Propagation Characteristics Of Surface Acoustic Waves Research Articles

Theoretical investigation of Rayleigh surface acoustic wave propagation characteristics in c-axis-zigzag ScAlN film/silicon substrate structure

Surface acoustic wave (SAW) resonators are key components of mobile communication systems, and the development of wideband SAW resonators is especially required because next-generation mobile communication systems require high-speed data transmission using wide frequency bands. In this study, two layered structures—(i) a c-axis-tilted ScAlN bilayer film/silicon substrate and (ii) a c-axis-zigzag ScAlN film/silicon substrate—are proposed for highly coupled SAW resonators, and the electromechanical coupling coefficient K2 of the non-leaky Rayleigh-mode SAW propagating in these structures is investigated theoretically. With a proper c-axis tilt angle and thickness selection of the ScAlN film, the first-mode Rayleigh SAW in the c-axis-tilted ScAlN bilayer film/silicon substrate and c-axis-zigzag ScAlN film/silicon substrate offers high K2. The maximum K2 was 9.56%, obtained in the c-axis-zigzag ScAlN film/silicon substrate structure, which was 2.5 times the maximum K2 in the c-axis-tilted ScAlN monolayer film/silicon substrate structure; this is because the c-axis-zigzag ScAlN films increase the shear vertical component of the SAW particle displacement, most of which is concentrated in the c-axis-zigzag ScAlN film on the silicon substrate. It is also important that the second-mode SAW (Sezawa wave) in the c-axis-zigzag ScAlN film/silicon substrate structure is not excited when the K2 value of the first-mode SAW is maximized. The techniques for fabricating a c-axis-tilted ScAlN film and a c-axis-zigzag ScAlN film have been reported, and well-established micromachining technology related to silicon semiconductors offers significant advantages in the manufacturing and processing of SAW resonators. Therefore, the c-axis-zigzag ScAlN film/silicon substrate structure has significant potential for SAW device applications.

Modulating the Performance of the SAW Strain Sensor Based on Dual-Port Resonator Using FEM Simulation.

Surface acoustic wave (SAW) strain sensors fabricated on piezoelectric substrates have attracted considerable attention due to their attractive features such as passive wireless sensing ability, simple signal processing, high sensitivity, compact size and robustness. To meet the needs of various functioning situations, it is desirable to identify the factors that affect the performance of the SAW devices. In this work, we perform a simulation study on Rayleigh surface acoustic wave (RSAW) based on a stacked Al/LiNbO3 system. A SAW strain sensor with a dual-port resonator was modeled using multiphysics finite element model (FEM) method. While FEM has been widely used for numerical calculations of SAW devices, most of the simulation works mainly focus on SAW modes, SAW propagation characteristics and electromechanical coupling coefficients. Herein, we propose a systematic scheme via analyzing the structural parameters of SAW resonators. Evolution of RSAW eigenfrequency, insertion loss (IL), quality factor (Q) and strain transfer rate with different structural parameters are elaborated by FEM simulations. Compared with the reported experimental results, the relative errors of RSAW eigenfrequency and IL are about 3% and 16.3%, respectively, and the absolute errors are 5.8 MHz and 1.63 dB (the corresponding Vout/Vin is only 6.6%). After structural optimization, the obtained resonator Q increases by 15%, IL decreases by 34.6% and the strain transfer rate increases by 2.4%. This work provides a systematic and reliable solution for the structural optimization of dual-port SAW resonators.

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.

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.

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.

Theoretical analysis of high electromechanical coupling surface acoustic wave propagating on lead-free Na0.5Bi0.5TiO3–BaTiO3 single crystal

The propagation properties of surface acoustic wave (SAW) on the Na0.5Bi0.5TiO3–BaTiO3 (NBBT) substrate with different crystal cuts were theoretically analyzed by Finite Element Method (FEM). The calculated results, for the NBBT with the optimized electrode type and thickness, indicate the existence of Rayleigh and Sezawa modes with high electromechanical coupling factor K2 ~18% and ~6.8% respectively, which are considerably higher than that of the conventional lithium niobate (LiNbO3) single crystal for SAW applications. The research provides a comprehensive understanding of the SAW propagation characteristics of lead-free NBBT, and explores the promising applications of NBBT in wideband SAW devices.

Numerical analysis of SAW propagation characteristics in Ca2Al2SiO7 crystal

The importance of surface acoustic wave (SAW) technology is to integrate signal processing with sensor functions. Recently, SAW sensors can operate at room temperature or around 100°C-200°C. The task associated with materials becomes relevant if it is necessary to increase the operating temperature of the device to 1000°C. A new piezoelectric calcium aluminate silicate (Ca2Al2SiO7) crystal of the tetragonal symmetry has stable piezoelectric properties up to the melting point temperature of 1500°C. The properties of surface acoustic waves a new Ca2Al2SiO7 single crystal are numerically modeled in the paper. The SAW velocity, the electromechanical coupling coefficient, and the power flow angle are modeled for various cuts of the Ca2Al2SiO7 crystal. The SAW has the maximal electromechanical coupling coefficient value (∼0.1%) on Z,X+45°-cut of the crystal. In the Z+63°, X-cut, the SAW electromechanical coupling coefficient is equal to 0.08%. Both of these crystal cuts show the absence of bulk acoustic wave generation by an interdigital transducer, and the Ca2Al2SiO7 crystal is a promising piezoelectric material for use in the SAW device applications.

3P3-8 Analysis and verification of surface acoustic wave propagation characteristics in cover glass/liquid layer/LiNbO3 structure

3P3-8 Analysis and verification of surface acoustic wave propagation characteristics in cover glass/liquid layer/LiNbO₃ structure

Finite Element Simulation of Miniaturized ZnO/Si SAW Sensor for Rapid Detection of Dichloromethane Gas

Air quality control is very crucial as poor air quality can lead to chronic respiratory organ diseases. Hence, detection of numerous toxic and hazardous gas is utmost significance. A low cost and high sensitivity gas sensor is crucial to monitor the excessive presence of the dangerous gas that can harm human’s health. In recent years, various type of gas sensors have been developed for various applications such as medicine, industry, automotive and environmental monitoring. One of the harmful gas is the dichloromethane gas. Dichloromethane (DCM) gas, CH2Cl2 is widely used in industry due to its organic characteristics. However, the excessive of the amount of the gas could bring harm to human’s health. Hence, a lot of sensing devices have been developed including surface acoustic wave (SAW) gas sensor. This paper presents the 2D finite element simulation of miniaturized ZnO/Si SAW gas sensor for rapid detection of DCM gas. Using a powerful finite element analysis software known as COMSOL Multiphysics, the gas sensor is modelled according to the specific criteria using 2D approach. The effect of different thickness of ZnO thin film as piezoelectric layer is investigated on the SAW propagation characteristics. The resonance frequency of simulated ZnO/Si SAW gas sensor is 300 MHz with wavelength of 11.67μm. The shift in frequency is the measurement used to measure the changes occured to sense the presence or absence of DCM gas. The shift of resonance frequency is observed in the absence and presence of dichloromethane gas. This work has high potential to realize single chip gas sensor due to its silicon compatibility for rapid detection of harmful gas for environmental monitoring.

SAW propagation characteristics of TeO3/3C-SiC/LiNbO3 layered structure

Surface acoustic wave (SAW) devices based on Lithium Niobate (LiNbO3) single crystal are advantageous because of its high SAW phase velocity, electromechanical coupling coefficient and cost effectiveness. In the present work a new multi-layered TeO3/3C-SiC/128° Y-X LiNbO3 SAW device has been proposed. SAW propagation properties such as phase velocity, coupling coefficient and temperature coefficient of delay (TCD) of the TeO3/SiC/128° Y-X LiNbO3 multi layered structure is examined using theoretical calculations. It is found that the integration of 0.09λ thick 3C-SiC over layer on 128° Y-X LiNbO3 increases its electromechanical coupling coefficient from 5.3% to 9.77% and SAW velocity from 3800 ms−1 to 4394 ms−1. The SiC/128° Y-X LiNbO3 bilayer SAW structure exhibits a high positive TCD value. A temperature stable layered SAW device could be obtained with introduction of 0.007λ TeO3 over layer on SiC/128° Y-X LiNbO3 bilayer structure without sacrificing the efficiency of the device. The proposed TeO3/3C-SiC/128° Y-X LiNbO3 multi-layered SAW structure is found to be cost effective, efficient, temperature stable and suitable for high frequency application in harsh environment.

Theoretical investigation of surface acoustic wave propagation characteristics in periodic (AlN/ZnO)N /diamond multilayer structures

Propagation characteristics of surface acoustic wave (SAW) in periodic (AlN/ZnO)N/diamond multilayer structures were theoretically investigated using effective permittivity method. The phase velocity Vp, electromechanical coupling coefficient K2, and temperature coefficient of frequency (TCF) of the Sezawa mode are analyzed for different thicknesses-to-wavelength H/λ, thickness ratios of AlN to ZnO Rh, and periods of alternating ZnO and AlN layers N. Results show that, comparing with AlN/ZnO/diamond multilayer structure, the periodic (AlN/ZnO)N/diamond multilayer structure (N ≥ 2) shows excellent electromechanical coupling and temperature stable characteristics with significantly improved K2 and TCF. The largest coupling coefficient of 3.0% associated with a phase velocity of 5726 m/s and a TCF of −29.2 ppm/°C can be reached for Rh = 0.2 and N = 2. For a low TCF of −24.4 ppm/°C, a large coupling coefficient of 2.0% associated with a phase velocity of 7058 m/s can be obtained for Rh = 1.0 and N = 5. The simulated results can be used to design the low loss and good temperature stability SAW devices of gigahertz-band application.

Surface acoustic wave resonators based on (002)AlN/Pt/diamond/silicon layered structure

Performance of surface acoustic wave (SAW) resonators based on (002)AlN/Pt/diamond/silicon layered structure is demonstrated. Three resonators with different wavelengths and center frequencies in the GHz range are designed and constructed without using submicron device fabrication processes, due to the high acoustic velocity of the layered structure. The enhanced performance of the SAW resonator by introducing a thin metal layer between the diamond and AlN layers is demonstrated theoretically and experimentally. Dependence of the SAW propagation characteristics on the normalized AlN film thickness is determined and the experimental results are in good agreement with theoretical predictions. In particular, for the 1st wave mode, a very high SAW velocity of 13,656m/s and an electromechanical coupling coefficient of 0.37% are obtained. These results demonstrate that the (002)AlN/Pt/diamond/silicon layered structure is very promising for high-frequency SAW device applications.

Research on Propagation Characteristics of SAW Based on ANSYS

In order to get the propagation characteristics of surface acoustic wave (SAW) along the piezoelectric crystals surface, the scheme of achieving the propagation characteristics of SAW device based on finite element analysis with ANSYS was proposed in this paper. In this scheme, the model of SAW device was built by the finite element analysis, and the parameter of the electrode and the substrate material was set. The geometry model of SAW device was meshed, and the continuous entity was divided into finite element model. The actual problems of boundary conditions and load in mechanical and electrical were applied to the model. By means of simulating a SAW device with center frequency at 100 MHz, the comparison and analysis between the simulation results and the theory results were presented. Experiments results confirm that the SAW energy is confined into a zone close to the piezoelectric crystals surface and is 1 to 2 wavelengths thick, and the amplitude and energy of the SAW will decrease rapidly with increasing depth.

Analysis of two dimensional composite surface grating structures with applications to low loss microacoustic resonators

2D composite grating building blocks with hexagonal symmetry are proposed and analyzed as efficient reflectors and transducers in the design of low loss surface acoustic wave (SAW) resonators. Eigen-frequency and frequency response finite element analyses are used to study the propagation and excitation characteristics of SAWs in the 2D composite structures. The proposed structures have the advantage of being compatible with the planar SAW technology, while introducing design principles reminiscent to the semiconductor devices. More specifically, the frequency bandgap characteristics of the various resonator building blocks can be adjusted so that losses related to the SAW diffraction, impedance mismatch, and parasitic SAW radiation from the electrical contacts can be suppressed. Three distinct types SAW resonant topologies employing 2D gratings are deduced from the analytical results.

Effects of SAW Propagation with Electrochemical Deposition of Ge Film on LiNbO3 Substrate

We present the results of a basic study on surface acoustic wave (SAW) propagation characteristics with electrochemical deposition of Ge thin films for functional devices. We investigated forming Ge film on the SAW propagation path by using electrochemical deposition as a new process approach. Energy-dispersive X-ray spectroscopy (EDX) analysis of deposited particles indicated that the electrochemical deposition of Ge was successfully achieved by applying pulse-potential to the working electrode. The experimental results of the fabricated device show that the SAW propagation characteristics of LiNbO3 with Ge has a frequency shift toward a higher range due to the change in the mass-loading of SAW propagation after Ge deposition. These experimental results indicate the potential use for functional devices.

Surface Acoustic Wave Propagation Characteristics and Temperature Effects on Quartz under Periodic Aluminum Structure

In communication applications, surface acoustic wave (SAW) devices should have excellent temperature stability. For this purpose, a numerical procedure for analyzing the Rayleigh SAW propagation and temperature effect was established in this work. The theoretical method used here is the space harmonic method (SHM). The theoretical analysis showed a slightly enhanced reflectivity for the open grating and presented the centers of transduction and reflection as separate at a spatial distance of λ0/4. The computational frequency responses of a two-port resonator were similar to the experimental data. The temperature characteristics of quartz under aluminum grating were also studied in this work. The cut angle of the quartz with zero temperature coefficient of frequency (TCF) decreased with increasing aluminum grating thickness. The coupling-of-modes (COM) parameters of quartz with zero TCF were calculated.

Theoretical studies on a TeO2/ZnO/diamond-layered structure for zero TCD SAW devices

High-frequency surface acoustic wave (SAW) devices based on diamond substrate are useful because of their very high SAW velocity. In the present work, SAW propagation characteristics, such as phase velocity, coupling coefficient and temperature coefficient of delay (TCD) of a TeO2/ZnO/diamond-layered structure, are examined using theoretical calculations. The ZnO/diamond bi-layer structure is found to exhibit a high positive TCD value. A zero TCD device structure is obtained after integration with a TeO2 over layer having a negative TCD value. Introduction of a non-piezoelectric TeO2 over layer on the bi-layer structure (ZnO/diamond) increases the coupling coefficient. A relatively low thickness of TeO2 thin film (∼(1.6–3.1) × 10−3λ) is required to achieve temperature-stable SAW devices based on diamond.

Acousto-optical and SAW propagation characteristics of temperature stable multilayered structures based on LiNbO3 and diamond

Theoretical studies on the surface acoustic wave (SAW) properties of c-axis oriented LiNbO3/IDT/diamond and diamond/IDT/128° rotated Y–X cut LiNbO3 multilayered structures have been considered. Both layered structures exhibit a positive temperature coefficient of delay (TCD) characteristic, and a zero TCD device is obtained after integrating with an over-layer of either tellurium dioxide (TeO2) or silicon dioxide (SiO2). The presence of a TeO2 over-layer enhanced the electromechanical coupling coefficients of both multilayered structures, which acts as a better temperature compensation layer than SiO2. The temperature stable TeO2/LiNbO3/IDT/diamond layered structure exhibits good electromechanical coefficient and higher phase velocity for SAW device applications. On the other hand, a high acousto-optical (AO) figure of merit (30–37) × 10−15 s3 kg−1 has been obtained for the temperature stable SiO2/diamond/IDT/LiNbO3 layered structure indicating a promising device structure for AO applications.

Temperature stability of ZnO thin film SAW device on fused quartz

Surface acoustic wave (SAW) filters for low-frequency (38-65 MHz) applications have been developed using a radio frequency (RF)-magnetron-sputtered ZnO film on fused-quartz substrates. SAW propagation characteristics such as electromechanical coupling coefficient (K/sup 2/), SAW phase velocity (v), insertion loss, and temperature coefficient of delay (TCD) have been measured. The intergidital transducer (IDT)/ZnO/fused-quartz device structure yields almost zero TCD (1 ppm/spl middot//spl deg/C/sup -1/) with 0.316 /spl lambda/ thick ZnO layer (for the device operating at 60 MHz). Alternately, an overlayer of positive TCD material (ZnO itself) has also been deposited on the IDT/ZnO(<0.316 /spl lambda/)/fused-quartz device at a low substrate temperature to reduce the TCD. A modified layered structure consisting of ZnO/IDT/ZnO/fused quartz yields almost zero TCD (-3 ppm/spl middot//spl deg/C/sup -1/) with a 5.3-/spl mu/m-thick ZnO overlayer and a 8.1-/spl mu/m-thick (0.183 /spl lambda/) ZnO bottom layer. Experimentally obtained SAW propagation characteristics have been compared with the theoretical results.