| 摘要 |
877,026. Semi-conductor devices. NATIONAL LEAD CO. Aug. 6, 1959 [Aug. 11, 1958], No. 26962/59. Class 37. [Also in Group XXIII] A semi-conductor device, e.g. rectifier, thermistor or transistor, comprises a body of ntype semi-conductor material of titanium dioxide or barium or strontium titanate or a mixture thereof, and at least one metallic electrode applied to the body to form therewith an ohmic contact which retains a low and substantially constant resistance after repeated thermal cycling and over a wide voltage range. Preferably the electrode is prepared from a metal, e.g. Sn, Ti, which diffuses into the semi-conductor with the same or higher valence state than the cation of the semi-conductor which it displaces, or which goes interstitially in the crystal lattice of the semiconductor body. The embodiment shown in Fig. 2 comprises an n-type semi-conductor body 10 of mono-crystalline rutile or sintered barium or strontium titanate or a mixture thereof, including oxides of Sb, Ta, W, Nb, or of La or other rare earth metals, and ohmic electrodes 11, each constituted by a fired-on mixture of powdered metallic tin and a lowmelting glass frit composition. Leads 12 are secured to the electrodes 11 by soft soldering. In examples described, finely-divided barium titanate or barium strontium titanate, containing 0.2% lanthanum, is fired at 1350‹ C. for 20 hours to obtain body 10. Electrodes 11 are applied as a mixture of lead borate glass frit composition and finely-divided pure tin, in a ratio of 1 : 5 by weight, in a volatile organic medium, being subsequently air-dried at 125‹ C. for 1 hour, then fired at 450‹ C. for 30 minutes. Alternatively, the glass frit may comprise lead silicate or lead borosilicate, and the ratio of tin to glass frit should be in the range 3 : 1 to 10 : 1 by weight. In Fig. 4, electrodes 13 of titanium are applied to the body 10 by abrading the surfaces of the body and then pressing them against a titanium wheel which is turning at high speed. Silver paste, comprising powdered silver and glass in a liquid vehicle, is brushed on to the titanium electrodes to provide films 14, which are airdried and then fired at 425‹ C. for 10 minutes. The paste layers, which may alternatively contain platinum, are burnished before leads 15 are soft-soldered to them. The Specification mentions the use of Be, Zr, Nb, W, Ta as ohmic electrodes, and the non-ohmic character of indium-gallium and indium amalgam rubbed-on contacts. Specification 714,965 is referred to. |
