Preparation of YBa₂Cu₃O₇ films by low pressure MOCVD using liquid solution sources

Abstract
A hybrid low pressure MOCVD process is described for reproducible preparation of superconducting thin films of YBa₂Cu₃O₇. The process uses a single solution source of Y, Ba, and Cu [MATH]-diketonates dissolved in suitable organic solvents. This liquid precursor is atomized using an ultrasonic aerosol generator and transported as small droplets ( ≈ l μm) into a CVD reactor where solvent and precursor are first evaporated before deposition takes place at low pressure on heated substrates in a cold wall geometry. This process allows, with stable evaporation rates for all three precursors, to grow in-situ superconducting films with constant composition from film to film. Thin and thick films with high critical temperatures and critical currents have been obtained (Tc>80K, Jc>l0⁴ A/cm² at 77K in self field) which are highly c-axis oriented. Experimental details of this new process are described and the effects of different process parameters are studied in order to improve the quality of the deposited layers.