Patent GB-1327397-A (GB)
Title: Image storage system
IPC: H01J29/45
Filed: 1970-10-29
Abstract: 1327397 Cathode-ray storage tubes RCA CORPORATION 29 Oct 1970 [4 Nov 1969] 51391/70 Heading H1D An image storage system includes a storage tube which has a target electrode 11 comprising a substrate of a first conductivity type semiconductor material 35, e.g. N-type silicon, a 2-D array of regions of P-type material (36) diffused into one surface of the substrate and an insulating material (37), e.g. SiO 2  deposited between the regions of P-type material, means for storing a charge pattern in the P-N junctions corresponding to an incident image and means for producing a charge pattern on the insulator material corresponding to the pattern in the junctions. The tube comprises a cathode 15 producing an electron beam 16 which is deflected by components 18 and focused by components 17 through a collector grid on to the target 11 upon which the optical image is focused by lens 28. A layer of SiO 2  is deposited on the N-type Si substrate and is etched by a photoresist technique and P-type material is diffused into areas where SiO 2  is not present. Method of operation.-A potential of about 5V with respect to the cathode is applied by a 3-way switch 23 to the substrate 35 of the target and the scanning electron beam causes the diode array to be reverse-biased. Electron-hole pairs formed in substrate 35 by impinging light reduces the reverse bias on the diodes, the reduction being larger with increased light intensity. The electron beam current on scanning the diode array deposits charge on the P-regions in dependence on their reverse bias and the tube functions as a vidicon image pick-up device. During the erase cycle prior to image storage a potential of + 200 V is applied to substrate 35 for 1 frame interval during which the electron beam scans the target. The potential of + 200 V. is above the first cross-over point for SiO 2  when it becomes positively charged on electron impact due to secondary electron emission. The 200 V. is capacitatively coupled to the P-type regions 37 and the SiO 2  portions 36 such that on scanning by the electron beam the P-type regions remain at about +200 V. while secondary emission to collector 13 produces a voltage of about +215 V. in the SiO 2  regions. During the erase mode it is not necessary to block the incident light. During the storage cycle the target substrate potential is lowered to + 20 V. which is coupled to the scanned side of the target leaving the P-type regions and SiO 2  portions with potentials of about + 20 V. and + 35 V. respectively. The incident light of the image to be stored reduces the reverse bias in the diodes and the electron beam deposits most charge in the P-type regions where most light was incident. The insulator regions adjacent the lower potential P-type regions are lowered in potential by the beam because the beam deposits more electrons in the more positive insulator portions. Thus the insulator portions are negatively charged until the adjacent P regions draw the majority of the beam current such that the potential pattern on the diode array is transferred to the SiO 2  insulator portions. By interrupting the beam or removing the target potential the charge image stored may be retained. In the read mode the target is uniformly illuminated by source 29 and a target potential of +5V is applied. The 15 V. potential drop is coupled to the P-type regions and insulator portions such that on scanning the target most current will be conducted through the diode junctions adjacent the most positive insulator portions and thus the current drawn through load resistor 22 represents the stored image. The scanning beam does not erase the charge on the insulator regions in a single pass enabling the image to be extracted continuously and the scanning rate of the reading beam may be slower than that of the writing beam.