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Publication numberUS3368077 A
Publication typeGrant
Publication dateFeb 6, 1968
Filing dateMar 8, 1963
Priority dateMar 8, 1963
Publication numberUS 3368077 A, US 3368077A, US-A-3368077, US3368077 A, US3368077A
InventorsBenjamin Kazan
Original AssigneeElectro Optical Systems Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Infra-red image intensifier having a tunnel-emission cathode having a conductive mosaic
US 3368077 A
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Description  (OCR text may contain errors)

Feb. 6, 1968 Y KAZAN 3,368,077

INFRA-RED IMAGE INTENSIFIER HAVING A TUNNEL-EMISSION CATHODE HAVING A CONDUGTIVE MOSAIC Filed March 8, 1963 EMHTED EMTTED \NCIDENT TUNNEL Egg L!6HT RADIATKON ELECTRONS 55 BENJAM/N KAZA/V INVENTOR.

United States Patent O 3,368,077 INFRA-RED IMAGE INTENSIFIER HAVING A TUNNEL-EMISSION CATHODE HAVING A CONDUCTIVE MOSAIC Benjamin Kazan, Los Angeles, Calif., assignor to Electro- Optical Systems, Inc., Pasadena, Calif. Filed Mar. 8, 1963, Ser. No. 263,861 3 Claims. (Cl. 250-213) The present invention relates in general to the image intensifier tube art and more particularly relates to a new and improved image intensifier tube based on what are known as cold emission techniques.

With respect to the conventional image intensifier, an image of visible light falling on the photoemissive surface causes the emission of a pattern of electrons. These are accelerated and imaged on a phosphor screen to provide an intensified image corresponding to the input image. However, to a large extent, the operation is limited by the qualities of the photoemissive screen. More specifically, because its maximum quantum yield (number of photoelectrons emitted per absorbed quantum) is usually con siderably less than thirty percent, the overall gain of the device is limited. Moreover, due to the physical nature of the photoemissive process, satisfactory operation in the far infra-red region, for example, at wavelengths greater than one micron has heretofore not been possible. In addition, because the screen is very thin, the absorption of X- ray energy is very small, thus making direct excitation with images of such radiation impractical.

The shortcomings of these earlier image intensifier tubes are overcome by means of the present invention which permits the design of a new type of image intensifier tube capable of much higher gains than the conventional tube. Furthermore, image intensifier tubes con structed in accordance with the present invention are also capable of operation with input images in the far infra-red and in the X-ray regions whereas, as was previously mentioned, the conventional intensifier tube is restricted to visible and near infra-red radiation. These improvements in the operation of image intensifier tubes are made possible by applying the concept of either tunnel emission or internal avalanching to them which, in turn, involves the use of a new combination of materials and elements.

It is, therefore, an object of the present invention to provide an image intensifier tube that is capable not only of operating in the visible light region but also in the far infra-red and X-ray regions as well.

It is another object of the present invention to provide a sensitive image intensifier tube that will operate effectively where the detection of low-level images of visible light is involved.

It is a further object of the present invention to employ either tunnel-emission or internal avalanching principles to expand the efiiciency and range of operation of image intensifier tubes.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing in which an embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only and is not intended as a definition of the limits of the invention.

The drawing itself schematically illustrates a new type of image intensifier tube based on the concept of the present invention.

Referring now to the drawing, the tube envelope is designated 10, the faceplate portion of it being designated 10a. On the inside surface of faceplate 10a is a very thin transparent conductive coating 11, such as stannous oxide, over which a photoconductive layer 12 is coated. The photoconductive layer is about 1 mil thick or less and while a number of different photoconductive materials are available for forming such a layer, cadmium sulphide is an example of one such material that may be employed. Photoconductive layer 12 is covered with an image retaining mosaic of conducting elements 13 which, in turn, are covered with a thin insulating layer 114, the insulating layer being very thin, in the order, for example, of Angstroms. The conducting elements of the mosaic may be made of gold. Finally, a very thin metallic conducting film 15, such as gold, is provided on the surface of the insulating layer.

At the other end of tube envelope 10, opposite faceplate Ilia, is the fiat base 1% of the tube which, on its inside surface is coated over with a cathode luminescent phosphor layer 16, the phosphor layer having an aluminized coating 17 over it as is shown in the figure.

As is customary with these types of tubes, the inside of the tube is evacuated and contains focusing electrodes 18a and 1812. Alternatively, magnetic focusing may be used. Since the construction and operation of focusing electrodes are very well known in the art, it is deemed sufficient to merely schematically represent them in the figure and to mention that they focus the electrons emitted from the faceplate portion of the tube into an image at the baseplate portion of the tube. Of course, as is well known, focusing electrodes are customarily connected to sources of potential which are not shown in the figure. However, two voltage sources, respectively designated 20 and 21, are shown in the figure, source 20 providing approximately twenty volts between its terminals and source 21 providing approximately 10 kilovolts between its terminals.

Before considering the operation of the present invention, it should first be stated that cold emission involves the phenomena by which electrons are emitted into a vacuum when a large electric field is placed across a thin insulating layer, the reason for this phenomena being due, for example, either to a tunneling action or internal avalanching processes. The tunneling of electrons through thin insulating films and the observance of electron emission into a vacuum has been reported by C. Mead in Journal of Applied Physics, volume 32, pages 646-652, published in 1961. On the other hand, the internal avalanching process is discussed in an article by Messrs. H. Jacobs, J. Freely and F. A. Brand, in Physical Review, volume 88, page 492, published in 1952.

Considering now the operation, the effect of incident radiation at a local point on photoconductor 12 is to lower its resistance so that more voltage appears across insulating layer 14 at the corresponding point. As was previously mentioned, the insulating layer is assumed to be very thin, for example, in the order of 100 Angstroms, so that, in accordance with the principles mentioned, electric current flows through the insulator. By also making outer conducting metal film 15 very thin, it can be expected that a substantial fraction of the electrons moving through the insulator will be emitted into the vacuum.

Assuming that only about one-tenth of the total number of electrons emerge into the vacuum space, the overall quantum yield of the combined photoconductive coldemission cathode can nevertheless be made much higher than a photoemissive surface since the quantum yield of numerous photoconductive materials is many orders of magnitude higher than that of a photoemitter. At the same time, the use of a photoconductor makes possible operation in the far infra-red region since photoconductors sensitive in this range of the spectrum are existent, such as lead oxide activated with sulphur. For other applications, em-

bodirnents of the present invention can be used for operation Where the detection of low-level images of visible light is involved. Also, since photoconductive layers of sufficient thickness and high sensitivity to X-rays are available, image intensifier tubes encompassing the present invention can be used to convert and to intensify low-level X-ray images.

Having thus described the invention, what is claimed is:

1. An image intensifier tube comprising: a transparent conductive layer coated on the inside surface of the tube faceplate; a photoconductive layer over said transparent conductive layer; a mosaic of separate and distinct conducting elements covering said photoconductive layer; an insulating layer deposited over said mosaic; a metallic film deposited on the surface of said insulating layer; a phosphor layer deposited on the inside surface of the tube baseplate; and an aiuminized coating over said phosphor layer.

2. An image intensifier tube comprising: a transparent conductive layer coated on the inside surface of the tube faceplate; a photoconductive layer deposited over said transparent conductive layer; elements forming a plurality of tunnel-emission diodes mounted over said photoconductive layer; a luminescent screen deposited on the inside surface of the tube baseplate; and means for focusing electrons tunneling into the vacuum of the tube onto the screen.

3. The image intensifier tube defined in claim 2 wherein said tunnel-emission diode includes a mosaic of thin metallic elements mounted over said photoconductive layer, an insulating layer over said mosaic, and a thin metallic film deposited on the surface of said insulating layer.

References Cited UNITED STATES PATENTS 2,824,986 2/1958 Rome 250-213 X 2,889,488 8/1959 Kalfaian 313-66 2,903,596 9/1959 Reed 250-213 2,929,935 3/1960 Lempert a- 250-213 X 2,944,155 7/1960 Moyer 250-213 3,056,073 9/1962 Mead 317-234 3,107,303 10/1963 BerkOWitZ 250-213 3,148,297 9/1964 Schneeberger et a1. 313-94 3,246,200 4/1966 Kanter 315-94 RALPH G. NILSON, Primary Examiner.

E. STRICKLAND, M. AMBRAMSON,

Assistant Examiners.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2824986 *Apr 19, 1954Feb 25, 1958Westinghouse Electric CorpIncreasing contrast of the image intensifier
US2889488 *May 5, 1955Jun 2, 1959CsfDelay lines for crossed field tubes
US2903596 *Jan 18, 1956Sep 8, 1959Rauland CorpImage transducers
US2929935 *Jul 23, 1954Mar 22, 1960Westinghouse Electric CorpImage amplifier
US2944155 *Jan 30, 1957Jul 5, 1960Horizons IncTelevision pickup tube
US3056073 *Feb 15, 1960Sep 25, 1962California Inst Res FoundSolid-state electron devices
US3107303 *Dec 28, 1960Oct 15, 1963Bell Telephone Labor IncPositive or negative high gain image amplifier
US3148297 *Nov 27, 1959Sep 8, 1964Westinghouse Electric CorpElectron device with storage capabilities
US3246200 *Aug 23, 1962Apr 12, 1966Westinghouse Electric CorpCathode including photoconductive and tunneling layers
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3443104 *Feb 17, 1966May 6, 1969Rauland CorpImage intensifier tube with shading compensation
US3447043 *Dec 29, 1966May 27, 1969IttTunnel cathode in matrix form with integral storage feature
US3693018 *Dec 27, 1966Sep 19, 1972Varian AssociatesX-ray image intensifier tubes having the photo-cathode formed directly on the pick-up screen
US3710125 *Apr 29, 1970Jan 9, 1973Univ NorthwesternSecondary emission enhancer for an x-ray image intensifier
US3947852 *Jul 25, 1974Mar 30, 1976The United States Of America As Represented By The Secretary Of The ArmyElectron image recorder with semiconductive image intensifier
US4069438 *Sep 18, 1975Jan 17, 1978General Electric CompanyPhotoemissive cathode and method of using comprising either cadmiumtelluride or cesium iodide
US4521715 *Aug 30, 1982Jun 4, 1985Rca CorporationPhotoemissive cathode formed on conductive strips
US4914296 *Apr 21, 1988Apr 3, 1990The Boeing CompanyInfrared converter
Classifications
U.S. Classification250/214.0VT, 313/530
International ClassificationH01J31/50, H01J31/08
Cooperative ClassificationH01J2231/50036, H01J2231/50026, H01J31/50, H01J2231/50063, H01J2231/5056
European ClassificationH01J31/50