Epitaxial PZT films for MEMS printing applications

Films of piezoelectric and ferroelectric oxides have been widely investigated for various applications, including microelectromechanical systems (MEMS) for printing. Pb(Zr,Ti)O3 is of particular interest due to its excellent piezoelectric properties. Control of the density, crystalline orientation, and compositional uniformity is essential to obtain these properties. In this article, we review recent progress on the fabrication of epitaxial Pb(Zr,Ti)O3films, in which the aforementioned control can be achieved. We discuss the different approaches used for the deposition of the epitaxial piezoelectric layer as well as the achieved degrees of the epitaxy. Furthermore, the integration of these piezoelectric layers in MEMS and the corresponding performance are discusse

Multiple-magnon excitations shape the spin spectrum of cuprate parent compounds

Thanks to high resolution and polarization analysis, resonant inelastic x-ray scattering (RIXS) magnetic spectra of La2CuO4, Sr2CuO2Cl2 and CaCuO2 reveal a rich set of properties of the spin 1/2 antiferromagnetic square lattice of cuprates. The leading single-magnon peak energy dispersion is in excellent agreement with the corresponding inelastic neutron scattering measurements. However, the RIXS data unveil an asymmetric lineshape possibly due to odd higher order terms. Moreover, a sharp bimagnon feature emerges from the continuum at (1/2,0), coincident in energy with the bimagnon peak detected in optical spectroscopy. These findings show that the inherently complex spin spectra of cuprates, an exquisite manifestation of quantum magnetism, can be effectively explored by exploiting the richness of RIXS cross sections.Comment: 7 pages, 3 figure

Self-formed LaAlO3/SrTiO3LaAlO_3/SrTiO_3 Micro-Membranes

Oxide heterostructures represent a unique playground for triggering the emergence of novel electronic states and for implementing new device concepts. The discovery of 2D conductivity at the $LaAlO_3/SrTiO_3$ interface has been linking for over a decade two of the major current research fields in Materials Science: correlated transition-metal-oxide systems and low-dimensional systems. A full merging of these two fields requires nevertheless the realization of $LaAlO_3/SrTiO_3$ heterostructures in the form of freestanding membranes. Here we show a completely new method for obtaining oxide hetero-membranes with micrometer lateral dimensions. Unlike traditional thin-film-based techniques developed for semiconductors and recently extended to oxides, the concept we demonstrate does not rely on any sacrificial layer and is based instead on pure strain engineering. We monitor through both real-time and post-deposition analyses, performed at different stages of growth, the strain relaxation mechanism leading to the spontaneous formation of curved hetero-membranes. Detailed transmission electron microscopy investigations show that the membranes are fully epitaxial and that their curvature results in a huge strain gradient, each of the layers showing a mixed compressive/tensile strain state. Electronic devices are fabricated by realizing ad hoc circuits for individual micro-membranes transferred on silicon chips. Our samples exhibit metallic conductivity and electrostatic field effect similar to 2D-electron systems in bulk heterostructures. Our results open a new path for adding oxide functionality into semiconductor electronics, potentially allowing for ultra-low voltage gating of a superconducting transistors, micromechanical control of the 2D electron gas mediated by ferroelectricity and flexoelectricity, and on-chip straintronics.Comment: 8 pages, 4 figure

Epitaxial PZT films for MEMS printing applications

Films of piezoelectric and ferroelectric oxides have been widely investigated for various applications, including microelectromechanical systems (MEMS) for printing. Pb(Zr,Ti)O3 is of particular interest due to its excellent piezoelectric properties. Control of the density, crystalline orientation, and compositional uniformity is essential to obtain these properties. In this article, we review recent progress on the fabrication of epitaxial Pb(Zr,Ti)O3films, in which the aforementioned control can be achieved. We discuss the different approaches used for the deposition of the epitaxial piezoelectric layer as well as the achieved degrees of the epitaxy. Furthermore, the integration of these piezoelectric layers in MEMS and the corresponding performance are discussed

Effects of oxygen background pressure on the stoichiometry of a LaGaO3 laser ablation plume investigated by time and spectrally resolved two-dimensional imaging

The plume expansion dynamics strongly affects the growth and the chemistry of pulsed laser deposited thin films. The interaction with the background gas determines the kinetic energy of the species impinging on the substrate, their angular broadening, the plasma chemistry, and eventually the cations stoichiometric ratio in oxide films. Here, we exploit two-dimensional, spectrally resolved plume imaging to characterize the diverse effects of the oxygen background pressure on the expansion dynamics of La, Ga, and LaO species during pulsed laser deposition of LaGaO3. The propagation of the ablated species towards the substrate is studied for background oxygen pressures ranging from high vacuum up to 101 mbar. Our experimental results show specie-dependent effects of the background gas on the angular distribution of the precursors within the plume. These findings suggest that even in the presence of a stoichiometric ablation and of a globally stoichiometric plume, cations off-stoichiometry can take place in the forefront portion of the plume impinging on the substrate. We show that such effect can be compensated by a proper choice of process parameters

Enhanced critical temperature in epitaxial ferroelectric Pb(Zr_0.2Ti_0.8)O₃ thin films on silicon

The structural and electrical properties of epitaxialPb(Zr0.2Ti0.8)O3thin filmsgrown on 2 in. (001) silicon wafers were investigated. Using x-ray diffraction, the lattice behavior of the heterostructure has been studied as a function of temperature, suggesting a 250 °C increase of the Pb(Zr0.2Ti0.8)O3 ferroelectric-paraelectric transition temperature with respect to the bulk value. This significant enhancement of the critical temperature is understood in terms of a two-dimensional clamping effect

Optical Second-Harmonic Polarimetry on Hf0.5Zr0.5O2/La0.67Sr0.33MnO3 Interfaces

The interface-induced second-harmonic generation from ferroelectric hafnium–zirconium oxide (Hf0.5Zr0.5O2) epitaxial thin films, buffered with a La0.67Sr0.33MnO3 bottom electrode, is analyzed as a function of input and output polarization angles and the azimuthal angle of the sample for several film thicknesses. It is shown that the signal is generated mainly from the buffer side of the interface, rather than from the ferroelectric side. However, the ferroelectric film affects significantly the nonlinear optical properties of the underlying ferromagnetic buffer electrode. Several mechanisms accounting for these observations are discussed, from oxygen migration, to an electrostatic effect, including a possible modulation of the La0.67Sr0.33MnO3 magnetization by the upper ferroelectric film.The authors would like to acknowledge funding from the Italian Government, PRIN-TWEET (grant code 2017YCTB59), and from the Spanish Ministry of Science and Innovation, through the Severo Ochoa FUNFUTURE (CEX2019-000917-SMCIN, AEI/10.13039/501100011033), PID2020-112548RB-I00 (MCIN/AEI/10.13039/501100011033), and PID2019-107727RB-I00 (MCIN/AEI/10.13039/501100011033) projects. All authors would like to thank Silvia Picozzi (CNR-SPIN) and Christian Rinaldi (Politecnico Milano) for the useful discussions.info:eu-repo/grantAgreement/AGENCIA FINANCIADORA/PROGRAMA DE FINANCIACIÓN/REFERENCIA DEL PROYECTOPeer reviewe

Structural characterization of nanoparticles-assembled titanium dioxide films produced by ultrafast laser ablation and deposition in background oxygen

Ultrafast laser ablation of titanium dioxide and deposition of nanoparticles-assembled films in oxygen ambient gas at pressures going from high-vacuum up to several mbar is investigated. We identify various regimes of the plumes propagation into the background gas as well as of the material deposition rate. These reflect on the structural characteristics of the nanoparticles-assembled films: the film morphology changes from a structure with glue-like nanoparticulates, at low pressure, to a highly porous assembly of individual nanoparticles, at larger pressure. Our findings indicate that background gas pressure provides an interesting key for additional control on the structural characteristics of oxide nanostructures produced by femtosecond laser deposition