大森 達也

Abstract This paper proposes a high-sensitive measuring method for nonlinear harmonic responses in radio frequency (RF) SAW/BAW devices using a lock-in amplifier. The proposed system could detect the nonlinear complex harmonic responses generated in an RF SAW resonator, even if the responses are weaker than −140 dBm. The detection limit is extended by around 10 dB compared with the conventional technique using a cross-domain analyzer.

Herein, a time-resolved electrical measurement is developed to observe the transient impedance of organic photovoltaics (OPV) and traced the initial photocarrier generation dynamics with the time region from 10 ns to 190 μs. A light-triggered time-domain reflectometry is adopted to observe the initial carrier dynamics in OPV by synchronizing rectangular light pulses from LED with a transient impedance probe pulse. Both the rising and recovery processes of OPV are observed in detail. The time evolution of the photocarrier distribution is calculated based on the diffusion–recombination scheme and is discussed in the initial process of photocarrier generation.

SUMMARY The massive explosive eruption of the Hunga volcano on 15 January 2022 generated atmospheric waves that were recorded around the globe and affected the ionosphere. The paper focuses on observations of atmospheric waves in the troposphere and ionosphere in Europe, however, a comparison with observations in East Asia, South Africa and South America is also provided. Unlike most recent studies of waves in the ionosphere based on the detection of changes in the total electron content, this study builds on detection of ionospheric motions at specific altitudes using continuous Doppler sounding. In addition, much attention is paid to long-period infrasound (periods longer than ∼50 s), which in Europe is observed simultaneously in the troposphere and ionosphere about an hour after the arrival of the first horizontally propagating pressure pulse (Lamb wave). It is shown that the long-period infrasound propagated approximately along the shorter great circle path, similar to the previously detected pressure pulse in the troposphere. It is suggested that the infrasound propagated in the ionosphere probably due to imperfect refraction in the lower thermosphere. The observation of infrasound in the ionosphere at such large distances from the source (over 16 000 km) is rare and differs from ionospheric infrasound detected at large distances from the epicenters of strong earthquakes, because in the latter case the infrasound is generated locally by seismic waves. An unusually large traveling ionospheric disturbance (TID) observed in Europe and associated with the pressure pulse from the Hunga eruption is also discussed. Doppler sounders in East Asia, South Africa and South America did not record such a significant TID. However, TIDs were observed in East Asia around times when Lamb waves passed the magnetically conjugate points. A probable observation of wave in the mesopause region in Europe approximately 25 min after the arrival of pressure pulse in the troposphere using a 23.4 kHz signal from a transmitter 557 km away and a coincident pulse in electric field data are also discussed.

This paper describes the implementation of an autofocus function for a laser beam in a high-speed, phase-sensitive laser probe system for RF surface/bulk acoustic wave devices. This implementation can compensate for defocus caused during continuous measurements that take dozens of hours. After a brief explanation of the system used in this work, a detailed discussion is given on the employed evaluation function indicating focus status, which is a key factor determining autofocus reliability. It is shown that the sum of the energies of Laplacians is suitable as an evaluation function, which can be calculated by an image of the probing laser spot captured by a built-in CCD camera. Then, the implementation of the autofocus function in the current system is detailed. It is confirmed that this function can adjust the focus within almost ±20μm defocus conditions. Finally, it is confirmed how the implemented autofocus function works effectively to keep just-in-focus under disturbance.

This paper proposes a detection electronics which enables ultimate suppression of leakage signals in high-speed and phase-sensitive laser probe for radio frequency surface and bulk acoustic wave devices. Another merit is simpler circuit configuration than the conventional one. First, the complete suppression of leakage signals is verified. Then impact of the oscillator phase noise is examined by utilizing oscillators with various phase noise performance. This is because the proposed electronics is expected to be more sensitive to the oscillator phase noise than the conventional one. The result indicates that although performance degradation appears, it is practically negligible. In this electronics, the absolute phase can not be determined. This is not a demerit for use in the laser probe because additional phase shift caused by cables and printed circuit board is hard to calibrate.

This paper describes the coaxial integration of a Michelson interferometer (MI) and a Sagnac interferometer (SI) in a high-speed, phase-sensitive laser probe for surface acoustic wave/bulk acoustic wave devices. This combination enables the MI to be used for calibration of the vibration amplitude captured by the SI without sacrificing the measurement accuracy and speed of the SI-based laser probe. First, the system setup is detailed. Next, simultaneous measurement is performed using the SI and MI, and good coincidence is demonstrated between these measured results after correction of tiny misalignment between two optical axes. This means that the calibration can be performed simply by multiplying the data captured by SI by a coefficient of proportionality; this value of this can be determined by comparison with the data captured by simultaneous measurement for a tiny area. Finally, the procedure for absolute vibration amplitude measurement is proposed and its validity is confirmed by actual measurement.

This paper discusses loss mechanisms of temperature compensated surface acoustic wave (TC-SAW) devices using the SiO2 overcoated 128°YX-LiNbO3 (128-LN) substrate. Analysis is based on the finite element method (FEM) combined with the hierarchical cascading technique and the general purpose graphics processing unit. Three kinds of FEM model, i.e. 2.5D, three dimensional (3D) periodic and full 3D are analyzed without taking additional losses, i.e. material viscous loss, dielectric loss and electrode ohmic loss, and influence of scattering at structural discontinuities is evaluated solely. It is shown that although Q reduction is significant with an increase of the simulation dimension, in other words, that of the number of acoustic scattering mechanisms, estimated Q value is still considerably higher than reported values even for full 3D simulation. This result indicates that acoustic scattering at structural discontinuities is not a dominant loss mechanism in current TC-SAW devices employing the SiO2 overcoated 128-LN substrate.

It is known that nonlinear responses by transverse resonances are more emphasized than those by the main resonance in radio frequency bulk acoustic wave devices. This paper investigates this mechanism using the LCR-based nonlinear equivalent circuit proposed by the authors. Here a number of acoustic branches are newly added to take multiple transverse resonances into account, and amplitudes of nonlinear voltage sources in the model are determined by summation of currents flowing to acoustic branches. Parameters necessary for the analysis are determined experimentally. It is shown that simulated second and third harmonic responses agree well with the measurement. Next, the magnification mechanism is discussed. It is shown that mth harmonics generated by transverse modes are magnified by m-times approximately, and the factor of m is originated to that at the production between field components of transverse and main modes.

This article describes derivation of an equivalent circuit for nonlinear responses in film bulk acoustic resonators from the first-order perturbation analysis using the piezoelectric constitutive equations with the h-form. For simplicity, electrodes and piezoelectric layers are considered as mass and spring, respectively, in the derivation. Then, it is demonstrated that the second-and third-order harmonic responses can be simulated well by the circuit. In addition, nonlinearity in the Si substrate is also taken into account and its impact is discussed. It is also discussed how the frequency dependences vary with the nonlinearity mechanisms as a finding from the derived equivalent circuit.

This article describes the application of the hierarchical cascading technique (HCT) to the 3-D finite-element method (FEM) analysis of transverse-mode behaviors in surface acoustic-wave (SAW) devices. Mirror cascading is proposed as a speed-up technique for the HCT operation using the general-purpose graphic processing unit (GPGPU). Two methods are implemented for the analysis: one is impedance calculation and the other is the calculation of SAW scattering coefficients at boundaries. It is demonstrated that HCT enables rapid calculation for successive simulation with scanning design parameters. Thus, techniques discussed in this article are quite effective for the optimization of device structures. It is also shown that GPGPU can accelerate HCT calculation dramatically, especially for 3-D cases discussed in this article.

This paper describes a suppression technique for the lowest-order plate mode in wafer bonded surface acoustic wave (SAW) devices using LiTaO3 (LT) thin plate. When LT plate thickness is close to the SAW wavelength, say micron order, the lowest-order plate mode appears near the main resonance. It is shown that the plate mode can be suppressed by choosing LT cut angle, electrode thickness and LT plate thickness properly. It is also shown that when the acoustic length is finite, the leaky nature causes additional loss even when the LT plate is extremely thin. Detailed discussions are also given how the additional loss changes with the plate thickness.

This paper describes 3D FEM simulation of scattering at a border between IDT and reflector in SAW resonators using hierarchical cascading technique and general purpose graphic processing unit. SH-type SAW on the 42°YX-LiTaO3 substrate is chosen. It is shown how the reflector design affects the scattering loss at the border. It is also shown that scattering fields can be observed selectively by the use of the wavenumber domain analysis.

This paper describes derivation of an equivalent circuit for nonlinear responses in film bulk acoustic resonators from the first-order perturbation analysis using the piezoelectric constitutive equations with the h-form. For simplicity, electrodes and piezoelectric layer are regarded as a mass and spring in the derivation. Then it is demonstrated that the H2 response can be simulated well by the circuit.

This paper proposes use of traveling wave type excitation sources for the scattering analysis of acoustic waveguides using the finite element method (FEM). This technique allows to generate only one particular mode selectively. Scattering behavior at arbitrary boundaries can be evaluated accurately and quickly in frequency domain. After describing and demonstrating its operation mechanism in detail, this technique is applied to two cases. First, wave scattering properties are discussed at the end of a two-dimensional closed waveguide. Then the technique is applied to a three-dimensional open waveguide including periodic gratings. The results reveal effectiveness of this technique.

This paper proposes a technique to analyze surface acoustic wave (SAW) scattering at discontinuity in grating structures using the hierarchical cascading technique. The traveling wave excitation is applied to generate a specific SAW mode. Then the displacement distribution is obtained for the passive regions. The incident, reflected, and transmitted components are selectively evaluated by the Fourier transform so as to determine the scattering coefficients at the discontinuity. Rayleigh SAWs on the SiO2/128°YX-LiNbO3 structure and SH SAWs on the 42°YX-LiTaO3 structure are used as examples, and the behavior of two kinds of discontinuity are analyzed, and the obtained results are compared with those obtained by the COM model.

This paper proposes an application of a general purpose graphic processing unit (GPGPU) to the finite element method analysis based on the hierarchical cascading technique (HCT). It is proved that GPGPU can accelerate the HCT significantly, especially for large scale problems. Thanks to significant acceleration, full three-dimensional simulation is possible for practical surface acoustic wave (SAW) device structures. Besides admittance curve, the displacement field is calculated. It is shown that SAW scattering occurs at the boundary at busbar spaces between the interdigital transducer (IDT) and reflector regions.

This paper discusses the applicability of a single precision computation with a graphics processing unit for the finite elements method simulation of surface acoustic wave (SAW) devices using the hierarchical cascading technique (HCT). The HCT simulation is performed in both single and double precision, and the required computational time, memory size and accuracy are compared. Three SAW device structures are discussed; (a) a synchronous resonator on 42 YX-LiTaO3 (42-LT), (b) a double mode SAW (DMS) filter on 42-LT, and (c) a synchronous resonator on 42-LT/Si bonded wafer. It is shown that the single precision enables us to double the calculation speed and halve the memory size with negligible accuracy deterioration.

This paper investigates the impact of transverse mode resonances on second harmonic (H2) generation in radio-frequency bulk acoustic wave devices. Previous work indicated that second-order nonlinearity of the main mode can be well simulated by one-dimensional perturbation analysis using the h-form piezoelectric constitutive equations. This work expands the analysis to the two-dimensional case to investigate the influence of transverse resonances on the H2 generation. The result shows that transverse modes generate strong H2 responses, and this phenomenon is consistent with experimental results. The origin of the strong H2 generation is also discussed.

This paper proposes a technique to analysis SAW scattering at discontinuity in grating structures using the hierarchical cascading technique. The traveling wave excitation is applied to generate a specific SAW mode. Then the displacement distribution is obtained for the passive regions. The incident, reflected and transmitted components are selectively evaluated by the Fourier transform so as to determine the scattering coefficients at the discontinuity. Rayleigh SAWs on the SiO 2 /128°YX-LiNbO 3 structure are used as an example, and the behavior of discontinuity is analyzed, and obtained results are compared with those obtained by the COM model. These results agreed very well for this case.

This paper describes application of the hierarchical cascading technique (HCT)to the 3D FEM analysis of transverse mode behaviors in Surface acoustic wave (SAW)devices. Two methods are implemented; one is impedance calculation, and another is calculation of SAW scattering coefficients at boundaries. It is shown that HCT enables rapid calculation for successive simulation with scanning design parameters. Thus, techniques discussed in the paper are quite effective for optimization of device structures. It is also shown that GPGPU can accelerate the HCT calculation dramatically, especially for 3D cases discussed in this paper.

This paper proposes a technique to estimate surface acoustic wave (SAW) power flow angle (PFA) in periodic grating structures. First, the thin plate model is extended to take into account non-zero PFA. The relation between the lateral wavenumber and the frequency is derived in an analytical form under the longitudinal resonance condition. Then, the complex power flows in lateral and longitudinal directions are derived and PFA is estimated from the model parameters. Finally, the parameters are extracted by fitting the derived relation between lateral wavenumber and frequency with that calculated by finite element method. The influence of grating electrode on PFA is investigated on quartz and langasite substrates. The results confirm the validity of the technique.

This paper investigates the influence of coupling between Rayleigh and shear-horizontal (SH) surface acoustic waves (SAWs) on rotated Y-cut LiNbO3 to their electromechanical coupling. For the purpose, a coupling-of-mode (COM) model including the coupling between two SAWs is developed, and the coupling influences to their excitation in addition to electromechanical coupling factors are discussed. Then, its validity is confirmed by comparison of its results with the finite-element method analysis. Comparing with the conventional COM shows this extended COM model could fit the complex value area much better in the dispersion curve analysis. After that, variation of COM parameters with the device design is discussed. Then, all COM parameters are fit by polynomial equations and the procedures to find the optimal rotation angle are obtained in terms of the SH mode suppression. It indicates that the optimal angle changes rapidly at certain Cu thickness, which is due to decoupling between two SAW modes. At last, structure based on the low-cut LiNbO3 is discussed and the validity of this COM model is further confirmed.

This paper investigates applicability of double raised borders to the piston mode film bulk acoustic resonator (FBAR). It is shown that it offers significant improvement of the quality factor at the anti-resonance without sacrificing the spurious level when the structure is designed appropriately. This enhancement is attributed to the reduction of the mode-conversion and the increase of the reflection coefficient at the border region.

In this paper, we describe the study of time to failure (TTF) evaluation of radio frequency (RF) surface and bulk acoustic wave (SAW/BAW) devices for the International Electrotechnical Commission (IEC) standardization. As the passband shifts with T due to the nonzero temperature coefficient of frequency (TCF), its influence must be taken into account at the acceleration test. A technique to estimate the frequency-dependent TCF of RF SAW/BAW devices for the acceleration test of the TTF estimation is proposed. First, it is shown how the filter passband shifts with T, and its numerical model is proposed. Then, its impact on the power durability test is presented.

This paper describes extraction of parameters of an extended coupling-of-modes (COM) model including coupling between Rayleigh and shear-horizontal (SH) surface acoustic waves (SAW) on the SiO2-overlay/Cu-grating/LiNbO3-substrate structure. First, dispersion characteristics of two SAWs are calculated by the finite element method (FEM), and are fitted with those given by the extended COM. Then variation of COM parameters is expressed in polynomials in terms of the SiO2 and Cu thicknesses and the rotation angle Θ of LiNbO3. Then it is shown how the optimal Θ giving the SH SAW suppression changes with the thicknesses. The result agrees well with that obtained directly by FEM. It is also shown the optimal Θ changes abruptly at certain Cu thickness, and is due to decoupling between two SAW modes.

In this paper, we propose the use of the hierarchical cascading technique (HCT) for the finite element method (FEM) analysis of bulk acoustic wave (BAW) devices. First, the implementation of this technique is presented for the FEM analysis of BAW devices. It is shown that the traveling-wave excitation sources proposed by the authors are fully compatible with the HCT. Furthermore, a HCT-based absorbing mechanism is also proposed to replace the perfectly matched layer (PML). Finally, it is demonstrated how the technique is much more efficient in terms of memory consumption and execution time than the full FEM analysis.

This paper investigates how lateral propagation of Rayleigh and shear horizontal (SH) surface acoustic waves (SAWs) changes with rotation angle θ and SiO2 and electrode thicknesses, hSiO2 and hCu, respectively. The extended thin plate model is used for purpose. First, the extraction method is presented for determining parameters appearing in the extended thin plate model. Then, the model parameters are expressed in polynomials in terms of hSiO2, hCu, and θ. Finally, a piston mode structure without phase shifters is designed using the extracted parameters. The possible piston mode structures can be searched automatically by use of the polynomial expression. The resonance characteristics are analyzed by both the extended thin plate model and three-dimensional (3D) finite element method (FEM). Agreement between the results of both methods confirms validity and effectiveness of the parameter extraction process and the design technique.

This paper investigates piston mode operation (PMO) when two kinds of surface acoustic waves (SAWs) exist and are coupled to each other. The extended thin plate model is used for the analysis. First, a PMO condition is derived in a closed form. It is verified that PMO is possible without adding phase shifters by the use of two SAW coupling. It is also shown that this operation offers suppression of the transverse modes for a wider frequency range than the conventional PMO. Then, parameters defined in the model are extracted for various SiO2-overlay/Al-grating/128° YX-LiNbO3 substrate structures, and the structure satisfying the PMO condition is designed. Finally, the structure is also analyzed using the 3-D finite element method. The result agrees well with that calculated by the extended thin plate model.

The piston mode operation (PMO) is quite effective for realization of spurious-free and low-loss SAW resonators. The scalar potential (SP) analysis indicates that 'phase shifters' are necessary for PMO at edges of the acoustic aperture. Nakamura, et al., pointed out that for SAW resonators using SiO2/LiNbO3 structure, PMO is possible by simply removing SiO2 in the dummy electrode region [1]. This phenomenon cannot be explained by the SP theory, and was expected to be due to existence of the spurious SH SAW in addition to the main Rayleigh SAW or vice versa.

The authors has been developing phase-sensitive and fast mechanical scanning laser probe system as a diagnosis tool for RF SAW/BAW devices. This paper describes implementation of the frequency scanning function to the system. Little modification of the preexisting hardware and a newly developed Windows GUI program enable automated frequency scanning operation without sacrificing original functions. A data filtering program optimized for use in batch processing was newly developed for post processing of vast data acquired by the frequency scanning. As a demonstration, field distributions of a one-port SAW resonator on 42YX-LiTaO3 were captured for the frequency span from 820 to 880 [MHz] with every 0.25 MHz step (241 frequency points). After around 31.5 hours in total, we got an animation revealing how SAW field changes with the frequency.

Further reduction of nonlinearity is demanded in RF SAW/BAW devices, but even their generation mechanisms have not been fully understood. Although phase possesses comparable information to amplitude, it has not been paid much attention in the nonlinear signal measurement. Nonlinear vector network analyzers (NVNAs) may be used for the purpose. However, NVNAs have limited linearity than spectrum analyzers (SAs), and it seems to be very complex to apply NVNAs for the measurement of intermodulation distortion (IMD).

This paper proposes use of traveling wave type excitation sources for the scattering analysis of RF SAW/BAW devices using the finite element method(FEM). By generating a single mode selectively, scattering behavior at arbitrary edges can be evaluated efficiently in frequency domain. After describing its detailed mechanism, two examples are presented for the use in SAW and BAW models. The results revealed effectiveness of this technique in these applications.

Suppression of the SH-SAW response is mandatory to design TC SAW devices on θ degree rotated Y-cut LiNbO3. However, it is not easy because K2 for SH SAW changes rapidly with θ, and its optimal value in terms of the SH-SAW suppression is dependent on electrode and SiO2 thicknesses. The authors found that the optimal θ always locates close to θ where difference in velocities of two SAWs is minimum. This suggested that their coupling is responsible for variation of their K2.

This paper discusses lateral propagation of surface acoustic waves (SAWs) in periodic grating structures when two types of SAWs exist simultaneously and are coupled. The thin plate model proposed by the authors is extended to include the coupling between two different SAW modes. First, lateral SAW propagation in an infinitely long periodic grating is modeled and discussed. Then, the model is applied to the Al-grating/42° YX-LiTaO3 (42-LT) substrate structure, and it is shown that the slowness curve shape changes from concave to convex with the Al grating thickness. The transverse responses are also analyzed on an infinitely long interdigital transducer on the structure, and good agreement is achieved between the present and the finite-element method analyses. Finally, SAW resonators are fabricated on the Cu grating/42-LT substrate structure, and it is experimentally verified that the slowness curve shape of the shear horizontal SAW changes with the Cu thickness.

This paper discusses design of surface acoustic wave/bulk acoustic wave (SAW/BAW)-based band reject filters composed of the impedance converters, where capacitive elements are replaced with SAW/BAW resonators. First, basic properties of the unit cell are studied. It is shown how basic properties of a unit cell change with the design. It is also shown that when two notches caused by the resonators are placed in proximity, two synergy effects occur: 1) an extra matching point appears on one side of the transition band. This makes the insertion loss at the point smaller and the transition band steeper and 2) the dip level becomes deeper, and the total rejection level improves. Then, two resonators are fabricated, measured, and combined with inductors in circuit simulator to demonstrate functionality of the basic cell design. Finally, the wide rejection band filter is designed by cascading multistages, and effectiveness of the device configurations is demonstrated.

In this paper, we investigate the impact of the coupling with shear horizontal (SH) surface acoustic wave (SAW) on the propagation of Rayleigh SAW in periodic grating structures on 128°YX-LiNbO3. First, the frequency dispersion behavior with longitudinal and lateral wavenumbers of Rayleigh SAW is calculated using the finite element method (FEM) software COMSOL. It is shown that the coupling causes (1) the satellite stopband and (2) variation of the anisotropy factor. It is also shown these phenomena remain even when the electromechanical coupling factor of SH SAW is zero. Then, the extended thin plate model which can take coupling between two SAWs into account, is applied to simulate the result of FEM. Good agreement between these results indicated that the mechanical coupling is responsible for these two phenomena. Finally, including electrical excitation and detection, the model is applied to the infinitely long interdigital transducer (IDT) structure and the calculated result is compared with that obtained by the three-dimensional FEM. The excellent agreement of both results confirms the effectiveness of the extended thin plate model.

This paper discusses the possibility of realizing multimode filters composed of multiple single-mode resonators by using radio frequency surface and bulk acoustic wave (SAW/BAW) technologies. First, the filter operation and design principle are given. It is shown that excellent filter characteristics are achievable by combining multiple single-mode resonators with identical capacitance ratios provided that their resonance frequencies and clamped capacitances are set properly. Next, the effect of balun performance is investigated. It is shown that the total filter performance is significantly degraded by balun imperfections such as the common-mode rejection. Then, two circuits are proposed to improve the common-mode rejection, and their effectiveness is demonstrated.

The propagation characteristics of surface acoustic waves (SAWs) on rotated Y-cut X-propagating 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3(PMN-33%PT) substrate are theoretically analyzed. It is shown that besides the existence of a shear horizontal (SH) SAW with ultrahigh electromechanical coupling factor K2, a Rayleigh SAW also exists causing strong spurious response. The calculated results showed that the spurious Rayleigh SAW can be sufficiently suppressed by properly selecting electrode and its thickness with optimized rotating angle while maintaining large K2 of SH SAW. The fractional -3 dB bandwidth of 47% is achievable for the ladder type filter constructed by Au IDT/48oYX-PMN-33%PT resonators.

This paper proposes a frequency domain analysis (FDA) based on the finite element method (FEM) for calculating reflector scattering characteristics of SAW tags. This method is applicable not only to devices employing conventional single-crystal substrates but also multi-layered ones. First, reflection characteristics are calculated for a short reflector on 128°YX-LiNbO3 and compared with the result previously reported. Then the method is applied to short reflectors on the AlN/Si layered structure, and their applicability to SAW tags is discussed.

This paper describes lateral propagation of surface acoustic waves (SAWs) when two types of SAWs are coupled. For the analysis, the thin plate model proposed by the authors is extended to include interaction between two SAW modes. Firstly, lateral wave propagation in an infinitely long periodic grating is modelled and discussed, it is found that SAW slowness curves can be changed by mode coupling. Then, the model is applied to the analysis of two-dimensional SAW propagation on the Al grating on the 42°YX-LiTaO3 (42-LT) substrate structure to investigate how the lateral SAW propagation changes with the Al grating thickness. Finally, SAW resonators on 42-LT substrate with Cu electrodes are fabricated and the results confirm the feasibility of the model.

This paper is aimed at examining the validity of material constants reported for the use in surface acoustic wave (SAW) device simulations. At first, based on the full set of material constants calculated by the first principle, bulk acoustic wave (BAW) velocities are calculated for ScxAl1-xN and compared with published experimental results. Then, the effects of ScxAl1-xN material constants with different Sc contents on acoustic characteristics are calculated and the influences of shear vibrations on SAW characteristics are recognized. Then series of SAW devices are fabricated on ScxAl1-xN film/Si substrate structure with various Cu and ScAlN thicknesses hCu and hScAlN, respectively, and measured variations of phase velocity V and effective electromechanical coupling factor Ke2 with these parameters are compared with the calculation. The fairly well agreed results indicate a reliable set of ScxAl1-xN material constants for SAW device simulations.

This paper discusses SAW-BAW-based band reject filters. They are composed of the impedance converters, where capacitive elements are replaced with SAW/BAW resonators. First, basic properties of the unit cell are studied. It is shown how basic properties of a unit cell change with the design. It is also shown that when two notches caused by the resonators are placed in proximity, two synergy effects occur: (i) an extra matching point appears on one side of the transition band. This make the insertion loss at the point smaller and the transition band steeper, and (ii) the dip level becomes deeper, and the total rejection level becomes better. Then, the wide rejection band filter is designed by cascading multi-stages, and effectiveness of the device configurations is demonstrated.

This paper is aimed at examining the validity of material constants reported for use in surface acoustic wave (SAW) device simulations. First, based on the full set of material constants calculated by first principle, bulk acoustic wave velocities are calculated for ScxAl1-xN and compared with published experimental results. Then, the effects of the ScxAl1-xN material constants with different Sc content on acoustic characteristics are calculated and the influence of shear vibrations on SAW characteristics are recognized. Then, a series of SAW devices are fabricated on ScxAl1-xN film/Si substrate structure with various Cu and ScAlN thicknesses h Cu and h ScAlN, respectively, and measured variations of phase velocity V and effective electromechanical coupling factor with these parameters are compared with the calculation. The fairly well-agreed results indicate a reliable set of ScxAl1-xN material constants for SAW device simulations.

In this paper, we propose the use of the "longitudinal resonance condition" for the characterization of the two-dimensional propagation of surface acoustic waves (SAWs) in periodic grating structures, and also show a procedure for extracting parameters required in the behavior model from the full-wave analysis. The condition is given by βxp = π, where p is the grating period and βx is the wavenumber of the grating mode in the longitudinal direction (x). This is based on the fact that in conventional SAW resonators, acoustic resonances including transverse ones occur when βx is real but the longitudinal resonance condition is mostly satisfied. The longitudinal resonance condition is applied to a simple model, and the wavenumber βy in the lateral direction (y) is expressed as a simple function of the angular frequency μ. The full-wave analysis is applied for SAWs propagating in an infinite grating on a 128°YX-LiNbO3 substrate, and the anisotropy parameter ã is extracted by the fitting with the derived equation. The fitted result agrees well with the original numerical result. It is also indicated that ã estimated by this technique is significantly different from the value estimated without taking the effects of the grating structure into account.

In this paper, we propose a physical model for the analysis of transverse modes in surface acoustic wave (SAW) devices. It is mostly equivalent to the scalar potential (SP) theory, but sufficiently flexible to include various effects such as anisotropy, coupling between multiple modes, etc. First, fundamentals of the proposed model are established and procedures for determining the model parameters are given in detailed. Then the model is implemented in the partial differential equation mode of the commercial finite element analysis software COMSOL. The analysis is carried out for an infinitely long interdigital transducer on the 128°YX-LiNbO3 substrate. As a demonstration, it is shown how the energy leakage changes with the frequency and the device design.

This paper reviews a phase-sensitive and fast-scanning laser probe system developed by the authors' group for the diagnosis of radio frequency (RF) surface and bulk acoustic wave (SAW/BAW) devices. The system is based on the Sagnac interferometer, which is insensitive to low frequency vibration. This feature allows us to maximize the scanning speed without sacrificing the signal-to-noise ratio of the measurement. It is demonstrated that high quality two-dimensional (2D) image of SAW/BAW field patterns can be captured in minutes order. Currently the maximum applicable frequency is 6 GHz. Because of the phase sensitivity, the measured field in the space domain is readily converted into the wavenumber domain by the 2D Fourier Transform.

This paper describes the trial of time-to-failure (TTF) estimation of RF SAW devices for IEC standardization. An on-wafer measurement system was constructed so as to perform the acceleration test in terms of applied power and/or chip temperature. The ladder type SAW filters in the 2GHz range fabricated on a 42°YX-LiTaO3 wafer were used as the DUT, and their TTFs were measured. The experiments showed that the acceleration by temperature and applied power obeys the Eyring's model well. It was also demonstrated that the chip temperature can be estimated form the cutoff frequency of the BAWradiation, which is identified easily from the VNA data. This technique seems quite feasible to monitor chip temperature of packaged RF SAW devices during the TTF measurement because no modification is necessary for the SAW device design.