Pb5Ge3O11 ferroelectric films prepared by a modified sol—gel method

Single-crystal Pb₅Ge₃O₁₁ films 5–105 μm thick, adhering well to platinum substrates, were prepared by pyrolysis of metalorganic precursors in combination with in situ sol-gel processing. The best films consisted of densely packed crystallites ranging in size from 200 to 300 μm, with hexagonal habits. A welldefined ferroelectric transition was revealed at 170–180°C. The typical parameters of the films are ɛ₂₀ = 30–40, tan δ ≃0.02, ɛ_max ≃200, P_s = 3.2 μC/cm²,E _c = 16 kV/cm, and ρ = 10⁸-10⁹ Ω cm, in agreement (except for ɛ_max) with those of lead germanate crystals     

The ferroelectric and optical properties of (Pb0.92La0.08)(Zr0.65Ti0.35)O3 thin films deposited by radio-frequency magnetron sputtering

Ferroelectric (Pb_0.92La_0.08)(Zr_0.65Ti_0.35)O₃ (PLZT) films have been prepared on Pt/Ti/SiO₂/Si and fused quartz substrates using radio-frequency (rf) magnetron sputtering at a deposition temperature of 650°C. X-ray diffraction analysis shows that the PLZT thin films on platinized silicon are polycrystalline with (100)-preferential orientation. A Al/PLZT/Pt capacitor has been fabricated and it shows that the films have excellent ferroelectric character, with saturation polarization (P _s), remanent polarization (P _r) and coercive field (E _c) of 32.8μC/cm², 24.3μC/cm² and 142 kV/cm, respectively. The PLZT thin films exhibit good insulating property and the leakage current density of the films on platinized silicon is only about 0.86 × 10⁻⁷ A/cm² at 200 kV/cm. By the optical transmission spectra measurements, the energy gap (E _g) of the PLZT films on fused quartz is found to be about 3.54 eV. The optical constants (n and k) of the films in the wavelength range of 250–900 nm are obtained by a Filmetrics F20 reflectance spectrometer.     

Growth and characterization of pulsed-laser-deposited polycrystalline Bi3.33Sm0.67Ti3O12 ferroelectric thin films

Ferroelectric Bi_3.33Sm_0.67Ti₃O₁₂ (BSmT) thin films have been fabricated on Pt/TiO_x/SiO₂/Si substrates by pulsed laser deposition and their structural and ferroelectric properties have been characterized. The structure and morphology of the films were characterized using X-ray diffraction, atomic force microscopy, and scanning electron microscopy. About 520-nm-thick BSmT films grown at 700 °C exhibit excellent ferroelectric properties with a remanent polarization (2P_r) of 41.8 μC/cm² and coercive field (E_c) of 91.0 kV/cm, at an applied electric field of 385 kV/cm. The leakage current density was 2.0 × 10^− 6 A/cm² at a dc electric field of 200 kV/cm. The films also demonstrate fatigue-free behavior up to 10⁹ read/write switching cycles with 1 MHz bipolar pulses at an electric field of 192 kV/cm. As a result, Sm-substituted bismuth titanate films with good ferroelectric properties and excellent fatigue resistance are useful candidates for ferroelectric memory applications.     

Structural, optical, and electric properties of BNT–BT0.08 thin films processed by sol–gel technique

Thin films with the composition [(Bi_0.5Na_0.5)TiO₃]_0.92–[BaTiO₃]_0.08 (hereafter BNT–BT_0.08) were deposited on Pt–Si by spin-coating from a stable sol precursor. The BNT–BT_0.08 film, crystallized on the Bi_0.5Na_0.5TiO₃ rhombohedral lattice, was obtained after annealing the film-gel at 700 °C. The films have a smooth surface (Rms = 2.76 nm) and grains with ferroelectric domains. The film showed a bandgap of 3.25 eV and a refractive index of 2.20 at a wavelength of 630 nm. The dielectric characteristics of BNT–BT_0.08 thin films were measured at room temperature and 10 kHz the dielectric constant (ε _r) was 243 and the loss tangent (tanδ) was 0.38. The remnant polarization (P _r) was 0.87 μC/cm² and the coercive field (E _c) was 220 kV/cm at 10 kHz and room temperature. The current density was approximately 2.7 × 10⁻⁵ A/cm² at low electric fields (100 kV/cm). BNT–BT_0.08 thin films shown piezoelectric properties (d _33eff = 100 pm/V) comparable to those of PZT thin films.     

Preparation and characterization of highly (1 1 1)-oriented (Pb,La)(Zr,Ti)O3 thin films by sol-gel processing

Lanthanum modified lead zirconate titanate (Pb_0.91La_0.09)(Zr_0.65Ti_0.35)O₃ (PLZT) ferroelectric thin films were grown on Pt/Ti/SiO₂/Si(1 0 0) and fused quartz substrates using a sol-gel method with rapid thermal annealing processing. The results showed that the highly (1 1 1)-oriented pervoskite PLZT thin film growth on Pt/Ti/SiO₂/Si(1 0 0) substrates. The electrical measurements were conducted on PLZT films in metal-ferroelectric-metal capacitor configuration. The PLZT thin films annealed at 600 °C showed well-saturated hysteresis loops with remanent polarization and coercive electric field values were 10.3 μC/cm² and 36 kV/cm, respectively, at an applied field of 300 kV/cm. At 100 kHz, the dielectric constant and dielectric loss of the film are 682 and 0.021, respectively. The PLZT thin film on fused quartz substrate, annealed at 600 °C, exhibited good optical transmittance, the band gap of optical direct transitions is 3.89 eV.     

Studies of BaTiO3 thin films on different bottom electrode

BaTiO₃ (BT) thin films were prepared on Pt/Ti/SiO₂/Si and Ru/Ti/SiO₂/Si substrates by a modified sol-gel technique. The microstructure of the films was characterized by atomic force microscopy (AFM), X-ray diffraction (XRD) and Raman spectroscopy. The results showed that BT thin films crystallized with perovskite structure. Compared to BT film on Pt/Ti/SiO₂/Si substrate, BT thin film deposited on Ru electrode has similar dielectric constant, while it has higher dielectric loss. C–E curve for BT film on Pt/Ti/SiO₂/Si was more symmetrical around zero-bias field than C–E curve for BT film on Ru/Ti/SiO₂/Si substrate. The tunability was 52.02% for BT film on Pt electrode, which was 33.42% on Ru electrode, at 275 kV/cm and room temperature. The leakage current density of BT on Pt electrode was about an order of magnitude lower than BT film on Ru electrode at the applied electrical field below 150 kV/cm. The leakage conduction mechanism was investigated.     

Annealing temperature dependence of effective piezoelectric coefficients for Bi3.15Eu0.85Ti3O12 thin films

The effects of annealing temperatures 600, 650, 700, and 750 °C on microstructure, chemical composition, leakage current, ferroelectric, dielectric, and piezoelectric properties of Bi_3.15Eu_0.85Ti₃O₁₂ (BET) thin films prepared by metal–organic decomposition were studied in detail. The largest spontaneous polarization 2P _s (98.7 μC/cm² under 300 kV/cm), remnant polarization 2P _r (81.7 μC/cm² under 300 kV/cm), dielectric constant ε_r (889.4 at 100 kHz), effective piezoelectric coefficient d ₃₃ (46.7 pm/V under 260 kV/cm), and lowest leakage current (1.3 × 10⁻⁶ A/cm² under 125 kV/cm) of BET thin film were obtained with annealing at 700 °C. The mechanisms concerning the dependence of the enhancement d ₃₃ are discussed according to the phenomenological equation, and the improved piezoelectric performance could make BET thin film a promising candidate for piezoelectric thin film devices.     

Comparative study of shunted bicrystal Josephson junctions

In order to optimize the series array performance of Y Ba₂Cu₃O_7−x (YBCO) grain boundary shunted junctions, a method to determine and control the junction resistance R_s and Au/YBCO contact resistivity ρ _c has been developed. 200 nm thick c-oriented YBCO films were grown by intermittent thermal coevaporation on bicrystal yttria-stabilized zirconia substrates. A gold contact overlayer of thickness d_n was deposited in situ. Normal junction resistances have been measured as a function of d_n and shunt width w. It was shown that, in accordance with theoretical estimates, the junction shunt resistance is essentially controlled by the c-axis Au/YBCO interface specific resistance and scales as . The product ρ _c ρ _n ≃ 3.10⁻¹⁴ Ω² cm ³ was estimated from the experimental data, leading to ρ _c ≈ 10⁻⁸ Ωcm ² for typical values of ρ _n for gold thin films.     

Properties of neodymium-doped Ca<Subscript>0.15</Subscript>Sr<Subscript>1.85</Subscript>Bi<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>18</Subscript> ferroelectric ceramics

Bismuth-layered compound Ca_0.15Sr_1.85Bi_4−xNd_xTi₅O₁₈ (CSBNT, x = 0–0.25) ferroelectric ceramics samples were prepared by solid-state reaction method. The effects of Nd³⁺ doping on their ferroelectric and dielectric properties were investigated. The remnant polarization Pr of CSBNT ceramics increases at beginning then decreases with increasing of Nd³⁺ doping level, and a maximum Pr value of 9.6 μC/cm² at x = 0.05 was detected with a coercive field Ec = 80.2 kV/cm. Nd³⁺ dopant not only decreases the Curie temperature linearly, but also the dielectric constant (ε_r) and dielectric loss tangent (tan δ). The magnitudes of ε_r and tan δ at the frequency of 100 kHz are estimated to be 164 and 0.0083 at room temperature, respectively.     

Preparation and characterization of Mn-doped BaTiO<Subscript>3</Subscript> thin films by magnetron sputtering

Barium titanate (BaTiO₃) thin films doped with Mn (0.1–1.0 at%) were prepared by r.f. magnetron sputtering technique. Oxygen/argon (O₂/Ar) gas ratio is found to influence the sputtering rate of the films. The effects of Mn doping on the structural, microstructural and electrical properties of BaTiO₃ thin films are studied. Mn-doped thin films annealed at high temperatures (700 °C) exhibited cubic perovskite structure. Mn doping is found to reduce the crystallization temperature and inhibit the grain growth in barium titanate thin films. The dielectric constant increases with Mn content and the dielectric loss (tan δ) reveals a minimum value of 0.0054 for 0.5% Mn-doped BaTiO₃ films measured at 1 MHz. The leakage current density decreases with Mn doping and is 10⁻¹¹ A/cm⁻² at 6 kV/cm for 1% Mn-doped thin films.     

Electrical properties and extension mechanism of Ohmic region of sol–gel derived Ba0.7Sr0.3TiO3 thin films by Zn doping

Undoped and 3 mol% Zn-doped barium strontium titanate thin films were deposited on Pt/Ti/SiO₂/Si substrates using a sol–gel method. The microstructure and morphology of the films were characterized by X-ray diffraction and atomic force microscopy. It showed that both films are polycrystalline with a perovskite structure and smaller grains were observed for the Zn-doped thin films. Dielectric measurements showed that the dielectric loss at 500 kHz was reduced from 0.042 to 0.019 by Zn doping, which was accompanied by a slight decrease of the dielectric constant from 303 to 273. At an applied electric field of 60 kV/cm, the leakage current density of the Zn-doped Ba_0.7Sr_0.3TiO₃ thin films was 2.5 × 10⁻⁸ A/cm², which was by two orders of magnitude lower than that of the undoped films. The leakage current characteristics also indicated that the Ohmic conduction region of barium strontium titanate thin films was extended by Zn dopant. The microstructure, electrical properties and extension mechanism of Ohmic conduction region of the Zn-doped barium strontium titanate thin films were discussed in relation to the effect of Zn doping.     

Preparation of high dispersed nickel pastes for thick film electrodes

Ultra-thinning of Ni paste films for BME-MLCC (Base Metal Electrode Multilayered Ceramic Capacitor) internal electrode was investigated. Adding various dispersants, ball-milling powder, and using the pre-dispersion process to improve Ni paste dispersion and properties of the paste electrodes/thick films, were employed. The paste containing 200 nm sized Ni powders, ethyl cellulose vehicle (η = 2.98 × 10⁴ mPa-s at 0.1 s⁻¹), and Emphos PS-21A as a dispersant proved to be the most desirable candidate. This paste thick film showed the smallest surface roughness (R _a = 0.10 μm and R _max = 0.97 μm) at a viscosity (η = 2.80 × 10⁵ mPa-s at 0.1 s⁻¹) adaptable to screen-printing. In addition, the Ni paste/thick film had the low sheet resistivity (ρ = 1.11 × 10⁻⁴ Ωcm) and an excellent microstructure after sintering at 1,290 °C for 3 h in a 97% N₂/3% H₂ atmosphere.     

Influence of bismuth on properties and microstructures of Sr0.5Ba0.5−xBixTiO3 thin films

The influence of bismuth (Bi) on the dielectric and ferroelectric properties of Sr_0.5Ba_0.5−xBi_xTiO₃ (BST, 0 ≤ x ≤ 0.030 mol) thin films was studied. The results showed that the dielectric constant (ε_r) and dielectric loss (tan δ) decreased, and temperature, T_m, for maximum and ε_r (Curie temperature), moved to lower temperature with increasing Bi content. The P_r, P_s and E_c were 0.22 μC/cm², 0.32 μC/cm² and 60 kV/cm, respectively for Sr_0.5Ba_0.485Bi_0.015TiO₃ thin films measured at 100 Hz, 20 V. The microstructure of BST thinfilms was studied by XRD and TEM. Tetragonal perovskite grains existed in BST thin films, but the grain size decreased with increasing doping ratio in BST. The characteristic absorption band for octahedron [TiO₂] (471.65 cm⁻¹) was shifted to lower wave number.     

Compositionally graded Pb(Zr,Ti)O3 thin films with different crystallographic orientations

Compositionally graded ferroelectric PbZr_xTi_1−xO₃ (PZT) films were deposited using a sputtering method and crystallized in situ at 500 °C. The films showed purely (100) or (111) crystallographic orientation when grown on Si/SiO₂/TiO₂/Pt substrates, while they exhibited c-axis epitaxial microstructure when prepared on MgO/Pt substrates. Their crystallographic orientation was controlled owing to a thin TiO_x layer sputtered on substrates prior to PZT deposition. Analysis performed by Auger depth profile clearly confirmed the variation of composition in the films. Coercive fields from 80 kV/cm to 200 kV/cm and remnant polarization as large as 45 μC/cm² were obtained. However, no typical offset was observed on hysteresis loops, unlike previous works related to graded PZT films.     

Preparation and characterization of indium oxide (In2O3) films by activated reactive evaporation

The electrical and optical properties of In₂O₃ films prepared at room temperature by activated reactive evaporation have been studied. Hall effect measurements at room temperature show that the films have a relatively high mobility 15 cm²v⁻¹s⁻¹, high carrier concentration 2·97 × 10²⁰/cm³, with a low resistivityρ = 1·35 × 10⁻³ ohm cm. As-prepared film is polycrystalline. It shows both direct and indirect allowed transitions with band gaps of 3·52eV and 2·94eV respectively.     

Piezoelectric,ferroelectric and mechanical properties of lead zirconate titanate/zinc oxide nanowhisker ceramics

New lead zirconate titanate/zinc oxide nanowhisker (PZT/ZnO_w) ceramics were fabricated by a conventional solid state processing and their structures, piezoelectric, ferroelectric and mechanical properties were studied. Both the PZT perovskite and ZnO phases can be observed from the X-ray diffraction patterns. The grain size of ceramics is reduced due to the ZnO_w addition. The incorporation of ZnO_w into the PZT ceramics improves the strength and toughness, while deteriorates the piezoelectric and ferroelectric properties. For the PZT/ZnO_w ceramics with 1–2 wt% ZnO_w, the mechanical properties become optimum, meanwhile maintain good piezoelectric and ferroelectric properties: σ _c = 376–484 MPa, σ _f = 115–121 MPa, K _IC = 1.41–1.54 MPa m^1/2, d ₃₃ = 442–490 pC/N, k _p = 0.54–0.55, ε _r = 3,322–3,980, Q _m = 99–101, tanδ = 1.6%–1.7%, P _r = 21.5–26.9 μC/cm² and E _c = 8.1–8.6 kV/cm.     

Frequency-dependent dielectric and electric modulus properties of Li–Ni–Sm–Fe–O spinel embedded in conducting polymer

Conducting polymeric nanocomposite containing Li–Ni–Sm–Fe–O spinel was synthesized by the chemical oxidizing of aniline in the presence of LiNi_0.5Sm_0.08Fe_1.92O₄ particles. The dielectric and electric modulus properties of the as-prepared samples were investigated over a frequency range from 10⁶ to 10⁹ Hz. The dielectric constant (ε′), dielectric loss (ε″) and dissipation factor (tan δ) for all samples presented relatively high values at low frequency and were found to decrease with the frequency. The values of ε′, ε″ and tan δ of the nanocomposite were lower than that of the pristine PANI. Electric modulus analysis had been carried out to understand the electrical relaxation process. The dielectric relaxation time for the nanocomposite became longer due to the introduction of LiNi_0.5Sm_0.08Fe_1.92O₄ particles lowering the crystallinity of PANI.     

Preparation and Characterization of Epitaxial-Grown Ba0.65Sr0.35TiO3 Thin Films by the Sol-Gel Process on Pt/MgO Substrates

Epitaxial-grown barium-strontium-titanate (BST, Ba_0.65Sr_0.35TiO₃) thin films have been successfully deposited on Pt/MgO (100) substrates using sol-gel techniques. Crack-free 350-nm-thick films were fabricated using a multilayer spinning technique and calcination at 650°C in oxygen for 1 hr. The X-ray diffraction pattern showed that (001) planes of BST films were mainly laid parallel to Pt (100) and MgO (100). The dielectric constant and dissipation factor for BST thin films at a frequency of 10 kHz were 480 and 0.02, respectively. The results of the temperature-dependence of the dielectric constant and dissipation factor showed that sol-gel–derived BST films had Curie temperatures of about 35°C and diffused ferroelectric phase transition characteristics. The leakage current density through the BST films was about 2.75 × 10^–7 A/cm² at an applied voltage of 3 V. The BST films exhibited a well-saturated ferroelectric hysteresis loop with remnant polarization P _r = 2.8 C/cm² and coercive field E _c = 52 kV/cm.     

Electrical Properties and Leakage Current Mechanisms of Bi<Subscript>3.2</Subscript>Gd<Subscript>0.8</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Thin Films Prepared by a Sol-Gel Method

Bi_3.2Gd_0.8Ti₃O₁₂ (BGTO) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates using the sol-gel method and rapid thermal annealing in an oxygen atmosphere. The effects of annealing temperature (500–800°C) on microstructure and electrical properties of thin films were investigated. X-ray diffraction analysis shows that the BGT thin films have a bismuth-layered perovskite structure with preferred (117) orientation. The intensities of (117) peaks increases with increasing annealing temperature. The leakage current density (J) was 3.69×10⁻⁸ A/cm² at 200 kV/cm. It was found that the leakage current was affected not only by the microstructure but also by the interface between the Pt electrode and BGTO thin films. In the low electric field region, the leakage current was controlled by Poole–Frenkel emission. In addition, the mechanism can be explained by Schottky emission from the Pt electrode in the high electric field region.     

Low-temperature magnetoresistance of biaxially strained 24-nm-thick La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> films

The lateral unit cell parameter in nanodimensional La_0.67Ca_0.33MnO₃ (LCMO) films grown on (001)-oriented LaAlO₃ substrates is significantly (approximately 4%) smaller than the value measured along the normal to the substrate plane. At T < 140 K, the temperature dependence of the resistivity ρ of LCMO films follows the relation ρ − ρ (T = 4.2 K) ≈ρ₂(H)T ^4.5, where ρ₂ is independent of the temperature but decreases with increasing magnetic field H. It is shown that this decrease is related both to a decay of the spin waves in ferromagnetic domains and to the transformation of antiferromagnetic phase inclusions into ferromagnetic ones.