SUPERCONDUCTING THIN FILMS FOR HIGH FREQUENCY MICROWAVE APPLICATIONS

THE PREPARATION OF EPITAXIAL TLBACACUO FILMS HAS BEEN DEMONSTRATED ON ONLY A SMALL NUMBER OF SUBSTRATES (LAALO3 AND SRTIO3). AT PRESENT, LAALO3 IS THE ONLY SUBSTRATE THAT PRODUCES FILMS SUITABLE FOR MICROWAVE APPLICATIONS. HOWEVER, THERE ARE SERIOUS LIMITATIONS TO ITS WIDESCALE USE. THE TWO MOST APPARENT PROBLEMS ARE THE HIGH ELECTRIC CONSTANT (24.5) AND TWINNING. NEAR-TERM ALTERNATIVE SUBSTRATES WHICH CAN ADDRESS THESE PROBLEMS ARE MGO OR SAPPHIRE. THIS PROJECT OUTLINES A PROGRAM TO PREPARE HIGH QUALITY, EPITAXIAL TLBACACUO FILMS ON MGO AND SAPPHIRE SUBSTRATES. SAPPHIRE, WHICH IS INEXPENSIVE AND READILY AVAILABLE IN LARGE AREAS HOWEVER, STILL SUFFERS FROM AN ANISOTROPY IN THE DIELECTRIC CONSTANT. TWO MAJOR PROBLEMS EXIST FOR THE EPITAXIAL GROWTH OF TBCCO FILMS ON SAPPHIRE. FIRST, THE LATTICE MISMATCH BETWEEN THE TBCCO AND SAPPHIRE STRUCTURES IS LARGE; AND SECOND, INTERDIFFUSSION OF ALUMINUM FROM SAPPHIRE AT ELEVATED TEMPERATURES RESULTS IN SERIOUS DEGRADATION OF THE SUPERCONDUCTING PROPERTIES ALTHOUGH A LARGE LATTICE MISMATCH ALSO EXISTS FOR MGO, NO INTERDIFFUSSION HAS BEEN OBSERVED. THE SOLUTION TO BOTH PORBLEMS IS TO BUFFER THE SUBSTRATE USING AN INERT EPITAXIAL LAYER, WHICH HAS A CLOSE LATTICE MATCH TO THE TBCCO STRUCTURE. EPITAXIAL TL-BASED FILMS VIA AN ESTABLISHED POST DEPOSITION ANNEALING PROCESS ON TOP OF THIN, HIGH QUALITY CEO2 BUFFER LAYERS IN BEING GROWN.