Longitudinal Piezoelectric Coefficient D33 Research Articles

Piezoelectric Response of ZnO Thin Films Grown By Plasma-Enhanced Atomic Layer Deposition

ZnO is a direct band gap semiconductor with attractive piezoelectrical, optical, and electrical properties, particularly appealing for a variety of functional devices. Especially the utilization of piezoelectric properties of ZnO nanostructures for transforming mechanical to electrical energy has attracted much research interest. For most of these so called nanogenerators, solution based deposition methods have been applied to create the desired nanostructures, often lacking a precise control of the deposition parameters. Atomic layer deposition, on the other hand, allows conformal and uniform deposition on high aspect ratio structures with Å-level thickness control. In this study, we investigate the piezoelectric response of ZnO thin films on flexible substrates as a starting point for piezoelectric nanostructures. The films are grown by plasma-enhanced atomic layer deposition (PE-ALD) to thicknesses below 100 nm by adapting diethylzinc and O2-plasma as reactants. In comparison to thermal ALD (where diethylzinc and water are used as reactants), PE-ALD allows the deposition of films with higher resistivity, an important property to minimize the leakage of piezoelectric charges. Commercially available Polyethylenterephthalat (PET) coated with Indium Tin Oxide (ITO) serves as the flexible substrate and bottom electrode, respectively. The deposition of ZnO thin films is carried out at substrate temperatures between room temperature and 100 °C, as a change in preferential crystal orientation from (100) to (002) can be observed in this temperature range. [1] The macroscopic piezoelectric characterization is performed in a home-built stamp station, in which a defined periodic force is exerted onto the samples and the generated piezoelectric charges are measured. Out of this, the longitudinal piezoelectric coefficient d33 can be obtained. Preliminary results show d33 coefficients > 7 pC/N, which is comparable to literature results. [2] The piezoelectric characterization is made for the different samples to understand how the d33 coefficient changes for films deposited at different substrate temperatures and thus having different crystal orientation. Since the [002] is the polar axis in the ZnO wurtzite crystal structure, films with preferred orientation in this direction are therefore expected to show higher d33 coefficients. The work lays the basis for developing functional piezoelectric generators and sensors in thin film form. However, the concepts can be easily transferred to depositions on lithographically defined templates in order to create nanostructured ZnO, which exhibits increased piezo response. [1] J.Pilz, A. Perrotta, G. Leising, A. M. Coclite, ZnO thin films grown by plasma-enhanced atomic layer deposition: material properties within and outside the “ALD window”, submitted. [2] M. Laurenti, S. Stassi, M. Lorenzoni, M. Fontana, G. Canavese, V. Cauda, C.F. Pirri, Evaluation of the piezoelectric properties and voltage generation of flexible zinc oxide thin films, Nanotechnology. 26 (2015) 215704. doi:10.1088/0957-4484/26/21/215704.

Influence of Porosity Orientation on Physical Properties in Porous PZT Ceramics

Orientation of porosity in porous media influences the pore network and their physical properties. Sacrificial cellulose templates arranged in different stacked layer orientation configurations with various distortion form the oriented pore network. The templates are embedded into non‐aqueous lead zirconate titanate (PZT) slurry (solid fracture of 48 vol%) and burn‐out while sintering. The porous PZT ceramics have a mean porosity of up to 39% Microcomputer tomography (μCT) measurement and SEM analysis are used for pore network analysis. The longitudinal and transversal piezoelectric coefficients (d33 and d31) and the relative permittivity ϵr vary between 15 and 98% according to the reference sample. The bending strength σb (double ring test) is reduced by 60% with increasing porosity compared to the dense sample.

Concurrent wafer-level measurement of longitudinal and transverse effective piezoelectric coefficients (d33,f and e31,f) by double beam laser interferometry

In a recently published paper [S. Sivaramakrishnan et al., Appl. Phys. Lett. 103, 132904 (2013)], the electrode-size dependence of the longitudinal effective piezoelectric coefficient (d33,f) of piezoelectric thin films measured by double beam laser interferometry was shown to be due to the substrate clamping effects. It was also shown that the true d33,f is measured when the ratio of the electrode size to the substrate thickness is approximately unity, in the case of a substrate with isotropic elastic properties and a Poisson's ratio of ∼0.3. In this paper, we further investigate the dependence of the critical ratio (rc) of the electrode size to the substrate thickness at which the true d33,f is measured on the substrate Poisson's ratio for isotopic substrates and for the important case of the anisotropic Si substrate. It turns out that it is the out-of-plane Poisson's ratio (-s13/s11) that is relevant for this measurement technique and not the in-plane Poisson's ratio which is highly anisotropic for the (001) oriented Si. Furthermore, we show that the transverse effective piezoelectric coefficient (e31,f) can also be determined from the same measurement of the electrode size dependence of d33,f. This provides a convenient non-destructive wafer-level measurement technique for the determination of both the piezoelectric coefficients simultaneously. Moreover, this technique is also capable of measuring e31,f under varying electric field excitation which is important for many applications such as actuators.

Simultaneously enhanced piezoelectric response and piezoelectric voltage coefficient in textured KNN‐based ceramics

Abstract<001> ‐textured 0.99(K0.49Na0.49Li0.02)(Nb0.97‐xSb0.03Tax)O3‐0.01CaZrO3 [abbreviated as 0.99KNLN0.97‐xSTx‐0.01CZ, x = 0.03, 0.07, 0.10, 0.15, 0.20, 0.25] ceramics were prepared by templated grain growth (TGG) method and a two‐step sintering process. Giant longitudinal piezoelectric coefficient d33 (391 pC/N) and piezoelectric strain coefficient d33* (630 pm/V under an AC E‐field of 20 kV/cm) can be obtained in the textured ceramics with x = 0.25. All textured ceramics display superior kp (>54%) and g33 (>23 × 10−3 Vm/N) which are in an order of magnitude with PZT ceramics. The maximum value of kp (~63.3%) obtained in textured ceramics with x = 0.15 is higher than that of famous textured LF4 ceramics. Excellent comprehensive properties suggest that <001> ‐textured 0.99KNLN0.97‐xSTx‐0.01CZ ceramics are promising candidates in the field of lead‐free piezoelectric materials.

Effects of slurry composition on the properties of 3-1 type porous PZT ceramics prepared by ionotropic gelation

In this study, 3-1 type lead zirconate titanate (PZT) ceramics with one-dimensional pore channels were produced by ionotropic gelation process of alginate/PZT suspensions. By increasing the sodium alginate concentration from 1.0wt% to 3.0wt%, the alginate/PZT suspensions turned from Newtonian to non-Newtonian behavior with substantial increase in apparent viscosity. Accordingly, 3-1 type PZT ceramics with porosity decreasing from 56.78% to 41.44% were obtained, while the pore size distribution became non-uniform gradually. Based on the structural features, the 3-1 type PZT ceramics possessed much higher relative permittivity (εr) than that of 3-0 or 3-3 type PZT ceramics with similar porosities. Increase in the porosity led to a moderate decline in the longitudinal piezoelectric strain coefficient (d33), a reduction in the dielectric loss factor (tan δ), and a high value of hydrostatic strain coefficient (dh). As a result, the 3-1 type PZT ceramics possessed a maximal hydrostatic figure of merit (HFOM) value of 5597×10–15Pa−1 when the porosity was 56.78%, which may be of help for low frequency hydrophones applications.

Modelling and fabrication of porous sandwich layer barium titanate with improved piezoelectric energy harvesting figures of merit

This paper demonstrates that porous ‘sandwich’ structures can provide an effective route for the design and optimisation of piezoelectric materials for energy harvesting applications, which is becoming an increasingly important technology for self-powered wireless networks and sensors. A numerical model is presented that accounts for the complex poling distribution throughout a layered ferroelectric and helps to develop a detailed understanding of the relationship between the geometry of the porous structure and the poling characteristics of porous ferroelectric materials, with good agreement with experimental data. Novel layered barium titanate ceramics were fabricated whereby dense outer layers surround a highly porous sandwich layer, and for specific layer geometries an unusual condition was achieved where the longitudinal piezoelectric strain coefficients (d33) increased as the thickness of the porous layer and total porosity level of the layered structure increased. The permittivity (ε33T) decreased with increasing thickness and increasing porosity level of the porous layer due to the presence of a low permittivity air phase. These two factors in combination led to an increase in the longitudinal energy harvesting figure of merit, d332/ε33T, for the layered structure, with a maximum of 3.74 pm2/N when the relative thickness of the porous layer was 0.52 and the porosity within this layer was ∼60 vol%. This harvesting performance of these novel structures is much larger than both dense barium titanate (1.40 pm2/N) and barium titanate with randomly distributed porosity at the same 60% volume fraction (2.75 pm2/N).

Controllable piezoelectricity of Pb(Zr0.2Ti0.8)O3 film via in situ misfit strain

The tetragonality (c/a) of a PbZr0.2Ti0.8O3 (PZT) thin film on La0.7Sr0.3MnO3/ 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 (PMN-PT) substrates was controlled by applying an electric field on the PMN-PT substrate. The piezoelectric response of the PZT thin film under various biaxial strains was observed using time-resolved micro X-ray diffraction. The longitudinal piezoelectric coefficient (d33) was reduced from 29.5 to 14.9 pm/V when the c/a ratio of the PZT film slightly changed from 1.051 to 1.056. Our results demonstrate that the tetragonality of the PZT thin film plays a critical role in determining d33, and in situ strain engineering using electromechanical substrate is useful in excluding the extrinsic effect resulting from the variation in the film thickness or the interface between substrate.

Low temperature aluminum nitride thin films for sensory applications

A low-temperature sputter deposition process for the synthesis of aluminum nitride (AlN) thin films that is attractive for applications with a limited temperature budget is presented. Influence of the reactive gas concentration, plasma treatment of the nucleation surface and film thickness on the microstructural, piezoelectric and dielectric properties of AlN is investigated. An improved crystal quality with respect to the increased film thickness was observed; where full width at half maximum (FWHM) of the AlN films decreased from 2.88 ± 0.16° down to 1.25 ± 0.07° and the effective longitudinal piezoelectric coefficient (d33,f) increased from 2.30 ± 0.32 pm/V up to 5.57 ± 0.34 pm/V for film thicknesses in the range of 30 nm to 2 μm. Dielectric loss angle (tan δ) decreased from 0.626% ± 0.005% to 0.025% ± 0.011% for the same thickness range. The average relative permittivity (εr) was calculated as 10.4 ± 0.05. An almost constant transversal piezoelectric coefficient (|e31,f|) of 1.39 ± 0.01 C/m2 was measured for samples in the range of 0.5 μm to 2 μm. Transmission electron microscopy (TEM) investigations performed on thin (100 nm) and thick (1.6 μm) films revealed an (002) oriented AlN nucleation and growth starting directly from the AlN-Pt interface independent of the film thickness and exhibit comparable quality with the state-of-the-art AlN thin films sputtered at much higher substrate temperatures.

Intrinsic orientation effect on the piezoelectric response of multi-domain 0.26Pb(In1/2Nb1/2)O3–0.46Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 crystals

The crystal intrinsic orientation effect on the piezoelectric response of multi-domain 0.26Pb(In1/2Nb1/2)O3–0.46Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 (PIN-PMN-0.28PT) crystals was investigated by coordinate transformation method. The results indicate that crystal intrinsic orientation effect plays a crucial role in determining the piezoelectric properties of multi-domain crystals. Almost 58% and 69% of the transverse piezoelectric coefficients d31 and d32, respectively, and 67% longitudinal piezoelectric coefficient d33 of multi-domain PIN-PMN-0.28PT crystals poled along [011]c originate from crystal intrinsic orientation effect. For [001]c poled multi-domain PIN-PMN-0.28PT crystals, intrinsic orientation effect contributes to the transverse and longitudinal piezoelectric coefficient at least 79% and 74%, respectively.

Synthesis of KCa2Nb3O10 Crystals with Varying Grain Sizes and Their Nanosheet Monolayer Films As Seed Layers for PiezoMEMS Applications

The layered perovskite-type niobate KCa2Nb3O10 and its derivatives show advantages in several fields, such as templated film growth and (photo)catalysis. Conventional synthesis routes generally yield crystal size smaller than 2 μm. We report a flux synthesis method to obtain KCa2Nb3O10 crystals with significantly larger sizes. By using different flux materials (K2SO4 and K2MoO4), crystals with average sizes of 8 and 20 μm, respectively, were obtained. The KCa2Nb3O10 crystals from K2SO4 and K2MoO4 assisted synthesis were protonated and exfoliated into monolayer nanosheets, and the optimal exfoliation conditions were determined. Using pulsed laser deposition, highly (001)-oriented piezoelectric stacks (SrRuO3/PbZr0.52Ti0.48O3/SrRuO3, SRO/PZT/SRO) were deposited onto Langmuir-Blodgett films of Ca2Nb3O10(-) (CNO) nanosheets with varying lateral nanosheet sizes on Si substrates. The resulting PZT thin films showed high crystallinity irrespective of nanosheet size. The small sized nanosheets yielded a high longitudinal piezoelectric coefficient d33 of 100 pm/V, while the larger sized sheets had a d33 of 72 pm/V. An enhanced transverse piezoelectric coefficient d31 of -107 pm/V, an important input parameter for the actuation of active structures in microelectromechanical systems (MEMS) devices, was obtained for PZT films grown on CNO nanosheets with large lateral size, while the corresponding value on small sized sheets was -96 pm/V.

Thickness-Dependent Monoclinic Phases and Piezoelectric Properties Observed in Polycrystalline (Pb0.94La0.04)(Zr0.60Ti0.40)O3 Thin Films

Ferroelectric thin films have received significant attention in view of their applications in microelectromechanical systems. Correlations between microstructure and polarization behavior have not been established. Polycrystalline (Pb0.94La0.04)(Zr0.60Ti0.40)O3 thin films with thicknesses ranging from 100 to 400 nm were prepared on the Pt(111)/Ti/SiO2/Si(100) substrates by a sol–gel method. Synchrotron X-ray diffraction results revealed that the films thinner than 150 nm possess an asymmetry-allowed monoclinic (MA) phase and undergo a MA–monoclinic MB–R phase sequence with increasing thickness. It was found that longitudinal piezoelectric coefficient d33 optimizes at 128 pm/V for 150 nm thick film. Above this thickness, a simple decreasing trend was observed. The presence of the monoclinic phase and (100) preferred orientation as well as crystalline quality are considered to play key roles in enhancing piezoelectric properties of the 150 nm thick film. Piezoelectric materials show a composition-related transition region where the crystal structure changes abruptly and the piezoelectric properties are maximal. In this study, an alternative approach is proposed in achieving excellent piezoelectric properties via a thickness-dependent constrain effect.

(100)-Textured KNN-based thick film with enhanced piezoelectric property for intravascular ultrasound imaging.

Using tape-casting technology, 35 μm free-standing (100)-textured Li doped KNN (KNLN) thick film was prepared by employing NaNbO3 (NN) as template. It exhibited similar piezoelectric behavior to lead containing materials: a longitudinal piezoelectric coefficient (d33) of ∼150 pm/V and an electromechanical coupling coefficient (kt ) of 0.44. Based on this thick film, a 52 MHz side-looking miniature transducer with a bandwidth of 61.5% at -6 dB was built for Intravascular ultrasound (IVUS) imaging. In comparison with 40 MHz PMN-PT single crystal transducer, the rabbit aorta image had better resolution and higher noise-to-signal ratio, indicating that lead-free (100)-textured KNLN thick film may be suitable for IVUS (>50 MHz) imaging.

Piezoelectricity in K1−xNaxNbO3: First-principles calculation**Project supported by the National Basic Research Program of China (Grant No. 2013CB632900).

The piezoelectric properties of K1−xNaxNbO3 are studied by using first-principles calculations within virtual crystal approximation. To understand the critical factors for the high piezoelectric response in K1−xNaxNbO3, the total energy, piezoelectric coefficient, elastic property, density of state, Born effective charge, and energy barrier on polarization rotation paths are systematically investigated. The morphotropic phase boundary in K1−xNaxNbO3 is predicted to occur at x = 0.521, which is in good agreement with the available experimental data. At the morphotropic phase boundary, the longitudinal piezoelectric coefficient d33 of orthorhombic K0.5Na0.5NbO3 reaches a maximum value. The rotated maximum of is found to be along the 50° direction away from the spontaneous polarization (close to the [001] direction). The moderate bulk and shear modulus are conducive to improving the piezoelectric response. By analyzing the energy barrier on polarization rotation paths, it is found that the polarization rotation of orthorhombic K0.5Na0.5NbO3 becomes easier compared with orthorhombic KNbO3, which proves that the high piezoelectric response is attributed to the flattening of the free energy at compositions close to the morphotropic phase boundary.

Dielectric and piezoelectric properties of porous PZT–PCN ceramics sintered at different temperatures

Porous lead zirconate titanate–lead cobalt niobate 0.8Pb(Zr1/2Ti1/2)O3–0.2Pb(Co1/3Nb2/3)O3 (PZT–PCN) piezoelectric ceramics were fabricated by introducing pore-forming agent polymethyl methacrylate (PMMA), and the effect of sintering behavior on their microstructure, dielectric, and piezoelectric properties were investigated. The optimum sintering procedure was designed according to the thermogravimetric analysis of pore former. Finally the electrical properties were measured.The porosity of PZT–PCN ceramics decreased and the grain size increased with an increase in the sintering temperature at a fixed PMMA addition.“An increase in density with sintering temperature from 1050 to 1250°C results into an increase in longitudinal piezoelectric coefficient (d33) and relative dielectric constant (εr). This ‘in turn’ enhanced the hydrostatic figure of merit (dhgh) of the ceramics material”.The hydrostatic figure of merit (dhgh) of 24% porous PZT–PCN ceramics was eleven times more than that of dense ceramic. This kind of porous ceramic could be a promising candidate for medical diagnostic devices.

Polarization rotation and piezoelectricity of electric field-induced monoclinic and triclinic structures in strained PbTiO3

Electric field-induced polarization rotation, phase changes, and piezoelectric effect of strained PbTiO3 films have been investigated using a phenomenological approach. Low-symmetry monoclinic and triclinic structures have been induced, and the type of intermediate phases during polarization rotation is closely related to both the initial state at zero electric field and anisotropy of the in-plane strain. The monoclinic MC and triclinic structures in general may exhibit high shear piezoelectric coefficient d35 and sometimes also remarkable enhancement of longitudinal piezoelectric coefficient d33 around the transition point. High piezoelectric activity and low critical field have been found in epitaxial PbTiO3 with equal but opposite in-plane strain where monoclinic MC is the only intermediate phase on the polarization path. The present results suggest that anisotropy of epitaxial strain may have significant impact on polarization rotation behavior and electromechanical coupling of ferroelectric thin films.

A high quality lead-free (Li, Ta) modified (K, Na)NbO3single crystal and its complete set of elastic, dielectric and piezoelectric coefficients with macroscopic 4mm symmetry

A high quality orthorhombic (K, Na, Li)(Nb, Ta)O3 single crystal with a large size of 9 × 9 × 11 mm3 was successfully grown using the top-seeded solution growth method. Its large size allowed us to perform comprehensive investigation on this crystal. A complete set of elastic, dielectric and piezoelectric coefficients was determined using combined resonance and ultrasonic methods. The longitudinal piezoelectric coefficient d33 and the transverse piezoelectric coefficient d31 of this lead-free piezoelectric single crystal are as high as 354 pC N−1 and −163 pC N−1, respectively, which are two times higher than those of KNN-TL ceramics and are comparable with those of PZT5. The electromechanical coupling factor k33 is as high as 82%, much higher than those of KNN-TL ceramics and PZT5. The coefficient d33,strain was found to be as high as 672 pm v−1 and the extrinsic contribution (~22%) was investigated by Rayleigh analysis. These high piezoelectric properties make this single crystal a promising candidate for replacing lead-based piezoelectric materials.

Pulsed DC magnetron sputtered piezoelectric thin film aluminum nitride – Technology and piezoelectric properties

Pulsed DC magnetron sputtered aluminum nitride (AlN) thin films are prepared on several seed layers and at different sputtering conditions. The piezoelectric c-axis (002) orientation of the AlN is analyzed with X-ray diffraction method. The transverse piezoelectric coefficient d31 is determined with a Laser-Doppler-Vibrometer at cantilevers and membranes by analytical calculations and finite element method. Additionally, thin film AlN on bulk silicon is used to characterize the longitudinal piezoelectric charge coefficient d33.

Orthorhombic-tetragonal phase coexistence and enhanced piezo-response at room temperature in Zr, Sn, and Hf modified BaTiO3

The effect of Zr, Hf, and Sn in BaTiO3 has been investigated at close composition intervals in the dilute concentration limit. Detailed structural analysis by x-ray and neutron powder diffraction revealed that merely 2 mol. % of Zr, Sn, and Hf stabilizes a coexistence of orthorhombic (Amm2) and tetragonal (P4mm) phases at room temperature. As a consequence, all the three systems show substantial enhancement in the longitudinal piezoelectric coefficient (d33), with Sn modification exhibiting the highest value ∼425 pC/N.

Fabrication and properties of PZT piezoelectric ceramic tubes with large length–diameter ratio

Lead zirconate titanate (PZT) ceramic tubes with large length–diameter ratio were fabricated by a viscous plastic processing-extrusion method at different sintering temperatures and holding times. The phase composition, microstructure, dielectric and piezoelectric properties of the tubes were investigated by XRD, SEM, precision impedance analyzer and d33 measuring instruments. A typical perovskite phase without other impurities was obtained for the tubes sintered at 1290°C for 2h. A homogeneous and compact structure with 2–5μm grain sizes was also observed. The relative dielectric constant (εr) and dielectric loss (tanδ) of PZT piezoelectric ceramic tubes were 2734 and 0.35, respectively. The longitudinal piezoelectric coefficient (d33) of PZT ceramic tubes was 528pCN−1.

Ferroelectric and Piezoelectric properties of (111) oriented lanthanum modified lead zirconate titanate film

Lanthanum modified lead zirconate titanate (PLZT) thick film with molecular formula of Pb0.92La0.08(Zr0.52Ti0.48)0.98O3 was grown preferentially along (111) direction on Pt/SiO2/Si (platinum/silicon oxide/silicon) substrate by spin coating of chemical solution. The directional growth of the film was facilitated by platinum (Pt) (111) template and rapid thermal annealing. X-ray diffraction pattern and atomic force microscopy revealed the preferential growth of the PLZT film. The film was characterized for ferroelectric and detailed piezoelectric properties in a parallel plate capacitor (metal–PLZT–metal) configuration. Ferroelectric characterization of the film showed saturated hysteresis loop with remanent polarization and coercive electric field values of 10.14μC/cm2 and 42kV/cm, respectively, at an applied field of 300kV/cm. Longitudinal piezoelectric coefficient (d33,f) was measured by employing converse piezoelectric effect where electrical charge response and displacement were measured with electrical voltage excitation on the sample electrodes. The effective transverse piezoelectric coefficient (e31,f) was derived from charge measurement with an applied mechanical excitation strain by using the four point bending method. d33,f and e31,f coefficients of PLZT films were found to be 380pm/V and −0.831C/m2 respectively.