Kazuhiko Yamanouchi

High temperature stable high electromechanical coupling substrates and application for surface acoustic wave devices

In this paper, in order to improve the TCF the propagation characteristics of SiO/sub 2//Rotated Y-cut, X-propagating LiNbO/sub 3/ leaky SAW substrates with a large electromechanical coupling coefficient (k/sup 2/) and zero temperature coefficient of frequency (TCF) are theoretically investigated. The results showed a large k/sup 2/ of leaky SAW over 0.2 (zero k/sup 2/ of Rayleigh mode), zero TCF and zero propagation attenuation in the case of short boundary at thin film thickness of H//spl lambda//spl eDot/0.15-0.25(H: SiO/sub 2/ film thickness, /spl lambda/:SAW wavelength) were obtained. The experimental results agreed to the theoretical ones.

Single crystal growth of KNbO3 and application to surface acoustic wave devices

Potassium niobate (KNbO 3 ) has large piezoelectric constants. The surface acoustic wave (SAW) substrates with high couplings are very important for wide-band SAW filters and SAW devices. Therefore, the large size KNbO 3 single crystals are required for SAW device applications. In this paper, the techniques of a large size of KNbO 3 using the top seeded solution growth techniques (TSSG) with large size of crucible of 60 mmo platinum are described. The results show that 50x50x 15 mm 3 single crystals are obtained. Also, the poling techniques of KNbO 3 crystal are investigated by using the nonlinear scanning dielectric microscope. The propagation characteristics of SAW and piezoelectric leaky surface waves in KNbO 3 single crystal were investigated theoretically. The results show that the electro-mechanical coupling coefficient of the surface wave propagating along the X-axis of the rotated Y-cut plane is extremely large: K 2 = 0.53, compared to K 2 of 0.055 for LiNbO 3 . The experimental results of the above KNbO 3 substrates agree with the theoretical ones. Also the KNbO 3 substrates showed experimentally the zero temperature coefficients of frequency (TCF) around 20 C.

Surface Acoustic Wave Filter Using Floating Electrode Slanted Finger Unidirectional Transducers

This paper describes a wide-band surface acoustic wave (SAW) filter designed to achieve large stop-band attenuation. The SAW filters using slanted finger interdigital transducers are suitable for mid- or wide-band filters. To achieve a stop-band attenuation of more than 80 dB, two SAW filters using slanted finger unidirectional transducers (SFUDTs) were cascaded. Since these SFUDT filters have center-to-center distances that differ by one-fourth of the acoustic wavelength at the center frequency, the triple transit echo was effectively compensated. A cascaded-pair SFUDT SAW filter with a fractional bandwidth of 15 percent was designed and fabricated on a 128°Y-X LiNbO3 substrate. An insertion loss of 14 dB, amplitude ripples of 0.5 dB and stop-band attenuation of 80 dB or more were achieved.

Piezoelectric acoustic boundary waves in the structure of multilayer thin films/electrode/piezoelectric substrates

The propagation characteristics and temperature coefficients of frequency characteristics of boundary waves, which concentrate the acoustic energy in the interface between the thin film-metal electrode and piezoelectric substrate using the structure of multithin film layers/metal electrode/piezoelectric substrates, are described. The new boundary waves are obtained by using higher velocity thin film as the top surface than internal ones of metal electrode and thin film. The materials with structures of AlN, Al2O3/SiO2/Al, Cu, Ag, Au/rotated Y-X LiNO3, and LiTaO3 are applied. The range of existence of boundary wave for thicknesses of thin films, electrodes on Y-X LiNbO3, LiTaO3, and temperature coefficient of frequency are shown. Experimental results of surface acoustic wave resonators show a good frequency response of admittance at 500 MHz range.

Theoretical analysis of SAW propagation characteristics under the strained medium and applications for high temperature stable high coupling SAW substrates

The important properties required for SAW substrates are a large electromechanical coupling coefficient (k2), small temperature coefficient of frequency (TCF), low propagation loss, etc. At present, there is no single crystal which satisfies all the above mentioned requirements. Recently the efforts to develop new SAW substrate with large k2 and small TCF have investigated. New KNbO8 single crystal substrates with extremely large electromechanical coupling coefficient (k2=53%) and zero TCF around room temperature are developed. LiNbO3 has good properties as a SAW substrate with a large size. Unfortunately LiNbO3 possesses the defect of large values of TCF. In this paper, SAW bonded composite substrates with a large k2, small TCF, low propagation loss and no dispersion using conventional bonders are investigated theoretically and experimentally. The propagation characteristics of SAW in the strained piezoelectric crystal using the higher-order elasticity theory have been analyzed. The theoretical results show zero TCF on LiNbO3/SiO2 substrates. At room temperature a relatively thin LiNbO3 is firmly bonded to a glass material with a small thermal expansion coefficient by using ultraviolet rays to stiffen the bonder. The experimental results of LiNbO3/glass substrate showed a TCF of -19 ppm/°C. The propagation properties were almost the same as those of the single crystal.

Theoretical and experimental results of unidirectional interdigital transducers using grating SAW substrates and zero TCF ladder type filters at 2 GHz range

Surface acoustic wave (SAW) filters employing unidirectional interdigital transducers (UDT) show low loss properties. We propose a new single phase unidirectional transducer (UDT) with about /spl lambda//4 electrode width for the best transducer efficiency. The new UDTs are obtained by IDT on a very thin dielectric grating or a very thin dielectric grating with /spl lambda//8 shifts. Good UDT properties are obtained for very thin SiO/sub 2/ grating thickness (about 0.03 /spl mu/m at 2 GHz with Al electrode thickness of 0.07 /spl mu/m). We describe the experimental results of wide band and very low loss filters with under 1 dB insertion loss in the 2 GHz range. We also show ladder type SAW resonator filters using high coupling SiO/sub 2//5/spl deg/Y-X LiNbO/sub 3/ with zero temperature coefficients of frequency (TCF). The experimental results show under 1.6 dB insertion loss with a wide band and zero TCF in the 2 GHz range. Finally, we show the narrower band width of ladder type filters using the new configuration of IDTs and reflectors on high coupling substrates.

5-10 GHz SAW resonators and low loss wide band resonator filters using zero TCF high electromechanical coupling SAW substrates

We show the SAW resonators and ladder type SAW resonator filters using high coupling SiO2/5°Y-X LiNbO3 with Zero Temperature Coefficients of Frequency (TCF). The theoretical analysis of 5~10GHz ladder type filters including the propagation attenuations and resistive loss of interdigital transducers are shown. Finally the experimental results below 2.5dB insertion loss with a wide band and zero TCF at 5~10GHz-range are shown.

Development of High-Efficiency Strip-Coupled Surface Acoustic Wave Convolver Using GaSb/InSb/AlGaAsSb/LiNbO3 Structures

We have fabricated a strip-coupled surface acoustic wave [SAW] convolver using GaSb/InSb/AlGaAsSb heterostructures grown on a LiNbO3 substrate. An InSb thin film with an AlGaAsSb buffer layer was grown on a 128° Y-X LiNbO3 substrate by molecular beam epitaxy; a very high electron mobility of 7000 cm2/(Vs) in 200-nm-thick InSb films was achieved. We have fabricated a strip-coupled SAW convolver as a new device and have achieved a very high output efficiency (F value) of -14 dBm for modified semiconductor and electrode structures.

GHz-range surface acoustic wave low loss filter at super low temperature

The 10 GHz-range surface acoustic wave (SAW) is of great importance in the field of physical acoustics and application of SAW devices, for example, in mobile and wireless communications. The temperature dependency of the propagation attenuation at 10 GHz-range is measured using the three-transducer system with an electrode width of less than 0.1 /spl mu/m, which is fabricated using an electron beam exposure and lift-off technique. The results show that the attenuation at room temperature is about 15 dB/(100 /spl lambda/) at 10 GHz. Next, the temperature dependency of the insertion loss of a floating electrode reflection type unidirectional transducer (FEUDT) whose electrodes are respectively fabricated from Al and the superconductor Nb, is investigated experimentally. In the case of Al-FEUDT at 8 GHz, the insertion loss at a low temperature is about 85 dB, which is 3.4 dB lower than the insertion loss at room temperature. The main cause of the decrease in the insertion loss is the decrease in the resistivity of the very thin and narrow metal electrodes. The results of Nb-FEUDT show a marked decrease in the insertion loss around the critical temperature Tc=9.23 K.

Phase linear ·flat wide band· low loss filters using new configuration of unidrectional up-chirp and down-chirp dispersive inter digital transducers

Dispersive transducers have sharp cut-off and flat wide band frequency characteristics. Also phase linear and very low loss characteristics are obtained by combining down-chirp and up-chirp unidirectional dispersive transducers (DUDIST and UUDIDT). We proposed the wide band filters combining DUDIDT and UUDIDT using the conventional UDT with the grating thin films. In this case, we could not obtained the low loss results. In this paper, the theoretical results of phase linear, flat wide band and low loss filters using combining new DUDIDT and UUDIDT are described. DUDIDT and UUDIDT are obtained by using new cofiguration of Dispersive IDT. The large unidirectinalities of DUDIDT and UUDIDT are obtained by using the change of the electrode width and thickness, and open and short -circuit electrode as the reflectors.