GB709945A - Improvements relating to mosaic target electrodes as are utilised in television pick-up tubes - Google Patents

Abstract

709,945. Cathode-ray tubes. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Aug. 8, 1952 [Aug. 8, 1951], No. 18647/51. Class 39(1) A mosaic target electrode, such as is utilized in television pick-up tubes, comprises a series of discrete conducting elements deposited on an insulating surface by evaporation of a metal through the interstices of a stencil, the area between the elements being provided with a further series of discrete conducting elements. In one method of making the mosaic a sheet of glass or mica provided with a conducting layer on one surface is mounted in a television tube, the tube is evacuated, and a layer of silver of a thickness of 20-40 per cent light absorption is deposited on the insulating surface by evaporation; the layer may then be baked at 300‹C in order to ensure aggregation but this is not necessary. The silver layer is oxidized by a high frequency discharge in oxygen, and bismuth or a bismuth-silver alloy is evaporated on to the silver layer through a stencil; the whole surface of the target is then sensitized with caesium. In an alternative method the bismuth or bismuth-silver alloy is deposited first through the stencil and a silver layer evaporated on top, the whole then being oxidized and photosensitized. When bismuth is used, the evaporation through the stencil may be performed first in a separate evacuated container. Pure silver may be used instead of bismuth or bismuth-silver alloy when the mosaic is required to be sensitive to infra-red radiation. This construction prevents the insulating parts between the conducting elements of a normal mosaic screen from being charged, and thus prevents what is known as "the photographic effect". Specification 498,134 is referred to.