Low temperature growth, characterization and applications of rf-sputtered SrTiO3 and BaSrTiO3 thin films
Author
Bayrak, Türkan
Advisor
Bıyıklı, Necmi
Date
2016-03Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
Among the several perovskite ferroelectric oxides, SrTiO3 (STO) and BaSrTiO3
(BST) thin lms have attracted signi cant attention due to their potential applications
in oxide-based electronics. However, reliability and performance of STO
and BST thin lms depend usually on the precise knowledge of microstructure,
as well as optical and electrical properties.
STO and BST thin lms were deposited at room-temperature on Si (100), UVgrade
fused silica, quartz substrates and TiO2 nano bers by radio frequency (RF)
magnetron sputtering using di erent plasma power, oxygen mixing ratios (OMRs)
and deposition pressure levels. As-deposited thin lms showed amorphous-like
nanocrystalline microstructure almost independent of the deposition conditions.
In
uence of post-deposition annealing at various temperatures of RF sputtered
STO thin lms were also investigated. All lms were found to be highly transparent
(>75%) in the visible region, and both STO and BST lms exhibited well
de ned main absorption edges: the calculated indirect and direct band gaps for
STO lms were in the range of 2.32 to 4.55 eV. The refractive index of the STO
lms increased with OMR and post-deposition annealing for 3 mTorr deposition
for STO, BST and STO annealing study. However, there is no correlation for
5 mTorr deposition. The refractive indices of BST lms were in the range of
1.90-2.07 at 550 nm depending on their deposition conditions. The optical band
gap of the BST lms were calculated the ranging in 3.60 to 4.30 eV.
Electrical dielectric constant values of the STO thin lms were extracted from
frequency or voltage dependent capacitance measurements using micro-fabricated
Ag/STO/p-Si device structures. High dielectric constant values reaching up to 100 were obtained. All STO samples exhibited more than 2.5 C/cm2 charge storage
capacity and low dielectric loss (less than 0.07 at 100 kHz). Post-deposition
annealing at 800oC for 1 h resulted in polycrystalline BST thin lms with increased
refractive indices and dielectric constants, along with reduced optical
transmission values. Frequency dependent dielectric constants were found to be
in the range of 46-72, and the observed leakage current was very small,less than
1 A. Our experimental results show that these low temperature grown STO and
BST lms have the potential for various electrical applications.
Keywords
NanocrystallinePolycrystalline
Annealing
Sputter deposition
Room temperature deposition
Butter y curve
Ferroelectric
Dielectric constant
Photocatalytic activity
Barium strontium titanate thin film
Strontium titanate thin film