Why Crystal Engineering of Oxides?

Abstract

This issue of the MRS Bulletin, on the crystal engineering of high Tc and related oxide films, essentially responds to four questions. The first three are∎ Why has a high Tc superconducting tunnel junction not yet been fabricated?∎ Is it possible to fabricate a high Tc tunnel junction and if so, how?∎ How can thin-film technology contribute to the progress of high Tc superconductor research beyond the fabrication of electronic devices?Experimental efforts to answer these questions and solve associated problems must focus on atomic-scale control and characterization of surfaces and interfaces, which we designate here as crystal engineering of high Tc and related oxide films. Meanwhile, we have started to realize that the crystal engineering technology of oxides need not be limited to high Tc super-conductor research; it can be extended to electronic materials research, where it may have a somewhat more profound significance. In this light, I would like to pose the fourth question, one that may be especially relevant to this particular topic in the near future:∎ Will we find or develop an electronic material superior to silicon?Ever since the first success in superconducting La-Sr-Cu-O film deposition in early 1987, extensive studies have been conducted on the fabrication of high Tc oxide films and devices. Success has been achieved to some extent in relatively simple devices using plain superconducting films or grain boundary and step edge junctions. Nobody, however, has succeeded in fabricating an SIS (superconductor-insulator-superconductor) runnel junction that shows a clear hysteresis in I-V characteristics at a temperature above 77 K. Such a junction is presumably the key to the wide electronic device application of high Tc superconductors, for example, for switching devices expected to work much faster than conventional semiconductor transistors.