Fabrication and characterisation of piezoelectric thick-film microcantilever deposited on stainless steel using electrohydrodynamic jet deposition

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.     

Low‐Cost,Damage‐Free Patterning of Lead Zirconate Titanate Films

The ability to pattern piezoelectric thin films without damage is crucial for the development of microelectromechanical systems. Direct patterning of complex oxides through microcontact printing was explored as an alternative to subtractive patterning. This process utilized an elastomeric stamp to transfer a chemical solution precursor of a piezoelectric material onto a substrate in a desired pattern. Polyurethane‐based stamps improved wetting of polar solutions on the stamp. This allowed for high‐fidelity patterning over multiple stamping cycles. Microcontact printing deposited patterned PbZr_0.52Ti_0.48O₃ layers from 0.1 to 1 μm in thickness. The lateral feature sizes attained varied from 5 to 500 μm. Upon crystallization at 700°C, the features formed phase‐pure perovskite PZT. The printed features had comparable electrical and electromechanical properties to those of continuous PZT films of similar thicknesses. For example, 1 μm thick PZT features had a permittivity of 1050 and a loss tangent of 0.02 at 10 kHz. The remanent polarization was 30 μC/cm², and the coercive field was 45 kV/cm. The piezoelectric coefficient e_31,f was ?7 C/m². These values indicated that the microcontact printing process did not adversely affect the PZT crystallization or properties for the thicknesses explored in this work.     

Additively patterned ferroelectric thin films with vertical sidewalls

The functional properties of electroceramic thin films can be degraded by subtractive patterning techniques used for microelectromechanical (MEMS) applications. This work explores an alternative deposition technique, where lead zirconate titanate (PZT) liquid precursors are printed onto substrates in a desired geometry from stamp wells (rather than stamp protrusions). Printing from wells significantly increased sidewall angles (from ~1 to >35 degrees) relative to printing solutions from stamp protrusions. Arrays of PZT features were printed, characterized, and compared to continuous PZT thin films of similar thickness. Three‐hundred‐nanometer‐thick printed PZT features exhibit a permittivity of 730 and a loss tangent of 0.022. The features showed remanent polarizations of 26 μC/cm², and coercive fields of 95 kV/cm. The piezoelectric response of the features produced an e_31,f of ?5.2 C/m². This technique was also used to print directly atop prepatterned substrates. Optimization of printing parameters yielded patterned films with 90° sidewalls. Lateral feature sizes ranged from hundreds of micrometers down to one micrometer. In addition, several device designs were prepatterned onto silicon on insulator (SOI) wafers (Si/SiO₂/Si with thicknesses of 0.35/1/500 μm). The top patterned silicon was released from the underlying material, and PZT was directly printed and crystallized on the free‐standing structures.     

A flexible piezoelectric pressure sensor based on PVDF nanocomposite fibers doped with PZT particles for energy harvesting applications

Flexible piezoelectric energy harvesters are a suitable choice for scavenging wasted mechanical energy because of the high demand for sustainable power sources. Flexible pressure sensors based on PVDF-PZT nanocomposite with different PZT volume fractions (0.011, 0.041, 0.096, 0.17, 0.3, and 0.37) were prepared in the form of fibers through an electrospinning method for piezoelectric energy harvesting application. According to the results, dielectric constant and piezoelectric coefficients (e.g. piezoelectric coefficient, and figure of merit) gradually increased with the doping of PZT particles into PVDF fibers. Dielectric constant (ϵ), piezoelectric coefficient (d), and figure of merit (d × g) for PVDF-PZT nanocomposite with 0.011 PZT volume fraction were 37.29, 10.51 pCN⁻¹, and 33.46 × 10⁻¹⁶ m²/N, respectively, and increased to 104.81, 22.93 pCN⁻¹, and 56.68 × 10⁻¹⁶ m²/N for PVDF-PZT nanocomposite fibers with a volume fraction of 0.37. As piezoelectric energy harvesters, piezoelectric sensitivity of PVDF-PZT nanocomposite fibers rose with increasing the PZT volume fraction. The generated output voltage was 184 mV under an applied force of 2.125 N with the piezoelectric sensitivity calculated as 173.507mV/Nμm for PVDF-PZT nanocomposite fibers with 0.37 PZT volume fractions which increased compared to pristine PVDF fibers (generated output voltage = 22 mV under applied force 2.4 N, piezoelectric sensitivity = 29.49 mV/Nμm). The achieved output power density of PVDF-PZT nanocomposite fibers with 0.37 PZT volume fractions was obtained 30.69μW cm⁻² higher than PVDF-PZT nanocomposite fibers with 0.011 PZT volume fractions (18.44μW cm⁻²).     

Microwave enhanced sintering of tape-cast ferroelectric films

Porous Pb(Zr_xTi_1−x)O₃(PZT) thick films that had been prepared by tape casting were densified by microwave energy. The microwave absorption effect is substantially correlated with the film thickness. In microwave-processed PZT thick films, rapid particle necking causes densification with no grain growth nearly in a short treatment time of 20 min at 820 °C. The same porous PZT thick films are difficult to densify in a conventional process. A 30-μm-thick PZT thick film has a pure perovskite structure. Self-supporting PZT thick films with a crack-free and uniform microstructure formed in a microwave process have larger coercive field than conventionally processed bulk PZT. The polarization, 14 μC/cm², of PZT thick films in a microwave process exceeds that, 7 μC/cm², of PZT bulk formed in a conventional process.     

Piezoelectric Properties of Ink‐Jet–Printed Lead Zirconate Titanate Thick Films Confirmed by Piezoresponse Force Microscopy

An ink consisting of Pb(Zr_0.53Ti_0.47)O₃ (PZT) particles with a median size of 170 nm and a narrow size distribution, in a dispersion of water and glycerol, and with a low viscosity and surface tension, was used for the fabrication of thick films by piezoelectric ink‐jet printing. This study reports the printing conditions, the subsequent thermal treatment of the as‐deposited layers, and the properties of the sintered PZT thick film. The film, sintered at 1100°C, had a locally dense microstructure and consisted of grains that are a few 100 nm across, as revealed by scanning electron microscopy. A local piezoelectric response of 15 pm/V was measured in the ink‐jet–printed PZT thick film by piezoresponse force microscopy.     

Interdependence of piezoelectric coefficient and film thickness in LiTaO3 cantilevers

Electromechanical energy demands on homogenous thick films of piezoceramics with sufficiently large piezoelectric constant and reproducible performance. Single-phase LiTaO₃ films deposited by sol-gel processing have been fabricated as cantilevers to investigate the interdependence of dielectric and piezoelectric properties as a function of film thickness. Phase pure LiTaO₃ films with varying thickness in the range of 2.07-4.37 µm on stainless steel substrates were obtained after calcination of samples at 650°C. The relative permittivity of optimized spin-coated films peaked at 479.73 (1 kHz), whereas the piezoelectric coefficient (d₃₃ mode) determined by piezoresponse force microscopy was in the range of 21-24 pm/V. The effect of poling was studied through the butterfly and phase curves. A figure of merit (FOM) up to 3.29 (10⁻¹⁸ m²/V²) was determined for cantilever devices, which were able to generate a peak-to-peak voltage of 0.046-0.15 V using a 1 MΩ resistor as an impedance load at a fixed acceleration of 1.5 m/s². While the power density was in the range of ~4-20 × 10⁻⁹ W/m³, which increased with the increasing film thickness. The leakage current density decreased in the range of 4 × 10⁻⁵-6 × 10⁻⁷ A/m² in the same direction. As both ferroelectric and piezoelectric properties of LiTaO₃ films are dependent on film thickness, an optimal energy conversion efficiency was obtained for a thickness of ~3 µm. Furthermore, these devices were tested up to a temperature of 150°C for voltage generation. Given the need for lead-free piezoelectric materials for environmental applications, these LiTaO₃ cantilevers are very promising for vibrational energy harvester (VEH) applications especially due to their cost effectiveness, small size, stability at higher temperatures, and repeatable properties, which makes them suitable for MEMS devices for industrial applications.     

High Piezoelectric Longitudinal Coefficients in Sol–gel PZT Thin Film Multilayers

A five‐layer stack of lead zirconate titanate (PZT) thin films with Pt electrodes was fabricated for potential applications in nanoactuator systems. The 1 μm thick PZT films were deposited by a sol–gel technique, the platinum electrodes by sputtering. The PZT films were crack‐free, in spite of the use of silicon as a substrate, suggesting an increased toughness of the metal–ceramic composite. For piezoelectric characterization, the intermediate electrodes were liberated by successive etching of the PZT and Pt layers, obtaining a functional three‐ layer stack. A total thickness change of 5.2 nm was achieved with 10 V, measured by double beam laser interferometry. The small signal response was obtained as 0.49 nm/V. Finite element simulations were made to account for the thickness change in the substrate due to the transverse piezoelectric effect. The average response corresponds to an average d_33,f of 120 pm/V. The multiple annealed buried layers show clearly a better performance with up to 175 pm/V. It is concluded that the electrode interfaces in the interior exhibit higher qualities, as supported by transmission electron microscopy, and that the multiple anneals were beneficial for PZT thin film quality.     

Electrophoretic deposition and sintering of thin/Thick PZT films

Electrophoretic deposition (EPD) is a simple, rapid, and low cost method for forming dense lead zirconate titanate (PZT) films down to 5 μm from particulate precursors. The three main steps of this process are: (1) formation of a charged suspension of the starting PZT powder; (2) deposition of the powder particles on an electrode under the influence of a dc electric field; and (3) fluxing and constrained sintering of the resulting particulate deposit at 900°C to form a dense continuous film. A 10 μm film formed using this process exhibited a polarization hysteresis equivalent to that of a bulk sample formed from the same starting powder, with a remnant polarization of 33 μC cm⁻².     

Fine‐Scaled Piezoelectric Ceramic/Polymer 2‐2 Composites for High‐Frequency Transducer

A novel technique was utilized to fabricate fine‐scaled piezoelectric ceramic/polymer 2‐2 composites for high‐frequency ultrasonic transducers. Lead zirconate titanate (PZT) was used as raw material. Tape‐casted acetylene black tapes were used to define kerfs after sintering. A one‐directional supporter was utilized to avoid distortion of PZT elements. PZT elements with 20 ± 2 μm width exhibited good consistency in longitudinal direction. A resonant method was utilized to evaluate the piezoelectric and dielectric properties of the composites. A 72‐μm‐thick composite with an aspect ratio of ~3.6 exhibited a k_t of 0.61 with satisfied piezoelectric and dielectric properties. A prototype high‐frequency ultrasonic transducer was fabricated and evaluated by an underwater pulse‐echo test. The center frequency was found to be 23.75 MHz, with ?6 dB bandwidth of 5.5 MHz.     

Growth of the ternary Pb(Mn,Nb)O3–Pb(Zr,Ti)O3 thin film with high piezoelectric coefficient on Si by RF sputtering

In this study, ternary ferroelectric 0.06Pb(Mn_1/3Nb_2/3)O₃–0.94Pb(Zr_0.48Ti_0.52)O₃ (PMN–PZT) thin film with high piezoelectric coefficient were grown on La_0.6Sr_0.4CoO₃-buffered Pt/Ti/SiO₂/Si substrate by RF magnetron sputtering method. The phase and domain structure along with the macroscopic electrical properties were obtained. Under the optimized temperature of 550°C and sputtering pressure 0.9 Pa, the PMN–PZT film owned large remnant ferroelectric polarization of 62 μC/cm². In addition, the PMN–PZT film had polydomain structures with fingerprint-type nanosized domain patterns and typical local piezoelectric response. Through piezoelectric force microscopy, the PMN–PZT thin film at nanoscale exhibited obvious domain reversal when subjected to in situ poling field. It was further found that the quasi-static piezoelectric coefficient of the PMN–PZT thin film reached 267 pC/N, which was about twice to that of the commercial PbZrO₃–PbTiO₃ (PZT) thin film. The optimized relaxor ferroelectric thin film PMN–PZT on silicon with global electrical properties shows great potential in the piezoelectric micro-electro-mechanical systems applications.     

Effect of excess lead on the structural and electrical characteristics of sol-gel synthesized RuO2/Pb(ZrxTi1−x)O3/RuO2

In this study, we investigated the effect of excess lead on the structural and electrical characteristics of lead zirconate titanate [Pb(Zr_xTi_1−x)O₃, PZT] thin films using the sol-gel spin coating method. X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and field-emission transmission electron microscopy were used to study the structural, morphological, chemical, and microstructural features, respectively, of these films as functions of the growth conditions (excess lead concentrations of 10, 20, and 25 mol%). The PZT thin film prepared at the 20 mol% condition exhibited the best electrical characteristics including a lower leakage current of 6×10⁻⁷ A/cm² at an electric field of 50 kV/cm, a larger capacitance value of 1.92 μF/cm² at a frequency of 1 kHz, and a higher remanent polarization of 20.1 μC/cm² at a frequency of 5 kHz. We attribute this behavior to the optimal amount of excess lead in this PZT film forming a perovskite structure and suppressing the reaction of PZT film with RuO₂ electrode.     

Electrical properties of high density PZT and PMN–PT/PZT thick films produced using ComFi technology

To achieve high actuation forces in piezoelectric film actuators and transducers it is desirable to have relatively thick films. Sol-gel derived films are often limited in the maximum thickness that is obtainable due to the increased probability of cracking and delamination during processing. Composite film (ComFi) technology combines conventional sol-gel processing with ceramic powder processing to enable thick (>2 μm) ferroelectric films to be deposited onto silicon substrates at temperatures as low as 710 °C. Ten micrometre thick films have been fabricated using three different piezoelectric powders [hard doped PZT, soft doped PZT and PMN–PT(85–15)]. The resultant films have high densities with relative permittivities of 800, 900 and 1800, respectively. The d₃₃ piezoelectric coefficients were found to be lower than corresponding values for the bulk material. This has been attributed to a combination of small grain size and the clamping effects of the rigid substrate. Hysteresis loop measurements show that greater fields are required to achieve a similar degree of polarisation to that of the bulk material. This indicates that the presence of the substrate also affects the ability to pole the material so further reducing the observed piezoelectric coefficient.     

PZT压电厚膜的发展及其应用

PZT压电厚膜材料是20世纪90年代发展起来的一种新型功能材料,它兼顾了块体材料和薄膜材料的优点,具有良好的压电、介电和热释电性能。简述了PZT压电厚膜的国内外研究进展,对PZT压电厚膜的制备方法做了简短的介绍,并对其改性研究做了较为详细的总结,最后,阐述了PZT压电厚膜在国内外的应用并展望了其前景。     

Impact of Sr-doping on structural and electrical properties of Pb(Zr0.52Ti0.48)O3 thin films on RuO2 electrodes

In this paper, we investigated the impact of Sr-doping on the structural properties and electrical characteristics of lead zirconate titanate [Pb(Zr_0.52Ti_0.48)O₃, PZT] thin films deposited on RuO₂ electrodes by a sol-gel process and spin-coating technique. We used X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and field-emission transmission electron microscopy to explore the structural, morphological, chemical, and microstructural features, respectively, of these films as a function of the growth condition (strontium doping concentrations varied from 1, 3, and 5 mol%). The PZT thin film processed at the 3 mol% Sr exhibited the best electrical characteristics, including a low leakage current of 2.27×10⁻⁷ A/cm² at an electric field of 50 kV/cm, a large capacitance value of 2.74 μF/cm² at a frequency of 10 kHz, and a high remanent polarization of 37.95 μC/cm² at a frequency of 5 kHz. We attribute this behavior to the optimal amount of strontium in the PZT film forming a perovskite structure and a thicker interfacial layer at the PSZT film-RuO₂ electrode interface.     

3DP process for fine mesh structure printing

Three dimensional printing (3DP) is a unique technique for creating complex shapes. However, printing feature sizes at less than 500 μm with high integrity and intricate structures have not been possible. In this study, TiNiHf shape memory alloy (SMA) powder was printed into 3D mesh structures of 300 μm wire width. Effects of printing layer thickness and binder saturation level on the integrity and dimensional accuracy of the 3D mesh structures were evaluated. 35 μm printing layer thickness and 170% binder saturation level offer the highest mesh structure integrity. Also, 35 μm printing layer thickness results in the smallest dimensional deviation from the designed 200 μm mesh width with the smallest standard deviation. Overall, 35 μm printing layer thickness and 170% binder saturation level are the most preferred printing condition for the designed 3D mesh structure.     

Processing and Properties of Screen-Printed Lead Zirconate Titanate Piezoelectric Thick Films on Electroded Silicon

The printing of lead zirconate titanate (PZT, Pb(Zr,Ti)O₃) piezoelectric thick films on silicon substrates is being studied for potential use as microactuators, microsensors, and microtransducers. A fundamental challenge in the fabrication of useful PZT thick-film devices on silicon is to sinter the PZT to high density at sufficiently low temperature to avoid mechanical or chemical degradation of the silicon substrate. The goal of the present study is to develop and implement suitable electrodes and PZT sintering aids that yield attractive piezoelectric properties for devices while minimizing reactions between the silicon, the bottom electrode, and the PZT thick film. A B₂O₃-Bi₂O₃-CdO sintering aid has been found to be superior to borosilicate glass, and the use of a gold/platinum bilayer bottom electrode has resulted in better thermal stability of the electrode/film structure. Films sintered at 900°C for 1 h have relative permittivity of 970 (at 1 kHz), remnant polarization of 20 μC/cm², coercive field of 30 kV/cm, and weak-field piezoelectric coefficient d ₃₃ of 110 pm/V.     

Key features in the development of unimorph stainless steel cantilever with screen-printed PZT dedicated to energy harvesting applications

The design and processing of vibrational energy harvester based on screen-printed piezoelectric lead zirconate titanate (Pb(ZrxTi1-x)O3 (PZT)) are described here. Two different structures, a simple cantilever and a complex zig-zag geometry made of PZT layer sandwiched between gold electrodes and supported on a metallic stainless steel substrate have been successfully fabricated by screen printing thick film technique. Compared to bulk PZT ceramics, the main limiting features at different scales are porosity, interfaces, and bending issues. The microstructural analysis of the interfaces in the cantilever has highlighted the formation of an interface between the substrate and the bottom electrode which ensures cohesion of the structure but can limit its dynamic. Bending has shown to be dependent on the thickness of the active piezoelectric layer. Dielectric and electromechanical characterizations performed on multilayers, bulk ceramics, and free-standing screen-printed disks are compared and discussed on the basis of interface issues.     

Effect of the slurry composition on the piezoelectric properties of PZT ceramics fabricated via materials extrusion 3D printing

Herein, the effect of the binder content in lead zirconate titanate (PZT) slurry has been systematically studied to improve the piezoelectric properties of PZT ceramics prepared via material extrusion 3D printing. For smooth printing, a slurry with a binder concentration ranging from 6 to 12 wt% was proposed. The porosity of the green body first decreased and then increased with an increase in the binder concentration, and the minimum porosity was obtained when the binder concentration reached 10 wt%. Samples with increased density were obtained after debinding and lead-rich atmosphere sintering. PZT piezoceramics fabricated using a binder content of 10 wt% exhibit the maximum relative density (96.9%), largest piezoelectric constant (342.6 pC/N) and dielectric constant (1621). Based on the above process, the wood pile structure and helical twentytetrahedral structural components were successfully fabricated using the material extrusion process. This research lays the foundation for the engineering application of 3D printing to fabricate high-performance piezoceramics with complex shapes.     

Electrohydrodynamic atomization deposition and mechanical polishing of PZT thick films

In this work, electrohydrodynamic atomization deposition, combined with mechanical polishing, was used for the fabrication of dense and even PZT thick films. The PZT slurry was ball-milled and the effect of milling time on the characteristics of the deposited films was examined. A time of 50 h was found to be the optimum milling time to produce dense films. It was found that the PZT thick films presented rough surface after deposition. In order to overcome this drawback the mechanical polishing process was employed on the deposited films. After the mechanical polishing the roughness (Ra) and peak-to-peak height (Rz) of the film surface were decreased from 422 nm to 23 nm and from 5 µm to 150 nm, respectively. Subsequently, an increase of ~10 pC N⁻¹ on piezoelectric constant (d_{33, f}) was obtained. In addition, it was observed that the d₃₃ was increased from 57 pC N⁻¹ to 89 pC N⁻¹ when the thickness was increased from 10 µm to 80 µm.