Surface Acoustic Wave Resonators Research Articles

Ultra-wide band and improved quality factor SH-type SAW devices by employing Mn-doped Pb(In1/2Nb1/2)O3– Pb(Mg1/3Nb2/3)O3–PbTiO3 thin film/diamond layered structure

This paper presents a piezoelectric layered structure composed of Mn-doped PIN-PMN-PT thin film combined with diamond for high electromechanical coupling factor (K2) and improved quality factor (Q) SAW devices. Comprehensive theoretical analysis of SAW resonator on the proposed structure is performed to calculate its SAW characteristics including K2, V (phase velocity) and Q. The influence of the Euler angle, Mn-doped PIN-PMN-PT layer's thickness and the electrode's thickness as well as electrode's materials on the SAW properties are investigated. It is shown that the maximum electromechanical coupling factor of the proposed structure has been theoretically shown up to be 79.5 % for the main mode called shear-horizontal (SH)-type SAW. The FOM(K2·Q) is enhanced to 868.5, which is more than two times larger than that of the previously reported work using pure PIN-PMN-PT. Such enhancement of FOM makes such structure has great potential application in ultra-wide band and high Q SAW filters operating at 1GHz–3GHz.

MEMS Surface Acoustic Wave Resonator Based on AlN/Si/Fe–Co–Si–B Structure for Magnetic Field Sensing

While various magnetic sensors have been developed over the years, the capability of passive wireless magnetic field detection is still lacking. Magnetic surface acoustic wave (MSAW) devices, combining magnetostrictive with piezoelectric materials, may be one of the candidates for wireless magnetic field sensing. This work proposes a novel microelectromechanical system (MEMS) MSAW resonator based on the AlN/Si/(Fe90Co10)78Si12B10 structure. The frequency responses of the resonator were measured when applying a dc magnetic field along the magnetic easy and hard axes. The results indicate that the resonator has higher magnetic sensitivity along the hard axis, with a maximum magnetic sensitivity of 11 kHz/Oe. When performing a magnetic field loop measurement for the hard axis, the resonator’s quality factor and resonance frequency showed almost the same variation tendency against the magnetic field. Moreover, the quality factor can attain about 3700 at the position of maximum magnetic sensitivity, which could simultaneously meet the needs of wireless interrogation and high sensitivity. Our work reveals that such an MEMS MSAW resonator has clear potential in the realization of wireless magnetic field sensors with miniaturization, low power, and high complementary metal–oxide–semiconductor (CMOS) compatibility for the future development of the Internet of Things (IoT).

Minimally diffracting quartz for ultra-low temperature surface acoustic wave resonators

We simulate and experimentally demonstrate the existence of an orientation of quartz, which minimizes diffraction losses in surface acoustic wave (SAW) resonators at ultra-low temperatures. The orientation is optimized for applications to quantum technologies, which benefit from high mechanical quality factors, strong electromechanical coupling, and narrow acoustic apertures. We fabricate narrow aperture SAW resonators on this substrate and measure internal quality factors greater than 100 000 at mK temperatures.

Acoustic charge transport in organic semiconductor films

We demonstrate the acoustic charge transport of optically induced excitons in two organic semiconductors, P3HT and MEH-PPV, up to a distance of 3 mm. The device consists of a surface acoustic wave (SAW) resonator transmitting SAW through a polymer layer where acoustic charge transport takes place and a polymer diode at the end to collect the charges. The voltage excitation is provided using an interdigital transducer (IDT) on a piezoelectric YZ lithium niobate substrate producing Rayleigh SAW at 42 MHz. Optical illumination up to 15 mW cm−2 intensity is applied to induce excitons in the polymer layer deposited on the lithium niobate substrate. The photogenerated excitons in the polymer are ionized by SAW field resulting in free carriers that are transported to the polymer diode by the travelling SAW. A surge in photovoltaic current in the diode is observed in the presence of SAW when the carriers are optically generated away from the diode. The maximum charge capacity and transfer efficiency of the acoustic transport are calculated for various SAW power and illumination intensities. A theoretical analysis of charge carrier dynamics in the presence of a moving SAW field is also performed using a semi-classical Hamiltonian of the system.

Rayleigh waves in nonpolar Al0.7Sc0.3N(112¯0) films with enhanced electromechanical coupling and quality factor

This work reports on the growth of 1 µm nonpolar a-plane Al0.7Sc0.3N(112¯0) thin films on an r-plane sapphire Al2O3(11¯02) via magnetron sputter epitaxy. The electro-acoustic properties of the film structures were characterized using surface acoustic wave (SAW) resonators. Measured electrical responses were found to be strongly anisotropic in terms of the wave propagation direction. We identified a sagittal polarized Rayleigh wave mode with large coupling (keff2= 3.7%), increased phase velocity (v= 4825 m/s), as well as high quality factor (Q > 1000) for SAW propagation along the c-axis [0001] and normalized thicknesses h/λ=0.2. Finite element method simulations using electro-acoustic properties of Al0.7Sc0.3N obtained from the density functional theory reproduce our experimental results.

Bulk GaN-based SAW resonators with high quality factors for wireless temperature sensor

Surface acoustic wave (SAW) resonator with outstanding quality factors of 4829/6775 at the resonant/anti-resonant frequencies has been demonstrated on C-doped semi-insulating bulk GaN. The impact of device parameters including aspect ratio of length to width of resonators, number of interdigital transducers, and acoustic propagation direction on resonator performance have been studied. For the first time, we demonstrate wireless temperature sensing from 21.6 to 120 °C with a stable temperature coefficient of frequency of –24.3 ppm/°C on bulk GaN-based SAW resonators.

First-Order Perturbation Analysis of Nonlinear Signal Generation in Surface Acoustic Wave Resonators on LiTaO3/SiO2/Si Structure Based on Coupling-of-Modes Theory.

This article describes the first-order perturbation analysis of nonlinear responses in surface acoustic wave (SAW) resonators on the LiTaO3/SiO2/Si structure, where bulk wave radiation is negligible near the main resonance while the longitudinal resonances are not. The coupling-of-modes (COMs) theory is employed as the platform for both the linear and nonlinear response analyses. Stress and dielectric flux are assumed to be generated by nonlinear mixture of linear strain and electric fields proportional to the SAW displacement and applied voltage, respectively, and they are newly introduced to the extended COM equations as excitation sources. The simulated third harmonic (H3) responses agree well with the experimental ones including that caused by longitudinal resonances, and effectiveness of the present method is demonstrated. Furthermore, this theory is applied to the infinitely long interdigital transducer (IDT) to highlight the impact of longitudinal resonances.

Laser Ultrasound Investigations of AlScN(0001) and AlScN(11-20) Thin Films Prepared by Magnetron Sputter Epitaxy on Sapphire Substrates.

The laser ultrasound (LU) technique has been used to determine dispersion curves for surface acoustic waves (SAW) propagating in AlScN/Al2O3 systems. Polar and non-polar Al0.77Sc0.23N thin films were prepared by magnetron sputter epitaxy on Al2O3 substrates and coated with a metal layer. SAW dispersion curves have been measured for various propagation directions on the surface. This is easily achieved in LU measurements since no additional surface structures need to be fabricated, which would be required if elastic properties are determined with the help of SAW resonators. Variation of the propagation direction allows for efficient use of the system’s anisotropy when extracting information on elastic properties. This helps to overcome the complexity caused by a large number of elastic constants in the film material. An analysis of the sensitivity of the SAW phase velocities (with respect to the elastic moduli and their dependence on SAW propagation direction) reveals that the non-polar AlScN films are particularly well suited for the extraction of elastic film properties. Good agreement is found between experiment and theoretical predictions, validating LU as a non-destructive and fast technique for the determination of elastic constants of piezoelectric thin films.

Sc and Er Co-Doped AlN Surface Acoustic Wave Devices

Co-doping AlN film with various elements of rare earth or transition metals has been considered as a good method to significantly improve its piezoelectric responses of surface acoustic wave (SAW) devices. In this paper, we investigated the influences of different Er/Sc atomic percentage ratio on the piezoelectric and acoustic wave properties of the Er and Sc co-doped AlN films prepared by RF magnetron sputtering. Results show that c/a-axis ratio of the AlN films decreases after doped with Sc, whereas those of the AlN films co-doped with Er and Sc increase as the Er/Sc ratio increases. The reasons can be explained from the competitions of Sc and Er elements for occupying the Al atoms sites, and the larger ion radius of the Er compared that of Sc, which causes significant increase of c/a. Resonant frequency and Rayleigh wave velocity of the SAW resonators fabricated using these co-doped AlN films decrease as the Er/Sc ratio increases. Electromechanical coupling coefficient (k2 eff ) of the SAW devices increases after the AlN film is single doped with either Sc or Er element, but decreases after co-doping with both Er and Sc.

ε-Ga2 O3 : An Emerging Wide Bandgap Piezoelectric Semiconductor for Application in Radio Frequency Resonators.

The explosion of mobile data from the internet of things (IoT) is leading to the emergence of 5G technology with dramatic frequency band expansion and efficient band allocations. Along with this, the demand for high-performance filters for 5G radio frequency (RF) front-ends keeps growing. The most popular 5G filters are constructed by piezoelectric resonators based on AlN semiconductor. However, AlN possesses a piezoelectric constant d33 lower than 5pm V-1 and it becomes necessary to develop novel semiconductors with larger piezoelectric constant. In this work, it is shown that strong piezoelectricity exists in ε-Ga2 O3 . High-quality phase-pure ε-Ga2 O3 thin films with a relatively low residual stress are prepared. A switching spectroscopy piezoelectric force microscope (SS-PFM) measurement is carried out and the piezoelectric constant d33 of ε-Ga2 O3 is determined to be ≈10.8-11.2pm V-1 , which is twice as large as that of AlN. For the first time, surface acoustic wave (SAW) resonators are demonstrated on the ε-Ga2 O3 thin films and different vibration modes resonating in the GHz range are observed. The results suggest that ε-Ga2 O3 is a great material candidate for application in piezoelectric devices, thanks to its wide bandgap, strong piezoelectric property, small acoustic impedance, and low residual stress.

A GHz Operating CMOS Compatible ScAlN Based SAW Resonator Used for Surface Acoustic Waves/Spin Waves Coupling

ScAlN/Si, a CMOS compatible material, was used to manufacture GHz operating surface acoustic wave devices, targeting manipulation and control of spin waves via SAW devices. A thin ScAlN piezoelectric layer was deposited on high resistivity (111) oriented Silicon and two port SAW devices were processed using advanced nanolithographic techniques. The Surface Acoustic Wave and Spin Wave coupling was performed via a thin magnetostrictive layer (Ni) placed between the SAWs interdigitated transducers. Both Rayleigh (4.67 GHz) and Sezawa (8.05 GHz) propagation modes could be observed. The amplitude of the S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> parameter around the two resonances was measured for values of the magnetic field <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu _{0}\text{H}$ </tex-math></inline-formula> from −280 to +280 mT, at different angles ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta $ </tex-math></inline-formula> ) between the SAW propagation direction and the magnetic field direction. A maximum decrease of 2.54 dB occurred in S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> for the Rayleigh mode at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu _{\textbf {0}}\text{H}$ </tex-math></inline-formula> = −90 mT, and of 7.24 dB for the Sezawa mode at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu _{0}\text{H}$ </tex-math></inline-formula> = −203 mT, both at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta $ </tex-math></inline-formula> = 45°. These values were extracted from time gated processing of the frequency domain raw data. Nonreciprocity associated to the coupling was analyzed for the two propagation modes.

High-Frequency Surface Acoustic Wave Resonator with Diamond/AlN/IDT/AlN/Diamond Multilayer Structure.

A high-frequency surface acoustic wave (SAW) resonator, based on sandwiched interdigital transducer (IDT), is presented. The resonator has the structure of diamond/AlN/IDT/AlN/diamond, with Si as the substrate. The results show that its phase velocity and electromechanical coupling coefficient are both significantly improved, compared with that of the traditional interdigital transduce-free surface structure. The M2 mode of the sandwiched structure can excite an operation frequency up to 6.15 GHz, with an electromechanical coupling coefficient of 5.53%, phase velocity of 12,470 m/s, and temperature coefficient of frequency of −6.3 ppm/°C. This structure provides a new ideal for the design of high-performance and high-frequency SAW devices.

Highly Sensitive and Selective Surface Acoustic Wave Ammonia Sensor Operated at Room Temperature with a Polyacrylic Acid Sensing Layer.

In this study, polyacrylic acid (PAA) films were deposited onto a quartz surface acoustic wave (SAW) resonator using a spin-coating technique for ammonia sensing operated at room temperature, and the sensing mechanisms and performance were systematically studied. The oxygen-containing functional groups on the surfaces of the PAA film make it sensitive and selective to ammonia molecules, even when tested at room temperature. The ammonia molecules adsorbed by the oxygen-containing functional groups of PAA (e.g., hydroxyl and epoxy groups) increase the membrane’s stiffness, which was identified as the primary mechanism leading to the positive frequency shifts. However, mass loading due to adsorption of ammonia molecules is not a major reason as it will result in a negative frequency shifts. When the PAA coated SAW sensor was exposed to ammonia with a low concentration of 500 ppb, it showed a positive frequency shift of 225 Hz, with both good repeatability and stability, as well as a good selectivity to ammonia compared with those to C2H5OH, H2, HCl, H2S, CO, NO2, NO, and CH3COCH3.

Dual resonance modes in two-port SAW resonator sensors: an analysis through scattering matrix approach

We report dual resonance modes occurring in two-port surface acoustic wave (SAW) resonators attached with typical sensing film and investigated the significance in sensing applications. Two-port SAW resonators operating at 303 MHz frequency were modelled using the scattering matrix approach and resonance frequency characteristics of the resonators were studied for mass loading caused by an arbitrary film attached between the interdigital transducers of the resonator. Depending on the mass loading, symmetric and antisymmetric modes occur around the near resonance frequency of the SAW device. Either a single-mode or both modes are dominant depending on the phase shift caused by the mass loading of the film. Choosing arbitrary film thickness could result in complexity to track the resonance frequency shift and degrade sensing performance. The approach used for analysis can aid to determine the optimum sensing film thickness for two port SAW resonator-based sensors that can exhibit better linearity.

Sensitivity enhancement analysis of frequency tuned-SAW resonator with temperature for sensor applications

Cooling of quartz-SAW devices leads to a noticeable increase in sensitivity. However, the effect of heating on the output characteristics of quartz-SAW resonators in terms of sensitivity has not yet been studied. Here we examine the inverse parabolic temperature characteristics of a quartz-SAW resonator in order to study the effect of temperature rise on the sensitivity. Various characteristics of a quartz SAW resonator are measured such as frequency shifts, phase, and group delay by Vector Network Analyzer (VNA) over a temperature range of 5 °C to 150 °C. It is shown that the sensitivity could be increased at certain combinations when the operating frequency (fo) is tuned away from the centre frequency (fc) along with temperatures higher or lower than room temperature. Sensitivity increases up to 24-fold was achieved when T > 120 °C and fo > fc. This study of temperature tuning of SAW device will be useful for enhancing the sensitivity in various SAW sensing applications for various industrial purposes.

A General FEM Model for Analysis of Third-Order Nonlinearity in RF Surface Acoustic Wave Devices Based on Perturbation Theory.

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.

A Room-Temperature Surface Acoustic Wave Ammonia Sensor Based on rGO/DPP2T-TT Composite Films.

Surface acoustic wave (SAW) sensors based on reduced graphene oxide/poly (diketopyrrolopyrrolethiophene-thieno [3,2-b]thiophene-thiophene) (rGO/DPP2T-TT) composite sensing films for the detection of ammonia were investigated at room temperature in this study. The rGO/DPP2T-TT composite films were deposited onto ST-X quartz SAW resonators by a drop-casting method. FESEM, EDS, and XRD characterizations showed that the rGO/DPP2T-TT composite film was successfully synthesized and exhibited numerous wrinkles and a rough structure, which are crucial for gas adsorption. The frequency response to 500–1400 ppb ammonia shown by the prepared SAW sensor coated with rGO/DPP2T-TT composite film increased linearly as the ammonia concentration increased. The sensor based on a rGO/DPP2T-TT composite film exhibited a positive frequency shift of 55 Hz/ppm, and its frequency response to 500 ppb ammonia was 35 Hz. The sensors thus show promising potential in detecting sub-ppm concentration levels of NH3 at room temperature, which opens up possibilities for applications in the noninvasive detection of NH3 in the breath. As a result, the rGO/DPP2T-TT composite sensor can be a good candidate for in situ medical diagnosis and indoor/outdoor environment monitoring.

Research on Highly Sensitive Strain Sensing Element Based on Surface Acoustic Wave Resonator

SAW strain sensing element is an important part of SAW strain sensor. It is of great significance to design and analyze it. In this paper, the influence of piezoelectric substrate and electrode structure parameters on the performance of SAW strain sensing element is simulated and analyzed, using ST-quartz as piezoelectric material and aluminum as electrode material, a high-performance surface acoustic wave strain sensing element was designed, fabricated and measured. By analyzing the measured results, the strain sensitivity of frequency ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SSF</i> ), strain coefficient of frequency <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SCF</i> ) and temperature coefficient of frequency ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TCF</i> ) of the SAW strain sensing element are 550.9Hz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> , 1.26 ppm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> and −1.22 ppm/°C respectively. The experimental results meet the design requirements well. This research provides a good guidance for the application of SAW strain sensor.

SAW Resonators and Filters Based on Sc0.43Al0.57N on Single Crystal and Polycrystalline Diamond.

The massive data transfer rates of nowadays mobile communication technologies demand devices not only with outstanding electric performances but with example stability in a wide range of conditions. Surface acoustic wave (SAW) devices provide a high Q-factor and properties inherent to the employed materials: thermal and chemical stability or low propagation losses. SAW resonators and filters based on synthetized by reactive magnetron sputtering on single crystal and polycrystalline diamond substrates were fabricated and evaluated. Our SAW resonators showed high electromechanical coupling coefficients for Rayleigh and Sezawa modes, propagating at 1.2 GHz and 2.3 GHz, respectively. Finally, SAW filters were fabricated on /diamond heterostructures, with working frequencies above 4.7 GHz and ~200 MHz bandwidths, confirming that these devices are promising candidates in developing 5G technology.

Influence of Structural Parameters on Performance of SAW Resonators Based on 128° YX LiNbO3 Single Crystal.

The seeking of resonator with high Q and low insertion loss is attractive for critical sensing scenes based on the surface acoustic wave (SAW). In this work, 128° YX LiNbO3-based SAW resonators were utilized to optimize the output performance through IDT structure parameters. Once the pairs of IDTs, the acoustic aperture, the reflecting grid logarithm, and the gap between IDT and reflector are changed, a better resonance frequency of 224.85 MHz and a high Q of 1364.5 were obtained. All the results demonstrate the structure parameters design is helpful for the performance enhancement with regard to SAW resonators, especially for designing and fabricating high-Q devices.