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.     

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.     

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.     

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.     

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.     

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.     

Effects of Substrate and Annealing Temperatures on the Characteristics of SrBi4Ti4O15 Thin Films

In this study, radio frequency (RF) sputtering was used as the method and the layer-structured bismuth compound of SrBi₄Ti₄O₁₅ + 4 wt% Bi₂O₃ ferroelectric ceramic was used as the target to deposit the SrBi₄Ti₄O₁₅ (SBT) thin films. The addition of excess Bi₂O₃ content in the target ceramic was used to compensate the vaporization of Bi₂O₃ during the sintering and deposition processes. SBT ferroelectric thin films were deposited on Pt/Ti/SiO₂/Si under optimal RF magnetron sputtering parameters with different substrate temperatures for 2 h. After that the SBT thin films were post-heated using rapid temperature annealing (RTA) method. The dielectric and electrical characteristics of the SBT thin films were measured using metal-ferroelectric-metal (MFM) structure. From the physical and electrical measurements of X-ray diffraction pattern, scanning electronic microscope (SEM), I-V curve, and C-V curve, we had found that the substrate temperature and RTA-treated temperature had large influences on the morphology, the crystalline structure, the leakage current density, and the dielectric constant of the SBT thin films.     

(Zr/Ti) ratio effect on RF magnetron sputtered lead titanate zirconate films

Abstract

Sputtered Pb(Zr_xTi_1?x)O₃ thin films with various (Zr/Ti) compositions ranging from 15/85 to 70/30 were grown and characterised in terms of structural and electrical properties. PZT thin films, with 0.7–0.8μm thickness, were deposited on Si/SiO₂/Ti/Pt by sputtering followed by conventional annealing. The sputtering conditions were the same for all the compositions. There were no apparent differences in crystallographic orientation as a function of Zr/Ti and the films a-lattice constant evolution is not exactly identical to the one of bulk ceramics. The permittivity increases when the Zr concentration increases and decreases just after the mor-photropic composition i.e. Zr-rich films. The ferroelectric properties are very sensitive to the Zr/Ti ratio. For example, the coercive field increases when the Ti concentration in the film increases.     

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.     

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.     

Preparation and Properties of Bi4 − x Nd x Ti3O12 Thin Films by Chemical Solution Deposition

Neodymium-modified Bi₄Ti₃O₁₂, (Bi, Nd)₄Ti₃O₁₂ (BNT) ferroelectric thin films have been prepared on Pt/TiO_x/SiO₂/Si substrates using metal-organic precursor solutions by the chemical solution deposition method. The BNT precursor films crystallized into the Bi layered perovskite Bi₄Ti₃O₁₂ (BIT) as a single-phase above 600C. The synthesized BNT films revealed a random orientation having a strong 117 reflection, whereas non-substituted BIT thin films exhibited a random orientation with strong 00l diffractions. Among Bi_{4 – x}Nd_xTi₃O₁₂ [x = 0.0, 0.5, 0.75, 1.0] thin films, Bi_3.25Nd_0.75Ti₃O₁₂ thin films showed a well-saturated P-E hysteresis loop with the highest P_r (22 C/cm²) and a low E_c (69 kV/cm) at an applied voltage of 5 V. The Nd-substitution with the optimum amount for the Bi site in the BIT structure was effective not only for promoting the 117 preferred orientation but also for improving the microstructure and ferroelectric properties of the resultant films.     

Ferroelectric Properties of Bi3.25Nd0.75Ti3O12 Thin Films Prepared by MOD Process

Ferroelectric Bi_{4 – x}Nd_xTi₃O₁₂(BNdT) thin films with the composition (x = 0.75) were prepared on Pt/Ti/SiO₂/Si(100) substrate by metal-organic deposition. The films were annealed by various temperatures from 550 to 650C and then the electrical and structural characteristics were investigated for the application of FRAM. Electrical properties such as dielectric constant, 2Pr and capacitance were quite dependent on the thermal heat treatment. The measured 2Pr value on the BNdT capacitor annealed at 650C was 56 C/cm² at an applied voltage of 5 V. No fatigue was observed up to 8 × 10¹⁰ read/write switching cycles at a frequency of 1 MHz regardless of annealing temperatures.     

Structure and dielectric properties of Ba(Sn0.2Ti0.8)O3 thin films grown on different substrates by a sol-gel process

Ba(Sn_0.2Ti_0.8)O₃ (BTS) thin films were deposited on Pt/Ti/SiO₂/Si and LaNiO₃/Pt/Ti/SiO₂/Si substrates by a sol-gel processing technique, respectively. The influences of substrates on the phase and microstructure of the thin films were examined. Dielectric properties of the thin films were investigated as a function of frequency and direct current electric field. The results showed that the substrates strongly influenced the microstructure and the dielectric properties of the films. The properties of BTS thin films on LaNiO₃/Pt/Ti/SiO₂/Si substrates were superior to that of the films grown on Pt/Ti/SiO₂/Si substrates.     

Properties of Chemical Solution Deposited Polycrystalline Neodymium-Modified Bi4Ti3O12

Thin films of neodymium-modified bismuth titanate Bi_3.44Nd_0.56Ti₃O₁₂ (BNT) were grown on Pt/TiO₂/SiO₂/Si substrates using chemical solution deposition method. The capacitors made by applying top Au electrodes on BNT films showed significantly improved values of the remanent polarization as compared to that using bismuth titanate Bi₄Ti₃O₁₂ (BT) films. The 2P _r value for the BNT capacitors was determined to be equal to 38 C/cm² at an applied voltage of 24 V, whereas, for Bi₄Ti₃O₁₂ (BT) capacitors a value of 20 C/cm² was measured at the same applied voltage. The maximum piezoelectric and pyroelectric coefficients of 22 pm/V and 112 C/m² K respectively, were measured for the BNT thin films.     

The Study of Ferroelectric La-Doped PbTiO3 Thin Films Prepared by RF Magnetron Sputtering

Ferroelectric La-modified lead titanate (PLT) thin film were grown on Pt/Ti/SiO2/Si by sputtering the Pb_0.93La_0.07TiO₃ targets containing an amounts of excess 8% PbO. The effects of sputtering and annealing conditions on the crystalline structures and the surface morphologies of the PLT thin films have been investigated. The remanent polarization (Pr) and the coercive field of the PLT film through rapid thermal annealing (RTA) was 10.2 μC/cm² and 45 kV/cm respectively. The maximum pyroelectric coefficient reached 19 nC/cm².K at 20°C.     

The Effect of La-Doped Bi4Ti3O12 Buffer Layer on Crystallinity and Ferroelectric Properties of PbZr0.58Ti0.42O3/Bi3.25La0.75Ti3O12 Multilayered Thin Films

PbZr_0.58Ti_0.42O₃ (PZT) ferroelectric thin films with Bi_3.25La_0.75Ti₃O₁₂ (BLT) buffer layer of various thickness were fabricated on Pt/TiO₂/SiO₂/p-Si(100) substrates by rf-magnetron sputtering method. The pure PZT film showed (111) preferential orientation in the XRD patterns, and the PZT/BLT films showed (110) preferential orientation with increasing thickness of the BLT layer. There were no obvious diffraction peaks for the BLT buffer layer, for its thin thickness in PZT/BLT multilayered films. There were the maximum number of largest-size grains in PZT/BLT(30 nm) film among all the samples from the surface images of FESEM. The growth direction and grain size had significant effects on ferroelectric properties of the multilayered films. The fatigue characteristics suggested that 30-nm-thick BLT was just an effective buffer layer enough to alleviate the accumulation of oxygen vacancies near the PZT/BLT interface. The comparison of these results suggests that the buffer layer with an appropriate thickness can improve the ferroelectric properties of multilayered films greatly.     

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.     

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.     

Structural,electrical, and multiferroic properties of Aurivillius Bi<Subscript>6</Subscript>Fe<Subscript>2</Subscript>(Ti<Subscript>3-x</Subscript>V<Subscript>x</Subscript>)O<Subscript>18+δ</Subscript> thin films prepared by chemical solution deposition

Aurivillius type five-layered V-doped Bi₆Fe₂(Ti_3-xV_x)O_18+δ (x = 0.00, 0.03, 0.06, and 0.09) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. All the thin films were crystallized in Aurivillius structures, which have been confirmed by using X-ray diffraction and Raman spectroscopy studies. On comparing the thin films, the Bi₆Fe₂(Ti_2.94V_0.06)O_18+δ thin film showed the most enhanced electrical and multiferroic properties, with a leakage current density value about four orders of magnitude lower than that of the Bi₆Fe₂Ti₃O₁₈ thin film, for example. All of these thin films showed anti-ferromagnetic hysteresis loops at room temperature. The significant decrease in the concentration of oxygen vacancies and the formation of a stable structure caused by doping with the donor V⁵⁺-ion are related to the improved properties in the V-doped Bi₆Fe₂(Ti_3-xV_x)O_18+δ thin films.     

Phase Formations and Electrical Properties of Various (Bi, La)4Ti3O12 Thin Films by Chemical Solution Deposition

The phase formation and electrical properties of (Bi, La)₄Ti₃O₁₂ (BLT) thin film and V-, Sm-doped BLT thin films prepared by the chemical solution deposition method on Pt/TiO₂/SiO₂/Si substrates have been investigated. It was observed that the microstructure and electrical properties of BLT thin films dramatically varied with V- and Sm-doping. The crystallinity and grain size of BLT thin films were definitely increased by V- and Sm-doping into BLT films, which resulted in the enhancement of remanent polarization in doped BLT films. The remanent polarization (Pr) of Sm-doped BLT films annealed for 3 min by an RTA system was about 9 C/cm². The V- and Sm-doped BLT films also exhibited good fatigue characteristics under bipolar stressing to 10¹⁰ cycles.