Deposition and dielectric properties of CaCu3Ti4O12 thin films deposited on Pt/Ti/SiO2/Si substrates using radio frequency magnetron sputtering

Polycrystalline CaCu₃Ti₄O₁₂ thin films were deposited on Pt(111)/Ti/SiO₂/Si substrates using radio frequency magnetron sputtering. The phase formation and the physical quality of the films were crucially dependent on the substrate temperature and oxygen partial pressure. Good quality films were obtained at a substrate temperature of 650 °C and 4.86 Pa total pressure with 1% O₂. The dielectric constant (∼ 5000 at 1 kHz and 400 K) of these films was comparable to those obtained by the other techniques, eventhough, it was much lower than that of the parent polycrystalline ceramics. For a given temperature of measurements, dielectric relaxation frequency in thin film was found to be much lower than that observed in the bulk. Also, activation energy associated with the dielectric relaxation for the thin film (0.5 eV) was found to be much higher than that observed in the bulk ceramic (0.1 eV). Maxwell-Wagner relaxation model was used to explain the dielectric phenomena observed in CaCu₃Ti₄O₁₂ thin films and bulk ceramics.     

High dielectric constant in CaCu3Ti4O12 thin film prepared by pulsed laser deposition

We investigate the dielectric properties of c-axis-oriented epitaxial CaCu₃Ti₄O₁₂ thin film prepared by pulsed laser deposition. The dielectric constants are found to be in the order of 10³-10⁴, depending on the mean grain size for the as-deposited thin films. Furthermore, ac conductivity is measured in the frequencies of 0.1-100 kHz and temperatures of 77-350 K. We find that the dissipation is due to hopping polarization of charge carried at high frequencies and is influenced by interfacial effect at low frequencies. Our results of high dielectric constant and its variation with temperature, the low dielectric loss and the stability of the film show that CaCu₃Ti₄O₁₂ thin film may become a good candidate for certain technological applications.     

Structural and dielectric properties of (001) and (111)-oriented BaZr0.2Ti0.8O3 epitaxial thin films

We have grown and characterized BaZr_0.2Ti_0.8O₃ (BZT) epitaxial thin films deposited on (001) and (111)-oriented SrRuO₃-buffered SrTiO₃ substrates by pulsed laser deposition. Structural and morphological characterizations were performed using X-ray diffractometry and atomic force microscopy, respectively. A cube-on-cube epitaxial relationship was ascertained from the θ-2θ and φ diffractograms in both (001) and (111)-oriented films. The (001)-oriented films showed a smooth granular morphology, whereas the faceted pyramid-like crystallites of the (111)-oriented films led to a rough surface. The dielectric response of BZT at room temperature was measured along the growth direction. The films were found to be ferroelectric, although a well-saturated hysteresis loop was obtained only for the (001)-oriented films. High leakage currents were observed for the (111) orientation, likely associated to charge transport along the boundaries of its crystallites. The remanent polarization, coercive field, dielectric constant, and relative change of dielectric permittivity (tunability) of (111)-oriented BZT were higher than those of (001)-oriented BZT.     

Effect of copper-oxide segregation on the dielectric properties of CaCu3Ti4O12 thin films fabricated by pulsed-laser deposition

We investigated the effects of post-deposition cooling conditions on the surface morphologies and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) thin films grown by pulsed-laser deposition on Pt/TiO₂/SiO₂/Si substrates. CCTO thin films cooled under the typical cooling parameters, i.e., slow cooling (3 °C/min) at high oxygen pressure (66 kPa) showed a severe segregation of nanoparticles near the grain boundaries, which was identified to be copper oxide from electron probe micro analyzer mapping. On the other hand, we could not observe any segregation on the film surface when the samples were cooled fast (∼ 20 °C/min) at relatively low oxygen pressure (100 Pa). The dielectric constant, ε_r, of CCTO thin films deposited at 750 °C with severe surface segregation (ε_r ∼ 750 at 10 kHz) was found to be much lower than that (ε_r ∼ 2000 at 10 kHz) of CCTO thin films with smooth surface. As the copper-oxide segregation becomes more serious, which preferentially occurs at relatively high ambient oxygen pressure and temperature, the degradation in the dielectric properties of CCTO films becomes larger. The variation of dielectric constant of CCTO films with no copper-oxide segregation could be related to the presence of an impurity phase at grain boundaries.     

Twinning of YBa2Cu3O7 thin films on different substrates

The twinning of YBa₂Cu₃O₇ (YBCO) thin films with c-axis orientation on (001) MgO, (001) SrTiO₃, (012) LaAlO₃, (110) NdGaO₃ and (001) NdGaO₃ substrates, prepared by laser ablation, has been examined using a combination of and θ/2θ scans at a four-circle diffractometer. On all substrates, except for (001) NdGaO₃, the tetragonal to orthorhombal phase transition results in four different orientations of YBCO twins relating to the substrate. On (001) NdGaO₃ only two different twin orientations, accompanied by a slight lattice monoclinization, has been observed.     

Structural and dielectric properties of LuFe2O4 thin films grown by pulsed-laser deposition

Epitaxial LuFe₂O₄ thin films are deposited on sapphire substrate by pulsed-laser deposition. Different growth conditions are tackled and it is found that substrate temperature is the most critical condition for the film growth; while below 750 °C the film crystallization is poor. The Lu:Fe ratio is also found to be important in forming the LuFe₂O₄ phase in the films; while higher content of Fe oxide than that of stoichiometric LuFe₂O₄ in the target is favorable for the formation of the LuFe₂O₄ phase. However, impurity phases such as Fe₃O₄ and Fe₂O₃ are induced in the film with a Fe oxide enriched target. A large dielectric tunability under electric field is revealed in the film; while the dielectric tunability decreases as the frequency increases, and eventually the dielectric tunability disappears above 500 MHz.     

Microstructural evolution and dielectric properties of Cu-deficient and Cu-excess CaCu3Ti4O12 ceramics

The microstructural evolution and dielectric properties of CaCu_3−xTi₄O_12−x (3 − x = 2.8-3.05) ceramics were investigated. Normal grain growth behavior was observed at Cu/Ca ≤ 2.9, while abnormal grain growth was observed at Cu/Ca ≥ 2.95. A CuO-rich intergranular liquid phase at Cu/Ca ≥ 2.95 and angular grain morphology were the main reasons for abnormal grain growth. However, the abundant intergranular liquid at Cu/Ca = 3.05 significantly affected the relative dielectric permittivity and dielectric loss. The CuO composition is the key parameter that determines the microstructure and dielectric properties of CCTO ceramics.     

Chemical stability of CaCu3Ti4O12 thin films grown by MOCVD on different substrates

Calcium copper titanate, CaCu₃Ti₄O₁₂ (CCTO), thin films have been fabricated by Metal Organic Chemical Vapor Deposition on silicon substrates buffered with two different low-k interlayers, namely SiO₂ and Si₃N₄. Depositions have been carried out from a molten mixture consisting of the Ca(hfa)₂ • tetraglyme, Ti(tmhd)₂(O-iPr)₂, and Cu(tmhd)₂ [Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; tetraglyme = 2,5,8,11,14-pentaoxapentadecane; Htmhd = 2,2,6,6-tetramethyl-3,5-heptandione; O-iPr = iso-propoxide] precursors. The chemical stability of CCTO films on both the SiO₂ and Si₃N₄ low-k layers has been investigated by transmission electron microscopy in the perspective of their implementation in capacitor devices.     

Effect of the microwave oven on structural, morphological and electrical properties of SrBi4Ti4O15 thin films grown on Pt/Ti/SiO2/Si substrates by a soft chemical method

Thin films of SrBi₄Ti₄O₁₅ (SBTi), a prototype of the Bi-layered-ferroelectric oxide family, were obtained by a soft chemical method and crystallized in a domestic microwave oven. For comparison, films were also crystallized in a conventional method at 700 °C for 2 h. Structural and morphological characterization of the SBTi thin films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. Using platinum coated silicon substrates, the ferroelectric properties of the films were determined. Remanent polarization P_r and a coercive field E_c values of 5.1 μC/cm² and 135 kV/cm for the film thermally treated in the microwave oven and 5.4 μC/cm² and 85 kV/cm for the film thermally treated in conventional furnace were found. The films thermally treated in the conventional furnace exhibited excellent fatigue-free characteristics up to 10¹⁰ switching cycles indicating that SBTi thin films are a promising material for use in non-volatile memories.     

Preparation of highly c-axis-oriented Bi4Ti3O12 thin films and their crystallographic, dielectric and optical properties

Bismuth titanate (Bi₄Ti₃O₁₂) thin films with a high c-axis orientation up to 99% were prepared on (100)-oriented silicon wafers by r.f. planar magnetron sputtering using a Bi₂TiO₅ ceramic target at a substrate temperature of 600 °C. From the Auger electron spectroscopy depth profile of the film, there is no evidence of interdiffusion of a specific element between the film and the substrate. Relative dielectric constant of these films depends on film thickness. The behavior was explained assuming a low-dielectric-constant interface layer. Using this assumption, the relative dielectric constant of Bi₄Ti₃O₁₂ film was estimated to be approximately 140. This value is close to that along the c axis in a bulk form. The remanent polarization and the coercive field were 0.8 μC cm⁻² and 20 kV cm⁻¹, respectively.     

Effect of yttrium doping on the dielectric properties of CaCu3Ti4O12 thin film produced by chemical solution deposition

Pure and yttrium substituted CaCu₃Ti_4 − xY_xO_{12 − x / 2} (x = 0, 0.02, 0.1) thin films were prepared on boron doped silica substrate employing chemical solution deposition, spin coating and rapid thermal annealing. The phase and microstructure of the sintered films were examined using X-ray diffraction and scanning electron microscopy. Dielectric properties of the films were measured at room temperature using electrochemical impedance spectroscopy. Highly ordered polycrystalline CCTO thin film with bimodal grain size distribution was achieved at a sintering temperature of 800 °C. Yttrium doping was found to have beneficial effects on the dielectric properties of CCTO thin film. Dielectric parameters obtained for a CaCu₃Ti_4 − xY_xO_{12 − x / 2} (x = 0.02) film at 1 KHz were k ∼ 2700 and tan δ ∼ 0.07.     

Chemical deposition of Al2O3 thin films on Si substrates

Uniform Al₂O₃ films were deposited on silicon substrates by the sol–gel process from stable coating solutions. The technological procedure includes spin coating deposition and investigating the influence of the annealing temperature on the dielectric properties. The layers were studied by Fourier transform infrared spectroscopy and Scanning Electron Spectroscopy. The electrical measurements have been carried out on metal–insulator–semiconductor (MIS) structures. The C–V curves show a negative fixed charge at the interface and density of the interface state, Dit, 3.7 × 10¹¹ eV^− 1cm^− 2 for annealing temperature at 750 °C.     

Microwave dielectric properties of W-doped Ba0.6Sr0.4TiO3 thin films grown on (001) MgO by pulsed laser deposition with a variable oxygen deposition pressure

The microwave dielectric properties of Ba_0.6Sr_0.4TiO₃ 1 mol% W-doped thin films deposited using pulsed laser deposition, are improved by a novel oxygen deposition profile. The thin films were deposited onto (001) MgO substrates at a temperature of 720 °C. A comparison is made between three different oxygen ambient growth conditions. These include growth at a single oxygen pressure (6.7 Pa) and growth at two oxygen pressures, one low (6.7 Pa) and one high (46.7 Pa). Films were deposited in a sequence that includes both a low to high and a high to low transition in the oxygen deposition pressure. Following deposition, all films were post-annealed in 1 atm of oxygen at 1000 °C for 6 h. The dielectric Q (defined as 1 / tanδ) and the dielectric constant, ε_r, were measured at room temperature, at 2 GHz, using gap capacitors fabricated on top of the dielectric films. The percent dielectric tuning (defined as (ε_r(0 V) − ε_r(40 V)) / ε_r(0 V) × 100) and figure of merit (FOM) (defined as percent dielectric tuning × Q(0 V)) were calculated. The film deposited using the two-stage growth conditions, 6.7 / 46.7 Pa oxygen, showed a maximum Q(0 V) value with high percent dielectric tuning and gave rise to a microwave FOM twice as large as the single stage growth condition. The improved dielectric properties are due to initial formation of a film with reduced interfacial strain, due to the formation of defects at the film/ substrate interface resulting in a high Q(0 V) value, followed by the reduction of oxygen vacancies which increases the dielectric constant and tuning.     

Fabrication and characterization of Fe3O4 thin films deposited by reactive magnetron sputtering

Fe-O thin films with different atomic ratio of iron to oxygen were deposited on glass and thermally oxidized silicon substrates at temperatures of 300, 473 and 593 K, by reactive magnetron sputtering in Ar+O₂ atmosphere. The composition and structure of the thin films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrical resistivity. It was found from XRD that with increasing the oxygen partial pressure in the working gas, the crystalline structure of the Fe-O films deposited at the substrate temperature of 473 K gradually changed from α-Fe, amorphous Fe-O, Fe₃O₄, γ-Fe₂O₃ to Fe_21.34O₃₂. The structure and chemical valence of the Fe₃O₄ films were analyzed by electron microscopy and XPS, respectively.     

Improved dielectric properties of CaCu3Ti4O12 thin films on oxide bottom electrode of La0.5Sr0.5CoO3

We report on the effect of La_0.5Sr_0.5CoO₃ (LSCO) bottom electrode to the dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) thin films grown on Ir/Ti/SiO₂/Si substrates. Compared with the films grown directly on Ir/Ti/SiO₂/Si substrates, the dielectric constant has been increased greatly about 100%, and the dielectric loss decreased to lower than 0.2 in the frequency range of 1-100 kHz. The origin has been discussed in details based on the analysis of the X-ray diffraction and impedance spectra measurements. Results of the impedance spectra suggest that the absence of undesired interfacial layer between Ir/CCTO thin films might be one of the major reasons of the improvement of the dielectric properties when the LSCO was introduced as the bottom electrode.     

Structural order and magnetic properties of Fe3Si/Si(100) heterostructures grown by pulsed-laser deposition

The single-phase Fe₃Si thin films with preferred (220) growth orientation were prepared on Si(100) substrates by pulsed-laser deposition. Different states of order were developed by changing the substrate temperature from room temperature to 500 °C. X-ray diffraction, Mössbauer spectroscopy and macroscopic magnetic measurements were used to analyze changes of structural order and magnetic properties with the substrate temperature. The results show that over the whole range of substrate temperatures considered all films are of Fe₃Si single phase, highly oriented along the (220) plane. With increasing the substrate temperature, the structural order type changes from A2 through B2 to DO₃ and the order degree gradually increases. Meanwhile, the saturation magnetization remarkably decreases with the increase of the substrate temperature, induced by Si segregation from the substrate and embedment into the film probably as the amorphous phase. The room temperature grown film has a high saturation magnetization of 917 kA m^− 1, which nearly equals that of bulk DO₃-Fe₃Si.     

Enhancement of remnant polarization in multilayered Bi4Ti3O12/(Bi3.25La0.75)Ti3O12 films obtained by chemical solution deposition

Enhancement of remnant polarization was observed in artificially multilayered Bi₄Ti₃O₁₂ (BT)/(Bi_3.25La_0.75)Ti₃O₁₂ (BLT) films_. The multilayer were prepared on platinum coated silicon substrate by chemical solution deposition and compared with the single-phase BT, BLT and (Bi_3.5La_0.5)Ti₃O₁₂ films_. The multilayered film with a stacking periodicity of 60 nm BLT/30 nm BT shows a remnant polarization (2Pr) of about 61 μC/cm², which is much higher than those of the single-phase films. In addition, the multilayered films show a good fatigue-endurance character. After post-annealing the multilayered films at 700 °C for a long time (20 h), its remnant polarization decreased to a value close to the corresponding uniform film. Some possible mechanisms behind the polarization enhancement were proposed.     

Sol-gel derived CaCu3Ti4O12 ceramics: Synthesis, characterization and electrical properties

The giant dielectric constant material CaCu₃Ti₄O₁₂ (CCTO) has been synthesized by sol-gel method, for the first time, using nitrate and alkoxide precursor. The electrical properties of CCTO ceramics, showing an enormously large dielectric constant ? ∼ 60,000 (100 Hz at RT), were investigated in the temperature range from 298 to 358 K at 0, 5, 10, 20, and 40 V dc. The phases, microstructures, and impedance properties of final samples were characterized by X-ray diffraction, scanning electron microscopy, and precision impedance analyzer. The dielectric permittivity of CCTO synthesized by sol-gel method is at least three times of magnitude larger than that synthesized by other low-temperature method and solid-state reaction method. Furthermore, the results support the internal barrier layer capacitor (IBLC) model of Schottky barriers at grain boundaries between semiconducting grains.     

Influence of Fabrication Parameters on the Phase Formation and Dielectric Properties of CaCu3Ti4O12 Ceramics

The giant dielectric permittivity materials CaCu 3 Ti 4 O 12(CCTO) were synthesized by conventional solid-state reaction techniques.X-ray diffraction and Raman scattering for the powder indicate that the powder calcined at 950 C for 12 h has been completely transformed into the purer CCTO phase.Furthermore,the morphology and size of the grains of the ceramics sintered at 1090 C in the dwell time range from 0 to 26 h were observed by scanning electron microscopy(SEM).Dielectric properties of the polycrystalline CCTO ceramics were characterized in a broad frequency range(100 Hz-1 MHz) and at a temperature ranged from 300 to 500 K.The longer sintering time may lead to more defect structures and the enhanced conductivity,also leads to substantial improvements in permittivity.Grain size and density differences were not large enough to account for the enhancement in dielectric permittivity.Based on the observations,it is believed that the primary factor affecting dielectric behavior is the development of internal defects.The CCTO ceramics sintered at 1090 C for 15 h exhibit lower dielectric loss(～0.05) near room temperature,and the dielectric relaxation behavior above 1 kHz was observed to follow the Arrhenius law.The activation energy(E a) of 0.65 eV indicates that the doubly ionized oxygen vacancies in the grain boundaries are responsible for the dielectric relaxation of the CCTO ceramics.     

Dielectric and optical properties of CaCu3Ti4O12 thin films containing Ag nanoparticles

Simple sol-gel techniques are used to prepare thin films of a high dielectric constant perovskite CaCu₃Ti₄O₁₂, containing different amounts of metallic silver nanoparticles. The formations of the silver nanoparticles are verified by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and optical absorption studies. The dielectric properties are found to be significantly affected by the presence of the silver nanoparticles. A maximum in the dielectric constant is observed at an intermediate metal particle concentration. This is explained in terms of the polarization at the particle-dielectric interface and the internal barrier layer capacitor effect. The optical absorption spectrum is compared with Mie theory in electrodynamics for the optical absorption of small particles to extract the particle size of the silver particle. Non-uniform distributions of Ag particles through the thickness of the thin films are reported.