PZT Thin Films Research Articles

Piezoelectric MEMS microphones based on rib structures and single crystal PZT thin film

In this study, a controllable mass‒frequency tuning method is presented using the etching of rib structures on a single-crystal PZT membrane. The rib structures were optimized to reduce the membrane mass while maintaining the stiffness; therefore, the center frequency could be increased to improve the low-frequency bandwidth of microphones. Additionally, this methodology could reduce the modulus and improve the sensitivity for the same resonant frequency, which typically indicates the maximum acoustic overload point (AOP). The PZT film was chosen because of its greater density; the simulation results showed that PZT could provide a greater frequency tuning (24.9%) compared to that of the AlN film (5.8%), and its large dielectric constant enabled the optimal design to have small electrodes at the maximum stress location while mitigating the sacrificial capacitance effect on electrical gain. An analytical model of rib-structure microphones was established and greatly reduced the computing time. The experimental results of the impedance tests revealed that the center frequencies of the six microphones shifted from 74.6 kHz to 106.3 kHz with rib-structure inner radii ranging from 0 μm to 340 μm; this result was in good agreement with the those of the analytical analysis and finite element modeling. While the center frequency greatly varied, the measured sensitivities at 1 kHz only varied within a small range from 22.3 mV/Pa to 25.7 mV/Pa; thus, the membrane stiffness minimally changed. Moreover, a single-crystal PZT film with a (100) crystal orientation and 0.24-degree full width at half maximum (FWHM) was used to enable differential sensing and a low possibility of undesirable polarization. Paired with a two-stage differential charge amplifier, a differential sensing microphone was experimentally demonstrated to improve the sensitivity from 25.7 mV/Pa to 36.1 mV/Pa and reduce the noise from −68.2 dBV to −82.8 dBV.

A high sensitivity and wide frequency band vector hydrophone using PZT-based four spiral beam structure

The utilization of a high sensitivity and wide frequency band vector hydrophone exhibits significant potential in the exploration of underwater target. However, enhancing these performance remains a challenge due to limitations in materials and structures. Herein, we report a micro-electro-mechanical system (MEMS) vector hydrophone (FSPVH) built on lead zirconate titanate (PZT) film with four spiral beam structure and polyamide (PA) microsphere. The optimization of the structural dimensions and PZT thin film distribution has been the result of simulation. The FSPVH have been fabricated using MEMS technology, and the prototype has been assembled. The FSPVH was tested in a standing bucket wave calibration system. The results show that FSPVH achieve a sensitivity of −181.5 dB (0 dB = 1 V/μPa) at 1100 Hz, and the work bandwidth is 20–1330 Hz. Meanwhile, it exhibits a satisfactory “8″ shape directivity. This work provide theory and technique supports of vector hydrophone with high sensitivity and wide frequency band.

Revealing Fast Negative Capacitance in PbZr0.2Ti0.8O3 Thin Film with Acicular Ferroelastic Domains.

Negative capacitance effects with fast response times hold great potential for reducing the power consumption in high-frequency nanoelectronics. Nevertheless, the negative capacitance effect faces considerable complexity arising from the dynamic interplay among electrostatic, nucleation energies, and domain evolution. This intricate balance poses a formidable challenge to achieving fast negative capacitance. Herein, we have achieved a fast negative capacitance time of ∼16.23 ns in PbZr0.2Ti0.8O3 (PZT) thin film, and our investigation confirms the presence of acicular ferroelastic domains within the PZT thin film. Under reversal electric fields, these acicular ferroelastic domains undergo a unique flipping process, transitioning through domain expansion and contraction. This distinct domain flipping manner accelerates the nucleation and growth of ferroelectric domains, thereby facilitating the observed fast negative capacitance. The realization of fast negative capacitance holds substantial promise for reducing operational time and power consumption, offering prospects for the design of nanoelectronics with significantly lower power requirements.

Multi-step switchable superdomain architecture with enhanced photoelectrical performance in epitaxial ferroelectrics

Ferroic domains and relevant topological defects, such as domain walls and vortices, have gained significant attention as functional units for potential advancements in nanoelectronics. Pb(ZrxTi1-x)O3 (PZT) is a tetragonal ferroelectric material at room-temperature, exhibiting remarkable piezoelectricity and intricate domain structures. In this work, we explore the ferroelectric properties, photoelectric reactions, and efficient manipulation pathways of the unconventional superstructures in epitaxial (101)-oriented PZT thin films. Employing piezoresponse force microscopy (PFM) and conductive atomic force microscopy (cAFM), we unveil the three-dimensional polarization configurations of the superdomain structures inherently featuring conductive charged domain walls. Our findings reveal an increase in photoactivity at the head-side charged domain walls, attributed to the band-bending mechanism. Additionally, we discover the enhanced photoelectrochemical (PEC) performance in the superdomain structures compared to the (101)-oriented PZT films with conventional c/a domains. Furthermore, time-dependent pulse voltages are utilized to dynamically assess local currents and realize direct conductivity modulation by manipulating distinct polarization states. The elucidation of the photoelectrical mechanism and delineation of diverse pathways for intermediate state control underscore the potential of ferroelectric superdomains in constructing functional photoelectronic nanodevices.

Sm-doped PZT thin film with high piezoelectric properties by sol-gel method

Sm-doped PZT thin film with high piezoelectric properties by sol-gel method

Investigation of dielectric properties of Fe and Co coated thin films on PbZrTiO3

PbZr1-xTixO3 ceramic material, which has ferroelectric-piezoelectric properties, attracts great attention from researchers due to its electrical and electromechanical properties. In this study, Fe and Co materials with ferromagnetic properties were coated separately on the ferroelectric-piezoelectric PbZr0.5Ti0.5O3 (PZT) ceramic material by vacuum evaporation technique. The variation of dielectric properties such as dielectric constant, dielectric loss, loss tangent, cole-cole diagram of the prepared thin films with frequency was examined. Dielectric constant, dielectric loss, loss tangent, cole-cole diagram of pure PZT, Fe-coated PZT and Co-coated PZT thin films were measured with an impedance analyzer as a function of frequency (in the range of high frequency) at room temperature.

Investigation on liquid medium integration for piezoelectric MEMS tunable liquid lenses

In this paper, the design, fabrication and evaluation of a novel piezoelectric MEMS varifocal liquid lens are presented. The device consists of a thin film PZT actuator integrated with a liquid lens, featuring a new design with a modified disk-shaped actuator that enhances the overall displacement range. The primary innovation lies in simplifying the assembly process between the liquid/soft lens and the piezoelectric actuator, eliminating the need for vacuum bonding. Two types of liquid/soft lens materials, ionic gel and silicone oil, were investigated in different integration configurations to find the most suitable method. Analytical calculations and FEM simulations were conducted to optimize the actuator’s maximum displacement, which in turn maximizes the change in the device’s focal length. The developed actuator achieved around 15 µm of static displacement under a 40 V DC applied voltage, which matched well with simulation results. The shifting of the focus was clearly observed through a microscope, with the focal length estimated to change from infinity to about 31.6 mm at 35 V DC.

Fabrication and characterization of monocrystalline-based composite Pb(Zr, Ti)O3 thin film patterned with a polycrystalline crack stopper structure

This paper presents a novel form of Pb(Zr,Ti)O3 (PZT) thin film with a structure in which monocrystalline (Mono) PZT is sectioned with narrow mesh-like polycrystalline (Poly) PZT. The motivation is to overcome the inherent brittleness of piezoelectric Mono thin films. The design assumes that the Poly pattern will stop crack propagation within the Mono area. As a proof of concept, a Mono-Poly PZT composite thin film with a 20 μm-pitch and 2 μm-wide Poly pattern was sputter-deposited on a patterned underlayer on a Si substrate. Its piezoelectric properties were close to those of pure Mono PZT thin films, while its dielectric constant was significantly lower than those of pure Poly PZT thin films. Indentation tests confirmed the Poly patterns effectively stops crack propagation, which is likely to improve the mechanical durability of the overall film.

Substrate dependence of the self-heating in lead zirconate titanate (PZT) MEMS actuators

Lead zirconate titanate (PZT) thin films offer advantages in microelectromechanical systems (MEMSs) including large motion, lower drive voltage, and high energy densities. Depending on the application, different substrates are sometimes required. Self-heating occurs in the PZT MEMS due to the energy loss from domain wall motion, which can degrade the device performance and reliability. In this work, the self-heating of PZT thin films on Si and glass and a film released from a substrate were investigated to understand the effect of substrates on the device temperature rise. Nano-particle assisted Raman thermometry was employed to quantify the operational temperature rise of these PZT actuators. The results were validated using a finite element thermal model, where the volumetric heat generation was experimentally determined from the hysteresis loss. While the volumetric heat generation of the PZT films on different substrates was similar, the PZT films on the Si substrate showed a minimal temperature rise due to the effective heat dissipation through the high thermal conductivity substrate. The temperature rise on the released structure is 6.8× higher than that on the glass substrates due to the absence of vertical heat dissipation. The experimental and modeling results show that the thin layer of residual Si remaining after etching plays a crucial role in mitigating the effect of device self-heating. The outcomes of this study suggest that high thermal conductivity passive elastic layers can be used as an effective thermal management solution for PZT-based MEMS actuators.

Research on pyroelectric enhancement mechanism of PZT thin films and optimization design of infrared detectors

In this paper, the PZT10/90 thin film was successfully deposited on the Pt/TiO2/SiO2/Si substrate using RF magnetron sputtering, and the dielectric and pyroelectric properties of the thin film were measured and characterized. The measurements show that the dielectric constant of the PZT10/90 thin film is further reduced compared to the previously reported PZT30/70 thin films, which is beneficial for improving the figure of merit of the PZT. The dielectric constant and loss tangent of the PZT10/90 thin film are 173 and 0.016 at 1kHz and the pyroelectric coefficient of the thin film is 20 nC·cm-2·K-1 at room temperature. In addition, a pyroelectric infrared detector based on the PZT thin film was designed, a feasible detector fabrication process was proposed, and the structure of the pyroelectric infrared detector was optimized using simulation software based on the finite element method. The developed infrared detector has promising applications in the fields of spectroscopic instruments and smart seekers.

Innovation of sustainable energy generating from lightweight vehicle applications

This research introduces the Sustainable Energy Generation Pad (SEGP), a cutting-edge solution for generating alternative energy from lightweight vehicles, such as bicycles and electric bikes. The SEGP consists of seven layers, incorporating thin-film PZT cells, an energy collector circuit, and non-interlaced composite material layers. Its primary goal is to harness clean energy from mechanical vibrations and kinetic energy generated during vehicle operation, reducing reliance on traditional fossil fuels and promoting eco-friendly transportation. Simulations show that under ideal conditions (150–450 lbs weight, 10–12 mph speed), the 1XSEGP generates 0.59–1.35 W/ride in 0.34 s, and the 2XSEGP produces 1.42–3.42 W/ride in the same time frame. However, real-world implementation introduces complexities due to speed variations, material imperfections, and road conditions. In practice, the 1XSEGP generates 0.33–0.41 W/ride, and the 2XSEGP yields 0.54–0.67 W/ride in the same time frame, with a total rider and bicycle weight of about 160 lbs. While simulations are optimistic, prototype results confirm the SEGP’s potential for sustainable energy generation in lightweight vehicles. This research opens the door to more environmentally friendly alternative energy generation from lightweight transport, promising a newer, cleaner energy source and a more sustainable future.

Multiple factors of regulation for transient negative capacitance in PbZr(1−x)Ti(x)O3 ferroelectric thin films

The negative capacitance (NC) of ferroelectric (FE) materials can effectively break the ‘Boltzmann tyranny’ and drive the continuation scaling of Moore’s law. In this work, to find a novel way for amplifying the transient NC, a series network of external resistors and PbZr(1−x)Ti(x)O3 (PZT) FE capacitors was constructed. Uniform modeling and simulation were performed using Kirchhoff’s current law, electrostatics equations, and Landau–Khalatnikov equations. The derived results revealed that the mismatch of switching rate between free charge and polarization during FE domain switching is responsible for the transient NC generation. Some interesting results were obtained for the regulation of the transient NC by various factors such as the strain between the FE film and substrate, the viscosity coefficient, the ratio of Ti components, the external resistance magnitude, and the operating temperature. This work provides considerable insight into the control of FE transient NC, and offers guidance for obtaining larger and longer transient NC in the widely used PZT thin films.

In-situ study on piezoelectric responses of sol-gel derived epitaxial Pb[Zr,Ti]O3 thin films on Si substrate

Pb[Zr,Ti]O3 (PZT) thin films with the Zr/Ti ratio of 45/55, 52/48, and 60/40 (PZT(45/55), PZT(52/48), and PZT(60/40), respectively) are deposited on (001)SrRuO3/(001)Pt/ZrO2/Si by sol-gel method. We confirm that the epitaxial (001)Pt electrode facilitate the epitaxial growth of the PZT thin films along the c-axis direction. Basic characteristics such as structural, dielectric, and ferroelectric properties are examined. Furthermore, direct and converse piezoelectric properties are evaluated using effective transverse piezoelectric coefficients, |e31,f|. In particular, the epitaxial PZT thin films manifest a dependence of the converse |e31,f| on applied voltages with the values as follows; 9.7–11.5 C/m2, 11.2–12.5 C/m2, and 11.7–12.3 C/m2 for the epitaxial PZT(45/55), PZT(52/48), and PZT(60/40), respectively. Moreover, by analyzing bias-resolved in-situ reciprocal space map (RSM) obtained from synchrotron radiation X-ray diffraction (SR-XRD) which allows for the understanding on the transition of crystal structures, we explore the voltage-induced contributions for the converse |e31,f|.

Development of an Air-Coupled Piezoelectric Micromachined Ultrasonic Transducer Using Sol-Gel PZT Thin Film for Fast-Prototyping

Development of an Air-Coupled Piezoelectric Micromachined Ultrasonic Transducer Using Sol-Gel PZT Thin Film for Fast-Prototyping

Bottom Electrode Effects on Piezoelectricity of Pb(Zr0.52,Ti0.48)O3 Thin Film in Flexible Sensor Applications

Piezoelectric thin films grown on a mechanical, flexible mica substrate have gained significant attention for their ability to convert mechanical deformation into electrical energy though a curved surface. To extract the generated charge from the PZT thin films, bottom electrodes are typically grown on mica substrates. However, this bottom electrode also serves as a buffering layer for the growth of PZT films, and its impact on the piezoelectric properties of PZT thin films remains understudied. In this work, the effect of Pt and LaNiO3 bottom electrodes on the piezoelectric effect of a Pb(Zr0.52,Ti0.48)O3 thin film was investigated. It was observed that the PZT thin films on LNO/Mica substrate possessed weaker stress, stronger (100) preferred orientation, and higher remanent polarization, which is beneficial for a higher piezoelectric response theoretically. However, due to insufficient grain growth resulting in more inactive grain boundaries and lattice imperfections, the piezoelectric coefficient of the PZT thin film on LNO/Mica was smaller than that of the PZT thin film on a Pt/Mica substrate. Therefore, it is concluded that, under the current experimental conditions, PZT films grown with Pt as the bottom electrode are better suited for applications in flexible piezoelectric sensor devices. However, when using LNO as the bottom electrode, it is possible to optimize the grain size of PZT films by adjusting the sample preparation process to achieve piezoelectric performance exceeding that of the PZT/Pt/Mica samples.

Compositional Modification of Epitaxial Pb(Zr,Ti)O3 Thin Films for High‐Performance Piezoelectric Energy Harvesters

AbstractIn this study, Piezoelectric energy harvesters (PEHs) are fabricated based on epitaxial Pb(Zr,Ti)O3 (PZT) thin films deposited by an RF magnetron sputtering with varied Zr/[Zr+Ti] ratio. For a compatibility with micro‐electromechanical systems, the epitaxial PZT thin films are deposited on Si substrates (PZT/Si). The morphotropic phase boundary (MPB) are formed in the compositional range of 0.44 ≤ Zr/[Zr+Ti] ≤ 0.51 of the epitaxial PZT/Si, which is far broader than that of the bulk PZT. Meanwhile, effective transverse piezoelectric coefficient (|e31,f|) values are evaluated by the direct and converse piezoelectric effects using the unimorph cantilever method. Among the compositions, the rhombohedral‐dominant MPB (MPB‐R) of Zr/[Zr+Ti] = 0.51 exhibits a direct |e31,f| of 10.1 C m−2 and a relative permittivity (εr) of 285, leading to the maximum figure of merit of 40 GPa in this study. On the other hand, the maximum converse |e31,f| of 14.0 C m−2 is measured from the tetragonal‐dominant MPB (MPB‐T) of Zr/[Zr+Ti] = 0.44. At a resonance frequency, the MPB‐T presents a high output power density of 301.5 µW−1/(cm2 g2) under an acceleration of 3 m−1 s−2, which is very promising for the high‐performance PEH applications.

Photoinduced modification of optical properties of ferroelectric PZT thin films

This study investigates ultrafast photoinduced changes in optical properties of ferroelectrics (PZT) on femtosecond to nanosecond timescales, using broadband transient reflectivity studies. Surprisingly, spectral features were observed below the bandgap, which could not be attributed to ground state bleaching, excited state absorption, and/or stimulated emission. A model based on probe energy independent changes in refractive index and extinction coefficient showed good agreement with experimental results. Three relaxation processes were phenomenologically considered for the temporal evolution. Laser-induced heating was ruled out as the cause of short timescale behavior and photorefractive effect was suggested as a potential mechanism for changes in the optical properties.Graphical abstract

Anomalous electron channeling in PZT thin films

The study of the surface of lead zirconate-titanate (PZT) thin films using a scanning electron microscope (SEM) identified the patterns of electron channeling on the surface of the perovskite phase crystals. However, the observation conditions were completely uncommon and contradicted model representations. Thus, there was enough evidence to believe that the observed patterns of electron channeling were an anomaly. It was necessary to conduct an additional detailed study of the perovskite crystal in a PZT thin film in order to clarify which conditions could cause this anomaly. In particular, the method of electron backscatter diffraction (EBSD) in SEM was used to study the crystallographic specific features of the crystal. The method is based on the collection and automatic processing of electron diffraction patterns which calculate a corresponding crystallographic orientation for each point on the scanned crystal surface. As a result, the study revealed the unusual features of the crystallographic structure of perovskite in a PZT thin film that provided an opportunity for the manifestation of anomalous electron channeling. The research showed that the crystal lattice of perovskite experienced an axially symmetric monotone bend, which determined the round shape of the crystal. The study demonstrated the possibility of producing ferroelectric crystals with a curved crystallographic surface. In order to describe the growth of round perovskite crystals from the amorphous phase in PZT thin films, the author provided a dislocation model where the continuous bending of the perovskite crystal lattice could be explained by the accommodationof mechanical stresses with a decrease in the phase volume of the film material. In addition, it was shown that the bands observed in the electron channeling patterns corresponded to crystallographic planes, while any distortions of the pattern indicated a local deformation of the lattice in a highly symmetrical uniformly curved perovskite crystal in a PZT thin film

Crystallization features and physical properties of the thin-film heterostructure of lead zirconate titanate – lead oxide

Various diagnostic techniques aimed at studying the structure and physical properties (synchronous thermal analysis, atomic force microscopy operating in the current measurement mode, electron-probe X-ray spectral microanalysis, dynamic method for determining the pyroelectric response) were used to study the crystallization features and physical properties of the thin-film heterostructure PZT – PbO1+x formed by a two-stage technique of RF magnetron sputtering of a ceramic target. During the first stage, amorphous films were deposited on a “cold” platinized silicon substrate, while the second stage involved high-temperature annealing in air. It was shown that annealing of amorphous films and crystallization of the intermediate pyrochlore phase are accompanied by additional oxidation of the structure resulting in the formation of lead orthoplumbate and lead dioxide and additional oxidation of organic inclusions. The presence of a liquid phase of lead oxide contributes to the formation of the pyrochlore phase. It was found that lead oxide layers have significantly higher through conductivity than perovskite blocks. It was assumed that the increased conductivity of lead oxide layers is associated with lead dioxide, which has high conductive properties. Self-polarized thin films were detected to have an abnormal electrical response to the strobing thermal exposure, including the typical pyroelectric response, local photoconductivity shunted by layers of the perovskite phase, and through photoconductivity. The presence of photoconductivity is also associated with the conductive properties of lead dioxide

Interface Structure, Dielectric Behavior and Temperature Stability of Ba(Mg1/3Ta2/3)O3/PbZr0.52Ti0.48O3 Thin Films.

Multilayer films can achieve advanced properties and a wide range of applications. The heterogeneous interface plays an important role in the performances of multilayer films. In this paper, the effects of the interface of Ba(Mg1/3Ta2/3)O3/PbZr0.52Ti0.48O3 (BMT/PZT) thin films on dielectric behavior and temperature stability are investigated. The heterogeneous interface structures are characterized by Auger electron spectroscopy (AES). The PZT-BMT interface is different from the BMT-PZT interface in thickness. For the PZT-BMT interface, the PZT thin films are diffused to the whole BMT layers, and the interface thickness is about 90 nm, while the BMT-PZT interface's thickness is only about 8.6 nm. The presence of heterogeneous interfaces can improve the performances of BMT/PZT thin films and expand their applications. The dielectric constant of BBPP thin films is significantly lower than BPBP thin films, while the dielectric loss is exactly the opposite. The more interfaces there are, the greater the dielectric constant. The relationship between the electric-field-dependent dielectric constant curve and the P-E curve is established. The equivalent interface barrier of the diode is used to show that the dielectric peaks under the positive and negative voltage are different. Similarly, heterogeneous interfaces show a certain improvement in dielectric tunability and temperature stability.