PZT Thick Films Research Articles

Electrical properties of UV-irradiated thick film piezo-sensors on superalloy IN718 using photochemical metal organic deposition

Lead zirconate-titanate thick films of perovskite structure Pb(Zr0.52Ti0.48)O3 were fabricated on the curved surface of IN718 superalloy substrate using photochemical metal organic deposition technique. The films were heated at 200°C, irradiated by UV lamp (365nm, 6W) for 10min, pyrolyzed at 400°C, and subsequently annealed at 700°C for 1h after successive multi-step coating with 10wt.% excess PbO. Fairly smooth, dense, and crack-free polycrystalline thick films of Au/PZT/Au structure were deposited on IN718. The films were characterized to investigate the effect of photochemical deposition process and substrate on the crystalline, morphological, dielectric, ferroelectric and piezoelectric properties. Remanent polarization (Pr=20.2μC/cm2), coercive field (Ec=−10kV/cm), permittivity (εr=324@1kHz), dielectric loss (tanδ≈3%), and piezoelectric charge coefficient (d33=113.4pm/V) of the PZT thick film transducers were measured and interpreted as regards domain wall motions. Consequently, the photochemical grown lead zirconate-titanate thick film on the superalloy substrate IN718 was confirmed to be consistent to structural health monitoring due to its acceptable electrical response.

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 50h 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 422nm to 23nm and from 5µm to 150nm, respectively. Subsequently, an increase of ~10pCN−1 on piezoelectric constant (d33, f) was obtained. In addition, it was observed that the d33 was increased from 57pCN−1 to 89pCN−1 when the thickness was increased from 10µm to 80µm.

Tailoring the Magnetoelectric Properties of Pb(Zr,Ti)O3 Film Deposited on Amorphous Metglas Foil by Laser Annealing

This study demonstrates the modulation of off‐resonance magnetoelectric (ME) response of the Pb(Zr,Ti)O3 (PZT)/ Metglas (FeBSi) bilayered composite by laser annealing. A continuous‐wave 532 nm Nd:YAG laser with varying fluences (210–390 J/mm2) was utilized to anneal the 2 μm thick PZT film deposited using granule spray in vacuum (GSV) technique on magnetostrictive amorphous Metglas foil. It was found that the dielectric and ferroelectric properties of the PZT film are strongly affected by the exposure to laser fluence. The ME voltage coefficient of PZT/Metglas increased with the fluence up to 345 J/mm2, reaching a high value of 880 mV/cm·Oe. The electrical and ME properties were correlated with the changes observed in crystallinity and grain size of the PZT film as well as with the alterations in microstructure and magnetic behavior of Metglas. Our results demonstrate that enhanced ME coupling can be realized in PZT/Metglas film composites by controlling the laser fluence.

Dielectric enhancement of PbZr0.3Ti0.7O3/LaNiO3 multilayer thick film

Multilayer thick films (∼4 μm) with compositional PbZr0.3Ti0.7O3/LaNiO3 layers and one‐layer PZT thick films were prepared on the silicon substrate by radio‐frequency magnetron sputtering. PbZr0.3Ti0.7O3/LaNiO3 multilayer thick film are characterized by highly preferential (100)‐oriented growth and columnar microstructure due to alternately introducing LaNiO3 seeding layers. The effects of LaNiO3 layers on microstructure and electrical properties of PbZr0.3Ti0.7O3 thick films were investigated in detail. The results show that both PZT and PbZr0.3Ti0.7O3/LaNiO3 multilayer thick film were pure perovskite crystalline phase. The PbZr0.3Ti0.7O3 film texture was dense and well adhered on the LaNiO3 layer. PbZr0.3Ti0.7O3/LaNiO3 multilayer thick film possessed obvious enhanced dielectric properties compared with PZT thick film: ϵr ∼2450 (10 kHz) and tanδ ∼0.02 (10 kHz). Rayleigh law was used to analysis the behavior of the enhanced dielectric properties and the pinched‐shaped polarization‐electric field hysteresis loops. The larger Rayleigh parameter, α ∼51.1408 cm kV−1 (1 kHz) indicates the larger extrinsic contribution to permittivity and strong domain‐wall–defect charge interaction. The leakage current behaviors of the multilayer thick film were also investigated in detail.

Fabrication and characterization of fast response pyroelectric sensors based on Fe-doped PZT thin films

Pyroelectric IR-detectors based on Pb(1−y)Fey(Zrx,Ti(1−x))O3 thin film have been successfully fabricated via ex situ oxidization annealing of DC magnetron sputtered conductive Fe doped lead-zirconium-titanium thin film on Au/SiO2/Si substrates. Structural as well as electro-optical properties were characterized. The results indicate that Fe-doping has had a remarkable structural effect namely, grain-size reduction, enhanced device voltage responsivity, 67.23 mV/mJ, and current-sensitivity, 5.16 × 10−6 mA/mJ. Moreover the pyroelectric coefficient, 609 μC m−2 °C−1, and merit figure, 1.43 × 10−6 μC m J−1, were significantly enhanced in comparison to previous reports on composite thick and thin film PZT and non-PZT based device structures.

Micro-particle manipulation by single beam acoustic tweezers based on hydrothermal PZT thick film.

Single-beam acoustic tweezers (SBAT), used in laboratory-on-a-chip (LOC) device has promising implications for an individual micro-particle contactless manipulation. In this study, a freestanding hydrothermal PZT thick film with excellent piezoelectric property (d33 = 270pC/N and kt = 0.51) was employed for SBAT applications and a press-focusing technology was introduced. The obtained SBAT, acting at an operational frequency of 50MHz, a low f-number (∼0.9), demonstrated the capability to trap and manipulate a micro-particle sized 10μm in the distilled water. These results suggest that such a device has great potential as a manipulator for a wide range of biomedical and chemical science applications.

Positive Effect of an Internal Depolarization Field in Ultrathin Epitaxial Ferroelectric Films

The effect of intentionally introducing a large depolarization field in (001)‐oriented, epitaxial Pb(Zr0.2TiO0.8)O3 (PZT) ultrathin films grown on La0.67Sr0.33MnO3 (LSMO) buffered SrTiO3 (STO) substrates is investigated. Inserting between 3 and 10 unit cells of STO between two 3 nm thick PZT films significantly influences the out‐of‐plane (c) lattice constant as well as the virgin domain state. Piezoresponse force microscopy images reveal a nanoscale (180°) polydomain structure in these films. In comparison, a “reference” single layer PZT sample (6 nm thick without STO spacer) exhibits an elongated PZT c‐axis (0.416 nm) and is preferentially “down”‐polarized with large regions of monodomain contrast. It shows asymmetric switching loops (i.e., imprint) coupled with sluggish domain switching under external bias. It is shown that the insertion of STO drives a monodomain to 180° polydomain transition in the as‐grown state, which reduces the imprint by 80%. The insertion of the STO also profoundly improves dielectric leakage and hence the distribution of the applied electric field. Consequently, the critical pulse duration of the electric field required to initiate domain switching is reduced by two orders of magnitude relative to the reference sample. These results demonstrate the possibility of manipulating the depolarization field in such a way that it has positive effects on the ferroelectric behavior of ultrathin PZT films.

Presentation and characterization of novel thick-film PZT microactuators

We propose in this paper the characterization of a new generation of piezoelectric cantilevers called thick-films piezoelectric actuators. Based on the bonding and thinning process of a bulk PZT layer onto a silicon layer, these cantilevers can provide better static and dynamic performances compared to traditional piezocantilevers, additionally to the small dimensions.

Piezoelectric micro-lens actuator

This paper reports the design, simulation, fabrication and characterization of a piezoelectric actuation structure for out-of-plane micro-lens movement. The structure consists of eight unimorph piezoelectric actuators symmetrically attached to a lens holding frame at one end through eight connecting beams and to the silicon substrate at the other end. The unimorph piezoelectric actuator consists of a 1.5μm thick PZT (Lead Zirconate Titanate) film deposited on a 0.6μm thick ZrO2 seed layer that is coated on a 1μm thick SiO2 and 5μm thick monocrystalline silicon. The actuator is driven by a set of inter-digitated Pt/Ti top electrodes, of 10μm width and 5μm spacing, deposited on the 800μm long PZT film. The connecting beams and lens holding frame are single layers of 5μm thick silicon. Theoretical analysis of the actuator is confirmed by ANSYS simulation. The results show that the displacement range and response of the actuator can be controlled by the effective residual stress in the structure. The device has been successfully fabricated and characterized for its mechanical behavior. Both the simulation and theoretical results show good agreement with measurement. The actuator has been measured for its static out-of-plane displacement of 24μm at 60KV/cm with maximum displacement sensitivity to voltage of 0.52μm/V at 53KV/cm. The unloaded fundamental resonant frequency of the actuator is 2.42kHz. The resonant frequency is reduced to 752Hz after a 600μm diameter glass micro-lens weighing 320μg is loaded onto the lens holding frame. The static out-of-plane deflection characteristic is reduced slightly to 22μm deflection at 60KV/cm. The actuator demonstrates translation time of 10ms for 22μm displacement range with less than 5% ringing. In comparison to previously demonstrated lens actuation mechanism, the reported mechanism shows higher resonant frequency and hence suited for faster actuation.

Enhanced off-resonance magnetoelectric response in laser annealed PZT thick film grown on magnetostrictive amorphous metal substrate

A highly dense, 4 μm-thick Pb(Zr,Ti)O3 (PZT) film is deposited on amorphous magnetostrictive Metglas foil (FeBSi) by granule spray in vacuum process at room temperature, followed by its localized annealing with a continuous-wave 560 nm ytterbium fiber laser radiation. This longer-wavelength laser radiation is able to anneal the whole of thick PZT film layer without any deteriorative effects, such as chemical reaction and/or atomic diffusion, at the interface and crystallization of amorphous Metglas substrate. Greatly enhanced dielectric and ferroelectric properties of the annealed PZT are attributed to its better crystallinity and grain growth induced by laser irradiation. As a result, a colossal off-resonance magnetoelectric (ME) voltage coefficient that is two orders of magnitude larger than previously reported output from PZT/Metglas film-composites is achieved. The present work addresses the problems involved in the fabrication of PZT/Metglas film-composites and opens up emerging possibilities in employing piezoelectric materials with low thermal budget substrates (suitable for integrated electronics) and designing laminate composites for ME based devices.

Processing of rf-sputtered lead zirconate titanate thin films on copper foil substrates

Pb(Zr0.52Ti0.48)O3 (PZT) thin films on copper foils were fabricated via rf magnetron sputtering and ex situ crystallized in a forming gas atmosphere. The PZT/Cu system is interesting due to the low oxygen partial pressure (pO2) required during crystallization to prevent Cu oxidation, as well as the mismatch of substrate and film coefficients of thermal expansion. The formation of a Cu2O interlayer at pO2 levels not thermodynamically predicted suggests that the film and substrate cannot be thought of as being in equilibrium. It was expected that thicker films would provide a stronger barrier to oxygen diffusion from the ambient to the substrate, but instead Cu2O formation was found to increase with PZT film thickness. Therefore, the PZT film likely plays an active role in substrate oxidation, perhaps as a source of oxygen. Cu oxidation was significantly minimized by wrapping the films in a sacrificial copper envelope during crystallization. This likely resulted in a gettering of oxygen, which buffered the local pO2 inside the envelope near the—Cu–Cu2O thermodynamic equilibrium curve during heating. Two distinct mechanisms may be responsible for the oxidation of the Cu substrate. These can explain the film thickness and crystallization temperature dependence of the Cu2O interlayer formation, as well as justify the use of a Cu envelope. The dielectric response and hysteresis are shown for samples with varying amounts of the Cu2O interlayer. A dielectric relaxation near 1 kHz was correlated to the presence of the interlayer.

Electrohydrodynamic jet printing of PZT thick film micro-scale structures

This paper reports the use of a printing technique, called electrohydrodynamic jet printing, for producing PZT thick film micro-scale structures without additional material removing processes. The PZT powder was ball-milled and the effect of milling time on the particle size was examined. This ball-milling process can significantly reduce the PZT particle size and help to prepare stable composite slurry suitable for the E-Jet printing. The PZT micro-scale structures with different features were produced. The PZT lines with different widths and separations were fabricated through the control of the E-Jet printing parameters. The widths of the PZT lines were varied from 80μm to 200μm and the separations were changed from 5μm to 200μm. In addition, PZT walled structures were obtained by multi-layer E-Jet printing. The E-Jet printed PZT thick films exhibited a relative permittivity (ɛr) of ∼233 and a piezoelectric constant (d33, f) of ∼66pCN−1.

Static/dynamic trade-off performance of PZT thick film micro-actuators

Piezoelectric actuators are widespread in the design of micro/nanorobotic tools and microsystems. Studies toward the integration of such actuators in complex micromechatronic systems require the size reduction of these actuators while retaining a wide range of performance. Two main fabrication processes are currently used for the fabrication of piezoelectric actuators, providing very different behaviors: (i) the use of a bulk lead zirconate titanate (PZT) layer and (ii) the use of thin film growth. In this paper, we propose a trade-off between these two extreme processes and technologies in order to explore the performance of new actuators. This resulted in the design and fabrication of thick film PZT unimorph cantilevers. They allowed a high level of performance, both in the static (displacement) and dynamic (first resonance frequency) regimes, in addition to being small in size. Such cantilever sizes are obtained through the wafer scale bonding and thinning of a PZT plate onto a silicon on insulator wafer. The piezoelectric cantilevers have a 26 μm thick PZT layer with a 5 μm thick silicon layer, over a length of 4 mm and a width of 150 μm. Experimental characterization has shown that the static displacements obtained are in excess of 4.8 μm V−1 and the resonance frequencies are up to 1103 Hz, which are useful for large displacements and low voltage actuators.

Screen-printed ultrasonic 2-D matrix array transducers for microparticle manipulation

This paper reports the development of a two-dimensional thick film lead zirconate titanate (PZT) ultrasonic transducer array, operating at frequency approximately 7.5MHz, to demonstrate the potential of this fabrication technique for microparticle manipulation. All layers of the array are screen-printed then sintered on an alumina substrate without any subsequent patterning processes. The thickness of the thick film PZT is 139±2μm, the element pitch of the array is 2.3mm, and the dimension of each individual PZT element is 2×2mm2 with top electrode 1.7×1.7mm2. The measured relative dielectric constant of the PZT is 2250±100 and the dielectric loss is 0.09±0.005 at 10kHz. Finite element analysis was used to predict the behaviour of the array and to optimise its configuration. Electrical impedance spectroscopy and laser vibrometry were used to characterise the array experimentally. The measured surface motion of a single element is on the order of tens of nanometres with a 10Vpeak continuous sinusoidal excitation. Particle manipulation experiments have been demonstrated with the array by manipulating Ø10μm polystyrene microspheres in degassed water. The simplified array fabrication process and the bulk production capability of screen-printing suggest potential for the commercialisation of multilayer planar resonant devices for ultrasonic particle manipulation.

High performance PZT thick film actuators using in plane polarisation

Piezoceramic thick films offer the possibility of integrated functional components in planar design. They can be applied as sensors, actuators, ultrasonic transducers, transformers and generators. Typically, piezoceramic thick films are excited through the film thickness. In contrast, in-plane mode of excitation will be beneficial especially for actuator applications. The use of interdigitated electrodes (IDEs) enables in-plane excitation of piezoceramic thick films. Actuator performance of cantilever structures with through thickness and in-plane polarised piezoceramic thick films are investigated. The performance of in-plane polarised cantilevers depends on the particular IDE spacing. Using finite element simulations of the E-field distribution, geometrical and design efficiencies are considered and compared to experimentally derived data.

Displacement improvement of piezoelectric membrane microactuator by controllable in-plane stress

Aiming to improve the displacement of the piezoelectric membrane microactuators, controllable in-plane tensile stress was introduced by applying a bias voltage on the idle part of PZT. The stress generated by the bias voltage was calculated by an analytical model based on the theory of plates and shells. Analytical result shows that tensile stress with a magnitude of 10MPa can be generated under 100V bias voltage. The stress is large enough to cause the change of piezoelectric coefficient d31 as well as the displacement of the actuator. Then the experimental results on the PZT thick film actuators demonstrated that d31 was remarkable increased for both the disc actuator and the ring actuator under an appropriate bias voltage, improving the displacement by 6% and 42%, respectively. Furthermore, the resonance frequency shifts were observed as a result of Young's modulus change under the bias voltage.

Preparation and characterization of lead zirconate titanate thick films prepared by chemical solution deposition for MEMS applications

Lead zirconate titanate (PbZrxTi1−xO3, PZT) films are widely used in silicon based microelectromechanical systems (MEMS) due to their high piezoelectric and electromechanical coupling coefficient. Si3N4 is often needed as a masking layer to protect Si during wet etching. In this paper, the preparation and characterization of Pb(Zr0.52Ti0.48)O3 thick films deposited on Pt/Ti/Si3N4/SiO2/Si substrate by chemical solution deposition were studied. PZT films with a thickness of 2μm were spin-coated on the substrates and pyrolyzed at 350°C, and then annealed at 650°C. PZT thick films exhibit highly (100) preferential orientation. The dielectric constant and loss tangent of the films are 2370 and 0.046 at 1kHz, respectively. The remnant polarization (Pr) and the coercive fields (Ec) are 32μC/cm2 and 56kV/cm, respectively. PZT films on patterned Si wafers have been studied for the applications on biosensors and medical ultrasound transducers.

Effect of Additive on Surface Properties of Solution Coated PZT Ferroelectric Film

In order to meet the requirements of large-scale industrial production, a hybrid sol-gel route which was used to fabricate PZT thick film attract a lot due to its low price [1]. However, surface imperfections, such as crack, pore and thickness nonuniform must be controlled. In this work, in order to get perfect film additive such as formylamine, acetic acid, polyvinylpyrrolidone (PVP) were studied. The surface morphologies were characterized by the Dimension 3100 atomic force microscope (AFM) and the Quanta 400 FEG Field emission environmental scanning electron microscope (SEM) respectively. The effect of additives on film thickness was studied by the JA.Woollam MD2000D Elliptic polarization spectrometer. The results show us that the additive can improve the the defects such as crack, porous and thickness nonuniform of PZT films effectively. We got crack-free, nonporous and compact PZT piezoelectric films when the PZT sol was acetic acid 20%, formylamine 15% and PVP 1% inside.

Thin-film piezoelectric bimorph actuators with increased thickness using double Pb[Zr,Ti]O3 layers

We studied the effects of increasing the thickness of bimorph structures containing double layers of Pb(Zr,Ti)O3 (PZT) thin films. Thick PZT films allow high-voltage application (e.g. in terms of coercive electric field and breakdown voltage) and large generative force, which are effective in microelectromechanical systems (MEMS) applications. Improvement of the deposition conditions and electrode structures facilitates the fabrication of the thin-film PZT/PZT bimorph structure. The PZT/PZT bimorph with a total thickness of 5.8 µm, deposited using a radio-frequency (RF) magnetron sputtering system is much thicker than conventional bimorph structures. The characteristics of the two piezoelectric layers were similar to each other and revealed good electric and ferroelectric characteristics with a remanent polarization of 20 µC cm−2 and a coercive electric field of 50 kV cm−1. PZT/PZT bimorph cantilevers were fabricated in order to evaluate their characteristics for actuator applications. The residual stress of the bimorph cantilever was reduced by an annealing process. The vibration test on the fabricated bimorph cantilevers during electrical voltage application revealed a twice as large displacement as compared with a single layer actuation, and the piezoelectric coefficient value d31 was estimated to be −61 pm V−1, which is better than the value of conventional PZT/PZT bimorph cantilevers (−13 pm V−1). It was also shown that the influence of the temperature change is much less than that in unimorph structures with similar dimensions. The evaluated results demonstrate that the PZT/PZT bimorph structures are effective as MEMS devices.

High performance screen printed Pb(Zr0.46Ti0.54)O3−Pb(Zn1/3Nb2/3)O3−Pb(Ni1/3Nb2/3)O3 thick films by one-step co-firing method

High performance screen-printed PNN−PZN−PZT thick films have been successfully prepared using a new one-step co-firing method at relatively low sintering temperature, leaving out preceding binder removal and subsequent electrode-made processes. And the dependence of microstructure, densification and electrical properties on the content of sintering aids has been investigated. The specimens with 1wt% sintering aids sintered at 850°C exhibits markedly enhanced piezoelectric and dielectric properties: d33=202 pC/N, ε33T/ε0=987, tanδ=1.8%, Tc=295°C, and Pr=14.02μC/cm2. Furthermore, there is no obvious Ag diffusion into PZT thick films, indicating the favorable coherence. Such prominent properties of PZN−PNN−PZT thick films using one-step co-firing method can be applied to multilayer thick films and further MEMS device applications.