US3246200A - Cathode including photoconductive and tunneling layers - Google Patents

Cathode including photoconductive and tunneling layers Download PDF

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Publication number
US3246200A
US3246200A US219023A US21902362A US3246200A US 3246200 A US3246200 A US 3246200A US 219023 A US219023 A US 219023A US 21902362 A US21902362 A US 21902362A US 3246200 A US3246200 A US 3246200A
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Prior art keywords
layer
current
photoconductive
voltage
work function
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Expired - Lifetime
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US219023A
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English (en)
Inventor
Kanter Helmut
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CBS Corp
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Westinghouse Electric Corp
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Publication date
Priority to NL296890D priority Critical patent/NL296890A/xx
Application filed by Westinghouse Electric Corp filed Critical Westinghouse Electric Corp
Priority to US219023A priority patent/US3246200A/en
Priority to DEW35093A priority patent/DE1215270B/de
Priority to NL63296890A priority patent/NL140098B/nl
Priority to GB33315/63A priority patent/GB1015002A/en
Priority to JP4385063A priority patent/JPS3930128B1/ja
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/34—Photo-emissive cathodes
    • 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
    • H01J29/38—Photoelectric screens; Charge-storage screens not using charge storage, e.g. photo-emissive screen, extended cathode
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2201/00—Electrodes common to discharge tubes
    • H01J2201/34—Photoemissive electrodes
    • H01J2201/342—Cathodes
    • H01J2201/3421—Composition of the emitting surface
    • H01J2201/3425—Metals, metal alloys

Definitions

  • the present invention relates to electron discharge devices, and more particularly to electron discharge devices utilizing photoconductors.
  • the above device has a certain disadvantage that only photoconductors of a very low dark conductivity can be used so as to keep the dark emission current lo-w.
  • To have a highly light sensitive device it is necessary that the unilluminated or dark condition of the photoconductor be readily distinguished from its illuminated condition; To keep the darkcurrent of the photoconductor at a minimum, it may be necessary to cool the device.
  • such a device would not be effective as infrared sensitive photoconductors as such photoconductors generally'have characteristically high dark current. Therefore, it would be very advantageous to substantially eliminate any dark current flowing in the non-illuminated state of the photoconductor. This is because a greater sensitivity may be achieved by having substantially no electron emission in the dark state as compared to the high electron emission in the illuminated state; thus, resulting discharge device of high sensitivity.
  • the present invention accomplishes the above eliminating objectives by placing a layer of photoconductive material and a layer of insulating material having a tunneling characteristic between a transparent film and a low work function film. Dark currents are substantially eliminated due to'the insulating layer when the photoconductor is in its dark state; while a copious supply of electrons is permitted to pass through the structure into vacuum when the photoconductor is in its illuminated state.
  • FIGURE 1 is a schematic drawing embodying the teachings of the present invention.
  • FIGURE 2 is a plot of energy versus distance for the structure of FIGURE 1;
  • FIGURE 3 is a plot of the current versus voltage characteristic of the device of FIGURE 1.
  • an electron discharge device having an envelope T, which may be evacuated to form a vacuum v therein.
  • An anode electrode A is disposed at one end of the envelope T and has an external terminal a.
  • a grid electrode G Disposed within the envelope T is a grid electrode G, which'has an external terminal g.
  • the cathode structure is evaporated onto the wall W.
  • a thin, metal film M Onto the wall W is evaporated a thin, metal film M, which is electrically conducting but transmissive to light such as indium.
  • the metal film M may be of a thickness of approximately 200' Angstroms.
  • a layer PC of photoconductive material such as cadmium sulfide.
  • the photoconductive layer PC may be of a thickness from 1 to microns.
  • an insulating layer N is disposed adjacent to the photoconductive layer PC by, for example, evaporation.
  • the insulation layer N should be of a thickness of approximately 50 to 100 Angstroms.
  • the insulating layer N may, for example, be of aluminum oxide or magnesium oxide. The thickness of the insulating layer N is selected so that the layer will have a tunneling characteristic when a sufiicient potential is applied across the layer. That is, the current-voltage characteristics of the device should have a steep rise in current for a relatively small increase in voltage.
  • a metallic layer L is evaporated onto the insulating layer N.
  • the electrode L may comprise an alkali metal, such as potassium, or an earth alkali metal, such as barium, deposited onto the insulating layer N.
  • the layer L may comprise a metal layer that is oxidized at its surface to provide a low work function, such as barium oxidized to form barium oxide.
  • the layer L could be formed by alloying a metal layer with another material, for example, gold alloyed with barium.
  • Another method of providing the low work function layer L would be to deposit a monolayer of a low work function material on a metal surface such as a monolayer of cesium deposited on a layer of antimony.
  • a mesh in a matrix pattern on the insulating layer N.
  • the layer L may be of thickness of approximately Angstroms.
  • a low work function barrier is provided at the layer L to vacuum interface, so that, electrons may readily pass through the cathode structure into the vacuum v.
  • a source of direct potential V is provided with its positive terminal connected to the thin metallic layer L and with its negative terminal connected to the transparent metallic layer M.
  • the voltageVa will provide sufficient energy to accelerate a portion of the electrons through the low work function layer L.
  • the tunneling current will equal the dark current of the device.
  • the voltage that appears across the insulating layer N will cause some electrons to tunnel through the forbidden region of the insulating material N into the conduction band of the insulating material and then be accelerated by the potential appearing across the layer N.
  • the electrons in the conduction band of the photoconductive layer PC must have sufficient energy to tunnel through the forbidden region of the insulating layer N into the conduction band of the insulating layer N, where additional energy must be supplied, for a portion of the electrons to penetrate the metal layer L and be emitted into the vacuum v. If the Fermi level Efl of the metal layer L and the Fermi level at the vacuum interface are too high, most of the electrons will not have sufiicient energy to penetrate into the vacuum v.
  • the Fermi level Efl of the metal layer L is reduced by using a low work function material, such as potassium, it will require less energy for the electrons to be able to penetrate the low work function layer L into the vacuum v, abovethe substantially lowered work function of the vacuum-metal interface, as is shown in FIG. 2.
  • a copious supply of relatively low energy electrons Will be permitted to be emitted into the vacuum v with a substantial degree of stability.
  • the discharge device may operate in the well known manner with the electrons being controlled by the operation of the grid and anode electrodes.
  • the present device substantially eliminates dark current, its utilization in infrared detection devices would be highly advantageous.
  • An electron emissive device including, a first layer comprising a light transparent electrically conductive material, a second layer disposed adjacent said first layer and comprising a photoconductive material, a third layer disposed adjacent said second layer and comprising an insulating material having a field emission characteristic, the thickness of said third layer being selected to provide a current-voltage characteristic having a relatively large increase in current for a relatively small increase in voltage, and a fourth layer disposed contiguous said third layer comprising material having a low work function surface.
  • a photocathode electron emissive device including, a first layer comprising a light transparent electrically conductive material, a second layer disposed contiguous said first layer and comprising a photoconductive material, a third layer disposed adjacent said second layer and comprising an insulating material having a thickness of less than 150 Angstroms, the thickness of said .third layer being selected to provide a current-voltage characteristic having a relatively large increase in current for a relatively small increase in voltage, and a fourth layer disposed contiguous said third layer and comprising a low Work function alkali metal.
  • a photooathode electron emissive device including, a first layer comprisinga light transparent electrically conductive material, a second layerdisposed adjacent said first layer and comprising a photoconductive material, a third layer disposed adjacent said second layer and comprising an insulating material having a thickness of less than 100 Angstrorns, the thickness of said third layer being selected to provide a current-voltage characteristic having a relatively large increasein current for a relatively small increase in voltage, and a fourth layer disposed contiguous said third layer comprising a metallic material coated with a monolayer of an alkli metal to have a low work function.
  • a photocathode-electron emissive device including, a first layer comprising a light transparent electrically transparent conductive material, a second layer disposed adjacent said first layer and comprising a photoconductive material, a third layer disposed adjacent said second layer and comprising an insulating having a field effect characteristic, the thickness of said third layer being selected to provide a current-voltage characteristic having a relatively large increase in current for a relatively small increase in voltage, and a fourth layer disposed contiguous said third layer comprising a material oxidized at its surface to have a low work function, and excitation means to apply an electrical potential across said second and third layers.
  • An electron discharge device responsive to light including, an anode, a grid, and a cathode, said cathode comprising a first layer comprising a light transparent electrically conductive material, a second layer disposed adjacent said first layer and comprising a photoconductive material, a third layer disposed adjacent said second layer and comprising an insulating material having a field effect characteristic, the thickness of said third layer being selected to provide a current-voltage characteristic having a relatively large increase in current for a relatively small increase in voltage, and a fourth layer disposed contiguous said third layer comprising a material having a low work function.
  • An electron discharge device responsive to light including, an anode, a grid, and a cathode, said cathode comprising a first layer comprising a light transparent electrically conductive material, a second layer disposed adjacent said first layer and comprising .a photoconductive material, a third layer disposed adjacent said second layer comprising an insulating material having a thickness of less than 100 Angstroms, the thickness of said third layer being selected to provide a current-voltage characteristic having a relatively large increase in current for a relatively small increase in voltage, and a fourth layer disposed contiguous said third layer :and comprising a 10W UNITED STATES PATENTS 9/1958 McNaney 313-65 1/1961 Roberts et a1. 3l3-65 GEORGE N. WESTBY, Primary Examiner.
US219023A 1962-08-23 1962-08-23 Cathode including photoconductive and tunneling layers Expired - Lifetime US3246200A (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
NL296890D NL296890A (nl) 1962-08-23
US219023A US3246200A (en) 1962-08-23 1962-08-23 Cathode including photoconductive and tunneling layers
DEW35093A DE1215270B (de) 1962-08-23 1963-08-16 Photokathode
NL63296890A NL140098B (nl) 1962-08-23 1963-08-20 Fotogevoelige elektronen emitterende elektrode voor een elektronenbuis, en elektronenbuis voorzien van een dergelijke elektrode.
GB33315/63A GB1015002A (en) 1962-08-23 1963-08-22 Improvements in or relating to photosensitive electron emission device
JP4385063A JPS3930128B1 (nl) 1962-08-23 1963-08-22

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US219023A US3246200A (en) 1962-08-23 1962-08-23 Cathode including photoconductive and tunneling layers

Publications (1)

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US3246200A true US3246200A (en) 1966-04-12

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US (1) US3246200A (nl)
JP (1) JPS3930128B1 (nl)
DE (1) DE1215270B (nl)
GB (1) GB1015002A (nl)
NL (2) NL140098B (nl)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3321659A (en) * 1963-12-12 1967-05-23 Westinghouse Electric Corp Radiation sensitive electron emissive device
US3368077A (en) * 1963-03-08 1968-02-06 Electro Optical Systems Inc Infra-red image intensifier having a tunnel-emission cathode having a conductive mosaic
US3408521A (en) * 1965-11-22 1968-10-29 Stanford Research Inst Semiconductor-type photocathode for an infrared device
US3706920A (en) * 1971-03-18 1972-12-19 Us Army Tunnel electron emitter cathode
FR2215699A1 (nl) * 1973-01-30 1974-08-23 Commissariat Energie Atomique
US4002938A (en) * 1974-07-12 1977-01-11 Thomson-Csf X-ray or γ-ray image tube
US4521715A (en) * 1982-08-30 1985-06-04 Rca Corporation Photoemissive cathode formed on conductive strips
FR2573574A1 (fr) * 1984-11-16 1986-05-23 Messerschmitt Boelkow Blohm Photocathode pour le domaine infrarouge
US9877792B2 (en) 2005-01-24 2018-01-30 Intuitive Surgical Operations, Inc. Compact counter balanced arms
US9968405B2 (en) 2005-01-24 2018-05-15 Intuitive Surgical Operations, Inc. Modular manipulator support for robotic surgery

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2850657A (en) * 1956-08-20 1958-09-02 Gen Dynamics Corp Cathode ray tube current amplifying means
US2970219A (en) * 1955-08-18 1961-01-31 Westinghouse Electric Corp Use of thin film field emitters in luminographs and image intensifiers

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2970219A (en) * 1955-08-18 1961-01-31 Westinghouse Electric Corp Use of thin film field emitters in luminographs and image intensifiers
US2850657A (en) * 1956-08-20 1958-09-02 Gen Dynamics Corp Cathode ray tube current amplifying means

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3368077A (en) * 1963-03-08 1968-02-06 Electro Optical Systems Inc Infra-red image intensifier having a tunnel-emission cathode having a conductive mosaic
US3321659A (en) * 1963-12-12 1967-05-23 Westinghouse Electric Corp Radiation sensitive electron emissive device
US3408521A (en) * 1965-11-22 1968-10-29 Stanford Research Inst Semiconductor-type photocathode for an infrared device
US3706920A (en) * 1971-03-18 1972-12-19 Us Army Tunnel electron emitter cathode
FR2215699A1 (nl) * 1973-01-30 1974-08-23 Commissariat Energie Atomique
US4002938A (en) * 1974-07-12 1977-01-11 Thomson-Csf X-ray or γ-ray image tube
US4521715A (en) * 1982-08-30 1985-06-04 Rca Corporation Photoemissive cathode formed on conductive strips
FR2573574A1 (fr) * 1984-11-16 1986-05-23 Messerschmitt Boelkow Blohm Photocathode pour le domaine infrarouge
US9877792B2 (en) 2005-01-24 2018-01-30 Intuitive Surgical Operations, Inc. Compact counter balanced arms
US9968405B2 (en) 2005-01-24 2018-05-15 Intuitive Surgical Operations, Inc. Modular manipulator support for robotic surgery
US10786318B2 (en) 2005-01-24 2020-09-29 Intuitive Surgical Operations, Inc. Compact counter balanced arm
US10898281B2 (en) 2005-01-24 2021-01-26 Intuitive Surgical Operations, Inc. Modular manipulator support for robotic surgery

Also Published As

Publication number Publication date
GB1015002A (en) 1965-12-31
DE1215270B (de) 1966-04-28
NL296890A (nl)
JPS3930128B1 (nl) 1964-12-24
NL140098B (nl) 1973-10-15

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