Digital Superconducting Electronics: Where Does It Fit?

The discoveries since 1986 of materials which exhibit superconducting properties at temperatures considerably above those previously known or believed possible have led to a renewed interest in superconducting electronics. Some of these materials have been shown to have transition temperatures above the boiling point of liquid nitrogen (77K), some above 100k, rekindling the hope that room temperature superconductors can be found. As yet that dream has not been realized, but the temperatures already achieved will allow greatly simplified, more efficient cooling systems and the possibility of hybrid superconducting-semiconducting systems with all elements operating at the same temperature. In parallel with the search for new materials, work has progressed steadily, but with less fanfare, on developing the applications of the mature, low temperature superconducting materials. This work has yielded numerous clemonstrations of applications in which digital superconducting electronics can offer significant performance advantages, In some instances these applications will not receive wide acceptance until a manufacturable high transition temperature technology exists; in others the benefits are so great and cooling techniques are so advanced that they deserve serious consideration for implementation in low temperature technology. In addition many of the lessons learned in developing low temperature circuits and systems will be transferable to higher temperature material versions.