Keramischer Kondensator und Verfahren zu seiner Herstellung

摘要

1,047,439. Solid electrolytic capacitors. STANDARD TELEPHONES & CABLES LTD. Jan. 31, 1964, No. 4200/64. Heading H1M. [Also in Division C1] A barrier layer ceramic capacitor includes a porous body 1 which has been formed by sintering together substantially spherical grains of ceramic material of uniform size and composition Ba 1-x La2x/ 3 TiO 3 , where x lies between 0.01 and 0.15, the porosity of the body lying between 20 and 26%, the core of the body 2 having a resistivity of less than 102 ohm-cm. and the body having surface layer 3 of resistivity in excess of 1011 ohm-cm. A coating of a semi-conductor oxide, e.g. manganese dioxide or thallium oxide, which acts as a solid electrolytic material, intimately contacts the surface layer throughout the porous body; ohmic contacts 9 and 7 are provided to the semiconductor oxide and to the core and an opaque and moisture impervious encapsulation 10 is provided either by means of an epoxy resin coating or a hermetically sealed metal case. To prepare the ceramic core lanthanum and barium titanate are mixed in the required molecular proportions in the form of a powder of particle size 1 to 5 microns, a binder of camphor is added and then the mixture is rotated and agitated to produce spherical agglomerates. Agglomerates of uniform size are selected and fired at 1200-1260‹ C. this temperature being critically dependent on the ceramic composition being used, it being necessary to produce spherical grains which will not crush during compaction and yet will have sufficient surface activity to permit of sintering. After this presintering operation the grains are compacted together and sintered at 1350-1500‹ C. to produce a body having a porosity between 20 and 26%. The resulting porous body is fired in a reducing atmosphere of nitrogen and hydrogen so as to reduce its resistivity to about 10-2 ohm-cm. and then subjected to reoxidization in air or oxygen at a temperature and for a time which produces the desired capacitance and resistivity of the reoxidized layer. One end of the prepared core has its pores blocked off by impregnation with silicone rubber and then the rest of the body has a manganese dioxide layer applied by dipping several times in dilute manganese nitrate solution, which is dried after each dipping and pyrolitically decomposed to manganese dioxide. After this the blocked off end is ground to expose the ceramic core, and chromium and silver is deposited by evaporation on to this part of the core and also over a separate portion of the manganese dioxide layer, followed by a layer of pure silver. Alternatively aluminium, nickel, copper or gold may be applied by evaporation or sputtering techniques. The final encapsulation is in a moisture proof opaque case or covering to exclude light and moisture, which both effect the resistivity of the reoxidized ceramic layer.