Piezoelectric Properties Of Thin Films Research Articles

Flexible Piezoelectric Sensors Based on Ionic Liquid‐doped Poly(L‐Lactic Acid) for Human Coughing Recognition

AbstractCough is a common symptom of various respiratory diseases. However, recognizing a subject's cough using acoustic imaging can be challenging due to the complexity of coughing and the vulnerability of acoustic acquisition to external interference. This research aims to address these issues by utilizing a flexible piezoelectric ionic liquid‐doped poly(L‐lactic acid) (PLLA) sensor to gather the pressure signals from the human surface. 1‐butyl‐3‐methylimidazolium bis (trifluoromethylsulfonyl)imide ([BMIm]TFSI) ionic liquid (IL) can enhance the piezoelectric performance of PLLA thin film, the corresponding output voltage, and impact sensitivity are improved to three times and 105.1% for the PLLA/IL thin film with 1 wt% IL, 140 °C annealing 2 h and four times drawing ratio. The effect of IL on the crystallization behavior and piezoelectric properties of thin films during their preparation is investigated. The flexible PLLA/IL sensor is integrated into a wearable electronic system which collects and transmits piezoelectric signals from cough‐induced vibrations to the filter for denoising, then the acquired cough data are decomposed using the Empirical Mode Decomposition method and trained in a multi‐layer perception model to detect human coughing. It's evident that the flexible piezoelectric PLLA/IL sensors can be applied to human coughing recognition and show great potential applications in intelligent healthcare.

Structure-Piezoelectric Property Relationships of Thin Films Composed of Electrospun Aligned Poly(vinylidene fluoride) Nanofibers.

In the past two decades, many studies on piezoelectric nanofibers (NFs) prepared from poly(vinylidene fluoride) (PVDF) and its copolymers, including single NFs, randomly oriented nonwoven mats, and aligned NFs, have been reported. However, studies on the relationships between the PVDF NF diameter, the orientation of the β-phase crystals inside NFs, and the piezoelectric properties of the NFs are still limited. In this study, the effect of the fiber diameter on the internal molecular packing/orientation and piezoelectric properties of aligned PVDF NF thin films was investigated. Herein, piezoelectric thin films composed of densely packed, uniaxially aligned, PVDF NFs with diameters ranging from 228 to 1315 nm were prepared by means of electrospinning with a rotating collector and successive hot-pressing and poling. The effect of the diameters of PVDF NFs on their internal structures, as well as the piezoelectric properties of the thin films, was investigated. All prepared NFs mainly contained β-phase crystals with a similar total crystallinity. The orientation of the β-phase crystals inside the NFs increased with an increase in the fiber diameter, resulting in an improved transverse piezoelectric coefficient (d31) for the thin films. The output voltage of the prepared thin films reached a maximum of 2.7 V at 104 Hz.

Lattice distortion induced by rare‐earth ions doping in (Bi0.5Na0.5)TiO3‐based thin films with high piezoelectric properties

AbstractHigh‐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(Sr0.7Bi0.2□0.1)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.

Influence of annealing ambience on structural and piezoelectric properties of single crystal LiTaO3 thin film

The crystal-ion-slicing technology is a promising technology for fabricating high-quality single crystal piezoelectric thin films. This work attempted to investigate the influence of annealing ambience on the properties of LiTaO3 thin films fabricated by crystal-ion-slicing technology. Here, two 4-inch 42° rotated Y-X propagation LiTaO3 thin films were fabricated, as well as the LiTaO3 thin films were annealed in vacuum and O2 environment, respectively. The results demonstrate that the LiTaO3 thin films annealed in O2 environment possesses more homogeneous and denser structure and fewer defects. The Zratio of the resonators fabricated on the LiTaO3 thin films annealed in O2 environment is approximately 85.3 dB and the Q-factor reaches 5107, indicating the excellent piezoelectric properties of thin films.

Improved piezoelectric performance via orientation regulation in novel BNT-BT-SBT thin film

Lead-free piezoelectric thin films are urgently needed in microelectronic and microelectromechanical systems. In this work, (1-x)(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-x(Sr0.7Bi0.2□0.1)TiO3 (abbreviated as BNT-BT-xSBT) piezoelectric thin films were prepared successfully. The optimal piezoelectric performance can be achieved when x = 0.02 at morphotropic phase boundary (MPB). Further, to explore the impacts of orientation control on the properties of thin films, (100), (110), and (111)-oriented BNT-BT-0.02SBT thin films were prepared on Nb-SrTiO3 single crystal. The (110) preferred orientation thin film can achieve a high inverse piezoelectric coefficient (d33*) of 170 pm/V, which has a great improvement contrasted with non-oriented films. From the perspective of engineering domain configuration, the high d33* of (110)-oriented thin film can be characterized that the ferroelectric domain can get a complete flip in the direction of non-easily polarized axes. In short, orientation regulation is of great importance in improving the piezoelectric properties of thin films and has important applications in microelectronic sensing.

Piezoelectric, dielectric and ferromagnetic properties in epitaxial multiferroic Pb(Zr0.45,Ti0.55)O3/Co0.8Fe2.2O4 thin film treatment by nanosecond pulsed laser deposition

Recent years have seen a considerable research interest in multiferroic materials for their potential application as sensors and actuators. However, the scarcity of these materials in a single phase and the weak coupling of their ferroic components have directed research toward multiferroic heterostructures. These systems operate by coupling the magnetic and electric properties of two materials, generally ferromagnetic and ferroelectric, via strain. In this paper, thin films have been grown by chemical solution deposition (CSD) using spin coating technique using rotations peed of 4500 rpm and time of 50 s and dried at 120○C for 20 min. The optical, dielectric, magnetic, ferroelectric, ferromagnetic, and piezoelectric properties of thin films have been investigated by Uv- Visible spectrophotometer (300-2500) nm, X-Ray Diffraction (XRD), Vibrating Sample Magnetometer (VSM), Transmission Electron Microscope (TEM), and Scanning Electron Microscope (SEM) respectively. PZT/CFO thin films deposited at different temperatures from 400 °C, 500 °C and 600 °C. The as-deposited PZT/CFO show week piezoelectricity and the effective piezoelectric coefficient d33 because the materials deposited on the films not only the PZT layer but also the CFO layer, which decreases the piezoelectricity of these films. PZT/CFO Films were then recorded to enhance all physical properties (dielectric, optical, structural, surface morphology, and magnetic properties) as the sintering temperature increased. The images of a thin film before and after treatment with Nd-YAG, which have Power from 10 mw to 5300 mw, Pulse width: 7 ns pulsed laser, Repetition Rate: 10 HZ, and wavelength spectrum in (IR, Vis) laser beam indicate that sample prepared before treated has a lot of porous and agglomeration which decreases after treatment.

Manipulation of defects to achieve fast domain switching and enhance the piezoelectric properties of thin films

High-performance lead-free piezoelectric films play an important role in micro-electromechanical systems (MEMS), and the inevitable defects can affect the performance of the films. In particular, the coupling between defects and domain wall motion can be regarded as a general strategy for regulating the piezoelectric properties of thin films. Here, based on the existing vacancy defects in 0.8Bi0.5Na0.5TiO3-0.2(Sr0.7Bi0.2□0.1)TiO3 system, we control the balance of A-site defects through the introduction of rare earth La ions, release the rapid switching of domain structures and enhance the piezoelectric response of the thin film. The maximum inverse piezoelectric coefficient can reach 425.9 pm V−1. Under the in-situ electric field, a fast response of the domain structure can be observed, which is closely related to the reduction of defect concentration and releasing the pinning effect of domain walls. Also, phase coexistence was observed by TEM, which is attributed to the optimization of MPB by defect regulation. It is hoped that this process of balancing defects can provide a certain reference for the improvement of piezoelectric properties of thin films.

Phase composition, crystalline structure and piezoelectric properties of thin films of polyvinylidene fluoride obtained by the spin-coating method

The regularities of the formation of the structural state and the piezoelectric properties of PVDF films with a thickness of about 170 nm, obtained by spin-coating on glass substrates, are studied. Using the methods of IR spectroscopy, X-ray diffraction, and Raman spectroscopy, the dependences of the ratio of crystalline α- and β-phases on the initial acceleration and maximum substrate rotation speed are established. The optimal values of these parameters are found that provide the maximum concentration of the β phase (∼ 60 %) with spontaneous electric polarization. It was shown that in the films studied, the value of the piezoelectric coefficient d33, determined by the method of piezoresponse force microscopy, can take anomalously large values (up to 74 pm/V). This is due to the fixing effect of the glass substrate, which provides significant residual deformation of the polymer films.

Polarization behavior of` lead-free 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 thin films with enhanced ferroelectric properties

(Bi0.5Na0.5)TiO3 based ferroelectric lead-free thin films have great potential for modern micro-devices. However, the multicomponent feature and volatile nature of Bi/Na makes the achievement of high quality films challenging. In this work, the morphotropic phase boundary composition, 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 thin films were successfully prepared by CSD method. Dense films with low dielectric loss and low leakage current density were obtained. A well-defined polarization hysteresis loop with a high remnant polarization was observed in the thin films. Moreover, the polarization behavior of the film at original state, under electric field and upon heating was investigated by PFM. A self-polarization and asymmetric domain switching behavior were observed. High temperature induced depolarization and the self-polarization recovered upon cooling. The thin films with good quality show a promising potential for the application in electrical devices, and the in-depth investigation of the polarization behavior improves the understanding of ferroelectric and piezoelectric properties of thin films.

Flexible highly-effective energy harvester via crystallographic and computational control of nanointerfacial morphotropic piezoelectric thin film

Controlling the properties of piezoelectric thin films is a key aspect for designing highly efficient flexible electromechanical devices. In this study, the crystallographic phenomena of PbZr1–x Ti x O3 (PZT) thin films caused by distinguished interfacial effects are deeply investigated by overlooking views, including not only an experimental demonstration but also ab initio modeling. The polymorphic phase balance and crystallinity, as well as the crystal orientation of PZT thin films at the morphotropic phase boundary (MPB), can be stably modulated using interfacial crystal structures. Here, interactions with MgO stabilize the PZT crystallographic system well and induce the texturing influences, while the PZT film remains quasi-stable on a conventional Al2O3 wafer. On the basis of this fundamental understanding, a high-output flexible energy harvester is developed using the controlled-PZT system, which shows significantly higher performance than the unmodified PZT generator. The voltage, current, and power densities are improved by 556%, 503%, and 822%, respectively, in comparison with the previous flexional single-crystalline piezoelectric device. Finally, the improved flexible generator is applied to harvest tiny vibrational energy from a real traffic system, and it is used to operate a commercial electronic unit. These results clearly indicate that atomic-scale designs can produce significant impacts on macroscopic applications.

Evolution of electromechanical and morphological properties of piezoelectric thin films with thermomechanical processing

Piezoelectric polymers (PVDF and its co-polymers) in film and nanofiber forms are increasingly used for sensing, actuation and energy harvesting. Given the semi-crystalline structure of these polymers, their electromechanical coupling behavior changes with thermomechanical processing. This article reports on the evolution of the mechanical properties, piezoelectric properties and morphology of P(VDF-TrFE) poly[(vinylidenefluoride)-co-trifluoroethylene] piezoelectric polymer thin films fabricated by spin-coating during thermal annealing and drawing, studied via tensile test, polarized optical microscopy, X-ray diffraction, polarized FTIR, and piezoresponse force microscopy (PFM). The results show that annealing and drawing process result in ∼10 and 13 folds improvement in the elastic modulus and strength of the films, respectively. In addition, the piezoelectric constant and electromechanical coupling improves by 30% and more than 17 times, respectively. These changes are accompanied by 65% increase in the percentage of the crystallinity of the semi-crystalline piezoelectric films, compared to the as-fabricated films.

Modeling and characterization of piezoelectric beams based on an aluminum nitride thin‐film layer

This paper presents a method to determine the mechanical properties of piezoelectric thin films. The vibrational behavior of microcantilevers and clamped–clamped beams actuated by aluminum nitride (AlN) piezoelectric films were analyzed in order to investigate the suitability of these devices as characterization tools. Different geometries of resonators composed of a free‐standing structure made up of a TiPt/AlN/TiPt piezoelectric stack were tested. The out‐of‐plane motion of the resonators was assessed by laser Doppler vibrometry. An AlN Young's modulus of about 200 GPa was extracted from resonance‐frequency measurements by means of Comsol software simulations that allow taking into account AlN underetching. This value of Young's modulus was compared to the one measured by a nanoindentation technique. The quality of crystallinity was also assessed using X‐ray diffraction (XRD) measurements. We then estimated the residual stress (about 200 MPa) using an interferometry measurement.

Correlation between nanomechanical and piezoelectric properties of thin films: An experimental and finite element study

Piezoelectric materials perform mechanical-to-electrical energy conversion and have unique and enhanced properties, particularly in the thin film form. In this work, the nanomechanical properties of strontium-doped lead zirconate titanate thin films are investigated by nanoindentation. Finite element modeling of the nanoindentation process allows for a comparison of the simulated and experimentally measured load–displacement curves. New insights correlating the nanomechanical and piezoelectric properties of thin films have been obtained which will enable more efficient design of piezoelectric energy harvesting devices.

Spectroscopic imaging in piezoresponse force microscopy: New opportunities for studying polarization dynamics in ferroelectrics and multiferroics

Abstract

Nonlinear Properties of the ZnO Thin Films and Their Experimentally Verification by Laser Interferometry

The paper is focused to the nonlinear electromechanical properties of piezoelectric thin films subjected to the high electric field. The influence of the electric filed on the piezoelectric body is presented by the change of the elastic and piezoelectric modules. Experimentally, the zinc oxide (ZnO) thin film samples of (002)-orientation were prepared by RF magnetron sputtering the Pt/Ti/SiO2/Si substrates. The thin film samples were investigated under high electric field excitations and corresponding strains. The samples exhibit frequency dispersion and nonlinear piezoelectric response, i.e. the nonlinear dependence of the mechanical displacement d 0 (or effective piezoelectric coefficient d 33,eff) on the electric field. In the frequency range (0.1 – 1.5) kHz, the remarkable frequency dispersion of the mechanical displacement d 0 was found on the ZnO samples. The characteristic nonlinearities and hysteresis are presented, using the data, measured on the PZT (60/40) (111) thin film sample. The nonlinear electromechanical properties of the ZnO thin films were investigated by original double beam laser interferometer at room temperature. The results are discussed and compared with already published data.

Thin Film Piezoelectric MEMs Devices

Thin film piezoelectric devices, processed in Si‐related processes, are attractive for ultrasound transducers and piezoelectric switches. Thin film ultrasound transducer enable large bandwidth (> 100%), high frequency operation. In piezoelectric micromachined ultrasonic transducers (PMUTs) the ultrasonic waves are generated by flexural motion of the membrane, which is coupled to strain in the piezoelectric film. We have investigated the piezoelectric properties of thin films for ultrasound transducers and piezoelectric switches. Thin film piezoelectric ultrasound transducers as well as piezoelectric switches have been designed, processed and characterized. Thin film piezoelectric devices with excellent quality and reliability have been realized.

Relationships between material properties of piezo-electric thin films and device characteristics of film bulk acoustic resonators

The relationships between the material properties of piezo-electric thin films (such as ZnO and AlN) and the frequency response characteristics of film bulk acoustic resonator (FBAR) devices based on those films are examined. ZnO and AlN films are deposited by RF magnetron plasma reactive sputtering. Issues in film growth are focused on electric bias application, oxygen incorporation, and two-step deposition. The XRD spectra, AFM topographies, and SEM images measured from all the deposited films present the optimal condition for both ZnO and AlN films to have excellent piezo-electric properties. For ZnO films, excessive injection of oxygen deteriorates the crystal quality and increases the surface roughness. Applying negative d.c. bias during deposition contributes to the improvement of crystal quality of ZnO films as well as the enhancement of acoustic coupling capability of ZnO-based FBAR devices. By adopting the two-step method to deposit AlN films, the films reveal the highly (002)-preferred growth nature and the RMS surface roughness values are drastically reduced, which also leads to the remarkable improvement in the acoustic coupling coefficient of AlN-FBAR devices.

PZT 박막의 압전특성에 미치는 공정변수의 효과

We have studied the effect of crystallization temperature, composition and film thickness, which are the fundamental processing parameters of lead zirconate titanate(PZT) thin film fabrication, in the respect of the piezoelectric properties by our pneumatic loading method(PLM). A great deal of research has been done in the field of characterization for piezoelectric thin films after the first report on the measurement for the piezoelectric coefficient of thin films in 1990. Even though the piezoelectric properties of thin films are very critical factors in the micro-electro mechanical system(MEMS) and thin film sensor devices, a few reports for the piezoelectric characterization are provided for the last decade unlikely the bulk piezoelectric devices. We have found that the piezoelectric properties of thin films are improved as the increase of crystallization temperature up to 750<TEX>$\^{C}$</TEX> and this behavior can be also explained by the analysis of dielectric polarization hysteresis loop, X-ray diffraction and scanning electron microscopy. The effect of Zr/Ti composition has been also studied. This gives us the fact that the maximum piezoelectricity is found near Morphotropic Phase Boundary(MPB) as bulk PZT system does.

Piezoelectric and electrical properties of PZT-PSN thin film ceramics for MEMS applications

Piezoelectric and electrical properties of PZT-PSN ceramics have been investigated as a function of WO 3 addition from 0 to 6.0 wt%. The dielectric and piezoelectric characteristics of PZT-PSN ceramics have been investigated at different calcination (800–900°C) and sintering (1100–1300°C) temperatures. The grain size increased in proportion to adding the amount of WO 3 and increasing the sintering temperatures. Anisotropic properties of electromechanical coupling coefficient and piezoelectric coefficient are proven to be dependent on processing temperatures and amount of addition. For the specimen with 0.6 wt% WO 3 addition, using a calcination temperature of 800°C and a sintering temperature of 1100°C, the mechanical quality factor and electromechanical coupling coefficient were 1560 and 0.48, respectively. Thin films were deposited in situ onto Pt/Ti/SiO 2/Si substrates by pulsed laser deposition using a Nd:YAG laser. The microstructure, dielectric, electrical, and piezoelectric properties of thin films with the compound ceramics have been systematically investigated for microtransformer and MEMS applications.

Observation of Piezoelectric Relaxation in Ferroelectric Thin Films by Continuous Charge Integration

A continuous charge integration technique is used to measure the effective longitudinal piezoelectric coefficient (d33) of thin films. Measurements are performed by applying a static force normal to the films and recording the stress-induced polarization with a charge integrator. Measurements for the as-deposited PbZr0.53Ti0.47O3 (PZT) thin films show that the piezoelectric effect is strongly time-dependent and the relaxation is well described by the stretched exponential law. It was demonstrated that the continuous charge integration technique is highly useful for the characterization of the piezoelectric properties of thin films.