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.     

Piezoelectric micromachined ultrasonic transducers with thick PZT sol gel films

The fabricated micro machined ultrasonic transducers (pMUT) was based on piezoelectric laminated plates operating at flexural modes. The fabricated bimorph pMUT transducers were composed of 5-layers. A 4 μm thick lead zirconate titanate (PZT) thin film deposited by a sol–gel method was used. The piezoelectric layer exhibited a capacitance corresponding to a permitivity of ɛ _r = 1,200. The electromechanical coupling coefficient (k ²) and quality factor (Q) were measured as k ² = 4.4% and Q = 145 in air for a low frequency transducer (240 kHz). The effect of DC bias voltage on frequency and k ² has been studied. The 16.9 MHz transducer yielded values of Q = 25 in air and k ² = 3%.     

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.     

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.     

Fabrication and evaluation of PZT/Ag composites and functionally graded piezoelectric actuators

Metallic Ag as the second phase was added into PZT ceramic matrix to fabricate piezoelectric composites and functionally graded actuators by gradually altering Ag concentration, aimed to improve mechanical properties and to solve possible interfacial debonding usually observed in conventional bimorph-type piezoelectric actuator. The PZT/Ag composites were obtained by directly co-firing PZT and Ag powders at 1200^∘C for 1 h. The fracture strength σ _f and fracture toughness K _IC , as well as the corresponding piezoelectric properties, were firstly evaluated upon the PZT/Ag composites for Ag concentrations of 0–30 vol%. The mechanical properties for the PZT/Ag composites were found to be greatly enhanced compared with pure PZT ceramics: from 69 to 129 MPa for σ _f and from 1.0 to 3.7 MPa.m^1/2 for K _IC . With increasing Ag concentration, the piezoelectric constant d ₃₃ of PZT/Ag composites was found to decrease from 419 to 86 pC/N. Then, a functionally graded actuator was fabricated and evaluated in terms of electric-induced curvature k. The PZT/Ag FGM actuator with size of 12 mm × 3 mm × 1 mm has a curvature k of 0.03–0.17 m⁻¹ that corresponds to applied voltages of 100–500 V. A comprehensive comparison was made on the mechanical property enhancements by the metal particles dispersion, and the bending displacements produced by the FGM actuators between the PZT/Ag and previously fabricated PZT/Pt systems.     

Use of mass loading to operate a thin film ultrasonic transducer in the 300 kHz–10 MHz frequency range

Thin film ultrasonic transducers have been designed which operate over an important frequency range, 300 kHz to 10 MHz. The transducers were made using piezoelectric aluminium nitride films a few microns thick. The films would have a fundamental thickness mode resonance at 1–3 GHz if fabricated as an unsupported film, however operation at much lower frequencies has been demonstrated when the transducers are fabricated on bulk substrates. This would enables them to be used in ultrasonic non-destructive testing in circumstances where the film can be deposited directly onto the object under test. We have found that the major factors influencing the below-resonance operation of the thin film transducers are the device impedance, the spectrum of the excitation pulse, and any mechanical (mass) loading applied to the back face of the transducer. Results are presented showing that the evolution of device impedance as a function of device area could be predicted using a PSpice model of the thin film transducer. The ability of the transducer to generate longitudinal mode pulses rather than shear wave pulses was found to depend on increasing the mechanical loading at the back face of the transducer. This mechanism for pulse generation was confirmed by Finite Element Modelling using PZFlex.     

Inorganic ceramic/polymer ferroelectric composite electrets

Ferroelectric composites are now an established alternative to conventional ferroelectric ceramic materials and to the more recently discovered ferroelectric polymers. These materials due to their unique blending of polymetric properties of mechanical flexibility, formability and low cost with high electro-active properties have been been suggested to be a viable alternative both in piezoelectric and pyroelectric transducer applications. This review is devoted to the piezoelectric and pyroelectric properties exhibited by these type of composites with a special reference to those made of ceramic particles embedded in a polymer matrix (i.e. 0-3 connectivity type composite). A review of models predicting the electro-active properties of 0-3 composites is presented together with a proposal for a new mixed connectivity cubes model to be applicable to the case of high ceramic loading and/or when the ceramic grain size incorporated in the polymer matrix is comparable to the thickness of the sample. A review of the experimental results of the piezo- and pyroelectric properties of various ferroelectric composite materials, reported by several workers, is also presented in this paper. Special reference is made to composites made from calcium modified lead titanate and poly(vinyldene fluoride-trifluorethylene) emphasizing their advantages in the poling process which is a critical phase in the process of obtaining successful electro-active 0-3 composite electrets     

Piezoelectric Energy Harvesting under High Pre-Stressed Cyclic Vibrations

Cymbal transducers have been found as a promising structure for piezoelectric energy harvesting under high force (∼ 100 N) at cyclic conditions (∼ 100–200 Hz). The thicker steel cap enhances the endurance of the ceramic to sustain higher ac loads along with stress amplification. This study reports the performance of the cymbal transducer under ac force of 70 N with a pre-stress load of 67 N at 100 Hz frequency. At this frequency and force level, 52 mW power was generated from a cymbal measured across a 400 kΩ resistor. The ceramic diameter was fixed at 29 mm and various thicknesses were experimented to optimize the performance. The results showed that the PZT ceramic of 1 mm thickness provided the highest power output with 0.4 mm endcap. In order to accommodate such high dynamic pressure the transducer and cap materials were modified and it was found that the higher piezoelectric voltage constant ceramic provided the higher output power. Electrical output power as a function of applied ac stress magnitude was also computed using FEM analysis and the results were found to be functionally coherent with experiment. This study clearly demonstrated the feasibility of using piezoelectric transducers for harvesting energy from high magnitude vibration sources such as automobile.     

Chemically derived seeding layer for {100}-textured PZT thin films

PZT thin films are used extensively in micro electromechanical systems (MEMS) due to its high piezoelectric coefficients. The electromechanical responses can be optimized by using textured films where the transverse coefficient e_31,f is of particular importance for MEMS structures such as cantilevers, bridges and membranes. It has been shown that {100}-textured PZT of morphotropic composition fabricated by chemical solution deposition (CSD) provides the highest transverse coefficient [1]. This specific texture can be obtained using a seeding layer of sputter deposited PbTiO₃ [2]. However, in a CSD process it is advantageous to also be able to produce the seed layer by chemical methods. The piezoelectric and dielectric properties of 2 μm PZT film seeded by CSD PbTiO₃ measured by a new 4-point bending setup are presented.     

Effect of heating rate on the structure evolution of (K0.5Na0.5)NbO3–LiNbO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)(K_0.5Na_0.5)NbO₃–xLiNbO₃ (abbreviated an KNLN) have been synthesized by traditional ceramics process. Effects of heating rate on the phase structure, microstructure evolution and piezoelectric properties of (1 − x)(K_0.5Na_0.5)NbO₃–xLiNbO₃ were investigated. Results show that the heating rate has no effects on the phase structures. However, the fracture surface of the 0.94(K_0.5Na_0.5)NbO₃ −0.06 LiNbO₃ ceramics transforms from intergranular fracture mode to a typical transgranular fracture mode with the increasing of the heating rate. This result is ascribed to the presence of agglomerates of grains which exhibit different sintering behavior at diverse heating rates. The 0.94(K_0.5Na_0.5)NbO₃–0.06LiNbO₃ ceramic sintered at 1080°C with heating rate of 5°C/min shows the optimum piezoelectric properties(d ₃₃ = 210 pC/N, k _p = 0.403 and k _t = 0.498).     

Piezoelectric PZT films for MEMS and their characterization by interferometry

Piezoelectric films can be used in micro-electro-mechanical system (MEMS) devices because the piezoelectric effect can provide high forces with relatively low energy losses. The energy output by a piezoelectric film per unit area is proportional to the film thickness, so it is desirable to have relatively thick films. Chemical solution deposition (CSD) techniques were used to prepare lead zirconate titanate (PZT) thin films with Zr/Ti ratios of 30/70 and 52/48. Usually CSD processing is restricted to making crack-free single layer films of ca 70 nm thick, but modifications to the sol-gel process have permitted the fabrication of dense, crack-free single layers up to 200–300 nm thick, which can be built-up into layers up to 3 μm thick. Thicker PZT films (> 2 μm single layer) can be produced by using a composite sol-gel/ceramic process. Knowledge of the electro-active properties of these materials is essential for modeling and design of novel MEMS devices and accurate measurement of these properties is by no means straightforward. A novel double beam common path laser interferometer has been developed to measure the piezoelectric coefficient in films and the results were compared with the values obtained by Berlincourt method. A laser scanning vibrometer was also used to measuring the longitudinal (d ₃₃) and transverse (d ₃₁) piezoelectric coefficients for PZT films and ceramics and the results were compared to those obtained by the other methods. It was found that for thin film samples, the d _33,f values obtained from the Belincourt method is usually larger than those obtained from the interferometer method but smaller than those from the vibrometer method and the reasons for this are discussed.     

Thickness mode high frequency MEMS piezoelectric micro ultrasound transducers

Thickness mode piezoelectric micro-electromechanical system (MEMS) ultrasound transducers, operating in the 50–75 MHz range, have been fabricated using a composite sol gel technique in combination with wet etching. The composite sol gel technique involves producing a PZT powder/sol composite slurry, which when spun down yields films a few micrometers thick. Repeated layering, and infiltration, has been used to produce PZT films between 20 and 40 μm thick. Due to the low firing temperature (<720°C) it has also been possible to integrate these PZT films with a micro-machined silicon support wafer. These PZT thick films have been structured using a wet etching technique to create free standing pillars that have been shown to resonate in thickness mode in the frequency range of 50–75 MHz. Examples of these structures and their resonant behaviour are presented.     

Fabrication and properties of 1-3-2 multi-element piezoelectric composite

A design method is presented for 1-3-2 type multi-element piezoelectric composite so as to provide basis for the development and study of transducer and transducer array. The composite samples have been fabricated by a twice dice-filling process from lead zirconate titanate (PZT-4), epoxy resin and silicone, the properties of the composites have been measured and investigated physically. The results show that the piezoelectric, dielectric and electromechanical coupling properties of the composite exhibit a good consistency, while it has a high thickness electromechanical coupling factor K _t and a wide bandwidth of pulse-echo signal. The impedance plot of every element indicates good behavior that all elements show excellent frequency consistency, and on the other hand the chance of coupling of lateral resonance and thickness resonance is very small, and with a clear thickness resonance mode at around 100?kHz. Silicon has extremely decoupling properties which can efficiently block the transmission of the acoustic vibrations and eliminate coupling effect among elements. And the farther the distance between the incentive element and receiving element is, the smaller the response signal become, while the response signal decay rate exhibits the trend of increase, the largest up to 95%.     

Direct writing of lead zirconate titanate piezoelectric structures by electrohydrodynamic atomisation

Direct writing, consisting of the directed deposition of individual droplets of ceramic suspension using ink jet printing can be used to produce piezoelectric structures with feature sizes in excess of 100 μm. This work presents an alternative direct writing technique, consisting of directed individual droplets produced by electrohydrodynamic atomisation (EHDA), where feature sizes an order of magnitude smaller can be achieved. This technique opens up the possibility of using direct writing technology to produce integrated MEMS devices. Low toxicity lead zirconate titantate (PZT) sol has been used in conjunction with the EHDA process to produce isolated features and lines with dimensions as small as 20 μm. These features, when fired, form the perovskite PZT crystal structure. Using an X–Y stage to move the sample, it is possible to create a variety of structures.     

Actuation performance analysis of piezo-composite unimorph actuator with d33 actuation mechanism of piezo-electric ceramic layer

The performance improvement of the LIPCA (Lightweight Piezo-Composite curved Actuator) is investigated in this paper. The LIPCA is known as the best layered piezo-composite unimorph actuator because of not only high performance but also its flexible analytical design model and simple fabrication technique. Besides, originated from efforts to develop highly induced-strain piezoelectric ceramic, the IDEAL (Inter-Digitated Electrode Actuation Layer) have shown to be a potential candidate in unimorph or bimorph actuator designs. In a latest model of IDEAL designs, the inter-digitated electrodes (IDEs) had been proposed to be embedded directly into the piezoelectric ceramic wafer. Hence, the resulting stacked-type transducer is able to have full d₃₃ actuation mechanism which can produce almost twice larger strain than that produced by the conventional d₃₁ actuation mechanism. Therefore, by replacing the original actuation layer with IDEAL in the lay-up structure of the conventional LIPCA design, one can expect improvement to the performance of the actuator, e.g., gaining higher of out-of-plane actuation displacement. The modified design of LIPCA had been investigated considering mechanical properties of an inhomogeneous IDEAL. As the result, an IDEAL fabricated with low-elastic-modulus IDEs have shown to give considerably improvement on actuation performance of the LIPCA. Following that sense, a new homogenization model applied to the embedded IDEAL is proposed and able to convince the previously obtained result.     

Effect of BiScO 3 doping on the structure and properties of BiFeO 3 -BaTiO 3 piezoelectric ceramics

High temperature lead-free piezoelectric ceramics 0.67BiFeO3–0.33BaTiO3 doped with 0.35 mol% MnO2 and xBiScO3 (x = 0, 0.005, 0.01, 0.015, 0.02) were prepared by conventional...     

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.     

Effects of ZnO on the piezoelectric properties of Pb (Mn1/3 Sb 2/3 )O 3 -Pb(Zr,Ti)O 3 Ceramics

Perovskite-types 0.05Pb(Mn_1/3Sb_2/3)O₂-0.95Pb- (Zr_0.5Ti_0.5)O₃ (PMS-PZT) was synthesized by conventional bulk ceramic processing technique. ZnO as a dopant up to 0.5 mol% was incorporated into the PMS-PZT system, and the effects on piezoelectric properties were investigated. Pyrochlore phase was not detected to form during the synthesis of the PMS-PZT system with 0–0.5 mol% ZnO addition. The highest density of 7.92 g/cm³ was obtained when sintered at 1200^∘C for 2 h. Piezoelectric properties as a function of ZnO content were evaluated using a gain phase analyzer. Piezoelectric charge constant (d ₃₁) and piezoelectric voltage output coefficient (g ₃₁) increased up to −130 pC/N and −24.9 × 10³Vm/N, respectively, with increasing ZnO content. Mechanical quality factor (Q _m) was shown to reduce considerably with increasing ZnO content. When 0.3 mol% of ZnO was added into the system, electromechanical coupling factor (k _p) and relative dielectric constant (ε₃₃ ^T /ε_o) reached to the maximum of 56% and 1727, respectively.     

Fabrication of piezoelectric MEMS devices-from thin film to bulk PZT wafer

Integrating patterned functional piezoelectric layer onto silicon substrate is a key technique challenge in fabrication of piezoelectric Micro Electro Mechanical System (pMEMS) devices. Different device applications have different requirements on the thickness and in-plane geometry of the piezoelectric layers and thus have their own processing difficulties. In this paper, the techniques of integrating piezoelectric function into pMEMS has been discussed together with some diaphragm-based pMEMS devices which have relatively lenient requirement on patterning of the piezoelectric layers. Sol-gel thin film can meet the requirement of most of the sensor applications. The composite thick film is one of the promising solutions for thick film devices due to its good processing compatibility. Si/Pb(Zr _x Ti_1 − x )O₃ wafer bonding technique makes it possible to thin down the ceramic wafer to less than 10 μm by using chemical mechanical polishing, which, therefore, provide us another approach to integrate thick piezoelectric layer on silicon to cover the need of most of the thick film devices. Directly make double side aligned electrode patterns on bulk piezoelectric wafer/plate by using photolithography opens up a new area of pMEMS. The advantage of using bulk piezoelectric wafer/plate in pMEMS is that we can select commercial available ceramics or single crystals with excellent piezoelectric properties and thus ensure the overall performance of the devices.     

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.