GB1386687A - Image pickup tube - Google Patents

Abstract

1386687 Image pick-up tubes; photo-conductive targets TOKYO SHIBAURA ELECTRIC CO Ltd 15 Sept 1972 42854/72 Headings H1D and H1K An image pick-up tube is provided with a signal pick-up electrode disposed on the peripheral portion of the target outside the scanned area, thereby reducing the capacitance of the target and its retention of residual images. The target shown in Fig. 3 comprises a photo-conductive layer 18 of cadmium selenide two microns thick deposited on the faceplate and covered with a layer 21 of cadmium selenite on which an insulating layer 20 of arsenic trisulphide is formed; the pick-up electrode 19 is an annular frame of tin oxide, aluminium, or tin and extends around the periphery of the target and round the edge of the layer 21. In modifications the layer 21 may be omitted (Fig. 2, not shown), and the electrode 19 may be flat and extend under the edge of layer 18 (Fig. 4, not shown). The layer 18 should have a resistivity between 10<2> and 10<10> ohm-cm. The resistive layer 20 may be of arsenic disulphide, zinc sulphide or selenide, germanium selenide, or antimony trisulphide. These targets are unsatisfactory when transmitting an image in the form of a black frame, and this disadvantage may be avoided by providing a conductive layer corresponding to the scanned area. The conductive layer may be provided on the inner surface of the faceplate (Figs. 6 and 9, not shown), and should be of complementary shape to electrode 19; where the latter is annular the conductive layer should be circular (Fig. 8, not shown), and when the conductive layer is rectangular the edges of electrode 19 should extend inwards to leave a rectangular opening (Fig. 7, not shown). The conductive layer may be covered with insulation (Fig. 13, not shown), or may be provided on the outer surface of the faceplate (Figs. 10 and 11, not shown). In another construction (Fig. 12, not shown), the inner surface of the faceplate is provided with a transparent conductive layer which forms the pick-up electrode, and this is covered with insulation over its central portion corresponding to the scanned area.