F. Craciun

Oriented PbZrxTi1−xO3 thin films obtained at low substrate temperature by pulsed laser deposition

One step deposition of oriented thin films of PbZrxTi1−xO3 onto (100)- and (111)-Si substrates by pulsed laser ablation at low substrate temperatures (375°C) is reported. X-ray diffraction analysis showed that the films grew with preferential (111) orientation on both substrates but energy dispersive spectroscopy revealed different compositions despite identical targets and substrate temperatures. Direct piezoelectric measurements showed good piezoelectric properties of the films, obtained in the absence of any subsequent poling.

Epitaxial piezoelectric PZT thin films obtained by pulsed laser deposition

Abstract Epitaxial lead zirconate–titanate (PZT) thin films with good piezoelectric properties were deposited in situ on Au(111)/Si(111) substrates with a Nd-YAG laser ablation technique. The experiments have been done at relatively low substrate temperatures. Energy dispersive spectroscopy (EDS), X-ray diffraction and SIMS were used to determine the composition, the crystallographic structure and the elemental distribution of the deposited films. All the films exhibited perovskite structures with preferential alignment of the (111) planes parallel to the film surface. Remarkable orientation has been obtained for films deposited at low substrate temperatures, with only very small amounts of non-piezoelectric pyrochlore phase. This is very important for deposition on semiconducting substrates, in order to avoid high temperature stresses and microcracking. Direct measurements revealed good piezoelectric properties in the absence of any subsequent poling, due to the intrinsic orientation of the films.

Piezoelectric thin films: Processing and properties

Publisher Summary This chapter reviews the available experimental and theoretical studies of piezoelectric thin films. The most important techniques of deposition are presented, with emphasis on the particular growth conditions for obtaining piezoelectric thin films of high technological interest. Piezoelectric materials can be classified according to different criteria. Usually they are divided into 70 polar piezoelectric materials and nonpolar piezoelectric materials. Polar materials are also called “pyroelectric” because they show production of electric charge as a consequence of uniform heating. Among the 20 non-centrosymmetric piezoelectric classes, 10 have a spontaneous polarization. Polar materials can be classified as ferroelectrics and nonferroelectrics. From the applications point of view the most important piezoelectrics belong to the ferroelectric class. In ferroelectrics the piezoelectric effect is produced by a variation of the intrinsic net dipole moment as a consequence of an applied stress. The large piezoelectric response in these materials is mainly because of the large relative displacement of cationic and anionic sublattices induced by the macroscopic strain.

Reactive pulsed laser deposition of piezoelectric and ferroelectric thin films

Abstract Piezoelectric (ZnO) and ferroelectric (PZT) thin films were deposited on different substrates (Au coated Si, Al 2 O 3 Corning glass etc.) by reactive pulsed laser deposition, by using a pulsed Nd-YAG laser. ZnO films were deposited starting from high purity Zn plates while the PZT films were obtained from sintered targets, in different deposition conditions. The influence of the process parameters on the physical and chemical properties of the deposited films was analyzed by SIMS, XPS, XRD, SEM and TEM. XRD analysis showed that the ZnO films were c-axis oriented, while SEM on cross-sections showed evidence of a columnar structure. On PZT thin films XRD showed evidence of a crystalline pseudo-perovskite structure with (111) orientation, while surface and cross-section SEM studies showed evidence of a compact round grain structure. Electrical measurements on both ZnO and PZT films found good piezoelectric coefficients. The ferroelectric properties of the PZT films have been characterized by a Sawyer-Tower circuit. Samples of ZnO and PZT were selected and employed in the construction of acceleration sensor and bulk acoustic wave (BAW) devices. Results on frequency response and sensitivity of constructed devices as well as electroacustical characteristics are presented and discussed.

Influence of the radiofrequency plasma beam addition on the properties of pulsed laser deposited films

The modifications of microstructure and of physical properties induced by the use of an additional radiofrequency beam discharge during the pulsed laser deposition (PLD) process has been investigated for different classes of materials. The materials concerned are piezoelectric oxides (ZnO), gate dielectric oxides (ZrO2), ferroelectric oxides (BaTiO3), ferroelectric relaxors (Pb1-xLax)(Zr0.65Ti0.33)O3 (PLZT) with variable La contents, respectively. Using a special configuration of the radio frequency discharge, a beam of excited and/or ionized oxygen species was produced and directed towards the substrate. RF plasma excited species identified in the spectra and impinging the substrate surface are very reactive at the surface with metals ions, neutral and sub-oxides which arrive from the laser plasma, with respect to discharge-off conditions. Thus, the RF plasma contribution is very important between the laser pulses, especially in the early after-pulse stages, when the surface of the fresh deposited film is not completely stabilized. A parametric study has been performed to evidence the corroborative effects induced by RF beam and other parameters as laser wavelength (265 nm, 355 nm, 530 nm and 1060 nm), laser fluence (2 - 25 J/cm2), oxygen pressure (0.2 - 0.8 mbar), substrate temperaeture (RT-650°C) on the composition and crystallinity and on dielectric and ferroelectric properties.

High Permittivity (1 - x)Ba(Zr(0.2)Ti(0.8))O3 - x(Ba(0.7)Ca(0.3))TiO3 (x = 0.45) Epitaxial Thin Films with Nanoscale Phase Fluctuations.

Epitaxial (1 - x)Ba(Ti0.8Zr0.2)TiO3 - x(Ba0.7Ca0.3)TiO3, x = 0.45 (BCZT 45), thin films have been deposited on (001) SrTiO3 (STO) and (001/100) SrLaAlO4 (SLAO) substrates by pulsed laser deposition. X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) confirmed the epitaxial growth of the films. A high structural quality has been evidenced for the BCZT/STO films. Geometric phase analysis (GPA) associated with the HRTEM enabled us to obtain microstrain analysis and the in-plane and out-of-plane lattice parameter variation on different areas. Tetragonality ratio fluctuations at nanoscale level which are relevant for the existence of nanodomains have been evidenced on the BCZT/STO films. The in-plane dielectric constant has been measured on interdigital electrodes deposited by lift-off technique on the top of the films. High values of dielectric permittivity (>3000) combined with low dielectric loss (<0.01) are obtained for BCZT 45 film deposited on STO substrate, showing nearly constant values between 1 kHz and 10 MHz. The high dielectric permittivity of BCZT thin films was attributed to their high structural quality and to the loss of rotation stability of the polarization associated with the presence of nanodomains. This results into a divergence of fluctuations of polarization direction and a peak of dielectric susceptibility. The enhanced switching of such nanodomain configuration was probed by piezoforce microscopy, by writing and reading domains during topography scanning.

Joining Chemical Pressure and Epitaxial Strain to Yield Y-doped BiFeO3 Thin Films with High Dielectric Response.

BiFeO3 is one of the most promising multiferroic materials but undergoes two major drawbacks: low dielectric susceptibility and high dielectric loss. Here we report high in-plane dielectric permittivity (ε’ ∼2500) and low dielectric loss (tan δ < 0.01) obtained on Bi0.95Y0.05FeO3 films epitaxially grown on SrTiO3 (001) by pulsed laser deposition. High resolution transmission electron microscopy and geometric phase analysis evidenced nanostripe domains with alternating compressive/tensile strain and slight lattice rotations. Nanoscale mixed phase/domain ensembles are commonly found in different complex materials with giant dielectric/electromechanical (ferroelectric/ relaxors) or magnetoresistance (manganites) response. Our work brings insight into the joined role of chemical pressure and epitaxial strain on the appearance of nanoscale stripe structure which creates conditions for easy reorientation and high dielectric response, and could be of more general relevance for the field of materials science where engineered materials with huge response to external stimuli are a highly priced target.

Ferroelectric thin films deposited by pulsed laser deposition

Influence of substrate and electrode on the properties of PbZr0.53Ti0.47O3 (PZT) thin films grown by pulsed laser deposition technique (1060 nm wavelength Nd:YAG laser light, 10 ns pulse duration, 10 Hz repetition rate, 0.35 J/pulse, 25 J/cm2 laser fluence, deposition rate about 1 angstrom/pulse) was studied. The substrate temperatures were in the range 380 degree(s)C-400 degree(s)C. Oriented crystalline PZT layers with 1-3 micrometers thickness were deposited on glass substrates plated with Au/Pt/NiCr electrodes, from a PZT commercial target in oxygen reactive atmosphere. The deposited PZT films with perovskite structure were preferentially oriented along the (111) direction as revealed from XRD spectra. Piezoelectric d33 coefficients up to 30 pC/N were obtained on as deposited films. Ferroelectric hysteresis loops at 100 Hz revealed a remanent polarization of 15 (mu) C/cm2 and a coercive field of 100 kV/cm. A comparison with properties of PZT films deposited using a KrF laser and with SrBi2Ta2O9 (SBT) films is reported.

Impact of thickness variation on structural, dielectric and piezoelectric properties of (Ba,Ca)(Ti,Zr)O 3 epitaxial thin films

It is shown that the dielectric and piezoelectric properties of Ba(Ti0.8Zr0.2)O3-x(Ba0.7Ca0.3)TiO3 (x = 0.45) (BCTZ 45) epitaxial thin films have a nontrivial dependence on film thickness. BCTZ 45 epitaxial films with different thicknesses (up to 400 nm) have been deposited on SrTiO3 by pulsed laser deposition and investigated by different combined techniques: conventional and off-axis X-ray diffraction, high resolution transmission electron microscopy and dielectric and piezoforce microscopy. The changes occurring in epitaxial films when their thickness increases have been attributed to a partial relaxation of misfit strain, driving the induced tetragonal symmetry in very thin films to the original rhombohedral symmetry of the bulk material in the thickest film, which influences directly and indirectly the dielectric and piezoelectric properties.

Multifunctional Oxides Obtained by PLD: Applications as Ferroelectric and Piezoelectric Materials

In this chapter we provide an overview of the results obtained on both lead based and lead free ferroelectric thin films deposited by PLD, in relation with the actual scientific and economic tendencies. There is an increasing trend to replace or to reduce the use of toxic elements such as lead, but there is no obvious complete solution for this problem, both types of multifunctional oxides having attractive properties. The perovskite materials, ABO3 oxides, environmental-friendly or not, will continue to be studied and their properties enhanced through different methods. Moreover, based on these properties (piezoeletric, ferroelectric, transport, optical or magnetic), new functionalities of the material can be added or modified with the help of material nanostructuring techniques. Properties of lead based oxides thin films such as PLZT and PMN-PT were investigated. PLZT thin films with different compositions have interesting dielectric and electro-optic behaviour. The effect of self-polarization in thin PMN-PT relaxor films could be of interest for pyrosensors and other applications based on the pyroelectric effect. As regarding the lead-free oxide materials, the obtaining and the characterisation of SBN and NBT-BT thin films will be presented. For the SBN thin films, the resulting value of the electro-optic coefficient r eff was calculated to be higher than the values reported for LiNbO3. Having a rather high Curie temperature, of 128 °C, compared to the higher Sr content compositions, the SBN:50 thin films can be potentially used in electro-optic devices operating near room temperature. Solid-solution systems (1−x)NBT-xBT based on Na0.5Bi0.5TiO3 (NBT) and BaTiO3 (BT) were investigated: for compositions situated at the morphotropic phase boundary between rhombohedral and tetragonal phase, high piezoelectric coefficient values and huge electric field-induced strain have been obtained.