Ohmic contact system

TLDR: In this paper, a preselected barrier layer, such as nickel, which functions to prevent the penetration of subsequently applied process materials such as solder, which might adversely affect the underlying gold layer, is deposited on the gold layer.

Abstract: An ohmic contact system for a ceramic body having a predetermined relationship between various physical characteristics, such as temperature and resistance, for example, a wafer of semiconducting barium titanate having a positive temperature coefficient of resistance. A film of germanium is deposited on at least one surface of the wafer to protect the surface properties thereof. A layer of a preselected metal which adheres well to germanium and is readily bondable, such as gold, is deposited on the germanium film. A layer of a preselected barrier layer, such as nickel, which functions to prevent the penetration of subsequently applied process materials, such as solder, which might adversely affect the underlying gold layer, is deposited on the gold layer. An exterior layer of a readily solderable material which adheres well to the underlying nickel layer, such as gold, is deposited on the nickel layer. An external electrical conductor may then be readily soldered to the external gold layer to provide a good ohmic and mechanical contact to the wafer. An additional base layer of a preselected material, such as palladium, which adheres well to nickel and to gold may be deposited intermediate the nickel layer and the exterior gold layer to provide an improved base for the external gold layer.