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A LiNbO3 (LN)/SiO2/Si multilayered structure was recently reported as a new platform for achieving wideband radio frequency (RF) filters. However, the in-band ripples in filters resulting from the spurious Rayleigh mode lead to deteriorated performance, and thus, a wide Rayleigh elimination window (REW) is highly desired for realizing spurious-free wideband surface acoustic wave (SAW) filters with a wide design space and good process tolerance. Here, we investigated the spurious mode suppression on the LN/SiO2/Si platform theoretically and experimentally through modulating the cut angle ($\theta $) of LN. The ${K}^{{2}}$ dispersion characteristics of the main mode (shear-horizontal wave) and spurious mode (Rayleigh wave) on LN/SiO2/Si substrates were systematically analyzed by the finite-element method (FEM), along with bulk LN for comparison. It is found that the REW is wider on LN/SiO2/Si than bulk LN, as Rayleigh wave can be totally eliminated with Cu electrode normalized thickness (${h}_{\text {Cu}}/\lambda $) ranging from 0.1 to 0.19 when $\theta $ is between 19° and 22° on the LN/SiO2/Si platform, in contrast to the quite narrow REW on bulk LN restricted to some specific ${h}_{\text {Cu}}/\lambda$. To verify the simulation results, resonators were prepared on 15°YX-LN/SiO2/Si, 20°YX-LN/SiO2/Si, bulk 15°YX-LN, and bulk 20°YX-LN. In addition, the typical spurious-free wideband SAW filter with ${h}_{\text {Cu}} = {200}$ nm based on the 20°YX-LN/SiO2/Si platform demonstrates high performance with a center frequency (${f}_{\text {c}}$) of 1.27 GHz, a minimum insertion loss (ILmin) of 0.7 dB, and a 3-dB fractional bandwidth (FBW) of ~20.1%. This work provides a workable solution in fabricating spurious-free wideband and low-loss SAW filters for fifth-generation (5G) applications. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW) filters are at the center of the radio frequency module in mobile terminals. With the increase of SAW frequency and the miniaturization of devices, the heat generation becomes prominent in SAW devices, providing a potential platform for thermal energy harvesting. Here ferromagnetic materials are embedded into SAW delay lines to demonstrate that thermal energy can be harvested to generate robust transverse electrical signals via anomalous Nernst effect, which are comparable with the anomalous Hall signals when an electric current is intensively applied. The transverse voltage exhibits nonreciprocal features, both amplitude and polarity are dependent on the propagation direction of SAW in contrast to its longitudinal counterpart, which only changes the amplitude but remains polarity with opposite SAW direction. The finding provides a different platform for thermoelectric energy conversion and opens a window for thermal energy harvesting and acoustic or heat flow sensing in SAW devices. [ABSTRACT FROM AUTHOR]

This research aims to overcome the tradeoff between bandwidth, temperature stability of frequency, and loss in surface acoustic wave filters. A novel multilayered structure, SiO2/Cu-grating/ $15^{\circ }~{Y}$ - ${X}$ LiNbO3/SiO2/sapphire, is proposed. Resonators based on the multilayered structure are studied theoretically and experimentally. The results show that the multilayered structure can sufficiently suppress leaky wave and spurious responses, which significantly degrade the performance of devices based on conventional SiO2/Cu-grating/ $15^{\circ }~{Y}$ - ${X}$ LiNbO3 structure. Fabricated resonators exhibit high performance including low frequency drift, large coupling, and large quality factor. A multilayered structure filter is designed, fabricated, and measured, resulting in a flat and clean passband with a small minimum insertion loss of only 1.01 dB. A large 3-dB fractional bandwidth of 14.74% is achieved, as well as a low temperature coefficient of frequency of approximately −18 ppm/°C. This research proposes a useful solution for high-performance filters in fifth-generation networks. [ABSTRACT FROM AUTHOR]

This article presents a general-purpose model that enables efficient and accurate calculation of third-order nonlinear signals in surface acoustic wave (SAW) devices. This model is based on piezoelectric constitutive equations combined with perturbation theory, which can be analyzed by full finite element method (FEM). For validation, third-order harmonic (H3) responses and intermodulation distortions (IMD3) in SAW resonators are simulated, and their calculation results fit well to experimental data in the literature. Then, the generation mechanisms of the third-order nonlinearity in SAW resonators are discussed. The dominant generation mechanisms for different nonlinear signals and the relation between electrode materials and H3 peak magnitude are revealed, which provides an important guideline for further nonlinear suppression. [ABSTRACT FROM AUTHOR]

An increasing demand for surface acoustic wave filters with high performances contributes to the necessity of reducing sizes and costs. The present work proposes a multilayered structure of high-velocity layer/SiO2/interdigital transducers (IDTs)/piezoelectric-single-crystal substrate to further validate the strengths of packageless devices. Resonators based on the SiNx/SiO2/IDTs(Cu)/15°Y-X LiNbO3 structure are simulated and analyzed. One-port resonators are designed, fabricated and tested on the basis of the simulation, and results validates the feasibility of no encapsulation. Finally, by using this multilayered structure, a packageless filter with a center frequency of 2.14 GHz and an ultra-small size of 0.695 × 0.490 × 0.122 mm3 is successfully designed and realized, maintaining well-balanced performances. This work has demonstrated the strengths of packageless devices which can be obtained by utilizing the proposed multilayered structure, and may promote the development of device miniaturization. [2021–0035] [ABSTRACT FROM AUTHOR]

The rapid development of the fifth-generation (5G) wireless system is driving strong demand for high-performance radio frequency filters. This work studies shear horizontal surface acoustic wave (SAW) devices using 15°-rotated Y-cut X-propagating (15°Y-X) LiNbO3/SiO2/SiC multilayered substrates. Single-crystalline 15°Y-X LiNbO3 films are bonded to SiO2/SiC handling substrates by the smart cut technology. On the basis of accurate finite-element-method simulations, LiNbO3/SiO2/SiC wafer configurations are optimized to suppress spurious resonance due to Rayleigh-mode and transverse-mode responses, and one-port resonators with a clean spectrum, a high electromechanical coupling coefficient of 22.00%, and an admittance ratio (impedance ratio) over 65 dB are successfully implemented. Based on the characteristics of the resonators, high-performance filters with a center frequency of 1.28 GHz, a large 3-dB fractional bandwidth of 16.65%, and a low minimum insertion loss of 1.02 dB are successfully designed and fabricated. Furthermore, no ripples in the passband of the filters are observed. Additionally, the filters exhibit a temperature coefficient of center frequency of −63.8 ppm/°C and a large power durability of 33.2 dBm. This work confirms the high performances of the SAW devices using the 15°Y-X LiNbO3/SiO2/SiC multilayered substrate, and this type of SAW device exhibits a prospect of commercial applications in the 5G wireless system. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW) devices based on multi-layer structures have been widely used in filters and sensors. The electromechanical coupling factor (K2), which reflects energy-conversion efficiency, directly determines the bandwidth of the filter and the sensitivity of sensor. In this work, a new configuration of dual-mode (quasi-Rayleigh and quasi-Sezawa) SAW devices on a ZnO/SiC layered structure exhibiting significantly enhanced K2 was studied using the finite element method (FEM), which features in the partial etching of the piezoelectric film between the adjacent interdigitated electrodes (IDTs). The influences of piezoelectric film thickness, etching ratio, top electrodes, bottom electrodes, and the metallization ratio on the K2 were systematically investigated. The optimum K2 for the quasi-Rayleigh mode and quasi-Sezawa mode can exceed 12% and 8%, respectively, which increases by nearly 12 times and 2 times that of the conventional ZnO/SiC structure. Such significantly promoted K2 is of great benefit for better comprehensive performance of SAW devices. More specifically, a quasi-Rayleigh mode with relatively low acoustic velocity (Vp) can be applied into the miniaturization of SAW devices, while a quasi-Sezawa mode exhibiting a Vp value higher than 5000 m/s is suitable for fabricating SAW devices requiring high frequency and large bandwidth. This novel structure has proposed a viable route for fabricating SAW devices with excellent overall performance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The rapid development of large-volume and high-speed mobile communication systems has increased the demand for high-frequency and wide-band surface acoustic wave (SAW) devices. In this work, ZnO films and V-doped ZnO (V:ZnO) films with (0002) orientation were grown on SiC substrates using a magnetron sputtering method. High-frequency SAW resonators with the resonant frequency ranging from 4 GHz to 6 GHz were fabricated on the above structures. V:ZnO/SiC SAW resonators exhibited a significantly increased electromechanical coupling coefficient (K2) in the range of 2.80%–5.12%, in a wide normalized thickness range, which is more than a 75% increase compared to that of ZnO-based SAW resonators. Besides, the high quality factor Q ranging from 431 to 593 and an improvement in the figure of merit value were observed for the V:ZnO/SiC SAW resonators operating at 4–6 GHz. Finally, 4.58 GHz SAW filters using V:ZnO films with a larger bandwidth and a lower insertion loss were achieved. This work clearly shows that the ZnO/SiC SAW properties can be improved by V doping, and the V:ZnO/SiC structures have great potential for application in high-frequency and wide-band SAW filters. [ABSTRACT FROM AUTHOR]

In this letter, highly (0002) oriented ZnO piezoelectric films were deposited on high acoustic velocity SiC substrates. Surface acoustic wave (SAW) devices on ZnO/SiC layered structure operating in the fundamental mode with high frequency to the 7-GHz range were successfully fabricated for the first time. The comprehensive experimental and theoretical investigations about phase velocities ${V}_{p}$ , the electromechanical coupling coefficients ${K}^{{2}}$ , and quality factors Q of one-port SAW resonators have been studied considering various ZnO normalized thicknesses ${h}/\lambda $. The resonators with large ${K}^{{2}}$ and high Q are implemented over 5–7 GHz demonstrating ${K}^{{2}}$ of 0.47%–2.83% and Q of 146–549. Specifically, a high ${K}^{{2}}$ of 2.83% and a large Q of 549 are simultaneously achievable for the resonator at 5.19 GHz. Finally, with the high ${V}_{p}$ of ZnO/SiC structure being up to 6800 m/s at ${h}/\lambda = {0.14}$ , a 6.8-GHz SAW filter was achieved. Our work shows that the ZnO/SiC structure is of great potential for high-frequency SAW devices application. [ABSTRACT FROM AUTHOR]

High quality ZnO/SiC composite structure have great potential in integrating surface acoustic wave devices with semiconductor devices. To achieve high quality ZnO on 6H-SiC, ZnO films were sputtered with various power by radio frequency magnetron sputtering. It was observed that all films possessed hexagonal wurtzite crystal structure with c-axis orientation. With the increasing of sputtering power, the growth rate rose steadily while the in-plane orientation of ZnO thin films gradually degraded. The FWHM of rocking curve, stress, intensity of visible emission reached a maximum at 125 W and then decreased with sputtering power further increasing. Films deposited at 75 W exhibited narrowest rocking curve of 1.44°, lowest visible emission and stress with orientation relationship: $${(0002)_{{\text{ZnO}}}}\parallel {(0006)_{{\text{SiC}}}}$$ and $${[11\bar {2}0]_{{\text{ZnO}}}}\parallel {[11\bar {2}0]_{{\text{SiC}}}}$$ . TEM and XPS results show that the interlayer is responsible for the degraded in-plane orientation, while the various point defects in non-equilibrium sputtering results in those visible emission. Those results demonstrate that increasing sputtering power greatly deteriorate quality of ZnO on 6H-SiC by interlayer and amount of point defects, while exorbitant sputtering power can recover these properties by increasing adatom mobility to some degree. [ABSTRACT FROM AUTHOR]

• A novel structure for high-frequency, large-coupling and low-cost surface acoustic wave devices is presented. • The phase velocity was increased by 50%. • The electromechanical coupling factor remained close to 20%. • The leaky nature was weakened and the quality of the response was ensured. With the development of fifth-generation wireless systems, the Internet of Things, and health services, surface acoustic wave (SAW)-based filters and sensors have attracted considerable interest. This study presents a new structure for high-frequency, large-coupling, and low-cost SAW devices that helps implement high-frequency and wideband filters and enhances the sensitivity of sensors. The structure is based on 15°Y-X LiNbO 3 , thin SiO x /SiN x bilayer overlay, and Al electrodes. Furthermore, a low-cost fabrication process for SAW devices based on this structure was designed. Simulation and experimental results show that the bilayer substantially weakens the leaky nature of shear-horizontal-type SAWs with a phase velocity higher than that of a slow-shear bulk wave in LiNbO 3. Thus, the limitation related to the velocity of 4029 m/s was overcome, and the phase velocity reached approximately 4500 m/s, which means an increase of 50% compared with that of conventional Cu/15°Y-X LiNbO 3 devices. Consequently, the frequency dramatically increases, and the quality of the SAW response is ensured. Simultaneously, a large electromechanical coupling factor close to 20% can be achieved, which is still suitable for wideband filters and sensors with high energy transduction coefficients. This new structure is expected to become a major candidate for SAW devices in the future. [ABSTRACT FROM AUTHOR]

Recently, surface acoustic wave (SAW) devices based on layered structures are a popular area of research. Multilayered structures, including ZnO and GaN, have shown great performance and can be applied in diverse fields. Meanwhile, thin films, such as AlGaN and n-ZnO, can be added to these structures to form a 2-D electron gas (2DEG) which makes the devices tunable. This work systematically studies the basic properties of SAW devices based on ZnO and GaN multilayers via COMSOL Multiphysics. The sorts of structures with different crystal orientations are simulated, and various acoustic modes are considered. Results show that a range of phase velocity from about 2700 m/s to 6500 m/s can be achieved, and devices based on ZnO and GaN multilayers can meet the requirements of the electromechanical coupling coefficient from about 0 to 7%. Every structure's unique properties are valuable for diverse applications. For example, c-ZnO/c-GaN/c-sapphire structure can be used for high-frequency and large-bandwidth SAW devices, while SAW devices based on a-ZnO/a-GaN/r-sapphire and 2DEG are suitable for programmable SAW sensors. This work has great reference value for future research into SAW devices. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid full-wave analysis of surface acoustic wave (SAW) devices is proposed to achieve accurate and fast simulation. The partial differential equation (PDE) models of the physical system in question and graphics processing unit (GPU)-assisted hierarchical cascading technology (HCT) are used to calculate acoustic-electric characteristics of a SAW filter. The practical solid model of the radio frequency (RF) filter package is constructed in High Frequency Structure Simulator (HFSS) software and the parasitic electromagnetics of the entire package is considered in the design process. The PDE-based models of the two-dimensional finite element method (2D-FEM) are derived in detail and solved by the PDE module embedded in COMSOL Multiphysics. Due to the advantages of PDE-based 2D-FEM, it is universal, efficient and not restricted to handling arbitrary materials and crystal cuts, electrode shapes, and multi-layered substrate. Combining COMSOL Multiphysics with a user-friendly interface, a flexible way of modeling and mesh generation, it can greatly reduce the complicated process of modeling and physical properties definition. Based on a hybrid full-wave analysis, we present an example application of this approach on a TC-SAW ladder filter with 5° YX-cut LiNbO3 substrate. Numerical results and measurements were calculated for comparison, and the accuracy and efficiency of the proposed method were verified. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW)-based sensors have become highly valued for their use as nanosensors in industrial applications. Accurate prediction of the thermal stability is a key problem for sensor design. In this work, a numerical tool based on the finite element method combined with piezoelectric Lagrangian equations has been developed to accurately predict the thermal sensitivity characteristics of surface acoustic wave devices. Theoretical analysis for the geometric nonlinearity contributing to the frequency–temperature characteristic and material constants' dependency on temperature were taken into consideration. The thermomechanical equilibrium equation built on the three-dimensional finite element method (3D-FEM) mesh node took mesh movement into account because thermal expansion was employed. The frequency–temperature characteristics of different SAW modes, including Rayleigh waves and leaky waves excited on a piezoelectric substrate of quartz or lithium tantalate, respectively, were calculated. The theoretical accuracy of the proposed numerical tool was verified by experiments. [ABSTRACT FROM AUTHOR]