Ultra-thin SiO2 barriers have been developed for application to the integration of thin films of YBa2Cu3O7−x (YBCO) superconductors to silicon. The SiO2 barriers are formed by the selective oxidation of Si with 2–5 ML yttrium overlayers. The Y-promoted SiO2, barrier formed by this technique is highly stoichiometric and is an effective buffer which prevents YBCO/substrate interdiffusion. The technique has been applied to YBCO on Si and has resulted in a YBCO transition temperature of TC=78°K for a 70Å Y-promoted SiO2 barrier.
This technique has also been applied to the growth of multilayer YBCO films and fabrication of SIS junctions. For this purpose, a Y-promoted SiO2 barrier was prepared by the selective oxidation of a Y/Si/Y sandwich layer grown on thin fdm YBCO deposited on MgO by standard laser deposition. This resulted in a 20–40Å SiO2/Y2O3-, high quality barrier. Following barrier preparation, a second YBCO thin layer was deposited on the barrier yielding a YBa2Cu3O7−x-SiO2-YBa2Cu3O7−x (SIS) structure which was then patterned to yield 100μm diameter SIS junctions. Voltage-current measurements across the SIS junction have shown Joseph son junction behavior.