Electrical properties of (Ba,Sr)TiO[sub 3] thin films revisited: The case of chemical vapor deposited films on Pt electrodes (original) (raw)
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Dielectric properties of (Ba,Sr)TiO/sub 3/ MOD films grown on various substrates
Proceedings of the 13th IEEE International Symposium on Applications of Ferroelectrics, 2002. ISAF 2002., 2002
Ba 0.7 Sr0 0.3 )TiO 3 (BST) double layer capacitors with Pt electrodes were fabricated under identical conditions on different substrates: SiO 2 /Si(111), r-plane sapphire, polycrystalline alumina Al 2 O 3 (99.6%), Zirbconia/Yttria Stabilized Alumina (ZYSA) and glazed polycrystalline alumina. The formation of the crystalline structure of BST films, grown by metal-organic decomposition (MOD) at various thermal processing conditions, leads to significant change in the dielectric properties of the BST films. By preparing BST films of the same thickness and under the same processing conditions, we observed that they possess higher capacitance when grown on all types of alumina-based substrates compared to those on SiO 2 /Si substrates. The higher capacitance on alumina were always associated with larger dissipation factores, and lower or similar leakage current densities. The final tuning of dielectric properties of BST double layer capacitors on non-silicon substrates was correlated to the processing conditions. Furthermore, the processing parameters and the type of lower electrode should be optimized individually for each specific substrate. The lowest achieved leakage current density of Pt/BST/Pt capacitor (500x500 µm 2 ) on glazed alumina was 2.8x10 -9 A/cm 2 at 200 kV/cm with capacitance per unit area of 27 fF/µm 2 .
Thickness dependence of leakage current behavior in epitaxial (Ba,Sr)TiO3 film capacitors
Journal of Applied Physics, 2003
Thickness dependence of leakage current behaviors was investigated in epitaxial (Ba 0.5 Sr 0.5)TiO 3 thin films with different thicknesses of 55-225 nm prepared on Pt(001)/MgO(001) substrates by a radio-frequency magnetron sputtering technique. Below a certain critical film thickness (≤ 55 nm), the Schottky emission is a ruling leakage conduction mechanism over a wide electric field range. In contrast, in thicker films (> 55 nm), the Schottky emission still operates at low electric fields, however at high electric fields the Fowler-Nordheim (F-N) tunneling dominates. The transition film thickness appears to be associated with overlapping of the depletion layers formed at the top and bottom electrode interfaces.
Electrical characteristics of (Ba,Sr)TiO3 films accounted by partially depleted model
We investigated the leakage current versus voltage (I-V) characteristics, the capacitance versus thickness of (Ba 0:5 Sr 0:5 )TiO 3 film (C-t) characteristics, and the relaxation currents of sputtered (Ba 0:5 Sr 0:5 )TiO 3 films with the thickness of 40-166 nm. The I-V characteristics can be explained by the partially depleted model especially when the thickness of (Ba 0:5 Sr 0:5 )TiO 3 film exceeds 62 nm. The C-t characteristics indicate that the relative dielectric constant in the internal layer (out of the depletion layer) does not change by applied voltages. This can be explained by assuming that the electric field is concentrated at the partially depleted layer, and that the relative dielectric constant in the depletion layer decreases in accordance with the increasing of applied voltage. The relaxation currents may be explained by assuming that the relative dielectric constant in the depletion layer decreases in accordance with the increasing of applied voltage.
LEAKAGE CURRENT BEHAVIOR OF Al/Ba0. 5Sr0. 5TiO3/Pt THIN FILM CAPACITOR
mass-malaysia.net
Ba0.5Sr0.5TiO3TiO3 ferroelectric ceramic thin film is prepared via sol-gel technique and fabricated as Al/BST/Pt capacitor. The leakage current mechanism has been studied under positive bias using semiconductor parameter analyzer. The results show that the leakage current is Ohmic conduction at low applied electric field, space charge limited conduction at higher applied field, and it is Schottky emission for all applied electric field regions. The leakage current density increases from 3.63×10-8 to 7.66×10 A/cm as the electric field increases from 2.39×104 V/cm up to 3.91×104 V/cm, these values quite low compared to the values reported in the literature for the same value of applied field. Furthermore, the breakdown strength of BST thin film has been discussed; the results show that it has high breakdown strength.
Dielectric properties of (Ba,Sr)TiO3 thin film capacitors fabricated on alumina substrates
Double layer (DL) Ba0.7Sr0.3TiO3 (BST) capacitors with Pt electrodes have been fabricated with similar growth conditions on different substrates. The substrates used in the present study were r-plane sapphire, polycrystalline alumina Al2O3 (99.6% and 96%), and glazed polycrystalline alumina. BST films were grown by metal-organic decomposition (MOD) method. By varying the annealing conditions which affects the formation of the crystalline structure, significant changes in the dielectric properties of the BST films have been observed. BST films were characterized by Field Emission Scanning Electron Microscopy (FE-SEM) and Powder X-ray Diffractometer (PXRD). These observations showed that BST films grown at lower temperatures on alumina substrates exhibited the smallest grain size. BST films of the same thickness prepared under the same thermal processing conditions showed higher capacitance when grown on all types of alumina-based substrates compared to those deposited on control SiO2/Si. The higher capacitance on alumina was always associated with larger dissipation factor, and lower or similar leakage current density. The final tuning, of the dielectric properties of BST DL capacitors on non-silicon substrates, was correlated to the initial film formation temperature and post-annealing conditions of the BST films. The leakage current density, of DL BST capacitors fabricated on glazed alumina, becomes smallest when the BST processing temperature was lowered by 100 oC compared to the control SiO2/Si. The typical achieved leakage current density for 1500x1500 μm2 DL capacitors on glazed alumina was 3.8x10-9 A/cm2 at 250 kV/cm (36.5 fF/μm2), about 3 times lower than on SiO2/Si substrates (1.1x10-8 A/cm2 at 250 kV/cm, 31 fF/μm2).
Surface and Coatings Technology, 2006
A novel sandwich structure of Ba 0.7 Sr 0.3 TiO 3 /Cr/Ba 0.7 Sr 0.3 TiO 3 (BST/Cr/BST) was sputtered onto Pt/Ti/SiO 2 /Si substrate. With the insertion of a Cr layer, the leakage currents are decreased and the thermal stability of the specimens is enhanced. Temperature coefficient of capacitance (TCC) of specimens with BST(200 nm)/Cr(2 nm)/BST(200 nm) multifilms can achieve about 83% lower than those with BST (400 nm) monolayer. However, the dielectric constant of the BST(200 nm)/Cr(2 nm)/BST(200 nm) multifilms decreases to about 37% of that BST monolayer. The leakage current densities under an electric field of 125 kV/cm at 90°C are 4 × 10 − 4 A/cm 2 and 9 × 10 − 1 A/cm 2 for BST (200 nm)/Cr (2 nm)/BST (200 nm) and monolayer BST (400 nm), respectively. X-ray diffraction results indicate the formation of a CrO 3 secondary phase after annealing at 700°C or above in O 2 atmosphere. The root causes for the improvement of leakage currents and thermal stability with the insertion of nano-Cr interlayer are explored. The results show the insertion of Cr-nanolayer improves the electric properties for application in capacitors.
Impedance spectroscopic and dielectric analysis of Ba0.7Sr0.3TiO3 thin films
Journal of Alloys and Compounds, 2012
Polycrystalline Ba 0.7 Sr 0.3 TiO 3 thin film with Pt/BST/Pt/TiO 2 /SiO 2 structure was prepared by ion beam sputtering. The film was post annealed at 700 • C. The dielectric and electric modulus properties were studied by impedance spectroscopy over a wide frequency range [0.1-10 5 Hz] at different temperatures [175-350 • C]. The Nyquist plots (Z vs. Z) show the contribution of both grain and grain boundaries at higher temperature on the electric response of BST thin films. Moreover, the resistance of grains decreases with the rise in temperature and the material exhibits a negative temperature coefficient of resistance. The electric modulus plot indicates the non-Debye type of dielectric relaxation. The values of the activation energy computed from both plots of Z and M are 0.86 eV and 0.81 eV respectively, which reveals that the species responsible for conduction are the same. The scaling behavior of M /M max shows the temperature independent nature of relaxation time. The plot of normalized complex dielectric modulus and impedance as a function of frequency exhibits both short and long-range conduction in the film.
Defects-related leakage behavior and degradation mechanisms of (Ba,Sr)TiO3 films
The defect-related relaxation behaviors and the leakage of fresh and/or dc-electrically degraded specimens of Au/(Ba 0.5 Sr 0.5 )TiO 3 /Pt capacitors on the TiO 2 coated sapphire substrates were investigated. The relaxation behaviors of (Ba 0.5 Sr 0.5 )TiO 3 films are assumed to be the electron-detrapping in the depletion layer. The local electric field enhancement due to oxygen vacancies near the Pt/(Ba 0.5 Sr 0.5 )TiO 3 interface, which is estimated from the Poisson equation, was assumed to be sufficiently high as a cause of tunneling conduction, and assumed to be a cause of dc-electrical degradation.