Conventional Surface Acoustic Wave Research Articles

Equivalent Circuit Parameters of Surface-Acoustic-Wave Interdigital Transducers for ZnO/Diamond and SiO2/ZnO/Diamond Structures

Equivalent circuit parameters of surface-acoustic-wave transducers are reported for the [interdigital-transducer (IDT)]/ZnO/diamond, ZnO/IDT/diamond, SiO2/IDT/ZnO/diamond and SiO2/ZnO/IDT/diamond structures. The admittance mismatch, normalized susceptance and transformer turns ratio are calculated for each structure by applying the finite-element method (FEM). Their dependences on the thicknesses of the aluminum electrode, ZnO and SiO2 are examined. Experiments are also carried out to evaluate the admittance mismatch, the results of which agree with the calculated data. It is shown that these structures have large values of admittance mismatch compared with those of conventional surface acoustic wave (SAW) materials such as LiTaO3, LiNbO3 and quartz.

Longitudinally Coupled Resonator Filter Using Edge Reflection of Bleustein-Gulyaev-Shimizu and Shear Horizontal Waves with Various Bandwidths Realized by Selecting Substrates

A conventional surface acoustic wave (SAW) resonator filter requires reflectors with many grating fingers at both sides of the interdigital transducers (IDTs). On the other hand, a small-sized low-loss resonator filter without grating fingers can be realized by utilizing the reflection of a Bleustein-Gulyaev-Shimizu (BGS) wave or a shear horizontal (SH) wave at the edge of a substrate. As a result, the authors have developed longitudinally coupled resonator filters using the reflection of BGS and SH waves at the edges of a substrate. Longitudinally coupled resonator filters on piezoelectric ceramic substrates for the first intermediate frequency (IF) stage have been realized to be low-loss, small-sized and extremely wide bandwidth (fractional bandwidth of 15%) filters as compared to the ordinary resonator filters, and they can have various kinds of bandwidths (2 to 15%) by employing ceramic substrates with various electromechanical coupling factors. On the other hand, the edge-reflection-type resonator filters on LiTaO3 single crystal for various first IF stages have also been realized to be low-loss and small-sized filters. In spite of being a wire-bonding type of IF filter, the package size of this filter is the same as that of the radio frequency (RF) SAW filter.

Surface acoustic wave study of a double layer AlGaAs/GaAs 2D hole system

The temperature and frequency dependence of the surface acoustic wave (SAW) velocity shift has been studied in a double layer 2DHS for 0.34–4.2K and 112–560MHz. The measured velocity shift has been compared to the velocity shift calculated from conventional transport techniques. At ν=1, 2, 4, 6 and 8 maxima in SAW velocity shift have been detected. A hysteretic feature at ν=2 has been observed in both conventional magnetotransport and SAW measurements, which is probably due to slight parallel conduction.

Magnetically transduced surface acoustic wave devices

A type of surface acoustic wave (SAW) device is introduced in which coupling between the transducer and the acoustic medium is achieved using a magnetostrictive thin film. These magnetically transduced SAW devices have several advantages over conventional piezoelectric SAWs, and may expand the functionality of SAW devices in general. Several possible designs are presented, along with data from two prototypes. Results from these devices are promising, and they indicate that several acoustic modes, both surface and bulk, can be stimulated.

Temperature-compensated Love-wave sensors on quartz substrates

Love wave-based microacoustic sensors are suitable for sensing applications in the liquid phase, where conventional Rayleigh surface acoustic wave sensors cannot be used. Typically, they yield even higher sensitivities than comparable Rayleigh SAW devices offer in gas sensing. Up to now, Love-wave devices have been realized using commercially available standard crystal orientations. The latter are optimized to provide intrinsic temperature compensation for conventional SAW or bulk wave devices; however, they yield no temperature compensation for Love modes. To overcome this, new crystal orientations have been considered. In this contribution, we present an alternative crystal cut based on theoretical considerations and its experimental verification.

Analysis of Surface Acoustic Wave Grating Waveguides Considering Velocity Dispersion Caused by Reflectivity

Conventional surface acoustic wave (SAW) grating waveguide analyses ignore the changes in phase velocity in the grating region. In reality, velocity dispersion is caused by the reflectivity of finger electrodes, and phase velocity changes near the stop band. In this paper, a new approximate analytical model of a SAW grating waveguide is proposed. This model considers the dispersion of phase velocity, by placing a wave number along waveguide of a transverse mode in such a way that it becomes a solution of the coupling-of-modes (COM) theory. The results of the new model differ from those of conventional analyses. The frequency characteristics of 2-port resonators on 36.5°Y-X quartz and 45°X-Z Li2B4O7 are measured. Calculations using this new model show good agreement with measurements in terms of resonance frequencies and response levels, while those using conventional analyses vary largely. The adequacy of this model is confirmed by the experimental results.

SAW device modeling including velocity dispersion based on ZnO/diamond/Si layered structures

Surface acoustic wave (SAW) filter properties of ZnO/diamond/Si structures are calculated including velocity dispersion. The conventional SAW device modeling has previously been developed for bulk substrates. However, layered materials exhibit SAW velocity dispersion. The null frequency bandwidth of typical layered ZnO/diamond/Si structures is narrower than that calculated by conventional SAW device modeling techniques due to the velocity dispersion of the layered structures. The null frequency bandwidth of layered structures was calculated by the delta function model and the equivalent circuit model, including velocity dispersion, and compared with the experimental results. The dispersive equivalent circuit (DEC) model for layered structures is also presented. The results of these analysis are compared with the experimental results which show very good agreement.

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

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.

Electro-optic and electro-absorptive modulations of AlGaAs/GaAs quantum well using surface acoustic wave

The surface acoustic wave produced electron absorptive and electro-optic modulation in AlGaAs/GaAs quantum well structures are theoretically analyzed. The quantum well structures are optimized by maximizing the optical confinement of the modal field in the active region and the piezoelectric effect of surface acoustic wave on the quantum wells. The effect of penetration depth of the surface acoustic wave on the number (1–25 periods) of quantum wells, serving as the active region, is being studied. For 1–5 period structures, the quantum wells are designed on the top surface so that a strong piezoelectric effect can be obtained. For the 25-period structure, the quantum wells locate at a depth of two-thirds the acoustic-wave wavelength in order to obtain a uniform surface acoustic-wave-induced electric field. The results show that the single and five quantum well devices are suitable for absorptive modulation and optical modulation, respectively, while a general advantage of the 25-period quantum well modulator can shorten the modulation interaction length and increase the modulation bandwidth. The effective index change of these devices are at least ten times larger than the conventional surface acoustic wave devices. These results make the surface acoustic wave quantum well modulators more attractive for the development of acousto-optic device applications.

Surface Acoustic Wave Filter Composed of Interdigitated Interdigital Transducers and One-Port Resonators

This paper describes a design method for low-loss surface acoustic wave (SAW) filters with a large stop-band attenuation. The method employs a conventional interdigitated interdigital transducer (IIDT) SAW filter and conventional one-port SAW resonators, which are constructed on one chip and connected electrically. The resonators provide a large attenuation in a specified stop band. On the other hand, the resonators act as an element in a matching circuit for the IIDT SAW filter in the passband. An 880 MHz filter was designed and fabricated according to the proposed method. The side-lobe attenuation of 45 dB in the specified stop band and the insertion loss of 2.5 dB in the passband were realized.

High Q metal strip SSBW resonators using a SAW design

An experimental study of metal strip surface skimming bulk wave (SSBW) resonators using a surface acoustic wave (SAW) design is presented. Characteristics of SSBW and SAW resonators fabricated with the same photolithographic mask are compared and discussed. High Q low-loss SSBW resonators are achieved using a conventional two-port SAW resonator design and taking special care of the distance L between both interdigital transducers, the metal thickness h/lambda (lambda=acoustic wavelength) and the finger-to-gap ratio. Best overall performance of the SSBW devices in this study is achieved at L=nlambda/2-lambda/4 (compared with L=nlambda/2-lambda/8 for SAW resonators), h /lambda=1.6% (compared with 2% for SAW), and finger-to-gap ratio close to 1. The best device fabricated shows an unloaded Q of 5820 and an insertion loss of 7.8 dB at 766 MHz. The SSBW resonant frequency shows a stronger dependence on the metal thickness than the SAW one. This problem, however, is readily solved by frequency trimming using a CF(4) plasma etching technique. SSBW resonator can be trimmed by 0.2% down in frequency (compared with 0.05% for SAW) without affecting their performance.

Automated measurement and CAD analysis technique for accurate determination of UHF acoustic resonator equivalent circuit parameters

Many measurement techniques have been reported for accurate determination of equivalent electrical circuit parameters of HF and VHF acoustic resonators. Recent technological advances in the fabrication and processing of conventional bulk- and surface-wave resonators, and in the development of monolithic sputtered film resonators, have extended device operating frequencies into the UHF range. At UHF, resonator package and bond-wire parasitic reactances are nonnegligible and can significantly mask the impedance characteristics of the resonator itself and result in inaccurate determination of device equivalent circuit. This paper describes an automated resonator measurement and data analysis technique that has been developed for accurate determination of UHF acoustic resonator equivalent circuit parameters. The procedure consists of computer-controlled measurement of resonator input reflection coefficient using an HP4191 RF impedance analyzer. Subsequent automatic data transfer, in the form of a circuit analysis file, is used in conjunction with the Super Compact1 RF analysis/optimization software for determination and “removal” of effects of packaged resonator parasitic reactances from the measured data, based on device out-of-band impedance characteristics. The residual resonator motional arm impedance characteristic is calculated from which equivalent circuit element values are readily determined. The HP4191 RF analyzer control software enables determination and identification of individual resonator desired and spurious (anharmonic) resonances in specified search bands. This is extremely helpful when the resonator exact operating frequency is unknown as is often the case for sputtered, thin-film, monolithic devices. Examples will be given showing the results of measurement of UHF resonators including conventional surface acoustic wave (SAW), bulk-wave quartz and lithium niobate resonators, and monolithic sputtered aluminum nitride and zinc oxide and ZnO film resonators.

SAW Convolver Using Multi-Channel Waveguide

Theoretical and experimental results are reported for anew type of surface acoustic wave (SAW) convolver using a multi-channel waveguide fabricated on YZ-LiNbO3 substrate. The convolution signal is obtained from an output inter-digital transducer which picks up the SAW propagating in the direction normal to the waveguide. The F-factor, i.e., the convolution efficiency, is about 15 dBm higher than that of the conventional SAW convolver.

New SECAM Composite SAW IF Filter Separating the Sound and Picture Signals

A new Surface Acoustic Wave (SAW) filter for the French L/SECAM system has been developed. It has two input transducers and two output transducers which are constructed on 128°Y-XLiNbO3 and it separates the input signal into sound and picture signals for use in the L/SECAN system which uniquely utilizes an AM sound signal. The size is the same as that of the conventional SAW IF filter, and it is sealed in a TO-8 can package. Compared with previous models, this new SAW filter enables the TV IF circuit to lower the sound-picture crossbeat interference (the beat noise in speakers) by 3.4 dB and reduces the number of electrical parts.

Radiation conductance of SSBW IDT on rotated Y-cuts of LiNbO3

The letter deals with radiation conductance of an interdigital transducer (IDT) for surface skimming bulk waves (SSBWs) on 41°- and 64°-rotated Y-cuts of LiNbO3. The radiation conductance was estimated theoretically by two methods and was compared with experimental results. The frequency response of SSBW IDTs on these cuts of LiNbO3 is similar to that of a conventional surface acoustic wave transducer, but markedly different from the response obtained when launching SSBWs from an IDT on rotated Y-cuts of quartz.