Patent GB-1225854-A (GB)
IPC: H04N9/07
Filed: 1968-08-20
Abstract: 1,225,854. Cathode-ray storage tubes; photoconductive elements. WESTERN ELECTRIC CO. Inc. 20 Aug., 1968 [21 Aug., 1967], No. 39803/68. Headings H1D and H1K. In a television camera tube or a scan converter tube having a storage target comprising an array of diode rectifying barrier junctions which are periodically recharged to full reverse bias by a reading beam in the process of reading the information stored, interleaved comb structures 45, 46, Fig. 2, are provided over the diode array to permit, when suitably biased, a mutually exclusive read-out from different sets of diodes corresponding to the overlying holes 15 in the comb structures. In a two-colour camera tube, Fig. 1, where the target structure 11 includes on the gun side of an N- or P-type substrate 14, P- or N-type diode regions 15, respectively, an insulating layer 16 and a set of comb structures 45, 46, the light-receiving side is covered by an insulating layer 19 and a fieldeffect electrode 18 to inhibit electron-hole recombination and further by sets of colour filter, e.g. interference filter, strips 48 corresponding in number and position to the teeth of the comb structures 45, 46. Thus the stored image corresponding to light of only one particulat colour is read out when the respective comb structure is positively biased, the other comb structure being biased negatively and stopping the passage of electrons from the reading beam. The reading beam may be employed to supply electrons to the diode junctions or to remove electrons by secondary emission, depending on whether the junctions are NP or PN. The tube may be adapted for three or more colour-operation by by appropriate modification of the filter and comb structures. In a scan converter tube, Fig. 4 (not shown), interleaved comb structures (115, 116; 117, 118) are provided on both sides of the target (61) to prevent reading and writing, or charge storage in the same PN junction at the same time. In place of layers 18, 19 of Fig. 1, a heterojunction is provided on an e.g. N-type silicon substrate (64) by epitaxial deposition of an N-type germanium layer (68). The heterojunction between the germanium layer (68) and the substrate (64) provides trapping of electronproduced holes so that repetitive readouts by the reading fast-scan beam can be made without writing of new information in the diode junctions from which information is being read by the writing, slow-scan beam. The hetero-junction is unnecessary in a scan converter tube where the writing beam is fast scanning and the reading beam slow scanning. The diode junctions may be NP or PN and the reading beam may deposit electrons or remove electrons by secondary emission. More than two separate images may be stored and independently read out. In the manufacture of the target structure 11 of Fig. 1 a slice of monocrystalline N-type silicon, 0À5 to 15 mils thick is polished to form the substrate 14 and then oxidized and etched to form a multi-apertured silicon oxide insulating layer 16. Boron is then diffused through the layer 16 into the substrate to form P-type regions 15. To facilitate making a good ohmic contact 39 to the substrate 14 phosphorus is diffused into exposed areas of the substrate and a good ohmic contact 39 is made employing a vacuum evaporated metal, e.g. gold. A silicon dioxide layer 19 is formed on the light-receiving side of the substrate to a depth of 0À6 microns in the presence of steam at 950 C. or several hundred degrees lower. A thin gold layer 18 is then deposited over wet oxide layer 19 to a depth of 0À02 microns by vacuum deposition. Electrode 18 may be, however, a transparent layer of tin oxide.