ABSTRACT
This chapter concerns the underlying refractory Josephson junctions that have dominated the voltage standard field since perhaps 1990. Before going into the issues in the technical development of refractory tunnel junctions, the chapter describes that a large effort was made at the IBM Corporation to develop a computer technology using Josephson junctions based on Pb alloys, including Bi and Au. The chapter focuses on the tunnel junction technology needed for the refractory metals, of which the most important is Nb, having the highest transition temperature, 9.26 K, among the elements. Fabrication of non-hysteretic shunted Josephson junctions is of interest to exploit the rapid single flux quantum (RSFQ) computing circuitry as a successor to the latching circuitry investigated earlier at IBM. A general feature of the Josephson arrays is design such that the linear array of junctions also serves as a stripline for the microwave propagation to the junctions.
