Search

High-performance lead-free piezoelectric thin films are urgently required for microelectromechanical systems. In this study, thin films based on the 0.8Bi0.5Na0.5TiO3-0.2(Sr0.7Bi0.20.1)TiO3 system were prepared on Pt(111)/TiOx/SiO2/Si substrates by a sol--gel method. The large lattice distortions were induced by introducing five rare-earth ions with different ionic radii (Er/Pr/Sm/Nd/La) to achieve the purpose of regulating the piezoelectric response of the thin films with the maximum inverse piezoelectric coefficient up to 425.9 pm/V. X-ray diffraction, Raman spectroscopy, Piezoresponse force microscope, and additional testing methods were used to observe the phase composition and microstructure of the thin films to investigate the effect of doping rare-earth elements with different ionic radii at the A-site on lattice distortion, and to summarize the transformation law. This study is significant for improving the piezoelectric properties of thin films and has crucial applications in microelectronic sensing. [ABSTRACT FROM AUTHOR]

Piezoelectric thin films are extensively used as sensing or actuating layers in various micro-electromechanical systems (MEMS) applications. However, most piezoelectrics are stiff ceramics, and current polymer piezoelectrics are not compatible with microfabrication due to their low Curie Temperature. Recent polymer-composite piezoelectrics have gained interest but can be difficult to pattern. Photodefinable piezoelectric films could resolve these challenges by reducing the manufacturability steps by eliminating the etching process. But they typically have poor resolution and thickness properties. This study explores methods of enhancing the manufacturability of piezoelectric composite films by optimizing the process parameters and synthesis of SU-8 piezo-composite materials. Piezoelectric ceramic powders (barium titanate (BTO) and lead zirconate titanate (PZT)) were integrated into SU-8, a negative epoxy-based photoresist, to produce high-resolution composites in a non-cleanroom environment. I-line (365 nm) light was used to enhance resolution compared to broadband lithography. Two variations of SU-8 were prepared by thinning down SU-8 3050 and SU-8 3005. Different weight percentages of the piezoelectric powders were investigated: 5, 10, 15 and 20 wt.% along with varied photolithography processing parameters. The composites' transmittance properties were characterized using UV-Vis spectroscopy and the films' crystallinity was determined using X-ray diffraction (XRD). The 0–3 SU-8/piezo composites demonstrated resolutions < 2 μm while maintaining bulk piezoelectric coefficients d33 > 5 pm V−1. The films were developed with thicknesses >10 μm. Stacked layers were achieved and demonstrated significantly higher d33 properties. [ABSTRACT FROM AUTHOR]

Capacitors are ubiquitous and crucial components in modern technologies. Future microelectronic devices require novel dielectric capacitors with higher energy storage density, higher efficiency, better frequency and temperature stabilities, and compatibility with integrated circuit (IC) processes. Here, in order to overcome these challenges, a novel 3D HfO2 thin film capacitor is designed and fabricated by an integrated microelectromechanical system (MEMS) process. The energy storage density (ESD) of the capacitor reaches 28.94 J cm-3, and the energy storage efficiency of the capacitor is up to 91.3% under an applied electric field of 3.5 MV cm-1. The ESD can be further improved by reducing the minimum period structure size of the 3D capacitor. Moreover, the 3D capacitor exhibits excellent temperature stability (up to 150 °C) and charge-discharge endurance (107 cycles). The results indicate that the 3D HfO2 thin film MEMS capacitor has enormous potential in energy storage applications in harsh environments, such as pulsed discharge and power conditioning electronics. [ABSTRACT FROM AUTHOR]

In this manuscript, a simple method combining atomic layer deposition and magnetron sputtering is developed to fabricate high‐performance Pd/SnO2 film patterns applied for micro‐electro‐mechanical systems (MEMS) H2 sensing chips. SnO2 film is first accurately deposited in the central areas of MEMS micro hotplate arrays by a mask‐assistant method, leading the patterns with wafer‐level high consistency in thickness. The grain size and density of Pd nanoparticles modified on the surface of the SnO2 film are further regulated to obtain an optimized sensing performance. The resulting MEMS H2 sensing chips show a wide detection range from 0.5 to 500 ppm, high resolution, and good repeatability. Based on the experiments and density functional theory calculations, a sensing enhancement mechanism is also proposed: a certain amount of Pd nanoparticles modified on the SnO2 surface could bring stronger H2 adsorption followed by dissociation, diffusion, and reaction with surface adsorbed oxygen species. Obviously, the method provided here is quite simple and effective for the manufacturing of MEMS H2 sensing chips with high consistency and optimized performance, which may also find broad applications in other MEMS chip technologies. [ABSTRACT FROM AUTHOR]

The objective of this work is to describe the current state of the rapidly evolving field of 3D piezoelectric microelectromechanical systems (piezoMEMS), and where it needs to go to fully leverage the potential performance benefits offered by atomic layer deposition (ALD). We define 3D piezoMEMS as the application of piezoelectric ALD films to 3D, high aspect-ratio, mechanically pliable structures. Since there are so few existing reports of 3D piezoMEMS, a literature review of ALD films applied to conventional microelectromechanical system (MEMS) devices is given. ALD processes for piezoelectric thin films are reviewed in the context of relevant applications such as transducers and actuators. Examples include aluminum nitride, hafnium zirconate, doped-hafnia, lead zirconate-titanate, lead hafnate, and lead hafnate-titanate. New concepts for ALD-enabled 3D piezoMEMS actuators are presented with supporting theoretical calculations that show that chip-scale mechanical work densities could be improved by ≫ 10 × compared to conventional planar piezoMEMS. 3D fabrication methods are also discussed, while the future needs of atomic layer processing are highlighted. [ABSTRACT FROM AUTHOR]

Conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) PEDOT:PSS is the most widely used material in stretchable and flexible electronics not only due to its good electrical and mechanical properties but also its use in numerous biomedical sensing applications. This article investigates the electromechanical behavior of PEDOT:PSS and its nanocomposite thin film. The films were rod-coated on a chemically treated, cost-effective single-component polymer that was previously characterized as an alternative available substrate material for stretchable and flexible microelectromechanical systems (MEMS) based devices. The results show that the films exhibit stable resistive behavior in response to various applied mechanical loads such as stretching, twisting, combined stretching, and twisting and forced vibrations. The films also show good thermal stability at relatively high temperatures. The prepared films also reveal their applicability as thermal actuators. It was also found that adding nanophases of silver material in PEDOT:PSS enhances the performance of thin films. These results also suggest that the rod-coated PEDOT:PSS and its composite thin films may have versatile applications like stretchable, twistable, and vibration-tolerant conductors, thermal actuators, and devices for future low-cost MEMS devices. [ABSTRACT FROM AUTHOR]

Current methods for thin film sensors preparation include screen printing, inkjet printing, and MEMS (microelectromechanical systems) techniques. However, their limitations in achieving sub-10 μm line widths hinder high-density sensors array fabrication. Electrohydrodynamic (EHD) printing is a promising alternative due to its ability to print multiple materials and multilayer structures with patterned films less than 10 μm width. In this paper, we innovatively proposed a method using only EHD printing to prepare ultra-micro thin film temperature sensors array. The sensitive layer of the four sensors was compactly integrated within an area measuring 450 μm × 450 μm, featuring a line width of less than 10 μm, and a film thickness ranging from 150 nm to 230 nm. The conductive network of silver nanoparticles exhibited a porosity of 0.86%. After a 17 h temperature-resistance test, significant differences in the performance of the four sensors were observed. Sensor 3 showcased relatively superior performance, boasting a fitted linearity of 0.99994 and a TCR of 937.8 ppm/°C within the temperature range of 20 °C to 120 °C. Moreover, after the 17 h test, a resistance change rate of 0.17% was recorded at 20 °C. [ABSTRACT FROM AUTHOR]

• A multi-scale indentation model (MSI) for the stiff film-compliant substrate structures is established. • Two dimensionless numbers g /(E s −1/3 E f 1/3 t f) and τ 0 /(E s 2/3 E f 1/3 t f) are proposed to evaluate the indentation size effect. • The predicted bending stiffness by the MSI model is consistent with the experimental results. As critical components or platforms, stiff film-compliant substrate structures are widely used in micro-electro-mechanical systems (MEMS) and other devices, in which their indentation behavior plays an important role. In this work, a multi-scale indentation model (MSI) for stiff film-compliant substrate structures is established based on the strain gradient theory and the surface elastic model. With this model, the indentation size effect of the structure is investigated from three aspects: the load-depth relationship, the distribution of bending moments in the film, and the surface morphology. The results show that the indentation size effect is mainly caused by the characteristic length and the surface residual stress of the film, and it is sensitive to the modulus ratio of the film to the substrate but has little relation with Poisson's ratio and the contact radius. Based on the above analysis, two dimensionless numbers are proposed to evaluate the indentation size effect of stiff film-compliant substrate structures. Besides, the predicted bending stiffness by the theoretical model is consistent with the experimental result, which verifies the effectiveness of the MSI model. Our research sheds light on the understanding of the indentation size effect of stiff film-compliant substrate structures and provides theoretical guidance for the design of related devices. [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]

We fabricated ferroelectric films of the organic molecular diisopropylammonium chloride (DIPAC) using the dip-coating technique and characterized their properties using various methods. Fourier-transform infrared, scanning electron microscopy, and X-ray diffraction analysis revealed the structural features of the films. We also performed ab-initio calculations to investigate the electronic and polar properties of the DIPAC crystal, which were found to be consistent with the experimental results. In particular, the optical band gap of the DIPAC crystal was estimated to be around 4.5 eV from the band structure total density-of-states obtained by HSE06 hybrid functional methods, in good agreement with the value derived from the Tauc plot analysis (4.05 ± 0.16 eV). The films displayed an island-like morphology on the surface and showed increasing electrical conductivity with temperature, with a calculated thermal activation energy of 2.24 ± 0.03 eV. Our findings suggest that DIPAC films could be a promising alternative to lead-based perovskites for various applications such as piezoelectric devices, optoelectronics, sensors, data storage, and microelectromechanical systems. [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 systems (MEMS) are used as sensors, actuators, energy harvesters, accelerometers, and communication modules. Aluminum nitride (AlN) is an especially attractive piezoelectric material because its fabrication process allows it to be integrated into semiconductor circuitry to deliver a fully integrated solution. Microelectromechanical resonators with AlN sandwiched between n‐type silicon (Si) and top metal electrode with and without a silicon oxide layer are designed and fabricated. The effect of the oxide film is up to a fourfold increase in quality factor (Q) that is consistent from very high frequency (VHF) to super high frequency (SHF). This effect is demonstrated using thin plate bulk acoustic wave modes from 70–80 MHz using the second contour mode and first width extensional mode and from 9.5–10.5 GHz using high overtone thickness modes. To explore potential applications of AlN‐transduced Q‐enhanced MEMS devices in harsh environments, measurements from −200 °C to +200 °C are performed. The Q enhancement is persistent across a wide temperature range for both VHF and SHF resonators with the added oxide layer. Furthermore, AlN‐on‐Si resonators that have a comparable temperature coefficient of frequency to silicon carbide‐based resonators in commercial applications are demonstrated. [ABSTRACT FROM AUTHOR]

In our recently published paper (Y.-Y. Wang et al., High performance LaNiO3-buffered, (001)-oriented PZT piezoelectric films integrated on (111) Si, Appl. Phys. Lett. 121, 182902, 2022), highly (001)-oriented PZT films with a large transverse piezoelectric coefficient e31,f prepared on (111) Si substrates were reported. This work is beneficial for the development of piezoelectric micro-electro-mechanical systems (Piezo-MEMS) because of (111) Si's isotropic mechanical properties and desirable etching characteristics. However, the underlying mechanism for the achievement of a high piezoelectric performance in these PZT films going through a rapid thermal annealing process has not been thoroughly analyzed. In this work, we present complete sets of data in microstructure (XRD, SEM and TEM) and electrical properties (ferroelectric, dielectric and piezoelectric) for these films with typical annealing times of 2, 5, 10 and 15 min. Through data analyses, we revealed competing effects in tuning the electrical properties of these PZT films, i.e., the removal of residual PbO and proliferation of nanopores with an increasing annealing time. The latter turned out to be the dominating factor for a deteriorated piezoelectric performance. Therefore, the PZT film with the shortest annealing time of 2 min showed the largest e31,f piezoelectric coefficient. Furthermore, the performance degradation occurred in the PZT film annealed for 10 min can be explained by a film morphology change, which involved not only the change in grain shape, but also the generation of a large amount of nanopores near its bottom interface. [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]

Thin-film piezoelectric materials are advantageous in microelectromechanical systems (MEMS), due to large motion generation, high available energy and low power requirements. In this kind of application, thin piezoelectric films are subject to mechanical and electric cyclic loading, during which damage can accumulate and eventually lead to fracture. In the present study, continuum damage mechanics and asymptotic theory are adopted to model damage evolution in piezoelectric thin films. Our purpose is to develop a new interface model for thin piezoelectric films accounting for micro-cracking damage of the material. The methods used are matched asymptotic expansions, to develop an interface law, and the classic thermodynamic framework of continuum damage mechanics combined with Kachanov and Sevostianov's theory of homogenization of micro-cracked media, to characterize the damaging behavior of the interface. The main finding of the paper is a soft imperfect interface model able to simulate the elastic and piezoelectric behavior of thin piezoelectric film in the presence of micro-cracking and damage evolution. The obtained interface model is expected to be a useful tool for damage evaluation in MEMS applications. As an example, an electromechanically active stack incorporating a damaging piezoelectric layer is studied. The numerical results indicate a non-linear evolution of the macroscopic response and a damage accumulation qualitatively consistent with experimental observations. [ABSTRACT FROM AUTHOR]

With the development of technology, systems gravitate towards increasing in their complexity, miniaturization, and level of automation. Amongst these systems, ultrasonic devices have adhered to this trend of advancement. Ultrasonic systems require transducers to generate and sense ultrasonic signals. These transducers heavily impact the system's performance. Advancements in microelectromechanical systems have led to the development of micromachined ultrasonic transducers (MUTs), which are utilized in miniaturized ultrasound systems. Piezoelectric micromachined ultrasonic transducers (PMUTs) exhibit higher capacitance and lower electrical impedance, which enhances the transducer's sensitivity by minimizing the effect of parasitic capacitance and facilitating their integration with low-voltage electronics. PMUTs utilize high-yield batch microfabrication with the use of thin piezoelectric films. The deposition of thin piezoelectric material compatible with complementary metal-oxide semiconductors (CMOS) has opened novel avenues for the development of miniaturized compact systems with the same substrate for application and control electronics. PMUTs offer a wide variety of applications, including medical imaging, fingerprint sensing, range-finding, energy harvesting, and intrabody and underwater communication links. This paper reviews the current research and recent advancements on PMUTs and their applications. This paper investigates in detail the important transduction metrics and critical design parameters for high-performance PMUTs. Piezoelectric materials and microfabrication processes utilized to manufacture PMUTs are discussed. Promising PMUT applications and outlook on future advancements are presented. [ABSTRACT FROM AUTHOR]

The BiFeO3-based film is one of the most promising candidates for lead-free piezoelectric film devices. In this work, the 1 μ m-thick Bi( Fe 0. 9 3 Mn 0. 0 5 Ti 0. 0 2 )O3 (BFMT) films are grown on the ITO/glass substrate using a sol-gel method combined with spin-coating and layer-by-layer annealing technique. These films display a large saturated polarization of 95 μ C/cm2, and a remanent polarization of 70 μ C/cm2. Especially, the films are self-poled caused by an internal bias field, giving rise to asymmetric polarization-electric field (P − E) loops with a positive shift along the x -axis. A stable self-polarization state is maintained during the applied electric field increasing to 1500 kV/cm and then decreasing back. The weak dependence of P − E loops on frequency (1–50 kHz) and temperature (25–125 ∘ C) indicate that the internal bias field can be stable within a certain frequency and temperature range. These results demonstrate that the self-polarized BFMT thick films can be integrated into devices without any poling process, with promising applications in micro-electro-mechanical systems. [ABSTRACT FROM AUTHOR]

Integration of high-performance lead zirconate titanate (PZT) piezoelectric films onto (111) Si substrates is beneficial for the development of piezoelectric micro-electro-mechanical systems (Piezo-MEMS) because of (111) Si's isotropic mechanical properties and desirable etching characteristics. These features will greatly reduce complications in micro-device fabrication and patterning of PZT/Si heterostructures. However, piezoelectric performance of a PZT film is usually dominated by its preferred crystalline orientation, with (001) being superior than (110) and (111). Such a vectorial dependence seriously restricts applications of PZT films grown on (111) Si, which are usually not (001)-textured. In this work, highly (001)-oriented PZT thick films (∼1.5 μm) with a 53/47 Zr/Ti ratio were prepared on (111) Si substrates via a multi-layer buffering technique, i.e., through the use of a (111)Pt/Ti bi-layer and a LaNiO3 buffer layer. The PZT films were sputter-deposited at a low temperature (350 °C) and then crystallized in a (001) texture via a rapid thermal annealing (RTA). The e31,f transverse piezoelectric coefficient was up to ∼11.6 C/m2 for PZT films with a RTA time of 2 minutes. Such an e31,f value is comparable to that of PZT films grown on (100) Si. This work opens up many possibilities for Piezo-MEMS by demonstrating the desirable combination of a large piezoelectricity in (001) PZT with a good patternability of (111) Si. [ABSTRACT FROM AUTHOR]

The integration of piezoelectric and micro-electro-mechanical system (MEMS) technologies is promoting the rapid development of the MEMS industry. However, due to the lack of excellent in-plane and out-of-plane piezoelectric coefficients, good ambient temperature stability, and high mechanical durability, the reported two-dimensional piezoelectric thin films are facing severe challenges in the development of MEMS. Therefore, based on density functional theory calculations, we simulated the VIA group (the sixth main family in the periodic table of elements) functional MXenes, namely, Sc2CXY (Sc2COS, Sc2COSe, Sc2CSO, and Sc2CSeO). The results show that this kind of material has good dynamic, thermal, and mechanical stability. Importantly, the structure exhibits good in-plane and out-of-plane piezoelectric effects due to the inversion asymmetry, bandgap adjustability, flexibility, and different electronegativity. Among them, the piezoelectric strain value of d33 is one to three orders of magnitude higher than that of d22 or d31, which makes these materials can become a strong candidate for advanced equipment such as nano-wearable electronics, robot bionic skin, and piezoelectric products for MEMS. [ABSTRACT FROM AUTHOR]

Potassium sodium niobate [(K,Na)NbO3, KNN] films are promising lead-free piezoelectric materials for microelectromechanical systems (MEMS) devices. We previously developed technologies for forming high-quality KNN films by sputtering, which showed excellent piezoelectric properties comparable to lead zirconate titanate (PZT) films. In the present study, we addressed several challenges with the aim of introducing KNN films into commercialized MEMS devices. First, we optimized the dielectric and piezoelectric properties to realize a suitable performance for actuator and sensor devices. The sensor-type KNN films had a low dielectric constant (248) and a self-poling function, which are greatly beneficial for sensor device performance and the fabrication process. The actuator-type KNN films had a very high e31 value of −13.5 C/m2, which is almost comparable to the top level of PZT films. Next, we found that the DC stress lifetime of KNN films strongly depended on the material used for the adhesion layer of the top electrode. When we used a Pt/RuO2 top electrode, the actuator-type KNN films had a long lifetime (>130 000 s, 300 kV/cm and 200 °C), which is long enough to be used for commercialized MEMS devices. Furthermore, we realized 8-in. KNN wafers with good thickness uniformity across the wafer (±3.5%) by introducing a mass-production-ready sputtering tool: the EB-2500 produced by Canon Anelva. In the near future, these promising results will open the way to replace PZT with KNN in the piezoMEMS industry. [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]

In this article, the presented work aims to scavenge maximum electrical outputs by using the novel microelectromechanical system flared-U shaped spring based piezoelectric vibration energy harvester (PVEH). The performance studies were carried out by employing four different variations of lead zirconate titanate (PZT) piezoelectric material namely PZT-4, PZT-5A, PZT-5H, and PZT-8 in the same size and shape of the proposed device. The maximum output powers employing PZT-4, PZT-5A, PZT-5H, and PZT-8 piezoelectric materials are 7.156 nW, 8.657 nW, 10.738 nW, 5.701 nW over 30 Hz, 28.4 Hz, 28.6 Hz, and 30.2 Hz, resonant frequency, respectively, at input acceleration of 0.07 g. From the finite element method simulator COMSOL Multiphysics 5.4 (licensed version) simulation-based outcomes, it is inferred that PZT-5H piezoelectric material performs better than other variations of PZT, such as PZT-4, PZT-5A, and PZT-8 piezoelectric materials. [ABSTRACT FROM AUTHOR]

To meet the growing demand for better piezoelectric thin films for microelectromechanical systems (MEMSs), we have developed an SM-doped Pb(Mg1/3, Nb2/3)O3–PbTiO3 (Sm-PMN-PT) epitaxial thin film as a next-generation piezoelectric thin film to replace Pb(Zr, Ti)O3 (PZT). The inherent piezoelectricity $\left |{ {e}_{{31},{f}} }\right |$ achieved 20 C/m2, which is greater than those of intrinsic PZT thin films and the best Nb-doped PZT thin film. Besides, the simulation results show that the $\left |{ {e}_{{31},{f}} }\right |$ value of the single Sm-PMN-PT film could be around 26 C/m2. Meanwhile, the breakdown voltage of the as-deposited thin film was higher than 300 kV/cm. These results suggest the high potential of the Sm-PMN-PT epitaxial thin film for piezo-MEMS actuators with large displacement or force. [ABSTRACT FROM AUTHOR]

To explore new lead-free piezoelectric materials that is both environmentally friendly and healthy to provide the possibility for material selection for microelectromechanical systems. Lead-free piezoelectric (1- x)(0.8Bi 0.5 Na 0.5 TiO 3 -0.2Bi 0.5 K 0.5 TiO 3)- x Bi(Ni 0.5 Zr 0.5)O 3 thin films (abbreviated as BNT-BKT- x BNZ) (x =0.00, 0.01, 0.02, 0.03, 0.04) were prepared on Pt(111)/Ti/SiO 2 /Si substrates by a sol-gel method. Impacts of Bi(Ni 0.5 Zr 0.5)O 3 content on the microstructure, dielectric, ferroelectric, and piezoelectric properties were also investigated detailedly. It found that the Bi(Ni 0.5 Zr 0.5)O 3 composition had a great influence on the increase of relaxor and the decrease of the oxygen vacancies, which is influential to the promotion of thin-film properties. Thin-film of BNT-BKT-0.02BNZ showed the optimum electrical properties with the polarization of 40.27 μC/cm2, dielectric constants of 477 and effective inverse piezoelectric coefficient reach up to 125.9 p.m./V. Results revealed that the BNT-BKT thin films with 0.02 mol% Bi(Ni 0.5 Zr 0.5)O 3 -doped are a kind of lead-free piezoelectric materials with superior manifestations with a great development prospect for applications. [ABSTRACT FROM AUTHOR]

Accurate and efficient measurements of the piezoelectric properties of AlN and AlScN films are very important for the design and simulation of micro-electro-mechanical system (MEMS) sensors and actuator devices. In this study, a process control monitor (PCM) structure compatible with the device manufacturing process is designed to achieve accurate determination of the piezoelectric coefficients of MEMS devices. Double-beam laser interferometry (DBLI) and laser Doppler vibrometry (LDV) measurements are applied and combined with finite element method (FEM) simulations, and values of the piezoelectric parameters d33 and d31 are simultaneously extracted. The accuracy of d31 is verified directly by using a cantilever structure, and the accuracy of d33 is verified by in situ synchrotron radiation X-ray diffraction; the comparisons confirm the viability of the results obtained by the novel combination of LDV, DBLI and FEM techniques in this study. [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]

This paper presents a lead zirconate titanate (PZT) thick-film microcantilever fabricated on a stainless-steel substrate using electrohydrodynamic jet (E-jet) deposition. PZT thick-film functional layer arrays were produced directly on stainless-steel substrates via E-jet deposition to form microcantilevers with a width of only 150 μm and thickness of 62 μm. The method can realise batch manufacturing of microscale cantilevers, improve the PZT active layer energy and microcantilever fracture toughness under vibrational deformation, and eliminate the need for complex photolithography and etching processes. The microcantilever accurately realised the correct mode shapes, consistent with simulation results. The vibrational amplitude of the microcantilever reached 5.14 μm, while Q m was up to 688.1, considerably larger than those of thick-film silicon-based microcantilevers and free-standing microcantilevers with similar sizes. An effective electromechanical coupling coefficient, K eff , of approximately 0.13 was obtained. The potential for efficient applications in microelectromechanical system piezoelectric devices was confirmed. [ABSTRACT FROM AUTHOR]

Piezoelectric materials perform mechanical-to-electrical energy conversion and have unique and enhanced properties, particularly in the thin film form. In this work, the chemical potential of free surface for piezoelectric solids is defined and the mechanical field, electric field, and stability of a piezoelectric ceramic thin film are linearly analyzed. Expressions of the perturbed stress and electric field intensities, to first order approximation in perturbed amplitude to wavelength ratio, are derived, which show that the stresses and electric field intensities are directly proportional to the lattice mismatch and the perturbed amplitude, and decrease with increasing perturbed wavelength. The critically perturbed wavelength, which the flat film for the perturbation is stable, is obtained. [ABSTRACT FROM AUTHOR]

The aim of the present study is to present an effect boundary element method (BEM) for electroelastic analysis of ultrathin piezoelectric films/coatings. The troublesome nearly singular integrals, which are crucial in applying the BEM for thin‐structural problems, are calculated accurately by using a nonlinear coordinate transformation method. The advanced BEM presented requires no remeshing procedure regardless of the thickness of the thin structure. Promising BEM results with only a small number of boundary elements can be achieved with the relative thickness of the thin piezoelectric film is as small as 10−8, which is sufficient for modeling many ultrathin piezoelectric films as used in smart materials and micro‐electro‐mechanical systems. The present BEM procedure with thin‐body capabilities is also extended to general multidomain problems and used to model ultrathin coating/substrate piezoelectric structures. The influence of relative layer‐to‐substrate thickness and the bimaterial mismatch parameters are carefully investigated. Excellent agreement between numerical and theoretical solutions has been demonstrated. [ABSTRACT FROM AUTHOR]

Lifetime and reliability in realistic operating conditions are important parameters for the application of thin-film piezoelectric microelectromechanical systems (piezoMEMS) based on lead zirconate titanate (PZT). Humidity can induce time-dependent dielectric breakdown at a higher rate compared to dry conditions, and significantly alter the dynamic behavior of piezoMEMS-devices. Here we assess the lifetime and reliability of PZT-based micromirrors with and without humidity barriers operated at 23°C in an ambient of 0 and 95 % relative humidity. The correlation of the dynamic response, as well as the ferroelectric, dielectric, and leakage properties, with degradation time was investigated. In humid conditions, the median time-to-failure was increased from ${2.7\times }{10}^{4}{[1.9\times }{10}^{4}{-4.0\times }{10}^{4}{]}$ s to ${1.1\times }{10}^{6}{[0.9\times }{10}^{6}{-1.5\times }{10}^{6}{]}$ s at 20 $\text{V}_{{\mathrm {AC}}}$ continuous unipolar actuation, by using a 40 nm thick Al2O3 humidity barrier. However, the initial maximum angular deflection, polarization, and dielectric permittivity decreased by about 6, 11, and 12 %, respectively, for Al2O3 capped devices. For both bare and encapsulated devices, the onset of electrothermal breakdown-events was the dominant cause of degradation. Severe distortions in the device’s dynamic behavior, together with failure from loss of angular deflection, preceded time-dependent dielectric breakdown in 95% relative humidity. Moreover, due to the film-substrate stress transfer sensitivity of thin-film devices, water-induced degradation affects the reliability of thin-film piezoMEMS differently than bulk piezoMEMS. [2020-0228] [ABSTRACT FROM AUTHOR]

In this work, we address the modelling of piezo-micromirrors with large opening angles. We focus on various sources of nonlinearites induced by the interaction with the surrounding fluid and by occurrence of geometric large transformations. Specific attention is also devoted to the piezoelectric coupling coefficient. Piezoelectric thin films have gained attention as key materials for the actuation of micro devices since they provide high drive forces, enabling devices with higher performances compared to electrostatic actuation. However they also induce material nonlinearities that cannot be neglected. The model is validated using experimental data obtained for various excitation levels. [2020-0229] [ABSTRACT FROM AUTHOR]

A non-linearly decreasing piezoelectric coefficient with an external electric field is an intrinsic property of a fully poled ferroelectric film, which has been observed in the measured longitudinal piezoelectric responses. However, for transverse piezoelectric responses, the observed converse piezoelectric coefficients (e 31,f) have displayed a different trend. Here we show that this disagreement can be rationally resolved by utilizing a small field e 31,f test under a sweeping direct current bias voltage, in which the field-dependent transverse piezoelectric response of a (001)-film is analyzed in a stepwise manner. Understanding of this nonlinear field-dependence will help improve the design of transverse piezoelectric devices. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We have developed a unique sputter deposition technique for a pure-perovskite (001)/(100)-oriented samarium-doped Pb(Mg1/3, Nb2/3)O3–PbTiO3 (Sm-PMN-PT) epitaxial thin film on Si as a future piezoelectric transducer thin film in microelectromechanical systems (MEMSs). This technique bases on the use of a “Pb(Zr,Ti)O3 (PZT)-based seed layer” and “separate sputter deposition.” Undesired orientations and phases of such a relaxor-based ferroelectric are usually generated during the sputter deposition. This technique was demonstrated to provide preferential (001)/(100) orientation and pure-perovskite phase to the monocrystalline thin film. The fabricated film had excellent homogeneousness of the content distribution. Considering a practical thickness, a 2- $\mu \text{m}$ -thick monocrystalline thin film was grown on an Si substrate with this technique. Then, the piezoelectricity $\vert {e}_{{31},{f}}\vert $ of the Sm-PMN-PT/PZT stacked film was evaluated through an actuation test of the unimorph cantilever. As a result, it measured 16–17 C/m2, which is almost comparable with intrinsic PZT polycrystalline thin films with high $\vert {e}_{{31},{f}}\vert $ values. Considering that the actuation voltage was divided into Sm-PMN-PT and PZT layers, the inherent piezoelectricity of the Sm-PMN-PT thin film is expected to be higher. Optimization of the phase in the film by tuning the composition ratio also will further improve the piezoelectricity. We believe that this achievement is a great step to discover a giant piezoelectricity relaxor-based thin film beyond PZT for MEMS. [ABSTRACT FROM AUTHOR]

This paper discusses the growth and evolution of residual stresses in (0002) preferentially oriented aluminum nitride (AlN) layers on Si (111) wafers by sputtering technique for the development of micro-electro-mechanical system (MEMS) accelerometer. The microstructure of the deposited films exhibited vertical columnar structures. Residual stresses in the sputtered AlN films are − 1.2 GPa, − 0.8 GPa, and − 0.25 GPa for the film thickness of 600 nm, 750 nm, and 900 nm respectively. The effect of the residual stress on the piezoelectric MEMS acceleration sensor structure is analyzed. The presence of residual stress reduced the resonant frequency (up to 14.72%) and bandwidth (up to 27.3%) of the accelerometer. The locations of the von-Mises stress maxima are shifted from the beam edges (adjoining to the proof-mass) to the whole proof-mass area. The normalized stress sensitivity (which defines the piezoelectric charge sensitivity) is reduced by two orders due to the residual stress in the AlN layers. [ABSTRACT FROM AUTHOR]

Piezoelectric thin films are vulnerable to fracture, which results in degradation of the structural integrity and device performance in piezoelectric microelectromechanical systems (PiezoMEMS). This work explains the fracture process as a combination of a crack initiation event in the piezoelectric film followed by crack propagation through the remaining layers. Biaxial bending tests using the Ball-on-three-Balls (B3B) technique were performed on stacks containing Pb(Zr 0.52 Ti 0.48)O 3 (PZT) thin films of varying thicknesses grown on Si wafers (coated with thin LaNiO 3 /SiO 2 layers). The fracture initiates in the PZT film, arrests in the compressive SiO 2 layer, prior to failure of the Si substrate. Weibull analyses show a significant effect of the thin film thickness on the stack's strength; the characteristic strength and Weibull modulus being σ 0 ∼1110 MPa and m ∼28, σ 0 ∼1060 MPa and m ∼26, and σ 0 ∼880 MPa and m ∼10 for the 0.7 µm, 1.3 µm, and 1.8 µm film stack, respectively and σ 0 ∼ 1820 MPa and m ∼3 for the Si wafer. A stress-energy criterion using finite fracture mechanics explains the dependence of crack initiation load on the PZT layer thickness, whereas linear elastic fracture mechanics is employed to rationalize crack propagation through the stack. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Recent studies on piezoelectricity in 2D materials, such as graphene, have revealed their potential in multiple applications including microelectromechanical systems. In this work, we reveal piezoelectricity in few-layer graphene sheets deposited on amorphous Si3N4 membranes. The response in the center of square membrane of 6.7 × 6.7 mm2 size reaches about 14 nm at resonance and could be further enhanced by adjusting the composite structure. Resonance piezoelectric phenomena are fully consistent with the earlier piezoresponse force microscopy observations on free-standing piezoelectric graphene and open up a possibility of using 2D materials in micromechanical applications. [ABSTRACT FROM AUTHOR]

In this paper, a D33-mode piezoelectric micro-accelerometer with Pb1.1(Zr0.52Ti0.48)O3(PZT) thin film is designed, fabricated and tested. Both the polarization and deformation directions of the piezoelectric thin film are horizontal in this structure. With the high sensitivity and natural frequency, the D33-mode piezoelectric micro-accelerometer possesses improved practicality. The influence of filling factor (Γ) and interdigital electrode width (b) on the output voltage is analyzed in this work. The micro-electro-mechanical systems technology is then used to fabricate the piezoelectric accelerometer device, which is based on the Sol–Gel PZT piezoelectric thin film. Performance of the piezoelectric accelerometer micro-devices with the different Γ and b is tested on the vibration table. The experimental results show that the sensitivity of D33-mode piezoelectric accelerometer is inversely to the filling factor and interdigital electrode width. The piezoelectric accelerometer with a filling factor of 0.5 and an interdigital electrode width of 5 μm can generate an output voltage of 149.83 mV. [ABSTRACT FROM AUTHOR]

We have made an attempt to fabricate free standing warpage free PZT thick films of 100 µm thickness by tape casting method. The poly crystalline nature and nanoscale polarization switching of free standing thick film were confirmed using X-ray diffraction technique and piezo force microscopy, respectively. The piezoelectric coefficient (d33) of 100 µm free-standing Pb(Zr0.56Ti0.44)O3 [PZT] thick film was calculated using double beam laser interferometer and found to be 400 pm/V. From the results, it indicates that free-standing PZT thick films are suitable candidate for miniaturization of harvesting device by directly bonding them on microsystem components for microelectromechanical systems (MEMS) applications. [ABSTRACT FROM AUTHOR]

Film bulk acoustic wave resonators have demonstrated great potential in the detection of volatile organic compounds owing to their high sensitivity, miniature size, low power consumption, capacity for integration, and other beneficial characteristics. However, it is necessary to functionalize the surfaces of these resonators to enhance the adsorption and discrimination of volatile organic compounds. Here, we report a convenient and reliable method for functionalizing the surfaces of film bulk acoustic wave resonators with hydrophobins via self-assembly to enable highly sensitive and polarity sensitive detection of volatile organic compounds. Experiments conducted using various concentrations of five volatile organic compounds possessing different polarities demonstrated that the hydrophobin coating enhanced the responsivity of the proposed sensor. The obtained results were in good agreement with the Brunauer–Emmett–Teller model of multilayer physisorption, which suggests that the hydrophobin coating enhanced the sensitivity by improving the monolayer adsorption capacity. Our work demonstrates that the combination of multifunctional biosurfactants and microelectromechanical devices can permit high-performance gas sensing. [ABSTRACT FROM AUTHOR]

Integrated nanoelectromechanical systems (NEMS) exhibit enormous potential for replacing current microelectromechanical systems in various fields, such as 5G/6G wireless communication, in the future. However, their advancement is impeded by the challenge of achieving nanometer-thick ferroelectric oxide films with a high piezoelectric coefficient of d 33. Herein, the nm-thick flexible Hf 0.5 Zr 0.5 O 2 (HZO) films were deposited on mica substrates, and they exhibited a remnant polarization of ≥ 8.1 μC/cm2 at 25–320 °C and a high d 33 value of 37.8 pC/N at 25 °C. After the HZO films with inter-digitated electrodes were fully polarized, the flexible HZO film with a dynamic bending strain of 0.102 % at 4 Hz produced an open-circuit voltage of 1.1 V. This HZO film with strong piezoelectricity can promote the development of novel NEMS and flexible piezoelectric sensors. • The flexible Hf 0.5 Zr 0.5 O 2 (HZO) films exhibit a remnant polarization of ≥ 8.1 μC/cm2 at 25–320 °C. • The ferroelectric polarization can withstand switch for 1010 cycles. • The 10-nm-thick flexible HZO film shows a high d 33 value of 37.8 pC/N at 25 °C. • The flexible HZO film with dynamic bending can produce an open-circuit voltage of 1.1 V. [ABSTRACT FROM AUTHOR]

Piezoelectric Micromachined Ultrasonic Transducer (PMUT) is a microelectromechanical system (MEMS). Unlike bulk piezoelectric transducers which use the thickness mode motion of a plate of piezoelectric ceramic, PMUT are based on the flexural motion of a thin membrane coupled with a thin piezoelectric film. The paper offers algorithm for simulation design of PMUT sensor with high level of detail. It is intended for students, professors and designers. The design of experiment (DoE) includes application of theory for: PMUT, Amplifier, Schmitt-trigger, SR-trigger, sample-and-hold scheme, analog-to-digital converter, controller and RF-transmitter. The methodology belongs to edge computing. With the chosen detail level, the algorithm is a good base for design of network element in IoI-environment. [ABSTRACT FROM AUTHOR]

Simplified one-dimensional models for composite beams with piezoelectric layers, which are intrinsically three-dimensional structures, are important for many applications, including piezoelectric energy harvesters. To reduce the dimensionality of the system, assumptions on the stress/strain state in the transverse direction are typically made. The most common are those of null transverse stress, used for narrow beams, null transverse deformation, used for wide beams, and continuous interface strain, suited for thin piezoelectric layers (we call this assumption thin film continuous). We show that the models based on these assumptions are often used uncritically for beam geometries for which large errors may result. In particular, null transverse stress fails even for narrow beams if the thickness is much smaller than the beam width. We give clear geometric criteria that, for any geometry, allow the selection of the most accurate model among the three. We also develop a single, unified beam equation encompassing the three models and compare the analytical results from this equation with finite element simulations over a wide range of beam lengths, widths, and layer thicknesses. The selection criteria and the unified beam equation form a valuable tool for fast and accurate design of composite piezoelectric beams. [ABSTRACT FROM AUTHOR]

In this contribution, we discuss the implementation of a novel microelectromechanical-systems (MEMS)-based energy harvester (EH) concept within the technology platform available at the ISAS Institute (TU Vienna, Austria). The device, already presented by the authors, exploits the piezoelectric effect to convert environmental vibrations energy into electricity, and presents multiple resonant modes in the frequency range of interest (i.e. below 10 kHz). The experimental characterisation of a sputter deposited aluminium nitride piezoelectric thin-film layer is reported, leading to the extraction of material properties parameters. Such values are then incorporated in the finite element method model of the EH, implemented in Ansys Workbench™, in order to get reasonable estimates of the converted power levels achievable by the proposed device solution. Multiphysics simulations indicate that extracted power values in the range of several µW can be addressed by the EH-MEMS concept when subjected to mechanical vibrations up to 10 kHz, operating in closed-loop conditions (i.e. piezoelectric generator connected to a 100 kΩ resistive load). This represents an encouraging result, opening up the floor to exploitations of the proposed EH-MEMS device in the field of wireless sensor networks and zero-power sensing nodes. [ABSTRACT FROM AUTHOR]

Highlights • A theoretical study of sensor using MEMS diaphragm embedded with FBAR is presented. • The response frequencies of FBAR under load are calculated using Mason model by ADS. • The frequencies shift of FBAR varies linearly with load vapors. • The sensitivity of this sensor for chloroform is approximately 2.5 Hz/ppm. Abstract Film bulk acoustic resonators (FBAR) are widely applied in mass, bio-sensing and pressure sensors. In this work, a theoretical study of the VOC sensor based on polymer-coated diaphragm embedded with FBAR is presented. The sensing film swells and leads to the deformation of diaphragm when it is exposed to organic vapor. The FBAR is used to transform the deformation into a measurable output frequency. A model of the interaction between diaphragm embedded FBAR and sensing layer is presented. In this model, the stress distribution of the FBAR area under vapor loads is obtained using the finite element analysis (FEA) based on the equivalence principle of polymer swelling. Then, the longitudinal elastic coefficient variation of piezoelectric film in FBAR under the bending stress is deduced using the first principle methods. Next the longitudinal wave velocity of the piezoelectric film is also obtained. Finally the response frequencies of the FBAR are calculated based on Mason model using ADS software. The simulation results show that the output resonant frequency shift of vapor sensor varies linearly with concentration of vapor and the sensitivity of this sensor for chloroform is approximately 2.5 Hz/ppm. To improve the performance of kind of vapor sensor, this analysis methods will be useful for optimizing the design parameters of FBAR and sensing film. [ABSTRACT FROM AUTHOR]

Graphical abstract A MEMS-based vibration energy harvester with highly c-axis oriented AlN piezoelectric thin film is designed and investigated, which has maximum output power density of 854.55 μW/cm3/g2. Furthermore, the high-precision coupled distributed parameter model of the device is derived and verified. Highlights • A MEMS-based AlN energy harvester with high output power density is designed. • The highly c-axis oriented aluminum nitride piezoelectric thin film is deposited. • The high-precision coupled distributed parameter model is derived and verified. • The engine fault monitoring node based on the AlN energy harvester is designed. Abstract Piezoelectric vibration-based energy harvesting is a promising alternative for the durable and reliable power supplies for the low-powered wireless sensor networks nodes. However, improving the piezoelectric vibration-based energy harvester’s energy conversion efficiency related closely on the structure parameters and materials become significant and urgent. In this paper, a micro-electromechanical systems (MEMS) cantilever-based aluminum nitride (AlN) vibration energy harvester is presented, modeled, optimized and fabricated. The c-axis oriented AlN piezo thin film is deposited by the pulsed direct-current magnetron sputtering with the optimized process parameters. Furthermore, the coupled distributed parameter model is derived in detailed, verified by using the ANSYS finite element analysis, and applied to the optimization of structural parameters and load resistance. Finally, the prototype of the device is fabricated by the standard bulk-silicon technology. As a result, at 1 g and 210.85 Hz, the maximum output root mean square (RMS) voltage can reach to 4.66 V, the output average power and output average power density of the prototype is up to 56.4 μW and 854.55 μW/(cm3·g2) at a load resistance of 146.6 kΩ, respectively. The experimental results agree well with theoretical analysis. The derived CDP model has an important and effective guiding role in cantilever based piezoelectric vibration energy harvester for structural design and performance optimization, especially for the device with long tip mass. The prototype has wide application prospects in the fields of the wireless sensor network node such as the structural health monitoring system. [ABSTRACT FROM AUTHOR]

Highlights • Novel piezoelectric energy harvesting device with multilayered PZT thin films. • 71 % of power harvesting versus theoretical limit. • Full batch fabrication without bonding bulk piezo-ceramics and proof mass. Abstract This study aims to report the design of high-performance piezoelectric MEMS energy harvesters using a full batch MEMS-fabrication process with a Si proof mass and multilayered Pb(Zr,Ti)O 3 (PZT) thin films without bonding of a proof mass and/or bulk piezoelectric ceramics. These devices contain sputtered multilayered PZT thin films with internal metal electrodes as a thick energy-conversion layer. The thickening of the piezoelectric layer by multilayer sputter deposition technique enabled the batch fabrication of high-performance piezoelectric MEMS harvesters. These fabricated device with the footprint of 10 × 10 mm2 was found to provide a high output power of 53.7 μW per gravitational acceleration. These results are expected to be useful for the future development of alternatives to batteries for autonomous sensor systems. [ABSTRACT FROM AUTHOR]

In this work, acoustic delay lines (ADLs) based on solidly mounted structures were studied to achieve low insertion loss (IL) and wide fractional bandwidth (FBW). By adopting the guided shear-horizontal wave (SH-wave) in thin-film lithium niobate on insulator (LNOI) configuration, the acoustic energy is constrained near the surface to attain high piezoelectric coupling (${K}^{2}$) to yield low IL and wide FBW. Proposed ADLs were designed with Au electrodes in X-cut LNOI to obtain sufficient ${K}^{2} > 27$ % up to 1-GHz, thus allowing a better IL-FBW tradeoff. Fabricated prototype ADLs with wavelength ($\lambda$) of $4~\mu \text{m}$ (940 MHz) and $6~\mu \text{m}$ (640 MHz) achieve IL around 10 dB and FBW around 9% simultaneously using conventional bidirectional transducers. Such a performance is comparable to suspended plate wave ADL counterparts while retains enhanced mechanical robustness for batch-manufacturing and packaging. [2020-0057] [ABSTRACT FROM AUTHOR]

Piezoelectric MEMS energy harvesters based on thin films are compact and cost-effective microgenerators for scavenging environmental vibrations. This technology is promising for the replacement of electrochemical batteries in low power autonomous sensors and microdevices capturing vibrations in the μW-mW range. Most of piezoelectric MEMS devices, reported in the last few years, exhibit low generated power/voltage and are not suitable for practical applications. This work reviews the current status of MEMS energy harvesters based on piezoelectric thin films, highlighting approaches/strategies to face the two main challenges to be addressed for high performance devices, namely generated power and frequency bandwidth. The paper introduces the theoretical principles and the main figures of merit of energy conversion in piezoelectric thin films and devices. After an overview on piezoelectric thin films for energy harvesting applications, highlighting their key properties, the manuscript reports a comprehensive survey on the state of the art for this device technology. The last section summarizes the review, highlighting key issues to be addressed and providing an insight into the future outlook to realize devices for practical applications. [ABSTRACT FROM AUTHOR]