Rayleigh-type SAW Research Articles

High Order Rayleigh-Type SAW Devices for Advanced 5G Front-ends with Improved Performance

Abstract This paper presents a piezoelectric layered structure composed of a rotated LiNbO3 thin film combined with a diamond film for improved comprehensive performance SAW devices. Theoretical analysis of SAW resonator on the proposed structure is performed to calculate its SAW characteristics including electromechanical coupling coefficient (K2 ), frequency (f), and quality factor (Q). It is found that a high-order Rayleigh mode is effectively excited and exhibits not only high frequency but also large K2 and high Q. The influences of the Euler angles, layer stack configurations of LiNbO3, and the electrode on the SAW properties are investigated systematically to optimize the device performance of the proposed structure. The results show the resonator can operate at frequency of 6.6 GHz with a large K2 of 13.58% and high Q of 2134, which makes the proposed layered structure a good potential solution for high-performance wideband SAW filters operating over 5 GHz.

Analysis of Sezawa mode Rayleigh-type SAWs on ScAlN film/floated electrode layer/ScAlN film/high velocity substrates

Surface acoustic wave (SAW) devices for frequency filters are increasingly required to have high performance in future mobile communications. The coupling factors K 2 for Rayleigh-type SAW (RSAW) on ScAlN film/high velocity substrate structures can be enhanced by introducing polarization-reversal structure into the ScAlN film. However, the growth of polarization-reversal ScAlN films with high crystal orientation would be very difficult. In this study, the Sezawa mode RSAWs on layered structures consisting of ScAlN films with floated intermediate electrode layer/high velocity substrates were analyzed by using Farnell and Adler’s SAW propagation analysis and finite element method. We found that the K 2 values of the Sezawa modes were enhanced by inserting the floated intermediate electrode layer without using polarization reversal structure, which were higher than those of the polarization-reversal ScAlN films/high velocity substrates. The enhancement of K 2 would be due to the improvement of the SAW energy concentration at the ScAlN film surface.

Finite element simulation and experimental study of laser-generated surface acoustic waves on determining mechanical properties of thin film

The laser-generated surface acoustic wave (LSAW) nondestructive testing (NDT) technique is a promising method to characterize the mechanical properties of thin films. In this study, based on the thermoelastic mechanism, a finite element method (FEM) is put forward to simulate the LSAW in the film/substrate structure, and the effect of the temporal and spatial distribution of the Gaussian pulse laser on the Rayleigh-type SAW signals is revealed. For the SiO2 and low dielectric constant (low-k) dense Black Diamond™ (SiOC:H, BD) films with the thickness of 500 and 1000 nm, the typical displacement waveforms of SAW at a series of probing points along the propagation direction are obtained. By analyzing the full width at half maximum (FWHM) of the signal, the optimal NDT experimental conditions for laser are determined with the minimum possible pulse rising time and the linewidth less than 10 μm. Based on the FEM simulation result, the LSAW NDT experiment is carried out and the dispersion curve of SAW is calculated to characterize Young's modulus of the SiO2 and low-k samples. It is found that the experimental results are in good agreement with the simulation results. This study verifies the validity of FEM simulation of LSAW in layered structures containing thin film and that the laser parameters determined by FEM fit perfectly in characterizing the mechanical properties of thin films.

Langmuir-Blodgett Films of Arachidic and Stearic Acids as Sensitive Coatings for Chloroform HF SAW Sensors.

Properties of the Langmuir-Blodgett (LB) films of arachidic and stearic acids, versus the amount of the films' monolayers were studied and applied for chloroform vapor detection with acoustoelectric high-frequency SAW sensors, based on an AT quartz two-port Rayleigh type SAW resonator (414 MHz) and ST-X quartz SAW delay line (157.5 MHz). Using both devices, it was confirmed that the film with 17 monolayers of stearic acid deposited on the surface of the SAW delay line at a surface pressure of 30 mN/m in the solid phase has the best sensitivity towards chloroform vapors, compared with the same films with other numbers of monolayers. For the SAW resonator sensing using slightly longer arachidic acid molecules, the optimum performance was reached with 17 LB film layers due to a sharper decrease in the Q-factor with mass loading. To understand the background of the result, Atomic Force Microscopy (AFM) in intermittent contact mode was used to study the morphology of the films, depending on the number of monolayers. The presence of the advanced morphology of the film surface with a maximal average roughness (9.3 nm) and surface area (29.7 µm2) was found only for 17-monolayer film. The effects of the chloroform vapors on the amplitude and the phase of the acoustic signal for both SAW devices at 20 °C were measured and compared with those for toluene and ethanol vapors; the largest responses were detected for chloroform vapor. For the film with an optimal number of monolayers, the largest amplitude response was measured for the resonator-based device. Conversely, the largest change in the acoustic phase produced by chloroform adsorption was measured for delay-line configuration. Finally, it was established that the gas responses for both devices coated with the LB films are completely restored 60 s after chamber cleaning with dry air.

Evaluation of bulk and surface acoustic waves propagation properties of (K,Na)NbO3 films deposited by hydrothermal synthesis or RF magnetron sputtering methods

In this study, the bulk and surface acoustic waves (BAW and SAW) propagation properties of (K,Na)NbO3 (KNN) films deposited by hydrothermal synthesis or RF magnetron sputtering methods were evaluated to investigate the applicability of such films to high-frequency devices. For the {100} c -oriented KNN epitaxial films deposited by the hydrothermal synthesis method, a BAW phase velocity of 6900 m s−1 and an electromechanical coupling coefficient k t 2 of 8.4% were obtained. From the measured Rayleigh-type SAW properties, a large electromechanical coupling coefficient K 2 of 4.0% in the 1st mode was obtained in the {110} c -oriented KNN epitaxial films. On the other hand, for the preferentially {100} c -oriented KNN film deposited on Pt(111) by RF magnetron sputtering, a BAW phase velocity of 7850 m s−1 and k t 2 of 7.4% were obtained. For the 0th mode of the Rayleigh-type SAW, a propagation loss of 0.13 dB/λ (λ: wavelength) at 440 MHz and a temperature coefficient of frequency of –42 ppm °C−1 were obtained for the {100} c -oriented KNN epitaxial film deposited on STO(100) by the RF magnetron sputtering method.

Acousto-optic Bragg diffraction using longitudinal leaky surface acoustic wave

In this study, to increase the amount of frequency shift by adopting a longitudinal leaky surface acoustic wave (LLSAW) with a higher phase velocity than a Rayleigh-type SAW to a waveguide-type acousto-optic Bragg deflector, a Ti-diffused optical waveguide was fabricated on an X-cut 36°Y-propagating LiNbO3 substrate with a high electromechanical coupling factor for the LLSAW and its diffraction properties were evaluated. The diffraction of the guided light by the LLSAW was observed for the first time. The diffraction efficiency in the TE0 mode was approximately 50% for an optical wavelength of 0.633 µm.

Surface acoustic wave characterization of optical sol-gel thin layers

Controlling the thin film deposition and mechanical properties of materials is a major challenge in several fields of application. We are more particularly interested in the characterization of optical thin layers produced using sol-gel processes to reduce laser-induced damage. The mechanical properties of these coatings must be known to control and maintain optimal performance under various solicitations during their lifetime. It is therefore necessary to have means of characterization adapted to the scale and nature of the deposited materials. In this context, the dispersion of ultrasonic surface waves induced by a micrometric layer was studied on an amorphous substrate (fused silica) coated with a layer of ormosil using a sol-gel process. Our ormosil material is a silica-PDMS mixture with a variable polydimethylsiloxane (PDMS) content. The design and implementation of Surface Acoustic Wave InterDigital Transducers (SAW-IDT) have enabled quasi-monochromatic Rayleigh-type SAW to be generated and the dispersion phenomenon to be studied over a wide frequency range. Young’s modulus and Poisson’s ratio of coatings were estimated using an inverse method.

A surface acoustic wave biosensor for interrogation of single tumour cells in microcavities.

In this study, biological cells are sensed and characterized with surface acoustic wave (SAW) devices utilising microcavities. After tumour cells in media are transported to and trapped in microcavities, the proposed platform uses SAW interaction between the substrate and the cells to extract their mechanical stiffness based on the ultrasound velocity. Finite element method (FEM) analysis and experimental results show that output phase information is an indicator of the stiffness modulus of the trapped cells. Small populations of various types of cells such as MCF7, MDA-MB-231, SKBR3, and JJ012 were characterized and characteristic moduli were estimated for each cell population. Results show that high frequency stiffness modulus is a possible biomarker for aggressiveness of the tumour and that microcavity coupled SAW devices are a good candidate for non-invasive interrogation of single cells.

Comprehensive characterization of surface acoustic wave resonators using relaxor based ferroelectric single crystals

One-port surface acoustic wave resonators (SAW) were fabricated and characterized using Y-cut X propagating relaxor based ferroelectric single crystals of Pb(Mg1/3Nb2/3)O3-33%PbTiO3 and Pb(In1/3Nb2/3)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT). The experimental results demonstrated ultrahigh electromechanical coupling factor K2 of ∼60% for shear horizontal SAW and a relatively strong spurious resonance due to the Rayleigh-type SAW which can be sufficiently suppressed with Au electrode of large thickness. Characteristics of temperature stability, sensitivity to DC bias voltage, and homogeneity for the two resonators were evaluated and compared. The results showed similar instability of domain structure, and PIN-PMN-PT resonators have better temperature stability, but inferior homogeneity compared to that of PMN-33%PT resonators.