| Popis: |
During the last five years, the surface resistance Rs(10 GHz, 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 smaller than 200 micro-ohms, close to the theoretical value of 100 micro-ohms obtained by a straightforward calculation from BCS theory. This improvement of Rs is 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, ... All of these methods require obviously heating sample holders in order to obtain in situ crystal oriented layers. Such high quality films have allowed us to make demonstrator devices such as low loss narrow band filters (BW 104 for low phase noise oscillators), high Q inductances (Q > 104 for circuit matching of antennae in the MHz range). |
