Electromechanical Coupling Coefficient Research Articles

Influence of growth temperature on the properties of aluminum nitride thin films prepared by magnetron sputter epitaxy

High quality, uni-polar, epitaxial AlN with minimum oxygen content promises excellent surface acoustic wave and bulk acoustic wave resonator characteristics such as high electromechanical coupling coefficient and power handling capabilities, which is particularly useful for RF filter applications. By systematically varying the growth temperature, the study investigates its impact on the oxygen levels, defect states, and crystallographic texture of the AlN thin films using a combination of atomic force microscopy, X-ray diffraction, time-of-flight secondary ion mass spectrometry, spectroscopic ellipsometry, scanning transmission electron microscopy, as well as room temperature and temperature dependent I–V measurements. The research demonstrates that the films grown at a temperature of 700°C exhibit the most favorable results. These films exhibit the lowest oxygen levels, possess epitaxial growth, and display the highest crystalline quality (XRD AlN 0002 ω−FWHM=1.3°). Additionally, these films demonstrate a significant reduction in sub-bandgap absorption. By comparing the cathode current measured during deposition, we suggest that the presence of an impurity layer formed during idle time between depositions as a possible source of oxygen in the sputter chamber. In addition, the study presents a possible model to explain the mixed polarity observed in AlN and proposes various ways to achieve uni-polar AlN on silicon substrates.

High performance SAW resonator with spurious mode suppression using double-layer electrode transverse modulation

This work aims to solve the problem of tradeoff between various properties and spurious mode suppression in surface acoustic wave (SAW) resonators. A high-angle rotated Y-cut LiNbO3 (LN)/SiO2/Si multilayered structure was proposed to balance the electromechanical coupling coefficient (K 2) and temperature coefficient of frequency (TCF), and the propagation characteristics of Rayleigh mode were simulated by the finite element method. For the widely existing spurious modes, the shear-horizontal wave and longitudinal modes were eliminated by optimizing the cut angle of LN and electrode thickness, and a method of double-layer electrode transverse modulation was proposed to suppress the transverse modes. This method reduces the mass loading effect by replacing the electrode from Cu to Cu/Al. Moreover, the Al thicknesses in different regions are changed to perform the transverse modulation, and thus a widespread suppression of transverse modes is achieved by exciting the piston mode and enhancing the energy constraint, with a significant improvement on quality factor at the resonance frequency. Eventually, the spurious-free SAW resonator has the K 2 of 9.5% and the TCF close to zero. This work provides a feasible scheme for the design of high performance SAW resonators with spurious mode suppression.

High Electromechanical Coupling Coefficient of Longitudinally Excited Shear Wave Resonator Based on Optimized Bragg Structure.

In this work, a longitudinally excited shear-wave resonator (YBAR) based on single-crystalline lithium tantalate (LiTaO3, LT) thin film is proposed. The YBAR has a 200 nm X-cut thin film and molybdenum electrode. A high effective electromechanical coupling coefficient (k2eff) of up to 19% for the suspension-type structure was obtained. Furthermore, a Bragg reflector (SiO2/Pt) with optimized layer thickness ratio was employed to improve the performance of the YBAR. Compared to the acoustic wave resonators with the conventional quarter-wave (λ/4) Bragg reflector, the proposed YBAR with an optimized Bragg reflector can reflect both the longitudinal and shear waves efficiently, and resonators with spurious-free response and high quality (Q) value were achieved. This work provides a potential solution to enabling high coupling micro-acoustic resonators with high Q factor in the 5G/6G communication system.

Magnetic field tunable piezoelectric resonator for MEMS applications

In this report, the Ni0.50Mn0.35In0.15/Pb0.96La0.04Zr0.52Ti0.48O3 (Ni-Mn-In/PLZT) bulk acoustic wave (BAW) resonator has been fabricated using the sputtering deposition technique. The magnetoelectric effect in the Ni-Mn-In/PLZT resonator has been investigated. The increase in magnetoelectric coupling coefficient (MECC) with the increment in the frequency of applied HAC is observed. The potential of the Ni-Mn-In/PLZT BAW resonator as a magnetic sensor is tested by measuring the shift in the resonant frequency of the reflective (S11 parameter) response in the presence of the externally applied magnetic field. The Ni-Mn-In/PLZT resonator exhibits a frequency shift of 730 MHz in the 1200 Oe magnetic field, among the largest magnetic field-induced frequency shifts in literature. The rarely reported complete dependence of acoustic velocity, coupling coefficients, magnetic sensitivity, and frequency peak shift on the strength of the external magnetic field is investigated. The acoustic velocity increases from 1237 m/s to 1394 m/s, and the electromechanical coupling coefficient increases from 0.0199 % to 0.0206 % after applying the 1200 Oe magnetic field. The reflective responses have been fitted using the Modified-Butterworth Van Dyke (MBVD) model in terms of hardly reported RLC equivalent circuits. The experimental results and extracted parameters from MBVD modeling exhibit high accuracy. This interaction between multiferroic orders and elastic resonance peaks opens a new window for highly sensitive future magnetic field sensors, wireless communication devices, and magnetic field tunable filters.

Lead zirconate titanate-based ceramics with high piezoelectricity and broad usage temperature range

Piezoceramics have long faced the challenge of achieving both a high Curie temperature (TC) and outstanding electrical properties due to thermal depolarization. To address this, we introduced a novel two-step synergistic strategy in synthesizing lead zirconate titanate (PZT)-based x[(1–y)BiYO3-yFe2O3)]-(1–x)Pb(Zr0.53Ti0.47)O3 [abbreviated as xBYF(y)-PZT] ceramics, where co-doping of Fe2O3 and BiYO3 significantly influences dielectric and piezoelectric properties. Our breakthrough composition, 0.01BYF(0.6)-PZT, showcases a unique coexistence of rhombohedral and tetragonal phases. It boasts impressive figures, including a piezoelectric coefficient d33 of 467 pC N−1, a TC of 381 °C, an electromechanical coupling coefficient (kp) of 68%, and a coercive field (Ec) of 12 kV cm−1, displaying both “softening” and “hardening” characteristics. In-depth analysis with in-situ X-ray diffraction and transmission electron microscopy unveils the critical role of multiphase coexistence and local heterostructures in enhancing piezoelectric responses through synergistic effects. Notably, this innovative composition with x = 0.01 showcases exceptional thermal stability across a broad operating temperature range (30–350 °C) and delivers an in-situ d33 value of 790 pC N−1. These compelling findings underscore the potential of BYF-modified PZT ceramics as promising candidates for high-temperature piezoelectric applications.

Hydroacoustic performance analysis and testing of a novel piezoelectric material transducer

In order to address the high sensitivity requirements of underwater detection systems, this paper designs two new piezoelectric material hydroacoustic transducers, single metal plate and bimetal plate arrays, based on 1–3 piezoelectric composites. By changing the piezoelectric ceramic's original structure to improve its piezoelectric properties, the transducer's overall performance is improved. The comparison of theoretical analysis and finite element simulation results shows that the single metal plate and double metal plate array structures use air instead of polymer to reduce the loss with a higher electromechanical coupling coefficient compared with 1–3 composite materials. 1–3, mono- and bi-metal plate array structure transducers were prepared in turn and tested for hydroacoustic performance. According to the results, the double metal plate array structure has a higher electromechanical coupling coefficient, transmit voltage response, and receive sensitivity compared to the 1–3 piezoelectric composites andsingle metal plate array transducers. The maximum transmit voltage response and receive sensitivity values are 179.8 dB and −173.8 dB, respectively. The bimetallic version of the array structure transducer can be applied to underwater detection systems, which have the ability to detect weaker signals.

Design, Optimization and Performance Assessment of Single Port Film Bulk Acoustic Resonator through Finite Element Simulation.

In this paper, the study is supported by design, FEA simulation, and practical RF measurements on fabricated single-port-cavity-based acoustic resonator for gas sensing applications. In the FEA simulation, frequency domain analysis was performed to enhance the performance of the acoustic resonator. The structural and surface morphologies of the deposited ZnO as a piezoelectric layer have been studied using XRD and AFM. The XRD pattern of deposited bulk ZnO film indicates the perfect single crystalline nature of the film with dominant phase (002) at 2θ = 34.58°. The AFM micrograph indicates that deposited piezoelectric film has a very smooth surface and small grain size. In the fabrication process, use of bulk micro machined oxide (SiO2) for the production of a thin membrane as a support layer is adopted. A vector network analyzer (Model MS2028C, Anritsu) was used to measure the radio frequency response of the resonators from 1 GHz to 2.5 GHz. As a result, we have successfully fabricated an acoustic resonator operating at 1.84 GHz with a quality factor Q of 214 and an effective electromechanical coupling coefficient of 10.57%.

Progress in manufacturing and processing of Al-Sc alloy targets

The development of the fifth-generation mobile communication technology (5G) puts forward higher requirements for radio frequency (RF) filters. Due to its higher frequency and larger bandwidth, bulk acoustic wave (BAW) filter will become the mainstream RF filter solution. Scandium doped aluminium nitride (AlScN) piezoelectric film has attracted much attention due to its excellent piezoelectric response coefficients and electromechanical coupling coefficients. The doped Sc concentration will directly affect the piezoelectric coefficient and electromechanical coupling coefficient of the film. The most common technique for producing AlScN thin films is magnetron sputtering of targets made of Al-Sc alloy. However, with the increase of Sc content, the solid-liquid solidification interval, the number of intermetallic compounds, and the brittleness of the material will all increase significantly. Additionally, it will result in component macro-segregation, uneven phase distribution, and poor processing deformability. Therefore, it is extremely difficult to manufacture and process Al-Sc alloy targets. The mainstream processes for preparing Al-Sc alloy targets are divided into direct reaction method and powder metallurgy method. This paper reviews the research progress in manufacturing and processing of Al-Sc alloy targets.

Research on Stacked Piezoelectric Cymbal Vibrator.

As demand for haptic feedback increases, piezoelectric materials have become one of the best candidate materials due to their small size, high electromechanical coupling coefficient, and fast response. A stacked piezoelectric cymbal vibrator is proposed based on the common cymbal-type transducer, which is composed of a piezoelectric stack to drive and a cymbal disk to amplify displacement. A coupling theoretical model between the piezoelectric stack and the cymbal-type structure is established. The longitudinal and radial displacements of the stacked piezoelectric cymbal vibrator are calculated in the low frequency range (<1000 Hz) by the theoretical model and the finite element method. The theoretical and numerical results are in good agreement. The results show that the radial displacement can be converted into longitudinal displacement and then effectively amplified by the cymbal disk with an amplification ratio of 30. The feature is conducive to its widespread application in the field of consumer electronics.

Investigation of PZT Materials for Reliable Piezostack Deformable Mirror with Modular Design.

This article presents a study of the electrophysical properties of a piezoceramic material for use in adaptive optics. The key characteristics that may be important for the manufacturing of piezoelectric deformable mirrors are the following: piezoelectric constants (d31, d33, d15), capacitance, elastic compliance values s for different crystal directions, and the dielectric loss tangent (tgδ). Based on PZT ceramics, the PKP-12 material was developed with high values of the dielectric constant, piezoelectric modulus, and electromechanical coupling coefficients. The deformable mirror control elements are made from the resulting material-piezoceramic combs with five individual actuators in a row. In this case, the stroke of the actuator is in the range of 4.1-4.3 microns and the capacitance of the actuator is about 12 nF.

Design of heterostructure one-port SAW resonator with improved bandwidth using Si and LiNbO3 layer

In this research work, we have designed a heterostructure one-port surface acoustic wave (SAW) resonator. The multi-layer one port SAW resonator is made of a silicon (Si) substrate as base material, 128 ͦ rotated Y-cut X- propagated lithium niobate (LiNbO3) as piezoelectric substrate, and Inter Digital Transducers (IDTs) made of aluminium. This model is designed to operate on a wide frequency of 4–5 GHz with a resonance frequency of 4.74 GHz. Various parameters are taken into consideration during the study and analysis such as high-quality factor, wider bandwidth, better electromechanical coupling coefficient, and a true Figure of merit (FoM). The obtained Quality factor and the electromechanical coupling coefficient (k2) of the designed model are 2700 and 0.18. By using the wide range of frequencies, the bandwidth for the designed model is 1.74 MHz. The obtained results show that the device’s performance of the one port multilayer SAW resonator using the Al/128°YXLiNbO3/Si multi-layered substrate exhibits a commercial application in the 5 G wireless communication system.

Study of electrode structures for 5.89 GHz A1 mode Lamb wave resonators to achieve fs×kt2×Q > 247×109 Hz

This work demonstrates a laterally excited shear bulk acoustic wave resonator (XBAR) based on a 300-nm-thick ZY-cut Lithium Niobate thin film, which takes advantages of high frequency, large electromechanical coupling coefficient (kt2) and high quality factor (Q). A bi-electrode structure was proposed to weaken the effects of mechanical and electrical loading introduced by the metal electrodes, while enhancing the coupling between the electric field and stress. In addition, the electrode configurations including interdigitated electrodes (IDEs) number, metal coverage and effective electrode length were studied to eliminate spurious modes and improve resonators’ performance. The fabricated devices can achieve the resonant frequency of 5.89 GHz using the first-asymmetric (A1) mode Lamb wave in suspended LiNbO3 thin film. Combined with the high operating frequency and high kt2 characteristics of the A1 mode Lamb wave, the measured results show that the designed bi-electrode structure XBAR achieves a kt2 value of 14 % and a high Q value of 300.

Multiphysics Modeling and Analysis of Sc-Doped AlN Thin Film Based Piezoelectric Micromachined Ultrasonic Transducer by Finite Element Method.

This paper presents a Piezoelectric micromechanical ultrasonic transducer (PMUT) based on a Pt/ScAlN/Mo/SiO2/Si/SiO2/Si multilayer structure with a circular suspension film of scandium doped aluminum nitride (ScAlN). Multiphysics modeling using the finite element method and analysis of the effect of different Sc doping concentrations on the resonant frequency, the effective electromechanical coupling coefficient (keff2) and the station sensitivity of the PMUT cell are performed. The calculation results show that the resonant frequency of the ScAlN-based PMUT can be above 20 MHz and its keff2 monotonically rise with the increasing doping concentrations in ScAlN. In comparison to the pure AlN thin film-based PMUT, the static receiving sensitivity of the PMUT based on ScAlN thin film with 35% Sc doping concentration is up to 1.61 mV/kPa. Meanwhile, the static transmitting sensitivity of the PMUT is improved by 152.95 pm/V. Furthermore, the relative pulse-echo sensitivity level of the 2 × 2 PMUT array based on the Sc doping concentration of 35% AlN film is improved by 16 dB compared with that of the cell with the same Sc concentration. The investigation results demonstrate that the performance of PMUT on the proposed structure can be tunable and enhanced by a reasonable choice of the Sc doping concentration in ScAlN films and structure optimization, which provides important guidelines for the design of PMUT for practical applications.

High-stability quinary lead-based piezoelectric ceramics with high piezoelectric properties

Piezoceramics with the formula Pb0.93Sr0.06Ba0.01(Mg1/3Nb2/3)0.035(Ni1/3Nb2/3)0.2 (Sb1/2Nb1/2)0.015(ZrxTi1−x)0.75O3 + 0.5 wt. % Li2CO3, where x = 0.51, 0.50, 0.49, 0.48, 0.47, and 0.46, have been made using the one-step solid-state method. The phase structure and electrical properties were systematically investigated in the quinary system. Here, the crystalline structure transformed gradually from the rhombohedral to tetragonal phase with decreasing Zr content. More importantly, the effective piezoelectric coefficient d33* of the ceramics demonstrates an excellent thermal stability below the Curie temperature. Meanwhile, piezoelectric ceramics with x = 0.49 exhibited the extraordinary electrical properties near the morphotropic phase boundary. A huge piezoelectric coefficient d33 = 853 pC/N, high Curie temperature TC = 152 °C, and the electromechanical coupling coefficients kp = 67.4%, kt = 63.5%, and k33 = 67.4% were obtained at the composition of x = 0.49, which may lead a promising future for the transducer applications.

Functionality in frequency tuning of magnetoelectric heterostructure integrated highly flexible bulk acoustic wave resonator

Functional flexible piezo-resonators are of vital interest for designing micro-electrometrical system (MEMS) based high-frequency wearable devices. The magnetoelectric (ME) heterostructure comprising highly magnetostrictive Ni–Mn–In and piezoelectric AlN films was fabricated over flexible substrates to develop the bulk acoustic wave (BAW) resonator. The BAW resonators fabricated over Ni and Kapton substrates show the fundamental resonance at ∼5.535 and 5.400 GHz, respectively. The comparative study of frequency tuning for both resonators has been executed in the presence of a dc magnetic field. A larger frequency shift (ΔfR) of ∼540 MHz was detected at 1200 Oe for a device fabricated over Ni with a sensitivity of ∼5.4 Hz/nT. However, it is 360 MHz in the case of Kapton, with a sensitivity of ∼3.0 Hz/nT. Moreover, the BAW resonator over the magnetostrictive Ni substrate shows a higher tunability of ∼11.4% compared to ∼8.5% for the resonator fabricated over non-magnetostrictive Kapton. The equivalent modified Butterworth–Van Dyke circuit parameters have been extracted by fitting the experimental data with and without an external magnetic field using advanced design system. The effect of an external magnetic field has been thoroughly investigated on device parameters, such as electromechanical coupling coefficient (K2), acoustic velocity, quality factor (Q), and figure of merit. The anisotropic functionality of the fabricated resonator has been studied by measuring the tunability of the resonator in parallel and perpendicular magnetic fields. The present study motivates the incorporation of flexible magnetostrictive substrates for futuristic multifunctional MEMS magnetic field sensor applications.

Surface tension effect on flexoelectric energy harvesting based on extended isogeometric analysis

This study presents a numerical framework to model the effect of surface tension on a flexoelectric energy harvesting system with liquid inclusions. The equivalent Young’s modulus and Poisson’s ratio of the liquid inclusions embedded in flexoelectric composites considering the surface tension are derived for the first time. An extended isogeometric analysis (XIGA) based on non-uniform rational B-splines (NURBS) is developed to model and solve the electromechanical response of weak discontinuities in flexoelectric composites. The interface between liquid and solid materials is implicitly represented by the level set method. Several numerical examples are presented as linear dielectric solids embedded with liquid inclusions under mechanical compression and different electric circuit configurations, including square matrixes and truncated pyramids. The simulation results indicate that a significant enhancement in the electromechanical coupling coefficient can be obtained by considering the effect of surface tension in open- and closed-circuit configurations. The maximum electric potential and energy conversion are higher in the open-circuit configuration. In addition, the XIGA simulation shows that the energy conversion of the flexoelectric devices increases as the size of the structural system and Young’s modulus of the flexoelectric material decrease. The maximum energy conversion capability of the flexoelectric composite, including the effect of surface tension, is enhanced by 32.4% with a central inclusion and 57% or higher with random inclusions. Finally, the influence of the length scale on the flexoelectricity is analyzed.

Analysis and Optimization of Bending Vibration Modes of a Trilaminar Bending Ring Transducer with Unequal Diameters

In this study, we propose a fast calculation method that utilizes Kirchhoff’s hypotheses and electroelasticity theory to derive the resonant frequency, antiresonant frequency, and effective electromechanical coupling coefficient of a trilaminar bending ring transducer with unequal diameters. The accuracy of the theoretical method is validated through finite element analysis (FEM) and experimental tests. Furthermore, we perform optimization of the effective electromechanical coupling coefficient of the first-order bending vibration of the trilaminar bending ring transducer. Our optimization results indicate that, under the free inner and fixed outer boundary conditions, the effective electromechanical coupling coefficient initially increases to a maximum value and then rapidly decreases as r1/r2 increases. This behavior can be attributed to the out-of-phase vibrations and the in-phase electric field excitation on both sides of the bending ring vibration nodal circle. Finally, we present the optimized size configuration required to achieve the maximum effective electromechanical coupling coefficient. This study provides theoretical guidance for the design and optimization of trilaminar bending ring transducers with unequal diameters and has the potential to significantly advance the field of crosswell seismic source technology.

Investigation of the equivalent circuit and performance of an ultrasonic transducer under a force load

In ultrasonic processing technology applications, the force load can cause a drift in the resonance frequency of the ultrasonic transducer and significantly reduce its mechanical quality factor. The traditional equivalent circuit of an ultrasonic transducer can only be used to calculate performance parameters without a force load but not with a force load. Based on Mason’s equivalent circuit, a new equivalent circuit for ultrasonic transducers under a force load is derived while considering the effects of the force load on the material parameters and various types of losses in piezoelectric ceramics. Furthermore, performance parameters are analyzed, such as the resonance frequency, effective electromechanical coupling coefficient, and mechanical quality factor. The ultrasonic transducer sample is produced and the experimental platform is constructed for applying force loads on the ultrasonic transducer. The theoretical model is verified by static loading on the ultrasonic transducer. The proposed equivalent circuit provides theoretical guidance for tracking the exact resonance frequency and performance parameters of force-loading ultrasonic transducers.

Fabrication of grain-oriented PbNb2O6-based high temperature piezoelectric ceramics

Grain-oriented Sr and Ti modified lead metaniobate (Pb0.96Sr0.04)Nb1.96Ti0.05O6 (PSNT) ceramics with 4 mol% excess of Nb2O5 were prepared by templated grain growth method. The needle-like PSNT templates were obtained through the molten salt synthesis method. The effects of the template concentration (5, 10, 20 and 30 wt%) on the texture degree, microstructure, and electrical properties of textured ceramics were investigated. Improved electromechanical properties were found along the direction perpendicular to the sheet in textured PSNT ceramics, which shows the preferential orientation. An excess of templates would seriously deteriorate the properties of textured ceramics. The textured PSNT ceramics with 5 wt% templates exhibit high Curie temperature Tc of 545 °C, and improvement in piezoelectric coefficient d33 by 9% (d33 = 98 pC/N) and g33 by 45% (g33 = 42 × 10−3 Vm/N), as well as electromechanical coupling coefficient k31 by 18% (k31 = 0.26) compared to randomly oriented ceramics. The study demonstrates that grain-orientation controlling in PN-based ceramics is a potential way to improve the piezoelectric properties while maintaining high Curie temperature.

Enhanced piezoelectric and optical properties of tetragonal Sm‐doped Pb(In1/2Nb1/2)–Pb(Mg1/3Nb2/3)–PbTiO3 crystals

AbstractRelaxor ferroelectric single crystal Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) has received extensive research and attention due to its excellent piezoelectric, electromechanical, and other properties. In particular, tetragonal relaxor ferroelectric single crystals have shown greater application potential in high‐temperature devices due to their higher Curie temperature and better stability. However, the low piezoelectric performance of tetragonal crystals also greatly limits its application, and research on its optical properties is not sufficient. In this paper, the tetragonal phase Sm–PIN–PMN–PT single crystal was obtained by the Bridgman method, and its piezoelectric and electro‐optical properties are studied. At the same time, we gave a complete set of piezoelectric, dielectric, and elastic coefficient matrices. The results show that the crystal has excellent piezoelectric and electromechanical properties. The piezoelectric coefficient can reach 905pC/N, the electromechanical coupling coefficient k33 is 85%, and the kt is 72%. The transmittance of the sample polarized along [001] direction can reach 66%. The effective electro‐optical coefficient γc is 60 pm/V at room temperature and can reach 86 pm/V at 70°C. It has a wide operating temperature range and stable performance with frequency variation, which has certain reference significance for application in new electro‐optical devices.