High-Temperature Superconductor Step-Edge Fabrication for the Implementation of RSFQ Circuits
Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005.
High-temperature superconductive (HTS) logic has become a large research field worldwide. The HTS advantages compared to the low-temperature circuits are the reduced cooling requirements, increased or comparable operation speeds and the "ease" of manufacturing. The potential of HTS logic circuits is vast and surpassed by very few other technologies. However, before these circuits can reach the market, suitable simulation packages and fabrication processes have to be designed. The simulation of HTS Rapid Single Flux Quantum (RSFQ) circuits are performed at temperatures between 30 and 77 Kelvin. The noise sources in Josephson junctions (JJ’s) are investigated and incorporated into these simulations. The results show that it is possible to operate these circuits in this temperature range. An objective of this thesis is the fabrication of HTS step-edge JJ’s. A process to fabricate these junctions was investigated and improved. This includes the etching of substrate steps with the use of the argon ion mill, deposition of the YBCO thin films with the Pulsed Laser Deposition (PLD) system and the etching of the final circuit by the use of dry or wet etching.