A. Porch et al., THE COPLANAR RESONATOR TECHNIQUE FOR DETERMINING THE SURFACE IMPEDANCE OF YBA2CU3O7-DELTA THIN-FILMS, IEEE transactions on microwave theory and techniques, 43(2), 1995, pp. 306-314
We describe how coplanar microwave resonators fabricated from patterne
d thin films of YBa2Cu3O7-delta (YBCO) can be used to measure the ab-p
lane microwave surface impedance Z(s) = R(s) + jX(s) of the films, in
particular the absolute value and temperature dependence of the magnet
ic penetration depth lambda. The current distribution of the resonator
is calculated by modelling the resonator as a network of coupled tran
smission lines of rectangular cross-sections; this is then used to est
imate the ab-plane lambda(T) from the measurements of resonators of di
fferent geometries patterned onto the same him, We obtain values of la
mbda(0) in the range 150-220 nm, The unloaded quality factors of the l
inear resonators at 7.95 GHz are around 45000 at 15 K and around 6500
at 77 K, We estimate the corresponding values of the intrinsic R(s) at
7.95 GHz to be 23 mu Omega and 110 mu Omega at 15 K and 77 K, respect
ively, These values are comparable with those of other high quality un
patterned YBCO films reported in the literature, Z(s) for the best opt
imised films appears to be insensitive to the effects of patterning.