GB1098616A - Improvements relating to capacitors and their manufacture - Google Patents

Abstract

1,098,616. Capacitors. INTERNATIONAL BUSINESS MACHINES CORPORATION. May 26, 1965 [May 27, 1964], No. 22347/65. Heading H1M. A body of dielectric material for a capacitor is manufactured by firing a finely divided mixture of two dielectric materials having different dielectric constant/temperature characteristics and a glassy binder present in such proportion that it forms at least 15% by volume of the eventual body. The binder keeps the granules of the two materials separate and prevents their interaction during fabrication so that the dielectric constant of the formed body is related to the aggregate of the dielectric constants of the individual materials and may be substantially independent of temperature over a selected range. The dielectric materials may be ferroelectric, e.g. compounds having the perovskite structure and each of the two materials, which have different Curie temperatures, may be a mixture of barium titanate and strontium titanate, or lead titanate or lead zirconate. The glass binder may be barium borosilicate, lead borosilicate or bismuth trioxide. A body having a dielectric constant substantially independent of temperature at 45‹ C. and above is formed by mixing equal quantities of two dielectric materials, the first comprising a sintered mixture of 85% barium titanate and 15% strontium titanate, the second a sintered mixture of 75% barium titanate and 25% strontium titanate, and the glass binder and firing. In the capacitor shown, a first electrode 12 of e.g. platinum, gold or silver, is deposited on ceramic base 11, and the above described mixture, dispersed in a squeegee medium applied by screening to form dielectric layer 13. After firing, the second electrode 14 is applied e.g. by silk screen ing.