Aiying Wu

Domain populations in lead zirconate titanate thin films of different compositions via piezoresponse force microscopy

Pb (ZrxTi1−x)O3 (PZT) thin films with (111) texture were deposited onto commercially available Pt/Ti/SiO2/Si substrates via the sol–gel technique. Piezoforce microscopy (PFM) was then used to analyse the evolution of domain populations as a function of the Zr content x. Domain structures of virgin films, local piezoelectric properties of individual grains and piezoelectric histograms were studied in films with different compositions (x = 0.2–0.6), which cover both the tetragonal and rhombohedral sides of the phase diagram. In films with low Zr content mainly single-domain grains were observed. As the Zr content increased, a larger fraction of polydomain grains was found. The local piezoelectric response measured inside sufficiently big grains indicated that the strongest piezoelectric effect occurs in PZT30/70 (x = 0.3) films. This was attributed to two different effects: high out-of-plane polarization achieved due to the (111) texture and influence of the dielectric constant. In tetragonal films with their lower dielectric constants the electric field seen by a ferroelectric is higher as compared to other compositions, giving rise to an apparent increase of the effective piezoelectric response measured by PFM. The analysis of the domain images indicated that sol–gel derived PZT films are slightly self-polarized near the free surface. With increasing Zr/Ti ratio, the variation of domain populations resulted in reversing the sign of the average piezoelectric response at x≈0.3. It is demonstrated that PFM histograms are extremely sensitive to PZT composition and can be used as a signature of complex domain structures in ferroelectric thin films.

Activated Solutions Enabling Low‐Temperature Processing of Functional Ferroelectric Oxides for Flexible Electronics

Functional ferroelectric oxides for flexible electronics are achieved from activated solutions enabling low-temperature processing and large-area deposition directly on polymeric substrates. This processing technology reaches the lower limit temperature of crystallization at 300 °C, using a strategy that combines seeded diphasic precursors and photochemical solution deposition. Properties of these materials are comparable to those of high-temperature-processed counterparts and organic ferroelectrics.

Processing and seeding effects on crystallisation of PZT thin films from sol-gel method☆

Abstract Lead zirconate titanate PZT ( 52 48 ) thin films on alumina substrates were prepared by the sol-gel method. In order to prepare pure perovskite phase films at lower temperature, the study of the processing conditions and of seeding effects on the crystallisation behaviour of the PZT perovskite phase was carried out by X-ray diffraction and scanning electron microscopy analysis. The obtention of the perovskite phase was seen to be highly dependent on the preparation conditions of the sols. The viscosity behaviour of the stock sols was analysed by rheological studies in order to obtain data allowing verification of the stability of the stock solutions. A considerable improvement on the crystallisation of the pure perovskite phase at lower temperatures was observed when PZT seeds were added to the sols.

Piezoforce microscopy study of lead-free perovskite Na0.5Bi0.5TiO3 thin films

As a promising lead-free ferroelectric material, Na0.5Bi0.5TiO3 (NBT) was synthesized as thin films via a classic 2-methoxyethanol sol-gel route and chemical solution deposition method. Perovskite structure with random orientation of crystallites has been obtained on platinized silicon wafer at low temperature (460°C). Piezoelectric activity in such films was detected using electrical analysis. X-ray diffraction and piezoresponse force microscopy (PFM) have been used to analyze NBT thin films with different microstructures and properties dependent on fabrication and annealing processes.

Seeding studies in PZT thin films

Lead zirconate titanate (PZT) solid solutions exhibit excellent ferroelectric, piezoelectric, pyroelectric, and electrooptical properties and, therefore, are very attractive for the electronic industry. Low-temperature thermal treatment of the films enhances the incorporation of sol-gel derived PZT thin films into integrated circuits. The nucleation temperature of the perovskite phase and the temperature to get a pure perovskite phase can be lowered using heterogeneous nucleation. In this work, thin films of PZT with a zirconium to titanium ratio of 52/48 have been prepared by the sol-gel method using metal alkoxides. Different types of crystalline seeds were used, and their effects on the perovskite phase crystallization were compared. The crystallographic and morphological properties of the films have been analyzed by X-ray diffraction and scanning electron microscopy.

Low dielectric loss BaNd2Ti5O14 thick films prepared by an electrophoretic deposition technique

BaNd2Ti5O14 (BNT) films 12–52μm thick were fabricated on platinum metallic foils by electrophoretic deposition (EPD). 52-μm-thick BNT film exhibits a dielectric constant and a loss tangent of 107 and 0.0006 (Q of 1600) at 1MHz, respectively. Variation in permittivity is less than 0.02% at a bias voltage ±8kV∕cm. Change of film permittivity with temperature (30–120°C) is below +58.5ppm∕°C, pointing to a good thermal stability. Preliminary microwave measurements indicate that the losses are not significantly increased up to the gigahertz regime. EPD derived BNT thick films on metallic foils are attractive candidates for microwave communication devices.

Nanoporous piezo- and ferroelectric thin films.

Nanoporous barium titanate and lead titanate thin films (∼100 nm calculated from ellipsometric data) are prepared starting from sol-gel solutions modified with a commercially available block-copolymer and evaporation-induced self-assembly methodology. The tuning of the thermal treatment followed by in situ ellipsometry allows the decomposition of the organic components and of the structuring agent leading to the formation of porous tetragonal crystalline perovskite structures as observed by XRD, HRTEM, SEM, and ellipsoporosimetry. Both nanoporous barium titanate and lead titanate thin films present local piezoelectric and ferroelectric behavior measured by piezoresponse force microscopy (PFM), being promising platforms for the preparation of the generation of new multifunctional systems.

Kinetic aspects of the formation of seeded lead zirconate titanate thin films

Abstract The crystallization kinetics and microstructure development of PZT thin films on platinum passivated silicon substrates prepared using different concentration of PZT seeds dispersed in PZT sols are studied. TEM analysis showed that perovskite seeds did not dissolve in the precursor sol but maintained a crystalline state before annealing. It was shown that using perovskite PZT nanopowders as seeds results in the crystallization of a single perovskite phase in the PZT film either at lower temperatures or at shorter annealing times. The seeded PZT films exhibited enhanced crystallization kinetics and the overall activation energy for the perovskite crystallization was reduced from 219 kJ/mol (unseeded) to 174 kJ/mol for 1wt% seeded PZT film and to 146 kJ/mol for 5 wt% seeded films. These results support the statement that the presence of nanometric PZT seed particles lowers the activation energy needed to reach the critical nuclei size for the crystallization process.

Structural and electrical properties of seeded lead zirconate titanate thin films

Abstract Films of lead zirconate titanate (PZT) (52/48) on platinum passivated silicon substrates were prepared from sol precursors with the addition of perovskite PZT seeds (52/48, 0–5 mol.%). The phase evolution and microstructure of the films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. The effect of seeds on the crystallization kinetics is discussed. For the different films X-ray rocking curves were constructed and the crystallographic orientation of the films is discussed, stressing the influence of seeds on the orientation of the films. Ferroelectric properties were measured and compared between films prepared with and without seeds. The addition of perovskite seeds to the PZT precursor sols induced the formation of the pure perovskite phase at lower temperatures in thin films. Although seeded films show less intense preferred orientation, they show superior ferroelectric properties over unseeded ones.

Ni and Zn doped MgTiO3 thin films: Structure, microstructure, and dielectric characteristics

The addition of low loss ilmenite impurities, can effectively tailor the dielectric properties of MgTiO3 without modifying the crystal structure. In the present study, the modification of the structural and dielectric properties of sol gel derived MgTiO3 films by doping with Ni and Zn is exploited. The change of the dielectric response and unit cell parameters of doped MgTiO3 is correlated with Ni and Zn occupancy. The temperature stability of MgTiO3 thin films is improved with doping, while the dielectric losses are aggravated with both Zn and Ni doping, which is correlated with the localized d electrons of the dopant cations. The dielectric permittivity decreased with Ni doping while it increased with Zn, which is attributed to the lower ionic polarizability of Ni2+ (1.23 A3) as in comparison with Mg2+ (1.32 A3) while Zn2+ has a higher ionic polarizability (2.04 A3).