Properties of thin and ultra-thin YBCO films grown by a Co-evaporation technique

An original system has been set up to grow epitaxially high quality YBCO thin films in a very reproducible way. This in-situ quasi-MBE technique allows us to prepare films whose cationic composition is kept close to 1:2:3 within 2%, and which therefore display very good crystallographic properties together with a very Bat surface, Moreover, shadow masks are used to grow up to 4 films of different thicknesses in a single run and to make in-sim contact pads and caps. As a result, we routinely obtain YBCO c-axis films with a Tc(R=0) over 89.5 K (for 50 nm thick films on SrTiO3 and MgO) and a resistivity at RT in the 250 mu Omega cm range. The reproducibility is excellent, and the spread in resistivities for 2 films in a single run is less than 2%, Ultra-thin films (5 nm to 50 nm thick) whose electrical properties can hence be closely studied have been grown successfully in a single run.