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.     

Characterization of the CeO2 thin films for insulation layer and Pt/SrBi2Ta2O9/CeO2/Si MFISFET structure

Abstract

CeO₂ and SrBi₂Ta₂O₉ (SBT) thin films for MFISFET (metal-fcrroelectrics-insulator-semiconductor field effect transistor) were deposited by rf sputtering and pulsed laser deposition method, respectively. The effects of oxygen partial pressure during deposition for CeO₂ films were investigated. The oxygen partial pressure significantly affected the preferred orientation, grain size and electrical properties of CeO₂ films. The CeO₂ thin films with a (200) preferred orientation were deposited on Si(100) substrates at 600°C. The films deposited under the oxygen partial pressure of 50 % showed the best C-V characteristics among those under various conditions. The leakage current density of films showed order of the 10^?7～10^?8 A/cm² at 100 kV/cm. The SBT thin films on CeO₂/Si substrate showed dense microstructure of polycrystalline phase. From the C-V characteristics of MFIS structure composed of the SBT film annealed at 800°C, the memory window width was 0.9 V at ±5 V. The leakage current density of Pt/SBT/CeO₂/Si structure annealed at 800°C was 4×10^?7 A/cm² at 5 V.     

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.     

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.     

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.     

Characterization of Ba(Zr0.05 Ti0.95)O3 thin film prepared by sol-gel process

Ba(Zr_0.05Ti_0.95)O₃ (BZT) thin film (∼330 nm) was grown on Pt/Ti/SiO₂/Si(100) substrate by a simple sol-gel process. The microstructure and the surface morphology of BZT thin film were studied by X-ray diffraction and atomic force microscopy. The optical properties of BZT thin film were obtained by spectroscopic ellipsometry. The optical bandgap was found to be 3.74 eV of direct-transition type. Ferroelectric and dielectric properties of BZT thin film were also discussed. The electrical measurements were conducted on BZT films in metal-ferroelectric-metal (MFM) capacitor configuration. The results showed the film exhibited good ferroelectrity with remanent polarization and coercive electric field of 3.54 μC/cm² and 95.5 kV/cm, respectively. At 10 kHz, the dielectric constant and dielectric loss of the film are 201 and 0.029, respectively.     

Pulsed Laser Deposited Ba(Mg1/3Ta2/3)O3 Microwave Dielectric Thin Films

Ba(Mg_1/3Ta_2/3)O₃ (BMT) microwave dielectric thin films were successfully synthesized by a modified pulsed laser deposition (PLD) process, which includes low temperature (200°C) deposition and high temperature (>500°C) annealing. Crystalline structured BMT thin films were obtained when the PLD-deposited films were post-annealed at a temperature higher than 500°C in oxygen atmosphere. The characteristics of BMT thin film, including crystallinity, grain size, film roughness, and dielectric properties were improved with annealing temperature, achieving dielectric constant K = 23.5 and dissipation factor tan δ = 0.015 (at 1 MHz) for the 800°C-annealed films.     

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.     

Effect of Oxygen Plasma on Growth, Structure and Ferroelectric Properties of SrBi2Ta2O9 Thin Films Formed by Pulsed Laser Ablation Technique

Growth of SrBi₂Ta₂O₉ (SBT) thin films has been carried out in the presence of O₂-plasma created by applying a potential at an auxiliary ring electrode placed near the substrate. Effect of plasma excitation potential and polarity, especially negative polarity, on the formation of a proper SBT phase at 700°C and in modifying crystallite orientation and microstructure of SBT films over (1 1 1) oriented Pt film coated over TiO₂/SiO₂/Si(1 0 0) substrates has been demonstrated. Preferred c-axis orientation of SBT films changes to (a–b) orientation with decrease in plasma excitation potential from –700 to –350 V and eliminates secondary Bi₂Pt phase formation even at 600°C Microstructural study show a 2-dimensional large flat c-oriented crystallites formed at –700 V change to small crystallites in conformity with the changed aspect ratio for crystallites in (a–b) plane parallel to film plane. Spectroscopic ellipsometric results are in agreement with the microstructural data. These affects are attributed to O₂-ion bombardment during film growth which reduces nucleation barrier for growth of crystallites in (a–b) plane. O₂-plasma sustains the cationic species formed by laser ablation, which along with O ₂ ⁺ ions, provide necessary activation energy and enhance the oxidation rates required for SBT phase formation even at 700°C. SBT films grown in O₂-plasma show enhancement in remnant polarization value from 1.2 to 6.6 C/cm² and display ferroelectric properties superior to those formed without plasma. Further O₂-plasma eliminates post deposition annealing step for observance of enhanced polarization values. This study shows O₂-plasma excitation potential could be exploited as a new process parameter in laser ablation growth of ferroelectric oxide thin films.     

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.     

Micro-structure and ferroelectric properties of BiFeO3 thin films formed on Pt-coated r-plane sapphire substrates

Magnetoelectric BiFeO₃ (BFO) materials exhibit ferroelectric and ferromagnetic properties simultaneously, therefore they have a potential to be applied in magnetic as well as ferroelectric devices. BFO thin films were formed by depositing sol-gel solutions on Pt-coated r-plane sapphire dielectric substrates. We did not observe any secondary phase such as Bi₂Fe₄O₉ on the r-plane sapphire substrates, which is generally observed on Si substrates. We observed small ferroelectric grains of about 0.1 μm on Pt/sapphire structures. The leakage current density in BFO films was found to be decreased dramatically after optimizing process conditions of stoichiometric BFO chemical solution. The leakage current densities were in the range of 10^{− 7} A/cm² at room temperature and 10^{− 9} A/cm² at 80 K under 0.4 MV/cm applied electric field. The main reason for low leakage current is considered to be reduction of oxygen vacancies due to the presence of exclusive Fe^{3 +} valance state in the films. An applied electric field higher than 0.5 MV/cm was required to pole the BFO films, which made it difficult to obtain the saturated polarization at room temperature. We could measure the saturated remanent polarization in the BFO films at 80 K and the obtained remanent polarization was 100 μC/cm².     

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.     

MOCVD preparation of SBTN thin films from two organometallic sources bottles

Abstract

SrBi₂(Ta_0.7Nb_0.3)₂O₉ (SBTN) films were first prepared on (111)Pt/Ti/SiO₂/Si substrates by MOCVD from only two organometallic source bottles. Bi(CH₃)₃ and the mixture of Sr[Ta(O°C₂H₅)₆]₂ and Sr[Nb(O°C₂H₅)₆]₂ were used as source materials. High compositional reproducibility was obtained; the Nb/(Ta+Nb) ratio was the same as the mixing ratio of the source. Sr/(Ta+Nb) and Bi/(Ta+Nb) ratios can be controlled by the reactor pressure and the input gas flow rate ratio of the source gases. Almost single phase of SBTN was obtained for the film deposited at 500°C and the following heat-treated at 800°C in O₂ atmosphere. Pr and Ec values of 330 nm-thick SBTN film were 8.5 μC/cm² and 91 kV/cm, respectively and were larger than those of SrBi₂Ta₂O₉ film. There was no degradation after 5x10¹⁰ cycles polarization switching.     

Laser ablation preparation and property of bismuth-layer-structured SrBi2Ta2Ta2O9 and Bi4Ti3O12 ferroelectric thin films

Abstract

Bismuth-layer-structured ferroelectric thin films, SrBi₂Ta₂O₉ and Bi₄Ti₃O₁₂, have been prepared by laser ablation method on both Pt sheets and Si wafers at low temperatures of 400 ～ 500°C. These thin films have been characterized by XRD, XPS, AFM, C-V, D-E hysteresis and J-V measurement. SrBi₂Ta₂O₉ thin films have a good (105) preferential orientation, and Bi₄Ti₃O₁₂ thin films have (117) and c-axis orientation on these substrates. Ferroelectric film-SiO₂-Si structures show good C-V hysteresis curve owing to Si surface potential controlled by the D-E hysteresis. D-E hysteresis is obtained in Bi₄Ti₃O₁₂ thin film prepared on Pt sheet, and the remnant polarization and the coercive force are 7.5 μC/cm² and 72 kV/cm, respectively.     

Preparation and characterization of SrBi2Ta2O9 thin films by low-oxygen-concentration annealing technique

SrBi₂Ta₂O₉ thin films were successfully prepared at a low annealing temperature using a low-oxygen-concentration annealing technique. It was possible to obtain a single perovskite phase at 600 °C in 0.7% oxygen concentration and fluorite phase was observed at 600 °C in 100% oxygen. In addition, the SrBi₂Ta₂O₉ thin films annealed at 650 °C in 0.7% oxygen were well crystallized and composed of dense crystal grains with a size of 70 nm. The remanent polarization and leakage current density of the SrBi₂Ta₂O₉ thin film obtained using this new technique were 7 μC/cm² and 3 × 10⁻⁹ A/cm² (at 5 V), respectively. The final remanent polarization after 10⁹ switching cycles was nearly constant. © 1999 Scripta Technica, Electr Eng Jpn, 129(4): 1–6, 1999     

Low-Temperature Process of Ferroelectric (Y0.95,Bi0.05)MnO3 Thin Films and Their Structural and Electrical Properties

[(Y_0.95,Bi_0.05)MnO₃] (YBM) films have been grown on Y₂O₃ buffered Si (001) by pulsed-laser deposition (PLD). We have compared the structural and dielectric properties of YBM films with those of typical YMnO₃ films from the viewpoint of lowering the process temperature. The highly c-axis oriented YBM film have been obtained on Y₂O₃/Si (001) at 700°C, which is a significantly reduced growth temperature from that of typical YMnO₃ films (850°C). The Bi modification was effective for the low temperature processing of YBM films. These highly c-axis oriented YBM films was obtained only at high ambient oxygen pressures, for example above 100 mTorr, contrary to YMnO₃ films which requires low ambient oxygen pressure for the growth of c-axis preferred orientation. The dielectric constant and dissipation factor was 29 and 0.017 at 1 MHz, respectively. The memory window due to ferroelectric polarization switching was found in a capacitance-voltage (C-V) characteristic. The YBM/Y₂O₃/Si structure with above characteristics of YBM films exhibited the C-V memory window of 1.2 V at a sweep voltage of 5 V. The flat-band voltage shifted symmetrically with increasing the sweep voltage up to 8 V due to little charge injection from Si. As a result, the memory window increased progressively with increasing the sweep voltage and amounted to 2 V at a sweep voltage of 8 V. The leakage current density was below 5 × 10^?7 A/cm² at a bias voltage of 8 V.     

Preparation of Epitaxial Bi4Ti3O12 Thin Films on LaAlO3(012) Substrates by a Spin Coating-Pyrolysis Process

Bismuth titanate Bi₄Ti₃O₁₂ thin films were prepared on LaAlO₃(012) substrates by a spin coating-pyrolysis process using metal naphthenates as starting materials. The c-axis oriented Bi₄Ti₃O₁₂ thin films, which contained no second phases as –2 scans, were obtained by heat-treatment in air at temperatures of 600°C and above. X-ray diffraction pole-figure analysis showed that the Bi₄Ti₃O₁₂ thin film has an epitaxial relationship with the LaAlO₃ substrate.     

Based on the Study on Preparation and Properties of Co(II) and La3+-Doped TiO2 Electrochromic Film

Abstract

In order to improve the optical properties and coloration effect. Co(II) and La³⁺ doped TiO₂ thin films were synthesized via a sol–gel, by using butyl titanate as precursor on the surface of ITO conductive glass substrate. Several techniques were used to characterize produces. Adopting the Sol-gel technology, [CH₃(CH₂)₃O]₄Ti, La₂O₃, CoC_l2?6H₂O as the precursor, the composite membranes with different molar ratio of Ti, Ti/La, Ti/Co to be prepared on the ITO glass substrate, the optimum technological parameters for preparation of the base material of the electro-induced discoloration glass are determined. The structure and surface morphology optical and electrochromic properties of Co(II) and La³⁺-doped TiO₂ films were examined with X-ray diffraction (XRD) analysis, energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), and ultraviolet-visible spectrophotometer (UV-vis) DTA-TG analysis. It was found that:

1. The sintering temperature coating number, [CH₃(CH₂)₃O]₄Ti content of the TiO₂ film sample, and the doping category are the main factors that affect the structure and properties of the membrane based material;

2. Using two alcohol amine as chelating agent can effectively inhibit the formation of Ti (OH)₄ precipitation;

3. The properties of the TiO₂ glass film prepared by La₂O₃ and CoCl₂·6H₂O are fine;

4. Materials based on the preparation of a radiochromic film transmittance, high cyclic reversibility, cyclic voltammetry characteristics significantly, the results of the study for the electric induced radiochromic film-based material development and application provide a theoretical and experimental basis.

     

SOL-GEL PREPARATION AND CHARACTERIZATION OF MULTIFERROIC BiFeO3 THIN FILMS WITH VARIOUS BI/FE RATIO

ABSTRACT

BiFeO₃ thin films have been prepared on Pt/TiO₂/SiO₂/Si substrates by sol-gel method using precursor solutions of various elemental ratio (Bi:Fe = 1.1:1.0, 1.0:1.0, and 1.0:1.1). The θ < eqid2 > 2θ scan XRD patterns show all the films consist mainly of polycrystalline perovskite and the crystallinity of Bi:Fe = 1.1:1.0 is better than the others. SEM and AFM images show all BiFeO₃ film have rosette structures, which consist of perovskite phase and matrix phase. The leakage current density measured at the temperature of 80 K is lower than 10^?4 A/cm² in all the films when the electric field reaches 1.6 MV/cm. The leakage mechanism of BiFeO₃ thin film is dominated by Schottky conduction at 80 K. At 80 K, the remanent polarizations at maximum applied voltage of 2.8 MV/cm are 100, 49, and 44 μC/cm² for the ratio of Bi:Fe = 1.1:1.0, 1.0:1.0, and 1.0:1.1, respectively. The saturated magnetization of BiFeO₃ thin films at 80 K were found to be 14, 22.5, 15 emu/cm³ for the ratio of Bi:Fe = 1.1:1.0, 1.0:1.0, and 1.0:1.1, respectively. Among these ratio, BiFeO₃ thin film deposited from precursor of Bi:Fe = 1. 1:1.0 gives the best ferroelectric property.     

Ferroelectric Properties of (Bi, Sm)4Ti3O12 (BST) Thin Films Fabricated by a Metalorganic Solution Deposition Method

Ferroelectric properties of samarium substituted Bi₄Ti₃O₁₂ films, Bi_3.15Sm_0.85Ti₃O₁₂ (BST), were evaluated for use as lead-free thin film ferroelectrics for FeRAM applications. The BST films were fabricated on the Pt/Ti/SiO₂/Si(100) substrates by a metalorganic solution deposition method. The measured XRD patterns revealed that the BST films showed only a Bi₄Ti₃O₁₂-type phase with a random orientation. The BST film capacitors showed excellent ferroelectric properties. For the film capacitor annealed at 700C, 2P_r of 64.2 C/cm² and 2E_c of 101.7 kV/cm at applied electric field of 150 kV/cm were observed. The capacitor did not show any significant fatigue up to 1.5 × 10⁸ read/write switching cycles at a frequency of 1 MHz, which suggests that the samarium should be considered for a promising lanthanide elements to make a good thin ferroelectric film for memory applications.