High-frequency devices operating at 3 GHz or higher are required, for instance, for future 4th generation mobile phone systems in Japan. Using a substrate with a high acoustic velocity is one method to realize a high-frequency acoustic or elastic device. A Lamb wave has a high velocity when the substrate thickness is thin. To realize a high-frequency device operating at 3 GHz or higher using a Lamb wave, a very thin (less than 0.5 μm thick) single-crystal plate must be used. It is difficult to fabricate such a very thin single crystal plate. The authors have attempted to use a c-axis orientated epitaxial LiNbO(3) thin film deposited by a chemical vapor deposition system (CVD) instead of using a thin LiNbO(3) single crystal plate. Lamb wave resonators composed of a interdigital transducer (IDT)/the LiNbO(3) film/air gap/base substrate structure like micro-electromechanical system (MEMS) transducers were fabricated. These resonators have shown a high frequency of 4.5 and 6.3 GHz, which correspond to very high acoustic velocities of 14,000 and 12,500 m/s, respectively, have excellent characteristics such as a ratio of resonant and antiresonant impedance of 52 and 38 dB and a wide band of 7.2% and 3.7%, respectively, and do not have spurious responses caused by the 0th modes of shear horizontal (SH(0)) and symmetric (S(0)) modes.
In this study, several read/write (R/W) tests were conducted using a hard-disk-drive-type ferroelectric data storage test system based on scanning nonlinear dielectric microscopy (SNDM). A periodically inverted signal, which corresponded to artificial domain stripes formed on LiTaO 3 single crystal, could be read correctly with a bit rate of 2 Mbps using this test system. Bit writing on a 50-nm-thick epitaxial LiTaO 3 film at 20 Mbps was also demonstrated. In addition, a noncontact probe-height control technique was adapted to solve the problem of tip abrasion. The gap distance between a probe and a medium surface was successfully controlled on the nanometer order using a noncontact SNDM technique with sharp-pointed tungsten needle probes prepared by electrolytic polishing. Bit writing under a noncontact state was also studied. Artificial domain dots with diameters of less than 100 nm could be formed under the noncontact state.
It has been considered that it is difficult to realize a high-frequency device of 3 GHz or more, for instance, for a fourth generation mobile phone system in Japan, using a conventional surface acoustic wave (SAW) substrate. In this study, we attempted to fabricate a highfrequency resonator using Lamb waves, which has a high velocity and consists of a thin LiNbO 3 film deposited by chemical vapor deposition (CVD). As a result, a 1-port Lamb wave resonator composed of an electrode/thin epitaxial LiNbO 3 film/air-gap/base substrate was fabricated. The measured resonator has a high resonant frequency of 4.5 GHz, which corresponds to a very high velocity of 14,000 m/s, a large impedance ratio of 52 dB, and a relatively wide bandwidth of 7.2%.
In this paper, we report a new structure of a shear horizontal (SH) type boundary acoustic wave for cellular phone applications. Such a structure composed of electrodes with a low shear wave velocity between two materials, namely, the SiO 2 film/Au-electrode/LiNbO 3 substrate, is proposed. The ladder filter used in this paper had this structure. By changing the propagation angle of the acoustic wave, the electromechanical coupling factor k 2 range from 0 to 16% was obtained, as well as a normalized bandwidth range 0.67 to 1.85 fold as large as that of a 36 -46 Y-X LiTaO 3 leaky surface acoustic wave (LT-LSAW) filter. In addition, an excellent temperature coefficient of delay time (TCD ¼ 25 ppm/ C) and a large mutual coupling coefficient 12 (¼ 0:15) were also obtained.
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