US3526543A - Photoconductive film - Google Patents

Photoconductive film Download PDF

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US3526543A
US3526543A US612866A US3526543DA US3526543A US 3526543 A US3526543 A US 3526543A US 612866 A US612866 A US 612866A US 3526543D A US3526543D A US 3526543DA US 3526543 A US3526543 A US 3526543A
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film
layer
photoconductive
target
conductive transparent
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US612866A
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Akira Sasano
Mitsuru Oikawa
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Hitachi Ltd
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Hitachi Ltd
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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
    • H01J29/45—Charge-storage screens exhibiting internal electric effects caused by electromagnetic radiation, e.g. photoconductive screen, photodielectric screen, photovoltaic screen

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  • a photoconductive film to be used as a target of a vidicon and the like said film being formed by laminating a film layer of metal and a photoconductive layer upon a conductive transparent layer and characterized in that the photoelectric current is increased by reducing the dark current.
  • This invention relates to an improvement in a photoconductive film to be used as a target of a vidicon and the like, and it is an object of the invention to provide a sensitive photoconductive film wherein the photoelectric current is increased by reducing the dark current.
  • the drawing is a sectional diagram of photoconductive film embodying the present invention.
  • a conventional photoconductive film used as a target of a visual vidicon has been formed by laminating a conductive transparent layer and a photoconductive layer on a glass substrate which constitutes a vidicon tube.
  • the variation in the electrical conductivity of the photoconductive layer caused by the incident light is converted to the variation in the current of the radiating electron beam, and said variation is detected as an output current by the conductive transparent layer which works as a signal electrode.
  • a film which employs a NESA film (SnO trademark) as the conductive transparent layer 2 and Sb S film as the photoconductive layer has a transparent signal electrode and enjoys a high electrical conductivity. Therefore, this photoconductive film works rather well. However, since the dark current is large in this device, it is impossible to increase the photoelectric current.
  • the present invention is intended to obviate the deficiencies described above.
  • the present invention consists of a photoconductive film formed by laminating a film layer of metal and a photoconductive layer on a conductive transparent layer.
  • the drawing shows an example of the photoconductive film according to the invention, wherein reference numeral 1 designates a glass substrate, 2 a conductive transparent layer, 3 a film layer and 4 a photoconductive layer. Good results were obtained with this device when the conductive transparent layer 2, the film layer 3, the photoconductive layer 4 were made to be 300-600 A., -100 A. and 3-5 in thickness, respectively.
  • said film layer 3 changes the formof the energy bands of the photoconductive body by the contact thereof with the photoconductive layer and ac- 3,526,543 Patented Sept. 1, 1970 "ice cordingly, by suitably selecting the metal to be used for the film layer, the contactness with the photoconductive layer can be freely changed.
  • the electrical resistance of the photoconductive layer can be increased and thereby the characteristics of the photoconductive layer can be improved.
  • both the film layer 3 and the conductive transparent layer 2 work as a signal electrode and, in addition, the conductive transparent layer 2 has a high electrical conductivity. Therefore, the film layer 3 may not have a high electrical conductivity and so a thin evaporated film or the like can be used as said film layer. Thus, the reduction of the transparency against the incident light can be minimized.
  • the metals most used for the film layer are Ag, Al and Cu and they are particularly suitable when the photoconductive layer is formed of As Se AS28623, As SeS AS2S3, or Se.
  • EMBODIMENT 1 As the film layer, Ag is evaporated on a NESA film adhered to a glass substrate. Upon said film layer is evaporated As Se to form a photoconductive layer and thus a photoconductive target is provided.
  • this target is used with a target voltage of 60 v.
  • the dark current is 0.005 ,ua.
  • the photoelectric current is 0.2 u'a. with an illumination of 2.5 luX.
  • the dark current is 0.03 a and the photocurrent is 0.1 [1.21. with an illumination of 10 lux when said conventional target is used with a target voltage of 5 v.
  • the reduction of a dark current and the increase of a photocurrent are achieved.
  • EMBODIMENT 2 As the film layer, Al is evaporated on a NESA film adhered to a glass substrate. On said film layer is evaporated As Se to form a photoconductive layer and thus a photoconductive target is provided.
  • this target is used with a target voltage of 20 v., the dark current is 0.004 a. and the photoelectric current is 0.3 ,ua. with an illumination of 2.5 lux. Also in this case, comparison with the known target as described in Embodiment 1 shows that a good result is obtained with this novel target.
  • EMBODIMENT 3 As the film layer, Al is evaporated on a NESA film adhered to a glass substrate. On said film layer is evaporated As Se S to form a photoconductive layer and thus a photoconductive target is provided.
  • this target is used with a target voltage of 50 v.
  • the dark current is 0.002. ,ua. and the photocurrent is 0.1 p.21. with an illumination of 2.5 lux.
  • the dark current is 0.012 a. and the photoelectric current is 0.08 a. with an illumination of 10 lux.
  • the reduction of a dark current and the increase of a photocurrent are achieved.
  • EMBODIMENT 4 As the film layer, Al is evaporated on a NESA film adhered to a glass substrate. On said film layer is evaporated As Se S to form a photoconductive layer and thus a photoconductive target is provided.
  • this target is used with a target voltage of 50 v.
  • the dark current is 0.002 ,aa.
  • the photoelectric current is 0.05 a. with an illumination of 2.5 lux.
  • the dark current is 0.01 ,ua. and the photocurrent is 0.05 a. with an illumination of lux.
  • the reduction of a dark current and the increase of a photocurrent are achieved.
  • the photoconductive film according to the invention can reduce the dark current present at a conventional photoconductive target consisting of a conductive transparent layer and photoconductive layer. Accordingly, it has become possible to increase a target voltage and hence to increase the photoelectric current. Also, the increase with time of the dark current can be prevented.
  • the contactmess with the photoconductive layer can be adjusted by suitably selecting the film layer.
  • the invention can equally be applied to the case where As S Se or the like is used for the photoconductive layer.
  • the present invention makes it possible to fabricate a photoconductive film having good characteristics unattainable by a conventional film consisting of a conductive transparent layer and a. photoconductive layer, and hence it has become possible to provide a highly eflicient vidicon. Therefore, the present invention has a wide range of industrial applications.
  • a photoconductive film consisting essentially of a substrate, a conductive transparent layer of a material which is more transparent than a correspondingly conductive semitransparent metal layer formed on said substrate, a metal film selected from the group consisting of Al, Ag, and Cu films on said conductive transparent layer, and a photoconductive layer consisting of a material selected from the group consisting of As Se As Se S, As SeS and As S said metal film providing a layer of high electric resistance as a result of the contact thereof with said photoconductive layer.
  • a photoconductive film consisting essentially of a substrate, a conductive transparent layer comprising SnO formed on said substrate, a metal film selected from the group consisting of aluminum, silver and copper formed on said conductive transparent layer, and a photoconductive layer consisting of a material selected from the group consisting of As Se As Se S', As SeS and AS253, said metal film providing a layer of high electric resistance as a result of the contact thereof with said photoconductive layer.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Light Receiving Elements (AREA)

Description

Sept. 1, 1970 I AKIR sAsANQ ETAL 3,526,543
PHOTOCONDUCTIVE FILM Filed Jan. 51, 1967 INVENTORS fine/2n dives/v0 1/7811? Om'mun ATTORNEY United States Patent O 3,526,543 PHOTOCONDUCTIVE FILM Akira Sasano, Kokubunji-shi, and Mitsuru Oikawa, Tokyo, Japan, assignors to Hitachi, Ltd., Tokyo, Japan, a Japanese corporation Filed Jan. 31, 1967, Ser. No. 612,866 Claims priority, application Japan, Feb. 28, 1966, 41/ 11,678 Int. Cl. B44d 1/18 US. Cl. 117-217 7 Claims ABSTRACT OF THE DISCLOSURE A photoconductive film to be used as a target of a vidicon and the like, said film being formed by laminating a film layer of metal and a photoconductive layer upon a conductive transparent layer and characterized in that the photoelectric current is increased by reducing the dark current.
This invention relates to an improvement in a photoconductive film to be used as a target of a vidicon and the like, and it is an object of the invention to provide a sensitive photoconductive film wherein the photoelectric current is increased by reducing the dark current.
Other objects, features and advantages of the invention will become apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings, in which:
The drawing is a sectional diagram of photoconductive film embodying the present invention.
A conventional photoconductive film used as a target of a visual vidicon has been formed by laminating a conductive transparent layer and a photoconductive layer on a glass substrate which constitutes a vidicon tube. In this apparatus, the variation in the electrical conductivity of the photoconductive layer caused by the incident light is converted to the variation in the current of the radiating electron beam, and said variation is detected as an output current by the conductive transparent layer which works as a signal electrode. Among the photoconductive films of this kind, a film which employs a NESA film (SnO trademark) as the conductive transparent layer 2 and Sb S film as the photoconductive layer has a transparent signal electrode and enjoys a high electrical conductivity. Therefore, this photoconductive film works rather well. However, since the dark current is large in this device, it is impossible to increase the photoelectric current.
In order to improve said defect, an attempt has been made to employ a semitransparent evaporated metal layer as the signal electrode, but since the transverse electrical conductivity is required for the signal electrode, the layer must be thick. This, in turn, lowers the transparency of the layer and thus it has been difficult to put said layer to practical use.
The present invention is intended to obviate the deficiencies described above.
The present invention consists of a photoconductive film formed by laminating a film layer of metal and a photoconductive layer on a conductive transparent layer.
The drawing shows an example of the photoconductive film according to the invention, wherein reference numeral 1 designates a glass substrate, 2 a conductive transparent layer, 3 a film layer and 4 a photoconductive layer. Good results were obtained with this device when the conductive transparent layer 2, the film layer 3, the photoconductive layer 4 were made to be 300-600 A., -100 A. and 3-5 in thickness, respectively.
The existence of said film layer 3 changes the formof the energy bands of the photoconductive body by the contact thereof with the photoconductive layer and ac- 3,526,543 Patented Sept. 1, 1970 "ice cordingly, by suitably selecting the metal to be used for the film layer, the contactness with the photoconductive layer can be freely changed. Thus, the electrical resistance of the photoconductive layer can be increased and thereby the characteristics of the photoconductive layer can be improved.
In a photoconductive film formed in this way, both the film layer 3 and the conductive transparent layer 2 work as a signal electrode and, in addition, the conductive transparent layer 2 has a high electrical conductivity. Therefore, the film layer 3 may not have a high electrical conductivity and so a thin evaporated film or the like can be used as said film layer. Thus, the reduction of the transparency against the incident light can be minimized.
The metals most used for the film layer are Ag, Al and Cu and they are particularly suitable when the photoconductive layer is formed of As Se AS28623, As SeS AS2S3, or Se.
Now, the embodiments of the invention will be described.
EMBODIMENT 1 As the film layer, Ag is evaporated on a NESA film adhered to a glass substrate. Upon said film layer is evaporated As Se to form a photoconductive layer and thus a photoconductive target is provided. When this target is used with a target voltage of 60 v., the dark current is 0.005 ,ua. and the photoelectric current is 0.2 u'a. with an illumination of 2.5 luX. On the other hand, in a conventional target consisting of a NESA film and an evaporated As Se film, the dark current is 0.03 a and the photocurrent is 0.1 [1.21. with an illumination of 10 lux when said conventional target is used with a target voltage of 5 v. Thus, the reduction of a dark current and the increase of a photocurrent are achieved.
EMBODIMENT 2 As the film layer, Al is evaporated on a NESA film adhered to a glass substrate. On said film layer is evaporated As Se to form a photoconductive layer and thus a photoconductive target is provided. When this target is used with a target voltage of 20 v., the dark current is 0.004 a. and the photoelectric current is 0.3 ,ua. with an illumination of 2.5 lux. Also in this case, comparison with the known target as described in Embodiment 1 shows that a good result is obtained with this novel target.
EMBODIMENT 3 As the film layer, Al is evaporated on a NESA film adhered to a glass substrate. On said film layer is evaporated As Se S to form a photoconductive layer and thus a photoconductive target is provided. When this target is used with a target voltage of 50 v., the dark current is 0.002. ,ua. and the photocurrent is 0.1 p.21. with an illumination of 2.5 lux. On the other hand, when a conventional target consisting of a NESA film and an evaporated As Se S film is used with a target voltage of 10 v., the dark current is 0.012 a. and the photoelectric current is 0.08 a. with an illumination of 10 lux. Thus, evidently the reduction of a dark current and the increase of a photocurrent are achieved.
EMBODIMENT 4 As the film layer, Al is evaporated on a NESA film adhered to a glass substrate. On said film layer is evaporated As Se S to form a photoconductive layer and thus a photoconductive target is provided. When this target is used with a target voltage of 50 v., the dark current is 0.002 ,aa. and the photoelectric current is 0.05 a. with an illumination of 2.5 lux. On the other hand, when a conventional target consisting of a NESA film and an evaporated As Se S film is used with a target voltage of 30 v., the dark current is 0.01 ,ua. and the photocurrent is 0.05 a. with an illumination of lux. Thus, the reduction of a dark current and the increase of a photocurrent are achieved.
It is to be noted that the increase in dark current due to the passage of time, as seen in a conventional target consisting of a NESA film and an evaporated film of As Se As Se S, As SeS or the like, is not found in the photoconductive target according to Embodiments l to 4. This fact is also preferable for increasing the sensitivity of a photoconductive layer. Further, though the embodiments using Al or Ag for the film layer are described hereinabove, other kinds of metal like Cu can also be used to obtain the same effect.
As is fully described hereinabove, the photoconductive film according to the invention can reduce the dark current present at a conventional photoconductive target consisting of a conductive transparent layer and photoconductive layer. Accordingly, it has become possible to increase a target voltage and hence to increase the photoelectric current. Also, the increase with time of the dark current can be prevented.
Further, since both the conductive transparent layer and the film layer Work as a signal electrode in the photoconductive film according to the invention, the contactmess with the photoconductive layer can be adjusted by suitably selecting the film layer. The invention can equally be applied to the case where As S Se or the like is used for the photoconductive layer. Thus, the present invention makes it possible to fabricate a photoconductive film having good characteristics unattainable by a conventional film consisting of a conductive transparent layer and a. photoconductive layer, and hence it has become possible to provide a highly eflicient vidicon. Therefore, the present invention has a wide range of industrial applications.
What is claimed is:
1. A photoconductive film consisting essentially of a substrate, a conductive transparent layer of a material which is more transparent than a correspondingly conductive semitransparent metal layer formed on said substrate, a metal film selected from the group consisting of Al, Ag, and Cu films on said conductive transparent layer, and a photoconductive layer consisting of a material selected from the group consisting of As Se As Se S, As SeS and As S said metal film providing a layer of high electric resistance as a result of the contact thereof with said photoconductive layer.
2. A photoconductive film as defined in claim 1, wherein said metal film comprises Al and said photoconductive layer is As Se 3. A photoconductive film as defined in claim 1, wherein said metal film comprises Ag.
4. A photoconductive film as defined in claim 1, wherein said metal film comprises Cu.
5. A photoconductive film as defined in claim 1, wherein the thickness of (a) the conductive transparent layer is about 300 600 angstroms, (b) the metal film is about 10100 angstroms and (c) the photoconductive layer is about 3-5;.
6. A photoconductive film consisting essentially of a substrate, a conductive transparent layer comprising SnO formed on said substrate, a metal film selected from the group consisting of aluminum, silver and copper formed on said conductive transparent layer, and a photoconductive layer consisting of a material selected from the group consisting of As Se As Se S', As SeS and AS253, said metal film providing a layer of high electric resistance as a result of the contact thereof with said photoconductive layer.
7. A photoconductive film as defined in claim 6, Wherein the thickness of (a) the conductive transparent layer is about 300-600 angstroms, (b) the metal film is about 10-100 angstroms and (c) the photoconductive layer is about 3-5 References Cited UNITED STATES PATENTS 2,822,300 2/ 1958 Mayer et al 117-4201 2,833,675 5/1958 Weimer 117-201 2,844,543 7/1958 Fotland 117201 3,350,595 10/1967 Kramer 117217 ALFRED L. LEAVITT, Primary Examiner C. K. WEIFFENBACH, Assistant Examiner US. Cl. X.R. 117227; 313-94
US612866A 1966-02-28 1967-01-31 Photoconductive film Expired - Lifetime US3526543A (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2822300A (en) * 1954-03-29 1958-02-04 Horizons Inc Photoconductive material
US2833675A (en) * 1953-10-01 1958-05-06 Rca Corp Method of imparting red response to a photoconductive target for a pickup tube
US2844543A (en) * 1955-03-18 1958-07-22 Horizons Inc Transparent photoconductive composition
US3350595A (en) * 1965-11-15 1967-10-31 Rca Corp Low dark current photoconductive device

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2833675A (en) * 1953-10-01 1958-05-06 Rca Corp Method of imparting red response to a photoconductive target for a pickup tube
US2822300A (en) * 1954-03-29 1958-02-04 Horizons Inc Photoconductive material
US2844543A (en) * 1955-03-18 1958-07-22 Horizons Inc Transparent photoconductive composition
US3350595A (en) * 1965-11-15 1967-10-31 Rca Corp Low dark current photoconductive device

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