YBCO CVD

For the CVD of YBCO, /3-diketonates with the general molecular formula shown below have been found to be the most suitable precursors [56,57]. 

The dependence of upon film composition for CVD-derived YBCO films using Y(dpm)3, Ba(dpm)2, and Cu(dpm)2 precursors under 1.25 Torr oxygen partial pressure with Ts = 750°C is shown in Figure 2-21 [146], Elemental determination by X-ray spectroscopy (EDS) was used to assay film stoichiometry. The dashed circle in Figure 2-21 corresponds to superconducting films, with the smaller solid circle indicating the range... 

Figure 2-21. Part of the YBCO phase diagram illustrating the dependence of critical temperature T on the average stoichiometry for samples of YBCO thin films grown by CVD on MgO at 800°C. (From Waffenschmidt et al. [146].)...

Figure 2-24. Intensity ratios of the (200) and (006) reflections of CVD grown YBCO films as a function of substrate temperature. (From Li et al. [152].)...

Figure 2-26. X-ray diffraction patterns of YBCO films deposited on SrTiOj (100) at 650 °C by thermal CVD a) P(02) = 0.36 Torr and b) PiOz) = 0.036 Torr. (From Yamane et al. [155].)...

YBCO films grown on MgO (100) using Y(dpm)3, Ba(dpm)2(phen)2, and Cu(dpm)2 precursors under 1 Torr nitrous oxide partial pressure and at a substrate temperature of only 500°C exhibited Tc = 80 K [163], Using identical precursors and 1 Torr nitrous oxide partial pressure, ultrathin YBCO films (9 nm) on SrTiOa (100) have been grown by CVD with Ts = 600 °C [164]. These ultrathin films exhibit T.- = 79 K. 

Metal halides have also been used as CVD precursors to YBCO films by Ottosson et al. at the University of Uppsala [I87. The sublimation temperatures of the YCI3, Bah. and CuCI precursors were 820°C, 950 C, and 340 C. respectively. These were used in combination with gaseous H2O/O2 at 20Torr in the deposition chamber to grow c-axis oriented YBCO films in situ on calcium stabilized zirconia substrates at 750-950°C. The YBCO films exhibited 7 . = 40 K [187]. 

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