Toshimaro Yoneda

Very Small-Sized Resonator Filter Using Shear Horizontal Wave on Quartz

By composing interdigital transducers (IDTs) and reflectors consisting of films made of a heavy metal such as Au, Ta or W on an ST cut 90°X propagation (direction perpendicular to X-axis) quartz substrate, the authors realized a new type of shear horizontal (SH) wave. This wave has an excellent temperature characteristic, a large electromechanical coupling factor (k), and a large reflection coefficient at reflector electrodes. The square of this electromechanical coupling factor (k2=0.28~0.34%) and the reflection coefficient at reflector electrodes are 2.2~2.6 times and 30~35 times, respectively, as large as those of a Rayleigh wave on an ST cut X propagation quartz substrate. The authors applied this technology to filters for the first intermediate frequency (first IF) stage of a global system for mobile communications (GSM) in the nominal center frequency from 200 to 400 MHz. As a result, we succeeded in developing the first IF filter having a low insertion loss, an excellent temperature characteristic (frequency shift: 1 ppm/°C) and a small package size (3×3 mm2), which is as small as a radio frequency (RF) surface acoustic wave (SAW) filter, for the first time.

Resonator filters using shear horizontal-type leaky surface acoustic wave consisting of heavy-metal electrode and quartz substrate

The authors have succeeded in exciting a new type of leaky surface acoustic wave (LSAW) having only a shear horizontal (SH) component that has a large electromechanical coupling factor, a large reflection coefficient, and excellent temperature stability, by combining interdigital transducers (IDTs) and reflectors made of heavy-metal films such as gold (Au), tantalum (Ta), and tungsten (W) on the ST-cut 90/spl deg/ X propagation (direction perpendicular to the X-axis) quartz substrate. This LSAW does not have a propagation decay. The square of the electromechanical coupling factor is 2.1-2.7 times larger than, the reflection coefficient is 30 times larger than, and the temperature characteristic is the same as those of a Rayleigh wave on an ST-cut X propagation quartz substrate. The authors applied this SH LSAW to resonators and resonator filters. As a result, we succeeded in developing the low loss and very small-sized resonators and resonator filters (1/5-1/4 of conventional device sizes) with IDTs with a small number of finger pairs and very small reflectors, for the first time.

Very small-sized resonator IF filter using shear horizontal wave on quartz substrate

A shear horizontal (SH) wave is excited by composing interdigital transducers (IDTs) and reflectors consisting of films made of heavy metal on ST cut 90/spl deg/-X propagation quartz substrate (propagation direction is perpendicular to X-axis). This wave has a large electromechanical coupling factor, a large reflection coefficient and an excellent temperature characteristic. The square of the electromechanical coupling factor is 2.0-2.6 times, the reflection coefficient at reflectors grating electrodes is 30 times as large as that of Rayleigh wave on an ST cut X propagation quartz substrate, and the temperature coefficient of frequency is equal to that. The authors applied this SH wave to filters for the first intermediate frequency (first IF) stage of a global system for mobile communications (GSM). As a result, we succeeded in developing the low loss and very small-sized filter (3/spl times/3/spl times/1.03 mm: typical dimensions) having a high rejection out of band for the first time.

Small-sized resonator IF filter using shear horizontal wave on heavy metal film/quartz substrate

By composing interdigital transducers (IDTs) and reflectors made of a heavy metal film such as Au, Ta, or W on an ST cut 90/spl deg/X propagation (direction perpendicular to X-axis) quartz substrate, the authors have succeeded in exciting a new type of shear horizontal (SH) wave. This wave has a large electromechanical coupling factor, a very large reflection coefficient and excellent temperature characteristics. Though a conventional longitudinally-coupled resonator filter using Rayleigh waves on an ST cut X propagation quartz substrate requires more than 300 fingers of Al grating reflector on each side of the Al-IDTs, our newly developed resonator filter, utilizing this SH wave, requires only about 10 grating fingers for the reflector at most due to the large reflection coefficient. The authors applied this SH wave to filters for the first intermediate frequency (IF) stage of global system for mobile communications (GSM), personal handy phone system (PHS) and personal digital cellular (PDC in Japan) system. As a result, we succeeded in developing low loss and small-sized IF filters (3/spl times/3/spl times/1.03mm/sup 3/) having a high stop band rejection, a sufficient bandwidth without expansion coil, and excellent temperature properties for the first time.

Preparation of (K, Na)NbO 3 -CaTiO 3 film by RF magnetron sputtering

Lead-free piezoelectric (K, Na)NbO₃-CaTiO₃ (KNN-CT) films were prepared on Pt/Ti/SiO₂/Si substrates by RF magnetron sputtering. Co-sputtering using a number of KNN-CT targets which vary in compositions of Na/(K+Na) ratio and amount of CaTiO₃ provided variations in compositions of KNN-CT films. The obtained KNN-CT films had compositions corresponding to the average compositions of the used targets represented by chemical formula of (1-n)(K_1-x, Na_x)NbO₃-nCaTiO₃ (x=0.460-0.617, n=0.000-0.065) and the compositional dependencies of their piezoelectric properties were studied. Most KNN-CT films with n>0.000 exhibited relatively high transverse piezoelectric coefficients |e₃₁ *|=|d₃₁|/s_11,p>6.0C/m² (where s_11,p is elastic compliance of the KNN-CT films), whereas n=0.000 |e₃₁ *|<;5.0C/m². In XRD analysis, (002) peak angle of these pseudocubic perovskite films increased with increase of n. From these results, we conclude that CaTiO₃ was successfully substituted as part of KNN and piezoelectric constant increased by effect of CaTiO₃. In addition, the KNN-CT films with x=0.587-0.617 and n=0.027-0.053 exhibited higher |e₃₁ *| than any other x and n. Moreover, by 750°C post-annealing process, |e₃₁ *| of the KNN-CT film with x=0.587 and n=0.040 was enhanced and the highest |e₃₁ *|=11.7C/m² was confirmed. This result of our experiment shows one of highest piezoelectric coefficient for lead free piezoelectric films.