Preparation of Pb0.98La0.02(Zr0.65Ti0.35)O3 films and their fine patterning

The photosensitive lanthanum-doped lead zirconate titanate (PLZT) gel films were prepared by chemical modification with acetylacetone (AcAcH), and their fourier transform infrared (FT-IR) spectra and ultraviolet visible (UV-Vis) spectra were measured. The results show that the chelate rings of AcAcH with Ti or Zr are formed in the PLZT gel films. With irradiation of UV light, the chelate rings are photolyzed, and lead to a change of the solubility of the PLZT gel films in methanol. Transmission electron microscope (TEM) observations show that the perovskite phase is crystallized in PLZT thin film after heat treatment at 700 °C, whose grain sizes are less than or equal to 60 nm. The PLZT thin films exhibited hysteresis loops and good fatigue properties.     

Polarization fatigue and photoinduced current in (Pb0.72La0.28)Ti0.93O3 buffered Pb(Zr0.52Ti0.48)O3 films on platinized silicon

We report a study on the fatigue behavior of Pb(Zr_0.52Ti_0.48)TiO₃ (PZT) films deposited on Pt/Ti/SiO₂/Si substrates by a sol-gel method with single- and double-sided (Pb_0.72La_0.28)Ti_0.93O₃ (PLT) buffer layers, with an attempt to clarify the role of the top and bottom PLT buffer layers on the fatigue endurance (FE) of the PZT films. It is revealed that the existence of the PLT buffer layer and the level of driving alternating-current electric switching field strongly influence the fatigue properties. In terms of the existence of an asymmetric built-in electric field near the top and bottom interfaces between the film and metal electrode, we explain the observed fatigue properties.     

Structure and dielectric performance of K-doped (Pb0.5Ba0.5)ZrO3 thin films

In the present investigation (Pb_0.5Ba_0.5)ZrO₃ (PBZ) thin films doped by K (KPBZ) from 0 to 5 mol% were successfully deposited on Pt-buffered silicon substrates by a sol-gel method. The K content dependence of microstructure and electrical properties of KPBZ thin films were studied in detail. It was found that, although all the films displayed a pure perovskite structure without obvious difference, the surface roughness of KPBZ films was decreased with increasing K content. Dielectric measurements showed that the figure of merit (FOM) values of KPBZ thin films were greatly increased by K-doping, and at the same time that the temperature-dependent stability was also improved. Thus, K doping is a promising way to optimize the overall electrical properties of PBZ thin films for potential application in tunable devices.     

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.     

The optical properties of Bi3.25La0.75Ti3O12 thin films with different thickness prepared by chemical solution deposition

Bi_3.25La_0.75Ti₃O₁₂(BiLT) thin films with different thickness were successfully deposited onto fused quartz by chemical solution deposition. X-ray diffraction analysis shows that BiLT thin films are polycrystalline with (0 0 2)-preferred orientation. The dispersion of refractive indices of the BiLT thin films was investigated by the optical transmittance spectrum. The optical band gap energy was estimated from the graph of (hνα)² versus hν. The results show that the refractive index and band-gap energy of the BiLT thin films decrease with the films thickness.     

Stress-induced shifting of the morphotropic phase boundary in sol-gel derived Pb(Zr0.5Ti0.5)O3 thin films

The structure evolution of Pb(Zr_0.5Ti_0.5)O₃ thin films with different thicknesses on the Pt(1 1 1)/Ti/SiO₂/Si substrates has been investigated using X-ray diffraction and Raman scattering. Differing from Pb(Zr_0.5Ti_0.5)O₃ bulk ceramic with a tetragonal phase, our results indicate that for PZT thin films with the same composition monoclinic phase with Cm space group coexisting with tetragonal phase can appear. It is suggested that tensile stress plays a role in shifting the morphotropic phase boundary to titanium-rich region in PZT thin films. The deteriorated ferroelectric properties of PZT thin films can be attributed mainly to the presence of thin non-ferroelectric layer and large tensile stress.     

Insulating properties of rapid thermally processed Bi2Ti2O7 thin films by a chemical solution decomposition technique

Crack-free Bi₂Ti₂O₇ thin films on silicon substrates were prepared using chemical solution decomposition technique, and then treated by rapid thermal annealing. The microstructure of the films was studied by scanning electron microscopy. The effects of different fabricating procedures and various annealing temperatures and times on the leakage current density were investigated. The results show that the leakage current density decreases with increasing annealing temperature, while increases with increasing annealing time. Annealing temperature has a much stronger effect on the insulating properties of Bi₂Ti₂O₇ thin films than that of annealing time.     

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.     

Microgeometry effect on the properties of Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 ferroelectric ceramics

Porous Pb_0.99(Zr_0.95Ti_0.05)_0.98Nb_0.02O₃ ferroelectric ceramics with different pore size were prepared by solid-state sintering in air. The microstructural effect on the properties has been systematically investigated by SEM, ferroelectric hysteresis, strain-electric field curves and breakdown strength measurements. The results demonstrate that the microgeometry has a subtle effect on the ferroelectric and dielectric properties. However, the results also demonstrate that the electric field induced strain and the dielectric breakdown strength decreases with the increase of pore size.     

Quantitative dependence of the properties of Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 ferroelectric ceramics on porosity

Porous Pb_0.99(Zr_0.95Ti_0.05)_0.98Nb_0.02O₃ ferroelectric ceramics with a pore size of the order of the crystalline grain size were prepared and the microstructure and the properties were investigated. Based on this microstructure, the net porosity of the ceramics can be attributed to the intentionally introduced extrinsic porosity and thus the quantitative dependence of ferroelectric and dielectric properties of the ceramics on the porosity can be established respectively. A good agreement with experimental measurements was obtained. Our work represents the first attempt to tailor the properties of ferroelectric ceramics via varying the porosity from the viewpoint of application.     

Effect of annealing ambient on structure and ferroelectric properties of Pb(Zr0.4Ti0.6)O3 thin films on LaNiO3 coated Si substrates

Pb(Zr_0.4Ti_0.6)O₃ [PZT(40/60)] thin films were deposited onto LaNiO₃ (LNO) coated Si substrates by sol-gel technique. Three kinds of gases, air, O₂ and N₂, were used as the annealing ambient. The effect of the annealing ambient on their structure and ferroelectric properties was investigated. The results showed that both the films annealed in air and O₂ were the complete perovskite phase with (1 0 0) preferential orientation, while those annealed in N₂ were random orientation including some pyrochlore phases. As compared with the air ambient, either too much O₂ or too much N₂ was detrimental to the ferroelectric properties of PZT films. The difference in structure and ferroelectric properties was mainly associated with the intermediate phases and the concentration of domain pinning centers in the films.     

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.     

Electrical properties tailoring in Ni-particle-dispersed (Ba0.95Ca0.05)(Ti0.96Zr0.04)O3 composites

Ni-particle-dispersed (Ba_0.95Ca_0.05)(Ti_0.96Zr_0.04)O₃ (BCTZ/Ni) piezoceramic composites were prepared via sintering at 1300 °C in industrial N₂ gas. Structural characterizations showed that the metallic Ni was not oxidized and the BCTZ preserved the perovskite structure. The Ni particles were uniformly distributed in the BCTZ ceramic matrix. The relative dielectric constant ?_r of the BCTZ/Ni composites increased from 1362 to 3910 with increasing Ni content from 0 to 20 vol.%, which is explained by the Maxwell equation as well as the micro-capacitor model. The percolation theory of insulator–metal transitions is also applied to correlate the rapid increase of dielectric constant with Ni content. The piezoelectric constant d₃₃ gradually decreased from 230 to 50 pC N⁻¹, giving a gradient profile of piezoelectric property. We demonstrate that the electrical properties can be effectively tailored by dispersing metal particles into piezoceramics.     

Room temperature multiferroic properties of (Bi0.95La0.05)(Fe0.97Mn0.03)O3/NiFe2O4 double layered thin film

(Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film was prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. X-ray diffraction and Raman scattering spectroscopy studies confirmed the formation of the distorted rhombohedral perovskite and the inverse spinel cubic structures for the (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film. The (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film exhibited well saturated ferromagnetic (2 M_r of 18.1 emu/cm³ and 2H_c of 0.32 kOe at 20 kOe) and ferroelectric (2P_r of 60 μC/cm² and 2E_c of 813 kV/cm at 866 kV/cm) hysteresis loops with low order of leakage current density (4.5 × 10⁻⁶ A/cm² at an applied electric field of 100 kV/cm), which suggest the ferroelectric and ferromagnetic multi-layers applications in real devices.     

Resistive hysteresis in BiFeO3 thin films

Capacitor-like Au/BiFeO₃/SrRuO₃ thin film with (1 1 1) orientation was grown on the SrTiO₃ (1 1 1) substrate by radio frequency magnetic sputtering. It shows a resistive switching behavior, where a stable hysteresis in current–voltage curve was well developed by applying an optimum voltage at room temperature, and it reached the saturation at a bias voltage of 8 V. The Child's law in V_max → 0 direction and the interface-limited Fowler–Nordheim tunneling in 0 → V_max direction, together with the polarization reversal in the BiFeO₃ barrier, are shown to involve in the observed resistive hysteresis.     

Preparation and super-hydrophilic properties of TiO2/SnO2 composite thin films

SnO₂-TiO₂ composite thin films were fabricated on soda-lime glass with sol-gel technology. By measuring the contact angle of the film surface and the degradation of methyl orange, we studied the influence of SnO₂ doping concentration, heat-treatment temperature and film thickness on the super-hydrophilicity and photocatalytic activity of the composite films. The results indicate that the doping of SnO₂ into TiO₂ can improve their hydrophilicity and photocatalytic activity, and the composite film with 1-5 mol% SnO₂ and heat-treated at 450°C is of super-hydrophilicity. The optimal SnO₂ concentration for the photocatalytic activity is 10 mol% and larger film thickness is helpful to reduce the contact angle of the composite films.     

2D spinodal phase-separated TiO2 films prepared by sol-gel process and photocatalytic activity

For the purpose of obtaining oxide thin films with high photocatalytic activity, we have successfully prepared the TiO₂ anatase polycrystalline films with a two-dimensional spinodal phase-separated structure (2D-SPSS) in micron size by the sol-gel dip-coating method from a titanium tetraisopropoxide solution containing polyoxyethylene(20) nonylphenyl ether. It has been also found that TiO₂ films with a variety of morphologies in addition to the 2D-SPSS can be formed by controlling the molar ratio of water to titanium tetraisopropoxide. The methylene blue photodegradation activity of the 2D-SPSS TiO₂ film was higher than that of dense TiO₂ film prepared from a TiO₂ sol without co-existing polymer. This fact can be interpreted in terms of possessing a high specific surface area available for the photocatalytic reaction.     

A study on the electrical properties of Pb(Zr, Ti)O3 thin films crystallized by the electrical resistive heating of Pt thin film

The electrical properties of Pb(Zr, Ti)O₃ thin films annealed by Pt thin film heater were investigated. By the thin film heater, we successfully crystallized Pb(Zr, Ti)O₃ thin films at a high temperature above 750 °C in a few seconds. The thin film heater has some advantages, such as a low thermal budget, little Pb-loss and enhanced surface morphology compared with the conventional furnace because it has a fast heating rate. The electrical properties of the Pb(Zr, Ti)O₃ thin film crystallized by thin film heater improved considerably comparing to those crystallized in conventional furnace. The remanent polarization, breakdown field, and leakage current density measured to be 22.7 μC/cm², 853 kV/cm, and 6.93 × 10⁻⁷ A/cm², respectively.     

Luminescent properties of Gd2Ti2O7: Eu phosphor films prepared by sol-gel process

Gd₂Ti₂O₇: Eu³⁺ thin film phosphors were fabricated by a sol-gel process. X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 800 °C and the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free phosphor films were obtained, which mainly consisted of grains with an average size of 70 nm. The doped Eu³⁺ showed orange-red emission in crystalline Gd₂Ti₂O₇ phosphor films due to an energy transfer from Gd₂Ti₂O₇ host to them. Both the lifetimes and PL intensity of the Eu³⁺ increased with increasing the annealing temperature from 800 to 1000 °C, and the optimum concentrations for Eu³⁺ were determined to be 9 at.%. of Gd³⁺ in Gd₂Ti₂O₇ film host.     

Thickness effect on electrical properties of Pb(Zr0.52Ti0.48)O3 thick films embedded with ZnO nanowhiskers prepared by a hybrid sol-gel route

Silicon-based lead zirconate titanate thick films embedded with zinc oxide nanowhiskers (ZnO_w-PZT) were prepared by a hybrid sol-gel route. ZnO_w-PZT films with thickness from 1.5 μm to 4 μm are perovskite structure and have smooth surface without any cracks. As the thickness increases, the remanent polarization and dielectric constant increase, but the coercive field and tetragonality decrease. Compared with PZT films, the ZnO_w-PZT film has the close tetragonality and electrical properties which are different from those of bulk PZT-based ceramic doped with ZnO powder. The thickness dependences of the ferroelectric and dielectric properties are attributed to the relaxation of internal stress.