Development of 2-2 piezoelectric ceramic/polymer composites by direct-write technique

The Micropen™ direct-write technique was used to fabricate ceramic skeletal structures to develop piezoelectric ceramic/polymer composites with 2–2 connectivity for medical imaging applications. A lead zirconate titanate PZT paste with ∼35 vol.% solids loading was prepared as a writing material and the paste’s rheological properties were characterized to evaluate its feasibly for Micropen deposition. A serpentine pattern was designed and deposited in AutoCAD and with a 100 μm pen tip, respectively. After debinding and sintering, the microstructural analysis showed that the ceramic structures were fully densified, with good bonding among layers. Typical single-layer thickness was ∼50 μm, and sintered line width was ∼120 μm. The composites containing 30–45 vol.% PZT were fabricated within 1 cm² area, with thicknesses ranging from 350 to 380 μm. Their electromechanical and dielectric properties were measured and found similar to that of composites fabricated by other techniques. The k _t was ∼0.61, d ₃₃ was 210–320, with Q _m of ∼6 and dielectric constant of 650–940.     

Poling Conditions of Pre-Stressed Piezoelectric Actuators and Their Displacement

The poling procedure has always been the key issue in producing piezoelectric actuators with optimised performance. This is also true with the relatively new category of pre-stressed bender actuators, where mechanical bias achieved with a passive layer is introduced in the actuators during manufacturing. Due to these factors, the behaviour of the actuator under poling is different compared to its bulk counterparts. In this paper, two different thicknesses of commercial PZT 5A and PZT 5H materials were used in bulk actuators and pre-stressed benders realised by new method. Pre-stress was introduced by using a post-fired biasing layer utilising sintering shrinkage and difference in thermal expansion. The hysteresis loop of the actuators was measured under 0.5–7.0 MV/m electric fields at 25–125^∘C temperatures, providing information about their remnant polarisation and coercive field before poling. The results showed that high electric field and 25^∘C temperatures in poling provided higher remnant polarisation and coercive electric field than using 125^∘C temperature at poling. Difference was especially significant in coercive electric field values where up to 114.8% difference was obtained for PZT 5H bulk actuator and 65.9% for pre-stressed actuators. Higher coercive fields can be utilized as increased operating voltage range of piezoelectric devices. The differences in results obtained here and by others can be explained by the different pre-stress level, stronger clamping of the thicker passive layers of the RAINBOW and THUNDER actuators and passive ring area introducing high tensile stresses. The same conditions were used to pole the actuators, after which the displacement and dielectric constant of the actuators were measured. The displacement measurements showed that remnant polarisation has good correlation with displacement. This fact can be used in estimating pre-stressed actuator performance before actual poling. The dielectric constant measurements with a small signal after poling gave even better correlation than the remnant polarisation.     

Pneumatic valve with a pressure regulator for bimorph type PZT actuator

The pressure regulator which is used for controlling the reducing pressure in the piezoelectrically driven pneumatic valve has been studied. The pneumatic valve of this study is two-stage type and consists of a piezoelectric actuator, a controller, a poppet valve and a pressure regulator. Nominal flow of 50 lpm, maximum operating pressure of 0.9 MPa and frequency characteristic of 10 Hz or higher are required in this pneumatic valve. The pressure regulator is needed because piezoelectric actuator has no ability to control the pressure of 0.9 MPa directly. In this study, a bimorph type PZT actuator of 25.2 mm(L) × 7.2 mm(W) × 0.5 mm(H) with constant of −220 × 10⁻¹² CN⁻¹ was proposed and investigated. Maximum operating force of 0.052 N and maximum displacement of 63 μm were achieved from the fabricated PZT actuator. From the analysis results, an orifice diameter of 0.6 mm was selected for a piezoelectric actuator. The pressure regulator which can be operated under 0.15 MPa easily was designed and manufactured. Performance and effects of design parameters were simulated by the Simulink of Matlab software, and it was confirmed that the performance characteristics of manufactured pressure regulator are superior in the common use pressure range of 0.5 to 0.7 MPa. The results show that the proposed pressure regulator is suitable for the pneumatic valve with a PZT actuator.     

Piezoelectric Ring-Morph Actuators for Valve Application

This paper presents piezoelectric ring-morph actuators designed to produce a large flexural displacement for valve actuation application. The ring-shaped piezoelectric plate in the actuator produces a radial contraction or expansion and causes the center part of the metal disc to generate a large flexural displacement. The PZT ring creates a space under the metal disc which permits it to bend with a curvature larger than that of the conventional bimorph in the axis direction of the ring-morph when the PZT ring under the metal disc contracts. A prototype with diameter of 25.4 mm and thickness of 0.55 mm could produce a total stroke (static displacement) of over 130 m under a driving voltage of ±300 V and a load of 2 N. The maximum generative force of ring-morph actuator was about 30 N.     

PZT thick films by diol chemical solution deposition

Process optimization and properties of lead zirconate titanate (PZT) films for piezoelectric micromachined ultrasonic transducers (pMUTs) for scanning probe devices will be presented. The goal of the work was a replacement of the tetragenic and mutagenic solvent and a decrease of time-consuming PZT 2–methoxy ethanol (2MOE) route. An alternative diol-based solution synthesis process was developed and “Design Of Experiment” (DOE) was used to achieve processing optimization for thick and crack free films. Tight parameter control allowed to develop a highly reproducible PZT diol process. The crystallization behaviour of crack-free PbZr_0.53Ti_0.47O₃ films (1–5 μm) with oriented perovskite structure was examined by X-ray diffraction and surface analysis using scanning electron microscopy. Piezoelectric and dielectric properties were examined. The effective transverse piezoelectric coefficient e _31,f of sol–gel processed films was investigated for 4 μm thick layers. Best properties were achieved with {1 0 0}-textured films, where a remanent e _31,f value of −7.3 C/m² was measured for 4.1 μm thick films.     

Study of 1–3 PZT Fibre/Epoxy Composites with Low Volume Fraction of Ceramics

Lead zirconate titanate (PZT) fibres were prepared by the viscous suspension spinning process (VSSP). Pre-sintered PZT powder mixed with poly (acrylic acid) was spun in a spinnerette to form fibres. The diameter of the fibre was 0.4 mm. The piezoelectric and ferroelectric properties of the single fibre were studied. The piezoelectric coefficient (d₃₃) and the remnant polarization P_r for a single fibre were found to be 490 pC/N and 26 μC/cm², respectively, which are comparable with that in the bulk sample. The fibres were used to fabricate 1–3 PZT fibre/epoxy composites with low volume fraction of PZT (<0.2). Different theoretical models were used to calculate the piezoelectric coefficient (d₃₃) of the composites and compared with experimental results.     

Electrically conductive carbon-coated ceramic fiber media

Porous ceramic fiber composites were coated with pyrolytic carbon by the decomposition of either propane or infiltrated phenolic resin in a nitrogen atmosphere at 800–900^∘C. The amount of carbon coating was varied to tailor the electrical conductivity of the carbon-coated composites. The electrical and thermal conductivity of the composites were measured at room temperature using a two-point method and a hot-wire one, respectively. Up to 30 wt% pyrolytic carbon, the electrical conductivity σ showed linearly increasing tendency and was fitted by the effective conductivity according to the parallel rule of a mixture σ =ΣV _i⋅σ_i with an effective conductivity of pyrolytic carbon σ_c and volume fraction of coated carbon V _c. The electrical conductivity of coated carbons prepared from propane at 900^∘C and phenolic resin at 800^∘C was of the order of 10⁰ and 10⁻¹ S cm⁻¹, respectively.     

Study on precision piezoelectric rotary step motors with inner anchor/loosen and outer drive

A new precision rotary piezoelectric (PZT) actuator is proposed to improve its drive performance. Based on piezoelectric technology, the actuator adopts the principle of bionics, with a new method of stator inner anchor/loosen/rotor outer drive and a distortion structure of a thin shelf flexible hinge. This structure improves the stability of the anchor/loosen and step rotary. Its characteristics are evaluated by finite element analysis. The experiment shows that the new rotary PZT actuator works with higher frequency (40 Hz), higher speed (325 μrad/s), wider movement (360°), high resolution (1 μrad/step) and high torque (30 N·cm). The novel actuator can be applied in wide movement and high resolution driving devices such as those for optics engineering, precision positioning and some other micro-manipulation fields. __________ Translated from Proceedings of the Chinese Society for Electrical Engineering, 2007, 27(15): 100–105 [译自: 中国电机工程学报]     

Anisotropic piezoelectric properties of 1–3 ceramic / polymer composites comprising rods with elliptic cross section

This paper is concerned with the study of effective piezoelectric properties of 1–3 ferroelectric ceramic / polymer composites. The aim of this paper is to show the role of a combination of the electromechanical properties of components and microgeometry of the 1–3 composite in determining its anisotropic piezoelectric response. The system of ceramic rods in the form of elliptic cylinders is an important microgeometric factor that influences the piezoelectric coefficients and their anisotropy. Examples of the piezoelectric response and anisotropy are analysed for the 1–3 composites based on either “soft” or “hard” ceramic and having either piezo-active or piezo-passive matrix. Combinations of the ceramic and polymer components are found that provide different volume-fraction dependences of the piezoelectric coefficients d_3j^* d_{3j}^{*} and g_3j^* g_{3j}^{*} : both monotonic, both non-monotonic, monotonic d_3j^* d_{3j}^{*} and non-monotonic g_3j^* g_{3j}^{*} , and vice versa. Examples of volume-fraction dependences of electromechanical coupling factors k_3j^* k_{3j}^{*} are also considered. A comparison of the effective piezoelectric coefficients calculated by the effective field method and the finite element method is carried out for different compositions in wide ranges of the ratio of semiaxes of the ellipse and of volume fractions of the components. Good agreement between data calculated by means of the aforementioned methods is obtained for the 1–3 structure comprising the elliptic cylinders.     

Non-uniform electric field in poling of structurally graded monolithic piezoactuator

In this paper the effect of a non-uniform electric poling field and its optimisation for structurally graded piezoelectric actuators are investigated. The two compared actuator structures were both based on commercial PZT 5H bulk discs with thicknesses of 375 µm (Ø 25 mm), where one was machined into a graded structure with a step-like decrease of the thickness towards the centre and one intact. The hysteresis loops of the pre-stressed concave shaped actuators were measured under 0.5–5.0 kV/mm electric fields at 25–100°C temperatures, and the remanent polarization and coercive electric field were determined. The graded structured actuator obtained ～10% higher coercive field compared to the non-graded actuator, when measured at 25°C and 5.0 kV/mm. On the other hand the remanent polarisation values of the graded actuator were slightly lower than non graded bulk values. However the maximum decrease was only 9.6% under 5.0 kV/mm. The results show that strain and stress gradients in the structure are generated when exposed to an electric field. Furthermore, as a consequence of the restricted dimension changes, an inherent bending of the monolithic ceramic structure was obtained which can be utilised, for example, in miniaturised micro-machined actuators or in larger pre-stressed benders.     

An Overview of Rapidly Prototyped Piezoelectric Actuators and Grain-Oriented Ceramics

Rapid prototyping (RP) has been used to fabricate a series of piezoelectric actuators, including spiral and tube actuators, to study the actuation mechanism in these geometries, and to obtain enhanced properties. PZT spiral actuators showed large displacement in mm range, and moderate blocking force. Unimorph spirals (PZT/metal shim) and dual-material (piezoelectric/electrostrictive) PMN-PT spirals were also prototyped and characterized. Tube actuators with inward and outward wall curvature showed slight improvement in axial and radial displacements compared to conventional straight-walled tube actuators. In order to improve the performance of ceramic actuators with polycrystalline microstructures, grain-oriented ceramics of bismuth titanate, lead metaniobate, and PMN-PT were investigated. Texturing was achieved by incorporating anisometric seeds into RP feedstock, aligning them during fabrication, and growing the seeds (templates) at elevated temperatures. Synthesis of anisometric seeds and pertinent processing conditions of the textured ceramics are presented. The feasibility of making net shape single crystal components was also explored. Single crystals of 0.65PMN-0.35PT were grown in FDC components using embedded (111) and (110) SrTiO₃ seeds at 1250°C.     

The effect of calcining temperature on the properties of 0-3 piezoelectric composites of PZT and a liquid crystalline thermosetting polymer

We report on the optimisation of a recently developed high performance 0-3 piezoelectric composite comprising of the piezoelectric Lead Zirconate Titanate (PZT) powder and a liquid crystalline thermosetting matrix polymer (LCT). The matrix polymer is a liquid crystalline polymer comprising of an HBA-HNA backbone with phenylethynyl end-groups. The use of a high performance polymer makes the composite a possible candidate to be used in sensor applications at elevated temperatures. The composite properties were optimised by calcining the PZT powder at different temperatures, prior to mixing the powders into the LCT matrix. The aim is to study the effect of the calcining temperature on the piezoelectric properties of the composite The PZT powders were characterised by X-ray diffraction and scanning electron microscopy. The dielectric constant and piezoelectric charge constant (d ₃₃ ) of the composite samples was measured. It was found that a relationship exists between the calcining temperature of the PZT powder and the piezoelectric properties of the composites. A maximum voltage constant of g ₃₃  = 63 mVm/N was obtained for a composite containing 40% (by volume) of PZT powder calcined at 1150°C.     

Characteristics of PMW-PNN-PT-PZ thick films on various bottom electrodes

Characteristics of piezoelectric thick films on various bottom electrodes prepared by screen printing method were investigated. The composition of the ceramics used in this study was 0.01Pb(Mg_1/2W_1/2)O₃–0.41Pb(Ni_1/3Nb_2/3)O₃–0.35PbTiO₃–0.23PbZrO₃ + 0.1wt% Y₂O₃ +2.0 wt.%ZnO(PMW-PNN-PT-PZ). The Ag and the Ag-Pd electrodes were coated on SiO₂/Si substrate by screen printing method and Pt electrode was deposited on Ti/ SiO₂/Si substrate by DC sputtering system. The piezoelectric PMW-PNN-PT-PZ thick films were fabricated on each electrode and annealed by rapid thermal annealing (RTA). The PMW-PNN-PT-PZ piezoelectric thick films on Ag/SiO₂/Si has higher remanent polarization (P _r) of 22.4 μC/cm².     

Dielectric properties and morphotropic phase boundaries in the xPb(Zn1/3Nb2/3)O3−(1−x)Pb(Zr0.5Ti0.5O3 pseudo-binary system

Ceramics in the xPb(Zn_1/3Nb_2/3)O₃−(1−x)Pb(Zr_0.5Ti_0.5)O₃ [xPZN–(1−x)PZT] solid solution system are expected to display excellent dielectric, piezoelectric, and ferroelectric properties in compositions close to the morphotropic phase boundary (MPB). The dielectric behavior of ceramics with x = 0.1−0.6 has been characterized in order to identify the MPB compositions in this system. Combined with X-ray diffraction results, ferroelectric hysteresis measurements, and Raman reflectivity analysis, it was consistently shown that an MPB exists between x = 0.2 and x = 0.3 in this binary system. When x ≤ 0.2, the tetragonal phase dominates at ambient temperatures. In the range of x ≥ 0.3, the rhombohedral phase dominates. For this rhombohedral phase, electrical measurements reveal a profound frequency dispersion in the dielectric response when x ≥ 0.6, suggesting a transition from normal ferroelectric to relaxor ferroelectric between 0.5 ≤ x ≤ 0.6. Excellent piezoelectric properties were found in 0.3PZN–0.7PZT, the composition closest to the MPB with a rhombohedral structure. The results are summarized in a PZN–PZT binary phase diagram.     

PZT thick films on different ceramic substrates; piezoelectric measurements

The piezoelectric, microstructural and electrical characteristics of thick PZT films on relatively inert alumina substrates and on two LTCC tapes, i.e., Du Pont 951 and Electro Science Labs 41020 were studied. A thick-film paste was prepared from the pre-reacted PZT powder (PbZr_0.53Ti_0.47O₃) and printed and fired on LTCC tapes and on alumina substrates, respectively. Dielectric permittivities, dielectric losses, remnant polarizations and coercive fields were measured. The dielectric constants (100–150) of thick films fired on LTCC substrates are low. The piezoelectric coefficients d ₃₃ were measured by different methods, i.e. Berlincourt piezometer, interferometry and piezoresponse force microscope (PFM). The d ₃₃ values on LTCC substrates are low (30–70 pm/V) as compared with values obtained on alumina substrates (around 120 pm/V). Lower dielectric constants and piezoelectric coefficients d ₃₃ of films on LTCC substrates are attributed to the formation of phases with a low permittivity due to the diffusion of silica from LTCC substrates into PZT films. The d ₃₃ constants of samples with different thicknesses of PZT layers (from 20 to 160 μm) at first increase with the increasing thickness of PZT layers and then decrease for thicker films. As the cracks in the structure were not observed the reason for the decreasing d ₃₃ values for thicker films is still unclear.     

Effects of complex doping on microstructural and electrical properties of PZT ceramics

The influence of complex dopants including donor and acceptor ions on microstructure and electrical properties of PZT (Zr/Ti = 53/47) ceramics was investigated. The prepared PZT ceramics modified with complex soft dopants, La⁺³ and Nb⁺⁵, showed that the piezoelectric properties were enhanced and stable with the compositional variations, which made it possible to establish the higher reliability and reproducibility of the piezoelectric performances. For 1.0 mol% La and 1.2 mol% Nb doped composition, the maximum value, k _P = 0.66, was obtained. Unlike single element doping, the complex doping of both the donor and acceptor ions caused various compensation effects for the piezoelectric properties of the PZT ceramics. The improved piezoelectric properties, i.e., enhanced Q _m with remaining higher k _p , were obtained in the PZT composition complexly doped with La⁺³ and Fe⁺³. For 1.0 mol% La and 2.0 mol% Fe doped PZT composition, relatively high Q _m and k _p values of 580 and 0.53, respectively, were obtained. It was also shown that the PZT composition had the rather lowered dielectric constant, ε _r = 800, and considerably low loss, tanδ = 0.003. By changing the dopants compositions, the properties can also be tailored over wider range.     

Piezoelectric and dielectric characteristics of low temperature sintering Pb(Ni1/3Nb2/3)O3-Pb(Mn1/3Nb2/3)O3-Pb(Zr1/2Ti1/2)O3 ceramics for multilayer piezoelectric actuator

In this study, in order to develop the composition ceramics for multilayer piezoelectric actuator, PNN substituted PMN-PZT ceramics were fabricated using Li₂CO₃ and Na₂CO₃ as sintering aids, and their piezoelectric and dielectric characteristics were investigated. With the increase of the amount of PNN substitution, dielectric constant (εr), electromechanical coupling factor (k _p), and piezoelectric constant (d ₃₃) of specimens showed the maximum value at each sintering temperature, and crystal structure changed from tetragonal to rhombohedral. At the sintering temperature of 950^∘C, the density, εr, k _p, d ₃₃, Q_m and Tc of 12 mol% PNN substituted PMN-PNN-PZT composition ceramics showed the optimal values of 7.79 g/cm³, 1160, 0.599, 419pC/N, 894 and 332^∘C, respectively, for low loss multilayer piezoelectric actuator application.     

Application of Ag–ceramic composite electrodes to low firing piezoelectric multilayer ceramic actuators

Ag–ceramic composite materials were investigated as low-cost internal electrodes for low firing piezoelectric multilayer ceramic actuators (MLCA). Ag–ceramic pastes were prepared by adding Pb(Mg_1/3Nb_2/3)O₃–Pb(Zr_0.475,Ti_0.525)O₃ (PMNZT) ceramic powders to a commercial Ag paste in the range of 0 to 50 wt.%. PMNZT/Ag–PMNZT multilayered laminates were fabricated using tape casting and subsequently cofired at 925°C for 10 h. The addition of PMNZT into Ag electrode decreased the thermal shrinkage mismatch between the composite layers, which led to improve mass producibility of MLCA through reducing delamination probability during cofiring process.     

Preparation and Characterization of PZT films Fabricated on Si Substrate

Lead zirconium titanate (PZT) films (Zr/Ti=45:55) with a high dielectric constant are prepared successfully on the low-resistance Si substrate in sol–gel dip-coating process with PT film used as the buffer layer. The dielectric and ferroelectric properties of the films as well as the relationship between crystallization and preparing condition are studied. It is shown that the PZT ferroelectric thin films with a (110) preferred orientation and a well-crystallized perovskite structure could be obtained after annealing at 800°C for 15 min. The particle size of the sample is about 14–25 nm. The P–E hysteresis loops are measured by means of the Sawyer-Tower test system with a compensation resistor at room temperature. The remanent polarization (P _r) and coercive electric field (E _c) of the measured PZT thin films are 47.7 μC/cm² and 18 kV/cm, respectively. The relative dielectric constant ε _r and the dissipation factor tgδ of the PZT thin films were measured with an LCR meter and were found to be 158 and 0.04–0.005, respectively. Translated from “Preparation and Characterization of PZT Films Fabricated on Si Substrates” published in Chinese Journal of Semiconductors, 2004, 25(4): 404–409 (in Chinese)     

Thin Film Piezoelectrics for MEMS

Thin film piezoelectric materials offer a number of advantages in microelectromechanical systems (MEMS), due to the large motions that can be generated, often with low hysteresis, the high available energy densities, as well as high sensitivity sensors with wide dynamic ranges, and low power requirements. This paper reviews the literature in this field, with an emphasis on the factors that impact the magnitude of the available piezoelectric response. For non-ferroelectric piezoelectrics such as ZnO and AlN, the importance of film orientation is discussed. The high available electrical resistivity in AlN, its compatibility with CMOS processing, and its high frequency constant make it especially attractive in resonator applications. The higher piezoelectric response available in ferroelectric films enables lower voltage operation of actuators, as well as high sensitivity sensors. Among ferroelectric films, the majority of the MEMS sensors and actuators developed have utilized lead zirconate titanate (PZT) films as the transducer. Randomly oriented PZT films show piezoelectric e _31,f coefficients of about ?7 C/m² at the morphotropic phase boundary. In PZT films, orientation, composition, grain size, defect chemistry, and mechanical boundary conditions all impact the observed piezoelectric coefficients. The highest achievable piezoelectric responses can be observed in {001} oriented rhombohedrally-distorted perovskites. For a variety of such films, e _31,f coefficients of ?12 to ?27 C/m² have been reported.