One-port Surface Acoustic Wave Research Articles

Advancements in One-Port Surface Acoustic Wave (SAW) Resonators for Sensing Applications: A Review

Advancements in One-Port Surface Acoustic Wave (SAW) Resonators for Sensing Applications: A Review

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.

Design of heterostructure one-port SAW resonator with improved bandwidth using Si and LiNbO3 layer

In this research work, we have designed a heterostructure one-port surface acoustic wave (SAW) resonator. The multi-layer one port SAW resonator is made of a silicon (Si) substrate as base material, 128 ͦ rotated Y-cut X- propagated lithium niobate (LiNbO3) as piezoelectric substrate, and Inter Digital Transducers (IDTs) made of aluminium. This model is designed to operate on a wide frequency of 4–5 GHz with a resonance frequency of 4.74 GHz. Various parameters are taken into consideration during the study and analysis such as high-quality factor, wider bandwidth, better electromechanical coupling coefficient, and a true Figure of merit (FoM). The obtained Quality factor and the electromechanical coupling coefficient (k2) of the designed model are 2700 and 0.18. By using the wide range of frequencies, the bandwidth for the designed model is 1.74 MHz. The obtained results show that the device’s performance of the one port multilayer SAW resonator using the Al/128°YXLiNbO3/Si multi-layered substrate exhibits a commercial application in the 5 G wireless communication system.

Analysis of CNT-based SAW sensor for the detection of volatile organic compounds

This paper presents a multi-layer one-port surface acoustic wave (SAW) sensing device and its response based on the adsorption of different volatile organic compounds (VOCs). The finite element method was used to model and simulate a multi-layered SAW device. A piezoelectric substrate 128ᵒ YX-cut Lithium Niobate (LiNbO3), polyisobutylene (PIB) polymer, and carbon nanotube (CNT) multilayer SAW resonating sensor was modeled and used for generating Rayleigh waves. Electromechanical coupling coefficient (K2), admittance (Y11), S-parameter (S11), and metallization ratio (MR) were computed for the proposed heterostructured device. The sensing properties of proposed SAW sensor was investigated for several organic compounds such as trichloroethylene (C2HCl3), trichloromethane (CHCl₃), acetone (C3H6O), acetonitrile (C2H3N), cyclohexane (C6H12), dichloromethane (CH2Cl2) and diethyl ether (C4H10O). Eigenfrequency analysis of the SAW sensor was evaluated from 100 ppm to 500 ppm gas concentration at room temperature. The observed results were compared with the existing research and found to be more effective in terms of sensitivity.

Nondestructive Measurement by One-Port Surface Acoustic Wave Resonator for Accurate Evaluation of Film Thickness

Abstract A new method for nondestructive testing of SiO2 film thickness using a portable one-port surface acoustic wave (SAW) resonator based on lithium niobate (LiNbO3) is proposed. First, the finite element method is used to simulate and analyze the relationship between the resonant frequency of SAW resonator and film thickness. Then, the vector network analyzer is used to nondestructively characterize the thickness of SiO2 film by SAW resonator. The relationship between the thickness and the corresponding resonant frequency in a certain range is obtained and given by a second order polynomial. The results show that the resonant frequency is negatively correlated with film thickness, where the resonant frequency changes from 339.27 to 318.40 MHz in the film thickness range of 100 to 2000 nm. To validate the prediction formula, when the film thicknesses are 201.20, 504.60, 842.10, and 1497.70 nm, the resonant frequency is used to verify the experimental fitting polynomial. The relative errors between the predicted thickness by SAW resonator and the actual film thickness are 1.60%, 0.34%, 0.67%, and 0.96%. The results show that SAW resonator has great potential in detecting thin film thickness with high sensitivity and accuracy.

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.

Extraction of Attenuation Parameter in Periodic Shorted Reflectors of One-Port SAW Resonator Using Scattering Matrix Approach

In this work, the well-known scattering matrix approach to the design of one-port surface acoustic wave (SAW) resonators is adapted toward extraction of the coupling-of-modes (COM) attenuation parameter, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> for Rayleigh SAW propagation on a periodic shorted aluminum grating. The attenuation close to resonance inside the reflectors of the one-port SAW resonator is extracted by matching the measured conductance of the resonator to its version calculated from the experimentally measured interdigital transducer (IDT) scattering coefficients, intrinsic substrate parameters, and geometry of the resonator. Based on the extracted value of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> , it was observed that the proposed method could predict the unloaded <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -factor of the resonator at a minor discrepancy of ~7.02%. At the same time, since the proposed method utilizes the measured IDT scattering coefficients to consider the effect of IDT losses on the measured conductance of the resonator, it offers a convenient scheme to directly extract the attenuation of SAW contributed by the reflectors of the device through numerical means while operating purely in the frequency domain. The proposed method could be applied to quantify the increase in attenuation caused by viscous damping of SAW inside sensing film-coated reflectors of one-port SAW resonator sensors, and thereby, aid to optimize the sensing film thickness to deploy these devices for high-resolution frequency-based sensing applications.

Design of 3D SAW Filters Based on the Spectral Element Method

Surface acoustic wave (SAW) devices are key components in 5G communication systems, and the design of SAW filters with high frequency, high performance and high reliability is a necessary and challenging task. In this work, SAW resonators with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LiNbO</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SiO</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Si</i> multi-layer structure are designed based on the spectral element method (SEM). Normally, however, massive computing resources are needed for solving a whole resonator directly by using full-wave numerical methods. To avoid simulating the large-aperture full structure of any SAW resonator, an equivalent small-aperture 3D structure can be modelled in the direction of the aperture by changing the internal resistance of the driving source to obtain the results of the full-scale aperture model. The one-port SAW resonators are then connected in the form of ladder networks to form band-pass SAWfilters. The numerical results show that the SEM is more computationally efficient than the finite element method under the same number of degrees of freedom, and the results of the 3D small-aperture model are consistent with the complete resonator.

Finite element simulation and characterization of one-port heterostructured surface acoustic wave resonator

The research work presents the study of a heterostructured surface acoustic wave (SAW) resonator consisting of an interdigital transducer (IDT), lithium niobate (LN), and silicon (Si) substrate. In the proposed structure, Silicon is the base substrate, above it layer of LN is placed then IDT is designed on it. The presented analysis includes the variation of the quality factor and electromechanical coupling coefficient with the change in the width of the piezoelectric layer. The electromechanical coupling coefficient (K 2), quality factor (Q-factor), velocity, resonance, admittance, and anti-resonance frequency have been studied for the thickness of the different layers of LN film. The higher quality factor of one port SAW devices reduces the energy loss and the K 2 of the devices indicates faster energy conversion. The Q-factor and K 2 are found to be depending on the thickness of LN, resonance, and anti-resonance frequency.

Toward Real Time Monitoring of Wafer Temperature in Plasma Chamber Through Surface Acoustic Wave Resonator and Mu-Negative Metamaterial Antenna

Surface acoustic wave (SAW)-based temperature sensors and wireless sensing systems were developed for real-time monitoring of the wafer surface temperature in a plasma chamber. A one-port SAW resonator was used for the temperature sensor because of its unique capabilities of 3less (wireless, batteryless, and chipless (no embedded interface electronics)). Three SAW sensors with different resonant frequencies of 380, 445, 475MHz were employed to distinguish individual sensor from the whole sensor units and prevent electromagnetic (EM) interference caused by a plasma driving frequency of 15.6 MHz in the plasma reactor. The changes of the reflection peaks in the measurement system were compared in three different cases. When the SAW sensor was connected to the antenna, the reflection peak corresponding to SAW resonant frequency was clearly observed in the reflection profile. When heat was applied to the SAW sensor by shining an infrared heater, only the reflection peak corresponding to the SAW resonant frequency was largely downshifted while the background reflection profile remained the same. High sensitivity and linearity were observed from the three sensors. The sensitivity increased on the same wafer surface as the center frequency of the sensor increased. A negligible change in the sensor resonance peak was observed when a plasma radiation was continuously illuminated on the sensor surface, indicating that the fabricated sensor with a Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> passivation layer protects well against energetic X-ray and EM radiations. The sensor resonance peaks were not changed by a plasma driving frequency of 15.6 MHz that was applied between top and bottom plates.

Scattering Matrix Approach to Design of One-Port Surface Acoustic Wave Resonator Sensors Utilizing Reflectors as Sensing Element.

It has been recently demonstrated that one-port surface acoustic wave (SAW) resonators known for their high Q value and relatively small device footprint could be utilized for in-liquid mass loading sensing applications where only the reflectors of the device are coated with the sensing film, while the interdigital transducer (IDT) is isolated from the sensing environment. The sensor relies on changes induced in reflectivity and phase velocity of SAW in the region of the reflectors upon detection of the measurand and is particularly advantageous for SAW resonator-type sensors as any contact of the sensing film with the IDT could change its static capacitance during sensing and thereby introduce serious instability in the sensor response. Accordingly, in the present work, the existing scattering matrix approach to the design of one-port SAW resonator filters, which does not cater to the integration of sensing film on the resonator surface, is adapted to develop a method to design one-port SAW resonator sensors utilizing reflectors as sensing element. The reflector block of the one-port SAW resonator is readily split into sensing-active and sensing-inactive parts using the SAW grating transmission matrix in order to study the changes introduced in input admittance of the device for varying level of coverage of the sensing film. The theoretical design approach presented in this work could be used to fabricate high-performance one-port SAW resonator sensors operating at its point of highest sensitivity while utilizing one of the device reflectors as sensing element, without the use of additional impedance matching circuit elements.

Investigation into effect of coupled resonance phenomenon towards sensitivity enhancement of SAW conductivity sensors integrated with ZnO nanorods

In this work, FEM simulation was used to investigate the sensitivity of a one-port surface acoustic wave (SAW) resonator sensor to changes in electrical conductivity of the sensing medium composed of ZnO nanorods offering elastic loading on the surface of the resonator. A system of coupled resonators was formed when the height of the ZnO nanorods attached to the surface of the resonator was adjusted such that the resonant frequency of the nanorod approached the original resonant frequency of the SAW resonator. It was observed that the use of ZnO nanorods of resonant dimensions as sensing medium could enhance the sensitivity of the composite SAW sensor to changes in electrical conductivity of the sensing medium by up to 79 times. The comparatively higher sensitivity of the SAW conductivity sensor utilizing ZnO nanorods at resonant dimensions as sensing medium was attributed to the fact that the system of coupled resonators thus formed operates at a state of high sensitivity to changes induced in piezoelectric stiffening of the substrate during SAW propagation. The observations from FEM simulation conducted in the present work suggests strong prospects for the use of coupled resonance phenomenon at nanoscale for enhancing the sensitivity of conductivity-based SAW gas sensors and UV detectors employing 1-D ZnO nanostructures as sensing medium.

A Hybrid Transmission-Line/SAW-Resonator Analog Signal-Interference Dual-Band Bandpass Filter

An analog signal-interference dual-narrowband bandpass filter (BPF) by combining transmission lines and surface-acoustic-wave (SAW) resonators is proposed. The filter is based on three-path transversal filtering sections (TFSs) with two embedded one-port SAW resonators. By cascading the TFSs in-series through transmission lines, passbands with enhanced fractional bandwidths (FBWs) (i.e., larger than the electromechanical coupling coefficient $k_{t}^{2}$ of the employed acoustic-wave resonator) can be realized. For the purpose of validation, a two-stage microstrip dual-narrowband BPF with two passbands located at 868.95 and 916.5 MHz has been designed, fabricated, and characterized. It demonstrated an insertion loss (IL) of 0.89 dB at 868.95 MHz, 1.57 dB at 916.5 MHz and a bandwidth (BW) of 3.2 MHz (FBW $=3.21\,\,k_{t}^{2}$ ) at 868.95 MHz, and 2.3 MHz (FBW $=1.92\,\,k_{t}^{2}$ ) at 916.5 MHz.

Development of chipless and wireless underground temperature sensor system based on magnetic antennas and SAW sensor

A chipless and wireless underground sensor system was developed based on two magnetic coil antennas with magnetic cores and a surface acoustic wave (SAW) resonator sensor to monitor temperature variations around buried utilities from the ground. A ∼250 MHz alternating current from the magnetic antenna generates a SAW along the piezoelectric substrate, and the returned SAW energy owing to the reflection bars on the sensor is reconverted to magnetic flux by the sensor’s interdigital transducer (IDT) and subsequently transmitted to a reader via magnetic antenna. By observing changes in the center frequency of the SAW sensor with temperature, we were able to monitor the underground temperature variations in real time. The developed magnetic coil antenna has a large diameter Ni0.8Fe0.2 core wound by Cu coil, and a convex shape at the core end to converge the magnetic flux and enhance the readout distance. Two types of temperature sensors, a one-port SAW resonator and two-port SAW reflective delay line, were fabricated on a 128° YX LiNbO3 and their characteristics were compared in terms of soil temperature. SAW generation by magnetic antenna followed by SAW propagation along the piezoelectric substrate were each confirmed by the AC voltages derived at the output IDT on the SAW sensor, and the amplitude of the SAW was greatly dependent on the current applied to the coil. In soil testing, long readout distance between the reader and underground SAW sensor was observed. The temperature sensors provided stable performance in terms of underground temperature changes, soil type, and soil compactness at that readout distance. The resultant sensitivity and linearity for the SAW resonator temperature sensor was 0.3 MHz/ºC and 0.96, respectively. COMSOL and coupling of Mode (COM) modeling were also performed to find the optimal sensor system parameters and predict the results in advance.

Fabrication and characterization of one-port surface acoustic wave resonators on semi-insulating GaN substrates**Project supported by the National Key Research and Development Program of China (Grant No. 2017 YFB0403002), the National Science Fund for Distinguished Young Scholars, China (Grant No. Y3CHC11001), and the National Natural Science Foundation of China (Grant No. 11604368).

One-port surface acoustic wave resonators (SAWRs) are fabricated on semi-insulating high-quality bulk GaN and GaN film substrates, respectively. The semi-insulating GaN substrates are grown by hydride vapor phase epitaxy (HVPE) and doped with Fe. The anisotropy of Rayleigh propagation and the electromechanical coupling coefficient in Fe-doped GaN are investigated. The difference in resonance frequency between the SAWs between [11 0] GaN and [1 00] GaN is about 0.25% for the Rayleigh propagation mode, which is smaller than that of non-intentionally doped GaN film (̃1%) reported in the literature. The electromechanical coupling coefficient of Fe-doped GaN is about 3.03%, which is higher than that of non-intentionally doped GaN film. The one-port SAWR fabricated on an 8- Fe-doped GaN/sapphire substrate has a quality factor of 2050, and that fabricated on Fe-doped bulk GaN has a quality factor as high as 3650. All of our results indicate that high-quality bulk GaN is a very promising material for application in SAW devices.

Sensitivity enhanced temperature sensor: one-port 2D surface phononic crystal resonator based on AlN/sapphire

According to the structure of a one-port surface acoustic wave (SAW) resonator, a one-port surface phononic crystal (SPC) resonator is designed. Both one-port SAW resonator and one-port SPC resonator are fabricated on AlN/Sapphire. Frequency responses and quality factors are studied. The one-port SAW resonator has a fundamental resonance mode at 693.07 MHz. Unlike the one-port SAW resonator, the one-port SPC resonator has two distinct resonance modes at 680.28 MHz and 698.91 MHz, respectively. From the simulation results by finite element method (FEM), these two resonance modes may come from the two cavities of the one-port SPC resonator. Frequency-versus-temperature behaviors of these two resonators are investigated. The results show that the frequencies of resonance modes of these two resonators are decreased linearly with the increased temperature. A new kind of temperature sensor is proposed by using frequency difference between these two resonance modes of the one-port SPC resonator. The eventual temperature coefficient of frequency (TCF) value of the temperature sensor is ppm °C−1 which is twice more than that of the one-port SAW resonator. All results prove that temperature sensitivity is enhanced by using two mode characters of one-port SPC resonator based on AlN/Sapphire.

Enhanced performance of AlN SAW devices with wave propagation along the 〈11−20〉 direction on c-plane sapphire substrate

This paper investigates the effect of acoustic wave propagation direction along the a-direction (〈11−20〉) and m-direction (〈1−100〉) on the frequency responses of c-plane AlN based surface acoustic wave (SAW) devices systematically. The experimental results indicate that the resonant frequency (), quality factor (Q), electromechanical coupling coefficient (), insertion loss and out-of-band rejection can be improved for the a-direction compared with the m-direction of an AlN based SAW resonator on sapphire. The Q is 1347 for a one-port SAW resonator along the a-direction, and the minimum insertion loss is 8.71 dB for a two-port SAW resonator along the a-direction. The insertion loss is 3.23 dB lower for the a-direction compared to the m-direction of the AlN film, which may be attributed to the larger acoustic power flow density. The is 45% higher for the a-direction compared to the m-direction of the AlN film, which may be attributed to the larger elastic constant. In addition, our finite element model simulation results reveal the C11 and C44 for the m-direction are 345 GPa and 102 GPa, while C11 and C44 for the a-direction is increased to 429 GPa and 128 GPa, respectively. Our work demonstrates that the a-direction is better than the m-direction of the AlN film for high performance SAW device applications.

High-Frequency Surface Acoustic Wave Devices Based on ZnO/SiC Layered Structure

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.

Finite element simulation of one-port surface acoustic wave resonator with thick interdigital transducer for gas sensing

The paper presents finite element simulation of a surface acoustic wave (SAW) one-port resonator with thick interdigital transducers (IDT) made of nickel metal for sensing dimethyl methylphosphonate (DMMP) gas by placing fluoroalcoholpolysiloxane (SXFA) sensing film in the space between thick IDT fingers. The absorption of DMMP gas changes density and thickness of SXFA film and affect the SAW propagation velocity, hence resonance frequency of the device. The change in resonance frequency is measured as sensor response. In this paper individual effects of change in density and thickness of SXFA film due to absorption of DMMP gas on sensor response are simulated. The results show that the change in thickness of the SXFA film placed in the space between thick IDT fingers of proposed device is dominant in sensor response and the sensitivity of the proposed device (2.1 kHz/mg/m3) is about 3.2 times greater than a conventional device using SXFA coated over the entire top surface of the device.

Influence of electrode width of interdigital transducer on third-order nonlinearity of surface acoustic wave devices on 42°YX-LiTaO3 substrate

In this paper, we discuss the influence of the electrode width of an interdigital transducer on the third-order nonlinearity of surface acoustic wave (SAW) devices. First, an estimation technique of third-order nonlinear signals based on the linear finite element method is proposed, and the variation of nonlinear signal level with electrode width is estimated. Then, several one-port SAW resonators with different electrode widths are fabricated, and measured nonlinear signal levels are compared with simulation. As predicted by the numerical simulation, nonlinear signal levels became large with electrode width. However, harmonics takes a minimum at a certain electrode width. This tendency disagrees with the simulation. The variation of nonlinear coefficients is evaluated by numerical fitting for the measured data using the nonlinear signal simulator proposed by the authors. As the result, it is concluded that the generation mechanism is not limited to the acoustic strain in electrodes.