橋本 研也

This paper deals with a miniaturized surface acoustic wave (SAW) filter employing two IDTs, two weighted reflectors and a multi-strip coupler (MSC). In the structure, the width-weighted reflectors are to be responsible for the frequency response of the filter. The reflectors are optimally designed to realize the specified frequency response by taking account of the SAW reflectivity of width-weighted electrodes. The filter having 3dB bandwidth of 4.0 MHz was designed at the centre frequency of 200 MHz and fabricated on 128°YX-LiNbO3. The total acoustic length of the filter was reduced to less than 5 mm. The experimental result obtained was in good agreement with the theoretical prediction.

This paper describes selective area PZT-preparation based on PZT precursor etching for sol-gel method, and its application to the fabrication of PZT disk transducers of nearly 1 mu m thickness without repeating any process. Using this method, we show that PZT disk transducers of 0.8 mu m thickness can be fabricated only by a single process. The piezo electricity of the transducers are discussed by ultrasonic pulse echo method.

This paper describes the leaky surface acoustic wave (LSAW) propagation characteristics at a discontinuous region in a grating structure. First, the dispersion relation of LSAWs propagating under a multielectrode-type grating is analysed. Then, the LSAW propagation on the discontinuous region is characterised by simply assuming that the LSAW behaviour under periodic part of the structure is identical with that under a totally periodic grating structure. It is concluded that the phase lag considerably decreases at the discontinuous region. This suggests that the energy storing effect may be weakened at the region where the periodic structure is broken. The simulation of one-port LSAW resonators shows that device performances are sufficiently evaluated only by taking account of the constant phase lag for a simulation tool based on the coupling-of-modes theory.

The irradiation of ultrasonic waves to liquid causes liquid flow toward the propagation direction of the ultrasonic waves. This paper proposes the application of this phenomenon, called acoustic streaming, to the development of micro-actuators such as micro-manipulators for small particles and micro-pumps for liquid. Since high-frequency ultrasonic waves induce acoustic streaming very efficiently only in the vicinity of the transducer, micro-manipulators are shown to be realised by using a two-dimensional ultrasonic transducer array and controlling electrical power supplied to each transducer. It is also concluded that micro-pumps could be developed by combining a transducer array with a topographic channel structure for liquid flow. © 1998, The Institute of Electrical Engineers of Japan. All rights reserved.

It is theoretically shown that highly piezoelectric boundary waves are propagated in various structures based on the combination of Si/SiO2/LiNbO3, and that the range of existence of these boundary waves is quite large. The non-leaky boundary waves propagating in [001]-Si-< 100 >/SiO2/YX-LiNbO3 structure with SiO2 thickness of 0.8 lambda possess the electromechanical coupling factor of 12% and temperature coefficient of velocity of 15ppm/degrees C, and are found to be applicable to practical devices, In particular, because of very confined energy distribution close to the SiO2/NbO3 boundary, devices employing the structure need Si and LiNbO3 substrates of only a few wavelength thickness. This suggests that devices could be developed by various methods such as wafer bonding and thin him deposition techniques.

A finite element study of a 3-electrode finger periodic SAW structure of ST-cut quartz was studied. This multiperiod analysis allows more interaction of the bulk acoustic wave modes with the surface acoustic wave modes. Plane strain assumptions were used to enable a two-dimensional analysis of straight crested acoustic waves in the structure. Adaptive finite element meshes were employed to reduce the size of the finite element problem. The results of this study may be useful for a full-scale finite element modeling of SAW resonators and filters. The effects of periodically missing or shifted fingers may be useful for generating/controlling leaky SAW. The physical difference between the modes shapes of the two fundamental SAW modes were compared and contrasted. The numerical results of frequency spectrum versus electrode geometry and electrode height, respectively, confirms empirical experience with these SAW modes. Possible couplings of the SAW modes with the BAW modes are shown. These couplings lead to SAW modes with some BAW mode characteristics. The couplings may be useful for improving frequency temperature behavior or generation of leaky SAW modes. On the other hand, they may lead to poor frequency temperature behavior or low Q devices.

The paper deals with the derivation of simple polynomials characterising SAW reflection by metallic gratings with various widths and thicknesses. Such polynomial approximation makes it possible to estimate COM parameters in makedly reduced computational time. Far very sophisticated SAW devices, this is of great use to develop high-speed simulation and design tools based on COM method. In the present study, it is shown how simply and accurately the SAW reflection by aluminium (Al) gratings on 128 degrees YX-LiNbO3 substrates is charcaterised by polynomial approximation.

This paper describes the preparation of piezoelectric ZnO films by target facing type of sputtering (TFTS) method. The method enables to generate high density plasma under a low gas pressure of the order of 10(-3)-10(-4) Torr. The film is grown by reactive sputtering of metal Zn target in the ambient gas of pure O-2. Although the high density plasma is basically generated by DC power source, a spark killer is successfully employed to stabilise glow discharge and enables to deposit ZnO films under a low gas pressure. The effects of the sputtering conditions on the ZnO films are discussed in detail, and it is shown how DC-TFTS method is effective in the preparation of high-quality ZnO films by applying them to surface acoustic wave devices operating in VHF and UHF ranges.

We describe the ultrasonic properties of lead zirconate titanate (PZT) thin films prepared by the sol-gel method. Tt is shown that the PZT thin film exhibits efficient transduction of bulk and surface acoustic waves in UHF-SHF range. A conversion loss of less than 4dB is achieved for bulk wave excitation and detection at 1.7 GHz, where the electromechanical coupling factor k(t) reaches 30%. This indicates that the PZT thin film is promising for use in the development of large-bandwidth resonators and filters in modern communication systems as well as for high-frequency ultrasonic transducer applications.

This paper describes theoretical studies on piezoelectric shear-horizontal (SH) type boundary waves propagating along the surface of a separation between piezoelectric and non-piezoelectric materials. According to the guiding mechanism for this type of waves, it is expected that the application of highly piezoelectric materials results in a wide range of existence of combinations for various materials. Numerical analysis shows that SH-type leaky boundary waves exist for combinations of Si/LiNbO3, Si/LiTaO3 and YAG/LiNbO3. The electromechanical coupling factor K-2 Of 10.0% is obtainable for SH-type leaky boundary waves in [001]-Si(110)/175 degrees YX-LiNbO3, in which the velocity is about 4,465 m/s and the attenuation due to leaky nature is substantially zero.

The paper proposes the method for the fast and accurate analysis of SAW propagation under metallic gratings consisting of multiple electrodes having unequal width, pitch and/or thickness: the grating structure is promising for developing single-phase unidirectional transducers (SPUDTs) with controlled passband shapes. The finite element method (FEM) is applied to the electroded region to take account of the effect of electrode thickness (mass-loading effect), and spectral domain analysis (SDA) to the substrate region for rapid computation. Electrical properties of the grating are determined by applying Aoki's theory to the results of FEM and SDA at the boundary. Two kinds of typical metallic gratings were analysed, and the unidirectionality was discussed for SPUDTs employing these grating structures.

The paper describes how the propagation loss alpha of leaky surface acoustic wave (LSAW) is dependent upon the Al thickness h of grating electrodes and rotation angle theta for rotated Y-X LiTaO3. Since the energy leak of LSAW originates from the coupling of the slow-shear field component with other components through the surface boundary conditions, zero alpha can be realised when the slow-shear component is decoupled. This means that the optimal theta giving zero alpha should change with h as well as the surface electrical boundary conditions. Since relatively large h of 0.07-0.1 wavelengths is needed for present LSAW devices, the optimal theta shifts to 40-42 degrees from the conventional value of 36 degrees. Thanks to the minimised propagation loss, experimental results showed that device performances are markedly improved only by increasing theta to circa 42 degrees from 36 degrees. We also describe the state-of-the-art of the performances obtainable in commercially available LSAW devices based on 42 degrees YX-LiTaO3.

Study of piezoelectricity and ultrasonic properties was done for PZT films of 0.22 to 2.65 mu m thickness prepared by sol gel method. First, bulk wave transducers were fabricated employing the PZT films deposited on a Si substrate, and their transducer performances based on thickness-longitudinal vibration were measured. Ultrasonic pulse echo trains were clearly observed with the bias voltage of 30 V. The minimum conversion loss reached 3.8 dB at 1.75 GHz. Next, an SAW delay line employing the PZT film was fabricated on a sapphire substrate. With the bias voltage of 30 V, the responses which may be attributed to SAWs were observed. The possibility of developing SAW devices on Si substrates was also experimentally discussed. Finally, a simple bulk wave PZT film/Si diaphragm resonator was fabricated by anisotropic etching of Si substrates, and the anti-resonance Q factor of about 84 was obtained at 1.7 GHz.

The irradiation of ultrasonic waves to liquid causes liquid flow toward the propagation direction of the ultrasonic waves. This paper proposes the application of this phenomenon, called acoustic streaming, to the development of micro-actuators such as micro-manipulators for small particles and micro-pumps for liquid. Since high-frequency ultrasonic waves induce acoustic streaming very efficiently only in the vicinity of the transducer, micro-manipulators are shown to be realised by using a two-dimensional ultrasonic transducer array and controlling electrical power supplied to each transducer. It is also concluded that micropumps could be developed by combining a transducer array with a topographic channel structure for liquid flow.

In this paper we propose a method of analysing surface acoustic waves (SAWs) propagating obliquely under a metallic grating with finite thickness. The discrete Green function originally developed for SAWs longitudinally propagating under the metallic grating is modified, and applied to the characterisation of obliquely propagating SAWs. The method is applied to the analysis of Rayleigh SAM's obliquely propagating on 128 degrees YX-LiNbO3 (128-LN), and the result is shown to be in good agreement with experiments, Leaky SAWs obliquely propagating on 36 degrees YX-LiTaO3 (36-LT) are also analysed and compared with the result obtained for 128-LN.

Liquid streaming induced by ultrasonic waves in VHF range is discussed. Theoretical analysis shows that the radiation pressure and net body force caused by liquid streaming are proportional to the second and the fourth power of frequency, respectively. Experiments were performed using a ZnO-flim/cover-glass composite transducer operated at 241 MHz. Strong Liquid streaming was observed and the water surface above the transducer was lifted to 5 mm with the acoustic power of 40 mW. This value roughly agreed with the theoretical prediction.

The paper describes how leaky surface acoustic wave (LSAW) propagation characteristics on LiTaO3 depend upon its rotation angle when the Al electrode thickness is increased. It is shown that the propagation loss arising from leaky nature changes parabolically with both the film thickness and rotation angle, and becomes zero when they are properly chosen. This means that even when the relatively thick electrodes are needed, zero propagation loss is always achieved by properly determining the rotation angle for LiTO3. When the electrode thickness is 0.07 similar to 0.1 wavelengths, for example, LSAWs on the 40 similar to 42 degrees Y-X LiTaO3 offer zero propagation loss without deteriorating other characteristics. Ladder filters for 800 MHz range were fabricated, which essentially need thick Al electrodes. As is predicted by theoretical calculation, experimental results showed that if the rotation angle theta is increased to circa 42 degrees from the conventional value of 36 degrees, the insertion loss and shape factor are improved by 0.7 dB and 0.26, respectively The result gives a valuable guideline for determining the optimal rotation angle of LiTaO3 to be used for high performance LSAW filters, which are one of the key components in RF sections of mobile communication systems.

The paper describes the development of a general-purpose simulator for high performance leaky surface acoustic wave (LSAW) devices. The derivation of the coupling-of-modes (COM) parameters for the simulator is based on a method developed originally for surface transverse wave devices: the method can skillfully takes the effect of back-scattered bulk acoustic waves into consideration. All the COM parameters for the analysis are determined as a function of electrode thickness, and the simulation itself is carried out in exactly the same way with the conventional COM analysis. A ladder-type LSAW filter on 36 degrees YX-LiTaO3 and an interdigitated-interdigital transducer type filter employing longitudinal-type LSAWs on (011)-Li2B4O7 are analysed, which concludes how effectively the developed simulator is applicable to assessing LSAW device performances. present simulator is demonstrated.

The paper describes the free distribution of the computer softwares developed for surface acoustic wave (SAW) and surface transverse wave (STW) device simulation. The complete sets of the softwares including mathematical subroutines are distributed in the form of FORTRAN source codes, where the logs and outputs of the test run as well as the manuals are also attached. Functions and applications of the softwares are discussed in detail. Free delivery and maintenance including related announcements of the software are entirely carried out through Internet. The registered users may execute, modify, and analyse the softwares for their computer environment without any prior consultation.

The paper describes the extended discrete Green function theory for the analysis of multi-electrode interdigital transducers having electrodes of unequal pitch and/or width. Such a configuration is effectively used to develop unidirectional transducers. First, the field distribution on double- and triple-electrode gratings is calculated by generalisation of Aoki and Ingebrigtsen's method. Then, the discrete Green function is derived by representing the total field as a sum of contributions from various grating modes. Finally, the impulse response model for transducers having various electrode configurations is derived from the discrete Green function.

Aiming at developing miniaturized ultrasonic image sensors with high spatial resolution, this paper proposes multilayered 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.

This paper proposes a method of deriving the discrete Green function for the analysis of surface acoustic wave (SAW) propagation and excitation under metallic-grating structures with finite thickness. The method uses the finite-element method (FEM) for the analysis of the grating electrode region, while the spectral domain analysis (SDA) is used for the analysis of the substrate region. This approach takes account of the mass-loading effect of grating electrodes as part of electrical quantities in a substrate, and makes it possible to employ Bl phi tekjaer et al.'s theory for rapid computation. Rayleigh SAWs and leaky SAWs propagating under metallic-grating structures on 128 degrees YX-LiNbO3 and 36 degrees YX-LiTaO3 (36-LT), respectively, were analysed. The dispersion relation calculated by the present method agreed very well with that obtained by the perturbation theory It is also shown that the electromechanical coupling factor for leaky SAWs on 36-LT increases with the thickness of grating electrodes, which is primarily due to the change in the SAW energy concentration near the surface.

This paper discusses the application of ZnO/Pyrex-glass composite diaphragm structure to thin-film bulk acoustic resonators (FBARs). Analysis of ZnO/Pyrex-glass composite diaphragm structure showed for thickness-longitudinal vibration that zero temperature, coefficient of frequency with relatively large electromechanical coupling constant of about 20% is realised for the second- and third-order resonances as well as for the fundamental resonance. An FBAR employing the ZnO/Pyrex-glass composite diaphragm structure was fabricated, and Q values of 970 and 858 were obtained, respectively. for the fundamental and second-order resonances at 298.7 MHz and 497.5 MHz.

The discrete Green function theory, which takes the mass-loading effect into consideration, is developed, and the propagation and excitation characteristics of a Bleustein-Gulyaev-Shimizu wave (BGSW) under metallic gratings of finite thickness are discussed. Acoustic fields in the grating electrodes are expressed as a sum of analytical solutions. while those in a substrate as the effective, acoustic impedance matrix. The effective permittivity for the grating structure, which gives the discrete Green function, is derived by minimising a functional defined by the acoustic fields at the boundary. Velocity dispersion of BGSW propagating on Al-grating/PZT-5H and Au-grating/PZT-5H structures is shown. and the mass-loading effect on the BGSW propagation and excitation is discussed.

This paper aims at discussing the possibility of applying an air-gap structure to the development of composite diaphragm ultrasonic transducer arrays. Analysis suggests that low-loss, wide-bandwidth transducers could be realised using Pyrex-glass/ZnO/Pyrex-glass composite diaphragms fabricated on an air-gap. It is also shown that the transducer performance is considerably improved with another polyimide matching layer. A transducer consisting of a Pyrex-glass/Zno/Pyrex-glass composite diaphragm on an air-gap was experimentally fabricated, and its basic performance was shown.

The paper proposes Lamb wave devices employing ZnO-film/Al-foil composite structure for the application to liquid and gas sensors. Theoretical analysis suggested that in particular, the velocity of the lowest-order antisymmetrical A(o) mode is significantly reduced by loading liquids, which is mainly due to the mass-loading effect. This was experimentally confirmed from the centre-frequency shift in water-loaded devices. It is concluded that devices based on A(o) mode possess the possibility of developing a mass-density sensor in liquids.

The paper describes the development of a simple but effective diagnosis system for SAW devices based on one of the time-frequency distributions, spectrogramme analysis. The system is realised by employing a personal computer, auxiliary memories and some input/output devices, by which SAW device response measured by a vector network analyser is data-processed, and the result is visualised to be displayed on a CRT. The system was applied to the analysis and identification of the second-order effects in SAW devices, and some visualised results were demonstrated.

The paper describes the development of high performance underwater ultrasonic transducers employing ZnO/Pyrex-glass composite diaphragm structure on a Si substrate. It is shown that the transducer successfully radiates and detects ultrasonics at the fundamental frequency of 155 MHz with a relative -3 dB band width of 11.1% and a minimum transduction loss of 4.3 dB, both of which are in good agreement with theoretical prediction. The possibility of the application of the transducer to sensor devices is described for the measurement of ultrasonic wave velocity in liquid.

The paper describes the use of weighted Tchebycheff-polynomials as the expansion functions for the boundary element method, by which SAW-IDTs with arbitrary metallisation ratio r (finger width relative to finder periodicity) were analysed. First, it is shown that the order of the polynomials N should be increased with r to keep the accuracy within a specified value: N = 2 results in negligible error for commonly employed IDTs with r of less than 0.9. Secondly, the r dependence of IDT input admittance was analysed and IDT behaviours were characterised at both fundamental and harmonic frequencies.

The paper proposes high frequency ultrasonic transducers employing a ZnO-film/Al-foil composite structure for application to non-destructive testing (NDT). Analysis suggested the possibility of realising wide bandwidth and high efficiency transducers by properly determining the Al foil and ZnO film thicknesses. It was experimentally shown that, being air-backed, the transducer efficiently launches ultrasonics into water at 102 MHz. No spurious response was observed, and a -3 dB bandwidth of 6.3 MHz was obtained. A simple experiment to confirm the applicability of the transducer to NDT was also performed.

The paper has attempted to employ the expansion functions of the charge distribution on an electrode proposed by Skeie and Ronnekleiv for the boundary element method (BEM) analysis of interdigital transducers (IDTs). The accuracy and extremely rapid convergence of the analysis were confirmed by the calculation of static capacitances for several types of IDTs. The analysis was also applied to the characterisation of a floating electrode unidirectional transducer with a large number of electrodes. This confirmed that BEM mentioned in the present paper could be used as an effective tool for SAW device simulation.

The paper describes acousto-optic Bragg diffraction by an IDT-launched, frequency-steered deep bulk acoustic wave (DBAW) beam, for use in an optic spectrum analyser (OSA). It was shown both theoretically and experimentally that the Bragg-diffracted light beam forms an image on a straight line on a projection screen, the change in the image position be ing almost proportional to DBAW frequencies. This behaviour is conveniently applied to an OSA system using a line CCD image sensor. It was also shown that an increased bandwidth could be realised by giving an incident light beam a proper amount of tilt against the DBAW beam. © 1986 The Japan Society of Applied Physics.