the life of present image orthicons is limited to about 500 hours.
  • Another object of the invention is to provide an image orthicon device having an improved target which may be readily made and has a high degree of mechanical 3,371,230 Patented Feb. 27, 1968 strength thereby permitting an image orthicon having long life.
  • a device of the image orthicon type having a storage target electrode comprising a layer of amorphous aluminum oxide.
  • the amorphous aluminum oxide of the target electrode may be either porous or non-porous but is preferably made having pores extending transversely almost entirely through it so as to further reduce lateral conduction and provide a higher degree of mechanical flexibility.
  • the storage target electrode has on the surface thereof facing the scanning electron gun of the device a thin layer of a conductive material, such as indium, which has the property of migrating or diffusing into the amorphous aluminum oxide so as to improve transverse conductivity.
  • the storage target electrode may have on the surface thereof facing the photocathode a layer of an insulating material having a secondary electron emitting characteristic which is higher than that of the amorphous aluminum oxide so as to produce a more pronounced charge image.
  • the aluminum oxide layer need only be supported at its periphery.
  • FIGURE 1 is a cross sectional view of a device of the image orthicon type embodying the present invention
  • FIGURE 2 is an enlarged partial cross sectional view of the storage target electrode assembly of the device of FIGURE 1;
  • FIGURE 3 is an enlarged partial cross sectional view of an alternative form of the storage target electrode assembly
  • FIGURE 4 is an enlarged partial cross sectional view of a further alternative of the storage target electrode assembly.
  • FIGURE 5 is an enlarged partial cross sectional view of a storage target electrode wherein features of the embodiments of FIGS. 3 and 4 are combined.
  • the camera tube comp-rises an envelope 10 of a suitable material such as glass having at one end thereof a light transmissive face plate 12. On the other surface of the face plate 12 is disposed a layer of photoemissive material 14.
  • the photocathode 14 may be of any suitable material well known in the art such as cesium antimonide.
  • an accelerating electrode 16 Positioned adjacent the photocathode 14 is an accelerating electrode 16 and axially spaced therefrom is an annular electrode 18 for supporting a target electrode 26.
  • the target electrode comprises a layer of amorphous aluminum oxide as will be more fully described hereinafter.
  • Between the target electrode 20 and the photocathode 14 is a very fine conductive mesh 22 closely spaced from the surface of the target 20.
  • the screen mesh 22 is conductively supported by the annular electrode 18.
  • An electron image is emitted from the photocathode 14 in accordance with the optional image imposed thereon.
  • a uniform focusing field focuses and accelerates electrons from the photocathode 14 to the target 20.
  • the electrons strike the target at a relatively high velocity causing a secondary emission greater than unity from the surface of the target 20.
  • the fine mesh screen 22 acts as a collector electrode of secondaries emitted from the target surface.
  • the emission of secondary electrons from the surface of the target 20 leaves areas of the target positively charged to an extent related to the density of electrons impingent thereon. In this manner, a positive electrostatic charge image is formed on the target 20.
  • the opposite side of the target 20 is scanned during tube operation by a low velocity electron beam emitted from an electron gun structure mounted at the opposite end of the tube envelope 10.
  • the tube is also provided with an alignment coil 32, an inner surface conductive coating 34, a decelerating electrode 36 and dcfiection coil 38 which are well known in the art.
  • the variout electrodes are provided at suitable potentials as is well known.
  • the deflection coil 38 causes the electron beam 30 to scan the surface of the target 20. Electrons from the beam 30 land on the target 20 to maintain the surface thereof at cathode potential. The remainder of the beam approaching the target at close to zero velocity is repelled by the target surface to form a return beam 31 which passes back along substantially the same path as the incident beam 30 and strikes a large dynode surface forming the first stage 70 of multiplier unit which comprises one or more additional dynodes 45, 46, 47, 48, 49 at successively higher positive potentials from which is derived the tube output signal.
  • FIG. 2 there is shown the storage target electrode assembly of the device of FIG. 1 including the annular electrode or support 18 which has suspended thereacross and solely supported therby the target electrode 20 of amorphous aluminum oxide.
  • the mesh 22 In front of the storage target electrode 20, facing the photocathode of the device is the mesh 22 which may be supported "by the same annular electrode 18, as shown, or may be independently supported if desired.
  • the amorphous aluminum oxide target electrode be made by beginning with a 99% pure aluminum foil formed by mechanical rolling or vacuum deposition and anodizing it in a suitable electrolyte to produce an aluminum oxide film of a desired thickness, as determined by bath concentration, time, temperature and current density of anodic formation, on both sides of the aluminum foil.
  • the anodized foils is then treated, for example with concentrated sodium hydroxide, so that the layer of aluminum oxide is removed from one surface.
  • all of the remaining aluminum is dissolved, for example by hydrochloric acid, leaving a free standing self-supporting film of amorphous aluminum oxide to be used as the target. It is then simply placed across the annular support member where it is held by molecular adhesion of it may be held by a support means which provides clamping.
  • the aluminum oxide layer may be either porous or non-porous and either form may be suitably used in the practice of the present invention.
  • nonporous layer is formed in electrolytes which do not attack or dissolve the aluminum oxide while a porous layor is formed in those which do.
  • a non-porous aluminum oxide target can be formed bv anodization in a 3% tartaric acid bath at an interelectrode voltage of from about 20 volts to about volts, a temperature of about 25 C. and for a time of about 20 minutes.
  • the initial layer is amorphous, as determined by X- ray diffraction, and it remains in the amorphous state throughout operation since it is never exposed to temperatures greater than about 375 C. and crystalline aluminum oxide is not formed until about 700 C.
  • the anodization process may use an electrolyte of a 5% chromic acid bath at about 10 volts, for a time of about 4.5 minutes, at a temperature of 25 C. This method results in a target having a thickness of from about 350 Angstroms to about 1000 Angstroms. Of course thicker targets may be formed but they are undesirable.
  • the porous aluminum oxide target 20 has a first portion 19 which is non-porous, presumably formed next to the aluminum foil, and a porous oxide portion 21 thereon.
  • the structure of the target has been determined by electron microscope analysis and the thickness of the target by X-ray attenuation measurements. The X-ray diffraction measurements indicate there is no crystalline structure.
  • the porous target used has approximately 800 pores or openings per square micron spaced approximately 360 angstroms apart. The pores have substantially round openings and are perpendicular to the surface of the oxide. They extend from one surface to the thin non-porous barrier layer 19 which has a thickness of about angstroms or less.
  • the porous target electrode Because the necessity of removing surface non-uniformities of the original aluminum foil is thereby avoided while in the preparation of a non-porous target it is necessary to have substantial uniformity of the starting foil.
  • the pores also aid in reducing lateral conductivity and in promoting transverse conductivity.
  • the presence of the pores makes the effective target thickness much thinner than the total oxide layer in that it substantially approaches the thickness of only the non-porous portion 19 since conductivity through the pores is much higher than through the aluminum oxide per se. It would not otherwise be possible to fabricate a target of any material which has such a small thickness (about 100 angstroms or less) and yet is mechanically stable and self-supporting.
  • the target 20 is mounted in the device so that the pores face the electron gun 50, however, no critical orientation in the direction of mounting has yet been observed.
  • Targets as shown in FIG. 2 have been successfully used and increased tube life has been obtained since the target exhibits electronic conduction which does not deteriorate with age. Also improved resolution and sensitivity have been obtained since the target is so thin and the time necessary for transverse conduction is very short.
  • the advantages of the target of FIG. 2 are especially evident at low light levels, such as about 10" foot candles and less. Low light level capability is, of course, desirable in any pickup device.
  • the target of FIG. 2 does exhibit a somewht undesirable property at high light levels in that a saturation effect occurs.
  • the nature of the effect is that a certain stickiness of the image is noted resulting from failure of the target from being discharged during a single scanning period.
  • the cause of the effect is presumably because the number of conductivity electrons in the aluminum oxide is not so large as to readily effect discharge.
  • this high light level saturation effect disappears upon a short period of exposure of the target to a white scene or with a period of about 12 hours of inoperation. Another way of avoiding the effect, and the preferred way, is described immediately following.
  • FIG. 3 there is shown a similar arrangement as that in FIG. 2 comprising the annular support member 18, the conductive mesh 22, the aluminum oxide layer 20 and in addition thereto a very thin layer 24 of conductive material on the gun side of the target.
  • a layer of conductive material which may suitably be and is preferably in indium, is desirable in order to avoid the previously described saturation effect which occurs in aluminum oxide targets under high light level conditions.
  • the indium also improves the transverse conductivity of the target resulting in improved overall sensitivity.
  • the indium layer is formed by evaporation and has a thickness of less than about 200 angstroms and may be as small as a monatomic layer.
  • the improvement caused by the indium layer cannot be readily explained by information presently known. It is believed that the improvement in transverse conductivity is due to the diffusion of indium into the aluminum oxide layer upon application of heat thereto, as occurs during baking out of the tube.
  • the use of indium is somewhat critical in that not all conductive materials produce the same effect but those which have the property of migrating into the aluminum oxide are believed to do so.
  • the indium is disposed on the gun side of the target and may also improve the beam landing characteristics of the scanning beam. Because of the thinness of the target and the indium layer no increase in lateral conductivity results by the use of the indium layer.
  • a storage target electrode assembly including the annular support member 18, the conductive mesh 22 and the aluminum oxide layer 20 having on the mesh side thereof a layer 26 which is an insulating material having a higher secondary electron emitting characteristic than the aluminum oxide.
  • examples of such materials are barium fluoride and potassium chloride.
  • the use of a better secondary electron emitting material is not at all necessary with the aluminum oxide target since aluminum oxide provides considerable improvement overconventional glass targets.
  • the layer 26 may provide somewhat higher gain with some resulting improvement in overall sensitivity.
  • this insulating layer should also be amorphous and may be formed by deposition in a gaseous atmosphere and may have a thickness of from about 100 angstroms to 1000 angstroms.
  • such a layer 26 may also be used in an embodiment which also includes an indium layer 24.
  • a pickup tube for a device of the image orthicon type compising a storage target electrode comprising a first layer of amorphous aluminum oxide and a second layer of an insulating m-aterial having a higher secondary electron emission characteristic than said amorphous aluminum oxide, means for impressing an electron image on the surface of said storage target electrode having said second layer thereon and means for scanning a uniform electron beam on the opposite surface of said storage target electrode.
  • a storage target electrode for a device of the image orthicon type comprising a first layer of amorphous aluminum oxide, a layer of indium disposed on one surface of said first layer and a layer of an amorphous insulating material having a higher secondary electron emission characteristic than said amorphous aluminum oxide on the opposite surface of said first layer.
  • a storage target electrode for a device of the image orthicon type comprising an insulating layer of amorphous aluminum oxide having a thickness of from 350 angstroms to about 1000 angstroms and having pores therein extending from one surface of said layer to within about 100 angstroms of the opposite surface of said layer, a layer of indium having a thickness of less than about 200 angstroms disposed on one surface of said insulating layer and a layer of an amorph-ous insulating material having a higher secondary electron emission characteristic than said amorphous aluminum oxide on the opposite surface thereof.
  • a storage target electrode comprising a layer of amorphous aluminum oxide, a layer of indium disposed on one surface and a layer of an amorphous insulating material having a higher secondary electron emission characteristic than said amorphous aluminum oxide on the other surface thereof, a peripheral support member providing the sole means of support for said storage target electrode, means including a photocathode for impressing a positive charge image on the surface of said storage target electrode having said secondary electron emissive material thereon and means including an electron gun forscanning a uniform electron beam on the surface of said storage target electrode having said indium thereon.

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  • Image-Pickup Tubes, Image-Amplification Tubes, And Storage Tubes (AREA)
  • Photoreceptors In Electrophotography (AREA)
US115551A 1961-06-07 1961-06-07 Electron discharge device with storage target electrode Expired - Lifetime US3371239A (en)

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Application Number Priority Date Filing Date Title
NL279364D NL279364A (enrdf_load_stackoverflow) 1961-06-07
US115551A US3371239A (en) 1961-06-07 1961-06-07 Electron discharge device with storage target electrode
GB14925/62A GB947959A (en) 1961-06-07 1962-04-17 Electron discharge device with storage target electrode

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US115551A US3371239A (en) 1961-06-07 1961-06-07 Electron discharge device with storage target electrode

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070096086A1 (en) * 2005-06-27 2007-05-03 Ying Wang Hole injection electrode

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2518434A (en) * 1945-07-12 1950-08-08 Emi Ltd Electron discharge device such as a television transmitting tube
US2558647A (en) * 1947-12-12 1951-06-26 Cinema Television Ltd Storage electrode type cathode-ray tube
US2731580A (en) * 1948-11-22 1956-01-17 Cinema Television Ltd Target electrodes for use in television pick-up tube or the like
US2922906A (en) * 1956-12-26 1960-01-26 Gen Electric Target electrode assembly
US2967344A (en) * 1958-02-14 1961-01-10 Rca Corp Semiconductor devices
US3030693A (en) * 1958-10-15 1962-04-24 Siemens Ag Method of producing transistor devices
US3067348A (en) * 1959-12-21 1962-12-04 Rca Corp Pickup tube target structure
US3109954A (en) * 1958-03-17 1963-11-05 Rca Corp Storage electrode having on the order of 106 metal conductors per square inch
US3179834A (en) * 1960-10-27 1965-04-20 Rca Corp Pickup tube target structure and method of manufacturing the same
US3202854A (en) * 1961-02-21 1965-08-24 Rca Corp Pickup tube target having an additive therein for reduced resistivity

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2518434A (en) * 1945-07-12 1950-08-08 Emi Ltd Electron discharge device such as a television transmitting tube
US2558647A (en) * 1947-12-12 1951-06-26 Cinema Television Ltd Storage electrode type cathode-ray tube
US2731580A (en) * 1948-11-22 1956-01-17 Cinema Television Ltd Target electrodes for use in television pick-up tube or the like
US2922906A (en) * 1956-12-26 1960-01-26 Gen Electric Target electrode assembly
US2967344A (en) * 1958-02-14 1961-01-10 Rca Corp Semiconductor devices
US3109954A (en) * 1958-03-17 1963-11-05 Rca Corp Storage electrode having on the order of 106 metal conductors per square inch
US3030693A (en) * 1958-10-15 1962-04-24 Siemens Ag Method of producing transistor devices
US3067348A (en) * 1959-12-21 1962-12-04 Rca Corp Pickup tube target structure
US3179834A (en) * 1960-10-27 1965-04-20 Rca Corp Pickup tube target structure and method of manufacturing the same
US3202854A (en) * 1961-02-21 1965-08-24 Rca Corp Pickup tube target having an additive therein for reduced resistivity

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070096086A1 (en) * 2005-06-27 2007-05-03 Ying Wang Hole injection electrode

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GB947959A (en) 1964-01-29
NL279364A (enrdf_load_stackoverflow)

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