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Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 3 • Date May 1995

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Displaying Results 1 - 25 of 26
  • Ultrafast generation of acoustic waves in copper

    Page(s): 331 - 338
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    The ultrafast generation of acoustic waves in copper films is investigated with a femtosecond optical pump and probe technique. By studying the generation at times before the electrons and the lattice come into equilibrium, the strength of their interaction can be measured and the dynamics of ultrafast electron diffusion can be studied. The acoustic strain pulses observed are bipolar in shape with exponential tails that are much broader than expected from simple thermoelastic stress generation. This can be explained by the supersonic diffusion of electrons over distances larger than the optical skin depth. The nonequilibrium diffusion equations governing stress generation are nonlinear, and are solved numerically. Using a linearized formulation, we also solve them analytically to a good approximation. The acoustic strain profile provides a 'snapshot' of the initial spatial temperature distribution of the lattice, thus allowing a sensitive probe of the nonequilibrium dynamics of the diffusion. The electron-phonon coupling constant can be estimated directly from the acoustic pulse duration, provided that the sound velocity and thermal conductivity are known. In general, the relaxation and diffusion of carriers is specific to the sample in question, whether metal or semiconductor, suggesting the use of this method for thin film characterization.<> View full abstract»

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  • Multi-layered ultrasonic transducers employing air-gap structure

    Page(s): 339 - 344
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    Aiming at developing miniaturized ultrasonic image sensors with high spatial resolution, this paper proposes multi-layered ultrasonic transducers employing air-gap structure. Theoretical analysis suggests that if the device is optimally designed, its performance is little affected by the layer supporting the air-gap structure, and that low-loss, wide-bandwidth transducers having practical mechanical strength could be developed. The transducer consisting of polymer/Pyrex-glass/ZnO/Pyrex-glass layers was fabricated, and a conversion loss of 11.6 dB and -3 dB relative bandwidth of 7.8% were obtained. The transducer was also applied to nondestructive testing, and its basic performance was shown.<> View full abstract»

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  • Piezoelectric properties of zinc oxide films on glass substrates deposited by RF-magnetron-mode electron cyclotron resonance sputtering system

    Page(s): 345 - 350
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    There are various types of electron cyclotron resonance (ECR) sputtering systems, DC-mode, RF-mode, etc. We reported that zinc oxide (ZnO) films on glass substrates deposited by DC-mode ECR and RF-mode ECR sputtering systems had shown excellent piezoelectric properties and c-axis orientations. The RF-mode ECR sputtering system was capable of depositing ZnO films on glass substrates without evidence of column and fiber grains in cross section and driving a 1.1 GHz fundamental Rayleigh surface acoustic wave (SAW). In this paper, the properties of ZnO film deposited by an RF-magnetron-mode ECR sputtering system, which has added magnets to the outside of a cylindrical zinc metal (Zn) target of the RF-mode ECR sputtering system, are investigated. It is confirmed that the SAW filters using ZnO films on an interdigital transducer (IDT)/glass substrate deposited by the RF-magnetron-mode ECR sputtering exhibit almost the same effective electromechanical coupling factors (keff) as the theoretical keff values calculated by finite element method (FEM) using the constants of ZnO single crystal (measured keff values are 97% of the theoretical values) and 0.6/spl sim/3.7 dB lower insertion loss in comparison with the films deposited by the DC-mode ECR and the RF-mode ECR sputtering system.<> View full abstract»

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  • ZnO films on {001}-cut <110>-propagating GaAs substrates for surface acoustic wave device applications

    Page(s): 351 - 361
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    A potential application for piezoelectric films on GaAs substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on {001}-cut <110>-propagating GaAs substrates are investigated in this article, including SAW velocity, effective piezoelectric coupling constant, propagation loss, diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 /spl mu/m and with films of different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K/sup 2/ and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO/sub 2/ or Si/sub 3/N/sub 4/ on {001}-cut GaAs samples are reported using two different techniques: 1) knife-edge laser probe, 2) line-focus-beam scanning acoustic microscope. It was found that near the <110> propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the <100> direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.<> View full abstract»

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  • Theoretical study on SAW characteristics of layered structures including a diamond layer

    Page(s): 362 - 375
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    Diamond has the highest surface acoustic wave (SAW) velocity among all materials and thus can provide much advantage for fabrication of high frequency SAW devices when it is combined with a piezoelectric thin film. Basic SAW properties of layered structures consisting of a piezoelectric material layer, a diamond layer and a substrate were examined by theoretical calculation. Rayleigh mode SAW's with large SAW velocities up to 12,000 m/s and large electro-mechanical coupling coefficients from 1 to 11% were found to propagate in ZnO/diamond/Si, LiNbO/sub 3//diamond/Si and LiTaO/sub 3//diamond/Si structures. It was also found that a SiO/sub 2//ZnO/diamond/Si structure can realize a zero temperature coefficient of frequency with a high phase velocity of 8,000-9,000 m/s and a large electro-mechanical coupling coefficient of up to 4%.<> View full abstract»

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  • Line-focus acoustic microscopy measurements of Nb/sub 2/O/sub 5//MgO and BaTiO/sub 3//LaAlO/sub 3/ thin-film/substrate configurations

    Page(s): 376 - 380
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    Line-focus acoustic microscopy has been used to measure the phase velocities of surface acoustic waves on bare MgO and bare LaAlO/sub 3/, and on Nb/sub 2/O/sub 5//MgO and BaTiO/sub 3//LaAlO/sub 3/ thin-film/substrate configurations. The thin films are polycrystalline materials. The substrates are anisotropic single-crystals. The measured angular variation of the surface acoustic wave velocities has been used to determine the elastic constants of MgO substrate and Nb/sub 2/O/sub 5/ thin-film. It has been assumed that the Nb/sub 2/O/sub 5/ films may be considered as essentially isotropic. The measurements for LaAlO/sub 3/ and BaTiO/sub 3//LaAlO/sub 3/ show anomalies which are attributed to twinning in the LaAlO/sub 3/ substrate.<> View full abstract»

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  • SAW velocity measurement of crystals and thin films by the phase velocity scanning of interference fringes

    Page(s): 381 - 386
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    We present principle and application of a novel noncontact velocity measurement of surface acoustic waves (SAW) on crystals and thin films using laser interference fringes scanned at the phase velocity of SAW. The scanning interference fringes (SIF) are produced by intersecting two laser beams with a frequency difference. The SAW velocity within the laser beam spot is measured as the ratio of observed SAW frequency and predetermined wave number of the SIF. The frequency measurement can be quite precise because of a large number of generated SAW carriers and amplitude enhancement effect. The SAW velocity measurement is free from the water loading effect accompanying the leaky SAW measurements. This principle was successfully applied to evaluate Si/sub 3/N/sub 4/ and SiO/sub 2/ films deposited on Si [001] surface.<> View full abstract»

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  • Elastic properties measurement of glass layers fabricated on silicon wafers for microelectronics and micromachines

    Page(s): 387 - 391
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    Elastic properties such as the Young's modulus, the Poisson's ratio and the density of Si-B-O glass layers fabricated on [100] silicon substrates by the flame hydrolysis deposition method were measured. Thicknesses of the layers were about 20 /spl mu/m. It was found that the Young's modulus decreased with the boron dopant concentration. The Poisson's ratio was about 0.26 regardless of the boron dopant concentration. The measured elastic properties will be used in the design of micromachines fabricated with silicon substrates and glass layers.<> View full abstract»

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  • High temperature stable GHz-range low-loss wide band transducers and filter using SiO/sub 2//LiNbO/sub 3/, LiTaO/sub 3/

    Page(s): 392 - 396
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    GHz-range low-loss transducers and filters are required for communication systems, especially mobile telephone communication systems. Many types of low insertion-loss transducers and filters utilizing the high electromechanical coupling coefficient (K/sup 2/) materials such as LiNbO/sub 3/ and LiTaO/sub 3/ have been developed. Unfortunately, these materials have large temperature coefficients of the frequency (TCF). In this paper, SAW substrates with high coupling coefficients and low propagation attenuations and small temperature coefficient of frequency in the GHz-range are theoretically and experimentally investigated. The experimental results show very low propagation loss of 0.02 dB//spl lambda//sub 0/ and larger K/sup 2/ than those of the substrates of LiNbO/sub 3/ and LiTaO/sub 3/ at the TCF of below -5 ppm//spl deg/C at 1/spl sim/2 GHz-range. The low-loss filter results using internal reflection types of IDT show the insertion loss of about 2.9 dB at 1 GHz and 4.9 dB at 2 GHz under the TCF's of 0 and +20 ppm//spl deg/C. These materials are applicable for devices at GHz-range because SiO/sub 2/ thickness is very thin such as below 1 /spl mu/m and the center frequency shift of the filter versus SiO/sub 2/ thickness is very small.<> View full abstract»

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  • Deposition parameter studies and surface acoustic wave characterization of PECVD silicon nitride films on lithium niobate

    Page(s): 397 - 403
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    Silicon nitride films were deposited by a plasma enhanced chemical vapor deposition technique using silane-ammonia as the reactant gas mixture. The influence of the process parameters such as flow ratio of the reactant gases, pressure, substrate temperature, RF power, time of deposition and electrode spacing on the deposition and etch rates were investigated. From the matrix of deposition conditions, the deposition parameters for high quality films applicable to surface acoustic wave (SAW) technology were found. Experimental results on the acoustic loss, reflectivity and velocity dispersion for the fabricated devices are presented.<> View full abstract»

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  • The characterization of sputtered polycrystalline aluminum nitride on silicon by surface acoustic wave measurements

    Page(s): 404 - 409
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    Polycrystalline aluminum nitride films were deposited on Si/sub 3/N/sub 4/ coated [100] silicon substrates by the reactive sputtering method. We have carried out experiments to evaluate the effect of AlN material parameters on the SAW characteristics. The SAW transducers were fabricated by forming interdigitated Al electrodes on top of the AlN films and transmission measurements made over the frequency range from 50 MHz to 1.5 GHz. The SAW characteristics were correlated with material parameters of crystallite orientation, grain size, surface morphology and oxygen concentration. A key material parameter affecting the SAW characteristics was found to be the preferred degree of crystallite orientation with the c-axis normal to the plane of the substrate. The better oriented the AlN grains, the stronger the SAW response, the higher the SAW phase velocity, and the lower the insertion and propagation losses over the entire frequency range of measurement. Above 500 MHz the propagation losses of the well oriented films followed a frequency squared dependence only slightly higher than the reported values for the best epitaxial films. The coupling factors deduced from the transducer characteristics are in the upper range of values reported by Tsubouchi for epitaxial AlN films deposited on the basal plane of sapphire. There was a strong correlation between the X-ray diffraction intensity from the (002) planes and the oxygen content in the films.<> View full abstract»

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  • Surface acoustic wave characterization of PECVD films on gallium arsenide

    Page(s): 410 - 415
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    Surface-acoustic-wave (SAW) measurement techniques can be effectively used to determine the acoustic properties of dielectric and piezoelectric films. Such films can be used for the development of semiconductor-integrated microwave-frequency surface and bulk acoustic wave devices. The acoustic properties of silicon nitride, silicon oxynitride, silicon carbide, and TEOS glass, deposited by plasma-enhanced chemical-vapor-deposition (PECVD) on GaAs, have been characterized using linear arrays of SAW interdigital electrodes operating in the harmonic mode over the frequency region from 30 MHz to above 1.0 GHz. The elastic constants of these amorphous films have been determined by fitting theoretical dispersion curves to the measured SAW velocity characteristics. Frequency-dependent SAW propagation-loss values have been determined from the observed linear change in loss as a function of transducer separation. Preliminary measurements of the temperature coefficient of frequency (TCF) for SAW propagation of the films on GaAs are also given.<> View full abstract»

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  • Effect of the beam-vessel angle on the received acoustic signal from blood

    Page(s): 416 - 428
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    In order to explore the feasibility of algorithms to determine the three dimensional (3D) velocity magnitude from the received ultrasonic blood echo from a single line of sight, the signal from small sample volumes is studied as a function of beam-vessel angle. As opposed to previous treatments of the effect of the beam-vessel angle on the received acoustic signal, a wideband signal is transmitted and the returned signal in each sample volume is analyzed. High-resolution experimental M-mode images of radio-frequency (rf) echo signals are used to visualize the flow in individual regions of interest. These experiments confirm the predictions of a theoretical model for the signal and its second moment. It is shown that the two major effects limiting the correlated signal interval are the spread of axial velocities within the sample volume and the transit time across the lateral beam width. Particularly for small beam-vessel angles, the spread of velocities limits the correlated signal interval. In addition, the experimental results demonstrate that accurate velocity estimation for low volume flow rates and particularly for large beam-vessel angles may involve detection of changes in the correlation magnitude. For low volume flow rates, the shape of the correlation surface can be affected by small regions of blood with a strong scattering intensity located near the initial region of interest.<> View full abstract»

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  • Synthetic aperture imaging for small scale systems

    Page(s): 429 - 442
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    Multi-element synthetic aperture imaging methods suitable for applications with severe cost and size limitations are explored. Array apertures are synthesized using an active multi-element receive subaperture and a multi-element transmit subaperture defocused to emulate a single-element spatial response with high acoustic power. Echo signals are recorded independently by individual elements of the receive subaperture. Each method uses different spatial frequencies and acquisition strategies for imaging, and therefore different sets of active transmit/receive element combinations. Following acquisition, image points are reconstructed using the complete data set with full dynamic focus on both transmit and receive. Various factors affecting image quality have been evaluated and compared to conventional imagers through measurements with a 3.5 MHz, 128-element transducer array on different gel phantoms. Multielement synthetic aperture methods achieve higher electronic signal to noise ratio and better contrast resolution than conventional synthetic aperture techniques, approaching conventional phased array performance.<> View full abstract»

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  • A study of quartz tuning fork resonators in the second flexural mode

    Page(s): 443 - 450
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    Quartz tuning fork resonators in the second flexural mode have been studied in less detail than those in the fundamental mode. It is necessary for quartz tuning fork resonators in the second flexural mode to be carefully designed from the viewpoint of total vibrational system design including the mounting leads and capsules, since vibration in the base portion of quartz tuning forks is more readily transmitted to the mounting leads and the capsules as a result of the larger amplitude in the base portion in the second flexural mode than in the fundamental mode. We will discuss here the characteristics in detail on the basis of experimental data and theoretical analysis. Considerations are presented in order to achieve optimal design.<> View full abstract»

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  • Estimating mean scatterer spacing with the frequency-smoothed spectral autocorrelation function

    Page(s): 451 - 463
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    The quasiperiodicity of regularly spaced scatterers results in characteristic patterns in the spectra of backscattered ultrasonic signals from which the mean scatterer spacing can be estimated. The mean spacing has been considered for classifying certain biological tissue. This paper addresses the problem of estimating the mean scatterer spacing from backscattered ultrasound signals using the frequency-smoothed spectral autocorrelation (SAC) function. The SAC function exploits characteristic differences between the phase spectrum of the resolvable quasiperiodic scatterers and the unresolvable uniformly distributed (diffuse) scatterers to improve estimator performance over other estimators that operate directly on the magnitude spectrum. Mean scatterer spacing estimates are compared for the frequency-smoothed SAC function and a cepstral technique using an AR model. Simulation results indicate that SAC-based estimates converge more reliably over smaller amounts of data than cepstrum-based estimates. An example of computing an estimate from liver tissue scans is also presented for the SAC function and the AR cepstrum.<> View full abstract»

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  • Quantization bit rate reduction in scanning tomographic acoustic microscopy

    Page(s): 464 - 477
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    The imaging capability of the scanning laser acoustic microscope has been enhanced by the addition of a quadrature detector for holographic imaging and rotational and frequency-varying hardware for tomographic reconstruction. Because of the expansion of data acquisition capability, the memory-intensive demands placed on the processing computer by these modifications require efficient methods of representing and storing the tomographic data while retaining the quality of image reconstruction. This paper reports the performance evaluation of low bit-rate data acquisition. Results show the feasibility of high-quality imaging at bit-rate savings at the level of 33%.<> View full abstract»

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  • Table of contents - Front cover

    Page(s): i
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    Freely Available from IEEE
  • [Inside front cover]

    Page(s): ii
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    Freely Available from IEEE
  • [Back inside cover]

    Page(s): iii
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    Freely Available from IEEE
  • Information for Contributors - Back Cover

    Page(s): iv
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    Freely Available from IEEE
  • First Call for Papers - 1995 IEEE International Ultrasonics Symposium

    Page(s): 478 - 479
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    Freely Available from IEEE
  • Final Announcement and Call for Papers - The 22nd International Symposium on Acoustical Imaging

    Page(s): 480
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    Freely Available from IEEE
  • Call for Papers - Special Issue on Applications

    Page(s): 481
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    Freely Available from IEEE
  • Call for Papers - Special Issue on Finite Element Applications in Ultrasonics

    Page(s): 482
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    Freely Available from IEEE

Aims & Scope

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control focuses on the theory, design, and application on generation, transmission, and detection of bulk and surface mechanical waves.

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Editor-in-Chief
Steven Freear
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