NEW SUBSTRATES FOR HTSC MICROWAVE DEVICES

A new substrate material LSAT, a 30/70 mole % solid solution between L aAlO3 anti Sr2AlTaO6, has been prepared for the purposes of eliminatin g twinning, strain and non-isotropic microwave properties found in pur e LaAlO3 substrates, At 300 K and 30/70 mob! %, LSAT is cubic with lat tice parameter of 7.737 Angstrom, The dielectric properties of single crystal LSAT (30/70 mole %) substrates have been measured at 10 GHz an d 300 K and determined 19 be: dielectric constant epsilon(r)=22.5; and , loss tangent tan(delta) less than or equal to 10(-3), High quality c -axis oriented high critical temperature superconducting (HTSC), YBa2C u3O7-delta (YBCO), thin films ham been deposited on (001) single cryst al LSAT substrates, The crystal quality of these films is excellent as evidenced by the full width half maximum (FWHM) rocking curve widths of typically 300 are-seconds, Critical current densities (as measured using magnetization) are about 4 x 10(6) A/cm(2) at 10 K. Microwave fi lm properties include an onset transition temperature (T-c) higher tha n 91 K, transition width (Delta T-c) less than 5 K, surface resistance R-s lower than copper (30 m Omega) at 85 K and 35 GHz for a film of t hickness 2500 Angstrom.