J. L. Sun

PbZr0.5Ti0.5O3/La0.5Sr0.5CoO3 heterostructures prepared by chemical solution routes on silicon with no fatigue polarization

PbZr0.5Ti0.5O3/La0.5Sr0.5CoO3 (PZT/LSCO) heterostructures have been grown directly on (100)Si by chemical solution routes. Field-emission scanning electron microscopy and x-ray diffraction analysis show that PZT and LSCO thin films are polycrystalline and entirely perovskite phase. PZT thin films grown on LSCO thin films showed no preferential orientation and excellent ferroelectricity. The remnant polarization Pr is about 22.8 μC/cm2 and the coercive field Ec is about 95 kV/cm at an applied electric field of 400 kV/cm. The ferroelectric capacitor has been fabricated and showed no polarization fatigue after 3×109 fatigue cycles. The Pt/PZT/LSCO capacitor is suitable for nonvolatile random access memory application.

High electric tunability of relaxor ferroelectric Langmuir–Blodgett terpolymer films

Poly(vinylidene fluoride-trifluoroethylene-chlorofloroethylene) terpolymer films have been fabricated on Al-coated polyimide substrates using the Langmuir–Blodgett (LB) technology. The electrical properties of the films have been investigated from 150 to 350 K. The temperature of the dielectric maximum and the measured frequency obeys the Vogel–Fulcher [J. Am. Ceram. Soc. 8, 339 (1925); Phys. Z. 22, 645 (1921)] law. The electric tunabilities of the films at room temperature are 42.6% and 80% under 50 and 240 MV/m, respectively. The reasons for the high tunability are discussed based on the special microstructure of the LB films.

Temperature dependence of ferroelectric and dielectric properties of PbZr0.5Ti0.5O3 thin film based capacitors

The temperature dependence of the ferroelectric and dielectric properties of PbZr0.5Ti0.5O3 thin films deposited on LaNiO3-coated SrTiO3 substrate was investigated. The results showed that both the saturation polarization and remanent polarization increased with decreasing temperature from 300 to ∼50 K, and decreased as the temperature continued to decrease below 40 K. The capacitance of the PbZr0.5Ti0.5O3 ferroelectric thin film capacitor as a function of small ac field and temperature was measured, and the data were processed using Rayleigh law. It was demonstrated that both the reversible and irreversible contributions to the dielectric constant decreased with decreasing temperature; however, they showed an increase when the temperature dropped below 50 K. The anomalous behavior of the temperature dependence may be attributed to a phase transition in the PbZr0.5Ti0.5O3 thin film in the vicinity of 50 K.

Optical and electrical properties of highly (100)-oriented PbZr1−xTixO3 thin films on the LaNiO3 buffer layer

In this paper, using wet chemical solution deposition processes, the (100)-highly oriented LaNiO3 buffer layers were grown on both silicon and platinized silicon wafers and, sequentially, the highly (100)-oriented PbZr1−xTixO3 thin films with various compositions were obtained on them. The misfit elastic strains were found to be critical factors to determine the orientation of PZT thin films, even though the used LaNiO3 buffer layer reduces the lattice mismatch between PZT films and silicon wafers. For the PZT thin films with x=0.5 and 0.6 on the LaNiO3/platinized silicon substrate, the infrared optical constant, ferroelectric, and dielectric properties were characterized and analyzed with relation to the film orientation and the film grain size. It was found that the finite grain size effect here played a key role in determining these optical and electrical properties. With nanoferroelectric thin films, it is the most useful way of controlling both grain size and crystallographic orientation to tune perf...

Evolution of electric field amplitude dependent scaling behaviors in ferroelectric films over a broad temperature range

The evolution of the electric field amplitude (V0) dependent scaling of dynamic hysteresis area (A∝V0α) with the temperature in Mn doped (Pb,Sr)TiO3 film was analyzed. α exhibited different values under three temperature regions, where (1) the intrinsic ferroelectric domain nucleation, growth, and reversal, (2) the competition between the polar nanoregions and mobile defects, and (3) the Joule loss during long range movement of oxygen vacancies were demonstrated. This study provides a quantitative criterion to distinguish the intrinsic ferroelectric hysteresis from artificial one.

Infrared optical properties of LaNiO3–platinized silicon and PbZrχTi1−χO3–LaNiO3–platinized silicon heterostructures

Using infrared spectroscopic ellipsometry, the optical constants of LaNiO3 thin films on Pt(111)–Ti–SiO2–Si substrates are obtained in the 2.5–12.6 μm range, in which the infrared optical constants decrease when the annealing temperature increases from 600 to 650u200a°C. At the same time, the infrared optical properties of PbZrχTi1−χO3(PZT) thin films with χ=0.3 and 0.5 on LaNiO3–Pt–Ti–SiO2–Si substrates are simultaneously studied with respect to annealing temperatures. The infrared optical properties are associated closely with the grain size and crystallographic orientation of the films induced by annealing temperature, combined by the particular substrate. For the Ni–PZT–LaNiO3–Pt multilayer heterostructures, the infrared absorptance better than 99% can be achieved for PZT pyroelectric thin film infrared microsensors.

Ultraviolet-infrared optical properties of highly (100)-oriented LaNiO3 thin films on Pt–Ti–SiO2–Si wafer

The optical constants of highly (100)-oriented LaNiO3 thin films on Pt(111)-Ti–SiO2–Si substrate derived by metalorganic deposition have been obtained using spectroscopic ellipsometry techniques in the wide wavelength range from ultraviolet to far infrared. In fitting the dielectric functions of LaNiO3, two harmonic oscillators are observed, one is believed to come from the valence–conduction interband transition and the other is attributed to the transition from a donor band to the conduction. Simultaneously the frequency of plasmon is also obtained, which results from the strong electron–electron interaction. Based on these optical and electrical properties, a promising application of LaNiO3 thin films in infrared microsensors has been proposed.

Changes in the interface capacitance for fatigued lead–zirconate–titanate capacitors

From the capacitance–voltage dependence of Pt/PbZr0.5Ti0.5O3/Pt capacitors, we mathematically separated the capacitance into two parts corresponding to two regions of the samples, the uniform electric-field region and the nonuniform region. They are correlated with the bulk ferroelectric film region and the Pt/PbZr0.5Ti0.5O3 Schottky barrier interface region, respectively. The calculations based on the in-series capacitor model show a slight decrease of dielectric permitivity for the fatigued bulk films. By assuming a much smaller dielectric permitivity of the interface region than that of bulk films, it was found that the interface capacitance decreased remarkably compared with that of the bulk ferroelectric film after fatigue. This decrease was attributed to the lowering of ferroelectricity in the interface layer, which suggests that the fatigue is mainly an interface state controlled process. The asymmetricity in the interface capacitance–voltage curve is attributed to the different defect concentratio...

Ferroelectric and optical properties of Bi3.25Nd0.75Ti3O12 thin films prepared by a chemical solution method

The ferroelectric and optical properties of Bi3.25Nd0.75Ti3O12 thin films deposited on (111)Pt/Ti/SiO2/Si substrates using a chemical solution method were investigated. Bi3.25Nd0.75Ti3O12 thin films were polycrystalline and had (117) random orientation with large rod-like grains. They showed good ferroelectricity with a remnant polarization of 13.8 µC cm−2 and a coercive field of 120 kV cm−1. The dielectric constant and the dissipation factor were about 200 and 0.040, respectively, at a frequency of 10 kHz. No polarization fatigue was observed for the Pt/Bi3.25Nd0.75Ti3O12/Pt capacitor after 109 switching cycles. The optical constants (refractive index and extinction coefficient) in the wavelength range of 200–1700 nm were obtained by spectroscopic ellipsometry measurements. The optical band gap was estimated to be about 3.61 eV. The dispersion of the refractive index in the interband transition region followed the single electronic oscillator model.

Effect of hydrolysis on properties of PbZr0.50Ti0.50O3 ferroelectric thin films derived from a modified sol–gel process

Abstract Lead zirconate titanate PbZr0.50Ti0.50O3 (PZT) ferroelectric thin films were successfully deposited on Pt(1xa01xa01)/Ti/SiO2/Si substrates by a modified sol–gel method using zirconium nitrate as a substitute for the conventional zirconium alkoxide. The precursor solutions were hydrolyzed with different H2O/Pb ratios. The effect of hydrolysis ratios of the solution on the microstructure for the PZT thin films were investigated via X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. The XRD results show that the PZT films exhibit (1xa01xa01)-orientation and the degree of the (1xa01xa01)-orientation decreases with the increase of hydrolysis ratio. These results indicate that the ferroelectric behavior can be improved by an appropriate choice of H2O/Pb ratio.