US 3192135 A
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June 29, 1965 c. D. ROBBINS METHOD OF MAKING A CONDUCTING PLUG TARGET Filed Jan. 26, 1962 I N VE N TOR CHA RLES L2 ROBE/N5 Qidwn.
A ENT United States Patent 3,192,135 METHOD OF MAKING A CQNDUCTING PLUG TARGET Charles D. Robbins, Stamford, Conn assignor to Machlett Laboratories, Incorporated, Springdale,
Conn, a corporation of (Ionnecticut Filed Jan. 26, 1962, Ser. No. 169,020 3 Claims. (Cl. 204-11) This invention relates to conducting plug targets and, more specifically to a target structure having particular applicability to television pickup electron discharge devices and a method of making the target structure.
One type of television pickup device is known as an image orthicon. Broadly, an image orthicon may be defined as a camera tube in which an electrical image is produced by a photoemitting surface and focused on a separate target, which target is scanned on its .opposite side by a low velocity electron beam. In this instance, the front of the image orthicon tube has a transparent front plate, on the rear side of which an optical image is focused. On the inside or rear side of the front plate there is usually a photocathode that releases electrons in direct proportion to the brightness of the image projected thereon. These photoelectrons are accelerated and focused on the target so as to create a charge pattern on the target that is also in direct proportion to the brightness of the image.
In the prior art targets, the image charge appearing on the front of the target is capacitively coupled to the scanned side of the target. It, therefore, requires that the target material have a high lateral resistivity to prevent leakage of the image charge across the face and must also be thin enough to provide good coupling of the image charge to the scanning side of the target. In addition, the resolution of the system is also determined by the lateral resistivity of the target material which is of the order of 10 to 10 ohm-centimeters.
To avoid the need for very thin, fragile glass discs of the order of to wavelengths of light thickness, as presently used in the art, I propose to utilize a target that is made of insulating material having conducting plugs extending from one side of the target to the other to directly couple the signals on one side of the target to the scanning beam which is on the other side thereof. V I have found that certain thin metal films, which have been oxidized or fluoridized, are particularly tough and flexible so as to allow repeated handling during the process of manufacture and, in addition, make excellent dielectricfilms having lateral resistivities useful as target material for storage devices.
My invention may also be utilized in a camera tube wherein the signal storage target is read by a scanning beam of light. A light-scanned target has certain advantages in low light level detection compared to an image orthicon-type of detector utilizing a scanning beam of electrons. I 4 The improvement in low level light detection results from certain effects which can best be explained when compared with a typical image orthicon tube. An image orthicon is a camera tube which features a scanning beam of electrons which is causedto impinge on a target. Incremental areas of the target are charged in accordance with the signal information, or scene, previously placed thereon. The return beam, modified by the charged target, represents the signal current which may then be suitground noise due to thermal agitation in the target.
3,192,135 Patented June 29, 1965 It will then be seen that, while the signal current is determined by the number of signal photoelectrons or charge per target element per target frame time, the noise current is determined by at least four factors. The first of these noise factors is due to the shot and the partition noises generated in the tubes image section. The second noise factor is due to target Johnson noise; that is, back- The third noise factor is the shot noise caused by the fluctuation in the number of scanning beam electrons, while the fourth noise factor is the noise generated in the output multiplier by the reading beam which is, for the image orthicon, the difference between the scanning beam current and the signal current. Thus, if the scanning beam were eliminated, a substantial amount of noise would also be eliminated.
The outstanding characteristic of a light-scanned tube (L-ST), and that characteristic which distinguishes it from an image orthicon, resides in the fact that its reading function is performed by means of a moving light beam instead of the scanning electron beam. Like the image orthicon, the L-ST has an image section, a storage target, a scanning section and an output multiplier. However, in an L-ST, its reading function is usually performed by means of a moving light beam such as that produced by a flying spot scanner.
In the L-ST, the image section has a front photo-cathode on which the incident photons from a viewed scene may be projected. The photo-cathode emits photoelectrons in areas corresponding to the incident photons which are accelerated in the image section and then focused' onto the mosaic target, by any of many well-known focusing arrangements, to charge incremental areas in accordance with the viewed scene. A flying spot scanner, such as that formed by a bright kinescope displaying a TV-type raster, as well as an associated optical system, is used to focus the raster on the rear or the reading portion .of the target. As the light spot traverses across the photomosaic target, the electrons stored there are released as soon as the light of the flying spot hits them. These electrons are then acted on by an electron-focusing system which causes them to be directed into an electron multiplying device wherein the' number 'of dynodes determines the total multiplication and provides the amplified, modulated electrical signal output. 7
The L-ST circumvents some of the major disadvantages usually encountered in electron beam read-out devices in that it yields a signal proportional to the charge stored on each element of the mosaic target. Thus, at low signal levels, the theoretical noise contained in the output signal will not contain the shot noise associated with the electron scanning beam since no electron scanning beam is present to generate noise. A further noise reduction comes about in eliminating the noise due to that portion of the electron scanning beam which is not effective in producing a signal but, instead, produces a constant background noise. t
A target in a form suitable for use in an image orthicon consists of a sheet-like insulator mesh having plug conductors extending from one side of the target through the insulator tothe other side of the target.
In a form suitable for use in an L-ST, the target consists of a foraminous sheet-like insulator mesh. In this latter instance, conductive writing and reading meshes are placed on the respective front and rear surfaces of the insulator mesh. The holes or foramina of the insulator mesh contain metallic plugs which are insulated from each other and from the reading and writing meshes. Additionally, photoemitting material is placed on the reading side of each metallic plug and is insulated from the conductive reading mesh. The spacing of the plugs from the meshes is such that the plug-to-reading mesh distance is less than the plug-to-writing mesh distance so that the capacity between the plug and the meshes is due primarily to the plug-to-riaading mesh spacing.
At this point, it should be pointed 'out that certain items of the L-ST target construction require attention. The first of these items is the requirement that there be no light from the scanning light beam leaking through the target structure. This then eliminates the possibility of the scanning beam exciting the. front photo-cathode and, thereby, producing false signals. The other item which must be considered is that the reading mesh itself must not be photoemissive as this too would produce a form of noise which would raise the lowest limit of power level necessary for effective operation.
It is, therefore, a principle object of the present invention to provide a storage target that is opaque to light and is a good electrical insulator.
It is a further object of the instant invention to provide a target structure having the desired lateral resistivity for use in a television pickup electron discharge device.
It is a still further object of the instant invention to prov vide a target that is easily manufactured, yet readily and consistently reproduced.
The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself,-however, both as to its organization and method of operation, together with further objects and advantages thereof, may be best understood by reference to the following description taken in conjunction with the accompanying drawings in which:
FIG. 1 represents a partial sectional elevational view of my novel target during the initial stages of its manufacture, and
FIG. 2 represents a partial sectional elevational view of my novel target when completed.
It should be understood that similar elements in each figure are similarly numbered.
Referring now to FIG. 1 for the method of manufacturing my novel target, it will be seen that assembly 12 is formed by first providing a foraminous conductive material 16 in the form of a sheet and having the dimensions of the desired target. Sheet 16, which may consist of copper, or nickel, or any other suitable conductor, is placed in a vacuum and an aluminum layer 14 is evaporated onto one side of the mesh. Aluminum layer 14 is then anodized completely in any one of many known processes. One such process is suggested by V. Hauser and W. Kerler in the Review of Scientific Instruments, vol. 25, No. 9, May, 1958. Once this layer 14 has become anodized, it now exhibits excellent insulating properties.
To accomplish the remaining steps, a cushion material 20 is provided and may consist of a plastic-type organic material, such asnitrocellulose. A thin conductive layer 18, usually of the same material as the mesh 16, is then evaporated onto the layer 20. This combination of con ductive layer 18 and cushion layer 20 is necessary to provide an electrical contact that will very closely adhere'to any variations or imperfections on the surface of the underside of mesh 16.
Conductive layer 18, having layer 20 as a backing, is then placed in close contact with layer 16. Assembly 12 is then placed in an appropriate plating solution where layers 16 and 18 act as a cathode and suitable conducting plug material 22 is deposited in theforamina. While plug material 22 is preferably chromium, it has been found that silver, gold, platinum, or rhodium may also be used. The important consideration is that the plug material be such that it will not react with any reagent subsequently used for the removal of layers 16 and 18.
When my device is to be utilized as the target in an image orthicon, sufficient material 22 is deposited in the foramina so that upper surface 24. of the conducting plug material 22 is level with the upper surface 25 of the insulating sheet 14.
However, if my novel target is to be used, for example, in a light-scanned tube, then the surface 24 will be somewhat lower than the surface 25, as will be subsequently described.
Once the foramina are filled, assembly 12 is then placed in a furnace and appropriately fired in a vacuum to dispose of the organic layer 20. If nitrocellulose is used, it will be necessary to fire the assembly at about 400 C. to completely burn it off. The remaining mesh 16 and layer 18 may then be removed by any solution capable of dis solving the material of the mesh and the layer. If copper is used for mesh 16 and layer 18, then the appropriate solution may consist of hydrogenscyanide, or sulphuric acid, or nitric acid, or any other solution or reagent that will appropriately dissolve the mesh material 16 and conducting layer 18, yet not attack layer 14 or plug materia1 22..
As shown in FIG. 2, my novel target 26' consists of in; sulating layer 14, supporting the conducting plugs 22. When, for example, the target 26 is utilized in an image orthicon, surface 24 of plugs 22 is at the same level as surface 25 oflayer 14.
When my device is to be utilized as the target for a light-scanned tube, it then becomes necessary for surface 24 to be somewhat below the level of surface 25. For a more detailed description of the placement of conductive layers on surfaces 25 and 27, as well as the placement of the suitable photoemitting material on conducting plugs 22, attention is directed to my copending application filed October 23, 1961, Serial No. 146,899, entitled Storage Tube Target and Method of Making the Same.
While I have described what is presently considered a preferred embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be'made therein without departing from the inventive concept contained therein, and it is, there- 'fore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.
What is claimed is:
1. The method of making a conducting plug target comprising coating one side of a conductive metal mesh with an aluminum film, anodizing said film to render it dielectric, mounting a continuous metal backing on the opposite surface of the mesh, electrodepositing conductive metal into the openings in the film and mesh, and thereafter removing the metal backing and mesh.
2.. The method of making a conducting plug target comprising coating one side of a conductive metal mesh with an aluminum film, anodizing said film to render it dielectric, mounting a continuous metal layer on one surface of a layer of cushion material, mounting the continuous metal layer upon the uncoated side of the mesh so that the metal layer will conform closely to the contours of the mesh, electrodepositing conductive metal into the openings in the film and mesh, and thereafter removing the metal layer, cushion material and mesh.
3. The method of makinga conducting plug target-comprising coating one side of a conductive nonanodizable metal mesh with an anodizable aluminum film, anodizing said film to render it dielectric, mounting a continuous metal layer on one surface of a layer of organic cushion material, mounting the continuous metal layer upon the uncoated side of the mesh so that the metal layer will conform closely to the contours of the mesh, electrodepositing conductive metal plugs into the openings in the film and mesh, firing the assembly in a vacuum at a temperature suflicient to remove the organic cushion material, and dissolving the metal layer and mesh in a solution which readily dissolves the metal layer and mesh without attacking the anodized film and the conductive plug material. 4
References Cited by the Examiner 6 Van de Pol 20411 Kuhlman 20411 Law 204-15 Teal 204-3 Teal 204--15 Morris 20415 JOHN H. MACK, Primary Examiner.
JOSEPH REBOLD, WINSTON A. DOUGLAS,