Y. Satoh

A design of antenna duplexer using ladder type SAW filters

This paper describes a design technology of a small antenna duplexer, especially package conditions, by using ladder type SAW filters. This requires not only optimizing the filter design but also the electrode materials and the package design which has matching circuitry for the duplexer configuration. The matching circuitry was incorporated into a microstrip structural pattern which is designed onto the surface of a multilayer ceramic package. To avoid the deterioration of in-band VSWR and reflection coefficient of the stop-band after rotating phase caused by the matching pattern, the characteristic impedance of the matching pattern was designed to be 1.06 times Zo. To obtain the high stop-band attenuation and Tx-Rx isolation characteristics, the package parasitic inductance was used by the multilayer structure design of the package.

A miniaturized 3 /spl times/ 3-mm SAW antenna duplexer for the US-PCS band with temperature-compensated LiTaO/sub 3//sapphire substrate

This paper describes a temperature-stable and miniaturized SAW antenna duplexer for the 1.9 GHz US-PCS band that uses a temperature-compensated 42/spl deg/ Y-X:LiTaO/sub 3//sapphire bonded substrate. In this duplexer, the temperature coefficient of frequency is reduced to half or two-thirds of that of a conventional LiTaO/sub 3/ substrate. Also, it is shown that our new duplexer has a smaller insertion loss and offers sufficient power durability. These improvements are mainly due to the characteristics of sapphire, such as its larger thermal conductivity and smaller dielectric constant. Furthermore, the performance of our SAW duplexer is compared with that of two kinds of BAW duplexers, which are competitive technologies. As a result, it is shown that our newly developed SAW duplexer offers equal or better performance in a smaller package. This implies that our SAW duplexer is the best and the smallest PCS duplexer.

Temperature compensated LiTaO/sub 3//sapphire saw substrate for high power applications

A new temperature-compensated SAW substrate for high power applications was developed based on bonded LiTaO3/sapphire. Because of its small thermal expansion coefficient, large Youngs modulus, and large electric resistivity, sapphire is an ideal material for a support substrate. In addition, the large thermal conductivity of sapphire brings efficient heat dissipation. Surface activated bonding was used and optimized to strongly bond LiTaO3 and sapphire without any damage or bow. Keywords-SAW; LiTaO3; sapphire; temperature compensation; surface activated bonding; heat dissipation; US-PCS;

12E-2 X-Band Filters Utilizing AlN Thin Film Bulk Acoustic Resonators

A filter with aluminum nitride thin-film bulk acoustic resonators (FBAR) for the X-band was developed. The FBAR has an air gap beneath the resonator to isolate acoustically from a substrate, and is extremely thin to operate in the X-band. The FBAR has two structural features - a sacrificial layer to make the air gap was very thin in order to prevent the resonator from cracking on the edge of the air gap, and a resonator was deformed to dome shape by stresses of the films to keep the air gap. The fabricated FBAR operated successfully with a keff 2 of 6.40%, a resonance Q of 246, and anti-resonance Q of 462. The fabricated filter had a center frequency of 9.07 GHz, a fractional bandwidth of 3.1%, a minimum insertion loss of -1.7 dB, and an out-of-band rejection of -21 dB.

Use of fluorine-doped silicon oxide for temperature compensation of radio frequency surface acoustic wave devices

This paper investigates acoustic properties, including the temperature coefficient of elasticity (TCE), of fluorine-doped silicon oxide (SiOF) films and proposes the application of the films to the temperature compensation of RF SAW devices. From Fourier transform infrared spectroscopy (FT-IR), SiOF films were expected to possess good TCE properties. We fabricated a series of SAW devices using the SiOF-overlay/Cu-grating/LiNbO3-substrate structure, and evaluated their performance. The experiments showed that the temperature coefficient of frequency (TCF) increases with the fluorine content r, as we expected from the FT-IR measurement. This means that the Si-O-Si atomic structure measurable by the FT-IR governs the TCE behavior of SiO2-based films even when the dopant is added. In comparison with pure SiO2 with the film thickness h of 0.3 wavelengths (λ), TCF was improved by 7.7 ppm/°C without deterioration of the effective electromechanical coupling factor K2 when r = 3.8 atomic % and h = 0.28λ. Fluorine inclusion did not obviously influence the resonators Q factors when r <; 8.8 atomic %.

Low loss ladder type SAW filter in the range of 300 to 400 MHz

Low loss SAW filters in the range of 300 to 400 MHz for communication systems have been developed, which have ladder circuit structure using 36° rotated Y-cut LiTaO3. This type of filter has low loss and high stop band rejection, however, a spurious mode appears, which depends on electrode thickness and a reflectors electrode pitch of a resonator. Low frequency range filters need thick Al electrodes more than 7% of wave length to shift the resonant frequency of spurious mode to a frequency range higher than the pass-band frequency range. To reduce the spurious response, the design of an electrode pattern and electrode material having more mass effect than Al were investigated by simulation and experiment. The spurious response can be suppressed by optimizing a reflectors electrode pitch. By using Au film, thin film of about 1.5% of wave length can be applied to a filter. SAW filters in the range of 300 to 400 MHz with fractional band width from 2 to 4% were manufactured and mounted in SMD type 5×7×1.4 mm ceramic packages, which have 2 dB minimum insertion loss and attenuation characteristics of about 40 dB. Input and output impedance of filter are 50 Ω

Analysis and Suppression of Side Radiation in Leaky SAW Resonators

This paper discusses side acoustic radiation in leaky surface acoustic wave (LSAW) resonators on rotated Y-cut lithium tantalite substrates. The mechanism behind side radiation, which causes a large insertion loss, is analyzed by using the scalar potential theory. This analysis reveals that side radiation occurs when the guiding condition is not satisfied, and the LSAW most strongly radiates at the frequency in which the LSAW velocities in the grating and busbar regions approximately correspond to each other. Based on these results, we propose a narrow finger structure, which satisfies the guiding condition and drastically suppresses the side radiation. Experiments show that the resonance Q of the proposed structure drastically improves to over 1000 by suppressing the side radiation, which is three times higher than for a conventional structure. Applying the proposed resonators to the ladder-type SAW filters, ultra-low-loss and steep cutoff characteristics are achieved in the range of 800 MHz and 1.9 GHz.

Development of ladder type SAW RF filter with high shape factor

The paper presents ion implantation technology to improve the shape factor of a ladder-type SAW RF filters for mobile communication systems. The improvement of the shape factor was confirmed experimentally. However we found that the SAW phase velocity is decreased by ion implantation. To stabilize and recover the SAW phase velocity, several annealing conditions were investigated. At the annealing condition of over 450/spl deg/C/spl times/1 hour, SAW phase velocity was recovered to almost the same as the initial velocity. In the past, the shape factor values of ladder-type SAW filters using a LiTaO/sub 3/ substrate have been almost 1.7. The ion implantation technology has been applied to a PDC (personal digital cellular) -1.5 GHz SAW band pass filter using a LiTaO/sub 3/ substrate. We have obtained the shape factor value of 1.4 under the following conditions; ion: double charge Ar/sup ++/, dose: 5/spl times/10/sup 13//cm/sup 2/, acceleration voltage: 180 keV.

Transversely coupled resonator filters with 0.1% fractional bandwidth in quartz

This paper describes the realization of transversely coupled resonator filters (TCF) with 0.1% fractional passband width in quartz substrate. The coupling of modes analysis in the transverse direction is applied to the TCF design for the investigation of the passband width determination. As a result, it is found that the passband width can be widened by making the surface acoustic wave (SAW) velocity difference between the interdigital transducer (IDT) region and the resonator gap region smaller. We propose to apply the grating structure to the common ground bar to reduce the SAW velocity difference, instead of uniform metal. We fabricate TCFs using the grating type common ground bar in quartz for specific applications.

A study of miniaturization technique of SAW antenna duplexer for mobile application

This paper describes the miniaturization techniques for surface acoustic wave antenna duplexers. Previous duplexer design consisted of two filters, one transmitter, one receiver, and matching circuit enclosed in one package. For package miniaturization, it is necessary to change the design of the structure. This includes the matching circuit, since it is designed on the surface of the package. Replacing previous tungsten material, the new matching circuit is achieved by a copper stripline embedded within the package. Package material also changes from aluminum oxide ceramics to glass ceramics. As for filter chip, transmitter and receiver filter are combined into one chip. A single layer of aluminum magnesium was examined, in order to provide better power durability.