Patent GB-753155-A (GB)
Title: A television pick-up tube
IPC: H01J29/45
Filed: 1954-03-16
Abstract: 753,155. Television pick-up tubes. RADIO CORPORATION OF AMERICA. March 16, 1954 [March 25, 1953; March 25, 1953; March 25, 1953], No. 7628/54. Class 39 (1). A television pick-up tube has a target comprising a transparent support 20, Fig. 2, a plurality of conducting signal strips 21 and photo-sensitive material 24, the signal strips being connected in sets, each set having double end connections and the sets being insulated from one another. The double end connections avoid unsatisfactory operation if the signal strips are of uneven thickness or have breaks. In one.form; Figs. 2, 3, the target comprises three sets of two conductive strips 21 at opposite ends of the structure and transversely extending transparent conductive strips 23 each contacting one strip 21 in each set but insulated from the other strips 21 by insulating filter strips 22. The filter strips are of the multi-layer interference type, i.e. having alternate layers of high and low refractive index. The red and blue filters may each comprise eleven layers alternately of ZnS and cryolite, each layer being a quarter wavelength of light thick, the wavelength being 4300 .U. for red filters and 5400 A.U. for blue filters. The green filters may comprise nine layers alternately of ZnSe and cryolite, the ZnSe layers having a thickness of three quarters of a wavelength of light at 6500 .U. and the cryolite a, thickness of a quarter wavelength at 6500 .U. A photoconductive coating 24 is formed on top. The target is formed by evaporating the materials in proper sequence through masks preferably in vacuum; strips 21, 23 may be of gold and photoconductive layer 24 of porous antimony sulphide. The filter strips 22 may extend only under layer 24, a separate insulating layer being provided at the cross-over points of 21, 23, Fig. 4 (not shown). It may be of ZnS or of superposed layers of ZnS and cryolite. The insulating layer is also provided, when the filter strips are omitted, i.e. in a monochrome arrangement. Members 22, 23 are parallel or perpendicular to the direction of scan and a low- or high-velocity scanning beam may be used. In a modification, Fig. 5, Fotoform glass plate 20 has conical holes 28 at opposite ends formed by exposing the sheet to U.V. light through a template, and etching away the exposed areas. Silver, copper or gold is evaporated through a mask into the holes to form plugs 29, while sheet 20 is rotated to ensure even formation of the plugs. Thus strips 23 are connected at each end to bus-bars 21 by plugs 29. If some of the bus-bars 21 are on the back and some on the front of the target the connections between the strips and bus-bars may be direct, or one direct and one via a plug 29, or both via plugs 29, Figs. 8, 9 (not shown). If the filter strips 22 are of conductive material they must be spaced apart, as shown, but when they are of insulating material they abut to avoid unfiltered light striking the photoconductive layer, Fig. 3. The green filter and signal strips are disposed between each of the red and blue strips and the bus-bars similarly arranged so as to facilitate operation with a high P.D. between red and blue signal strips, the green signal strips being at an intermediate potential. The strips 22, 23 may be of the same width. A D.C. potential is maintained across the photoconductive material by means of signal strips 23. To enable a satisfactory output to be taken from the signal strips a thin film may be formed by evaporation at the junctions of the signal strips and bus-bars; this gives a good capacitative coupling. Alternatively strips of conductive material formed by evaporation through a mask may be interposed at the junctions, Fig. 10 (not shown), the strips may be of Al, Ag or Au. In manufacture the bus-bars of gold and " interposed " strips of silver are successively evaporated through a mask and then the multilayer filter strips evaporated through a wire grill. Signal strips 23 are then formed by evaporation of gold through a wire grill in high vacuum. Undesired gold films between the strips 23 due to scattering are rendered harmless by baking for an hour at 135 C. The baking takes place before or after application of the photo-conductive layer by evaporation. Bad connections at the junctions between the signal strips and bus-bars due to the formation of a thin intermediate film of filter material or other insulating material during the evaporation process are avoided due to the " interposed " silver strips which are stated to react with the insulating material, e.g. ZnSe, to form a conductive film. Insulation where signal strips of one set cross over bus-bars of another set may be provided by insulating fingers formed by evaporation. The beam strikes the target normally due to a permeable electrode adjacent to the screen and to an external focusing coil, Fig. 1 (not shown). In some tubes the signal strips can be opaque. A prior art pick-up tube of generally similar construction, but without the double end connections, is referred to.