Synthesis of Oriented Ba2NaNb5O15 (BNN) Thin Films from an Alkoxy-derived Precursor

Ba₂NaNb₅O₁₅ (BNN) thin films with a tungsten bronze structure were fabricated using a precursor solution that was synthesized from barium, sodium, and niobium alkoxides. Highly (002)-oriented BNN films were prepared successfully on Pt(100)/MgO(100) substrates at 700°C, using a BNN underlayer. X-ray pole-figure measurement showed that the BNN films that crystallized on Pt(100)/MgO(100) substrates had two in-plane orientations. The remanent polarization and coercive field of the BNN film (thickness of 1.0 µm) that was crystallized at 700°C were 12.3 µC/cm² and 101 kV/cm, respectively, at –150°C (123 K). BNN films on fused silica substrates exhibited second harmonic generation upon irradiation with 1064 nm light.     

Chemical Processing of Potassium-Substituted Strontium Barium Niobate Thin Films through Metallo-organics

Transparent and highly oriented K _x (Sr_0.5Ba_0.5)_{1− x /2}Nb₂O₆ ( x = 0.2, 0.4) (KSBN) thin films have been synthesized by a chemical solution deposition method. A homogeneous and stable KSBN precursor solution was prepared by controlling the reaction of metallo-organics. K_0.4Sr_0.4Ba_0.4Nb₂O₆ ( x = 0.4, K_0.4SBN50) and K_0.2Sr_0.45Ba_0.45Nb₂O₆ ( x = 0.2, K_0.2SBN50) powders and thin films directly crystallized to the tetragonal tungsten bronze phase above 600°C. The thin films were crystallized on MgO(100) and Pt(100)/MgO(100) with c -axis preferred orientation. Two crystal lattice planes of K_0.4SBN50 and K_0.2SBN50 were intergrown at an orientation of 18.5° on MgO(100) and Pt(100)/MgO(100). K_0.4SBN50 thin film on Pt(100)/MgO(100) showed the typical hysteresis loop ( P _r= 22 µC/cm², E _c= 99 kV/cm at −190°C). The change in remnant polarization with temperature is strongly related to the diffuse phase transition of the epsilon- T curves.     

Potassium Lithium Niobate Films Derived from Aqueous Precursor Solution

Potassium lithium niobate (KLN) films, which were prepared using an aqueous precursor solution, were characterized in terms of crystallinity, morphology, and electrical properties; 1.0 μm thick KLN films free from cracks and pores could be prepared on MgO(100), Pt(100)/MgO(100), and Pt(111)/Ti/SiO₂/Si substrates by multiple coating and heating at 700°C. The films were composed of compact grains and had sintered textures. The films crystallized with (310) and (540) preferred orientations on MgO(100) and Pt(100)/MgO(100) substrates. The KLN film prepared on Pt(100)/MgO(100) substrate had ɛ'= 136 and tan δ= 0.026 at 1 kHz.     

Highly Oriented, Chemically Prepared Pb(Zr, Ti)O3 Thin Films

We have fabricated highly oriented, chemically prepared thin films of Pb(Zr_0.04Tio._0.60)O₃ (PZT 40/60) on both insulating and conducting substrates. While (100) MgO single crystals were used as the insulating substrates, the conducting substrates. were fabricated by RF magnetron sputter deposition of 100-nm-thick (100) Pt films onto (100) MgO substrates. For comparison, we also fabricated PZT 40/60 films that had no significant preferential orientation on platinized MgO substrates. Sputter deposition of an underlying amorphous Pt film was used to fabricate randomly oriented PZT 40/60 films. Highly (001) oriented PZT 40/60 films had higher remanent polarization (61 μC/cm² compared to 41 μC/cm²) and lower relative dielectric constant (368 compared to 466) than PZT 40/60 films that were randomly oriented.     

Synthesis of Highly Oriented Lead Zirconate–Lead Titanate Film Using Metallo-organics

Crack-free Pb(Zr,Ti)O₃ (PZT) thin films with preferred orientation were prepared successfully on MgO (100), SrTiO₃ (100), and Pt/Ti/SiO₂/Si substrates from metal alkoxide solutions. Calcination of precursor films in a H₂O─-O₂ gas mixture was found to be effective not only for low-temperature crystallization of perovskite PZT, but also for obtaining the preferred orientation of PZT films. Single-phase PZT films with high preferred orientation were synthesized on MgO (100) and Pt/Ti/SiO₂/Si substrates at 550° and 600°C for 2 h, respectively. The PZT film on the Pt/Ti/SiO₂/Si substrate showed a permittivity of 520, tan δ of 0.03, a remanent polarization of 24 μC/cm², and a coercive field of 54 kV/cm.     

Effects of Heating Profiles on the Orientation and Dielectric Properties of 0.5Pb(Mg1/3Nb2/3)O3-0.5PbTiO3 Thin Films by Chemical Solution Deposition

0.5Pb(Mg_1/3Nb_2/3)O₃-0.5PbTiO₃ thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by varying the film formation procedures and heating processes. Depending on the multilayer film formation and appropriate heating process, the films were grown with a preferential orientation. The films showed a (100)-preferred orientation and large grain-size distribution when they were directly heat-treated after deposition of amorphous layers. The films showed a (111)-preferred orientation and small grain-size distribution when formed layer-by-layer or directly heating amorphous thin films with a perovskite seed layer. These results were explained by the effect of a seed layer. Saturation polarization of the (111)-preferred films was ∼35 µC/cm², which was somewhat higher than that of the (100)-preferred film. In contrast, the dielectric constant of the (100)-preferred film was ∼1600, which was larger than that of the (111)-preferred film.     

Synthesis of Highly Oriented K(Ta,Nb)O3 (Ta:Nb = 65:35) Film Using Metal Alkoxides

Highly oriented K(Ta,Nb)O₃ (Ta:Nb = 65:35) (KTN) thin films of perovskite structure were synthesized successfully on Pt(100)/MgO(100) substrates from a metal alkoxide solution through reaction control. Homogeneous KTN coating solutions prepared from KOC₂H₅, Ta(OC₂H₅)₅, and Nb(OC₂H₅)₅ in ethanol were analyzed by ¹H, ¹³C, and ⁹³Nb NMR spectroscopy. The KTN precursor included a molecular-level mixture of K[M(OC₂H₅)₆] (M = Ta, Nb) units interacting in ethanol solution. X-ray pole figure measurement showed that perovskite KTN films crystallized on Pt(100)/MgO(100) substrates had not only a (100) orientation but also a three-dimensional regularity of grains. The remanent polarization and coercive field of the KTN film (thickness, 1.0 μm) crystallized at 700°C were 1.5 μC/cm² and 8.7 kV/cm, respectively, at 225 K.     

Pulsed laser deposition of Sm modified PbTiO3 ferroelectric thin films

Sm modified PbTiO³ thin films have been prepared by pulsed laser deposition on Pt/TiO₂/SiO₂/(100)Si substrates. It has been found that the Sm concentration of the films remains close its concentration in the target, however, a Pb loss exists during the deposition process. To compensate for the Pb loss we used Pb rich targets and an oxygen pressure of 0.1 mbar. Films deposited at 530°C are crystalline and preferentially oriented with the [100] film direction perpendicular to the substrate surface. In comparison to bulk ceramics, the films have a tetragonal distortion lower than that expected from their Sm concentration. This is likely due to the influence of the substrate. The films prepared are ferroelectric with aP_r = 3.2 μC/cm².     

Preparation of Dense BaTiO3 Ceramics with Submicrometer Grains by Spark Plasma Sintering

Dense BaTiO₃ ceramics consisting of submicrometer grains were prepared using the spark plasma sintering (SPS) method. Hydrothermally prepared BaTiO₃ (0.1 and 0.5 µm) was used as starting powders. The powders were densified to more than similar/congruent95% of the theoretical X-ray density by the SPS process. The average grain size of the SPS pellets was less than similar/congruent1 µm, even by sintering at 1000-1200°C, because of the short sintering period (5 min). Cubic-phase BaTiO₃ coexisted with tetragonal BaTiO₃ at room temperature in the SPS pellets, even when well-defined tetragonal-phase BaTiO₃ powder was sintered at 1100° and 1200°C and annealed at 1000°C, signifying that the SPS process is effective for stabilizing metastable cubic phase. The measured permittivity was similar/congruent7000 at 1 kHz at room temperature for samples sintered at 1100°C and showed almost no dependence on frequency within similar/congruent10⁰-10⁶ Hz; the permittivity at 1 MHz was 95% of that at 1 kHz.     

Preparation and Characterization of Tl-Ba-Ca-Cu-O Superconducting Films by Spray Pyrolysis and Tl-Diffusion Technique

The present work reports that highly c -axis-oriented Tl-Ba-Ca-Cu-O superconducting films with zero-resistance temperature up to 112 K were successfully prepared using the spray pyrolysis technique with a subsequent Tl-diffusion treatment. The insalating Ba-Ca-Cu-O precursor films (Ba:Ca:Cu = 2:2:3) were made by spray deposition of the related metal nitrate solution on a preheated (300°–400°C) MgO(001) single-crystal substrate. The presence of the superconducting phases of the resultant films depended strongly on the types of Tl sources used. The results showed that the formation of the super conducting phases could be achieved more readily by using the bulk Tl-Ba-Ca-du-O rather than Tl₂O₃ as a Tl source. In other words, the low Tl content in the TlBaCaCuO bulk source with a resulting low Tl-vapor pressure is favorable for the formation of a higher T _c superconducting phase. The dominant phases in the prepared films were mainly TlBa₂Ca₂Cu₃O/(1223 phase) and Tl₂Ba₂CaCu₂O_y(2212 phase). The critical current density of a film with a nearly single-phase(1223) structure was measured to be 1.2 × 10⁴ A/cm² at 77 K under zero magnetic field.     

Processing of Oriented K(Ta,Nb)O3 Films Using Chemical Solution Deposition

K(Ta,Nb)O₃ (KTN) thin films have been prepared by the chemical solution deposition method. KTN precursors consisted of a uniform mixture of K[Ta(OC₂H₅)₆] and K[Nb(OC₂H₅)₆] with interaction at the molecular level. Perovskite KTN thin films with the desired composition (Ta/Nb = 65/35, 50/50, and 35/65) were synthesized from the precursor solutions by the dip coating method. KTN thin films with (100) preferred orientation were successfully synthesized on MgO(100) and Pt(100)/MgO(100) substrates. X-ray pole figure measurements showed that grains of KTN films had a prominent three-dimensional regularity on MgO(100) and Pt(100)/MgO(100) surfaces. The Curie temperatures of KTN films decreased with increasing Ta/Nb ratio. Typical P-E hysteresis loops were observed for KTN thin films of three compositions on Pt(100)/MgO(100) substrates. The values of remanent polarization ( P _r) of KTN films increased as the Ta/Nb ratio changed from 65/35 to 35/65.     

Metal Propionate Synthesis of Magnetoresistive La1−x(Ca,Sr)xMnO3 Thin Films

A flexible chemical solution deposition (CSD) method for the preparation of magnetoresistive La_1−x (Ca,Sr)x MnO₃thin films based completely on metal propionates is pre-sented.A number of polycrystalline thin films with varying stoichiometries were deposited on different substrate ma-terials at temperatures between 550° and 850°C. The crys-tallization behavior on selected substrates was found to de-pend on the thin film stoichiometry. Magnetoresistivity and magnetization were measured as a function of temperature. For the selected samples, a magnetic Curie temperature TC, a metal–semiconductor transition, and magnetoresistive behavior were observed. These measurements demon-strated that La_1−x(Ca,Sr)x MnO₃ thin films with properties well known from films deposited by PLD or sputtering can be prepared by a simple, propionate-based CSD method.     

Fatigue-Free Lead Zirconate Titanate (Pb(Zr,Ti)O3)-Based Capacitors Co-modified by Lanthanum and Lithium for Nonvolatile Memories

Pb_0.98(La_{1− x} Li _x )_0.02(Zr_0.55Ti_0.45)O₃(PLLZT with 0.1 ≤ x ≤ 0.7) thin films were sol-gel-grown on Pt(111)/Ti/SiO₂/Si substrates, employing a thin lead zirconate titanate (PZT) template layer. Films annealed at >550°C showed a highly (111)-oriented preferential growth. Typical values of the switchable remanent polarization (2 P _r) and the coercive field ( E _c) of the PLLZT/PZT/Pt film capacitor for x = 0.3 were 50 μC/cm² and 39 kV/cm, respectively, at 5 V. All the PLLZT/PZT/Pt capacitors (for 0.1 ≤ x ≤ 0.7) exhibited fatigue-free behavior up to 6.5 × 10¹⁰ switching cycles, a quite stable charge retention profile with time, and high 2 P _rvalues, all which assure their suitability for nonvolatile ferroelectric memories.     

Preparation of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 Thin Films Via a Polyvinylpyrrolidone-Assisted Aqueous Sol–Gel Process and Dielectric Properties

Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMN–PT) thin films were prepared by spin coating using aqueous solutions of metal salts containing polyvinylpyrrolidone, where niobium oxide layers and lead—magnesium–titanium oxide layers were laminated on Pt(111)/TiO _x /SiO₂/Si(100) substrates and fired at 750° or 800°C. 250 ± 20 nm thick 0.7PMN–0.3PT thin films of a single-phase perovskite could be prepared, and the film fired at 750°C had dielectric constants and dielectric loss of 1900 ± 350 and 0.13 ± 0.03, respectively, exhibiting polarization-electric field hysteresis with a remanent polarization of 5.1 μC/cm² and a coercive field of 21 kV/cm.     

Effects of Plasma Bombardment on the Initial Growth of (Ba,Sr)TiO3 Films and Their Properties

Magnetron-sputtered (Ba,Sr)TiO₃ films were grown on Pt/SiO₂/Si and MgO substrates that were located inside and outside the plasma region. The effects of plasma bombardment on the properties of the grown films were observed. The films that were grown outside the plasma region exhibited better crystallinity, higher dielectric constants, higher electrical conductivity, and rougher surfaces than those that were grown inside the plasma region. However, plasma bombardment did not affect the initial growth of the films on Pt/SiO₂/Si or MgO substrates, as explored by atomic force microscopy. The films that were grown on Pt/SiO₂/Si showed island growth characteristics, whereas those that were grown on MgO substrates revealed layer-by-layer growth characteristics. Possible explanations for the different growth mechanisms are provided.     

Synthesis of Strontium Barium Niobate Thin Films through Metal Alkoxide

Highly oriented Sr_0.5Ba_0.5Nb₂O₆ (SBN50) thin films have been prepared using a sol-gel method. A homogeneous and stable strontium barium niobate (Sr_1-xBa_xNb₂O₆, SBN) precursor solution could be prepared via the reaction control of metal alkoxides. The SBN precursor was stabilized by the coordination of the 2-ethoxyethoxy group to metals. SBN thin films on MgO(100) crystallized to a mixture of orthorhombic and tetragonal phase at 700°C and then transformed completely to the tetragonal phase of tungsten bronze at 1000°C. Two crystal lattice planes of SBN were intergrown at an orientation of 18.5° on MgO(100). SBN50 thin films on Pt(100)/MgO(100) substrates exhibited the P-E hysteresis.     

Spin Coating of a Ca(Ti,Fe)O3 Dense Film on a Porous Substrate for Electrochemical Permeation of Oxygen

A dense Ca(Ti_0.75Fe_0.25)O_3−α (Ca(Ti,Fe)O₃) film, which is a mixed conductor of oxide ions and electrons/holes, was prepared on a porous CaTiO₃ substrate by a spin-coating method. The calcined Ca(Ti,Fe)O₃ powder with 2–3 μm grain sizes was mixed with a dispersant in ethanol to form the slurry for spin coating. A uniform Ca(Ti,Fe)O₃ green film was obtained at 1000–1500 rpm on the rotating porous CaTiO₃ substrate, which had an average pore diameter of a few micrometers. The optimum sintering conditions for the spin-coated films were a soaking temperature of 1235°C and a holding time of 2 h, in air. A dense, sintered Ca(Ti,Fe)O₃ film }20–50 μm thick was prepared by repeating the coatingsintering process. The gas-tight film prepared on the porous substrate exhibited higher electrochemical permeation of oxygen at an operating temperature of 1000°C compared with that of thicker, sintered Ca(Ti,Fe)O₃ disks.     

Synthesis of 10-μm-Thick Lead Zirconate Titanate Films on 2-in. Si Substrates for Piezoelectric Film Devices

To achieve micro-machined piezoelectric film devices, crack-free and dense 10-μm-thick lead zirconate titanate (PZT) films were successfully deposited onto 2-in. Pt/Ti/SiO₂/Si substrates using an automatic coating system, and disk-shaped structures with a diameter from 20 to 100 μm were fabricated by an RIE process. The prepared PZT thick film disks showed well-saturated P–E hysteresis curves and butterfly-shaped longitudinal displacement curves. The AFM-measured piezoelectric constant of the 30-μm-diameter PZT thick film disk after poling at 100 V for 10 min was AFM d ₃₃=290 pm/V. The resonant and anti-resonant frequencies of the thickness oscillation mode were observed at 180 MHz. The calculated thickness mode effective coupling factor was ( k _eff)²=0.1 for the poled 30-μm-diameter PZT thick film disks. These results suggest that the prepared PZT thick film disks are applicable for piezoelectric micro devices such as micro-machined ultrasonic transducers.     

Growth of Single-Crystal and Polycrystalline Thin Films of MgAl2O4 and MgFe2O4

Single-crystal and polycrystalline films of Mg-Al₂O₄ and MgFe₂O₄ were formed by two methods on cleavage surfaces of MgO single crystals. In one procedure, aluminum was deposited on MgO by vacuum evaporation. Subsequent heating in air at about 510°C formed a polycrystalline γ-Al₂O₈ film. Above 540°C, the γ-Al₂O, and MgO reacted to form a single-crystal MgAl₂O₄ film with {001} MgAl₂O₄‖{001} MgO. Above 590°C, an additional layer of MgAl₂O₄, which is polycrystalline, formed between the γ-Al₂O₃ and the single-crystal spinel. Polycrystalline Mg-Al₂O₄ formed only when diffusion of Mg²⁺ ions proceeded into the polycrystalline γ-Al₂O₃ region. Corresponding results were obtained for Mg-Fe₂O₄. MgAl₂O₄ films were also formed on cleaved MgO single-crystal substrates by direct evaporation, using an Al₂O₃ crucible as a source. Very slow deposition rates were used with source temperatures of ∼1350°C and substrate temperatures of ∼800°C. Departures from single-crystal character in the films may arise through temperature gradients in the substrate.     

The Effect of Deposition Temperature and Postanneal on the Bi3.63Pr0.3Ti3O12 thin Films Prepared by RF-Magnetron Sputtering Method

Praseodymium doped Bi₄Ti₃O₁₂ (BTO) thin films with composition Bi_3.63Pr_0.3Ti₃O₁₂ (BPT) were successfully prepared on Pt/Ti/SiO₂/Si substrates by RF-magnetron sputtering method at substrate temperatures ranging between 500° and 750°C. The structural phase and orientation of the deposited films were investigated in order to understand the effect of the deposition temperature on the properties of the BPT films. As the substrate temperature was increased to 700°C, the films started showing a tendency of assuming a c -axis preferred orientation. At lower temperatures, however, polycrystalline films were formed. The Pt/BPT/Pt capacitor showed an interesting dependence of the remnant polarization (2 P _r) as well as dc leakage current values on the growth temperature. The film deposited at 650°C showed the largest 2 P _r of 29.6 μC/cm². With the increase of deposited temperature, the leakage current densities of films decreased at the same applied field and the film deposited at 750°C exhibited the best leakage current characteristics. In addition, the ferroelectric fatigue and Raman measurements were carried out on the as-prepared, postannealed in air and postannealed in oxygen BPT films. It was revealed that the BPT film postannealed in air exhibited the weakest fatigue-resistance characteristics and highest frequency shifted Raman vibration modes, indicating the highest oxygen vacancy concentration in this film.