Patent GB-1202583-A (GB)
Title: Multiple copy electrostatic imaging apparatus
IPC: G03G15/05
Filed: 1967-09-28
Abstract: 1,202,583. Semi-conductor imaging device; cathode-ray tubes. RANK XEROX Ltd. 28 Sept., 1967 [29 Sept., 1966], No. 44122/67. Headings H1D and H1K. A charge pattern formed on the surface 12 of the device shown in Fig. 1 may be reproduced innumerable times on the heads of the conductive pins 7. The device comprises a layer divided'into alternate first and second areas, the first areas comprising a field-effect semiconductor material responsive to a light pattern impinging thereon or a charge pattern provided thereon, the second areas being non-responsive to the pattern, a matrix of conductive pins, individual pins being connected to the boundaries between the first and the second areas and means to establish an electrical potential between the first and the second areas. In one embodiment the surface 12 is uniformly electrostatically charged and exposed to an optical image. During the exposure step the pins are preferably grounded on a conductive plate and the switch 10 is left open to avoid excessive current flow. ZnO strips 15 dissipate the charge image-wise and any retained surface charge alters the bulk conductivity of the strips 15 thereby altering the conductivity of the circuit between adjacent conductive strips 19. This circuit comprises a fixed resistance portion (33) corresponding to part of an insulating strip 17 and a variable resistance portion (33, Fig. 4, not shown) corresponding to part of a field-effect material strip 15 with a conductive pin 7 between the two portions. When a potential is applied across this circuit the potential of the corresponding pin 7 will vary according to the conductivity value of the strip 15 and hence the pins vary overall image-wise. The electrostatic charge image reproduced at the ends 9 of the pins 7 is transferred to a dielectric sheet or paper by applying a potential to the sheet. Alternatively the image may be developed on the pins and the developed image transferred to an adhesive sheet. In another embodiment (Fig. 6, not shown) the input image is formed as a charge pattern on an insulating layer (61) of silicon monoxide or dioxide or calcium fluoride on the surface of strips 15, 17. The pattern is formed in a vacuum chamber by direct electron deposition or using a shaped electrode. The device shown in Fig. 1 has a glass plate 3 with a matrix of conducting pins 7 embedded therein, the pins protruding at both surfaces. A parallel series of gold lines 19 are evaporated on to the plate and overlaid with semi-conductor strips 15 and silica strips 17. The strips 15 may be of ZnO, PbO, CdO or CdS and may be laid down as a mixture of ZnO and dyestuffs in an insulating resin, by sputtering with Zn in an O 2  atmosphere or evaporating on Zn and subsequently oxidizing. The strips 17 are formed by vacuum deposition. In other alternative embodiments (a) a continuous layer (45) of semi-conductor is provided and portions (42) of it covered with opaque material (Fig. 2, not shown), for example black adhesive plastic or rubber tape or phenol-formaldehyde resin having dyes dispersed therein, or (b) the surface strips may be corrugated rather than flat (Fig. 7, not shown) thus giving greater resolution. A checker-board arrangement of responsive and non-responsive portions may be used. In addition to the semi-conductor being in itself a photo-conductor it may be bonded to a photoconductive material.