| Summary: | 博士 === 國立交通大學 === 電子工程學系 === 85 === Oxides display a wide variety of physical properties that are
well used in electric and optoelectronic devices. In this study,
we have explored the growth and properties of YBa2Cu3O7 (YBCO),
yttria-stabilized zirconia (YSZ), cerium dioxide, and (Ba,Sr)
TiO3 films on various substrates. Deposition variables in
sputtering including oxygen partial pressure, total pressure,
substrate temperature, power excitation, magnet assembly inside
the gun, and relative angle of sputter gun to substrate normal
during the growth procedure are changed to explore their effect
on the properties of grown films. The elimination of plasma
bombardment in the magnetron sputtering is found to be the most
important for growing high quality YBCO films. We adopted off-
axis sputtering to overcome the plasma bombardment effects at
first. However, off-axis sputtering has the inherent
disadvantage of a low deposition rate and a compositional
nonstoichiometry with pressure. Thus, we modified this
sputtering by changing the magnet assembly inside the gun and
using dc power excitation. YBCO films grown with this modified
sputtering exhibit better superconductivity and better
compositional stoichiometry with deposition pressure for
substrates over 8cm long. The deposition rate of thin films
prepared by this sputtering is higher than that prepared by the
conventional off-axis sputtering. In the aspect of the growth of
dielectric oxide films, we found that plasma bombardment caused
crystalline deterioration and compositional nonstoichiometry of
the films like its effect on YBCO growth. However, thin films of
dielectric oxides with simple and stable structures may still
crystallize even under plasma bombardment and epitaxial cerium
dioxide films can be grown on MgO and sapphire substrates. The
YSZ and (Ba,Sr)TiO3 films grown without plasma bombardment
exhibit higher dielectric constant than those with plasma
bombardment. The leakage current of those oxide films can be
controlled to around 1uA/cm2. The conduction mechanism in cerium
dioxide and YSZ film on Si is dominated by the space-charge-
limited current. In addition, we have characterized the initial
growth of a-axis YBCO films and (Ba,Sr)TiO3 films on various
substrates by using atomic force microscopy. The lattice-match
between the film and the substrate is not found to be the
dominant factor responsible for the observed growth mechanism.
On the other hand, the essential nature of the bulk oxide can be
decisive for the initial growth of oxide films. We have also
explored the characteristics of a superconductor bolometer. The
effect of film''s surface morphology on the performance of the
bolometer is emphasized. The results show that copper oxide
particles on the film''s surface are helpful for the absorption
and response of YBCO bolometers. The fundamental exploration of
oxide thin films leads the author to believe that magnetron
sputtering is a feasible method to deposit dielectric oxide
films applicable in electronic devices.
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