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Over the past five decades, LiNbO3 and LiTaO3 single crystals and thin films have been studied intensively for their exceptional acoustic, electro-optical, and pyroelectric and ferroelectric properties. Today, LiNbO3 single crystals in electro-optics are equivalent to silicon in electronics, and about 70% of radio-frequency (RF) filters, based on surface acoustic waves, are fabricated on these single crystals. These materials in the form of thin films are needed urgently for the development of the next-generation of high-frequency and/or wide-band RF filters or tuneable frequency filters adapted to the fifth generation of infrastructures/networks/communications. The integration of LiNbO3 films in guided nanophotonic devices will allow higher operational frequencies, wider bandwidth, and miniaturized optical devices in line with improved electronic conversion. Here, the challenges and the achievements in the epitaxial growth of LiTaO3 and LiNbO3 thin films and their integration with silicon technology and to acoustic and guided nanophotonic devices are discussed in detail. The systematic representation and classification of all epitaxial relationships reported in the literature have been carried out in order to help the prediction of the epitaxial orientations in the new heterostructures. Future prospects of potential applications and the expected performances of thin film devices are overviewed, as well. [ABSTRACT FROM AUTHOR]

In this paper, we present integrated lead-free energy converters based on a suitable MEMS fabrication process with an embedded layer of LiNbO3. The fabrication technology has been developed to realize micromachined self-generating transducers to convert kinetic energy into electrical energy. The process proposed presents several interesting features with the possibility of realizing smaller scale devices, integrated systems, miniaturized mechanical and electromechanical sensors, and transducers with an active layer used as the main conversion element. When the system is fabricated in the typical cantilever configuration, it can produce a peak-to-peak open-circuit output voltage of 0.208 V, due to flexural deformation, and a power density of 1.9 nW·mm−3·g−2 at resonance, with values of acceleration and frequency of 2.4 g and 4096 Hz, respectively. The electromechanical transduction capability is exploited for sensing and power generation/energy harvesting applications. Theoretical considerations, simulations, numerical analyses, and experiments are presented to show the proposed LiNbO3-based MEMS fabrication process suitability. This paper presents substantial contributions to the state-of-the-art, proposing an integral solution regarding the design, modelling, simulation, realization, and characterization of a novel transducer. [ABSTRACT FROM AUTHOR]

A Systematic study of domain Structure and residual stress evolution with film thickness and of phase transition in c/a epitaxial PbTiO3/LaAlO3 films using X- ray diffraction and Ranian spectroscopy is reported. Both techniques revealed that the films are under tensile residual stress in the film plane and that a-domains are more stressed than c-domains. The two components of the large A1(TO) Raman modes are associated with a- and c-domains and their intensity ratio correlates to the volume fraction of a-domains. The evolution of the Raman signature with temperature revealed that the spectrum of a-domains disappears around 480°C, whereas c-domains present an anomaly in their spectrum at 500° C but maintain a well- defined Raman signature up to 600°C. [ABSTRACT FROM AUTHOR]

Microfabrication procedure of piezoelectric micro electro-mechanical systems based on 5 μ m thick LiNbO 3 films on SiO 2 /Si substrate at wafer scale including deep dry etching of thick LiNbO 3 films by implementing pulsed mode of Ar/SF 6 gas was developed. In particular, two (YXlt)/128°/90°LiNbO 3 -Si cantilevers with tip mass were fabricated and characterized in terms of resonance frequency (511 and 817 Hz), actuation and acceleration sensing capabilities. The quality factor of 89.5 and the electromechanical coupling of 4.8% were estimated from measured frequency dependency of electrical impedance, fitted by using Butterworth-Van Dyke model. The fabricated piezoelectric micro-electro-mechanical systems have demonstrated highly linear displacement with good sensitivity (5.28 ± 0.02 μ m V -1 ) as a function of applied voltage and high sensitivity to vibrations of 667 mV g -1 indicating a suitability of the structure for actuation purposes and for acceleration or frequency sensing with high precision, respectively., (© 2024 IOP Publishing Ltd.)

Development of bulk acoustic wave filters with ultra-wide pass bands and operating at high frequencies for 5 th and 6 th generation telecommunication applications and micro-scale actuators, energy harvesters and sensors requires lead-free piezoelectric thin films with high electromechanical coupling and compatible with Si technology. In this paper, the epitaxial growth of 36°Y-X and 30°X-Y LiNbO 3 films by direct liquid injection chemical vapour deposition on Si substrates by using epitaxial SrTiO 3 layers, grown by molecular beam epitaxy, has been demonstrated. The stability of the interfaces and chemical interactions between SrTiO 3 , LiNbO 3 and Si were studied experimentally and by thermodynamical calculations. The experimental conditions for pure 36°Y-X orientation growth have been optimized. The piezoelectricity of epitaxial 36°Y-X LiNbO 3 /SrTiO 3 /Si films was confirmed by means of piezoelectric force microscopy measurements and the ferroelectric domain inversion was attained at 85 kV.cm -1 as expected for the nearly stoichiometric LiNbO 3 . According to the theoretical calculations, 36°Y-X LiNbO 3 films on Si could offer an electromechanical coupling of 24.4% for thickness extension excitation of bulk acoustic waves and a comparable figure of merit of actuators and vibrational energy harvesters to that of standard PbZr 1- x Ti x O 3 films., (© 2024 IOP Publishing Ltd.)

This work reports on an alternative and advantageous procedure to attain VO 2 -based thermochromic coatings on silicon substrates. It involves the sputtering of vanadium thin films at glancing angles and their subsequent fast annealing in an air atmosphere. By adjusting thickness and porosity of films as well as the thermal treatment parameters, high VO 2 (M) yields were achieved for 100, 200, and 300 nm thick layers treated at 475 and 550 °C for reaction times below 120 s. Comprehensive structural and compositional characterization by Raman spectroscopy, X-ray diffraction, and scanning-transmission electron microscopies combined with analytical techniques such as electron energy-loss spectroscopy bring to the fore the successful synthesis of VO 2 (M) + V 2 O 3 /V 6 O 13 /V 2 O 5 mixtures. Likewise, a 200 nm thick coating consisting exclusively of VO 2 (M) is also achieved. Conversely, the functional characterization of these samples is addressed by variable temperature spectral reflectance and resistivity measurements. The best results are obtained for the VO 2 /Si sample with changes in reflectance of 30-65% in the near-infrared at temperatures between 25 and 110 °C. Similarly, it is also proven that the achieved mixtures of vanadium oxides can be advantageous for certain optical applications in specific infrared windows. Finally, the features of the different structural, optical, and electrical hysteresis loops associated with the metal-insulator transition of the VO 2 /Si sample are disclosed and compared. These remarkable thermochromic performances hereby accomplished highlight the suitability of these VO 2 -based coatings for applications in a wide range of optical, optoelectronic, and/or electronic smart devices., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Phase composition of epitaxial/textured LiNbO3 films on sapphire substrates, grown by pulsed laser deposition, atmospheric pressure metal organic chemical vapor deposition and pulsed injection metal organic chemical vapor deposition was studied by conventional x-ray diffraction techniques. Raman spectroscopy, being highly sensitive to the symmetry of materials, was used as a countercheck in the compositional analysis. The wavenumbers of Raman modes of LiNb3O8 and Li3NbO4 phases were identified from Raman spectra of synthesized powders. Asymmetry of profiles of x-ray diffraction reflections of LiNbO3 films was studied. This asymmetry may have different origins which consequently may result in misleading conclusions about phase composition of textured LiNbO3 films.