A method for calculating the load characteristics of a traveling-wave-type ultrasonic motor (TWUM) is proposed. A systematic method using an equivalent circuit is suggested for estimating the performance of the motor, including its electrical and the mechanical parts. In the proposed method, a governing equation for the motor is derived to describe the relation between the applied voltage at an electrical terminal, vibration velocities, and the external forces at mechanical terminals of a vibrator. A method for estimating the forces between the rotor and the vibrator of the motor is presented and used to calculate the load characteristics. The numerically calculated load characteristics are shown to agree well with the measured ones, confirming the validity of the method. >

Characteristics estimation of a traveling wave type ultrasonic motor

High permittivity (k) gate dielectric films are widely studied to substitute SiO2 as gate oxides to suppress the unacceptable gate leakage current when the traditional SiO2 gate oxide becomes ultrathin. For high-k gate oxides, several material properties are dominantly important. The first one, undoubtedly, is permittivity. It has been well studied by many groups in terms of how to obtain a higher permittivity for popular high-k oxides, like HfO2 and La2O3. The second one is crystallization behavior. Although it’s still under the debate whether an amorphous film is definitely better than ploy-crystallized oxide film as a gate oxide upon considering the crystal boundaries induced leakage current, the crystallization behavior should be well understood for a high-k gate oxide because it could also, to some degree, determine the permittivity of the high-k oxide. Finally, some high-k gate oxides, especially rare earth oxides (like La2O3), are not stable in air and very hygroscopic, forming hydroxide. This topic has been well investigated in over the years and significant progresses have been achieved. In this paper, I will intensively review the most recent progresses of the experimental and theoretical studies for preparing higher-k and more stable, in terms of hygroscopic tolerance and crystallization behavior, Hf- and La-based ternary high-k gate oxides.

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Design of Higher-k and More Stable Rare Earth Oxides as Gate Dielectrics for Advanced CMOS Devices

Focused interdigital transducers (FIDTs) can generate surface acoustic wave (SAW) with high intensity and high beamwidth compression ratio. Owing to these features, they are very suitable to be used as the sources of microacoustic channels or waveguides in the near future. The focusing properties of FIDTs are dominated solely by their geometric shapes. Therefore, to obtain optimal performance, it is essential to analyze the FIDTs with a variety of geometric shapes. However, among the existing studies concerning the diffraction of FIDTs, a detailed analysis and design of FIDTs is still in paucity. In this paper, we adopted the exact angular spectrum of plane wave theory (ASoW) to calculate the amplitude fields of FIDTs on Y-Z lithium niobate (LiNbO/sub 3/) with the shape as a concentric circular arc and the concentric wave surface. Based on the calculation results, we discussed the variations of the amplitude fields induced by changing number of pairs, degree of arc, and geometric focal length. In addition, the focusing properties of FIDTs on the (100)-oriented GaAs substrate were also analyzed and discussed. We also summarized the guiderules for designing a FIDT via four important factors. It is worth noting that the results of this study provide an important basis for designing various FIDTs to fit the desired applications.

Analysis and design of focused interdigital transducers

Surface acoustic waves (SAW) on piezoelectric substrates can excite spin wave resonance (SWR) in magnetostrictive films through magnetoelastic coupling. This acoustically driven SWR enables the excitation of a single spin wave mode with an in-plane wave vector k matched to the magnetoelastic wave vector. A 2D frequency domain finite element model is presented that fully couples elastodynamics, micromagnetics, and piezoelectricity with interface spin pumping effects taken into account. It is used to simulate SAW driven SWR on a ferromagnetic and piezoelectric heterostructure device with an interdigital transducer configuration. These results, for the first time, present the spatial distribution of magnetization components that, together with elastic wave, exponentially decays along the propagation direction due to magnetic damping. The results also show that the system transmission rate S21(dB) can be tuned by both an external bias field and the SAW wavevector. Acoustic spin pumping at magnetic film/normal metal interface leads to damping enhancement in magnetic films that decreases the energy absorption rate from elastic energy. This weakened interaction between the magnetic energy and elastic energy leads to a lower evanescence rate of the SAW that results in a longer distance propagation. With strong magnetoelastic coupling, the SAW driven spin wave is able to propagate up to 1200 μm. The results give a quantitative indication of the acoustic spin pumping contribution to linewidth broadening.

Spin wave generation by surface acoustic waves

A cognitive radio system operating at frequencies from 400 MHz to 6 GHz requires tunable filters with a wide variable frequency range. Wide band resonators are required to realize such tunable filters consisting of resonators. However, it is difficult to fabricate a very high frequency and wide band resonator, such as 6 GHz and wider than 10%, respectively. The first antisymmetric (A1) mode of a Lamb wave on a LiNbO3 thin plate or film having a high velocity and a large electromechanical coupling factor is a suitable wave for fabricating an ultrawide band and high frequency resonator. This time, we attempted to fabricate a higher frequency Lamb wave resonator on a thin LiNbO3 single-crystal plate instead of the LiNbO3 film, though it has been considered difficult to form a very thin LiNbO3 crystal plate. A new one-port Lamb wave resonator showed a high frequency in the 5 GHz range, a wide bandwidth of 12%, and a high impedance ratio of 62 dB at resonant and antiresonant frequencies. Moreover, we applied the resonator to a ladder-type tunable filter, and obtained the tunable range of 9% from 5.58 to 6.06 GHz theoretically.

https://iopscience.iop.org/article/10.1143/JJAP.50.07HD11/pdf

5.4 GHz Lamb Wave Resonator on LiNbO3 Thin Crystal Plate and Its Application

A waveguide-type acoustooptic modulator (AOM) driven by a surface acoustic wave (SAW) in a tapered crossed-channel waveguide on a 128°-rotated Y-cut LiNbO3 substrate has been proposed for an optical wavelength of 1.55 µm. In this study, to clarify the conditions for a higher diffraction efficiency and a lower driving power, the diffraction properties of the waveguide-type AOM were measured and simulated. First, an AOM with an AO interaction region length of 3 mm was fabricated and the diffraction efficiency of 65% was obtained. Next, the measured values of the SAW power required for 100% diffraction (P100) for the driving frequencies of 125 MHz and 200 MHz were found to be in agreement with the calculated P100, which shows that there is an optimum driving frequency. Furthermore, optical frequency domain ranging using a frequency-shifted-feedback fiber laser with the waveguide-type AOM was demonstrated. Finally, the diffraction properties of the waveguide-type AOM are simulated using a beam-propagation method (BPM) and compared with the experimental results.

Diffraction properties and beam-propagation analysis of waveguide-type acoustooptic modulator driven by surface acoustic wave

An integrated acoustooptic frequency shifter in a crossed-channel waveguide is demonstrated at an optical wavelength of 1.55 ?m. A novel tapered device was designed to make the acoustooptic interaction region longer and thus the driving surface acoustic wave (SAW) power lower, and the device was fabricated by the proton-exchange method and post-annealing in a 128? rotated Y-cut LiNbO3 substrate. At SAW power of 1.4 W, a 40% diffraction efficiency and a bandwidth of 5 MHz centered at 196 MHz were obtained. The frequency shift of Bragg diffracted light was confirmed in an optical heterodyne experiment.

https://iopscience.iop.org/article/10.1143/JJAP.42.3063/pdf

An integrated acoustooptic frequency shifter driven by surface acoustic wave for 1.55 μm optical wavelength

The characteristics of surface acoustic waves on proton-exchanged 128°-rotated Y-cut LiNbO3 were investigated at a frequency of 100 MHz. The changes of the phase velocity and the electromechanical coupling coefficient as a function of the proton-exchange depth were measured. From these experiments, the elastic constants and the piezoelectric constants of the proton-exchanged layer were determined. The effects of annealing on the phase velocity and the surface acoustic wave propagation loss were also measured.

Surface Acoustic Wave Properties on Proton-Exchanged 128?-Rotated Y-Cut LiNbO3

The bulk wave, which is radiated into the substrate from the leaky surface acoustic wave (LSAW), can be suppressed by loading the substrate with a thin film of dielectric such as tantalum pentoxide (Ta2O5) and silicon dioxide (SiO2). Rotated Y-cut X-propagating lithium niobate (LiNbO3) is used for the substrate. For a certain range of the rotation angle, the attenuation of the LSAW can be suppressed by choosing the appropriate material and thickness for the film. For the free surface of 64° Y−X LiNbO3 with Ta2O5 film, and the metallized surface of 41° Y−X LiNbO3 with SiO2 film, the measured propagation losses decreased approximately to one-fourth to half of that of the sample without the thin film. It is shown that, even if the propagation path is a free surface, the particle displacement distribution in the LSAW is concentrated near the substrate surface by the loading with the thin film, as for the metallized surface. This result suggests that the bulk wave radiation in the LSAW excitation can be suppre...

Suppression of bulk wave radiation from leaky surface acoustic waves by loading with thin dielectric films

Lamb waves propagating on an AT-cut quartz substrate were studied. In this study, we propose a high-frequency resonator using a Lamb wave. A Lamb wave is excited on an extremely thin AT-cut quartz substrate which thickness is comparable to the wavelength of an elastic wave propagating on a substrate. This Lamb wave propagates at a higher phase velocity mode than surface acoustic waves. This realizes an RF resonator operable in a high frequency range in which a conventional quartz resonator hardly operates. A theoretical analysis of the reflection coefficient of a Lamb wave with a grating reflector was conducted. The analysis results and experimental results are compared and discussed in this study. A reflection coefficient which is 10 to 20 times higher than that for a Rayleigh-type surface acoustic wave is obtained.

Yasuhiko Nakagawa

Papers

Diffraction properties and beam-propagation analysis of waveguide-type acoustooptic modulator driven by surface acoustic wave

An integrated acoustooptic frequency shifter driven by surface acoustic wave for 1.55 μm optical wavelength

Surface Acoustic Wave Properties on Proton-Exchanged 128?-Rotated Y-Cut LiNbO3

Suppression of bulk wave radiation from leaky surface acoustic waves by loading with thin dielectric films

Characteristics of Reflection of Resonators Using Lamb Wave on AT-Cut Quartz