Takahiko Yanagitani 교수

The electromechanical coupling, elastic properties, and temperature coefficient of elastic constant c33D of ScxAl(1−x)N films with high Sc concentration (x) of 0–0.70 were experimentally investigated. Near the phase boundary, a Sc0.41Al0.59N film exhibited a maximum thickness extensional mode electromechanical coupling coefficient kt2 of 12% (kt = 0.35), which is almost double the value of 6.4% for typical pure AlN films. In the region of 0 < x < 0.2, the electromechanical coupling

ZnO film, in which the crystallite c axis lies in the substrate plane [(112¯0) textured ZnO], is a good candidate for application in shear mode piezoelectric devices. The relationships between the degree of crystallites alignment and the shear mode electromechanical coupling coefficient k15 in (112¯0) textured ZnO films have been investigated. Forty pure-shear mode high overtone bulk acoustic resonators consisting of the (112¯0) textured ZnO film were prepared. The film was varied in crystallite

A method for designing frequencies and modes in ultrasonic transducers above the very-high-frequency (VHF) range is required for ultrasonic non-destructive evaluation and acoustic mass sensors. To obtain the desired longitudinal and shear wave conversion loss characteristics in the transducer, we propose the use of a c-axis zig-zag structure consisting of multilayered c-axis 23° tilted ZnO piezoelectric films. In this structure, every layer has the same thickness, and the c-axis tilt directions

ZnO polycrystalline films have a strong tendency to grow their c-axis perpendicular to the film surface, even on an amorphous substrate. However, unusual (101¯0) preferred orientations in which the c-axis lies in the substrate plane are often observed when the film is exposed to ion irradiation during its growth. To investigate the effect of ion irradiation on the (101¯0) preferred orientation, ZnO films were fabricated using a 0–1 keV oxygen ion-beam-assisted electron-beam evaporation of zinc.

Giant shear mode electromechanical coupling coeficient k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> ' of 0.32 (k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> =10%) were found in the c-axis 33° tilted ScAlN films. High k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns

Thickness pure-shear mode film bulk acoustic wave resonators (FBARs) made of (1120) textured ZnO films have been fabricated. We also have fabricated FBAR structure consisting of two layers of the (1120) textured ZnO film with opposite polarization directions. This FBAR structure operated in second overtone pure-shear mode and allowed shear-mode FBARs at higher frequency. The effective electromechanical coupling coefficients k2 of pure-shear mode FBAR and second overtone pure-shear mode FBAR in t

The (1120) textured polycrystalline ZnO films with a high shear mode electromechanical coupling coefficient k15 are obtained by sputter deposition. An over-moded resonator, a layered structure of metal electrode film/(1120) textured ZnO piezoelectric film/metal electrode film/silica glass substrate was used to characterize k15 by a resonant spectrum method. The (1120) textured ZnO piezoelectric films with excellent crystallite c-axis alignment showed an electromechanical coupling coefficient k15

Weak piezoelectricity in GaN is a problem in bulk acoustic wave filters and heterostructure field-effect transistors. In this study, enhancement of piezoelectricity in c-axis direction by substituting Yb for Ga was experimentally demonstrated. Thickness extensional mode electromechanical coupling coefficient kt for the YbxGa1−xN films increases with the Yb concentration from x = 0 to 0.3. Yb0.30Ga0.70N film near the phase boundary exhibited a maximum kt of 3.1%, which is approximately 2.5 times

Using a conventional RF magnetron sputtering system, we have obtained two types of ZnO films on various kinds of substrate. One is a film with the c -axes of crystallites unidirectionally aligned in the substrate plane {(112̄0) textured film}. The other is a film with c -axes parallel and perpendicular to the plane (mixed texture film). The former is expected to realize a shear wave transducer on the surfaces of various materials. The alignment of c -axes of crystallites in the plane was then ca

This paper reports the fabrication and characterization of ZnO piezoelectric thin films in which the crystallite c-axis is unidirectionally aligned in the plane. The films were deposited by a conventional radio frequency (RF) magnetron sputtering apparatus without epitaxy. We have measured reflection coefficient S11 of the ZnO film/glass substrate composite shear mode resonator and confirmed that the resonator excites shear wave only in the very high frequency to ultra high frequency ranges (VHF

Abstract Polarization-inverted multilayers are promising for application in bulk acoustic wave (BAW) resonators, BAW transformers, surface acoustic wave (SAW) devices and nonlinear optics crystals (NLOs). However, is difficult to obtain a polarization-inverted multilayer by a conventional polarization control technique using a buffer layer. Recently developed ion beam-induced polarization inversion film growth is attractive for multilayer fabrication. Low-energy ion beam irradiation (several hun

The wireless power transfer with rectennas for sensors has attracted much attention in recent years. Although a charge pump is commonly used for voltage transformers in rectennas for RF voltage amplification, it is large, has low efficiency, and has poor impedance matching. Here, we propose small bulk acoustic wave piezoelectric transformers based on c-axis zigzag polarization-inverted ScAlN multilayers. The capacitive impedance ZC of an n-layer c-axis zigzag multilayer resonator is n times larg