Effective Electromechanical Coupling Coefficient Research Articles

Electrically Reconfigurable Surface Acoustic Wave Phase Shifters Based on ZnO TFTs on LiNbO3 Substrate

Abstract Reconfigurable surface acoustic wave (SAW) phase shifters have garnered significant attention owing to their potential applications in emerging fields such as secure wireless communication, adaptable signal processing, and intelligent sensing systems. Among various modulation methods, employing gate voltage-controlled tuning methodologies that leverage acoustoelectric interactions has proven to be an efficient modulation approach which requires a low bias voltage. However, current acoustoelectric devices suffer from limited tunability, intricate heterogeneous structures, and complex manufacturing processes, all of which impede their practical application. In this study, we present, for the first time, a novel material system for voltage-tunable SAW phase shifters. This system incorporates an atomic layer deposition (ALD) ZnO thin-film transistors (TFTs) on LiNbO3 structure. This structure combines the benefits of LiNbO3's high electromechanical coupling coefficient (K2) and ZnO's superior conductivity adjustability. Besides, the device possesses a simplified structural configuration, which is easy for fabrication. Devices with different mesa lengths were fabricated and measured, and two of the different modes were compared. The results indicate that both the maximum phase shift and attenuation of the Rayleigh mode and Longitudinal leaky surface acoustic wave (LLSAW) increase proportionally with mesa length. Furthermore, LLSAW with larger effective electromechanical coupling coefficients (Keff2) values exhibit greater phase velocity shifts and attenuation coefficients, with a maximum phase velocity tuning of 1.22% achieved. It is anticipated that the proposed devices will find utility in a variety of applications necessitating tunable acoustic components.

A Laterally Excited Bulk Acoustic Wave Resonator Based on LiNbO3 with Arc-Shaped Electrodes.

High frequency and large bandwidth are growing trends in communication radio-frequency devices. The LiNbO3 thin film material is expected to become the preferred piezoelectric material for high coupling resonators in the 5G frequency band due to its ultra-high piezoelectric coefficient and low loss characteristics. The main mode of laterally excited bulk acoustic wave resonators (XBAR) have an ultra-high sound velocity, which enables high-frequency applications. However, the interference of spurious modes is one of the main reasons hindering the widespread application of XBAR. In this paper, a Z-cut LiNbO3 thin film-based XBAR with arc-shaped electrodes is presented. We investigate the electric field distribution of the XBAR, while the irregular boundary of the arc-shaped electrodes affects the electric field between the existing interdigital transducers (IDTs). The mode shapes and impedance response of the XBAR with arc-shaped electrodes and the XBARs with traditional IDTs are compared in this work. The fabricated XBAR on a 350 nm Z-cut LiNbO3 thin film with arc-shaped electrodes operating at over 5 GHz achieves a high effective electromechanical coupling coefficient of 29.8% and the spurious modes are well suppressed. This work promotes an XBAR with an optimized electrode design to further achieve the desired performance.

Performance enhancement of galloping wind energy harvesting via bio-inspired V-shaped blade

ABSTRACT Galloping wind energy harvesting has promising applications in future distributed self-powered low-power devices. A novel V-shaped blade is figured out from Palm leaf galloping. The enhancement of galloping oscillation from the bio-inspired V-shaped blade is evaluated. The galloping wind energy harvester (WEH) with a V-shaped blade is developed by electro-mechanical modeling, finite element simulation, ground vibration tests, and wind tunnel tests. It is found that the structural damping, effective electro-mechanical coupling coefficient, and V-shape included angle have big effects on the harvesting performance. The cut-in wind speed of WEH is below 3 m/s. With an included angle of 115° and a wind speed of 6.5 m/s, the output voltage is 4.48 V and the power density is 90.00 μW/cm3. The V-shaped blade harvester exhibits a 151.69% increase in output voltage and a 575.00% increase in power density compared to the traditional brick blade (square cross-section) harvester. Tests indicate that the output frequency remains stable at the structural resonant despite increasing wind speed. This study provides insights into enhancing galloping oscillation and wind energy harvesting efficiency by optimizing the aerodynamic shape of vortex shedding bluffs.

Investigation of a cascaded piezoelectric transducer with cone horn for multi-mode power ultrasound application

To meet the ultrasonic application requirement of high power intensity and large mechanical displacement, a new theoretical method is used to study the multi-mode characteristic of the cascaded piezoelectric transducer with cone horn in this paper. Based on equivalent circuit and Kirchhoff’s law to obtain the frequency equation and vibration velocity expression of the transducer, then the resonance frequency and effective electromechanical coupling coefficient can be calculated, the velocity amplification ratio can be obtained in the meantime. This method is distinguish from traditional theoretical analysis, which avoids complex transformation of the multi-excitation sources in cascaded structure, and can calculate more performance parameters. The relationships between these performance parameters and the excitation position of the piezoelectric stack, the length and output end radius of the cone horn are analyzed and compared with the numerical simulation, and the optimized parameters of the transducer size are given. A transducer is manufactured for experimental test, the results show that the experimental value is in good agreement with theoretical calculation and finite element simulation. This work is expected to be used in the optimal analysis of the multi-mode transducer in high power ultrasonic field.

AlN/ScAlN composite films-based spurious free A1 mode lamb wave resonator with adjustable effective electromechanical coupling coefficient

AlN/ScAlN composite films-based spurious free A1 mode lamb wave resonator with adjustable effective electromechanical coupling coefficient

High Sensitivity Performance of Piezoelectric Micromachined Ultrasonic Transducer Employing Sc-Doped AlN Thin Film

Abstract Aluminum Nitride (AlN) based piezoelectric micromachined ultrasonic transducers (PMUTs) have been the prime choice in acoustic imaging, because it has advantages of high frequency and thus high resolution. However, low piezoelectric constants of AlN gives rises to limitation in transmitting sensitivity. Scandium (Sc) doping method for AlN can be used to improve its piezoelectricity. In this paper, single element PMUT based on ScAlN thin film was proposed and modeled by performing finite element method (FEM). Influence of different electrode configurations on PMUT performance were studied. The results show that, compared with other electrode configurations, PMUT has the best overall performance when the upper electrode is platinum (Pt) and the lower electrode is molybdenum (Mo). In addition, the acoustic field characteristics and its dynamic analysis of PMUT based on ScAlN in water were studied. The investigation results demonstrated that the relative pulse-echo sensitivity level M of PMUT is significantly improved with the increase of Sc doping concentration in AlN thin film. When the Sc concentration is 40%, the M reaches -44 dB, which is 20 dB higher than that without Sc (-64 dB). The PMUT based on the high Sc-doped AlN thin film has a larger effective electromechanical coupling coefficient and sensitivity, which is beneficial to the application in high sensitivity ultrasound imaging.

Piezoelectric Hinged Beam with Arc Mass Stopper for Vibration and Human Motion Energy Harvesting.

Compact reliable structure and strong electromechanical coupling are hot pursuits in piezoelectric vibration energy harvester (PVEH) design. PVEH with a static arc stopper makes piezoelectric stress uniformly distributed and widens the frequency band by collision but wastes space. This Article proposes a hinged PVEH with two arc mass stoppers (AS-H-PVEH). Two arc stoppers as movable masses increase the vibration energy and the effective electromechanical coupling coefficient to achieve strong electromechanical coupling. AS-H-PVEH generates a 4.1 mW power output at 11.6-12.0 Hz and 0.2 g. AS-H-PVEH sustains 4 g acceleration vibration for 10 min without attenuation. To offset the resonance frequency increase caused by arc contact, we discuss the magnetic coupling, and axial force effects are discussed. The design of the arc stopper radius, nonlinear electromechanical coupling model, and system parameter identification method are presented. The displacement varied mechanical quality factor and effective electromechanical coupling coefficient are considered in the modified model for the first time. The model obtained good agreement under experiments. The power generation and driven wireless sensor performance of AS-H-PVEH was verified. This research has important theoretical and application value for the performance optimization of PVEH with an arc stopper.

Effect of Filling Material Properties on 1-3 Piezoelectric Composite Performance.

The 1-3 piezoelectric composite is the key component of the acoustic transducer, which is widely used in detection, due to the high energy conversion efficiency, cheap raw material, and low aging. To reveal the influence of epoxy mixture, used to connect the piezoelectric column, on the composite performance, a 1-3 piezoelectric composite model was built. The effects of mixture properties on the impedance curves, vibration mode, and deformation displacement of the composite were determined. Six 1-3 piezoelectric composites with different filling mixture properties, by changing the glass microspheres' mass ratio in the epoxy, were prepared and measured to validate the model. The results showed that with the increase in the proportion of the glass microsphere in the epoxy mixture, the vibration coupling of the piezoelectric composites was gradually eliminated. The acoustic impedance was reduced by 12%. The electromechanical coupling coefficient and effective electromechanical coupling coefficient were increased by 5.4% and 8.3%, respectively. The density and Young's modulus decrease in filling mixture can significantly improve piezoelectric composite performance.

Electromechanical characterization of 3–2 ceramic-air composites

In this study, a type 3–2 ceramic-air composite was designed, and the impact of varying thicknesses on its electromechanical properties was analyzed. Initially, finite element simulation software was employed to model type 3–2 ceramic-air composites of differing thicknesses. This modeling facilitated the determination of resonance and anti-resonance frequencies, calculation of effective electromechanical coupling coefficients, and assessment of frequency discrepancies corresponding to each thickness. Subsequently, type 3–2 ceramic-air composites of various thicknesses were fabricated using the reverse cutting method. The experimental results corroborated the simulation outcomes, demonstrating consistency. In the final analysis, the performance parameters of conventional type 1–3 piezoelectric composites were evaluated alongside those of type 3–2 composites. Findings indicated an improvement of 0.8 in the thickness electromechanical coupling coefficient for type 3–2 composites compared to conventional type 1–3 composites. Consequently, type 3–2 composites show promise for the development of highly sensitive piezoelectric transducers.

Adjustable effective electromechanical coupling of Lamb wave resonator using AlN/Sc0.096Al0.904N composite films

With the rapid development of fifth-generation communication technology, there are more and more 5 G frequency bands and their bandwidths differ. Therefore, many researchers devote themselves to the study of resonators with adjustable electromechanical coupling coefficient. In this paper, we apply composite films to the Lamb wave resonator with a double-IDT configuration to achieve adjustable effective electromechanical coupling coefficient (Keff 2) of the first symmetric mode. The experimental results show that with the increase of the thickness ratio, the series resonant frequency ( fs ) of the resonator decreases from 2.567 GHz to 2.333 GHz; and the parallel resonant frequency ( fp ) of the resonator decreases from 2.608 GHz to 2.396 GHz. The Keff 2 is adjusted from 3.82% to 6.32% and the Δf ( fp−fs ) is adjusted from 41 to 63 MHz by using the AlN/Sc0.096Al0.904N composite films with different thickness ratios. This method may be an efficient way to adjust the bandwidth of the filter to meet the needs of different frequency bands.

Miniaturized Multi-Cantilever MEMS Resonators with Low Motional Impedance.

Microelectromechanical system (MEMS) cantilever resonators suffer from high motional impedance (Rm). This paper investigates the use of mechanically coupled multi-cantilever piezoelectric MEMS resonators in the resolution of this issue. A double-sided actuating design, which utilizes a resonator with a 2.5 μm thick AlN film as the passive layer, is employed to reduce Rm. The results of experimental and finite element analysis (FEA) show agreement regarding single- to sextuple-cantilever resonators. Compared with a standalone cantilever resonator, the multi-cantilever resonator significantly reduces Rm; meanwhile, the high quality factor (Q) and effective electromechanical coupling coefficient (Kteff2) are maintained. The 30 μm wide quadruple-cantilever resonator achieves a resonance frequency (fs) of 55.8 kHz, a Q value of 10,300, and a series impedance (Rs) as low as 28.6 kΩ at a pressure of 0.02 Pa; meanwhile, the smaller size of this resonator compared to the existing multi-cantilever resonators is preserved. This represents a significant advancement in MEMS resonators for miniaturized ultra-low-power oscillator applications.

Design and Fabrication of a Film Bulk Acoustic Wave Filter for 3.0 GHz-3.2 GHz S-Band.

Film bulk acoustic-wave resonators (FBARs) are widely utilized in the field of radio frequency (RF) filters due to their excellent performance, such as high operation frequency and high quality. In this paper, we present the design, fabrication, and characterization of an FBAR filter for the 3.0 GHz-3.2 GHz S-band. Using a scandium-doped aluminum nitride (Sc0.2Al0.8N) film, the filter is designed through a combined acoustic-electromagnetic simulation method, and the FBAR and filter are fabricated using an eight-step lithographic process. The measured FBAR presents an effective electromechanical coupling coefficient (keff2) value up to 13.3%, and the measured filter demonstrates a -3 dB bandwidth of 115 MHz (from 3.013 GHz to 3.128 GHz), a low insertion loss of -2.4 dB, and good out-of-band rejection of -30 dB. The measured 1 dB compression point of the fabricated filter is 30.5 dBm, and the first series resonator burns out first as the input power increases. This work paves the way for research on high-power RF filters in mobile communication.

Highly improved quality factor of the film bulk acoustic wave resonator by introducing a high quality ZnO buffer layer

The inferior film quality of sputtered AlN has hindered the further development of high-performance film bulk acoustic wave resonators (FBAR). In this work, the ZnO buffer layer was introduced into the FBAR to improve the performance of FBAR for the first time. Compared with its counterpart without the buffer layer, the devices with a buffer layer exhibited a far higher average quality factor (2π times the maximum energy stored in the FBAR/energy dissipated per period) of 2575 ± 136, which was about 64 % larger than that without a buffer layer. Benefiting from the enhanced crystalline quality of AlN, the device also showed an improved effective electromechanical coupling coefficient.

Giant Flexoelectric Effect in Snapping Surfaces Enhanced by Graded Stiffness

Flexoelectricity is present in nonuniformly deformed dielectric materials and has size-dependent properties, making it useful for microelectromechanical systems. Flexoelectricity is small compared to piezoelectricity; therefore, producing a large-scale flexoelectric effect is of great interest. In this paper, we explore a way to enhance the flexoelectric effect by utilizing the snap-through instability and a stiffness gradient present along the length of a curved dielectric plate. To analyze the effect of stiffness profiles on the plate, we employ numerical parameter continuation. Our analysis reveals a nonlinear relationship between the effective electromechanical coupling coefficient and the gradient of Young’s modulus. Moreover, we demonstrate that the quadratic profile is more advantageous than the linear profile. For a dielectric plate with a quadratic profile and a modulus gradient of − 0.9, the effective coefficient can reach as high as 15.74 pC/N, which is over three times the conventional coupling coefficient of piezoelectric material. This paper contributes to our understanding of the amplification of flexoelectric effects by harnessing snapping surfaces and stiffness gradient design.

Advanced technologies of FBAR for tuning effective electromechanical coupling coefficient

The film bulk acoustic wave resonator (FBAR) is one of the most popular devices in the radio frequency field. Numerous researchers are simultaneously working to develop an effective electromechanical coupling coefficient (keff2) tuning technology, aiming to meet the diverse bandwidth requirements of the 5 G era. Based on a traditional FBAR process, this work prepares several different devices and then analyzes the four factors that influence keff2 from the perspective of process, material, and design. The pillar structure achieves the largest keff2 tuning range of 2.84% (33 MHz). The composite piezoelectric film can tune the overall resonant frequency in a wide range, and its keff2 tuning range is 1.75% (12.5 MHz). The area effect tunes the fs in a small range, ultimately achieving a keff2 tuning range of 1.16% (11 MHz). Film stress regulation achieves keff2 tuning range of 2.73% (30 MHz), but it has the greatest difficulty. The integration of various keff2 tunable methods has important guiding significance for the design of FBAR filters in the future.

Design of a bulk-lead zirconate titanate ultrasonic transducer array addressing specific excitation modes

Conventional ultrasonic transducer arrays generally use simultaneous or delayed excitation methods to generate various types of wave fronts in ultrasonic testing. Such array excitation modes are relatively simple and unable to maximize the functions of the array elements or element apertures. Accordingly, this study developed a novel excitation ultrasonic transducer array with flexible excitation aperture. A minimum row-column-addressing planar array structure for ultrasonic transducers based on bulk lead zirconate titanate (PZT) was designed for industrial ultrasonic testing. In addition, a transducer structure design scheme and truth table for array addressing with excitation logic were provided. By performing an acoustic field simulation, this study analyzed the relationship between the longitudinal amplitude and resonant frequency of the array elements and the impedance distribution. The transducer was fabricated and packaged using a circuit board and bulk PZT array elements. Testing revealed that the resonant frequency of the array was 1.07 MHz, the effective electromechanical coupling coefficient was 0.40, and the fractional bandwidth of the pulse echo response and spectrum was 38.46%. Using an aluminum block, performance in single-element, row-, column-, and full-array excitation was tested, and echo curves were obtained for multiple apertures. Using a single-circuit module, the transducer realized flexible gating and excitation of the array elements. The research provided a new method for industrial ultrasonic transducer array design.

Research on high sensitivity integrated transmit and receive hydroacoustic transducer

In response to the application demand in the field of hydroacoustic for high efficiency transmitting and high sensitivity receiving, overlapping frequency bands of transmitting and receiving, and structurally integrated high frequency hydroacoustic transducer. In this paper, a high-sensitivity transducer with integrated transmit and receive is developed. The transducer consists of two parts: the transmitting unit is 1–3 type piezoelectric composite material; the receiving unit is single metal plate air column array structure, and the effective electromechanical coupling coefficient is improved by changing the piezoelectric ceramic structure, thus improving the receiving sensitivity. Through theoretical analysis and finite element analysis determined the conditions of integration of transmitting and receiving. Finally, the transducer prototype was fabricated and tested. The results showed that the resonant frequency of the transmitter unit was 249 kHz, the anti-resonant frequency of the receiver unit was 253 kHz, and the maximum transmit voltage response and receive sensitivity were 180.1 dB and −175.8 dB, respectively, which satisfied the transceiver condition and high sensitivity performance.

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.

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%.

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.