Low Temperature Preparation of y-bA-cU-0 Films by Omcvd
- PDF / 240,186 Bytes
- 4 Pages / 420.48 x 639 pts Page_size
- 83 Downloads / 180 Views
LOW TEMPERATURE
PREPARATION OF Y-Ba-Cu-O FILMS BY OMCVD
TAIJI TSURUOKA, RYODO KAWASAKI, HITOSHI ABE AND SUSUMU SHIBATA Research Laboratory, R&D Division, Oki Electric Industry Co., Ltd. 550-5, Higashiasakawa-cho, Hachioji, Tokyo 193, Japan ABSTRACT By using N2 0 for oxygen source, Y-Ba-Cu-O films prepared at 650"C the SrTiO3 substrates showed zero resistance at 79K. The deposition rate Y-Ba-Cu-O films on MgO(lO0) substrates by using N2 0 gas was nearly half that using 02 gas. X-ray diffraction patterns of Y-Ba-Cu-O films grown SrTiO3 (lO0) and MgO(lO0) substrates indicate c-axis orientation.
on of of on
INTRODUCTION Low temperature processing techniques are increasingly required in the manufacturing of superconducting devices, because low temperature processing minimize defect generation, defect propagation, and oxygen and impurity redistribution. However, until now, growth temperatures in excess of 800'C were required to obtain films with acceptable quality by OMCVD[13], while sputtering and MBE methods required only temperatures below 700"C to produce high quality films[4,51. Recently, we were successfully able to prepare Y-Ba-Cu-O superconducting films by OMCVD at a temperature of 650'C without need for postannealing. EXPERIMENTAL The samples were prepared in a horizontal cold-wall reactor previously described[6]. The substrates were placed on the susceptor and heated by radio frequency induction. The substrate temperature was measured with a alumel-chromel thermocouple which was set in the susceptor. The metallic composition ratios of Y, Ba and Cu were controlled by controlling bubbler temperature and carrier gas flow rate. Chelates of Ba, Y and Cu with a ligand of 2,2,6,6,-tetrametyl-3,5-heptanedione were used as source materials. In order to enhance the oxidation of the metalic species, N 0 gas was supplied in the reactor. Total gas pressure was maintained at 5060 Pa during deposition. After the deposition was complete, the films were then allowed to cool in 1 atm oxygen to 400'C at which temperature they were kept for 5 min prior to cooling to 150' C. The growth rate of Y-Ba-Cu-O films was measured by a microbalance. Substrates used in these experiments were SrTiO3 (lO0), MgO(lO0) and SI(l00). The electrical resistance of films was measured by the four-probe method and the crystal structure was examined by the X-ray diffraction (XRD) method. RESULTS AND DISCUSSION Fig. 1(a) shows the temperature dependence of normalized resistance for Y-Ba-Cu-O films grown on SrTi0 3 (100) substrates at growth temperatures of 600"C to 800'C using N2 0 gas as oxygen source. The film grown at a substrate temperature above 600"C showed metallic-like behavior as a function of temperature. Films grown at a substrate temperature of 650"C, 700"C, and 800"C showed zero resistance at 79K, 84K and 85 K, respectively. Films prepared at a substrate temperature of 600"C did not show zero resistance. The films grown using 02 gas, shown in Fig. 1(b), were not as good as those grown using N2 0 gas. When using 02 gas, a Mat. Res. Soc. Sy
Data Loading...
