Characteristics of Bi4Ti3O12 thin films on ITO/glass and Pt/Si substrates prepared by R.F. sputtering and rapid thermal annealing

Bi₄Ti₃O₁₂ thin films are deposited on ITO/glass and Pt/Ti/Si(100) substrates by R.F. magnetron sputtering at room temperature. The films are then heated by a rapid thermal annealing (RTA) process conducted in oxygen atmosphere at temperatures ranging from 550–700^∘C. X-ray diffraction examination reveals that the crystalinity of the films grown on Pt/Ti/Si is better than that of the films grown on ITO/glass under the same fabrication conditions. SEM observation shows that the films grown on Pt/Ti/Si are denser than those grown on ITO/glass substrates. Interactive diffusion between the Bi₄Ti₃O₁₂ film and the ITO film increases with the increase of annealing temperature. The optical transmittance of the thin film annealed at 650^∘C is found to be almost 100% when the effect of the ITO film is excluded. The relative dielectric constants, leakage currents and polarization characteristics of the two films are compared and discussed.     

Improvement of the thermal and chemical stability of Al doped ZnO films

To improve the stability of sputter-deposited ZnO:Al (AZO) films at high temperature above 300^∘C, an amorphous Zn-Sn-O (ZTO) film was deposited on the top of AZO films as an protective layer by co-sputtering of pure ZnO and SnO₂ targets. Amorphous ZTO films had resistivity in the range from 10⁻² to 10⁻³ Ωcm and were stable up to temperature of 400^∘C. Heat treatments of bare AZO films in the atmosphere at 400^∘C resulted in a dramatic increase in the resistivity accompanied by substantial decrease in carrier concentration and Hall mobility. The AZO films covered with the ZTO film showed remarkable improvement in thermal stability for subsequent heat treatments in the temperature range from 200 to 400^∘C in the atmosphere as well as chemical stability in weak acidic solution. X-ray photoelectron spectroscopy analysis showed that the improvement was attained by ZTO layer acting as diffusion barrier of oxygens and/or water vapors.     

Calculation of the intrinsic dead layers thicknesses from Au/Ba0.5Sr0.5TiO3/Pt thin film capacitors

Ferroelectric Ba_0.5Sr_0.5TiO₃ (BST) films were prepared on Pt/Ti/SiO₂/Si substrates by the sol-gel process. The films were spin-coated at 2000 rpm for 30 secs and then pyrolysed for 5 mins at the temperature of 350^∘C. This coating procedure was repeated for 3, 4, 5 and 6 times to obtain BST films with different thicknesses. After coating the films with the desired repetition times, the films were finally annealed in a conventional furnace at temperatures ranging from 600^∘C to 800^∘C with a 50^∘C interval in between. The films obtained with an annealing procedure of 750^∘C were polycrystalline with the presence of an impurity BaCO₃ phase. The capacitance and leakage current were measured and used to extract information on the metal-BST interface. With the series capacitance model and modified Schottky emission equation, the thickness of the dead layers for Au/BST and Pt/BST interfaces were calculated to be less than 6 nm and 5 nm, respectively.     

Synthesis and characterization of indium tin oxide (ITO) nanoparticle using gas evaporation process

In this paper, indium tin oxide (ITO) nanoparticle was synthesized by gas evaporation process, and its physical properties such as particle size, specific surface area, crystal structure, and composition ratio according to the heat-treating conditions were investigated to optimize them. The source material was charged in a chamber with vacuum circumstance of 1×10⁻⁵ torr, and the oxygen gas was supplied during evaporation. The In_xO_ySnO_z nanoparticle was synthesized, and the nanoparticle was heat-treated to have optimal point of particle size, crystal structure, and composition, etc. The synthesized nanoparticle was heat-treated with controlling such parameters as heat-treating temperature and environmental gas. Particle size, specific surface area, crystal structure, and concentration ratio of the synthesized ITO nanoparticle by using the method were analyzed with high resolution transmission electron microscopy (HRTEM), BET surface area analyzer, X-ray diffraction (XRD), and energy dispersion spectroscopy (EDS). As a result, in case of ITO nanoparticle synthesized at 300^∘C, its mean particle size is 5 nm and the surface area exceeds 100 m²/g. The XRD analysis indicates that the crystal structure of the particle is cubic one with orientation of (222), (400), (440). Also, the EDS analysis demonstrates that the concentration ratio of indium and tin is 91 at% and 9 at% in the lattice of the ITO nanoparticle. Since the lower sized ITO nanoparticle produces the ITO sputtering target with higher density and the ITO sputtering target with higher density makes the high quality ITO electrode, the synthetic condition of 300^∘C is considered to be optimal condition for enhancing the high quality ITO electrode.     

Dielectric properties of ZnNb2 O 6 -TiO 2 mixture thin films

ZnNb₂O₆-TiO₂ mixture thin films with multilayer structures were fabricated via a sol-gel spin coating process. TiO₂ layers were deposited on the pre-crystallized ZnNb₂O₆ layers in order to suppress the formation of the ixiolite phase which always forms in the bulk system. The phase constitution of the thin films, confirmed by X-ray diffraction (XRD), could be controlled by the annealing temperatures, which, in turn, influenced the dielectric properties of the thin films. TiO₂ layers crystallized as the anatase phase and then transformed to the rutile phase at temperatures higher than 725^∘C. Dielectric constants of the mixture thin films, measured at 1 MHz with an MIM (metal-insulator-metal) structure, increased from 27 to 41 with dielectric losses below 0.005 as the annealing temperature increased from 700^∘C to 900^∘C. The increase in the dielectric constants was understood to originate from the increasing amounts of the rutile phase. Temperature coefficients of capacitance (TCC) were also measured between 25^∘C and 125^∘C, which showed a decreasing manner from positive values to negative values with increasing annealing temperatures. When annealed at 850^∘C, the TCC of the thin films could be tuned to be approximately 0 ppm/^oC with dielectric constant and dielectric loss of 36 and 0.002, respectively.     

Hydrothermal growth of BaTiO3 thin films on printed circuit boards for integral capacitor applications

Polycrystalline BaTiO₃ films were hydrothermally grown on Ti-coated substrates from 80^∘C to 200^∘C. Films grown at 200^∘C exhibited the lowest dielectric loss of around 0.1. Proton incorporation was more severe for the 80^∘C film resulting in higher dielectric losses and leakage currents about two orders of magnitude higher. Post deposition oxygen plasma treatment removed incorporated protons and reduced the loss tangent but did not reduce defect density. As such, the leakage current of the 80^∘C film remained high. The films had dielectric constants of 275 to 675 from 100 Hz to 100 kHz and a value of 67 from 100 MHz to 3 GHz.     

Crystallinity and photocatalytic activity of liquid phase deposited TiO2 films

Anatase TiO₂ films were deposited on glass substrates at 50 and 200^∘C to investigate the effect of growth temperature on the photocatalytic acitivity of the films. It was observed that the films grown at 200^∘C were composed of columnar crystallites and were more porous than the films grown at 50^∘C which had more compact structures. Also, the film crystallinity increased from 75 to 90% if the higher growth temperature was used. Despite the higher crystallinity, it was observed that for crystallinities between 60 and 90%, the photocatalytic behavior of the films was more significantly affected by changes in the surface area.     

ZnGa2O4 thin films fabricated by Sol-gel spinning coating process

ZnGa₂O₄ thin film phosphors have been synthesized on ITO coated glass and soda-lime glass at a firing temperature of 500^∘C and an annealing temperature of 500^∘C and 600^∘C via a chemical solution method using Zinc acetate dihydrate, Gallium nitrate hydrate and 2-methoxiethanol as a solution. XRD patterns of the film phosphors synthesized showed the peaks of ZnGa₂O₄ crystalline phases. AFM surface morphologies of the ZnGa₂O₄ thin film phosphors revealed marked differences according to an annealing temperature of 500^∘C and 600^∘C under an annealing atmosphere (3% H₂/Ar). On the other hand, the sheet resistance of ZnGa₂O₄ thin film phosphors, which were measured by four-point probe instrument, was approximately 5.76 Ω /square and 7.86 Ω /square with annealing temperature, respectively. The ZnGa₂O₄ thin film phosphors exhibited blue emission spectra with peak wavelength of 434 nm and 436 nm by ultra-violet excitation around 230 nm.     

Study of nanocrystal TiO2 thin films by thermal annealing

The amorphous films were annealed in a wide temperature range (250–1000^∘C) and film properties of TiO₂ thin films were studied. Nano-sized anatase polycrystallites had been induced by thermal annealing for the films annealed at and above 300^∘C as confirmed by X-ray diffraction. Strong LO-phonon Raman modes, especially B_1g (395 cm⁻¹) and E _g (636 cm⁻¹) in Raman spectra and the absorption peak at 436 cm⁻¹ in absorbance spectra by Fourier transform infrared spectroscopy also indicated the existence of anatase phase in crystalline thin films. In addition, with the increase of the annealing temperature, the wettability of the film surface was enhanced as shown by the decrease of water contact angle from over 90^∘ to less than 40^∘. Moreover, upon UV laser irradiation on film surface, the water contact angle saturated at 10^∘ indicative of a highly hydrophilic surface for all the films, which arose from the dissociative adsorption of water molecules on the defect sits of the surface generated by the photocatalysis reactions of TiO₂. This behavior makes the film a good potential candidate for self-clean coatings.     

Preparation and electrical properties of 0.4Pb(Zn1/3Nb2/3)O3-0.6Pb(Zr0.4Ti0.6)O3 thin films by 2-step annealing method

Films of (1−x)Pb(Zn_1/3Nb_2/3)O₃-xPb(Zr_0.4Ti_0.6) O₃ (x = 0.6, 40PZN-60PZT) were deposited on Pt/TiO₂/ SiO₂/Si substrate through spin coating. Using a combination of homogeneous precursor solution preparation and two-step pyrolysis process, we were able to obtain the 40PZN-60PZT thin films of perovskite phase virtually without pyrochlore phase precipitation after annealing above 650^∘C. But since annealing done at the high temperatures for extended time can cause diffusion of Pt, TiO₂ and Si, and precipitation of nonstoichiometric PbO, we adopted 2-step annealing method to circumvent these problems. The 2-step annealed films show dense microstructure than the 1-step films annealed at higher temperature. Furthermore, the root-mean-square surface roughness of 220 nm thick films which are annealed at 720^∘C for 1 min and then annealed at 650^∘C for 5 min was found to be 3.9 nm by atomic force microscopy as compared to the 12 nm surface roughness of the film annealed only at 720^∘C for 5 min. The electrical properties of 2-step annealed films are virtually same and those of the 1-step annealed films annealed at high temperature. The film 2-step annealed at 720^∘C for brief 1 min and with subsequent annealing at 650^∘C for 5 min showed a saturated hysteresis loop at an applied voltage of 5 V with remanent polarization (P _r) and coercive voltage (V _c) of 25.3 μC/cm² and 0.66 V respectively. The leakage current density was lower than 10⁻⁵A/cm² at an applied voltage of 5 V.     

Optical Properties of LiTaO3 Thin films crystallized by RTA processes

High-performance pyroelectric infrared detectors have been fabricated using Lithium tantalite (LiTaO₃) thin films deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by diol-based sol-gel method and rapid thermal annealing (RTA) technique. The dielectric and pyroelectric properties of IR detectors of LiTaO₃ thin films crystallized by conventional and RTA processes are investigated. Experimental results reveal that the heating rate will influence strongly on dielectricity and pyroelectricity of LiTaO₃ thin films. The voltage responsivities (Rv) measured at 80 Hz increase from 5496 to 8455 V/W and the specific detecivities (D^∗) measured at 300 Hz increase from 1.94 × 10⁸ to 2.38 × 10⁸ cmHz^1/2/W with an increase of heating rate from 600 to 1800^∘C/min. However, the voltage responsivity and the specific detecivity decrease with heating rate in excess of 1800^∘C/min. The results show that the LiTaO₃ thin film detector with a heating rate of 1800^∘C/min exists both the maximums of voltage responsivity and specific detecivity.     

Nanostructural and optical features of nc-Si:H films prepared by nickel-induced crystallization

A 30-nm-thick Ni layer was deposited on top of the nc-Si:H (hydrogenated nanocrystalline Si) films by rf-magnetron sputter, and then heat-treatments were carried out at temperatures of 350–500^∘C. Si nanocrystallites were formed in the Ni/nc-Si:H bilayer films during the post-deposition heat-treatments. The intensity of the photoluminescence spectra of the post-deposition heat-treated films gradually increased at wavelengths of ∼420 as well as ∼580 nm with raising the annealing temperature from 350 to 500^∘C. It is highly likely that the increase of the photoluminescence intensity is caused by the increase in the total volume of the nanocrystallites in the films. It was found that the nickel-induced crystallization processing enhanced the formation of Si cystallites with the size of ∼2 and ∼5 nm in the films.     

Low frequency and microwave performances of Ba0.6Sr0.4TiO3 films on atomic layer deposited TiO2/high resistivity Si substrates

We report on high tunablity of Ba_0.6Sr_0.4TiO₃ (BST) thin films realized through the use of atomic layer deposited TiO₂ films as a microwave buffer layer between BST and a high resistivity (HR) Si substrate. Coplanar waveguide (CPW) meander-line phase shifters using BST/TiO₂/HR-Si and BST/MgO structures exhibited a differential phase shift of 95^∘ and 24.4^∘, respectively, at 15 GHz under an electric field of 10 kV/cm. The figure of merit of the phase shifters at 15 GHz was 30.6^∘/dB for BST film grown on a TiO₂/HR-Si substrate and 12.2^∘/dB for BST film grown on a MgO single crystal substrate. These results constitute significant progress in integrating BST films with conventional silicon technology.     

Synthesis and properties of ferroelectric Si-doped (Bi, Nd)4Ti3O12 thin films by chemical solution deposition

Ferroelectric Si-doped (Bi,Nd)₄Ti₃O₁₂ thin films have been prepared on Pt/TiO_x/SiO₂/Si substrates through metal-organic compounds by the chemical solution deposition. The Bi_3.25Nd_0.75Ti_2.9Si_0.1O₁₂ (BNTS) precursor films were found to crystallize into the Bi-layered perovskite Bi₄Ti₃O₁₂ single-phase above 600^∘C. The synthesized BNTS films revealed a random orientation having a strong 117 reflection. The BNTS thin films prepared between 600^∘C and 700^∘C showed well-saturated P-E hysteresis loops with P _r of 13–14 μ C/cm² and E _c of 100–110 kV/cm at an applied voltage of 5 V. The surface roughness of the BNTS thin films was improved by Si doping compared with that of undoped Bi_3.35Nd_0.75Ti₃O₁₂ films.     

Fabrication of Er3+/Pr3+ Co-doped soda-lime glass thin films using RF magnetron sputtering method and optical property characterization

Er^3+/Pr³⁺ co-doped soda-lime glass thin films have been fabricated using RF magnetron sputtering method and their structural and optical properties have been studied. Deposition rate, crystallinity, and composition of glass thin films were investigated by scanning electron microscopy, transmission electron microscopy, and electron probe micro area analysis. Refractive index, birefringence and binding characteristics have been investigated using a prism coupler and X-ray photoelectron spectroscopy. Er³⁺/Pr³⁺ co-doped soda lime glass thin films were prepared by changing substrate temperature (room temp. ∼550^∘C), RF power (90 W–130 W), and Ar/O₂ gas flow ratio at processing pressure of 4 mTorr. Glass thin films could be obtained at the optimized processing condition at 350^∘C, RF power of 130 W, and gas flow of Ar:O₂ = 40:0 with maximum deposition rate of 1.6 μm/h. Refractive index and birefringence increased from 1.5614 to 1.5838 and from 0.000154 to 0.000552, respectively, as the content of Pr³⁺ increased. Binding energy of Pr3d also increased as the content of Pr³⁺ increased.     

Growth mode in strained ZnO films on Al2O3(0001) during sputtering

We investigated the temperature dependence of growth mode in highly mismatched sputter-grown ZnO/Al₂O₃(0001) heteroepitaxial films using real-time synchrotron X-ray scattering. We find that the growth mode changes from 2 dimensional (2D) layer to 3D island in early growth stage with temperature (300^∘C–500^∘C). At around 400^∘C, however, intermediate 2D platelets nucleate in early stage, act as nucleation cores of 3D islands and transform to misaligned state during further growth. The results of the strain evolution during growth suggest that the surface diffusion is a major factor in determining the growth mode in the strained ZnO/Al₂O₃(0001) heteroepitaxy.     

Structure and dielectric properties of BaTi4O9 thin films for RF-MIM capacitor applications

BaTi₄O₉ thin films were grown on a Pt/Ti/SiO₂/Si substrate using RF magnetron sputtering. A homogeneous BaTi₄O₉ crystalline phase developed in the films deposited at 550^∘C and annealed above 850^∘C. When the thickness of the film was reduced, the capacitance density and leakage current density increased. Furthermore, the dielectric constant was observed to decrease with decreasing film thickness. The BaTi₄O₉ film with a thickness of 62 nm exhibited excellent dielectric and electrical properties, with a capacitance density of 4.612 fF/μm² and a dissipation factor of 0.26% at 100 kHz. Similar results were also obtained in the RF frequency range (1–6 GHz). A low leakage current density of 1.0 × 10⁻⁹ A/cm² was achieved at ± 2 V, as well as small voltage and temperature coefficients of capacitance of 40.05 ppm/V² and –92.157 ppm/^∘C, respectively, at 100 kHz.     

Zeolite coating on foamed stainless steel by in-situ crystallization method

Faujasite-type zeolite films were prepared on foamed stainless steel by the in-situ crystallization method. Precursor solutions were prepared by dissolving water glass and NaAlO₂in a NaOH solution and aged at room temperature for two days. The concentrations of the starting materials were varied from 0.29 to 2.3 M (in SiO₂concentration) keeping the molar ratios of Na₂O:SiO₂:Al₂O₃fixed at 3.6:3.0:1.0. The foamed stainless steel substrate had about 90% of porosity and an average pore size of 600 μ m. It was dip-coated in the precursor solution four times, then hydrothermally treated at 80^∘, 110^∘ and 150^∘C for 6–48 h. The XRD patterns and SEM photographs revealed that faujasite-type zeolite was formed predominantly at a SiO₂concentration of 1.1 M, temperature of 110^∘C and duration of 24 h, with a product particle size of 2–5 μ m. At higher concentrations of the precursor solution, hydroxylsodalite becomes the major product rather than faujasite-type zeolite. The adherence strength of the zeolite grains deposited on the foamed stainless steel is higher in the in-situ crystallization method than when a conventional solution method is used. Thus, the in-situ crystallization method is concluded to be effective for preparing zeolite films even on metal substrates.     

CuO formation control as a function of mixed ratio of Cu-free powders in the synthesis of YBCO superconductors on Cu substrates

YBa₂Cu₃O_x (Y123) superconducting films were fabricated on Cu substrates using a simple screen-printing method, from Cu-free powders (Y₂O₃ and BaCO₃). In the process, CuO, which causes superconducting properties of Y123 films to deteriorate, was formed on the film surface. By varying the atomic ratio of Y to Ba (Y:Ba = 1:1∼1:4), the ratio needed to prevent CuO formation was found for the film surface that had been heat-treated at 980^∘C for 17 s. The film, with the ratio of Y to Ba (Y:Ba = 1:1), is reheat-treated at 930^∘C for 9 min 30 s to form a superconducting Y123 phase. It was possible to prevent CuO formation by controlling the ratio of Cu-free powders in the mixture and to fabricate YBCO superconductors on Cu substrates using a two-step heat-treatment.     

Preparation of Pb(Mg1/3Nb2/3)O3-PbTiO3 thin films by MOCVD using ultrasonic nebulization

Thin films of Pb(Mg_1/3,Nb_2/3)O₃ (PMN) and Pb(Mg_1/3,Nb_2/3)O₃-PbTiO₃ (PMN-PT) were fabricated on Si and Pt/Ti/SiO₂/Si substrates by MOCVD using ultrasonic nebulization and their characteristics were investigated. PMN-PT films deposited at 350^∘C were annealed in a RTA (Rapid Thermal Annealing) system at 650^∘C for 30 sec to improve the micostructural properties. The crystallographic properties of PMN-PT films strongly depend on the content ratio of PbTiO₃. The content of pyrochlore phase in PMN-PT films decreased with the increase of Ti content and nearly single phase perovskite films were obtained at the composition of 80PMN-20PT. The PMN-PT films with perovskite phase showed a typical butterfly type C-V curve which verifies the ferroelectricity and had the relative dielectric constant of about 60.