Osamu Kawasaki

A novel temperature compensation method for SAW devices using direct bonding techniques

We have developed a novel temperature compensation method for SAW devices using a direct bonding technique. The SAW device applied this method was composed of a conventional piezoelectric substrate such as LiTaO/sub 3/ and LiNbO/sub 3/, directly bonded without any bonding agents to a glass substrate having a relatively low thermal expansion coefficient (TEC). The piezoelectric substrate and the glass substrate were bonded in an atomic scale and the interface was very uniform. Therefore, the thermal strain at the surface of the bonded substrate caused by the difference between the TECs of the substrates was quite uniform and stable. With this structure, the thermal expansion of the piezoelectric substrate was restrained and the elastic constant of the piezoelectric substrate was changed by the thermal strain. Using this technique, we have succeeded to improve the temperature coefficient of frequency (TCF) of the SAW devices without causing any deterioration in the frequency response. This novel temperature compensation method is very promising for RF-SAW device applications.

Novel composite piezoelectric materials using direct bonding techniques

Novel composite piezoelectric materials for new piezoelectric devices are reported. The fabrication process using direct bonding techniques, bonded interface microstructures, and usefulness for piezoelectric devices are also reported. Monocrystalline piezoelectric materials such as LiNbO/sub 3/ and LiTaO/sub 3/ were successfully bonded directly onto the same material or different materials including semiconductor, without using any adhesive or such, effecting physically and electro-acoustically optically satisfactory interfaces. Despite the relatively low temperature of the heat treatment, the interface was found uniform, virtually void-free, and to be accomplished in an atomic order by TEM observation. Applications to one-chip electro-acoustic ICs and optical guided wave devices are described.

Shock sensors using direct bonding of LiNbO/sub 3/ crystals

We have developed a shock sensor made with a bimorph type cantilever using by a technique of directly bonding piezoelectric single crystals. The cantilevers polarization-inverted structure was achieved by directly bonding LiNbO/sub 3/ single-crystal wafers having reverse polarization. This technique did not require any bonding agent. The basic characteristics of the shock sensor were evaluated. The resonance frequency of the cantilever having a length of 2 mm was 20 kHz. The sensor made from 140/spl deg/ rotated Y cut LiNbO/sub 3/ wafers had a high sensitivity of 6.4 mV/G, and excellent linearity.

Variable property crystal resonators by direct bonding techniques

Novel single-crystal bulk acoustic wave (BAW) resonators have been developed. These resonators realize desired electrical properties by directly bonding piezoelectric single crystals such as LiNbO/sub 3/ and LiTaO/sub 3/. The direct bonding technique fabricates composite piezoelectric substrates with new electrical properties depend on the combination of bonded wafers. For the first trial, polarization-inverted substrates have been fabricated by directly bonding two wafers of Z-cut LiNbO/sub 3/ single crystals having opposite polarization-direction. Second overtone resonators using these substrates provide excellent performance. Typically, the resonator has a high Q-value over 5,000, a figure of merit of 138, a capacitance ratio of 40, a resonant resistance of 30 /spl Omega/ and a frequency deviation of -50 ppm//spl deg/C.

Direct bonding of piezoelectric materials onto Si

New composite semiconductor-piezoelectric materials fabricated by direct bonding technology are reported. The fabrication process, analysis of the bonded interface microstructures, and their applications are also reported.

Even-order thickness-shear mode resonators using X-cut LiTaO/sub 3/ plates realized by a direct bonding technique

Even-order thickness-shear mode resonators with good temperature characteristics have been achieved by applying direct-bonding techniques to X-cut LiTaO/sub 3/ single crystals. The variations in the resonance frequency of their main fast thickness shear mode was less than 500 ppm over the temperature range of -10 to 60/spl deg/C. Moreover, the results of studies on strip type chip resonators using direct-bonded x-cut LiTaO/sub 3/ wafers suggest that fabrication of small sized resonators with no spurious response is feasible. Their typical Q-value was between 3000 and 5000, and the resonant resistance was 10-20 /spl Omega/ at 13 MHz. These values an ideal for a range of applications. We confirmed that the direct bonding technique was particularly suitable for realizing high frequency resonators because the thickness of the resonator could be double that of a conventional fundamental resonator.

New Piezoelectric Bimorph Structure Actuators with High Performances

Abstract We have developed three types of piezoelectric bimorph structure actuators. The first actuator has a displacement of over 3 mm at 100 Vpk and high reliability by resonance effect of the displacement magnifying part. The second one has a displacement of over 1 mm at 100 Vpk and high stability for change in driving frequency by combined two resonances. The third one has a linearity of displacement until 85% of fracture point and low temperature characteristics by a direct bonding technique that bonds piezoelectric single crystals without using adhesive.

A Low-Profile Ladder Filter for Portable Telephones Employing Length Expander Mode

A low-profile piezoelectric ceramic ladder filter was developed. It is less than 2 mm high. Therefore it is suitable for super compact portable telephones. New rectangular bar resonators using the length expander mode were presented and a ladder filter was constructed using these new resonators. The optimization of capacitance ratio and resonator support structure in resonator design and a new piezoelectric ceramic material were discussed. In particular, the heat resistant properties of the material and the vibration transmission to the support structure were considered. These properties were improved by using the new ceramic material and a new support structure. Finally an experimental filter was constructed. It exhibited excellent characteristics which satisfied the specifications for the second IF filter of a digital cellular telephone.