Advances in the application of high Tcsuperconductors to microwave devices for analog signal processing

During the last five years, the surface resistance Rs(10 GHs, 77 K) of YBCO thin films has decreased from a value of about 10 to 20 milliohms — i.e. the same as cooled pure copper or as bulk YBCO — down to values lower than 200 micro-ohms, close to the theoretical value of 100 micro-ohms obtained by a straightforward calculation from BCS theory. This improvement of Rsis due to a better quality of the material from random grain ceramics to quasi epitaxial films. These highly textured films can be obtained by many deposition methods : sputtering, laser ablation, co-evaporation, molecular beam epitaxy, MOCVD, using heating sample holders in order to obtain in situcrystal oriented layers. The value of the surface resistance is about one hundred times lower than that of usual metallizations, which can be used either to improve the specifications of some components by two order of magnitude such as high Q 3D resonators (Q > 106for low phase noise oscillators) and high Q inductances (Q > 104for circuit matching of antennae in the MHz range) or to reduce the size of voluminous devices such as filter banks for multiplexing or spectral analysis.