High quality YBa2Cu3O7-delta (YBCO) films have been epitaxially grown
on low dielectric constant, low loss tangent (001)MgF2 substrates usin
g a double buffer layer scheme. The YBCO films are (001) oriented, exh
ibit T(c)'s of 88-89 K with transition widths less-than-or-equal-to 0.
5 K and J(c)'s of 4 x 10(6) A/cm2 at 77 K in zero field. Dielectric re
sonator experiments indicate unloaded Q values in excess of 30 000 at
77 K and 24 GHz in the unpatterned films. Films patterned into meander
line resonators and operating at 10 GHz, 79 K, exhibit surface resista
nce (R(s))<1 OMEGA suggesting near-future realization of low loss supe
rconducting components in the millimeter-wave region.