Wireless sensor nodes (WSNs) are the fundamental part of an Internet of Things (IoT) system for detecting and transmitting data to a master node for processing. Several research studies reveal that one of the disadvantages of conventional, battery-powered WSNs, however, is that they typically require periodic maintenance. This paper aims to contribute to existing research studies on this issue by exploring a new energy-autonomous and battery-free WSN concept for monitor vibrations. The node is self-powered from the conversion of ambient mechanical vibration energy into electrical energy through a piezoelectric transducer implemented with lead-free lithium niobate piezoelectric material to also explore solutions that go towards a greener and more sustainable IoT. Instead of implementing any particular sensors, the vibration measurement system exploits the proportionality between the mechanical power generated by a piezoelectric transducer and the time taken to store it as electrical energy in a capacitor. This helps reduce the component count with respect to conventional WSNs, as well as energy consumption and production costs, while optimizing the overall node size and weight. The readout is therefore a function of the time it takes for the energy storage capacitor to charge between two constant voltage levels. The result of this work is a system that includes a specially designed lead-free piezoelectric vibrational transducer and a battery-less sensor platform with Bluetooth low energy (BLE) connectivity. The system can harvest energy in the acceleration range [0.5 g–1.2 g] and measure vibrations with a limit of detection (LoD) of 0.6 g.

LiNbO₃ has been little studied for the piezoelectric energy harvesting applications. Although it is a cheap piezoelectric material without lead and toxic elements, it beneficiates of technological maturity in single crystal fabrication for optical and acoustic applications. In this Letter, we propose to investigate a (YXlt)/128°/90° LiNbO₃ cut as it offers a transverse piezoelectric coupling of k₂₃ = 0.49, which is comparable to that of commonly used PZT ceramics. A flexible beam of 65 mm length and a tip mass made of a LiNbO₃ thick film bonded on silicon were studied under 0.1 g sinusoidal acceleration. The beam presented an open-circuit resonance frequency of 105.9 Hz and a displacement up to 1.5 mm. In the frame of a single degree of freedom lumped model with a rectifying bridge, the electromechanical coupling of the device (k_m²), the figure of merit ${k_m}^{2}Q$ , and the normalized average power density were compared to both Pb-based and Pb-free current devices. The generated power density by our device was 965 μW/cm²/g², which is among the highest reported values compared to both Pb- and Pb-free vibrational harvesting devices.

Filter market demands push the development of new piezoelectric materials to address the modern telecommunication challenges. Combining composite wafers with an epitaxial piezoelectric layer and a said high velocity and acoustic quality substrate is a promising way to answer those demands. However, the fabrication of high-quality LiNbO₃ films with reproducible physical properties is complicated by the difficulty in controlling volatile Li₂O incorporation into the film and of measuring its composition. So far, large-scale production of films with physical properties suitable for the targeted applications is not available. In this paper, lithium niobate films with controlled nonstoichiometry were deposited by means of pulsed injection metalorganic vapor phase deposition. We have demonstrated a high acoustical performance for surface acoustic wave devices operating in the frequency range of 3.7 GHz up to 5.3 GHz and based on grown epitaxial Z-axis oriented LiNbO₃ films on sapphire. An electromechanical coupling of 8% for the Rayleigh wave at 5.3 GHz was demonstrated experimentally.

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.

Lithium niobate is a lead-free material which has attracted considerable attention due to its excellent optical, piezoelectric, and ferroelectric properties. This research is devoted to the synthesis through an innovative sol–gel/spin-coating approach of polycrystalline LiNbO₃ films on Si substrates. A novel single-source hetero-bimetallic precursor containing lithium and niobium was synthesized and applied to the sol–gel synthesis. The structural, compositional, and thermal characteristics of the precursor have been tested through attenuated total reflection, X-ray photoelectron spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The LiNbO₃ films have been characterized from a structural point of view with combined X-ray diffraction and Raman spectroscopy. Field-emission scanning electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy have been used to study the morphological and compositional properties of the deposited films.

Precision control of resistivity/conductivity of LaNiO₃ (LNO) films is essential for their integration as electrodes in the functional heterostructures. This becomes possible if the relationship between processing parameters–composition–structure–resistivity is determined. LaNiO₃ films were deposited by three different chemical vapor deposition methods using different precursor supply systems: direct liquid delivery, pulsed liquid injection, and aerosol generation. The possibilities to ameliorate the efficiency of precursor evaporation and of film growth were studied. The relationship between deposition conditions and composition was determined. Detailed analysis of the epitaxial growth of LNO films on cubic and trigonal substrates and the influence of the rhombohedral distortion on the microstructural quality was done. The resistivity of LaNiO₃ films, grown by chemical vapor deposition, was mainly defined by microstructural defects and La/Ni composition. The high epitaxial quality LaNiO₃/LaAlO₃ films with nearly stoichiometric La/Ni ratio presented low resistivity, which was very close to that of bulk LaNiO₃. Their annealing in oxygen atmosphere had little effect on the resistivity, which suggests a minor presence of oxygen vacancies in the as-grown films.