SrTiO/sub 3/ buffer layers on MgO and Si substrates for high-T/sub c/ technology

Abstract

SrTiO/sub 3/ (STO) thin films have been sputtered on MgO [100] and on Si [100] substrates. On MgO the [100]-oriented STO buffer layers enabled the fabrication of high quality DyBa/sub 2/Cu/sub 3/O/sub 7-x/ (DBCO) films and ramp-type junctions (with I/sub c//spl times/R/sub n/ products in the order of 1 mV at 4 K) using exactly the same process as for single crystal STO substrates. On Si the fraction of [110]-oriented material in the STO films have been minimized to 2.5% by the optimization of the deposition conditions. Grain boundaries crossing the whole STO film and an amorphous layer between Si and STO could be observed. An Auger analysis revealed the presence of barium at the Si/STO interface that presumably diffused along the grain boundaries through STO to form barium silicate. By reducing both the DBCO deposition temperature and the STO thickness we could prevent this diffusion and improve the electrical properties. However rather poor crystalline quality and still non-satisfactory electrical characteristics were obtained (R/sub 300//R/sub 100//spl sim/1 and T/sub c/ (R=0) in the 40 60 K range). Overall these results suggest that, on MgO STO is a reliable buffer layer that enables the use of the technological processes handled on single crystal STO substrates. On Si the crystalline quality of the STO layers has to be improved in order to form an efficient diffusion barrier.