Lead-free Piezoelectric Films Research Articles

Orientation Dependence of Transverse Piezoelectric Properties of Epitaxial BaTiO3 Films

The orientation dependence of the piezoelectric properties of epitaxial BaTiO3 (BTO) films was investigated. The (001), (101), and (111)-oriented BTO films of 2–2.5 µm thickness were deposited on SrRuO3/Pt/MgO or SrRuO3/SrTiO3 substrates by rf magnetron sputtering. X-ray diffraction measurements showed that (001), (101), and (111)BTO films were epitaxially grown on the substrates. The lattice parameters of each BTO film were different from those of the bulk single crystal, and the unit cell volume of the BTO films was larger than that of bulk BTO. The transverse piezoelectric coefficients e31*=d31/s11 of (001)BTO films was almost independent of applied electric field, whereas e31* of (111)BTO increased with voltage owing to the domain motion. The piezoelectric properties of (101)BTO films strongly depended on the in-plane alignment of the crystal structure, and a relatively large e31* of -1.3 C/m2 could be achieved by enhancement of the domain motion. Although the absolute values of e31* are smaller than theoretical calculation values, we could demonstrate that the optimization of crystal orientation is effective for enhancing BTO-based lead-free piezoelectric films.

Properties of (K,Na)NbO 3-based lead-free piezoelectric films prepared by pulsed laser deposition

To investigate the properties of (K,Na)NbO 3-based lead-free piezoelectric films at the morphotropic phase boundary composition, we fabricated epitaxial [(K 0.5Na 0.5) 0.97Li 0.03] (Nb 0.8Ta 0.2)O 3 films on (001), (110) and (111)-oriented single crystal SrTiO 3 substrates by pulsed laser deposition. The structure and electrical properties of the films were studied. Dielectric constants of 540, 390 and 300 and remnant polarizations of 4.00, 1.05, and 0.35 μC/cm 2 were observed for the (001), (110) and (111) oriented films, respectively.

Piezoelectric K0.5Na0.5NbO3 thick films derived from polyvinylpyrrolidone-modified chemical solution deposition

Lead-free K0.5Na0.5NbO3 (KNN) ferroelectric films with enhanced thickness of 3.5 μm were prepared by a polyvinylpyrrolidone-modified chemical solution deposition method. A single perovskite phase with a dense morphology and (100) orientation was obtained at relatively low annealing temperature of 600 °C. A large effective piezoelectric coefficient d33, of 61 pm/V was demonstrated at 100 kHz without considering the substrate clamping effect. A well-saturated polarization hysteresis loop was obtained with a high remnant polarization Pr of 16.4 μC/cm2. These results showed that KNN is a promising lead-free piezoelectric film candidate, and that crystallizing the film at low processing temperature to obtain (100) orientation and dense morphology is critical to achieving excellent ferroelectric and piezoelectric properties.

CHEMICAL SOLUTION DEPOSITION AND ELECTRICAL PROPERTIES OF (100)-PREDOMINANT BaTiO3 THICKER FILMS

ABSTRACT Lead-free piezoelectric films with thickness larger than 1 μm integrated on silicon substrate have been receiving considerable attention for environmental concern and potential applications in micro-electro-mechanical systems. By chemical solution deposition, it is possible to process (100)-predominant 1 μm BaTiO3 films on LaNiO3/Pt/TiO x /SiO2/Si substrates by using the same thinner high crystallinity columnar films as buffer layers. We point out that this kind of buffer layer on the surface of LaNiO3/Pt electrode is effective to enhance the crystallinity and orientation degree of the BaTiO3 films. The 1 μm BaTiO3 films showed good dielectric and insulative characteristic against applied field. Also, the (100)-predominant 1 μm BaTiO3 films have excellent piezoelectric properties, piezoelectric coefficients d 33 higher than 50 pm/V have been detected by the atomic force microscope on the bare films, which is comparable to that of Pb(Zr,Ti)O3 films. These results indicate that the highly (100)-oriented BaTiO3should be a promising candidate as the lead-free piezoelectric films for micro-electro-mechanical systems applications.

Electrical properties of (1 0 0)-predominant BaTiO 3 films derived from alkoxide solutions of two concentrations

Lead-free piezoelectric films with thickness larger than 1 μm integrated on silicon substrates have been receiving considerable attention because of environmental concerns and their potential applications in microelectromechanical systems. We demonstrate that, by chemical solution deposition, it is possible to process (1 0 0)-predominant 1 μm BaTiO 3 films on LaNiO 3/Pt/TiO x /SiO 2/Si substrates using thinner high-crystallinity columnar BaTiO 3 films as buffer layers. We point out that this kind of buffer layer prepared with a lower concentration solution on the surface of an LaNiO 3/Pt electrode is effective in enhancing the crystallinity and orientation degree of final BaTiO 3 films prepared with a higher concentration solution. The 1 μm BaTiO 3 films show good dielectric and insulating characteristics against an applied field, and the conduction current shows Schottky emission behavior at modest voltage and space-charge-limited behavior at higher voltage. We also demonstrate that the (1 0 0)-predominant 1 μm BaTiO 3 films have excellent piezoelectric properties: piezoelectric coefficients d 33 higher than 50 pm/V have been determined for the bare films using atomic force microscopy, which are comparable to those of Pb(Zr,Ti)O 3 films. These results indicate that the (1 0 0)-predominant BaTiO 3 films should be promising candidates for microelectromechanical systems applications.

Development of Lead-Free Piezoelectric Thick Films with a/b-Axis-Oriented Bi<sub>4-x</sub>Pr<sub>x</sub>Ti<sub>3</sub>O<sub>12</sub>

Pr-substituted Bi4Ti3O12 (BPT, Bi4-xPrxTi3O12, x=0.1-0.4) polycrystalline thick films with a-/b-axes orientations and thickness of 2-3 μm were grown on sputter-grown IrO2 layers by chemical solution deposition method for developing lead-free piezoelectric film microdevices. Electric-field-induced strains measurements were performed by double-beam laser displacement meter and longitudinal strain of e=0.25 % under 400 kV/cm and piezoelectric coefficient d33=63 pm/V at 10 Hz were observed in BPT thick film of x=0.1 with a-/b-axes mixed orientations. The value of strain closely related to spontaneous polarization and monotonously decreased with increasing x. Microstructures of 3 μm-thick BPT films were fabricated by photolithography and dry etching processes with several tens micrometers in size.