Eiichi Takata

Surface acoustic wave duplexer for US personal communication services with good temperature characteristics

The transmission (Tx) and receiving (Rx) passbands of the Personal Communication Services (PCS) mobile phone system in the US are 1850–1910 MHz and 1930–1990 MHz, respectively. The transition bandwidth between Tx and Rx is very narrow, 20 MHz. A duplexer for the US-PCS employing surface acoustic waves (SAWs) requires a substrate which has good temperature stability, an optimum electromechanical coupling factor, a large reflection coefficient, and a good resonant mechanical Q value. Previously, there did not exist any substrate suitable for the US-PCS SAW duplexer. In this paper, we describe a new substrate that is suitable for the US-PCS SAW duplexer and a US-PCS SAW duplexer constructed with this new substrate.

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.

Characterization of piezoelectric properties of PZT thin films deposited on Si by ECR sputtering

Abstract Ferroelectric lead zirconate titanate (PZT) thin films are deposited at a low substrate temperature (530–590 °C) by an electron cyclotron resonance (ECR) sputtering method using two targets: a ceramic PZT and a lead metal target. Si wafers are employed as substrates. The piezoelectric constant e31 is 2.1 C m−2 without poling treatment for a PZT film deposited at 550 °C.

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.

SAW substrate, with coupling factor and excellent temperature stability suitable for duplexer of PCS in US

The pass-bands of a transmission (Tx) and a receiving (Rx) of the Personal Communication Services (PCS) Handy-phone in US are 1850-1910 MHz and 1930-1990 MHz, respectively. The transition bandwidth between the Tx and the Rx is very narrow as 20 MHz compared with other systems. A duplexer for the PCS using surface acoustic wave (SAW) requires a SAW substrate, which has a the good temperature stability, an optimum electromechanical coupling factor, and a large reflection coefficient. Some Rayleigh waves and leaky SAW (LSAW) on various substrate or structures have a good temperature characteristic, but almost all of them have not an optimum coupling factor and a large reflection coefficient for the US-PCS duplexer. In 2003, the authors reported a US-PCS SAW duplexer having good temperature stability, a steep frequency characteristic in transition band, a low loss, and a large out-of-band suppression. This paper describes the detail of the new substrate having the good temperature stability, the optimum electromechanical coupling factor, and sufficient reflection coefficient.

SAW substrate for Duplexer with Excellent Temperature Characteristics and Large Reflection Coefficient realized by using Flattened SiO2 Film and Thick Heavy Metal Film

Authors previously proposed a SAW PCS-duplexer with an excellent temperature coefficient of frequency (TCF) and a good frequency characteristic composed of a thick-SiO2/thin-Au-electrodes/LiTaO3 structure. However, a sheet resistance of thin Au electrode is large, compared with thick Al-electrode, so thin Au-electrode is not suitable for filters requiring low loss. Authors tried to use thick Cu electrodes with small resistance. By flattening large convex portions on the SiO2 surface, a SAW substrate suitable for US-PCS duplexer with low insertion loss and an excellent TCF was realized

Anodic bonding of lead zirconate titanate ceramics to silicon with intermediate glass layer

Abstract Anodic bonding was investigated for bonding lead zirconate titanate (PZT) ceramics to silicon wafers. Sputtered borosilicate glass was used as an intermediate layer. Well-bonded wafers were obtained by applying voltage of 300 V at 500 °C or 500 V at 400 °C. The bonded area increased while applied voltage was kept constant. The size of the bonded area depended on the resistivity of the ceramics at bonding temperatures. A cantilever was made with a PZT-Si bonded wafer, and its basic operation exhibited potential usefulness for application to microsensors and microactuators.

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.

Low loss intermediate-frequency resonator filter using shear horizontal type leaky surface acoustic wave on α-phase heavy metal film/quartz

By applying a new shear horizontal (SH)-type leaky surface acoustic wave (LSAW) excited by interdigital transducers (IDTs) and reflectors made of Ta or W on an ST-cut 90°X-propagation (direction perpendicular to X-axis) quartz substrate, we succeeded in fabricating very small resonator filters (1/5–1/4 of conventional device sizes). However, the Ta and W films used in our filters were β-Ta and β-W, which have resistances higher than that of an Al film. α-Ta and α-W films with very low resistivities have been successfully deposited in place of β-Ta and β-W films. The insertion loss of resonator filters consisting Ta- or W-electrode/ST-90°X quartz has been improved by 1.5–8 dB using the α-Ta or the α-W film electrode.

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.