Magnetic field induced ferroelectric and dielectric properties in Pb(Zr0.5Ti0.5)O3 films containing Fe3O4 nanoparticles

About 1.05 µm-thick Pb(Zr_0.5Ti_0.5)O₃ (PZT) films containing Fe₃O₄ nanoparticles were deposited on LaNiO₃-coated silicon substrates through a sol-gel technique. Fe₃O₄ nanoparticles were effectively dispersed into PZT solution under the involvement of polyvinylpyrrolidone. X-ray diffraction confirmed the coexistence of PZT and Fe₃O₄ phases without other impurity phases. Scanning electron microscope revealed that the thick composite films possess well-defined and crack-free microstructure. The composite films exhibit good ferroelectric and ferromagnetic properties at room temperature. An obvious magnetodielectric effect has been demonstrated in the Pb(Zr_0.5Ti_0.5)O₃/Fe₃O₄ composite films. Magnetic field induced change in ferroelectric polarization loop may support the possible magnetoelectric coupling between PZT and Fe₃O₄ phases.     

Epitaxial growth and electrical measurement of single crystalline Pb(Zr0.52Ti0.48)O3 thin film on Si(001) for micro-electromechanical systems

We report in this work the epitaxial growth and the electrical characteristics of single crystalline Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin film on SrTiO₃(STO)-buffered Si(001) substrate. The STO buffer layer deposited by molecular beam epitaxy allows a coherent oxide/Si interface leading enhanced PZT crystalline quality. 70 nm-thick PZT (52:48) layer was then grown on STO/Si(001) by sol-gel method. X-ray diffraction demonstrates the single crystalline PZT film on Si substrate in the following epitaxial relationship: [110] PZT (001)//[110] STO (001)//[100] Si (001). The macroscopic electrical measurements show a hysteresis loop with memory window of 2.5 V at ± 7 V sweeping range and current density less than 1 μA/cm² at 750 kV/cm. The artificial domains created by piezoresponse force microscopy with high contrast and non-volatile properties provide further evidence for the excellent piezoelectric properties of the single crystalline PZT thin film.     

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.     

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.     

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.     

Magnetoelectric effect in Pb(Zr0.95Ti0.05)O3 and CoFe2O4 heteroepitaxial thin film composite

Multiferroic epitaxial films, include SrRuO₃/Pb(Zr_0.95Ti_0.05)O₃/CoFe₂O₄ has been successfully deposited on SrTiO₃ substrate by pulsed-laser deposition technique. The results show that the prepared films exhibit a single phase. The Pb(Zr_0.95Ti_0.05)O₃ (PZT) film was highly textured with (1 0 0) orientation and gives good ferroelectric properties with saturated polarization of 15 μC/cm². The magnetic coercivity of CoFe₂O₄ film on Pb(Zr_0.95Ti_0.05)O₃ has been dampened to 0.9 kOe. The anisotropic magnetically behavior of CoFe₂O₄ film was changed to isotropic by using high Zr concentrated PZT as underneath layer. Heterostructure films show a good ferromagnetic and ferroelectric coupling that lead to the large magnetoelectricity of 287 mV/cm Oe.     

Microstructures, ferromagnetic, and ferroelectric properties in polyvinylpyrrolidone-assisted CoFe2O4/Pb(Zr0.53Ti0.47)O3 multiferroic composite thick films

CoFe₂O₄/Pb(Zr_0.53Ti_0.47)O₃ (CFO/PZT) multiferroic composite thick films with different CFO mass fractions have been prepared onto Pt/Ti/SiO₂/Si substrate by a hybrid sol–gel process and spin coating technique. Polyvinylpyrrolidone (PVP) was employed to be an assistance to the sol–gel solution for enhancing the film thickness and promising a crack-free film surface. After annealing at 650 °C in air for 1 h, phase structure, microstructure, magnetic and ferroelectric properties as well as leakage current of multiferroic thick films were investigated. X-ray diffraction indicated a deeply buried distribution of CFO particles in the PZT matrix. Scanning electronic microscopes showed crack-free surfaces and a decreasing film thickness from 7.2 μm to 6.2 μm with increasing CFO content. Furthermore, the saturated magnetization and remanent magnetization were also hence increased. In addition, mass fraction of CFO in PZT matrix was also estimated from 0.36% to 4.58% according to the relationship between M _s and magnetic content. Ferroelectric hysteresis loops revealed saturated polarization (P _s) and remanent polarization (P _r) were diluted by CFO till its mass fraction rising to 1.8%. After that, polarization was increased with further increasing CFO content. Enhanced leakage was demonstrated to be partially contributed to them. A critical content of 1.8% was hence confirmed, where ferroelectric and magnetic properties can be balanced, indicating a possible stress-transferred magnetoelectric coupling effect in this composite.     

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.     

Hysteresis loops of polarization and magnetization in (BiNd0.05)(Fe0.97Mn0.03)O3/Pt/CoFe2O4 layered epitaxial thin film grown by pulsed laser deposition

(BiNd_0.05)(Fe_0.97Mn_0.03)O₃ (BNFM)/Pt/CoFe₂O₄ (CFO) layered thin film was fabricated on (100) SrTiO₃ substrate by pulsed laser deposition. BNFM, Pt, and CFO layers were epitaxially grown on the substrate. Almost no increase of leakage current due to the formation of heteroepitaxial structure was found, and well-saturated hysteresis loops in the polarization vs electric field and magnetization vs magnetic field curves coexist at room temperature. The remnant polarization and remnant magnetization values were 55 μC/cm², and 70-145 mA/m, respectively.     

Effect of working pressure on the properties of BaTiO3-CoFe2O4 composite films deposited on STO (100) by PLD

The BaTiO₃-CoFe₂O₄ (BTO-CFO) composite films were grown on SrTiO₃ (STO) (100) substrates at 750 °C under various working pressures by pulsed laser deposition. The composite film grew into a supersaturated single phase at the working pressure of 10 mTorr, BTO and CFO (00 l) oriented hetero-epitaxial films on STO (100) at 100 mTorr, and a polycrystalline composite film at 500 mTorr. The slow growth rate at high working pressure led to the phase separation in the composite film. The CFO was compressively strained along out-of-plane due to the lattice mismatch with the BTO matrix phase. The BTO-CFO composite film grown at 100 mTorr showed reversible switching of ferroelectric polarization and magnetic hysteresis with strong magnetic anisotropy.     

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.     

Laser annealing of Pb(Zr0.52Ti0.48)O3 thin films for the pyroelectric detectors

Lead zirconate titanate (Pb(Zr_0.52Ti_0.48)O₃, PZT) thin films fabricated by magnetron sputtering technique on the Pt/Ti/SiO₂/Si substrates at room temperature, were annealed by means of CO₂ laser with resulting average substrate temperature below 500 °C. The crystal structure, surface morphology and pyroelectric properties of the PZT films before and after annealing were investigated by X-ray diffraction, atomic force microscopy, and pyroelectric measurements. The results show that the annealed PZT thin film with a laser energy density of 490 W/cm² for 25 s has a typical perovskite phase, uniform crystalline particles with a size of about 90 nm, and a high pyroelectric coefficient with 1.15 × 10^− 8 Ccm^− 2 K^− 1.     

Atomic layer deposition and post-deposition annealing of PbTiO3 thin films

Lead titanate thin films were deposited by atomic layer deposition on Si(100) using Ph₄Pb and Ti(O-i-Pr)₄ as metal precursors and O₃ and H₂O as oxygen sources. The influence of the Ti : Pb precursor pulsing ratio on the film growth, stoichiometry and quality was studied at two different temperatures, i.e. 250 and 300 °C. Uniform and stoichiometric films were obtained using a Ti : Pb precursor pulsing ratio of 1 : 10 at 250 °C or 1 : 28 at 300 °C. The as-deposited films were amorphous but the crystalline PbTiO₃ phase was obtained by rapid thermal annealing at 600-900 °C both in N₂ and O₂ ambient. Thin PbTiO₃ films were visually uniform and roughness values for as-deposited and annealed films were observed by atomic force microscopy.     

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.     

Pulsed laser deposition of epitaxial ferroelectric Pb(Zr,Ti)O3 films on silicon substrates

We report on the epitaxial growth and electrical properties of Pb_0.52Zr_0.48TiO₃ (PZT) thin films deposited by Pulsed Laser Deposition (PLD) on SrTiO₃ (STO)-buffered Si(001). Previously to PZT growth, 40 nm-thick (La,Sr)MnO₃ (LSMO) layer was deposited to serve as electrical bottom electrode. The 200 nm-thick PZT film epitaxy was optimized by PLD on STO-buffered Si(001).The high contrast of stable artificially poled ferroelectric surfaces evidences the good ferroelectric properties of the PZT thin film. The structural as well as the physical properties of the PZT/LSMO/STO/Si(001) structure prove that very good quality layers have been obtained for films grown on silicon substrate.     

Magnetoelectric properties of CoFe2O4–Pb(Zr0.52Ti0.48)O3 multilayered composite film via sol–gel method

CoFe₂O₄–Pb(Zr_0.52Ti_0.48)O₃ (CFO–PZT) multilayered composite film was prepared on Pt/Ti/SiO₂/Si substrate via a sol–gel method and spin-coating technique. Results show that PZT and CFO phases exist in the composite film, calcined at 700 °C, besides substrate phase, and no obvious impurity phases can be detected. The composite film exhibits layered structure with obvious boundary between CFO and PZT films. Ferroelectric and ferromagnetic properties were simultaneously observed in the composite film, evidencing the ferroelectric and ferromagnetic properties in the composite film. The composite film exhibits both good magnetic and electric properties, as well as, magnetoelectric (ME) effect. The saturation magnetization value of the composite film is lower than that of the pure CFO film derived by the same processing as a result of the effect of the nonferromagnetic PZT layers. Ferroelectric hysteresis loops reveal that saturated polarization and remanent polarization of the composite film are lower than those of the pure PZT films. The composite film exhibits a very large ME effect, which makes the composite film attractive for technological applications as devices.     

Effects of annealing process and Mn substitution on structure and ferroelectric properties of BiFeO3 films

The BiFe_1 − xMn_xO₃ (BFMO) (x = 0.03, 0.05 and 0.07) thin films were deposited on indium tin oxide/glass substrates using a metal organic decomposition method. X-ray diffraction analysis reveals that the structure of BiFeO₃ films is distorted somewhat by Mn substitution. The leakage measurements indicate that Mn doping content is a dominant factor affecting the leakage current of BFMO films. Due to the poor crystallinity, a small remanent polarization (P_r) is observed in the BFMO_x = 0.05 thin film annealed using the conventional method. The P_r values for the sequential-layer annealed BFMO films are found to be related to the intensity of (012) peak and the content of defect complexes between the oxygen vacancies and acceptors.     

The thickness effect of Bi3.25La0.75Ti3O12 buffer layer in PbZr0.58Ti0.42O3/Bi3.25La0.75Ti3O12 (PZT/BLT) multilayered ferroelectric thin films

A series of PbZr_0.58Ti_0.42O₃ (PZT) thin films with various Bi_3.25La_0.75Ti₃O₁₂ (BLT) buffer layer thicknesses were deposited on Pt/TiO₂/SiO₂/p-Si(100) substrates by RF magnetron sputtering. The X-ray diffraction measurements of PZT film and PZT/BLT multilayered films illustrate that the pure PZT film shows (111) preferential orientation, and the PZT/BLT films show (110) preferential orientation with increasing thickness of the BLT layer. There are no obvious diffraction peaks for the BLT buffer layer in the multilayered films, for interaction effect between the bottom BLT and top PZT films during annealing at the same time. From the surface images of field-emission scanning electron microscope, there are the maximum number of largest-size grains in PZT/BLT(30 nm) film among all the samples. The growth direction and grain size have significant effects on ferroelectric properties of the multilayered films. The fatigue characteristics of PZT and PZT/BLT films suggest that 30-nm-thick BLT is just an effective buffer layer enough to alleviate the accumulation of oxygen vacancies near the PZT/BLT interface. The comparison of these results with that of PZT/Pt/TiO₂/SiO₂/p-Si(100) basic structured film suggests that the buffer layer with an appropriate thickness can improve the ferroelectric properties of multilayered films greatly.     

Structural and magnetic properties of epitaxial SnFe2O4 thin films

Epitaxial thin films of SnFe₂O₄ are deposited on sapphire substrate by ablating the sintered SnFe₂O₄ target with a KrF excimer laser (λ = 248 nm and pulsed duration of 20 ns). X-ray diffraction study reveals that SnFe₂O₄ films are epitaxial along (222) direction. The optical bandgap of SnFe₂O₄ film is estimated using transmittance vs. wavelength data and is observed to be 2.71 eV. The presence of hysteresis loop at room temperature in magnetization vs. field plot indicates the ferromagnetic behavior of the film. It is observed that the coercive field and remnant magnetization decrease with increase in temperature.     

Sputter-epitaxy and electric properties of multiferroic Bim + 1Fem-3Ti3O3m + 3 thin films

Growth conditions suitable for sputter-epitaxy of Bi_m + 1Fe_m-3Ti₃O_3m + 3 (BFTO) thin films with layered structure have been investigated. The amount of oxygen during deposition was found to be specifically essential for obtaining a good-quality thin film of BFTO with a large m. The (001) epitaxial thin films of BFTO with m of nearly 10 which is expected to retain magnetic order up to room temperature have been successfully grown on (001) SrTiO₃ substrates under the determined optimum condition. The film exhibited leakage current as low as order of 10⁻²-10⁻¹ A/m² limited by Schottky emission at the interfaces between the electrodes and the film. In addition, the film showed a ferroelectric polarization curve with Pr = 6 μC/cm² for applied field of 35 MV/m at room temperature though the curve was unsaturated. These indicate that the BFTO (m = 10) thin films are promising as multiferroics at room temperature.