| 摘要 |
884,943. Capacitors; semi - conductors. STANDARD TELEPHONES & CABLES Ltd. April 22, 1960 [April 24, 1959], No. 14152/59. Class 37. A circuit element, e.g. a capacitor, comprises a ceramic dielectric material incorporating alkaline earth metal titanates (e.g. titanates of barium, strontium, or calcium) admixed in powder form with a rare earth (e.g. lanthanum) titanate together with a binder and lubricant, pressed into a required shape fired in an oxidizing atmosphere to produce a ceramic body, reduced in an atmosphere of e.g. hydrogen to render the ceramic semi-conductive, formed with a silver electrode composition and fired, and thereafter re-oxidized at the melting-point of silver whereby a highly insulating oxidized ceramic layer is formed below the electrode. The rare earth has a perovskite structure similar to the alkaline earth titanate, and titanates of formula, 2 e.g. La-TiO 3 may be produced by firing a 3 stoichematric mixture of rare earth and titanium oxides. Alternatively, the oxides may be added to the alkaline earth oxide mix prior to first firing. The capacitor may be of disc form (Fig. 1), comprising a conductive ceramic dielectric 1 having opposed silver electrodes 3, 3a underlying which are oxidized ceramic dielectric layers of high resistivity; the interior ceramic material remaining of low resistivity. Chemical proportions are given and one silver electrode and its underlying oxidized ceramic layer may be replaced by an ohmic contact of indium covered by a silver layer for the unit to operate as a rectifier with high forward to reverse resistance ratio. Two such units may be assembled in parallel in opposed polarity to constitute a varistor. Moisture may be excluded by varnishing or encapsulation. |
