GB1277568A - Light-transmissive window for an electron tube - Google Patents

Abstract

1277568 Sealing glass to quartz or silicon carbide; SiC layers PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 16 Dec 1970 [19 Dec 1969] 59705/70 Headings C1A and C1M [Also in Divisions C4 and H1] A conductive layer on the window of a cathode-ray display or pick-up tube comprises silicon carbide made conductive by donor or acceptor substances, this layer forming a substrate for luminescent or photo-conductive material. The window may be entirely of silicon carbide sealed to the envelope by an intermediate part of borosilicate glass, or it may be a layer of silicon carbide on a quartz plate sealed in known manner to the envelope with intermediate glass parts if necessary. In one example silicon carbide obtained by pyrolysis of a methyl-chlorosilane is sintered at 2200‹ C. for one hour in a graphite mould in argon containing less than 1 p.p.m. of nitrogen, and is subsequently heated at 2500‹ C. for 5 hours in a graphite crucible in helium containing less than 0À1 p.p.m. of nitrogen to grow crystals. One surface of a crystal is made conductive by diffusion of aluminium into it to give a resistivity of 0À5 ohm cm., and contacts are provided by melting strips of gold containing 5% tantalum on to the surface. In another example silicon carbide powder is heated at 2600‹ C. in an atmosphere of argon containing 0À01% nitrogen in a graphite crucible; a silicon carbide layer sublimes on to the lid which is at 2400‹ C., and after the carbon is burnt away in an oxygen atmosphere wafers are formed by grinding and sawing the layer. The layer has a resistivity of 1 ohm cm. due to the nitrogen doping and contacts are made by melting an alloy of nickel containing 10% molybdenum on to the wafer. In a further example a graphite plate is heated at 1550‹ C. in a flow of hydrogen containing 1% methylchlorosilane; nitrogen in the gas stream causes the resultant silicon carbide deposit to be conductive and have a resistivity of 200 ohm cm. In a final example a quartz disc is covered with a carbon suspension which is dried and heated to 110‹ C. in hydrogen for 8 hours to form a surface coating of silicon carbide; the disc is heated again in oxygen containing 1% nitrogen to burn away residual carbon and to make the surface conductive. If the tube is a vidicon, a layer of vapour-deposited lead monoxide is provided on the conductive surface, and for a display tube a layer of willemite is deposited on the surface.