Surface Acoustic Wave Characteristics Research Articles

Evaluation of fatigue damage of structural steel based on attenuation of laser-induced surface acoustic wave

ABSTRACT In this paper, the fatigue damage degree of low-alloy structural steel is evaluated by using the attenuation characteristics of laser-induced surface acoustic wave (SAW) during propagation. Taking the typical structural steel material Q345 as an example, a cracks model of fatigue damage is established, and the finite element method is used to solve the model. The results showed that the attenuation coefficient of SAW can reflect the depth and density of fatigue cracks. The surface measurement experiments of specimens with stress cycles of 0, 50000, 100000, 150000, and 200,000 showed that with the increase of stress cycles, the attenuation coefficient of SAW increases as a whole, indicating that it is feasible to evaluate the fatigue damage degree based on the attenuation of SAW. A method of applying tensile stress to the material to improve the sensitivity of fatigue damage evaluation is proposed. The tensile stress is used to offset the horizontal amplitude of the SAW, keeping the fatigue cracks in an open state and increasing the attenuation coefficient of SAW. The attenuation coefficient measurement experiment shows that this method is feasible.

Theoretical investigation of Rayleigh-type surface acoustic waves with high electromechanical coupling coefficient in c-axis-tilted ScAlN film/3C-SiC substrate structure

Surface acoustic wave (SAW) resonators are essential components of mobile communication technology. Advanced performance SAW resonators are needed to support beyond fifth-generation mobile communication technology, which aims to achieve unprecedentedly high data rates and low latency using wide frequency bands in the RF spectrum. This study theoretically investigates the propagation characteristics of a non-leaky Rayleigh-type SAW (RSAW) propagating in a c-axis-tilted ScAlN film/3C-SiC substrate structure. By appropriately selecting the c-axis tilt angle and the film thickness of the ScAlN film, a high electromechanical coupling coefficient (K2) value was obtained in the second-mode RSAW (Sezawa wave). The maximum K2 value for the Sezawa wave was 8.03%, with a phase velocity of 7456 m/s and a power flow angle of 0° under the structural conditions where the K2 value was maximized. These properties offer significant advantages for achieving wide frequency bands, high operating frequencies, and ease of design for SAW resonators. The structural conditions under which good propagation characteristics were obtained in the Sezawa waves were found to coincide with the conditions that maximize the electromechanical coupling coefficient of the quasi-longitudinal wave in the ScAlN film, and a significant increase in the shear vertical component of Sezawa wave particle displacement was observed. Additionally, ScAlN films with a 40% Sc concentration can be fabricated using sputtering and molecular beam epitaxy. Recent advancements have reported the production of high-quality 3C-SiC wafers and large 3C-SiC film/silicon wafers. Therefore, the c-axis-tilted ScAlN film/3C-SiC substrate structure shows great potential as a candidate for next-generation SAW resonators.

Analyzing surface acoustic wave characteristics through first-principles computational methods

Surface acoustic wave (SAW) characteristics were analyzed through first-principles calculations utilizing density functional theory. This study computed and compared the elastic constants, piezoelectric constants, dielectric constants, and densities of LiTaO3 and LiNbO3, which are standard materials for SAW filters, against empirical values. The velocities of SAWs and the electromechanical coupling coefficients for both Rayleigh and leaky waves were also determined, demonstrating the method’s sufficient precision for assessing SAW attributes. In addition, this approach was extended to the nitride perovskite LaWN3, evaluating its SAW characteristics. LaWN3 is projected to exhibit an electromechanical coupling coefficient comparable to that of LiTaO3 and LiNbO3, indicating its potential as a novel material for SAW filter applications.

Temperature Characteristics of Rayleigh Wave and Leaky Surface Acoustic Wave Propagating in Langasite and its Application in Temperature Sensor

Temperature Characteristics of Rayleigh Wave and Leaky Surface Acoustic Wave Propagating in Langasite and its Application in Temperature Sensor

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.

Finite element analysis on the propagation characteristics of laser-generated surface acoustic wave in V-groove weld

Thick-walled structures, such as marine engineering and rail transportation, are widely used in modern society. V-groove welding is a common welding method in thick structures. At the same time, the V-groove weld is also the area of a thick-walled structure in which defects are most easily formed. Laser-generated surface acoustic waves are a promising non-destructive testing method in most fields. This study examined the propagation characteristics of laser-generated surface acoustic waves in a V-groove weld. A two-dimensional finite element model with Q345 steel was constructed. A thermoelastic mechanism was adopted to generate the wave. The temperature and displacement fields were analyzed in detail. The results showed that wave transmission, reflection, and mode conversion are generated with an R wave at the junction, and the dispersion phenomenon of the R wave occurred in the welded area.

High electro-mechanical coupling coefficient SAW device with ScAlN on diamond

In this study, Sc concentration dependence of Sc x Al1−x N/AlN/poly-crystalline diamond/Si surface acoustic wave (SAW) characteristics at high Sc from 23.8% to 44.3% was investigated by fabricating one-port SAW resonator at high frequency. 3.8 GHz one-port resonator fabricated on Sc0.43Al0.57N showed an excellent performance of electro-mechanical coupling coefficient (K 2) as high as 6.34% for 2nd mode Sezawa wave, which enables a wide bandwidth in high frequency applications. The temperature coefficient of frequency was approximately −40 to −50 ppm deg−1 for the device fabricated with Sc concentration of 42.9%. This is a smaller value compared to conventional high K2 bulk materials such as LiNbO3. As the result, a high K2 6.34% material system at a higher Sc concentration of ScAlN/AlN/PCD was found to be possible at a high phase velocity of 7000 m s−1. Combined with the extremely high-power durability of diamond based device, high-power durable wideband SAW device at high frequency can be expected.

Influence of top-coat thickness of thermal barrier coating on time–frequency domain and dispersion characteristics of laser-induced surface acoustic wave

Thermal barrier coating is commonly used to insulate the hot end components of aero engine and gas turbine in order to meet extreme high temperature service conditions. The performance of the thermal barrier coating will be significantly impacted by thinning or even spalling during the service process. Given the uniqueness of thermal barrier coating in structure and composition materials, and the fact that laser-induced surface acoustic waves are extremely sensitive to material surface characteristic parameters, laser-induced ultrasonic technology is used to detect the thermal barrier coating in this paper. To characterize the size and defect of thermal barrier coating, the excitation mechanism and propagation law of surface acoustic waves are very crucial. Firstly, the surface acoustic wave propagation law is investigated using spectral analysis and wavelet transform. Then, to study the influence of top-coat thickness on laser-induced surface acoustic wave, the surface acoustic wave velocity dispersion curves of thermal barrier coating with different top-coat thicknesses are extracted using wavelet analysis. The simulative and experimental results indicate that the time–frequency domain and dispersion characteristics of laser-induced surface acoustic wave in multilayered heterostructure are strongly affected by the top-coat thickness. By the establishment of the relationship between phase velocity of laser-induced surface acoustic wave and top-coat thickness, a theoretical basis is provided to characterize the top-coat thickness of multilayered heterostructure.

Design and analysis of high-sensitivity multilayered structure surface acoustic wave sensor for dichloromethane gas detection

Micro- and nano-sensors are key devices used in various fields from medical to environmental science. With the progress of micro- and nano-fabrication technology and the use of newly designed materials, sensor design has been significantly improved, leading to the development of high-performance gas sensors. A novel multilayer structure gas sensor based on surface acoustic wave (SAW) is proposed for the detection of volatile harmful gas dichloromethane. The gas sensing characteristics of single-layer and multilayer SAW sensors were studied by using finite element method. The influence of geometric parameters on the sensor performance was analyzed and the optimal structure was determined. The propagation characteristics of SAW were obtained by transient simulation of the whole structure. The sensitivity of the sensor is evaluated by placing the sensor in different concentrations of dichloromethane gas. The results show that the sensitivity of the PIB/AlN/Diamond/Si SAW gas sensor is as high as 66.9 ppm/Hz under the optimal geometry structure, which is nearly 30 times higher than that of other single-layer and multilayer SAW sensors. This work provides a good solution for the design of high-sensitivity SAW sensors.

Analysis of propagation characteristics of Rayleigh surface acoustic waves on Yb0.33Al0.67N piezoelectric films/high-velocity substrates

Piezoelectricity of YbAlN films has recently been shown to be almost as high as that of ScAlN films. YbAlN film surface acoustic wave (SAW) resonators are expected to have a high coupling factor. We theoretically investigated the propagation characteristics of first-mode Rayleigh SAWs (RSAWs) on Yb0.33Al0.67N film/high-velocity Si, sapphire, AlN, SiC, BN, and diamond substrates. The first-mode RSAWs on the YbAlN layered structures had high coupling factors, higher than those on ScAlN layered structures. An enhancement of the effective coupling factor of the first-mode RSAWs was observed in polarity inverted YbAlN film/BN or diamond substrate structures.

Interface and Sensitive Characteristics of the Viscoelastic Film Used in a Surface Acoustic Wave Gas Sensor.

The surface morphology of viscoelastic-sensitive films significantly affects sensing characteristics of surface acoustic wave (SAW) sensors. Uniformity and compactness of the film surface directly influences detectability of the SAW sensor toward target gases. Viscoelastic fluoroalcoholpolysiloxane (SXFA) was prepared in this work using spin coating technology on an SAW delay line of 200 MHz and then used as coating for detection of dimethyl methylphosphonate (DMMP). Polarizing, atomic force, and scanning electron microscopies confirmed the uniformity of the SXFA surface. The particle diameter in the cluster region was 10-15 μm. The contact angle (5.72-26.69°), surface tension (21.053-29.155 mN/m), Gibbs free energy (-160.68 to -153.45 J/m2), and spreading coefficient (0.3028-6.9453 J/m2) of different concentrations of SXFA were obtained through experiments, and their relation was analyzed using the Young T equation and Gibbs adsorption isotherm. The glass transition temperature (-19.7 °C) and elasticity of SXFA were also discussed. The consistency of sensor preparation was confirmed by detecting DMMP with five SAW sensors prepared simultaneously. Seven consecutive tests showed that the SAW sensor presents satisfactory repeatability (standard deviation, s, 1.134; coefficient of variance, v, 0.065; and population mean deviation, δ, 0.913) at a concentration of 1.71 mg/m3 and acceptable linear relationship at a concentration range of 0.058-1.92 mg/m3, with a sensitivity of around 1.21 mv/(mg/m3). The sensor exhibited outstanding sensitivity and satisfactory linearity and repeatability to DMMP. Meanwhile, the sensing mechanism in gas adsorption was also discussed in terms of LSER formulation and hydrogen bonding formation between SXFA and DMMP.

Investigation of Surface Acoustic Wave Propagation Characteristics in New Multilayer Structure: SiO2/IDT/LiNbO3/Diamond/Si.

Surface acoustic wave (SAW) devices are widely used in many fields such as mobile communication, phased array radar, and wireless passive sensor systems. With the upgrade of mobile networks, the requirements for the performance of SAW devices have also increased, and high-frequency wideband SAW devices have become an important research topic in communication systems and other application fields. In this paper, a theoretical study for the realization of a layered SAW filter based on a new SiO2/IDT/128°YX-LiNbO3/diamond/silicon layered structure using the modeling software COMSOL Multiphysics is presented. The effects of lithium niobate (LiNbO3), an interdigital transducer (IDT), and SiO2 thin films on the evolution of the phase velocity, electromechanical coupling coefficient (k2), and temperature coefficient of frequency were studied by employing a finite element method simulation. Furthermore, a longitudinal coupling resonator filter was designed. To investigate the SAW characteristics of the filter, a transient analysis was conducted to calculate the electrical potential and particle displacement under the resonance condition and to analyze the frequency response. The study concluded that this new multilayer structure can be applied to design and manufacture a variety of high-frequency and wideband SAW filters with a temperature compensation function, for operation above the GHz range.

In-Situ Process and Simulation of High-Performance Piezoelectric-on-Silicon Substrate for SAW Sensor

This paper studied the manufacturing process of Piezoelectric-on-Silicon (POS) substrate which integrates 128° Y–X Lithium niobate thin film and silicon wafer using Smart-Cut technology. The blistering and exfoliation processes of the He as-implanted LN crystal under different annealing temperatures are observed by the in-situ method. Unlike the conventional polishing process, the stripping mechanism of the Lithium niobate thin film is changed by controlling annealing temperature, which can improve the surface morphology of the peeling lithium niobate thin film. We prepared the 128° Y–X POS substrate with high single-crystal Lithium niobate thin film and surface roughness of 3.91 nm through Benzocyclobutene bonding. After simulating the surface acoustic wave (SAW) characteristics of the POS substrate, the results demonstrate that the Benzocyclobutene layer not only performs as a bonding layer but also can couple more vibrations into the LN thin film. The electromechanical coupling coefficient of the POS substrate is up to 7.59% in the Rayleigh mode when hLN/λ is 0.3 and hBCB/λ is 0.1. Therefore, as a high-performance substrate material, the POS substrate has proved to be an efficient method to miniaturize and integrate the SAW sensor.

High-frequency and high-temperature stable surface acoustic wave devices on ZnO/SiO2/SiC structure

The explosive growth of wireless communication and the creation of new frequency bands for 5G systems increasingly require surface acoustic wave (SAW) with high operating frequency (i.e. 3–6 GHz) as well as high-temperature stability. In this work, high-frequency and high-temperature stable SAW devices using ZnO/SiO2/SiC layered structures were proposed and reported. SAW characteristics of the Sezawa wave mode, including the phase velocities (Vp), electromechanical coupling coefficients (K2) and temperature coefficient of frequency (TCF), were studied systematically by the finite element method. High-frequency SAW one-port resonators with the resonant frequency ranging from ∼4.5–5.4 GHz were fabricated on the above structures. With SiC substrate providing high velocity and SiO2 interlayer for temperature compensation, a 5.0 GHz and nearly zero TCF of 0.7 ppm °C−1 can be achieved in a SAW device based on ZnO/SiO2/SiC structure. The good performance of these devices demonstrates that the ZnO/SiO2/SiC structure is promising for high-frequency and good temperature-stability SAW device applications.

Analysis of longitudinal leaky surface acoustic waves on LiNbO3/amorphous layer/quartz structure

Recently, bonded structures comprising a quartz substrate and a LiNbO3 (LN) or LiTaO3 thin-plate have been attracting attention as a means of obtaining enhanced properties for surface acoustic wave (SAW) devices. It was reported that the bonding strength was extremely improved by utilizing an amorphous thin film as a middle layer. In this research, the propagation and resonance characteristics of longitudinal leaky SAWs on an amorphous layer inserted to the boundary between an X-cut 36°Y-propagating LN (X36°Y-LN) and X35°Y-quartz were investigated. For the metallized surface of an X36°Y-LN/Al2O3/X35°Y-quartz structure, an attenuation of 0.0001 dB /λ was obtained at an LT thin-plate thickness of 0.072λ (λ: wavelength), which was better than that of an X36°Y-LN/X35°Y-quartz structure. Utilizing a finite element method, we found that the admittance ratio and Q factor for the X36°Y-LN/Al2O3/X35°Y-quartz model were improved owing to the reduction of the leakage due to the shear-vertical particle displacement.

Analysis of leaky surface acoustic wave characteristics propagating on high piezoelectric ScAlN film/high velocity quartz substrate

Recently, it has been reported that leaky surface acoustic waves (LSAWs) and longitudinal LSAWs on piezoelectric LiNbO3 and LiTaO3 thin plates bonded to high velocity quartz substrates have high phase velocity, high coupling, and low attenuation. These lead to high-frequency operation, a wide band-width, and a high Q factor for next generation SAW filters. Moreover, we theoretically demonstrated that longitudinal LSAWs on high piezoelectric ScAlN films/quartz substrates also possesses high phase velocity, high coupling, and low attenuation. In this paper, LSAW characteristics on ScAlN films/quartz substrates were investigated theoretically. When the Euler angles and the film thickness of the ScAlN film and quartz substrate were optimized for LSAW, the LSAW resonators with (0° 90° 72°) Sc0.4Al0.6N film/(0° 128.5° 0°) quartz were found to have a high Q factor of ∼21 610 and a high coupling of ∼5.8%.

Surface Acoustic Wave Characteristics with a Layered Structure of IDT/θ° YX-LiTaO3/SiO2/AlN/diamond

A new layered surface acoustic wave (SAW) structure was proposed by Murata Co., Ltd recently. It was reported that such structure could achieve an incredible high performance including a higher quality factor Q and electromechanical coupling coefficient K2. For deeply understanding propagating characteristics and optimizing the performance of the SAWs in such structure, a layered structure of IDT/θ° YX-LiTaO3/SiO2/AlN/Diamond with different structural parameters were theoretically investigated by FEM method. The calculated admittance shows that four eigenmodes simultaneously exist in such layered structure including the main mode SH SAW. And compared with the Traditional SAW structure, the main mode could achieve a higher value of K2 with sacrificing its velocity a little. Different metal layers (Au, Al, and Cu) were examined as the electrode material. With Au employed, the K2 of the main mode is a little larger resulting from better suppression of the spurious modes. The optimum thickness of electrode and piezoelectric layer are 0.2 and 0.02λ, respectively. In this case, the K2 for the SH SAW achieves its maximum value of 12.20% with a large phase velocity of 3608 m/s. Furthermore, the pure SH SAW can be obtained with the Y-cut Euler angle θ from 0° to 60°, where its K2 has a wide range of 8.70 to 13.69%. Consequently, the work provides a theoretical guide for designing SAW devices of different bandwidth and operation frequency with such structure.

Analysis on Characteristics of ZnO Surface Acoustic Wave with and without Micro-Structures.

In this paper, we fabricate a surface acoustic wave (SAW) device with micro-structures on a zinc oxide (ZnO) thin film and measure its signal response. The manufacturing processes of the SAW device include the fabrication of micro-structures of a SAW element and its interdigital transducer by silicon micro-machining and the fabrication of a thin film of ZnO by RF magnetron sputtering. We, then, measure the SAW properties. This research investigates the properties of sputtered thin films for various amounts of O2/(Ar + O2) using Zn and ZnO targets. Regardless of target, the growth rate of the ZnO thin film decreases as the oxygen content increases. When the SAW is sputtered ZnO thin film using 30% oxygen, the digital signal of the SAW has better performance. The measurement signal of the SAW with micro-structures is similar to that without micro-structures.

High-velocity non-attenuated acoustic waves in LiTaO3/quartz layered substrates for high frequency resonators

Multilayered substrates for Surface Acoustic Wave (SAW) devices are able to combine SAW characteristics that cannot coexist in a single crystal substrate and, thus, meet the strong requirements of the new class of SAW devices developed for the next generations of communication systems. Recently, high performance resonators arranged on LiTaO3/quartz bonded wafers and utilizing shear horizontally polarized acoustic waves were reported. Leaky SAWs with quasi-longitudinal polarization propagate faster and can facilitate fabrication of high frequency SAW devices but generally leak strongly into the substrate. This paper describes how the LiTaO3/quartz structure can be optimized to allow longitudinal SAWs to propagate without attenuation. Due to the symmetry consideration, which is supplemented by a rigorous numerical simulation of the admittance functions of SAW resonators and an accurate extraction of the propagation losses, the found optimal LiTaO3 and quartz orientations with the optimized LiTaO3 thickness ensure the propagation of acoustic waves with a velocity exceeding 5400 m/s and an electromechanical coupling of 6.8% in resonators with Q factors up to 10,000. The optimal LT/quartz structures with plate thicknesses varying between 0.32 and 0.68 wavelengths can be employed in SAW resonators operating at high frequencies, up to 5 GHz. The existence of numerous orientations in quartz supporting the propagation of non-attenuated longitudinal SAWs is explained based on the concept of exceptional bulk waves, which is a part of SAW theory.

Investigation of Characteristics of Dual-band Ladder-type Surface Acoustic Wave for High-power Durability Duplexer

Investigation of Characteristics of Dual-band Ladder-type Surface Acoustic Wave for High-power Durability Duplexer