X. J. Meng

Structural, ferroelectric, dielectric, and magnetic properties of BiFeO3∕Pb(Zr0.5,Ti0.5)O3 multilayer films derived by chemical solution deposition

BiFeO3∕Pb(Zr0.5,Ti0.5)O3 (BFO/PZT) multilayer films have been grown on platinum-coated silicon substrate by chemical solution deposition. The remnant polarization is about 12μC∕cm2, which is much bigger than most of pure BFO thin films. P-E measurement shows that there are more obstacles affecting the motion of the domain wall in the multilayer films than those in the pure PZT films. This conclusion is also confirmed by measuring the dependence of capacitance with ac field under subswitching field. The frequency dependence of dielectric loss indicates that the dielectric loss (tanδ) of the multilayer is smaller than that of the PZT thin films at high frequency. Magnetic measurement indicates that the multilayer films are antiferromagnetic.

Dielectric responses and scaling behaviors in Aurivillius Bi6Ti3Fe2O18 multiferroic thin films

Dielectric responses and scaling behaviors of Aurivillius Bi6Ti3Fe2O18 (BTF2) multiferroic thin films were systemically detailed by the temperature-dependent dielectric/impedance spectroscopy. We clarified two dielectric relaxation processes presented in grain interior of the BTF2 films. One relaxation below ∼500 K was proposed to associate with the localized hopping process of carrier between Fe3+ and Fe2+ inside the grains. Another one above ∼500 K arose from the long-range movement of oxygen vacancies. The scaling behaviors implied that the distribution of relaxation times for oxygen vacancies was temperature independent while the dynamical processes for the hopping carriers presumably depended on temperature.

Low-temperature preparation of highly (100)-oriented Pb(ZrxTi1−x)O3 thin film by high oxygen-pressure processing

A method for thin-film fabrication employing high oxygen-pressure processing (HOPP) was developed. With this method, the highly (100) oriented Pb(ZrxTi1−x)O3 (PZT) thin film was fabricated at temperature as low as 400°C. HOPP is compatible to the ferroelectric PZT film integration with a readout integrated circuit. The sol-gel-derived PZT 50∕50 thin film showed a well-saturated hysteresis loop at an applied electric field of 367kV∕cm with Pr and Ec of 45μC∕cm2 and 121kV∕cm, respectively. Large electric leakage was attributed to remnant organic components, which was demonstrated by sputtered organic-free PZT films. The optimized Pr and Ec are of 26μC∕cm2 and 93kV∕cm under an applied electric field of 400kV∕cm.

Hopping conduction and low-frequency dielectric relaxation in 5mol% Mn doped (Pb,Sr)TiO3 films

The highly (00l)-oriented 5 mol % Mn doped Pb0.5Sr0.5TiO3 films with remarkable ferroelectric properties (2Pr=27.1 μC/cm2 and 2Ec=55.5 kV/cm) were fabricated on LaNiO3 coated silicon substrates by chemical solution deposition. The ac conductivity and the dielectric response of the films at various temperatures were studied. Hopping conduction accompanied by the dielectric relaxation at low frequencies was observed. The results can be correlated with the thermal-activated short range hopping of localized charge carriers through trap sites separated by potential barriers with different heights, i.e., localized electrons hopping between multivalence Mn sites (the activation energy of this hopping process is ∼0.4 eV), which is also established in terms of the correlated barrier hopping model.

Transition of the polarization switching from extrinsic to intrinsic in the ultrathin polyvinylidene fluoride homopolymer films

Polyvinylidene fluoride homopolymer thin films have been prepared by the Langmuir-Blodgett technique, and their electrical properties have comprehensively been studied. The polyvinylidene fluoride homopolymer films show better ferroelectricity with higher polarization and higher breakdown electric field than that of the poly(vinylidene fluoride-trifluoroethylene) copolymer films. Inspection on the thickness dependence of the coercive field of the polyvinylidene fluoride films suggests an extrinsic polarization switching occurs in the thickness range from 200 to 45 nm, and a non-extrinsic switching is observed in the range between 45 and 11 nm, which is ascribed to the transition range from extrinsic to intrinsic switching.

Electrical and optical properties of Pb(Mg1∕3Nb2∕3)O3–PbTiO3 thin films prepared by chemical solution deposition

92%Pb(Mg1∕3Nb2∕3)O3–8%PbTiO3 (PMNT) thin films have been prepared on Pt∕Ti∕SiO2∕Si substrate with a LaNiO3 (LNO) buffer layer and on sapphire substrate by a chemical solution deposition method, respectively. X-ray diffraction analysis shows that the PMNT thin films on Pt∕Ti∕SiO2∕Si substrate are polycrystalline with (110)-preferential orientation. Pt∕PMNT∕Pt capacitors have been fabricated and show a ferroelectric character with a spontaneous polarization (Ps) of 25.2μC∕cm2 and a remanent polarization (Pr) of 6.56μC∕cm2. The dielectric constant (er) and the dissipation factor (tanδ) at 1 kHz are 680 and 0.014, respectively. The band-gap energy of the PMNT thin films on the sapphire substrate was found to be about 4.03 eV by the optical transmission spectra measurement. The optical constants (n, k) of the PMNT thin films in the wavelength range of 2.5–12.6 μm were obtained by infrared spectroscopic ellipsometry measurement.

Structural and optical properties of Ba(Cox,Ti1−x)O3 thin films fabricatedby sol-gel process

Ba(Cox,Ti1−x)O3 thin films were prepared on fused quartz substrate by a sol-gel method. The results of x-ray diffraction showed that the films are perovskite phase and the change of lattice constant caused by different Co concentration is undetectable. Optical transmittance measurement indicated that Co doping has effect on the energy band structure. The energy gap of Ba(Cox,Ti1−x)O3 decreased linearly with the increase of Co concentration. It is inferred that the energy level of conduction bands decline with the Co content increasing. This result is similar to the phenomena found in binary semiconductor where the band gap decreases with the increasing of average atomic number.

Effect of Fe-doping concentration on microstructure, electrical, and magnetic properties of Pb(Zr0.5Ti0.5)O3 thin films prepared by chemical solution deposition

The highly (l00) oriented Pb(Zr0.5Ti0.5)O3 thin films with different Fe3+ doping concentrations were fabricated on LaNiO3-coated silicon substrates by chemical solution deposition. And the microstructure, ferroelectric, leakage, and magnetic properties were investigated. The results indicate that incorporation of Fe3+ into PZT thin films can promote the degree of the lattice distortion and greatly improve the surface roughness. In comparison with the pure PZT sample, the ferroelectric hysteresis loops of Fe-doped PZT samples demonstrate larger and larger polarizations and coercive fields with the increase in Fe3+ doping amount. Moreover, leakage mechanism of present films evolves from the space charge limited conduction to the “modified” space charge limited conduction, and then returns to the space charge limited conduction with increasing Fe3+ doping concentration. The occurrence of exchange bias in these Fe-doped PZT samples implies that the magnetic exchange interaction can be explained by the bound m...

Effects of Mn doping on dielectric and ferroelectric properties of (Pb,Sr)TiO3 films on (111) Pt/Ti/SiO2/Si substrates

A series of Mn doped Pb0.5Sr0.5TiO3 (PSMT) films with dopant concentrations from 0 to 10 mol % was fabricated on (111) Pt/Ti/SiO2/Si substrates by chemical solution deposition. Their microstructure, ferroelectric, and dielectric properties were investigated, and Mn doping was found to have a significant influence on the properties of (Pb,Sr)TiO3 film. The improved microstructure with increased grain size, remnant polarization, dielectric permittivity and its tunability by dc electric field, and reduced coercive field and dielectric loss was observed in the Mn doped samples. A PSMT film with 0.5 mol % Mn dopants exhibits the optimum characteristics with maximal remnant polarization (2Pr=25.28 μC/cm2), dielectric permittivity (1427) and tunability (74.5%, at 100 kHz), and minimal dielectric loss (0.015) at 1 kHz. The improvement was attributed to the improved microstructure, enhanced displacement of polar ions, and, most importantly, the suppression of oxygen-vacancy-induced ferroelectric domain pinning, wh...

Optical properties of SrTiO3 thin films deposited by radio-frequency magnetron sputtering at various substrate temperatures

SrTiO3 thin films were deposited on vitreous silica substrates at various substrate temperatures (300–700°C) by rf magnetron sputtering technique. The transition from amorphous phase to polycrystalline phase for the films occurred at the substrate temperatures of 300–400°C. Their optical properties were investigated by transmittance measurements. The fitting method was used to calculate the refractive index and the film thickness from the transparent region of the transmittance spectra. The refractive index increased and the film thickness decreased with the substrate temperatures increasing. The dispersion of the refractive index was studied by considering a single electronic oscillator model. The band gaps of the films were estimated from Tauc’s law and showed a decreasing tendency to that of the bulk SrTiO3 with the substrate temperatures increasing. These results provide some useful references for the potential application of SrTiO3 films in integrated optics devices.