Surface Acoustic Wave Velocity Research Articles

Surface Acoustic Wave Passband Control

An apparatus in one example comprises a piezoelectric layer, an input transducer, an output transducer, and at least one electrode set. The input transducer is configured to convert an input signal from an input source to a surface acoustic wave and send the surface acoustic wave from an input portion of the piezoelectric layer to an output portion of the piezoelectric layer. The input transducer comprises a set of input passbands. The output transducer is configured to receive the surface acoustic wave from the output portion of the piezoelectric layer. The output transducer comprises a set of output passbands. The at least one electrode set is configured to apply at least one voltage bias to at least one portion of the piezoelectric layer to create an electric field that controls an acoustic velocity of the surface acoustic wave through the at least one portion of the piezoelectric layer. The at least one electrode set is configured to control one or more of the set of input passbands and the set of output passbands by adjustment of the at least one voltage bias.

Design, Fabrication of Line-focus Lens-less Polyvinylidene Fluoride Transducers and Applications on Measuring Surface Acoustic Waves with V(f, z) Analytical Method

Line-focus-beam ultrasonic material property characterization system enables accurate measurements on the phase velocities of leaky surface acoustic waves(LSAW) or rayleigh-type leaky surface acoustic waves.But in view of the lens of the conventional acoustic microscopy is expensive and difficult to produce,new method of design and fabrication of two line-focus lens-less polyvinylidene fluoride(PVDF) transducers is presented for acoustic microscopy system utilizing a 40 ?m thick piezoelectric PVDF film to construct the active element.The transducers introduced here centre around 5 MHz and 11 MHz respectively.Different from high cost of equipments and measuring the oscillation period on an operation of tone-burst mode,an improved V(f,z) method based on tow-dimensional Fourier transform is developed for the broadband measurements.A defocusing system for measuring surface acoustic waves is established and a non-contact immersion experiment of a polished fused quartz is carried out.The LSAW velocity extracted by V(f,z) analytical technique is compared with the theoretical one and they both are in good agreement.

Laser Ultrasonic Technique for Evaluating Human Dental Enamel

A non-destructive laser ultrasonic surface acoustic wave technique has been demonstrated to quantitatively evaluate the elastic response of human dental enamel. We demonstrate the system performance by measuring surface acoustic wave velocity in sound and demineralised enamel. In addition, progressive measurements were made to monitor the change in the enamel elasticity during a two week remineralisation process. The results are presented and they confirm the efficacy, as well as illuminating the progress, of the treatment.

Numerical Results of Modeling Semiconductor Sensor Layers in SAW Gas Sensors

The paper presents the numerical results of investigations of the layered gas surface acoustic waves sensor. The base electric load of the piezoelectric acoustic line is predicted by the effect of surface acoustic waves velocity changes vs. surface conductivity, which depends on the profile concentration by gas diffused molecules into the porous film. Inside the sensor layer Knudsen’s model of gas diffusion was used.

Analytical Model of Semiconductor Sensor Layers in SAW Gas Sensors

In the paper a new theoretical model for analyzing a surface acoustic wave gas sensor is presented. Basing on the electric load of the piezoelectric acoustic line the effect of surface acoustic wave velocity changes vs. surface conductivity is predicted which depends on the profile concentration of gas molecules diffused into the porous film. Inside the sensor layer Knudsen’s model of gas diffusion was used.

Design of Double Mode SAW Filters Using IDT/(100) ZnO/(111) Diamond Structure

Propagation characteristics of surface acoustic waves (SAWs) in interdigital transducers (IDT)/(100) ZnO/diamond structures are investigated in this study using the finite element method. The effects of electrodes on phase velocity, coupling coefficient, and reflectivity of SAWs in the layered structures are illustrated. The extracted coupling-of-mode parameters are then applied to calculate frequency responses of double mode SAW filters using the transmission matrix method. Simulation results show a tailored filter applicable for wideband code division multiple access systems can be achieved.

Humidity sensing characteristics of Ga-doped zinc oxide film grown on a polycrystalline AlN thin film based on a surface acoustic wave

In this work, the effect of the Ga dopant concentration on the sensing responses of a surface acoustic wave (SAW) humidity sensor with a nanocrystalline ZnO/polycrystalline aluminum nitride (AlN)/Si-layered structure was investigated. Sol–gel derived Ga-doped ZnO was used as the sensing layer. The experimental results showed that the frequency shift of the SAW humidity sensors increased as the Ga dopant concentration increased from 0.0 to 3.0 wt% over a relative humidity (RH) range from 10 to 90% at 25 °C. The largest shift in the frequency response was at approximately 420 kHz for the sensor doped with 3.0 wt% Ga. The sensor demonstrated good short-term repeatability and low hysteresis. In addition, the SAW velocity of the sensors decreased slightly from 5105 to 5040 m/s as the Ga doping concentration increased from 0.0 to 3.0 wt% under 30% RH at 25 °C. The increase in temperature (16–37 °C) led to a reduction in the variability of the sensor transmission characteristics, such as the center frequency and the insertion loss caused by the different RH values (10–90%).

Surface acoustic wave properties of aluminum oxide films on lithium niobate

Aluminum oxide (Al 2O 3) films have been deposited on lithium niobate (LiNbO 3) substrates by electron beam evaporation without any interlayer between them to ensure a good adhesion of the Al 2O 3 films to LiNbO 3 substrates. As Al 2O 3 thin films can sufficiently increase the surface acoustic wave (SAW) velocity, they can be used to improve the performance of the SAW device. The SAW phase velocity in the Al 2O 3/LiNbO 3 structure was found to increase with the insertion of an Al 2O 3 film, which can be attributed to the stiffening effect of the Al 2O 3 layer. The velocity change ratio of SAW was about 4.39% (at 304 MHz) for the Al 2O 3 (9.7 μm)/LiNbO 3 sample. A comparison with other findings in literature reveals that this result is better than what is available from diamond-like carbon/SiC buffer layer/LiNbO 3 structure, whose the velocity change ratio is 2%.

Computation of plate wave dispersion diagrams and surface wave velocities without explicit boundary conditions

We discuss the computation of the band structure of plate waves using the plane wave expansion (PWE) method. This method is generally used to formulate eigenvalue problems to compute dispersion diagrams for solid-solid phononic crystals. We show how the free surface boundary condition can be included implicitly in the form of the PWE solution, thus leading to an efficient eigenvalue problem. This generic method for wave dispersion is non-iterative and does not require an initial guess for the solution. Furthermore, surface acoustic wave velocities can be estimated from the slowest wave for large wave vectors. Examples for a single plate and a multilayer plate are given, and extension to piezoelectric materials is discussed.

AlN substrates and epitaxy results

AbstractAluminum nitride (AlN) is a true bulk‐grown native substrate for III‐nitrides. The crystals are grown by seeded physical vapor transport (PVT) using AlN seeds. AlN has high thermal conductivity (comparable to, and perhaps higher than SiC), high bulk resistivity (>1x1011 Ohm cm), high bulk‐breakdown field (7‐8 MV/cm), the highest surface acoustic wave (SAW) velocity and since it has the smallest lattice constant of the III‐nitrides all AlInGaN compositions grown on AlN are in compression, thus making it easier to grow crack‐free epitaxy. Additionally, AlN is transparent down to nearly 200 nm, making it attractive for deep UV LED structures. AlN has excellent cleavage planes making it suitable for edge‐emitting lasers and low cost manufacturing. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

ZnO nanoparticle surface acoustic wave UV sensor

The response to ultraviolet illumination of ZnO nanoparticles deposited on LiNbO3 substrate was investigated using surface acoustic waves (SAWs) in the wide range of UV wavelengths from 280 to 375 nm. Deposition of ZnO nanoparticles caused a SAW transmission loss of 27 dB at 64 MHz due to the acoustoelectric attenuation. Acoustoelectric change in the SAW velocity by 3.78×10−4 under 375 nm illumination led to downshift in transmitted SAW phase by 5.5° at UV power density of 691 μW/cm2. The spectral measurements show the peak response at 345 nm with corresponding sensitivity on the order of 2.8 ppm/(μW/cm2).

Influence of the preparation temperature on the SAW velocity of partially oxidized Fe thin films

The influence of the preparation temperature on the surface acoustic wave (SAW) propagation velocity of iron thin films deposited by DC magnetron sputtering has been studied by High Resolution Brillouin Spectroscopy (HRBS). A clear different elastic behaviour has been found for sample grown at 200 K substrate temperature. Numerical simulation has been used to reproduce experimental elastic data and it is possible to relate the difference in elastic response in different samples to the existence of a FeO layer among other oxides. This effect is discussed in relation with the iron oxidation type that also affects the magnetic properties of iron thin films on silicon substrates.

Surface acoustic wave device properties of (B, Al)N films on 128° Y– X LiNbO 3 substrate

A c-axis orientated aluminium nitride (AlN) film on a 128° Y– X lithium niobate (LiNbO 3) surface acoustic wave (SAW) device which exhibit a large electromechanical coupling coefficient ( k 2) and a high SAW velocity property, is needed for future communication applications. In this study, a c-axis orientated (B, Al)N film (with 2.6 at.% boron) was deposited on a 128° Y– X LiNbO 3 substrate by a co-sputtering system to further boost SAW device properties. The XRD and TEM results show that the (B, Al)N films show highly aligned columns with the c-axis perpendicular to the substrate. The hardness and Young's modulus of (B, Al)N film on 128° Y– X LiNbO 3 substrates are at least 17% and 7% larger than AlN films, respectively. From the SAW device measurement, the operation frequency characteristic of (B, Al)N film on 128° Y– X LiNbO 3 is higher than pure AlN on it. The SAW velocity also increases as (B, Al)N film thickness increases (at fixed IDT wavelength). Furthermore, the k 2 of (B, Al)N on the IDT/128° Y– X LiNbO 3 SAW device shows a higher value than AlN on it.

Laser generation of surface acoustic modes guided by copper lines of sub-micron width on silicon

Surface acoustic waves guided by a copper line embedded in a silica film on a silicon wafer were generated and detected optically using the laser-induced transient grating technique. Lines as narrow as ∼0.2 μm yield a good signal despite the much larger size of the laser spot. The phase velocity of the guided mode is slightly lower than the surface acoustic wave velocity in the thin film structure. Good correlation between the acoustic frequency and the electrical resistivity of the copper lines results from the dependence of both measurements on the line width.

Brillouin light scattering characterization of the surface acoustic wave velocity in sp2 allotropes thin films

Carbon thin films have been deposited by DC magnetron sputtering at different substrate temperatures ranging from 200 K to 400 K. The influence of the preparation substrate temperature on the elastic properties has been evidenced by means of the High Resolution Brillouin Spectroscopy. Thus, the surface acoustic wave (SAW) velocity evolution could be assessed for the different samples. The observed variation is analysed in terms of the relative population of sp2 allotropes phases forming the film.

Ultrasonic Microspectroscopy of ZnO Single Crystals Grown by the Hydrothermal Method

A new set of acoustical physical constants for ZnO was obtained by ultrasonic microspectroscopy (UMS) using very conductive and resistive (001), (100), and (101)ZnO specimens, grown by the hydrothermal method. The specimens were selected from a lot of small ZnO crystals evaluated with the velocity of leaky surface acoustic waves (LSAWs) on a water-loaded specimen surface, in order to identify proper specimens or proper measurement positions for bulk-wave velocity measurements. The constants were determined with measured bulk-wave velocities, according to the determination procedures developed previously. Their accuracies were estimated by comparing the measured LSAW velocities with the calculated ones using the determined constants, within 3.1 m/s. We observed LSAW velocity distributions and bulk-wave velocity dispersions for some specimens that were related to the resistivity distributions on the specimen surfaces and inside the specimens. We established experiment procedures to apply our UMS technology to ZnO crystals in this study. This ultrasonic method is useful for further understanding ZnO crystal growth processes in the hydrothermal method. This application is extended to other class-6mm crystals.

Determination of elastic constants of generally anisotropic inclined lamellar structure using line-focus acoustic microscopy

A methodology for measuring elastic constants of different phases in materials with lamellar microstructure by line-focus acoustic microscopy is developed. The material microstructure investigated is modeled by generally anisotropic multilayers arbitrarily inclined to the sample surface on which acoustic microscopy measurements are performed. To calculate surface acoustic wave (SAW) propagation in such structures quasi-static effective elastic constants are determined and compared with calculated frequency-dependent constants. As a model material, practically important, Ti-6Al-2Sn-4Zr-2Mo alloy is selected. Time-resolved line-focus acoustic microscopy experiments are performed on a Ti-6242 alpha/beta single colony (Ti-6Al-2Sn-4Zr-2Mo alloy) and on a Ti-6Al alpha-phase single crystal for which elastic constants of different phases are determined using inversion of measured SAW velocities. To validate the experimental methodology, SAW velocities in an X-cut quartz crystal are measured as a function of sample orientation angle and compared with predictions based on the known elastic moduli of quartz.

Acoustoelectric effects in very high-mobility p-SiGe/Ge/SiGe heterostructure

Measurement results of the acoustoelectric effects [surface acoustic waves (SAW) attenuation and velocity] in a high-mobility p-SiGe/Ge/SiGe structure are presented. The structure was low-energy plasma-enhanced chemical vapor deposition grown with a two-dimensional (2D) channel buried in the strained Ge layer. The measurements were performed as a function of temperature (1.5–4.2 K) and magnetic field (up to 8.4 T) at different SAW intensities at frequencies 28 and 87 MHz. Shubnikov–de Haas-like oscillations of both SAW attenuation and the velocity change have been observed. Hole density and mobility, effective mass, quantum and transport relaxation times, as well as the Dingle temperature were measured with a method free of electric contacts. The effect of heating of the 2D hole gas by the electric field of the SAW was investigated. Energy relaxation time τε and the deformation potential constant determined.

Effect of substrate piezoelectricity on surface acoustic wave propagation in humidity-sensitive structures with porphyrin layers

The impact of air humidity on surface acoustic wave (SAW) propagation in different piezoelectric substrates (lithium niobate, lithium tantalate, and gallium nitride on sapphire) with nanostructured meso-tetra(4 sulfonatophenyl) porphyrin (TPPS4) overlays has been investigated. The humidity-induced increase in SAW attenuation is proportional to the electromechanical coupling constant of the substrate and is attributed to the viscoelastic loss due to interaction of water adsorbing TPPS4 material with electric field of the SAW. The humidity-induced decrease in SAW velocity does not depend on the substrate piezoelectric properties and is explained by the changes in TPPS4 layer mechanical properties due to adsorbed moisture.

Experiments for self-temperature-compensated characteristics of SAW gas sensor at fundamental and third-harmonic frequencies

A novel surface acoustic wave (SAW) gas sensor with self-temperature-compensated characteristics is proposed. Any type of piezoelectric crystal substrate irrelevant to their temperature coefficients of SAW velocities, can be adopted in this gas sensor. The sensing dynamic range can be extended utilising both the fundamental and third-harmonic frequency signals. Experimental results at the 75 MHz fundamental frequency and the 225 MHz third-harmonic frequency showed validity of the proposed sensor structure.