Multilayer substrate including layers of an alumina and

Abstract

A multilayer glass-ceramic substrate comprises insulator layers of a composition consisting essentially of, when components are expressed as oxides in percent by weight, 40-60 percent of aluminum oxide, 1-40 percent of lead oxide, 1-30 percent of boron oxide, 2-40 percent of silicon dioxide, 0.01-25 percent of at least one oxide of chemical element(s) of Group II of the periodic table, and 0.01-10 percent of at least one oxide of Group IV element(s) except carbon, silicon, and lead. Each insulator layer may be only from 190 microns down to 10 microns thick. The substrate has a flexural strength of 2,100 kg/cm.sup.2 or more. Preferably, the Group II element(s) is magnesium, calcium, strontium, barium, and/or zinc. The Group IV element(s) is zirconium, titanium, germanium, and/or tin. When the percentages are 40-60 for aluminum oxide, 4.1-16.6 for lead oxide, 1.0-10.0 for boron oxide, 14.0-39.1 for silicon dioxide, 0.1-4.8 for magnesium oxide, 2.0-10.0 for calcium oxide, 0.05-3.0 for barium oxide, 0.01-3.0 for zirconium oxide, and 0.01-2.5 for titanium oxide, the substrate has a flexural strength of 3,000 kg/cm.sup.2 or more and an interlayer leakage current of 8 microamperes or less. Each insulator layer has a structure of a vitreous network of borosilicate-lead series glass with the interstices occupied by crystals of aluminum oxide and microcrystalline structures which are obtained by reaction of aluminum oxide and glass of the borosilicate lead series.