Surface Acoustic Wave Resonators Research Articles

Non-Zero Power Flow Angles in Surface Acoustic Wave Resonators for Transverse Mode Suppression

Non-Zero Power Flow Angles in Surface Acoustic Wave Resonators for Transverse Mode Suppression

Comparison of aluminum nitride thin films prepared by magnetron sputter epitaxy in nitrogen and ammonia atmosphere

Wurtzite-type aluminum nitride (AlN) thin films exhibiting high thermal conductivity, large grain size, and low surface roughness are desired for both bulk acoustic wave and surface acoustic wave resonators. In this work, we use ammonia (NH3) assisted reactive sputter deposition of AlN to significantly improve these properties. The study shows a systematic change in the structural, thermal, and morphological properties of AlN grown in nitrogen (N2) and N2 + NH3 atmosphere. The study demonstrates that NH3 assisted AlN sputtering facilitates 2D growth. In addition, the study presents a growth model relating the 2D growth to improve the mobility of aluminum (Al) and nitrogen (N) ad-atoms in NH3 atmosphere. Consequently, the thermal conductivity and roughness improve by ≈76%, and ≈35%, while the grain size increases by ≈78%.

Magnon-Phonon Coupling of Synthetic Antiferromagnets in a Surface Acoustic Wave Cavity Resonator.

We used a surface acoustic wave (SAW) cavity resonator to study the coupling of acoustic magnons in a synthetic antiferromagnet (SAF) and phonons carried by SAWs. The SAF is composed of a CoFeB/Ru/CoFeB trilayer, and the scattering matrix of the SAW resonator is studied to assess the coupling. We find that the spectral line width of the SAW resonator is modulated when the frequency of the excited magnons approaches the SAW resonance frequency. Such a change in the spectral linewidth can be well reproduced using macrospin-like model calculations. From the model analyses, we estimate the magnon-phonon coupling strength to be ∼9.9 MHz at a SAW resonance frequency of 1.8 GHz: the corresponding magnomechanical cooperativity is ∼0.66. As the spectral shape hardly changes in a CoFeB single-layer reference sample, these results show that SAF provides an ideal platform to study magnon-phonon coupling in an SAW cavity resonator.

Design and Characterization of Surface Acoustic Wave-Based Wireless and Passive Temperature Sensing System.

The surface acoustic wave (SAW) temperature sensor has received significant attention due to its wirelessly powered, battery-free, and chipless capabilities. This paper proposes a wireless sensing system comprising a one-port SAW resonator, helix antenna, and transceiver circuit. The SAW resonator used in this system is based on aluminum nitride (AlN) thin film, which exhibits high velocity and excellent piezoelectric properties. Simulations and experiments were conducted to investigate the performance of the designed SAW resonator. A helix antenna was also designed using finite element simulation to facilitate signal transmission between the SAW temperature sensor and the transceiver. An impedance-matching network was introduced between the helix antenna and the SAW resonator to optimize signal transmission. When the wireless SAW temperature sensor was placed within a certain distance of the mother antenna, the reflection peak of the SAW resonator was observed in the spectrum of the return signal. The frequency of the echo signal increased almost linearly as the temperature increased during the temperature tests. The fitted temperature coefficient of frequency (TCF) was -31.34 ppm/°C, indicating that the wireless temperature sensing system has high-temperature sensitivity.

Modeling and testing of a highly sensitive surface acoustic wave pressure sensor for liquid depth measurements

The fluid depth/level measurement application extends from industry to domestic contexts. This article explores the underutilized potential of Surface Acoustic Wave (SAW) sensor-based devices for liquid depth and pressure measurements. Experiments conducted at room temperature address design challenges using a quartz Y34° cut single-port resonator. Theoretically predicted longitudinal strain sensitivity of −1.15 kHz/μStrain (−1.32 ppm/μStrain) was reduced to −421 Hz/μStrain (-0.48 ppm/μStrain) due to adhesive layer thickness. Numerical simulations investigate the effect of adhesive thickness on strain transfer from a cantilever to the Surface Acoustic Wave (SAW) sensor's top surface. The sensor is tested on a cantilever and integrated into a 20 μm thick diaphragm-based depth gauge, achieving a depth sensitivity of 42 Hz/mm (0.048 ppm/mm). This sensitivity results from bending of the SAW sensor under hydrostatic pressure, causing compression at the top SAW surface, which was an interesting observation. Additional numerical investigations confirm this behavior, aligning well with experimental findings. The article summarizes the comprehensive study of the SAW resonator’s performance and effect of adhesive thickness and provides a guide for designing thin diaphragm-based SAW pressure and depth sensors. It also identifies the device’s high sensitivity compared to other sensors in the literature and outlines potential avenues for future research.

Surface Acoustic Wave Resonator Chip Setup for the Elimination of Interfering Conductivity Responses.

A surface acoustic wave (SAW) resonator chip setup is presented that eliminates interfering signal responses caused by changes in the electrical environment of the surrounding media. When using a two-port resonator, applying electrically shielding layers between the interdigital transducers (IDTs) can be challenging due to the limited dimensions. Therefore, a layered setup consisting of an insulating polymer layer and a conductive gold layer was preferred. The SAW resonators were provided with polycarbonate housings, resulting in SAW resonator chips. This setup enables easy application of a wide range of coatings to the active part of the resonator surface, while ensuring subsequent electrical and fluidic integration of the resonator chips into a microfluidic array for measurements. The signal responses of uncoated SAW resonators and those with polymer coatings with and without a gold layer were tested with aqueous potassium chloride (KCl) solutions up to 3 mol/L, corresponding to conductivities up to 308 mS/cm. The use of a polymer coating at the thickness of the first Love mode resonance and a conductive gold layer completely reduced the electrical impact on the SAW resonator signal response, making small signals resulting from changes in viscosity and density of the KCl solutions visible.

Higher Order Mode Elimination for SAW Resonators Based on LiNbO₃/SiO₂/poly-Si/Si Substrate by Si Orientation Optimization

Higher Order Mode Elimination for SAW Resonators Based on LiNbO₃/SiO₂/poly-Si/Si Substrate by Si Orientation Optimization

Coupled Shear SAW Resonator With High Electromechanical Coupling Coefficient of 34% Using X-Cut LiNbO₃-on-SiC Substrate

Coupled Shear SAW Resonator With High Electromechanical Coupling Coefficient of 34% Using X-Cut LiNbO₃-on-SiC Substrate

Surface modification and coherence in lithium niobate SAW resonators

Lithium niobate is a promising material for developing quantum acoustic technologies due to its strong piezoelectric effect and availability in the form of crystalline thin films of high quality. However, at radio frequencies and cryogenic temperatures, these resonators are limited by the presence of decoherence and dephasing due to two-level systems. To mitigate these losses and increase device performance, a more detailed picture of the microscopic nature of these loss channels is needed. In this study, we fabricate several lithium niobate acoustic wave resonators and apply different processing steps that modify their surfaces. These treatments include argon ion sputtering, annealing, and acid cleans. We characterize the effects of these treatments using three surface-sensitive measurements: cryogenic microwave spectroscopy measuring density and coupling of TLS to mechanics, X-ray photoelectron spectroscopy and atomic force microscopy. We learn from these studies that, surprisingly, increases of TLS density may accompany apparent improvements in the surface quality as probed by the latter two approaches. Our work outlines the importance that surfaces and fabrication techniques play in altering acoustic resonator coherence, and suggests gaps in our understanding as well as approaches to address them.

Investigation of spurious mode suppression in 3.8 GHz shear-horizontal mode surface acoustic wave resonators based on LiNbO3/SiO2/Si multilayer structure

LiNbO3(LN)/SiO2/Si multilayer structures have recently attracted much attention due to their superior performance in realizing wideband radio-frequency acoustic filters. However, the spurious modes, which are commonly found in LN-on-insulator (LNOI) resonators, often cause in-band ripples and a deteriorated out-of-band suppression level. Although much research work has been done on the suppression of spurious modes in LNOI resonators operating in the <3 GHz region, little has been reported for >3 GHz devices. This work investigates the spurious mode suppression techniques for a 3.8 GHz shear-horizontal mode 36° YX-LNOI surface acoustic wave (SAW) device based on an LN/SiO2/Si multilayer structure. Specifically, we explore different techniques based on apodized electrodes, dummy electrodes and a double busbar structure. The measured results show that the effect of spurious mode suppression can be improved by combining the benefits of these techniques, which provides a promising solution for designing spurious-free LNOI SAW resonators operating above 3 GHz.

Synthesis of Electronic Frequency Tuning Units for Narrowband Ultra-Low Noise Oscillators with Surface Acoustic Waves Resonators

Synthesis of Electronic Frequency Tuning Units for Narrowband Ultra-Low Noise Oscillators with Surface Acoustic Waves Resonators

Theoretical and Experimental Study of High‐Electromechanical‐Coupling Surface Acoustic Wave Resonators Based on A‐Plane (112¯0)$\left(\right. 11 \overset{\cdot}{2} 0 \left.\right)$ Al0.56Sc0.44N Films

Herein, a high‐quality Al0.56Sc0.44N piezoelectric thin‐film‐based surface acoustic wave (SAW) resonator is developed. The Al0.56Sc0.44N is deposited on r‐plane Al2O3 substrate by reactive magnetron sputtering. X‐ray diffraction (XRD) spectroscopy shows that the grown Al0.56Sc0.44N films are single‐phased and a‐plane oriented. The full width at half maximum of the XRD rocking curve is only 0.4°, which is smaller than most of the reported values. The effects of normalized thickness of the piezoelectric layer, electrode materials, and thickness on acoustic properties of the SAW resonators are investigated through the 3D finite‐element method equipped with the hierarchical cascading technique. A monotonically decreasing resonant frequency can be obtained with the mass loading of both the electrode metals. For the devices with a Pt electrode, it is observed that the electromechanical coupling coefficient () exhibits a nonlinear characteristic of first increasing and then decreasing with the increase of electrode thickness. SAW resonators with a nonpolar a‐plane Al0.56Sc0.44N thin films are fabricated, showing an exceptionally high of 4.6%. This result demonstrates a significant potential of AlScN films with the a‐plane orientation in radio frequency application.

Monolithic Strong Coupling of Topological Surface Acoustic Wave Resonators on Lithium Niobate.

Coherent phonon transfer via high-quality factor (Q) mechanical resonator strong coupling has garnered significant interest. Yet, the practical applications of these strongly coupled resonator devices are largely constrained by their vulnerability to fabrication defects. In this study, topological strong coupling of gigahertz frequency surface acoustic wave (SAW) resonators with lithium niobate is achieved. The nanoscale grooves are etched onto the lithium niobate surface to establish robust SAW topological interface states (TISs). By constructing phononic crystal (PnC) heterostructures, a strong coupling of two SAW TISs, achieving a maximum Rabi splitting of 22MHz and frequency quality factor product fQm of ≈1.2 × 1013 Hz, is realized. This coupling can be tuned by adjusting geometric parameters and a distinct spectral anticrossing is experimentally observed. Furthermore, a dense wavelength division multiplexing device based on the coupling of multiple TISs is demonstrated. These findings open new avenues for the development of practical topological acoustic devices for on-chip sensing, filtering, phonon entanglement, and beyond.

Experimental Analysis of Rayleigh and Sezawa Modes Resonance Frequencies in SAW Devices Manufactured on Sc0.3Al0.7N/Si†

GHz operating single port SAW resonators have been manufactured on Sc0.3Al0.7N/Si substrate. The thickness of the ScAlN thin layer was 0.8 μm. Advanced nano‐lithographic techniques have been developed for devices manufacturing. Rayleigh and Sezawa modes have been evidenced on Sc0.3Al0.7N/Si structure. The targeted applications are temperature sensors for harsh environmental operations. The sensitivity and temperature coefficient of frequency (TCF) of the manufactured devices have been experimentally determined and analyzed. The mode shapes of the resonances that appear in the devices supported on Sc0.3Al0.7N/Si substrate were evidenced by finite element method (FEM) simulations. A technique that combines FEM with Coupling of Modes (COM) was used for the determination of the resonance frequencies. Simulations performed for the temperature dependence of the resonance frequency led to results close to the experimental ones for the Rayleigh mode as well as for the Sezawa mode for devices supported on Sc0.3Al0.7N/Si substrate. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Effect of bonding adhesive thickness on temperature characteristics and strain characteristics of SAW strain sensors

Accurate measurement of physical parameters based on sensing technology is an important basis for equipment structural health monitoring technology. In harsh environments, strain measurement techniques based on SAW sensors have attracted much attention. The bonding adhesive is a key step in the strain measurement process, and its effect on the accuracy of the measurement results cannot be ignored. In this paper, the one-port resonant SAW strain sensor is prepared using LiNbO3 as a piezoelectric substrate, Pt as an electrode and SiO2 as a protective layer. The strain characteristics and temperature characteristics of SAW strain sensors at the thickness of the bonding adhesive (Model: DOUBLE-BOND CHEMICAL®DB5016) are explored. The frequency–temperature curves of the SAW sensors show a quasi-linear decreasing trend with increasing temperature, and the temperature–frequency characteristics are similar for different bonding adhesive thicknesses. The strain sensitivity increases and then decreases with increasing temperature, and reaches a maximum at 150 °C. An increase in the thickness of the bonding adhesive leads to a decrease in the temperature linearity and an increase in the temperature sensitivity of the SAW strain sensor, which is maximized at a bonding adhesive thickness of 0.35 mm. The increase in the thickness of the bonding adhesive leads to a decrease in the strain linearity and strain sensitivity of the SAW sensor. The relationship between the strain transfer efficiency of the SAW sensor and the thickness of the bonding layer, the shear modulus of the bonding layer, the length of the sensor, the thickness of the sensor substrate and the shear modulus of the sensor is established through theoretical derivation. A theoretical foundation is provided for the accurate measurement of strain based on SAW technology.

Machine learning as a new strategy for designing surface acoustic wave resonators

Surface Acoustic Wave (SAW) technology has been widely applied in the fields such as communication and sensing. The performance of SAW devices is significantly influenced by designs of their key component, Interdigital Transducers (IDTs), and thus Coupling of Modes (COM) theory has been used as one of the most employed design tools for SAW devices due to its fast computational speed. Accuracy of this model is primarily dependent upon the COM parameters, but the traditional approach to obtain these parameters is heavily relied on accuracy of the input material properties, which has become a key issue for successful applications of this model. This paper proposed a new strategy to utilize the results obtained from the COM model as a dataset and then employ five different machine learning models for performing regression analysis and accurately extracting the COM parameters. To validate the accuracy of this approach, experimental verifications were performed using a 128°Y-X LiNbO3 based SAW resonator as an example. The machine learning model with the best predictive performance, i.e., Extreme Gradient Boosting, was used to predict the COM parameters corresponding to experimental results, which were subsequently used in conjunction with the COM model for further calculations and comparisons with the experimental results. Results showed that the calculated results exhibit the same trend of resonance Q-values as the experimental results, demonstrating its effective solution for accurately extracting COM parameters.

Application of an overlay for spurious suppression of multi-layered surface acoustic wave resonators with double busbar configuration

Abstract This paper discusses the suppression of a spurious resonance called the gap mode which appears when the double busbar configuration is applied to multi-layered surface acoustic wave resonators. Two kinds of overlay structures are proposed for the gap mode mitigation. First, the use of lossy ones is studied. The results indicate that the lossy overlay can effectively mitigate the gap mode response when the viscosity is adequate. The layer thickness has a negligible impact on the mitigation. Then, the discussion is extended to the application of high-acoustic-velocity materials as the overlay. The resonance frequency of the gap mode can be moved to the upper-frequency side without affecting the main resonance by simply depositing a high-velocity overlay to the gap region. Finally, the comparison and choice of overlay materials are also studied. The results point out that Si3N4 is the optimum choice for industrial use.

Experimental Study of Transverse Mode Suppression on Wideband Hetero Acoustic Layer Surface Acoustic Wave Resonator.

Transverse mode suppression is a great challenge for high-performance surface acoustic wave (SAW) resonators. Conventional methods work well on narrowband resonators, but their performances on wideband resonator have not been demonstrated. In this article, we give an in-depth study on the transverse mode suppression of wideband resonators using 11° YX-LiNbO3 (LN)/70 °Y90°X -quartz (Qz) hetero acoustic layer structure as a platform. Two groups of design, including new dummy electrode and zigzag shape apodization, are proposed. The measured results show that the shape of the dummy electrode is not the dominant factor to affect the transverse mode. The proposed zigzag shape apodization can effectively suppress the transverse, at the same time maintain the quality ( Q ) factor at the same level with the normal type. Additionally, stronger suppression ability can be realized with a tiny tradeoff of Q -factor.

Behaviors of higher-order modes in I.H.P. SAW devices and discussion of their suppression

In this work, behaviors of higher-order modes in an I.H.P. SAW device with a layered LiTaO3/SiO2/SiN/Si substrate are investigated, and techniques for their suppression are discussed. First, variation of the higher-order mode responses with structural parameters are analyzed using two-dimensional FEM. Then, on the basis of the calculated data, structural parameters are determined for higher-order modes suppression while retaining the main mode characteristics. In addition, the effectiveness of the optimized structure is confirmed using measured data from a fabricated one-port resonator and filters. In the measured data, it is shown that higher-order modes in a specific frequency range are successfully suppressed, while the main made characteristics, such as Bode-Q, bandwidth, and TCF, are almost equivalent to those of conventional I.H.P. SAW resonators and filters.

Modeling for High-Frequency Spurious Responses in Incredible High-Performance Surface Acoustic Wave Devices.

To ensure that surface acoustic wave (SAW) filters fulfill the requirements of Carrier Aggregation (CA) applications, the development of modeling tools that can forecast and simulate high-frequency spurious responses has been necessary. This paper presents an advanced methodology for extending the coupling-of-modes (COM) model to obtain precise modeling of the high-frequency spurious responses of incredible high-performance surface acoustic wave (I.H.P. SAW) devices. The extended COM (ECOM) model is derived by modifying the conventional COM model and extending it accordingly. The parameters used in this model are determined through numerical fitting. For validation, firstly, the ECOM model is applied to a one-port synchronous I.H.P. SAW resonator, and the simulation and measurement results match. Then, the structural parameters of the ECOM model are varied, and the accuracy of the model after the structural parameters are varied is verified. It is demonstrated that this model can be applied to the design work of SAW filters. Finally, the ECOM model is applied to the design of the I.H.P. SAW filter based on a 42°YX-LiTaO3 (LT)/SiO2/AlN/Si structure. By using this method, the I.H.P. SAW filter's high-frequency spurious response can be predicted more accurately.