Showing papers on "Surface acoustic wave published in 1998"

Surface Acoustic Wave Devices for Mobile and Wireless Communications

Abstract: Fundamentals of Surface Acoustic Waves and Devices: Introduction. Basics of Piezoelectricity and Acoustic Waves. Principles of Linear Phase SAW Filter Design. Equivalent Circuit and Analytic Models for a SAW Filter. SomeMatching and Trade-Off Concepts for SAW Filter Design. Compensation for Second-Order Effects in SAW Filters. Designing SAW Filters for Arbitrary Amplitude/Phase Response. Interdigital Transducers with Chirped or Slanted Fingers. IDT Finger Reflections andRadiation Conductance. Techniques, Devices and Mobile/Wireless Applications: Overview of Systems and Devices. SAW Reflection Gratings and Resonators. Single-Phase Unidirectional Transducers for Low-Loss Filters. RF and Antenna-Duplexer Filters forMobile/Wireless Transceivers. Other RF Front-end and Inter-stage Filters for Mobile/Wireless Transceivers. SAW IF Filters for Mobile Phones and Pagers. Fixed-Code SAW IDTs for Spread-Spectrum Communications. Real-Time SAW Convolvers for Voice and Data Spread-Spectrum Communications. Surface Wave Oscillators and Frequency Synthesizers. SAW Filters for Digital Microwave Radio, Fiber Optic, and Satellite Systems. Postscript. Subject Index.

Sound velocity of AlxGa1−xN thin films obtained by surface acoustic-wave measurements

Abstract: To determine the sound velocity in wurtzite AlxGa1−xN, we have used surface acoustic-wave (SAW) delay lines on AlxGa1−xN/c-Al2O3. AlxGa1−xN films with compositions from x=0 to x=1 were grown by plasma-induced molecular beam epitaxy. Starting from published data, we fine tuned the values of the elastic moduli used in numerical calculations such that the simulated and measured dispersion of the SAW were in good agreement. Based on these values, the surface and bulk acoustic-wave velocities of single-crystal AlxGa1−xN were determined as functions of the composition. The resulting SAW velocities ranged from 3700 to 5760 m/s for GaN and AlN, respectively.

State of the art in wireless sensing with surface acoustic waves

Abstract: Surface acoustic wave (SAW) devices can be turned into novel identification and sensor elements (transponders) that do not need any power supply and may be interrogated wirelessly. Such a transponder picks up an electromagnetic request signal and stores it until all echoes caused by multipath propagation have died away. Then, a characteristic response signal is beamed back to the interrogator unit. In radio-link sensors, a physical or chemical quantity influences the propagation properties of the SAW and consequently changes the response pattern of the device. This contribution surveys the operating principle of such sensors and their state-of-the-art performance. The discussion is supported by illustrative examples such as temperature sensors and sensors for mechatronic applications.

Passive remote sensing for temperature and pressure using SAW resonator devices

Abstract: Wireless sensing using passive sensors based on surface acoustic wave (SAW) technology is necessary for many applications. In this paper a new sensor design that uses the differential frequency output from two SAW resonators (SAWR) for temperature and pressure measurement is presented. The sensor, which consists of two SAWRs on the same substrate with different SAW propagation directions, relies on the variations of the SAW propagation velocity to measure environmental quantities such as pressure or temperature. The aim of this approach is to suppress the disturbing influences of the RF link (radio channel) between the interrogation unit and the passive sensor device. In this case, the output signal is a frequency difference and does not depend on changes in the radio channel during the transmission of the sensor signal.

Comparison between BAW and SAW sensor principles

Abstract: A comparison is given between piezoelectrically excited bulk acoustic wave (BAW) and surface acoustic wave (SAW) elements with respect to their primary sensitivity functions and principal capabilities for sensor applications. The importance of mode purity for high dynamic range sensors is emphasized. Characteristic sensor examples are reviewed, and the special demands on the electronics for BAW and SAW elements in the sensor field are described (e.g., cable problem, wireless SAW sensors). For a fair evaluation, a performance figure, SQ, defined as the product of reduced sensitivity S and resonator Q-value, is introduced. The potential of alternative piezoelectric materials for future sensor developments is discussed briefly.

Surface acoustic wave device package and method

Abstract: A method for packaging an acoustic wave device (10) without contaminating an active area (12) disposed on a face (14) thereof, including steps of: providing a substrate with a top (30) having conductive pads (18), bonding stud bumps (20) to a periphery (22) of the face (14) of the acoustic wave device, disposing a dam (26) onto the top (30) of the substrate and inside of the location of the conductive pads (18), aligning and connecting the stud bumps (20) to the conductive pads (18) on the top of the substrate to form electrically conductive interconnections between the acoustic wave device (10) and the substrate (16), flowing an underfill material (28) at the periphery (22) of the acoustic wave device and around the interconnections such that the underfill material (28) stops at a boundary (32) defined by the dam (26), and curing the underfill material (28) to mechanically reinforce and protectively encapsulate the interconnections.

Surface Brillouin scattering study of the surface excitations in amorphous silicon layers produced by ion bombardment

Abstract: Thin amorphous silicon layers on crystalline silicon substrates have been produced by argon-ion bombardment of (001) silicon surfaces. Thermally induced surface excitations characteristic of this example of a soft-on-hard system have been investigated by surface Brillouin scattering (SBS) as a function of scattering-angle and amorphous-layer thickness. At large scattering angles or for sufficiently large layer thickness, a second peak is present in the SBS spectrum near the low-energy threshold for the continuum of bulk excitations of the system. The measured spectra are analyzed on the basis of surface elastodynamic Green's functions, which successfully simulate their detailed appearance and identify the second peak as either a Sezawa wave (true surface wave) or a pseudo-Sezawa wave (attenuated surface wave) depending on the scattering parameters. The attributes of the pseudo-Sezawa wave are described; these include its asymmetrical line shape and variation in intensity with ${k}_{\ensuremath{\parallel}}d$ (the product of the surface excitation wave vector and the layer thickness), and its emergence as the Sezawa wave from the low-energy side of the Lamb shoulder at a critical value of ${k}_{\ensuremath{\parallel}}d.$ Furthermore, the behavior of a pronounced minimum in the Lamb shoulder near the longitudinal wave threshold observed in the experiments is reported and is found to be in good agreement with the calculated spectra. The elastic constants of the amorphous silicon layer are determined from the velocity dispersion of the Rayleigh surface acoustic wave and the minimum in the Lamb shoulder.

A multilayer structure for Love-mode acoustic sensors

Abstract: A novel multilayer structure, consisting of polymer/SiO 2 /ST-quartz, has been evaluated for Love-mode acoustic sensors. The properties of these new devices have been compared with those of SiO 2 /quartz and polymer/quartz devices. Mass sensitivity, insertion loss, temperature coefficient of the oscillation frequency and frequency stability are studied as a function of the layer thickness. Optimized devices exhibit higher sensitivity than both the SiO 2 /quartz and the polymer/quartz devices produced here. Reduced temperature coefficient of frequency can be obtained in the polymer/SiO 2 /ST-quartz devices due to a compensating effect of the polymer and SiO 2 films. Some of the devices have been operated efficiently in water with good stability, which is promising for biosensing applications.

History of SAW devices

Abstract: This paper gives a historical account of the development of Rayleigh-wave, or surface acoustic wave (SAW), devices for applications in electronics. The subject was spurred on initially by the requirements of pulse compression radar, and became a practical reality with the planar interdigital transducer, dating from 1965. The accessibility of the propagation path gave rise to substantial versatility, and a huge variety of devices were developed. Passive SAW devices are now ubiquitous, with applications ranging from professional radar and communications systems to consumer areas such as TV, pagers and mobile phones. The paper describes the extensive work, particularly in the 1970s, to investigate SAW propagation in crystalline media, including piezoelectric coupling diffraction and temperature effects. This led to identification of many suitable materials. Concurrently, many devices began development, including pulse compression filters, bandpass filters, resonators, oscillators, convolvers and matched filters for spread spectrum. In the 1970s, many of these became established in professional systems, and the SAW bandpass filter became a standard component for domestic TV. In the 1980s and 9Os, SAW responded to the new call for low-loss filters, particularly for mobile phones. With losses as low as 2 dB required (and subsequently achieved) at RF frequencies around 900 MHz, a raft of new technologies was developed. Additionally, for IF filters special techniques were evolved to reduce the physical size needed for narrow bandwidths. Such devices are now manufactured in very large quantities. In order to satisfy these needs, new types of surface wave, particularly transverse leaky waves, were investigated, and materials using such waves now have their place alongside more traditional materials.

Wireless sensing using oscillator circuits locked to remote high-Q SAW resonators

Abstract: This paper introduces a method of wireless read out of high Q surface acoustic wave (SAW) resonator sensors. The resonator is excited by a short RF pulse and decays after switching off the interrogating signal. In the measurement system, a gated phase locked loop (GPLL) locks to the resonance frequency of the SAW resonator within a few bursts. Then the frequency of the GPLL oscillator is synchronized to the resonance of the sensor and can be measured easily. The concept is intended to yield an alternative to interrogators with expensive signal processing. Considering the inherent limitations, the proposed system presents a low cost solution for temperature, force, torque, etc. measurements. We describe the sensors, the signals, and the implemented system. Results of temperature measurements using quartz resonators are presented, and merits and disadvantages are discussed.

Surface acoustic wave device

Abstract: PROBLEM TO BE SOLVED: To provide surface acoustic wave device whose frequency characteristic is small in change with lapse of time and which has high reliability. SOLUTION: Although this surface acoustic wave device connects a surface acoustic wave element 11 with a package 12 through an adhesive layer 16, the layer 16 is one-sidely provided on one of short sides of the element 11 of the layer 16 and more than half of the element 11 is floated up from a mounting plane 14. Then, even though a volumetric change occurs when the adhesive layer is stiffened, etc., the transformation of the surface acoustic wave element is drastically reduced. The floating part of the element 11 is also mechanically supported by connecting it to the package 12 through bonding wires 17.

Performance optimization of surface acoustic wave chemical sensors

Abstract: Acoustic wave devices coated with a thin layer of chemoselective material provide highly sensitive chemical sensors for the detection and monitoring of vapors and gases. In this work, a variety of coating materials and coating deposition techniques have been evaluated on surface acoustic wave (SAW) devices. A novel thin film deposition technique, matrix assisted pulsed laser evaporation (MAPLE), is utilized to coat high quality polymer films on SAW devices, and conventional pulsed laser deposition is used to deposit a passivation layer of diamond-like-carbon on a SAW device surface to prevent water adsorption. In addition, chemoselective coatings are formed by covalent attachment of functionalized species to the silica surface of SAW devices. The self-assembled monolayer or near monolayer structures are designed to populate the SAW device surface with the desirable hexafluoroisopropanol moeity. The rapid kinetic signals achievable with the various coated SAW sensors during vapor tests are examined as a function of the coating material and the quality of the thin films. In parallel to the thin film deposition, growth, and vapor testing, the electrical characteristics of the SAW sensor have been characterized. The quality factor and residual phase noise of polymer coated SAW devices are examined, and a prediction of the theoretical limit of the phase noise performance of the loop oscillator is made.

Surface acoustic wave filter

Abstract: PROBLEM TO BE SOLVED: To provide an element having arbitrary band width and having sharp shoulder characteristics by connecting plural resonators, which are composed of IDT electrodes coated with protecting films, on a piezoelectric substrate to a ladder type circuit and preparing the protecting films on the respective resonators more than two kinds of materials and/or making the thickness of protecting films different at two spots at least. SOLUTION: Protecting films 1 of respective surface acoustic wave(SAW) resonators are mutually separated and the thickness of films are made different in areas more than two spots or the kinds of protecting films 1 are made different more than two kinds. When the protecting films 1 are loaded on the SAW resonators, the resonance frequency of SAW resonators is lowered by a sonic velocity difference from a substrate S. Therefore, Δf=fa-fr (fr: resonance frequency, fa: anti-resonance frequency) is reduced rather than before loading. The thickness of protecting films 1 is controlled so as to make Δf different for respective resonators 2. Thus, by constituting a ladder type SAW filter by mixing the resonators 2 of large and small Δf, sharp shoulder characteristics and frequency characteristics flattened within a pass band are provided. COPYRIGHT: (C)2000,JPO

A surface-acoustic-wave gyro sensor

Abstract: This paper explains two novel methods to detect angular velocity by using a surface-acoustic-wave (SAW) device. In both methods, Coriolis forces, which act on the particles vibrating in the standing wave of a SAW, are applied. A novel gyro sensor is planned based on one of the two methods. For accurate fabrication, the dimensions of the electrodes are designed by using equivalent-circuit models. A SAW gyro sensor using a Rayleigh wave that propagated on a 128 ° Y -cut LiNbO 3 3 inch wafer with an operating frequency of 15 MHz has been designed and fabricated on trial.

Giant acoustoelectric effect in gaas/linbo3 hybrids

Abstract: The acoustoelectric effect in a hybrid of a strong piezoelectric material and a semiconductor layer containing a two-dimensional electron system is investigated. Caused by the very strong interaction between a surface acoustic wave and the mobile carriers in the semiconductor, the acoustoelectric effect is very large as compared to other materials, which might be interesting for device applications. Moreover, the tunability of the sheet conductivity of the electron system enables us to tune the magnitude of the acoustoelectric effect over a wide range. We present experimental results for a GaAs/LiNbO3 layered hybrid system at room temperature and describe our experimental findings quantitatively using a recently developed model calculation.

Monitoring of NH3 gas by LB polypyrrole-based SAW sensor

Abstract: Surface acoustic wave (SAW) devices have been fabricated and tested as sensors of NH3 in gaseous phase Polypyrrole films, prepared by Langmuir-Blodgett (LB) technique, have been deposited onto the surface of SAW devices as gas absorbent layers Simultaneous measurements of SAW phase velocity and attenuation have been carried out in order to investigate the sensing mechanisms The sensor response shows high sensitivity towards NH3 gas and excellent selectivity with respect to main interfering gases (CO, CH4, H2, O2), at room temperature The low cross-sensitivity permits the recognition of NH3 gas as one component of a mixture of interfering gases

A method for calibrating the line-focus-beam acoustic microscopy system

Abstract: Absolute accuracy of the line-focus-beam (LFB) acoustic microscopy system is investigated for measurements of the leaky surface acoustic wave (LSAW) velocity and attenuation, and a method of system calibration is proposed. In order to discuss the accuracy, it is necessary to introduce a standard specimen whose bulk acoustic properties, (e.g., the independent elastic constants and density) are measured with high accuracy. Single crystal substrates of gadolinium gallium garnet (GGG) are taken as standard specimens. The LSAW propagation characteristics are measured and compared with the calculated results using the measured bulk acoustic properties. Calibration is demonstrated for the system using two LFB acoustic lens devices with a cylindrical concave surface of 1-mm radius in the frequency range 100 to 300 MHz.

Surface acoustic wave device mounted with a resin film and method of making same

Abstract: It is an object on the invention to provide a SAW device sealed by resin, which is low priced and suited for decreasing its thickness and weight and requires no particular course for processing a substrate, and a method for fabricating the same. A functional surface of a piezoelectric substrate provided with interdigtal transducers and a mounting surface of a circuit substrate are opposed to each other to form vibration cavities for surface wave propagation areas therebetween. Electrical power is supplied to the piezoelectric substrate from the circuit substrate via electrode pads formed on respective inner surface of both the substrate and bumps inserted therebetween. A resin film adheres to the respective inner surfaces of both the substrates except the surface wave propagation areas to shield the vibration cavity from the environmental space. Apertures are previously formed at predetermined parts of the resin film by means of a laser. A resin film is temporarily adhered to the inner surface of the circuit substrate for instance, and positioning of both the substrates are adjusted relative to each other. Thereafter, both the substrates are permanently adhered to each other by hot-pressing them, and sealing is completed.

Study on Surface Acoustic Wave Characteristics of SiO2/Interdigital-Transducer/ZnO/Diamond Structure and Fabrication of 2.5 GHz Narrow Band Filter

Abstract: Surface acoustic wave (SAW) characteristics of the SiO2/interdigital-transducer(IDT)/ZnO/diamond structure were studied theoretically and experimentally. It was found that the 2nd mode in this structure can provide a zero temperature coefficient of frequency (TCF) as well as high velocity of 10,000 m/s and a large electromechanical coupling coefficient of 1.4%. Utilizing this wave, a 2.5 GHz narrow-band SAW filter was successfully fabricated with IDTs of 0.9 µm finger width, which resulted in superior characteristics for a retiming filter with a small insertion loss of 6.7 dB, Q value of 660 and small frequency deviation of 100 ppm in the temperature range from -40 to 85°C. The insertion loss is smaller than any other retiming filters which have ever been reported with quartz, a conventional SAW material, and also the frequency deviation with temperature is smaller than that in the case of ST-cut quartz.

Development of a saw gas sensor for monitoring so2 gas

Abstract: We have developed a new type of SO 2 gas sensor by applying a particular inorganic thin film on SAW (surface acoustic wave) devices. The sensor consists of twin SAW oscillators with a centre frequency of 54 MHz fabricated on LiTaO 3 piezoelectric single crystals. One delay line of the sensor is coated with a CdS thin film that selectively adsorbs and desorbs SO 2 , while the other is uncoated for use as a stable reference. Deposition of CdS thin film has been carried out by the spray pyrolysis method using an ultrasonic nozzle. Mass loading and electric-field changes induced by the SO 2 gas adsorbed onto the CdS film result in corresponding frequency shifts directly proportional to the gas concentration. The relative change in the frequency of the two oscillators is monitored with a digital signal-processing circuit. SO 2 sensor properties investigated include sensitivity, response time and repeatability. The sensor shows promising performance as a microsensing tool and is capable of measuring concentrations in air less than 200 parts per billion of SO 2 .

Viscoelastic behavior of antibody films on a shear horizontal acoustic surface wave sensor.

Abstract: To study the viscoelastic behavior of antibody films on a surface acoustic wave device, we have measured the influence of multiple layers of antibodies onto the propagation of the wave. Attenuation and sound velocity variation caused by up to 20 layers have been measured. The results can be interpreted with the propagation of a viscously damped Love wave in a film with an extremely low velocity of sound. From our results, we conclude that, for the one- or two-layer films normally used in acoustic wave immunosensing, a pure mass effect is dominant. For thick films, a saturation of the sensor response is observed.

Growth of ZnO thin films on interdigital transducer/Corning 7059 glass substrates by two-step fabrication methods for surface acoustic wave applications

Abstract: ZnO films were grown on interdigital transducer (IDT)/Corning 7059 glass substrates by RF planar magnetron sputtering using two-step fabrication methods for surface acoustic wave (SAW) applications. The crystalline structure of the as-deposited ZnO films was characterized by x-ray diffraction (XRD) and x-ray rocking curve analysis. The SAW properties, including coupling coefficient and insertion loss, were evaluated and compared with the theoretical results. ZnO films deposited by the two-step fabrication method exhibited a lower insertion loss and a closer agreement between the experimental coupling coefficients and the corresponding theoretical values in comparison with films deposited by the one-step fabrication method. The results could be useful in the design of high-coupling low-loss SAW devices.

Propagation Characteristics of Surface Acoustic Waves on Langasite

Abstract: The propagation characteristics of surface acoustic waves (SAW) on La3Ga5SiO14 were investigated by both experimental and numerical methods. The experimental results of the SAW velocity and the coupling coefficient (k2) on X-cut and Y-cut substrates were in good agreement with the numerical results using the material constants reported previously. However, the experimental results of the temperature coefficient of delay (TCD) differed from that of the numerical calculations. So, a modification of the temperature coefficients of the material constants was performed numerically by the measured data using the direct search of optimization method. The numerical results obtained using the new constants were in good agreement with the experiment result on the X-cut and Y-cut substrates. Other cuts were also studied using the new constants. Then it was confirmed theoretically and experimentally that the temperature stable cut was located at (0°, 140°, 22.5°) cut with k2 of 0.32% and TCD (second-order coefficient) of 5.2×10-8/°C2.

Acoustic sensors for physical, chemical and biochemical applications

Abstract: Since the late 1950s, it has been recognized that one can make sensitive high-resolution sensors by exploiting the effects of various measurands on propagating ultrasonic waves. The earliest and best-known acoustic-wave sensor is the quartz-crystal microbalance (QCM) employed as a mass sensor for monitoring film thickness in thin-film deposition systems and by researchers studying chemical interactions with thin films deposited on the crystals. H. Wohltjen first demonstrated that a rugged and sensitive gravimetric acoustic sensor could be made in the form of a delay-line oscillator employing an electronic amplifier and a surface acoustic wave (SAW) delay line operating at hundreds of MHz. Additional ultrasonic sensor modes and structures have been demonstrated: flexural modes in thin micromachined plates and narrow rods, thickness resonators made by thin-film deposition rather than mechanical thinning of single-crystal piezoelectrics, and transverse mode devices such as SAW devices having surface modifications or a single-crystal plate-mode device. Demonstrated applications of these devices include: measuring the density and viscosity of liquids, determining the rheological properties of polymer films, quantitative detection of the concentrations of volatile organic vapors with sensor arrays, detecting the outputs of a gas chromatographic column, and both selective and sensitive detection of biochemically active compounds by employing antibody-antigen, enzyme-substrate, and other receptor-protein pairs.

Surface acoustic wave devices and their manufacturing method

Abstract: A surface acoustic wave device has a main substrate; a comb-like electrode formed on one of the main surfaces of said main substrate; and a supplementary substrate joined with the other main surface of said main substrate, wherein said supplementary substrate has a smaller thermal expansion coefficient and a larger thickness than said main substrate.

Surface acoustic wave linear motor using silicon slider

Abstract: Using a silicon fabricated slider, the output force and the maximum traverse velocity of a surface acoustic wave motor has been improved up to 12 times larger force and twice faster speed than the previous motor which used a multi contact points slider. To obtain the high output force, large contact area between the slider and the stator transducer is required. Therefore a silicon slider was developed and tested. As a result, the maximum output force of 3.5 N and the maximum traverse velocity of 0.65 m/s were obtained. The maximum output force of 3.5 N was 90 times of the transducer weight. Such a high output force performance is produced by high power density of surface acoustic wave devices and friction drive.

Spatially resolved photoluminescence in GaAs surface acoustic wave structures

Abstract: The interaction between a surface acoustic wave (SAW) and the excitonic photoluminescence (PL) in GaAs SAW structures is investigated. The dependence of the PL on the SAW amplitude and illumination intensity is explained by a simple model based on the field-induced ionization of the excitons and on the screening of the SAW electric field by photogenerated carriers. Microscopic PL constitutes a powerful technique for spatially resolving electric-field distributions in SAW structures.

Surface and pseudosurface acoustic waves in superlattices

Abstract: We study theoretically the propagation of surface acoustic waves on the surface of a semi-infinite, periodic superlattice consisting of anisotropic, elastic layers of cubic symmetry. By the use of a transfer-matrix method the dispersion relations of surface modes predominantly polarized in the sagittal plane and also those polarized horizontally, are derived. Pseudosurface-wave (PSW) branches are also found inside the frequency bands of bulk acoustic waves. A remarkable feature is the existence of a PSW branch, which links a surface wave branch below the bulk bands to a branch inside a frequency gap. We present numerical examples for AlAs/GaAs superlattices with an AlAs top surface or a GaAs top surface. Focusing of ballistically propagating surface and pseudosurface waves is also studied.