MOCVD Routes to Tl₂Ba₂Ca_n-1Cu_nO_4+2nSuperconductor and Dielectric Insulator Thin Films

Abstract
The evolution of HTS device technologies will benefit from the development of MOCVD (Metal-organic Chemical Vapor Deposition) routes to high quality HTS films as well as to those of insulators with low dielectric loss and close HTS lattice matches. Reviewed here are research efforts at precursor design focusing on Ba sources. A novel low pressure TGA technique is used to compare volatilities of MOCVD precursors and to quantify the role of gas phase diffusion in film growth. To form high quality Tl₂Ba₂Ca_n-1Cu_nO_4+2n (n = 2.3) films. BaCaCuO(F) films are first deposited by MOCVD using the liquid precursors Ba(hfa)₂[MATH]mep, Ca(hfa)₂[MATH]tet, and solid Cu(dpm)₂ (hfa = hexafluoroacetylacetonate, dpm = dipivaloylmethanate. mep = methylethylpentaglyme, tet = tetraglyme). The film growth psocess is shown to be mass transport-limited, and an interesting ligand exchange process is identified. The superconducting TBCCO phase is formed following an ex-situ anneal in the presence of Tl₂O at temperatures from 820-900°C. Transport properties of TBCCO-2223 films include a T_c as high as 115K. J_c of 2x10⁵ A/cm² (77K), and R_s of 0.35m[MATH] (5K, 10 GHz). The MOCVD growth of low loss, lattice-matched dielectric NdGaO₃, PrGaO₃, Sr₂AlTaO₆, and SrPrGaO₄ films is also discussed. High quality YBa₂Cu₃O_7-x films have been grown upon MOCVD-derived PrGaO₃ substrates.