GB864120A - Improvements in or relating to semi-conductor devices - Google Patents

Abstract

864,120. Semi-conductor devices. SIEMENSSCHUCKERTWERKE A.G. April 25, 1957 [April 26, 1956], No. 13293/57. Class 37. In a semi-conductor device comprising a monocrystalline semi-conductor wafer with a first electrode and an associated PN junction extending over one face, and an electrode arrangement on the opposite face, the shortest distance of the edge of the first electrode from the outermost edge of said electrode arrangement being more than ten times larger than the wafer thickness. In one embodiment a PN junction device is made by assembling in superposed relationship a molybdenum or tungsten base-plate 5, a foil 4 of gold doped with 1% antimony, a wafer 2 of monocrystalline P-type silicon, and an aluminium foil 3, embedding the assembly in an inert material such as powdered graphite or magnesium and heating to fuse the parts together to form the device illustrated in the left-hand half of Fig. 1. On account of the geometry of the arrangement any short-circuit across the exposed edge of the PN junction (shown as a dotted line) is in series with a highresistance path to the edge of the ohmic electrode 3. This resistance may be further increased by reducing the thickness of the wafer beyond electrode 3 by grinding or corrosion and by making the wafer of high resistivity material. In a modification the gold electrode extends over the edges of the wafer to form a thin peripheral ring on the upper surface thereof. The device may be cooled by forming plate 5 with cooling fins or with ducts for fluid coolants, or by fixing the plate to a copper block of high heat capacity. A further embodiment consists of a transistor (Fig. 3) in which the junctionforming electrode 4 serves as collector. The emitter electrode 6 is in the form of an annulus which is disposed between and concentric with a circular electrode 3a and annular electrode 3b which are connected together to form the base electrode. Specification 864,121 is referred to.