Patent GB-1306761-A (GB)
Title: Direct viewing charge image storage tube
IPC: H01J29/10
Filed: 1971-06-09
Abstract: 1306761 Cathode ray storage tubes TEKTRONIX Inc 9 June 1971 [17 June 1970] 19751/71 Heading H1D A storage tube comprises a first storage target 10, Fig. 2, in the form of a mesh 28 coated with a highly porous insulating material 30 on which data can be recorded at high speed, a second storage target 10 comprising an electrode 40 and a second storage dielectric 38 capable of bi-stable storage, a high velocity (1 kV.) beam for writing, and at least one low velocity flooding beam. The storage dielectric 30 may be a porous metal oxide such as magnezium or aluminium oxide having less than 10% of the normal bulk density; in one example using magnesium oxide having a density of between 2 and 5% of its normal bulk density, the thickness of the layer is up to 30 microns and allows a writing speed of 300-600 million cm./sec. and a storage time of about one second. The second storage dielectric 12 may be a phosphor which provides a visible output and has a storage time of about one hour; an electrical output may be obtained by scanning with the writing beam. As shown, a mesh electrode 34 may be arranged in front of the storage targets and serves to repel positive ions which might damage the targets, and may also collect secondary electrons. There are four modes of operation, and the three electrodes 34, 28 and 40. are connected to appropriate potentials through respective fourposition switches. For bi-stable storage, electrode 34 is at 150v., electrode 28 at 200v., and electrode 40 at 100v. The writing beam passes through target 10 to impinge on target 12, and electrons from earthed flood guns drive the charged areas of the target up to the potential of electrode 40 and uncharged areas down to earth potential. Foe half-tone storage on target 10, electrode 34 is at 100v., electrode 28 at - 20v., and electrode 40 at 3kv. The writing gun then forms a positive-going charge image on target 10, and flood electrons passing through the target are modulated by the charge image and produce a corresponding display on the phosphor 38. In an image transfer mode of operation electrode 40 is connected to 100v. and electrode 28 is connected through an electronic switch first to - 20v. whilst data is stored on target 10 and secondly to 200v. when the flood electrons transfer the charge image to the second target 12. In the erase mode, both targets are connected to an erase pulse generator which firstly applies positive voltages to the targets to allow them to charge uniformly positive and then restores the targets to their quiescent voltage levels of - 20v. and 100-150v. respectively. In one modified bi-stable target construction (Fig. 3, not shown), the conductive electrode is a mesh, and the phosphor is deposited in the interstices of the mesh. In another modification (Fig. 4, not shown) the glass support plate is etched to provide a plurality of conical glass projections; the whole surface is covered with a conductive layer of tin oxide and with phosphor so that the tips of the projections extend through the phosphor to expose the conductive layer on the tips.