Takuo Hada

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.

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

Magnetic Sensor Based on Surface Acoustic Wave Resonators

In this paper, we describe a new type of magnetic surface acoustic wave (SAW) sensor that consists of interdigital transducers made of a magnetostrictive material, Ni, on a quartz substrate. This sensor can be used as an element of a resonator-type wireless SAW sensor system because it has a high Q. Moreover, it has the merits of being fabricated easily using the existing process for SAW devices because its structure is the same as that of general SAW resonators. When an external magnetic field of about 100 mT was applied perpendicularly to the direction of SAW propagation, the frequency change obtained was 200 ppm. In addition, the developed sensor was applied in a passive and wireless open/close sensing system and the reading distance obtained was 3 m.

Pyroelectric aluminum nitride micro electromechanical systems infrared sensor with wavelength-selective infrared absorber

This paper describes a micro electromechanical systems type wavelength-selective pyroelectric sensor, with highly c-axis oriented Aluminum nitride film as the pyroelectric material. Wavelength-selective infrared absorption is realized via periodic structures of holes patterned into the top metal electrode that also collects pyroelectric charge signal. The periodic hole array results in optical absorption resonances whose wavelength is determined by the hole pitch, demonstrated experimentally using a Fourier transform infrared spectrometer and numerically calculated using the finite difference time domain method. A significant difference in infrared absorption between patterned and unpatterned detectors is demonstrated through optical experiments comparing the pyroelectric responses.

SAW magnetic sensors composed of various Ni electrode structures on quartz

A shear horizontal type of surface acoustic wave (SAW) magnetic sensor composed of a Ni electrode of magnetrostrictive metal and an ST-cut 90°X quartz (propagation direction: perpendicular to X-axis) substrate was fabricated. In order to obtain a higher magnetic sensitivity, one-port SAW resonators composed of 3 kinds of Ni electrodes structures on the quartz, such as (a) grooved Ni electrodes, (b) additional overlaid Ni films on grooved Ni electrodes, and (c) Ni electrodes on the quartz, were fabricated. Their sensitivities were almost same, but the SAW resonator composed of (c) structure had highest Q. Using this SAW resonator, a passive, battery-less, and wireless communication system was realized.