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The demand for high-performance electromechanical resonators is ever-growing across diverse applications, ranging from sensing and time-keeping to advanced communication devices. Among the electromechanical materials being explored, thin-film lithium niobate stands out due to its strong piezoelectric properties and low acoustic loss. However, in nearly all existing lithium niobate electromechanical devices, the configuration is such that the electrodes are in direct contact with the mechanical resonator. This configuration introduces an undesirable mass-loading effect, producing spurious modes and additional damping. Here, we present an electromechanical platform that mitigates this challenge by leveraging a flip-chip bonding technique to separate the electrodes from the mechanical resonator. By offloading the electrodes from the resonator, our approach yields a substantial increase in the quality factor of these resonators, paving the way for enhanced performance and reliability for their device applications. [ABSTRACT FROM AUTHOR]

This study provides insights into the design and analysis of surface acoustic wave sensors customized for detecting volatile organic compounds (VOCs), utilizing an innovative AlN/diamond/Si multilayered configuration. The results are explored numerically using finite element method simulation within the COMSOL Multiphysics package. The potential of the AlN piezoelectric thin film on diamond on Si substrates for sensor development is examined. The phase velocities, electromechanical coupling coefficient, K 2 , and reflectivity are examined versus the normalized thicknesses of the substrates, considering both Rayleigh and Sezawa wave modes. Additionally, the temperature coefficient of frequency (TCF) is investigated. The results show that the TCF increases with reducing the thickness of the diamond. For instance, at khAIN = 2 where the maximum K 2 can be observed, the TCF increases from −17 to −14 to 3 ppm/°C for khdiamond = 0.5, 0.2, and 0.05, respectively. Furthermore, the sensor sensitivity to gas concentration in the air is examined for several VOCs using a thin polyisobutylene (PIB) layer for sensor demonstration. The study shows a remarkable sensitivity enhancement in sensor sensitivity achieved through the Sezawa wave mode compared to the Rayleigh counterpart. For example, in the case of tetrachloroethene gas (PCE), the sensor sensitivity reaches 197.73 Hz/ppm for the Sezawa mode, as opposed to 62.15 Hz/ppm for the Rayleigh mode. [ABSTRACT FROM AUTHOR]

Increasing prevalence of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) constitutes an emerging water safety issue globally. However, the effectiveness of current water treatment techniques in the control of ARGs dissemination remains controversial. Here, we develop a dual-zone strategy based on piezoelectric membrane filtration to efficiently eliminate waterborne antibiotic resistance. Following complete ARB inactivation and effective ARGs reduction in the retentate near the membrane surface (zone 1), a subsequent trans-membrane process (zone 2) further promotes ARGs elimination in the permeate, due to boosted interactions between ARGs and reactive oxygen species (ROS) generated from piezoelectric peroxymonosulfate activation and minimized ROS competition from inactivated ARB within piezocatalytic channels. The abundance of ARGs was largely reduced to ~1.0 × 103 copies·mL−1 in the permeate from ~5.0 × 106 copies·mL−1 in the feed solution. The singlet oxygen (1O2) is demonstrated to be primarily responsible for ARB inactivation, while 1O2, hydroxyl radical (•OH), sulfate radical (SO4·−) and superoxide radical (·O2−) can all participate in ARGs degradation. Our work demonstrates that the piezoelectric membrane-based dual-zone strategy has great potential to control the risk of ARGs dissemination. [ABSTRACT FROM AUTHOR]

The spectra of transmisson coefficients and absorption indices of single-domain and multidomain LaBGeO5 samples have been measured. It is shown that, to measure more exactly the optical rotation ρ, it is necessary to use the spectra of transmission coefficients not only for the cases of parallel and crossed polarizers but also at other angles between them. The obtained ρ values for both samples are described quite well by only dispersion using the Drude formula. This is in agreement with the fact that the ρ value should not change during transition to the single-domain state of the crystal at a given symmetry (P31 in the ferroelectric phase and P3121 in the paraelectric phase). It is shown that the Cherenkov-type second harmonic generation (SHG) is observed only in a polydomain sample, while the second-harmonic radiation is not polarized. The domain structure of the samples was observed by scanning electron microscopy and piezoelectric force microscopy. The presence of a labyrinth-like domain structure was shown for the multidomain sample, whereas for a single-domain sample no changes in contrast were observed within the scanned region. [ABSTRACT FROM AUTHOR]

Most reported thin-film piezoelectric energy harvesters have been based on cantilever-type crystalline ferroelectric oxide thin films deposited on rigid substrates, which utilize vibrational input sources. Herein, we introduce flexible amorphous thin-film energy harvesters based on perovskite CaCu3Ti4O12 (CCTO) thin films on a plastic substrate for highly competitive electromechanical energy harvesting. The room-temperature sputtering of CCTO thin films enable the use of plastic substrates to secure reliable flexibility, which has not been available thus far. Surprisingly, the resultant amorphous nature of the films results in an output voltage and power density of ~38.7 V and ~2.8 × 106 μW cm−3, respectively, which break the previously reported record for typical polycrystalline ferroelectric oxide thin-film cantilevers. The origin of this excellent electromechanical energy conversion is systematically explored as being related to the localized permanent dipoles of TiO6 octahedra and lowered dielectric constant in the amorphous state, depending on the stoichiometry and defect states. This is the leading example of a high-performance flexible piezoelectric energy harvester based on perovskite oxides not requiring a complex process for transferring films onto a plastic substrate. Traditional methods to incorporate polycrystalline thin film into flexible systems are often complicated and limited by their sizes. Here, the authors introduce flexible amorphous thin film energy harvester, based on perovskite oxides, on a plastic substrate for electromechanical energy harvesting. [ABSTRACT FROM AUTHOR]

A signal is primarily generated when two objects collide, with one falling from a specific height and the other disrupting its balance. This signal contains an important component that aids in the diagnosis of material damage. In this work, a piezoelectric thin film sensor made of polyvinylidene fluoride (PVDF) was employed to monitor the impact signal and process the recorded signal. By stacking a left and right piezoelectric film sensor, drop impact experiments were performed on rubber sheet material. The data-acquisition system captured the impact signal, and a signal processing tool was used to assess its performance. To determine the time-frequency domain visibility of the impact signal, the short-time Fourier transform (STFT) and continuous wavelet transform (CWT) were used. The detection of the elastic signal and impact force on the material is suitable for piezoelectric film. A steel impactor strikes a silicon rubber sheet at a speed of 3.43 m/s and exerts an average impact force of 72.6 kN. To make the impact signal more visible, the noise signal can be denoised using a bandpass filter. The continuous wavelet transform has a high time-frequency resolution compared to the short-time Fourier transform. Additionally, the analysis of non-stationary signals is improved by using STFT and CWT approaches. Thus, the elastic signal detection in the material may be recognized using the average total of the signals identified by the sensor. [ABSTRACT FROM AUTHOR]

Integration of thin-film oxide piezoelectrics on glass is imperative for the next generation of transparent electronics to attain sensing and actuating functions. However, their crystallization temperature (above 650 °C) is incompatible with most glasses. We developed a flash lamp process for the growth of piezoelectric lead zirconate titanate films. The process enables crystallization on various types of glasses in a few seconds only. The functional properties of these films are comparable to the films processed with standard rapid thermal annealing at 700 °C. A surface haptic device was fabricated with a 1 μm-thick film (piezoelectric e33,f of −5 C m−2). Its ultrasonic surface deflection reached 1.5 μm at 60 V, sufficient for its use in surface rendering applications. This flash lamp annealing process is compatible with large glass sheets and roll-to-roll processing and has the potential to significantly expand the applications of piezoelectric devices on glass. Direct growth of piezoelectric oxides on glass is difficult due to high processing temperatures. Here, the authors demonstrate a flash lamp process for the growth of films on various glasses in a few seconds only. The films have piezoelectric e33,f of −5 C m−2 and can be used in haptic devices. [ABSTRACT FROM AUTHOR]

Implant-associated infections due to the formation of bacterial biofilms pose a serious threat in medical healthcare, which needs effective therapeutic methods. Here, we propose a multifunctional nanoreactor by spatiotemporal ultrasound-driven tandem catalysis to amplify the efficacy of sonodynamic and chemodynamic therapy. By combining piezoelectric barium titanate with polydopamine and copper, the ultrasound-activated piezo-hot carriers transfer easily to copper by polydopamine. It boosts reactive oxygen species production by piezoelectrics, and facilitates the interconversion between Cu2+ and Cu+ to promote hydroxyl radical generation via Cu+ -catalyzed chemodynamic reactions. Finally, the elevated reactive oxygen species cause bacterial membrane structure loosening and DNA damage. Transcriptomics and metabolomics analysis reveal that intracellular copper overload restricts the tricarboxylic acid cycle, promoting bacterial cuproptosis-like death. Therefore, the polyetherketoneketone scaffold engineered with the designed nanoreactor shows excellent antibacterial performance with ultrasound stimulation and promotes angiogenesis and osteogenesis on-demand in vivo. Implantation-associated infections often lead to infections. Here, the authors propose a piezo-based nanoreactor to achieve US-excited tandem catalysis, endowing the polyetherketoneketone bone scaffold with on-demand antibacterial and osteogenic capacities. [ABSTRACT FROM AUTHOR]

For the development of spintronic devices, the control of magnetization by a low electric field is necessary. The microscopic origin of manipulating spins relies on the control of orbital magnetic moments (morb) by strain; this is essential for the high performance magnetoelectric (ME) effect. Herein, electric-field induced X-ray magnetic circular dichroism (XMCD) is used to determine the changes in morb by piezoelectric strain and clarify the relationship between the strain and morb in an interfacial multiferroics system with a significant ME effect; the system consists of the Heusler alloy Co2FeSi on a ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 substrate. Element-specific investigations of the orbital states by operando XMCD and the local environment via extended X-ray absorption fine structure (EXAFS) analysis show that the modulation of only the Fe sites in Co2FeSi primarily contributes to the giant ME effect. The density functional theory calculations corroborate this finding, and the growth of the high index (422) plane in Co2FeSi results in a giant ME effect. These findings elucidate the element-specific orbital control using reversible strain, called the 'orbital elastic effect,' and can provide guidelines for material designs with a giant ME effect. Schematic illustrations of the changes in the magnetic anisotropy by an applied electric field (E) in the strain directions are displayed. Under an applied E, the piezoelectric stress in the ferroelectric PMN-PT could be introduced in the tensile and compressive directions using positive and negative bias voltages, respectively, resulting in the changes in the magnetic anisotropy in the Co2FeSi layer. The XMCD spectra of Fe and Co L-edges in Co2FeSi under applying E showed the line shape changes only in the Fe site, which corresponds to the changes of orbital magnetic moment in Fe, while that in Co remains unchanged. [ABSTRACT FROM AUTHOR]

Flexoelectricity, referring to the electrical polarization generated by strain gradients, is an electromechanical coupling phenomenon in all dielectric materials. Based on the Kirchhoff plate theory, this paper investigates the influence of flexoelectricity on the electromechanical coupling response of piezoelectric circular nanoplates with different electric boundary conditions. Using the variational principle and Gibbs free energy, the governing equations and boundary conditions of piezoelectric nanoplates are derived. The analytical solutions of the deflection, polarization, and induced electric potential are obtained. The results show that the flexoelectric effect is size-dependent and has a more significant influence on the electrostatic responses than the piezoelectric effect at the nanoscale. The results also show that the induced electric potential due to the flexoelectric effect may be helpful for sensing or energy harvesting designs. [ABSTRACT FROM AUTHOR]

Transparent piezoelectric thin films on glass are sought after in piezoelectric microdevices. Here we report the fabrication of highly transparent (%T ≥ 70.0) Pb(Zr0.52Ti0.48)O3[PZT] thin films on indium tin oxide (ITO)-coated glass substrate. The effective transverse piezoelectric coefficient, e31,f, determined from both direct and converse piezoelectric effects for the PZT/ITO/glass unimorphs were 3.8 and 9.3 C m−2, respectively. Dielectric permittivity, ε r and dielectric loss, tan δ were 870 and 0.06, respectively. The high optical transparency and transverse piezoelectric coefficient obtained for the PZT/ITO/glass heterostructure suggest that they have good application potential in transparent piezoelectric thin film devices. [ABSTRACT FROM AUTHOR]

Based on the nonlocal strain gradient theory and flexoelectricity theory, a new model of transversely isotropic piezoelectric rectangular nano-plate subjected to a distributed load is proposed. The nonlocal effect, strain gradient effect and flexoelectric effect are all considered in the novel model. The governing equation and different boundary conditions for a clamped nano-plate under closed circuit and open circuit states are derived by Hamilton principle. Based on the new model, the electro-mechanical responses of piezoelectric nano-plate are numerically analyzed. When the dimensionless nonlocal scale coefficient is smaller than 3, both the central deflection and the central electric potential show significant size dependence. The nonlocal effect causes the nano-plate to be softened while the strain gradient effect makes it stiffened. Compared with the piezoelectric effect, the impact of the flexoelectric effect on the central electric potential plays a dominant role. In addition, the electric potential increases from each lateral edge to the center symmetrically, reaching a maximum at the central point. This paper elucidates the competitive relationship among the influencing effects and concurrently discovers that these effects have a comparable magnitude of impact on the electro-mechanical responses of nano-plate. [ABSTRACT FROM AUTHOR]

We report the structural, piezoelectric, multiferroic and magnetoelectric (ME) properties of the ternary 0.65BiFeO3–0.35[(1 − x)Bi0.5K0.5TiO3 − xBaTiO3] (0.0 ≤ x ≤ 1.0) (BF–BKT–BT) solid solutions. These samples show a rhombohedral to pseudo-cubic structure transition in the vicinity of x ~ 0.4, i.e., the morphotropic phase boundary (MPB), where the maximum piezoelectric coefficient d33 occurs. In addition, maximum electric-field (E) induced strain is also observed for x ~ 0.4 near the MPB. All the samples show good ferroelectricity and basically antiferromagnets at room temperature. The room-temperature E control of magnetization, i.e., converse ME effect, increases with increasing x, reaches a maximum near x = 0.6, and decreases again with x ≥ 0.8. In-situ X-ray diffraction studies at different applied E demonstrate an important role of E-induced variation in the phase fraction, Fe–O bond length and Fe–O–Fe bond angle in the converse ME effect. These results reveal a possible effective route to obtain multi-functional devices with both good piezoelectricity and ME effect in the BF–BKT–BT based systems. [ABSTRACT FROM AUTHOR]

Nanoparticles, films, and patterns are three critical piezoelectric elements with widespread applications in sensing, actuations, catalysis and energy harvesting. High productivity and large-area fabrication of these functional elements is still a significant challenge, let alone the control of their structures and feature sizes on various substrates. Here, we report a fast and versatile electrostatic disc microprinting, enabled by triggering the instability of liquid-air interface of inks. The printing process allows for fabricating lead zirconate titanate free-standing nanoparticles, films, and micro-patterns. The as-fabricated lead zirconate titanate films exhibit a high piezoelectric strain constant of 560 pm V−1, one to two times higher than the state-of-the-art. The multiplexed tip jetting mode and the large layer-by-layer depositing area can translate into depositing speeds up to 109 μm3 s−1, one order of magnitude faster than current techniques. Printing diversified functional materials, ranging from suspensions of dielectric ceramic and metal nanoparticles, to insulating polymers, to solutions of biological molecules, demonstrates the great potential of the electrostatic disc microprinting in electronics, biotechnology and beyond. In this work, authors demonstrate a fast and versatile microprinting technique to produce high-performance and customizable piezoelectric elements by employing a conductive spiny disc to electrostatically trigger instability to the liquid-air interface of the ink. [ABSTRACT FROM AUTHOR]

Poly(vinylidene fluoride) (PVDF) electrospun nanofibrous membranes (NFMs) have good piezoelectric properties compared to other polymer materials due to their electroactive phase. However, there is a limit to the content of the electroactive phase (FEA) in PVDF, which restricts the further improvement of PVDF NFMs' piezoelectric properties. This research prepared PVDF multilayer nanofibrous membranes (MNFMs) with a novel 3D structure by assembling electrospun PVDF nanofibers and electrospraying PVDF microspheres. The various properties of PVDF microspheres and PVDF MNFMs, including their crystalline structure, morphology, and piezoelectric properties, were discussed in detail. The addition of PVDF microspheres to PVDF NFMs hardly changed the FEA in PVDF MNFMs. However, the piezoelectric properties of PVDF MNFMs significantly increased compared to those of PVDF NFMs. PVDF MNFMs demonstrate good piezoelectric sensitivity and can detect the stress force as small as 0.25 N and finger tapping. The maximum output voltage of PVDF MNFMs was 112 mV, achieved when applying a force of 0.25 N at a frequency of 110 Hz. This value is three times higher than that of PVDF NFMs. [ABSTRACT FROM AUTHOR]

Vibrational behavior of a functionally graded graphene nanoplatelets-reinforced porous nanocomposite (FG GNPs-RPN) annular microplate with piezoelectric/metallic coverings is carried out in the current work in asymmetric condition. The microstructure is sited on Kerr elastic substrate and also is in a thermoelectrical media. The core's properties are varied over the thickness path based on different assumed forms. To determine the core's effective properties, Gaussian random field scheme, Halpin–Tsai, and extended rule of mixture models are appointed. Also, Gurtin–Murdoch and modified strain gradient theories are occupied to consider surface stress and small-scale impacts, respectively. The derivation process of the governing equations and associated boundary conditions was conducted via Hamilton's principle. Generalized differential quadrature scheme is chosen to attain the results. By validating the results' precision, the effects of different parameters on the frequencies are observed. It is perceived that adding GNPs enhances the frequencies by about 20–28%, and increasing porosity up to seventy percent leads the frequencies to decrease by about 8–15%. The simpler models of the under-evaluation microstructure are used in different productions; thus, the current model can be used to move on the edge of knowledge and future uses in numerous industries based on the obtained results. [ABSTRACT FROM AUTHOR]

Piezoelectric biomaterials have attracted great attention owing to the recent recognition of the impact of piezoelectricity on biological systems and their potential applications in implantable sensors, actuators, and energy harvesters. However, their practical use is hindered by the weak piezoelectric effect caused by the random polarization of biomaterials and the challenges of large-scale alignment of domains. Here, we present an active self-assembly strategy to tailor piezoelectric biomaterial thin films. The nanoconfinement-induced homogeneous nucleation overcomes the interfacial dependency and allows the electric field applied in-situ to align crystal grains across the entire film. The β-glycine films exhibit an enhanced piezoelectric strain coefficient of 11.2 pm V−1 and an exceptional piezoelectric voltage coefficient of 252 × 10−3 Vm N−1. Of particular significance is that the nanoconfinement effect greatly improves the thermostability before melting (192 °C). This finding offers a generally applicable strategy for constructing high-performance large-sized piezoelectric bio-organic materials for biological and medical microdevices. Piezoelectric biomaterials are limited by the challenges in domain orientation alignment and a weak piezoelectric effect. Here, Zhang et. al. present an active self-assembly strategy via nanoconfinement and in-situ poling, to obtain large-scale, high performance piezoelectric β-glycine nanocrystalline films. [ABSTRACT FROM AUTHOR]

A semi-analytical method is proposed for free and forced vibrations of a thin square binary material configuration plate containing circular plate-type resonators. The resonator embedded in the host plate consists of a rigid mass and a circular plate made of soft material. Based on the classical plate theory, the host plate and the resonator are modelled separately and then coupled by the condition of displacement compatibility. A set of local admissible functions is incorporated into the global admissible functions in the circular plate domain, to describe the non-smoothness and vibration localization of the displacement caused by the material difference between the host plate and the resonator. The resulting global admissible functions promote the capabilities of the Ritz method in predicting accurately the vibration characteristics of the plate with binary material configuration. The Ritz method with the constructed admissible functions is developed to extract frequencies and analytic mode functions of the plate under different boundary conditions. The plate subjected to a transverse harmonic excitation is discretized into a multi-degree-of-freedom system by the Lagrange approach with the analytic mode functions. The effects of boundary conditions, locations of the mass, and material properties on the vibration are explored. It is demonstrated that the mass location in the circular plate only affects the frequencies of the resonator and has almost no effect on the frequencies and the modes of global vibration, and the resonator with the appropriate material parameters reduces significantly the multi-mode plate vibration. [ABSTRACT FROM AUTHOR]

Considering the evolution of rotation sensing and timing applications realized in micro-electro-mechanical systems (MEMS), flexural mode resonant shapes are outperformed by bulk acoustic wave (BAW) counterparts by achieving higher frequencies with both electrostatic and piezoelectric transduction. Within the 1–30 MHz range, which hosts BAW gyroscopes and timing references, piezoelectric and electrostatic MEMS have similar transduction efficiency. Although, when designed intelligently, electrostatic transduction allows self-alignment between electrodes and the resonator for various BAW modes, misalignment is inevitable regarding piezoelectric transduction of BAW modes that require electrode patterning. In this paper transverse piezoelectric actuation of [011] oriented single crystal lead magnesium niobate–lead titanate (PMN–PT) thin film disks are shown to excite the tangential mode and family of elliptical compound resonant modes, utilizing a self-aligned and unpatterned electrode that spans the entire disk surface. The resonant mode coupling is achieved by employing a unique property of [011] PMN–PT, where the in-plane piezoelectric coefficients have opposite signs. Fabricating 1-port disk transducers, RF reflection measurements are performed that demonstrate the compound mode family shapes in the 1–30 MHz range. Independent verification of mode transduction is achieved using in-plane displacement measurements with Polytec's laser Doppler vibrometer (LDV). While the tangential mode achieves a 40o/s dithering rate at 335 kHz resonant frequency, the n = 2 wine-glass mode achieves 11.46 nm tip displacement at 8.42 MHz resonant frequency on a radius of 60 μm disk resonator in air. A single electrode resonator that can excite both tangential and wine-glass modes with such metrics lays the foundation for a BAW MEMS gyroscope with a built-in primary calibration stage. [ABSTRACT FROM AUTHOR]

The results of studying the acoustic and electromagnetic properties of KhM-12 (15-5 PH, also known as also known as UNS S15500) maraging iron–chromium–nickel alloy with addition of copper after thermal treatment of solution annealing at 1040°C for 0.5 h and subsequent aging at 480 and 565°C for 3 h are presented. The effect of uniaxial stretching of circular cross section samples on the velocities of longitudinal transverse and Rayleigh waves is investigated. The research used an acoustic mirror-shadow method on multiple reflections with the use of electromagnetic-acoustic and piezoelectric transducers based on polyvinylidene fluoride film for excitation and reception of waves. The values of the specific electrical conductivity of alloys and coercive force were measured. The elastic moduli and Poisson's ratio of the studied samples are calculated. [ABSTRACT FROM AUTHOR]

The rapid advent of the piezoelectric microelectromechanical systems (PiezoMEMS) field has created a tremendous demand for low hysteretic piezoelectric thin films on Si. In this work, we present the integration of epitaxial Pb(Mg0.33Nb0.67)O3-PbTiO3 (PMN-PT) thin films with Si to enable device fabrication using state of the art methods. With optimized buffer layers and electronic contacts, high-quality low hysteretic PMN-PT thin films are integrated with Si, which is a significant stride towards employing PMN-PT thin film for PiezoMEMS devices. It is found that the processing of the necessary SrTiO3 buffer layer is crucial to achieve the growth of phase-pure perovskite PMN-PT layers on Si. Furthermore, we propose the engineering of the electronic contact for the PMN-PT-on-Si capacitors to obtain low hysteretic polarization and displacement responses. [ABSTRACT FROM AUTHOR]

We report a non-resonant piezoelectric microelectromechanical cantilever system for the measurement of liquid viscosity. The system consists of two PiezoMEMS cantilevers in-line, with their free ends facing each other. The system is immersed in the fluid under test for viscosity measurement. One of the cantilevers is actuated using the embedded piezoelectric thin film to oscillate at a pre-selected non-resonant frequency. The second cantilever, the passive one, starts to oscillate due to the fluid-mediated energy transfer. The relative response of the passive cantilever is used as the metric for the fluid's kinematic viscosity. The fabricated cantilevers are tested as viscosity sensors by carrying out experiments in fluids with different viscosities. The viscometer can measure viscosity at a single frequency of choice, and hence some important considerations for frequency selection are discussed. A discussion on the energy coupling between the active and the passive cantilevers is presented. The novel PiezoMEMS viscometer architecture proposed in this work will overcome several challenges faced by state-of-the-art resonance MEMS viscometers, by enabling faster and direct measurement, straightforward calibration, and the possibility of shear rate-dependent viscosity measurement. [ABSTRACT FROM AUTHOR]

Piezoelectric microelectromechanical system (piezo-MEMS)-based mass sensors including the piezoelectric microcantilevers, surface acoustic waves (SAW), quartz crystal microbalance (QCM), piezoelectric micromachined ultrasonic transducer (PMUT), and film bulk acoustic wave resonators (FBAR) are highlighted as suitable candidates for highly sensitive gas detection application. This paper presents the piezo-MEMS gas sensors' characteristics such as their miniaturized structure, the capability of integration with readout circuit, and fabrication feasibility using multiuser technologies. The development of the piezoelectric MEMS gas sensors is investigated for the application of low-level concentration gas molecules detection. In this work, the various types of gas sensors based on piezoelectricity are investigated extensively including their operating principle, besides their material parameters as well as the critical design parameters, the device structures, and their sensing materials including the polymers, carbon, metal–organic framework, and graphene. [ABSTRACT FROM AUTHOR]

The development of fully solution-processed, biodegradable piezoelectrics is a critical step in the development of green electronics towards the worldwide reduction of harmful electronic waste. However, recent printing processes for piezoelectrics are hindered by the high sintering temperatures required for conventional perovskite fabrication techniques. Thus, a process was developed to manufacture lead-free printed piezoelectric devices at low temperatures to enable integration with eco-friendly substrates and electrodes. A printable ink was developed for screen printing potassium niobate (KNbO3) piezoelectric layers in microns of thickness at a maximum processing temperature of 120 °C with high reproducibility. Characteristic parallel plate capacitor and cantilever devices were designed and manufactured to assess the quality of this ink and evaluate its physical, dielectric, and piezoelectric characteristics; including a comparison of behaviour between conventional silicon and biodegradable paper substrates. The printed layers were 10.7–11.2 μm thick, with acceptable surface roughness values in the range of 0.4–1.1 μm. The relative permittivity of the piezoelectric layer was 29.3. The poling parameters were optimised for the piezoelectric response, with an average longitudinal piezoelectric coefficient for samples printed on paper substrates measured as d33, eff, paper = 13.57 ± 2.84 pC/N; the largest measured value was 18.37 pC/N on paper substrates. This approach to printable biodegradable piezoelectrics opens the way forward for fully solution-processed green piezoelectric devices. [ABSTRACT FROM AUTHOR]

The dynamic fracture characteristics of mode-III cracks are investigated. This is a crucial problem in piezoelectric devices. The theoretical solution to this problem is described using the integral-transform method (Laplace and Fourier transforms) and the Chebyshev point method. A crack-propagation model is provided to obtain the stress and electrical-displacement fields near the crack tips. The results show that crack propagation is related to the electromechanical coupling coefficient and film thickness. The effect of film thickness has not been considered in previous literature. In the case of multiple cracks, according to their mutual effects, the nondimensional DSIF inside the crack tip is more significant than that outside the crack tip, regardless of the number of cracks. When the film thickness is small, the change in the DSIF is significant, indicating appropriate circumstances, and a thinner film thickness is more conducive to safe design. Negative electrical-displacement loads always prevent crack propagation, whereas positive electric-displacement loads can promote or prevent crack propagation. Numerical examples are provided to highlight the result. [ABSTRACT FROM AUTHOR]

Ferroelectric (piezoelectric) Pb (Zr0.52Ti0.48) O3 (PZT) films were synthesized using an aerosol-assisted chemical vapor deposition technique on (111) Pt/Ti/SiO2/Si substrates. The optimum deposition temperature was 350 °C, followed by annealing at 650 °C for 1 h. Tetragonal perovskite phase and preferred orientation {0 0 1} in the PZT films were determined by two-dimensional grazing incidence diffraction using synchrotron X-ray radiation and nano-beam electron diffraction (NBED). The PZT film grains' texture, represented by inverse pole representation, correlates with (0 0 1) and (1 1 1) orientations with approximate XRD peak distribution width of Ω ≈ 35°. The elastic-to-plastic transition of the piezoelectric-based structural deformation of the PZT films is represented by the pop-in, which marks the limit in the elastic behavior at the yield stress for which the material starts exhibiting permanent deformation, with the yield point being Y = 2.5 ± 0.7 GPa for the Pb (Zr0.52Ti0.48) O3 film. The hardness (H = 7.5 ± 0.16 GPa), elastic modulus (E = 126 ± 3 GPa), and scratching were evaluated at the nanoscale, using a nanoindentation technique. No delamination or cracks were observed near the residual scratching stage. The switching of piezoelectric domains and domain polarization process, as a function of films' texture, in the representative Pb (Zr0.52Ti0.48) O3 films, were studied using Piezoresponse Force Microscopy (PFM). The values of the saturation polarization, remnant polarization, coercive field, and piezoelectric constant were Ps = 45 μC/cm2, Pr =30 μC/cm2, Ec = 22 kV/cm, and d33 = 137 pm/V, respectively. The local piezoelectric hysteresis loops and film nanostructure correlate with the polarization orientation. [ABSTRACT FROM AUTHOR]

BiFe0.93Mn0.07O3-0.82BiFe0.975Ti0.025O3-0.18CaTiO3 thin films were prepared on Pt/Si substrate by chemical solution deposition. The microstructure, ferroelectric and piezoelectric properties of the composite films under different annealing temperature were studied systematically. The thin film annealed at 500 °C possesses the maximum remanent polarization and piezoelectric coefficient of 112.6 µC/cm2 and 878.2 pm/V, respectively, which is comparable to most of BiFeO3-based orientated films. The results can be ascribed to the dense and uniform grain distribution in the surface morphology, and coexistence of rhombohedral twisted perovskite symmetrical structure (R3c space group) and pseudo-cubic structural phase. This work provides a feasible way to prepare high-quality lead-free composite ferroelectric films at low-cost. [ABSTRACT FROM AUTHOR]

Based on the thermo-electro-elastic coupling theory, the mathematical model for a surface heated piezoelectric semiconductor (PS) plate is developed in the time domain. Applying the direct and inverse Laplace transformations to the established model, the mechanical and electrical responses are investigated. The comparison between the analytical solution and the finite element method (FEM) is conducted, which illustrates the validity of the derivation. The calculated results show that the maximum values of the mechanical and electrical fields appear at the heating surface. Importantly, the perturbation carriers tend to concentrate in the zone near the heating surface under the given boundary conditions. It can also be observed that the heating induced elastic wave leads to jumps for the electric potential and perturbation carrier density at the wavefront. When the thermal relaxation time is introduced, all the field quantities become smaller because of the thermal lagging effect. Meanwhile, it can be found that the thermal relaxation time can describe the smooth variation at the jump position. Besides, for a plate with P-N junction, the effect of the interface position on the electrical response is studied. The effects of the initial carrier density on the electrical properties are discussed in detail. The conclusions in this article can be the guidance for the design of PS devices serving in thermal environment. [ABSTRACT FROM AUTHOR]

Doped TiAlN thin films are gaining unprecedented attention in recent times due to their functionality and tuneable properties to meet specific demands. The present article focuses on the influence of phosphorous-doped TiAlN thin films deposited using high-power impulse magnetron sputtering. Thin films of different elemental compositions of Ti, Al, and P were sputtered on AISI 5206 steel. The thin film cross-sectional morphology and architecture revealed dense and columnar structures. It was indicated that the (111) diffraction peaks in the XRD pattern shifted to higher angles, while the transverse optics (TO)/longitudinal optics (LO) frequency in the optic phonons region of Raman spectra shifted to the right with the modulation wavelength as the Al and P compositions increase. The elementary composition influences the mechanical properties with the maximum hardness of 28 GPa, and adhesion strength of 15 N attained in thin film with the highest Al and P content. The corrosion rate in all the thin films was reduced by at least two orders of magnitude compared with the uncoated samples. The addition of P increases the corrosion resistance of TiAl(P)N thin films. [ABSTRACT FROM AUTHOR]

Mechanical vibration, as an alternative of application of solid/liquid lubricants, has been an effective means to modulate friction at the macroscale. Recently, atomic force microscopy (AFM) experiments and model simulations also suggest a similar vibration-induced friction reduction effect for nanoscale contact interfaces, although an additional external vibration source is typically needed to excite the system. Here, by introducing a piezoelectric thin film along the contact interface, we demonstrate that friction measured by a conductive AFM probe can be significantly reduced (more than 70%) when an alternating current (AC) voltage is applied. Such real-time friction modulation is achieved owing to the localized nanoscale vibration originating from the intrinsic inverse piezoelectric effect, and is applicable for various material combinations. Assisted by analysis with the Prandtl—Tomlinson (P—T) friction model, our experimental results suggest that there exists an approximately linear correlation between the vibrational amplitude and the relative factor for perturbation of sliding energy corrugation. This work offers a viable strategy for realizing active friction modulation for small-scale interfaces without the need of additional vibration source or global excitation that may adversely impact device functionalities. [ABSTRACT FROM AUTHOR]

Bi2Mg2/3Nb4/3O7 (BMN) thin films are prepared on Pt–Si substrates by magnetron sputtering, the influence of oxygen on dielectric and energy storage properties of BMN thin films is systematically studied. Under the optimal oxygen argon ratio, the BMN thin films show an acceptable dielectric constant of 161 and low loss of 0.0032. With the increase in oxygen argon ratio, the dielectric loss decreases and the breakdown strength increases. A large recoverable energy density of 61.7 J/cm3 with a high efficiency of 74.6% is obtained for the BMN thin films prepared at oxygen-argon ratio of 1/2. Especially, the BMN thin films exhibit an excellent thermal stability in an ultrawide temperature range from − 100 to 200 °C and strong fatigue endurance during the 1 × 106 charge–discharge cycles. These results suggest that the BMN thin films are a promising candidate for lead-free energy storage application in equipment operation under adverse environments. [ABSTRACT FROM AUTHOR]

The development of next-generation piezoelectric micro-electro-mechanical systems (piezo-MEMS) demands reliable and reproducible processes to fulfil the ever-growing requirements. Research on doped PZT thin films with improved ferroelectric and piezoelectric thin films is on the rise; however, most of them mainly discuss the fabrication process flows and results. This paper attempts to present an overview of some of the key issues and challenges encountered in the device level fabrication of piezo-MEMS acoustic sensors using PZT thin films doped with Strontium and Lanthanum for underwater applications. A recipe on the technical challenges would have saved more time and cost for the researchers as several unsuccessful fabrications and damages were encountered. This paper discusses the issues starting from fabrication of sputtering target to deposition, annealing, patterning and isolation of device layers, electrical contacts, packaging as per the application requirements, etc. in detail. [ABSTRACT FROM AUTHOR]

Two problems of a one-dimensional (1D) piezoelectric quasicrystal (QC) wedge are investigated, i.e., the two sides of the wedge subject to uniform tractions and the wedge apex subject to the concentrated force. By virtue of the Stroh formalism and Barnett-Lothe matrices, the analytical expressions of the displacements and stresses are derived, and the generalized solutions for the critical wedge angles are discussed. Numerical examples are given to present the mechanical behaviors of the wedge in each field. The results indicate that the effects of the uniform tractions and the concentrated force on the phonon field displacement are larger than those on the phason field. [ABSTRACT FROM AUTHOR]

Polymeric foams are one of the most widely used piezoelectric materials due to their high piezoelectric properties, high flexibility, excellent special mechanical properties, thermal, electrical, and acoustic insulation, and low cost. Due to the cost and time-consuming nature of the experimental research, optimization of the piezoelectric properties of the polymeric foams requires the help of a precise theoretical model to predict these properties. So far, only one theoretical model has been proposed to predict the piezoelectric properties of the polymeric foams. However, some terms of this model are obtained experimentally and there is no comprehensive research that examines the piezoelectric properties of the polymeric foams with all its effective terms in a merely theoretical way. Therefore, in this research, different models are presented to calculate the two effective terms on the piezoelectric coefficient, including the Young modulus of the polymeric foams (Yf) and the effective relative permittivity (εeff). Then, the validity of the proposed theoretical models is investigated in comparison to the experimental results. The results based on the mean absolute error (MAE) parameter show that the best combined model to predict the piezoelectric properties of the polymeric foams is when the Wang and Sessler models are used to calculate Yf and εeff, respectively. According to the results, the average error of this combined model is less than 3%. [ABSTRACT FROM AUTHOR]

The ScxAl1-xN wurtzite structure has been shown theoretically and experimentally to exhibit significantly higher piezoelectric coupling compared to pure AlN. In this work, a plasma-assisted epitaxial growth method has been used to synthesize epitaxial (0002) ScxAl1-xN films on c-sapphire substrates from x = 0.07 to 0.30 by co-evaporating high-purity Sc and Al sources in the presence of a nitrogen plasma generated by an RF plasma source. Epitaxial ScxAl1-xN films with highly oriented (0002) grains and in-plane registry were produced on c-sapphire substrates that were pre-exposed to the nitrogen plasma to form an oxynitride seed layer. Growth of ScxAl1-xN films was carried out at 930°C under both metal-rich and N-rich conditions using precisely controlled Sc, Al, and N-plasma fluxes. Metal-rich depositions yielded non-(0002)-oriented ScxAl1-xN grains and intermetallic ScAl grains. Nitrogen-rich growth with a Sc/Al flux ratio of 1/3 produced the best (0002) epitaxy as determined by x-ray diffraction analysis. Surface acoustic wave resonator (SAWR) devices were fabricated from 500-nm-thick ScxAl1-xN and AlN films to extract their electromechanical coupling coefficients, k2. As the Sc concentration in the films increases, the degree of (0002) epitaxy is reduced, yet the value of k2 increases becasue there is more Sc in the wurzite lattice despite the decreased level of (0002) grain alignment. The use of a 10-nm-thick SixNy capping layer on top of the ScxAl1-xN films aids in preventing etching during SAWR device photolithography and also helps hinder film oxidation up to 800°C. [ABSTRACT FROM AUTHOR]

We demonstrate a memory device with bias electric field-manipulated multilevel resistance states based on ultra-thin and small area Fe70Ga30 (FeGa) films grown on BaZr0.2Ti0.8O3-0.5Ba0.7Ca0.3TiO3(BZT-0.5BCT) ferroelectric films. Studies have shown that BZT-0.5BCT ferroelectric films exhibit good ferroelectric properties with saturated polarization of 11.3 µC/cm2 and excellent piezoelectric properties with displacement up to 70 Å. A coercive field of 91 Oe is derived from the magnetic hysteresis loop of BZT-0.5BCT/FeGa composite films. Local ferroelectric domain and ferromagnetic domain structures have been probed, which confirm the multiferroicity of the composite films. By applying the bias electric field along the thickness of the films, current–voltage (I–V) behaviors of the FeGa films on the BZT–BCT films can be modulated, and multiple resistance states are generated. Based on the analysis of polarization switching behavior and the electrical transport characteristics, we ascribe this bias voltage modulation of the resistance state to strain-mediated converse magnetoelectric effect, interface bonding effect, and interface charge-co-mediated behaviors. This work suggests a promising approach for exploring multilevel and multifunctional data storage in multiferroic materials. [ABSTRACT FROM AUTHOR]

Polymer-based piezoelectric devices are promising for developing future wearable force sensors, nanogenerators, and implantable electronics, etc. The electric signals generated by them are often assumed as solely coming from the piezoelectric effect. However, triboelectric signals originated from contact electrification between the piezoelectric devices and the contacted objects can produce non-negligible interfacial electron transfer, which is often combined with the piezoelectric signal to give a triboelectric-piezoelectric hybrid output, leading to an exaggerated measured "piezoelectric" signal. Herein, a simple and effective method is proposed for quantitatively identifying and extracting the piezoelectric charge from the hybrid signal. The triboelectric and piezoelectric parts in the hybrid signal generated by a poly(vinylidene fluoride)-based device are clearly differentiated, and their force and charge characteristics in the time domain are identified. This work presents an effective method to elucidate the true piezoelectric performance in practical measurement, which is crucial for evaluating piezoelectric materials fairly and correctly. Difficulties in separating tribo and piezoelectric hybrid signals can lead to an overestimated contribution of the latter. Here, authors propose a method to separate these hybrid signals in the time domain, precisely extracting piezoelectric charge transfer for performance evaluation. [ABSTRACT FROM AUTHOR]

A modal analysis of forced vibrations caused by a time-harmonic force from a piezoelectric plate standing on a rigid foundation is presented. A 3D linearized elasticity theory for solids under initial stress (TLTESIS) is used. It is assumed that a uniformly distributed normal loadings acting on the lateral surfaces of the plate yield the initial stress state. The piezoelectric plate is under the action of a time-harmonic force poled in various directions. A mathematical model is developed, and the problem is solved employing the 3D finite-element method (3D-FEM). Some numerical results illustrating the influence of changes in the poling direction and other important factors, such as the initial stress, on the dynamic behavior of the plate are presented. [ABSTRACT FROM AUTHOR]

S i O 2 with the α -quartz structure is one of the most popular piezoelectrics. It is widely used in crystal oscillators, bulk acoustic wave (BAW) devices, surface acoustic wave (SAW) devices, and so on. G e O 2 can also be crystallized into the α -quartz structure and it has better piezoelectric properties, with higher piezoelectric coefficient and electromechanical coupling coefficients, than S i O 2 . Experiments on bulk crystals and theoretical studies have shown that these properties can be tuned by varying the Si/Ge ratio in the S i x G e 1 - x O 2 solid solution. However, to the best of our knowledge, thin films of S i x G e 1 - x O 2 quartz have never been reported. Here we present the successful crystallization of S i x G e 1 - x O 2 thin films in the α -quartz phase on quartz substrates ( S i O 2 ) with x up to 0.75. Generally, the films grow semi-epitaxially, with the same orientation as the substrates. Interestingly, the S i 0.75 G e 0.25 O 2 composition grows fully strained by the quartz substrates and this leads to the formation of circular quartz domains with an ordered Dauphiné twin structure. These studies represent a first step towards the optimization of piezoelectric quartz thin films for high frequency (> 5 GHz) applications. [ABSTRACT FROM AUTHOR]

The adhesive contact behavior between an elastic cylinder and a transversely isotropic piezoelectric cylinder under a pair of external forces and a mismatch strain is studied in this paper. By using the non-slipping JKR model, the considered problem can be reduced to the coupling singular integral equations, which can be solved analytically with the analytical function theory. The explicit analytical solutions of stress field within the contact region are obtained. The relationships between the contact size and external stimuli are set up by the Griffith energy balance criterion. Our analyses indicate that the elastic-piezoelectric system can be composed of any type of piezoelectric materials to obtain the same adhesive contact behaviors. There exists an increasing range of the contact width when exerting the negative mismatch strain on the cylinders, which can be increased by decreasing the Young's modulus and Poisson's ratio of the elastic cylinder. Furthermore, we find that the Young's modulus and Poisson's ratio of the elastic cylinder have little effect on the pull-off process of the elastic-piezoelectric adhesion system. The results obtained from this paper may be helpful for the design of the micro-electro-mechanical systems (MEMS) devices involving isotropic elastic solids and piezoelectric materials. [ABSTRACT FROM AUTHOR]

The crystal orientation of aluminium nitride (AlN) thin film poses a challenge in piezoelectric applications, where the orientation of (002) is desired for obtaining a high piezoelectric coefficient of the order of 10–12 V/m. Many processes to develop c-axis oriented AlN films with optimized parameters are reported specifically for piezoelectric applications. Of these, the sputtering has been a promising process with control over the target to substrate alignment angle and distance, sputtering parameters, the choice of bottom electrode, etc. The present study uses RF magnetron sputtering to investigate the impact of magnetron source orientation and the influence of working pressure on c-axis oriented AlN crystal growth. AlN thin films were deposited on Al and Mo bottom layers using magnetron sputtering under different source arrangements, namely parallel and confocal. Further, AlN was deposited under different working pressures with all other parameters being fixed. The structural and morphological properties of the prepared samples were studied. The analysis showed a parallel deposition set up with a smooth bottom layer and optimized working pressure promotes AlN to grow in (002) orientation suitable for piezoelectric applications. [ABSTRACT FROM AUTHOR]

The conditions for the parametric instability of magnons under the action of purely elastic pumping, which are modes of a composite acoustic wave resonator containing ferrimagnet and piezoelectric films on a single-crystal substrate, are considered. Electrical excitation of bulk acoustic waves occurs due to the piezoelectric effect (in a ZnO film) at resonant frequencies fn of the resonator. In a magnetically ordered layer (in a film of yttrium iron garnet), acoustic modes, when the threshold power is exceeded, excite magnons at frequencies fn/2. It is shown that, in the case of pumping by transverse acoustic modes, the threshold is several tens of times smaller than in the case of pumping by longitudinal modes and is approximately 100 μW, which is in agreement with experimental data. [ABSTRACT FROM AUTHOR]

In this paper, we are reporting for the first time, the piezosensing characterisations of the SiC thin film on silicon, synthesized from boron containing Liquid Polycarbosilane (PCS) as a precursor deposited by Modified Chemical Vapour Deposition (MoCVD) technique followed by the structural characterisation of the film. Comparison was done on the result of the both undoped and doped SiC thin film to highlight the effect of boron doping on the piezo property of the SiC. Interestingly, it was observed that piezoelectric coefficient (d33) of the boron doped SiC thin film was substantially higher (21.33 pm/V) than the undoped SiC thin film (16.21 pm/V). The enhancement in d33 was analysed considering the polarisation inside the thin film created by boron doping. The result shows a promising boron doped SiC thin film material for the application in high temperature piezo sensors. [ABSTRACT FROM AUTHOR]

This work focuses on the synthesis and deposition process for the fabrication of uniform amorphous thin (∼ 70 nm) unannealed films of potassium sodium niobate (KNN). The composition of deposited and dried (at 90 ∘ C ) films were confirmed using energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy (XPS). For unity K:Na ratios, piezo response force microscopy revealed large electromechanical response potentially due to tip-induced poling in pulsed DC measurements. Low thermal footprint of the process is likely to significantly lower the cost of devices requiring high performance piezoelectric materials and to maintain the final stoichiometry of the film. [ABSTRACT FROM AUTHOR]

Purpose: Piezoelectric thin film power generators are one of the future scopes of alternative energy-harvesting sources. In this paper, a wind-driven thin film piezoelectric energy harvester is explored and reported for both parallel and reticulate venation as well as for without venation. Methodology: The proposed harvester consists of a triangular-shaped cantilever, triangular leaf-like piezoelectric microthin film (PEMF) and a cantilever. The free end of the cantilever is fixed to the PEMF which is capable of harvesting wind energy by vibration. The leaf-like PEMF structure is 122 μm thick, made up of polyvinylidene fluoride (PVDF) coated with silver ink electrode on either side. In this work, the influence of wind velocity, vein structure and cantilever length on overall performance of the system is investigated experimentally. Conclusion: It is seen that under favorable conditions, leaf with reticulate venation showed more than 10% increase in voltage output than in parallel venation. It is found that an increase in cantilever length leads to a substantial increase in voltage output by promoting early onset of flutter. At a velocity of 10 m/s, a maximum open circuit voltage of 1.90 V and power output of 1.2 μW are obtained for L/Lb=1 for reticulate venation PEMF leaf. [ABSTRACT FROM AUTHOR]

In this paper, energy harvesting from a thin annular sectorial plate, which consists of an elastic layer bonded with two layers of piezoelectric materials, is studied analytically. The Rayleigh damping assumption is used in the model to consider the structural damping. To derive the governing equations, the Hamilton principle for an electro-elastic body is employed based on the classical plate theory, and to solve the derived equations, the Rayleigh–Ritz method is used. The modeling approach is verified against analytical solutions as well as experimental results for rectangular and annular sectorial plates. Finally, the impact of changing some parameters (material properties, electrical boundary conditions, geometrical parameters) on the performance of the system is investigated extensively. It is shown that the annular sector plate energy harvesters can deliver better performance compared to rectangular plate energy harvesters. [ABSTRACT FROM AUTHOR]

Considering the piezoelectric effect, the electro-elastic field of an infinite one-dimensional quasicrystal medium with two circular cylindrical inclusions is derived under antiplane shear and inplane electric loading. The boundary value problem of the composite material with circular cylindrical inclusions is analytically solved by the use of the conformal mapping technique and analytical continuation theory. The stresses in the phonon and phason fields and the electric displacements are obtained explicitly in the form of a power series both for the matrix and the inclusions. Some typical examples are analyzed to show the effect of the geometric parameters, material properties, and electro-mechanical loading on the electro-elastic fields in the matrix, inclusions, and interfaces. The limiting cases of circular cavities and rigid circular inclusions have also been investigated and discussed. [ABSTRACT FROM AUTHOR]

For three-dimensional (3D) mono-layer molecular thin-film lubrication, the elasticity of the substrate affects the tribological behaviors of a thin fluid film confined by two solid substrates. To account for the elastic effects, this study establishes a multi-scale method that combines an atomistic description of the near region with a coarse-grained description of the far region of the solid substrate to simulate the thin-film lubrication. It is demonstrated that for a given temperature range and film-substrate coupling strength, the multi-scale method is in excellent agreement with the fully atomistic simulation. This study reveals that the elastic response of the substrate can be effectively rendered in the hybrid scheme. In the application of the multi-scale method to investigate the tribological properties of the multi-layer molecular thin-film lubrication, it is determined that the systematic static friction coefficient monotonously decreases as the molecular layer thickness in the fluid film increases. In comparison to the mono-layer molecular thin-film lubrication, the multi-layer molecular thin-film lubrication plays a role in reducing the friction and wear of the system. [ABSTRACT FROM AUTHOR]

Flexible surface acoustic wave (SAW) device is one of hot point areas for wearable communication technology because of their ductility and bendability, but the deterioration problem of device performance after bending experiments is limiting its wide application for future wearable communication devices. In this work, the effect of sputtering power on microstructure properties and bending piezoelectric characteristics of aluminum nitride (AlN) film on polyimide (PI) with molybdenum (Mo) buffer layer for high-frequency flexible SAW device was discussed in detail from 200 W to 280 W. Microstructure results show that the high oriented (002) AlN films with narrow full width at half maximum (FWHM) of 0.29° and low roughness of 3.2 nm are obtained under 240 W sputtering power. Piezoelectric and frequency results of SAW devices after cyclic bending indicate that the relative piezoelectric coefficient d*33 is about 8.01 pm/V, and the center frequency of the flexible SAW devices is as high as 4.95 GHz, especially the piezoelectric and frequency characteristics can maintain high satiability after 10,000 bending cycles. This work may be of useful for the flexible high-frequency SAW devices in the wearable communication area. [ABSTRACT FROM AUTHOR]