Converse Piezoelectric Effect Research Articles

Characterization and Fatigue of the Converse Piezoelectric Effect in PZT Films for MEMS Applications

A measurement setup for the detailed study of the transverse piezoelectric coefficient e31,f in the converse (actuator) mode was developed. It allows the assessment of the piezoelectric stress in thin films on silicon cantilevers and provides for a correlation of this stress with large and small signal responses to ferroelectric polarization and dielectric response, both as a function of slowly sweeping electric field. This test is important for the understanding of piezoelectric thin films in microelectromechanical systems. The method is illustrated at hand of sol-gel lead-zirconate-titanate (PZT) thin films, and verified also with AlN and AlN-ScN alloy thin films. A 1-μm thick, sol-gel derived PZT(53/47) gradient-free sample showed a response of -18.3 C/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 100-kV/cm electric field. Reliability tests of PZT thin films were carried out with the same setup in an accelerated manner. The piezoelectric activity did not degrade significantly up to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> unipolar pulses at 100 kHz with an amplitude of -150 kV/cm. The increase in leakage toward the end of the cycles was explained by a thermal runaway effect.

Effects of residual and tunable strain on the transport properties and electroresistance effects in thin films of La0.39Pr0.24Ca0.37MnO3

The effects of residual and tunable strain on transport properties and electroresistance effects in thin films of La0.39Pr0.24Ca0.37MnO3 (LPCMO) have been investigated. Due to different lattice mismatch, thin films of LPCMO on SrTiO3 (STO) and 0.7PbMg1/3Nb2/3O3–0.3PbTiO3 (PMNPT) are in different residual strain states. As a result of the converse piezoelectric effect, applying an electric voltage across PMNPT can generate a tunable strain. It is found that the effects of tunable strain are in accordance with those of residual strain and the strain has significant influences on not only the transport properties but also the electroresistance effects. With the decrease of tensile in-plane strain, the system becomes more metallic and the electroresistance effects are weaker. These results have been discussed in terms of the evolution of lattice distortion and phase competition as the tensile in-plane strain changes.

Influence of the AlGaN barrier thickness on polarization Coulomb field scattering in an AlGaN/AlN/GaN heterostructure field-effect transistor**Project supported by the National Natural Science Foundation of China (Grant Nos. 61306113 and11174182).

In this study rectangular AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with 22-nm and 12-nm AlGaN barrier layers are fabricated, respectively. Using the measured capacitance–voltage and current–voltage characteristics of the prepared devices with different Schottky areas, it is found that after processing the device, the polarization Coulomb field (PCF) scattering is induced and has an important influence on the two-dimensional electron gas electron mobility. Moreover, the influence of PCF scattering on the electron mobility is enhanced by reducing the AlGaN barrier thickness. This leads to the quite different variation of the electron mobility with gate bias when compared with the AlGaN barrier thickness. This mainly happens because the thinner AlGaN barrier layer suffers from a much stronger electrical field when applying a gate bias, which gives rise to a stronger converse piezoelectric effect.

State space finite element analysis for piezoelectric precision positioning considering secondary converse piezoelectric effect

A microgripper component which is made of piezo-cantilever is presented in this paper. The modified mixed variational principle including piezoelectric materials is established and then the state-vector equations of laminated piezoelectric beams are derived directly from the principle. Finally the exact expressions of mechanical and electrical variables along the thickness direction based on the state-vector equation are simply given. Based on the semi-analytical solution of the state-vector equation, a state space finite element model is established. The static analysis is carried out for a laminated beam fully covered with piezoelectric actuating layers on the top and bottom surfaces of the substrate. Both the substrate and piezoelectricity of the laminated beam are considered as one-dimensional line solids and the same linear element is used to discretize the whole beam. This semi-analytical technique can guarantee the continuity of generalized displacements and generalized stresses inter-layers and the transfer matrix method can be applied. Furthermore the exact solution in one direction ensures there is no restriction on the thickness for the smart structures. At the end of this paper the influence of secondary converse piezoelectric effect (SCPE) on the deflection of the laminated beam covered with piezoelectric driving layers for static precision displacement control is investigated. The above mentioned state space finite element method is used to predict the deflection of the beam with and without SCPE. If the influence of SCPE is eliminated, the deflections of the clamped beam will increase by ~2.7%. In addition, the driving characteristic with different PZT/steel thickness ratio considering SCPE are also studied. The maximum influence of SCPE on deflection can reach ~3% for the beam fully covered with piezoelectric active layers, which should not be neglected in practical microoperation applications.

The Displacement Characteristics of Piezoelectric Ceramic Micro Actuators Evaluated by Laser Interferometer

Understanding and measuring the displacement characteristics of piezoelectric ceramic with electric field exciting are particularly important. The piezoelectric coefficient d33 as the indication of its displacement characteristics, is the key parameter of its energy transformation. In this paper, the characteristics of two kinds of piezoelectric ceramics, PZT4 and PZT5 were studied by the laser interferometer measurement. The influence factors of d33 were studied, including the frequency and amplitude of the exciting signal, the ways of holding, and the loading sequence. Then the measurement results of piezoelectric ceramic with laser interferometer and the quasi-static method were compared, the results showed they had consistence and the analysis of the piezoelectric coefficient d33 measurement by converse piezoelectric effect and by piezoelectric effect was discussed.

Inducing a Finite In-Plane Piezoelectricity in Graphene with Low Concentration of Inversion Symmetry-Breaking Defects

We show that a finite in-plane piezoelectricity can be induced in graphene by breaking its inversion center with any in-plane defect, in the limit of vanishing defect concentration. We first consider different patterns of BN-doped graphene sheets of D3h symmetry, whose electronic and piezoelectric (dominated by the electronic rather than nuclear term) properties are characterized at the ab initio level of theory. We then consider other in-plane defects, such as holes of D3h or C2v point symmetry, and confirm that a common limit value (for low defect concentration) of the piezoelectric response of graphene is obtained regardless of the particular chemical or physical nature of the defects (e11 ≈ 4.5 × 10–10 C/m and d11 ≈ 1.5 pm/V for direct and converse piezoelectricity, respectively). This in-plane piezoelectric response of graphene is one-order of magnitude larger than the out-of-plane previously investigated one.

A nonlinear formulation of piezoelectric shells with complete electro-mechanical coupling

A nonlinear piezoelectric shell model capable of accurately expressing the direct and the converse piezoelectric effect is presented. The developed theory is meant to encompass large strains, displacements and rotations that can occur in the shell as a consequence of a complete coupling between the mechanical and the electrical fields. Based on results present in the literature according to which a linear dependence of the electric potential on the shell thickness is not adequate to represent its electrical behavior, a specific structure of the field of admissible displacements is taken into account. Warping functions characterized by an ad-hoc polynomial expansion aimed at expressing their dependence on the shell through-the-thickness coordinate are here considered to describe the shear and the extensional deformability of the shell transverse fibers. Linear constitutive relations for a transversely isotropic continuum are considered. Finally, the governing equations of motion of the shell are obtained via enforcement of the virtual work theorem.

A nonlinear piezoelectric shell model: Theoretical and numerical considerations

A nonlinear piezoelectric shell model capable of accurately expressing the direct and the converse piezoelectric effect is discussed here with the support of numerical simulations. The theory under investigation is meant to be able to encompass a complete coupling between the mechanical and the electrical fields in the frame of geometrically exact shell formulations. To this aim, warping functions characterized by an ad hoc polynomial expansion in the shell through-the-thickness coordinate are considered to describe the shear and the extensional deformability of transverse fibers. The governing equations of motion are numerically implemented for the cases of a rectangular semi-cylinder and for a multilayered 90° rectangular cylinder. Numerical results show the effects of key geometric parameters and of the nature of the loading on the system response, evidencing that significant misrepresentations of the system behavior are possible if lower-order kinematics are taken into account.

Analysis for Smart Beam with Secondary Converse Piezoelectric Effect

Based on variational principle, the state-vector equation is established for driving analysis of a laminated beam with piezoelectric actuating layers. The beam are considered as a 2D line solid and the linear element is used. The influence of secondary converse piezoelectric effect (SCPE) on the displacement of the laminated beam is investigated. The state space finite element method is utilized to predict the deflection of the beam considering SCPE or not. If the influence of SCPE is eliminated, the displacement of the clamped beam increase by ∼2.7%. Furthermore, the effects with different PZT/steel thickness ratio considering SCPE are also studied.

Embedded Electromechanical Impedance and Strain Sensors for Health Monitoring of a Concrete Bridge

Piezoelectric lead zirconate titanate (PZT) is one of the piezoelectric smart materials, which has direct and converse piezoelectric effects and can serve as an active electromechanical impedance (EMI) sensor. The design and fabrication processes of EMI sensors embedded into concrete structures are presented briefly. Subsequently, finite element modeling and modal analysis of a continuous rigid frame bridge are implemented by using ANSYS and MIDAS and validated by the field test results. Uppermost, a health monitoring technique by employing the embedded EMI and strain sensors is proposed in this paper. The technique is not based on any physical model and is sensitive to incipient structural changes for its high frequency characteristics. A practical study on health monitoring of the continuous rigid frame bridge is implemented based on the EMI and strain signatures. In this study, some EMI and strain sensors are embedded into the box-sectional girders. The electrical admittances of distributed EMI active sensors and the strains of concrete are measured when the bridge is under construction or in operation. Based on the electrical admittance and strain measurements, the health statuses of the continuous rigid frame bridge are monitored and evaluated successfully in the construction and operation stages using a root-mean-square deviation (RMSD) index.

Surface mapping of field-induced piezoelectric strain at elevated temperature employing full-field interferometry.

Piezoelectric actuators and sensors are widely used for flow control valves, including diesel injectors, ultrasound generation, optical positioning, printing, pumps, and locks. Degradation and failure of material and electrical properties at high temperature typically limits these applications to operating temperatures below 200°C, based on the ubiquitous Pb(Zr,Ti)O3 ceramic. There are, however, many applications in sectors such as automotive, aerospace, energy and process control, and oil and gas, where the ability to operate at higher temperatures would open up new markets for piezoelectric actuation. Presented here is a review of recent progress and initial results toward a European effort to develop measurement techniques to characterize high-temperature materials. Full-field, multi-wavelength absolute length interferometry has, for the first time, been used to map the electric-field-induced piezoelectric strain across the surface of a PZT ceramic. The recorded variation as a function of temperature has been evaluated against a newly developed commercial single-beam system. Conventional interferometry allows measurement of the converse piezoelectric effect with high precision and resolution, but is often limited to a single point, average measurement and to limited sample environments because of optical aberrations in varying atmospheres. Here, the full-field technique allows the entire surface to be analyzed for strain and, in a bespoke sample chamber, for elevated temperatures.

Experimental research on the new Al0.25Ga0.75N/GaN HEMTs with a step AlGaN layer

In this paper, experimental results are reported about the new Al0.25Ga0.75N/GaN high electron mobility transistor (HEMT) with a step AlGaN layer. The rule of 2DEG concentration variation with the thickness of AlGaN epitaxial layer has been applied to the new AlGaN/GaN HEMTs: The step AlGaN layer is formed at the gate edge by inductively coupled plasma etching, the 2DEG concentration in the etched region is much lower than the other parts of the device. A new electric field peak appears at the corner of the step AlGaN layer. The high electric field at the gate edge is decreased effectively due to the emergence of the new electric field peak, and this optimizes the surface electric field of the new AlGaN/GaN HEMTs. The new devices have the same threshold voltage and transconductance as the conventional structure, -1.5 V and 150 mS/mm. That means, the step AlGaN layer does not affect the forward characteristics of the AlGaN/GaN HEMTs. As the more uniform surface electric field distribution usually leads to a higher breakdown voltage (BV), with the same gate to drain length LGD=4 m, the BV can be improved by 58% for the proposed Al0.25Ga0.75N/GaN HEMTs as compared with the conventional structure. At VGS=1 V, the saturation currents (Isat) is 230 mA/mm for the conventional Al0.25Ga0.75N/GaN HEMT and 220 mA/mm for the partially etched Al0.25Ga0.75N/GaN HEMT (LEtch=4 m, LGD=4 m). The decrease of Isat is at most 10 mA/mm. However, as the BV has a significant enhancement of almost 40 V, these drawbacks are small enough to be acceptable. During the pulse I-V test, the current collapse quantity of the conventional structure is almost 40% of the maximum IDS(DC), but this quantity in the new devices is only about 10%, thus the current collapse effect in Al0.25Ga0.75N/GaN HEMTs has a significant remission for a step AlGaN layer. And as the high electric field peak at the gate edge is decreased, the effect of the gate electrode on electron injection caused by this electric field peak is also included. The injected electrons may increase the leakage current during the off-state, and these injected electrons would form the surface trapped charge as to decrease the 2DEG density at the gate. As a result, the output current and the transconductance would decrease due to the decreased electron density during the on-state. That means, with the region partially etched, the electron injection effect of the gate electrode would be remissed and the stability of Schottky gate electrode would be improved. In addition, due to the decrease of the high electric field at the gate edge, the degradation of the device, which is caused by the high electric field converse piezoelectric effect, will be restrained. The stability of the partially etched AlGaN/GaN HEMT will become better.

Application of piezoelectric materials in a novel linear ultrasonic motor based on shear-induced vibration mode

A novel linear ultrasonic motor based on d15 effect of piezoelectric materials was presented. The design idea aimed at the direct utilization of the shear-induced vibration modes of piezoelectric material. Firstly, the inherent electromechanical coupling mechanism of piezoelectric material was investigated, and shear vibration modes of a piezoelectric shear block was specially designed. A driving point’s elliptical trajectory induced by shear vibration modes was discussed. Then a dynamic model for the piezoelectric shear stator was established with finite element (FE) method to conduct the parametric optimal design. Finally, a prototype based on d15 converse piezoelectric effect is manufactured, and the modal experiment of piezoelectric stator was conducted with laser doppler vibrometer. The experimental results show that the calculated shear-induced vibration modes can be excited completely, and the new linear ultrasonic motor reaches a speed 118 mm/s at noload, and maximal thrust 12.8 N.

Effect of biaxial strain induced by piezoelectric PMN-PT on the upconversion photoluminescence of BaTiO₃:Yb/Er thin films.

Thin films of Yb3+/Er3+ co-doped BaTiO3 (BTO:Yb/Er) have been epitaxially grown on piezoelectric Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) substrates. Biaxial strain can be effectively controlled by applying electric field on PMN-PT substrate. A reversible, in situ and dynamic modification of upconversion photoluminescence in BTO:Yb/Er film was observed via converse piezoelectric effect. Detailed analysis and in situ X-ray diffraction indicate that such modulations are possibly due to the change in the lattice deformation of the thin films. This result suggests an alternative method to rationally tune the upconversion emissions via strain engineering.

Cobalt ferrite sphere-coated buckhorn-like barium titanate: Fabrication, characterization, its dielectric resonance, and microwave attenuation properties

Barium titanate (BTO) with different morphology is prepared through hydrothermal method using titania spheres as precursor, then calcined at different temperatures and ultimately coated with cobalt ferrite (BTO/CFO). The dielectric dispersion of the composite containing BTO (75 wt. % ratio in paraffin wax) shows evidence of resonance behaviour in the microwave spectrum, rather than the usually observed relaxation mode. The imaginary part of permittivity (ε″) displays a strong peak in the 10–13 GHz frequency region, especially for buckhorn-like BTO (hydrothermally synthesized at 110 °C and calcined at 1100 °C). The dielectric response anomaly of BTO in special morphology is due to the emission of plane acoustic waves caused by electrostrictive and converse piezoelectric effects. An accepted model is adopted to simulate the resonance frequency. The minimum reflection loss of cauliflower-like BTO (hydrothermally synthesized at 110 °C, then calcined at 600 °C for 2 h, 75 wt. % ratio) in paraffin wax reaches −30.831 dB at 10.56 GHz with a matching thickness of 2 mm, lower than all the reported values. When the sintering temperature is changed to 1100 °C (buckhorn-like BTO), the minimum reflection loss value is −24.37 dB at 12.56 GHz under the thickness of 3 mm. After combination with CFO, the value reaches −42.677 dB when the thickness is 5.6 mm. The ginger-like BTO (hydrothermally synthesized at 200 °C and calcined at different temperatures) is inferior in microwave reflection reduction. The electromagnetic interference shielding effectiveness of buckhorn-like BTO composite is calculated to be −12.7 dB (94.6% shielding) at resonance frequency (2 mm, 11.52 GHz). This work clearly shows the potential to tune the dielectric property of ferroelectrics through control of morphology, facilitating new comprehension of the ferroelectrics in microwave regime.

Modelling and experiments of PLZT/PVDF hybrid drive method for non-contact shape adjustment

In order to improve the technical specifications of space reflectors, antennas and other payloads on Earth observation, space communication, deep space exploration and other fields of space applications, people urgently need to enhance the surface shape control accuracy of these large complex curvature flexible structures. Based on the photovoltaic effect and converse piezoelectric effect, this paper presents a non-contact shape-adjusting method which adopts a new space energy conversion: using the PLZT photovoltage, which is controlled by the ultraviolet, to activate the PVDF attached on the flexible structure surface, and adjust and control the structure's shape. This paper firstly built up the electric model of the PLZT/PVDF hybrid drive, derived the constitutive relation of light-electric-mechanical energy field conversion, and determined the key parameters inmathematical model by principle experiments. Then, taking aflexiblecantilever beam as thecontrol object, actuation equation of the PVDF bonded structure was built, and actuation properties and influence factors of the cantilever beam actuated by the PLZT/PVDF hybrid drive were simulated and analyzed. After that, the hybrid drive experiment system was built up, and deflecting effect of using ultraviolet illuminated PLZT to actuate PVDF bonded cantilever beam was tested, whose result verified the validity of theoretical modeling and simulation analysis. Lastly, characteristics of the hybrid drive method and conventional PVDF driving were compared, and space application direction of this method was pointed out.

An extended molecular statics algorithm simulating the electromechanical continuum response of ferroelectric materials

Molecular dynamics (MD) simulations of ferroelectric materials have improved tremendously over the last few decades. Specifically, the core-shell model has been commonly used for the simulation of ferroelectric materials such as barium titanate. However, due to the computational costs of MD, the calculation of ferroelectric hysteresis behaviour, and especially the stress-strain relation, has been a computationally intense task. In this work a molecular statics algorithm, similar to a finite element method for nonlinear trusses, has been implemented. From this, an algorithm to calculate the stress dependent continuum deformation of a discrete particle system, such as a ferroelectric crystal, has been devised. Molecular statics algorithms for the atomistic simulation of ferroelectric materials have been previously described. However, in contrast to the prior literature the algorithm proposed in this work is also capable of effectively computing the macroscopic ferroelectric butterfly hysteresis behaviour. Therefore the advocated algorithm is able to calculate the piezoelectric effect as well as the converse piezoelectric effect simultaneously on atomistic and continuum length scales. Barium titanate has been simulated using the core-shell model to validate the developed algorithm.

Piezoelectricity in collagen type II fibrils measured by scanning probe microscopy

The converse piezoelectric effect in collagen type II fibrils, the main collagen constituent in cartilage, was investigated using piezoresponse force microscopy. The fibrils exhibited shear piezoelectric behavior similar to that previously reported in collagen type I fibrils and followed the same cantilever-fibril angle dependence present for type I. A uniform polarization directed from the amine to carboxyl termini, as seen for collagen type I, was observed in all type II fibrils studied. The shear piezoelectric coefficient, d15, however, for type II was roughly 28–32% of the value measured for type I fibrils. Possible explanations for the reduced piezoelectric coefficient of type II collagen are provided.

Tuning of near-infrared luminescence of SrTiO3:Ni2+ thin films grown on piezoelectric PMN-PT via strain engineering.

We report the tunable near-infrared luminescence of Ni2+ doped SrTiO3 (STO:Ni) thin film grown on piezoelectric Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) substrate via strain engineering differing from conventional chemical approach. Through controlling the thickness of STO:Ni film, the luminescent properties of the films including emission wavelength and bandwidth, as well as lifetime can be effectively tuned. The observed phenomena can be explained by the variation in the crystal field around Ni2+ ions caused by strain due to the lattice mismatch. Moreover, the modulation of strain can be controlled under an external electric field via converse piezoelectric effect of PMN-PT used in this work. Consequently, controllable emission of the STO:Ni thin film is demonstrated in a reversible and real-time way, arising from the biaxial strain produced by piezoelectric PMN-PT. Physical mechanism behind the observation is discussed. This work will open a door for not only investigating the luminescent properties of the phosphors via piezoelectric platform, but also potentially developing novel planar light sources.

Sub-coercive and multi-level ferroelastic remnant states with resistive readout

Ferroelectric devices use their electric polarization ferroic order as the switching and storage physical quantity for memory applications. However, additional built-in physical quantities and memory paradigms are requested for applications. We propose here to take advantage of the multiferroic properties of ferroelectrics, using ferroelasticity to create a remnant strain, persisting after stressing the material by converse piezoelectricity means. While large electric fields are needed to switch the polarization, here writing occurs at subcoercive much lower field values, which can efficiently imprint multiple remnant strain states. A proof-of-principle cell, with the simplest and non-optimized resistance strain detection design, is shown here to exhibit 13-memory states of high reproducibility and reliability. The related advantages in lower power consumption and limited device fatigue make our approach relevant for applications.