Microstructure and electric properties of (104)/(014)-oriented Bi3.15Nd0.85Ti3O12 films on Pt (111)/Ti/SiO2/Si by sol-gel method

Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT) thin films with predominant (104)/(014) orientation were fabricated directly on (111)Pt/Ti/SiO₂/Si substrates through a sol-gel process. The volume fraction of (104)/(014)-oriented grains in the film was estimated to be about 65% according to X-ray pole figure. The BNdT film is dense and uniform and consists of columnar grains penetrating the whole film thickness. The (104)/(014)-oriented BNdT film capacitors showed excellent ferroelectric properties with 2P_r = 46.4 μC/cm² and E_c ≈ 140 kV/cm. The films also exhibit excellent piezoelectric property, with high piezoelectric coefficient d₃₃ ≈ 17 pm/V.     

Enhanced ferroelectric properties of Pb(Zr0.80Ti0.20)O3/PbO thin films prepared by radio frequency magnetron sputtering

The Pb(Zr_0.80Ti_0.20)O₃ (PZT) thin films with and without a PbO buffer layer were deposited on the Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by radio frequency (rf) magnetron sputtering method. The PbO buffer layer improves the microstructure and electrical properties of the PZT thin films. High phase purity and good microstructure of the PZT thin films with a PbO buffer layer were obtained. The effect of the PbO buffer layer on the ferroelectric properties of the PZT thin films was also investigated. The PZT thin films with a PbO buffer layer possess better ferroelectric properties with higher remnant polarization (P_r = 25.6 μC/cm²), and lower coercive field (E_c = 60.5 kV/cm) than that of the films without a PbO buffer layer (P_r = 9.4 μC/cm², E_c = 101.3 kV/cm). Enhanced ferroelectric properties of the PZT thin films with a PbO buffer layer is attributed to high phase purity and good microstructure.     

The influence of annealing temperatures on the properties of Bi2VO5.5/LaNiO3/Si thin films

Bi₂VO_5.5 ferroelectric thin films were fabricated on LaNiO₃/Si(100) substrate via chemical solution deposition. Ferroelectric and dielectric properties of the thin films annealed at 500-700 °C were studied. The thin film annealed at 700 °C exhibited more favorable ferroelectric and dielectric properties than those annealed at lower temperatures. The values of remnant polarization 2P_r and coercive field E_c for the film annealed at 700 °C are 10.62 µC/cm² and 106.3 kV/cm, respectively. The leakage current of the film is about 1.92 × 10^− 8 A/cm² at 6 V. The possible mechanism of the dependence of electrical properties of the films on the annealing temperature was discussed.     

Structural and ferroelectric properties of La modified Sr0.8Bi2.2Ta2O9 thin films

La modified SBT (Sr_0.8La_0.1Bi_2.1Ta₂O₉) thin films of different thickness were fabricated on Pt/Ti/SiO₂/Si substrates by the metalorganic decomposition technique. All the films were annealed layer-by-layer at 800 °C using a rapid thermal annealing furnace. X-ray diffraction analysis indicated that the relative intensity of the (2 0 0) diffraction peak [I(2 0 0)/I(1 1 5)] increased with the increase of the film thickness. Eventually, an a-axis preferentially oriented SLBT film was obtained. These results are discussed with respect to the anisotropy of the grain growth. The a-axis preferentially oriented SLBT film, whose relative intensity of the (2 0 0) peak [I(2 0 0)/I(1 1 5)] was 1.05, had a remanent polarization (2P_r) value of 21 μC/cm² and a coercive field (2E_c) value of 70 kV/cm under the electric field of 200 kV/cm.     

Synthesis of c-axis oriented AlN thin films on different substrates: A review

Highly c-axis oriented AlN thin films have been deposited by reactive sputtering on different substrates. The crystallographic properties of layered film structures consisting of a piezoelectric layer, aluminum nitride (AlN), synthesized on a variety of substrates, have been examined. Aluminum nitride thin films have been deposited by reactive pulsed-DC magnetron sputtering using an aluminum target in an Ar/N₂ gas mixture. The influence of the most critical deposition parameters on the AlN thin film crystallography has been investigated by means of X-ray diffraction (XRD) analysis of the rocking curve Full-Width at Half Maximum (FWHM) of the AlN-(0 0 0 2) peak. The relationship between the substrate, the synthesis parameters and the crystallographic orientation of the AlN thin films is discussed. A guide is provided showing how to optimize these conditions to obtain highly c-axis oriented AlN thin films on substrates of different nature.     

Ferroelectric properties of Bi3.4Dy0.6Ti3O12 thin films crystallized in N2

Bi_3.4Dy_0.6Ti₃O₁₂ (BDT) ferroelectric thin films were deposited on Pt/Ti/SiO2/Si substrates by chemical solution deposition (CSD) and annealed in an N₂ environment after pre-annealing in air at 400 °C. The effect of crystallization temperature on the structural and electrical properties of the BDT films was studied. The BDT films annealed in N₂ in the temperature range of 600 °C to 750 °C were crystallized well and the average grain size increased with increasing crystallization temperature, while the remanent polarization of the films is not a monotonic function of the crystallization temperature. The BDT films crystallized at 650 °C have the largest remanent polarization value of 2P_r = 39.4 μC/cm², and a fatigue-free characteristic.     

Properties of La-substituted Na0.5Bi4.5Ti4O15 ferroelectric thin films

Ferroelectric Na_0.5La_0.5Bi₄Ti₄O₁₅ (NaLaBTi) thin films were prepared by a chemical solution deposition method. The NaLaBTi thin films annealed at 750 °C under oxygen atmosphere were randomly oriented polycrystalline. Electrical properties of the NaLaBTi thin films were compared to Na_0.5Bi_4.5Ti₄O₁₅ thin films and better properties were observed in the NaLaBTi thin films. Remnant polarization (2P_r) and coercive electric field (2E_c) were 43 µC/cm² and 204 kV/cm at an applied electric field of 478 kV/cm, respectively. Leakage current density was 1.95 × 10^− 6 A/cm² at 100 kV/cm. Dielectric constant and dielectric loss were 805 and 0.05 at 1 kHz, respectively. Switchable polarization was suppressed by 15% after 1.44 × 10¹⁰ switching cycles.     

Enhanced ferroelectric properties in Bi-doped K0.5Na0.5NbO3 thin films prepared by pulsed laser deposition

Lead-free ferroelectric Bi-doped K_0.5Na_0.5NbO₃ (KNN) and undoped KNN films were prepared by pulsed laser deposition. Bi-doped film exhibited good crystallization and improved ferroelectric properties. The dielectric constant and loss tangent were 1038 and 0.138 at 1 kHz, respectively. The remanent polarization (P_r = 28 μC/cm²) of Bi-doped film was about four times larger than that of the undoped film, which attributed to the decrease of oxygen vacancies concentration. The coercive field (E_c = 24 kV/cm) of Bi-doped films was half of the undoped film. The conduction mechanisms of Bi-doped film determined to be Space-Charge-Limited-Current and Poole–Frenkle emission at low and high electric field, respectively.     

Synthesis and characterization of Nb2AlC thin films

We report on the synthesis and characterization of epitaxial c-axis oriented Nb₂AlC thin films deposited on c-axis sapphire (Al₂O₃) substrates by magnetron sputtering. Selected area electron diffraction reveal that independent of substrate temperature or film stoichiometry, there is the growth of a secondary phase not found in bulk, Nb₅Al₃C_x with a- and c-axis lattice constants of 7.746 Å and 5.246 Å, respectively. Scanning electron micrographs reveal large surface features, many with hexagonal shape and faceted texture. Atomic force microscopy topographical measurements indicate a surface roughness of approximately 15% of the total film thickness. Electrical transport measurements show typical metal-like conduction with a room temperature resistivity of ≈ 0.9 μΩ-m and a residual resistivity ratio of 2.5. A superconducting transition was found at ≈ 440 mK.     

Tl2Ba2CaCu2O8 thin films on 2 in. LaAlO3(0 0 1) substrates

High quality Tl₂Ba₂CaCu₂O₈ (Tl-2212) superconducting thin films are prepared on both sides of 2 in. LaAlO₃(0 0 1) substrates by off-axis magnetron sputtering and post-annealing process. XRD measurements show that these films possess pure Tl-2212 phase with C-axis perpendicular to the substrate surface. The thickness unhomogeneity of the whole film on the 2 in. wafer is less than 5%. The superconducting transition temperatures T_cs of the films are around 105 K. At zero applied magnetic field, the critical current densities J_cs of the films on both sides of the wafer were measured to be above 2 × 10⁶ A/cm² at 77 K. The microwave surface resistance R_s of film was as low as 350 μΩ at 10 GHz and 77 K. In order to test the suitability of Tl-2212 thin films for passive microwave devices, 3-pole bandpass filters have been fabricated from double-sided Tl-2212 films on LaAlO₃ substrates.     

Characterisation of YBa2Cu3O6+x films grown by the trifluoro-acetate metal organic decomposition route by infrared spectroscopy

Infrared reflectivity measurements have been performed at T = 300 K on c-axis oriented YBa₂Cu₃O_6+x films obtained by deposit of trifluoroacetate precursors on (100)-LaAlO₃ single crystalline substrates. A detailed simulation of the infrared spectra acquired on the thin films based on the use of an appropriate complex dielectric function model is proposed here. It allows us to determine with a single experiment the thickness and the residual porosity of the layers. To reinforce the statement of the infrared simulations, the results have been compared with the film porosity obtained by scanning electron microscopy imaging. Moreover the local grain orientation has been checked by polarized Raman microspectroscopy. Finally, the three complementary experimental ways give consistent results that justify the present approach.     

Influence of oxygen pressure on the structural, electrical and optical properties of VO2 thin films deposited on ZnO/glass substrates by pulsed laser deposition

The influence of oxygen pressure on the structural and electrical properties of vanadium oxide thin films deposited on glass substrates by pulsed laser deposition, via a 5-nm thick ZnO buffer, was investigated. For the purposes of comparison, VO₂ thin films were also deposited on c-cut sapphire and glass substrates. During laser ablation of the V metal target, the oxygen pressure was varied between 1.33 and 6.67 Pa at 500 °C, and the interaction and reaction of the VO₂ and the ZnO buffer were studied. X-ray diffraction studies showed that the VO₂ thin film deposited on a c-axis oriented ZnO buffer layer under 1.33 Pa oxygen had (020) preferential orientation. However, VO₂ thin films deposited under 5.33 and 6.67 Pa were randomly oriented and showed (011) peaks. Crystalline orientation controlled VO₂ thin films were prepared without such expensive single crystal substrates as c-cut sapphire. The metal-insulator transition properties of the VO₂/ZnO/glass samples were investigated in terms of electrical conductivity and infrared reflectance with varying temperatures, and the surface composition was investigated by X-ray photoelectron spectroscopy.     

High-temperature anomalies of dielectric constant in TiO2 thin films

Anatase and rutile TiO₂ thin films were prepared by chemical vapor deposition with precursors Ti(OPrⁱ)₄ and Ti(dpm)₂(OPrⁱ)₂ (dpm = 2,2,6,6-tetramethylheptane-3,5-dione and Prⁱ = isopropyl), respectively. The dielectric properties of TiO₂ thin films have been studied in 20-1100 K temperature range in air, in controlled Ar/O₂ atmospheres, and in vacuum with silicon-based metal-insulator-semiconductor Au/TiO₂/Si capacitors. High-temperature (T_c ∼ 980 K) anomalous behavior of dielectric constant was observed in both anatase and rutile TiO₂ thin films.     

Structural and optical studies of nanocrystalline V2O5 thin films

We report the structural and optical properties of nanocrystalline thin films of vanadium oxide prepared via evaporation technique on amorphous glass substrates. The crystallinity of the films was studied using X-ray diffraction and surface morphology of the films was studied using scanning electron microscopy and atomic force microscopy. Deposition temperature was found to have a great impact on the optical and structural properties of these films. The films deposited at room temperature show homogeneous, uniform and smooth texture but were amorphous in nature. These films remain amorphous even after postannealing at 300 °C. On the other hand the films deposited at substrate temperature T_S > 200 °C were well textured and c-axis oriented with good crystalline properties. Moreover colour of the films changes from pale yellow to light brown to black corresponding to deposition at room temperature, 300 °C and 500 °C respectively. The investigation revealed that nanocrystalline V₂O₅ films with preferred 001 orientation and with crystalline size of 17.67 nm can be grown with a layered structure onto amorphous glass substrates at temperature as low as 300 °C. The photograph of V₂O₅ films deposited at room temperature taken by scanning electron microscopy shows regular dot like features of nm size.     

Growth and electrical performance of Pb(Mg1/3Nb2/3)O3-PbTiO3-Pb(Fe1/2Nb1/2)O3 single crystals

For the first time, we have grown ferroelectric single crystals Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃-Pb(Fe_1/2Nb_1/2)O₃ (PMN-PT-PFN) from the melt by the simple slow cooling process. The chemical composition of the single crystals PMN-PT-PFN (0.59/0.31/0.10) is near the morphotropic phase boundary (MPB). X-ray diffraction (XRD) was used to study phase structure of the as-grown crystals, energy dispersive X-ray spectrometer (EDS) and electron probe micro-analyzer (EPMA) were employed to confirm the chemical composition and element distribution of the as-grown crystals, respectively. The ferroelectric, dielectric and piezoelectric properties of the as-grown PMN-PT-PFN (0.59/0.31/0.10) single crystal oriented along the (0 0 1) axis were measured, which showed that the remnant polarization (P_r), coercive electric fields (E_c), the Curie temperature (T_c) and the piezoelectric coefficient (d₃₃) were 50.2 μC/cm², 13.9 kV/cm, 158 °C and about 1800 pC/N, respectively. All the results indicated that the PMN-PT-PFN (0.59/0.31/0.10) single crystals are promising for applying to field of high frequency.     

Pb(Zr0.52Ti0.48)O3/TiNi multilayered heterostructures on Si substrates for smart systems

Ferroelectric/shape memory alloy thin film multilayered heterostructures possess both sensing and actuating functions and are considered to be smart. In this article, Pb(Zr_0.52Ti_0.48)O₃ (PZT) ferroelectric thin films and Ti-riched TiNi shape memory alloy thin films have been deposited on Si and SiO₂/Si substrates in the 400-600 °C temperature range by pulsed laser deposition technique. Deposition processing, microstructure and surface morphology of these films are described. The TiNi films deposited at 500 °C had an austenitic B2 structure with preferred (110) orientation. The surfaces of the films were very smooth with the root-mean-square roughness on a unit cell level. The structure of the TiNi films had a significant influence on that of the subsequently deposited PZT films. The single B2 austenite phase of the TiNi favored the growth of perovskite PZT films. The PZT/TiNi heterostructures with the PZT and TiNi films respectively deposited at 600 and 500 °C exhibited a polarization-electric field hysteresis behavior with a leakage current of about 2 × 10^− 6 A/cm².     

The effect of strain on nonlinear temperature dependence of resistivity in SrMoO3 and SrMoO3−xNx films

Highly oriented SrMoO₃ thin films have been fabricated by pulsed laser deposition of SrMoO₄ in hydrogen. The films are found to grow along the (1 0 0) direction on LaAlO₃ (1 0 0) and SrTiO₃ (1 0 0) substrates. The method has been extended for the fabrication of oxynitride thin films, using ammonia as the reducing medium. The resistivity measurements show nonlinear temperature dependent (Tⁿ) behaviour in the temperature interval of 10-300 K. The conduction mechanism is largely affected by the strain due to the substrate lattice. A combination of T and T² dependence of resistivity on temperature is observed for films having lesser lattice mismatch with the substrate. The X-ray photoelectron spectroscopic studies confirm the formation of SrMoO₃ and SrMoO_3−xN_x films.     

Dielectric and ferroelectric properties of Ba(Sn0.15Ti0.85)O3 thin films grown by a sol-gel process

Ferroelectric Ba(Sn_0.15Ti_0.85)O₃ (BTS) thin films were deposited on LaNiO₃-coated silicon substrates via a sol-gel process. Films showed a strong (1 0 0) preferred orientation depending upon annealing temperature and concentration of the precursor solution. The dependence of dielectric and ferroelectric properties on film orientation has been studied. The leakage current density of thin films at 100 kV/cm was 7 × 10⁻⁷ A/cm² and 5 × 10⁻⁵ A/cm² and their capacitor tunability was 54 and 25% at an applied field of 200 kV/cm (measurement frequency of 1 MHz) for the thin films deposited with 0.1 and 0.4 M spin-on solution, respectively. This work clearly reveals the highly promising potential of BTS compared with BST films for application in tunable microwave devices.     

Distribution of pyrochlore phase in Pb(Mg1/3Nb2/3)O3-PbTiO3 films and suppression with a Pb(Zr0.52Ti0.48)O3 interfacial layer

Thin films of the relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) on Pt/Ti/SiO₂/Si (Pt/Si) substrates both with and without a Pb(Zr_0.52Ti_0.48)O₃ (PZT) interfacial layer were investigated. Perovskite and pyrochlore coexistence was observed for PMN-PT thin films without a PZT interfacial layer. Interestingly, most of the pyrochlore phase was observed in single-coated films and in the first layer of multi-coated films. The pyrochlore phase exhibited grains with an average size of about 25 nm, which is smaller than those of the perovskite phase (about 90 nm). In contrast, for PMN-PT thin films grown on a PZT interfacial layer, the formation of a pyrochlore phase at the interface between PMN-PT layers and the substrate is completely suppressed. Moreover, small grains are not observed in the films with a PZT interfacial layer. The measured polarization-electric field (P-E) hysteresis loops of PMN-PT films with and without PZT layers indicate that enhanced electrical properties can be obtained when a PZT interfacial layer is used. These enhanced properties include an increase in the value of remanent polarization P_r from 2.7 to 5.8 μC/cm² and a decrease in the coercive field E_c from 60.5 to 28.0 kV/cm.     

Lead-free piezoelectric thin films of Mn-doped NaNbO3-BaTiO3 fabricated by chemical solution deposition

Lead-free piezoelectric thin films of NaNbO₃-BaTiO₃ were fabricated on Pt/TiO_x/SiO₂/Si substrates by chemical solution deposition. Perovskite NaNbO₃-BaTiO₃ single-phase thin films with improved leakage-current and ferroelectric properties were prepared at 650 °C by doping with a small amount of Mn. The 1.0 and 3.0 mol% Mn-doped 0.95NaNbO₃-0.05BaTiO₃ thin films showed slim ferroelectric P-E hysteresis and field-induced strain loops at room temperature. The 1.0 and 3.0 mol% Mn-doped 0.95NaNbO₃-0.05BaTiO₃ films showed remanent polarization values of 6.3 and 6.2 μC/cm², and coercive field of 41 and 55 kV/cm, respectively. From the slope of the field-induced strain loop, the effective piezoelectric coefficient (d₃₃) was found to be 40-60 pm/V.