Patent GB-1222445-A (GB)
Title: Improvements in or relating to electron beam light-electric translating arrangements
Inventor: CROWELL MERTON HOWARD
IPC: H01L27/00
Filed: 1968-05-24
Abstract: 1,222,445. Image pick-up tubes; photoconductive targets. WESTERN ELECTRIC CO. Inc. 24 May, 1968 [25 May, 1967], No. 24996/68. Headings HID and H1K. In an image pick-up tube in which the target structure comprises an array of rectifying barrier diode-junction regions 21 on a P- or N- type semi-conductor substrate 20 with an insulating layer 22 covering the intermediate regions, a semi-insulating layer 24 is provided over the insulating layer 22 and in contact with the rectifying barrier regions 21 to distribute charge from the insulating layer to the barrier regions. Layer 22 has a thickness of 0À01-0À6 micron and layer 24 a thickness of 0À8-2À5 microns, a resistivity 3 x 10<SP>9</SP>-3 x 10<SP>10</SP> ohm-cm., e.g. 1 x 10<SP>10</SP> ohm-cm., and a discharge time constant of 0À1-1 second. Layer 24 may comprise vacuum deposited silicon monoxide, antimony trisulphide, cadmium or zinc sulphide, arsenic trisulphide, antimony or arsenic triselenide, nickel or titanium oxide or mixtures thereof, or mixtures of high- and low-conductivity materials, e.g. silicon and silicon nitride. Silicon dioxide highly doped with gold may be used, e.g. by sputtering silicon dioxide and gold simultaneously. Layer 24 need not be connected to the battery 23. A transparent silicon dioxide insulating layer 28 is deposited on the light-receiving surface of the substrate 20 and covered with a transparent conductor electrode 27, e.g. a 200 Angstrom thick layer of evaporated gold. In a modification a thin semi-insulating silicon monoxide layer (34, Fig. 3) is formed over the insulating silicon dioxide layer (32). The silicon monoxide layer is formed at the interface between the silicon dioxide layer and a covering silicon layer which is masked and etched down to remove the silicon except -over the barrier regions (31) where silicon islands (35) are left. The silicon islands may be extended outward over the silicon dioxide layer to increase the effective capacitance of the diode junctions. Methods of manufacture.-the structure of Fig. 2 may be made by oxidizing a polished subsubstrate of N-type silicon to form the layer of silicon dioxide 22. An array of apertures of 8 microns diameter and 20 microns centre-tocentre spacing are then etched in the silicon dioxide layer and boron diffused into the exposed areas of the substrate at 1140‹ C. To facilitate the making of a good ohmic contact 25, phosphorus is diffused in at 925‹ C. The silicon dioxide layer 28 is formed in the presence of steam at 950‹ C. and the gold layer 27 by vacuum deposition. The silicon monoxide layer 24 is vacuum deposited at 100‹ C., e.g. to a thickness of 1 micron. The modified structure (Fig. 3) may be made by methods involving the deposition of a silicon layer either before (Fig. 5), or after (Fig. 4) the diffusion of boron into the substrate to form the junction regions. The silicon may be evaporated on to the silicon dioxide layer by sputtering through a mixed nitrogen-argon gas plasma to form a siliconsilicon nitride semi-insulating layer.