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This article reports a new concept of surface-acoustic-wave (SAW) resonator, which uses shear horizontal (SH) wave confined in a thin LiTaO3 (LT) layer supported by a quartz (Qz) substrate. The LT layer is 35–50°YX LT, and the quartz substrate is 35–60°Y90°X Qz. A negative temperature coefficient of frequency (TCF) of the SH SAW in the LT layer is compensated by the quartz substrate, which shows a wide range of positive TCF depending on the crystalline orientation. Excellent TCFs of 2 and −10 ppm/°C were measured for the series and parallel resonance frequencies, respectively. The strong confinement of the SH SAW in the LT layer results in the best level of resonance characteristics ever reported. The measured impedance ratio reached 84 dB. On the other hand, spurious waves other than the SH SAW are not confined in the LT layer due to the unique properties of quartz, which results in spurious-free characteristics throughout a wide frequency range.

High impedance ratio (Z-ratio), low temperature coefficient of frequency (TCF) and spurious free characteristic are three main requirements for surface acoustic wave (SAW) resonators. The reported LiTaO3/Quartz (Qz) hetero acoustic layer (HAL) resonator can satisfy them, but the bandwidth is too narrow. LiNbO3 (LN) is suitable for wideband resonators, but the TCF is too large due to its high coupling factor. In this work, we study wideband HAL SAW resonators combining LN and three kinds of substrates with positive TCF and small coefficient of thermal expansion, including Qz, ABC-G and ZERO glasses. By simulation, the Euler angles of (0°, 101°, 0°) for LN, (0°, 160°, 90°) for Qz, and the 0.1–0.2λ (λ is the wavelength) LN thickness are used. Results show LN/Qz, LN/ABC-G and LN/ZERO exhibit Z-ratio of 82.7 dB, 76.2 dB and 76.2 dB, respectively. LN/ABC-G shows the lowest TCF of −61 ppm C−1 at resonance frequency and −62 ppm C−1 at anti-resonance frequency.

This paper describes 4 and 7 GHz solidly-mounted structure bulk acoustic wave resonators (SM-BAWRs) using LiNbO3 (LN) thin plates. A Bragg reflector solidly supports the LN thin plate. The two kinds of SM-BAWRs use thickness extension mode in 0.81 and 0.5 μm thick 36°Y LNs. The Bragg reflector is made of Al or SiO2, and Ta films. The 0.81 μm thick LN SM-BAWRs with each acoustic layer thickness 0.23 wavelength (λ), which is almost optimum thickness, exhibited resonance frequency (f r) of 3.84 GHz, antiresonance frequency (f a) of 4.17 GHz, a bandwidth of 8.4%, an impedance (Z) ratio of 54 dB, and coupling factor k t 2 of 17.7%. Despite using an acoustic film 0.12λ much thinner than the optimum thickness, SM-BAWR using the 0.5 μm thick LN exhibited f r of 6.86 GHz, f a of 7.15 GHz, and Z ratio of 37 dB. Those results suggest a high potential for this device.

In this study, a first shear horizontal mode (SH 1 mode resonator) for high-frequency filters were investigated. From FEM simulation, it was confirmed that the SH 1 mode plate wave had a high phase velocity of 20 km/s and a high electro-mechanical coupling factor (k2) of 14% on (0°, 60°-70°, 0°) LiTaO 3 (LT) with a thickness of 0.1λ (λ: wavelength). The high k2 was achieved by forming an electrically shorted plane on the bottom LT surface (opposite side of an interdigital transducer electrode, IDT). The SH 1 mode plate wave resonator was fabricated on a 0.5 µm thick LT film supported with a Si substrate. The IDT had a λ of 4.5 µm and a thickness of 100 nm (0.02λ). The fabricated SH 1 mode plate wave resonator showed a resonance frequency (f r ) of 2.78 GHz, anti-resonance frequency (f a ) of 2.92 GHz, a bandwidth (BW) of 5%, and an impedance (Z) ratio of 38 dB. The anti-resonant phase velocity was calculated as high as 13,050 m/s, which showed a potential for high frequency filters. The poor impedance ratio was caused by the low mechanical quality factor (Q m ) of Cu IDT used in the fabrication and the not optimized fabrication process.

This paper reports simulation and experimental study to strongly excite high harmonic SAW using a grooved interdigital transducer (IDT). The grooved IDT is made by etching LiNbO 3 (LN) and filling the grooves with metal. Simulation was done to find promising designs. Then, SAW resonators with wavelengths (λ) of 5.2 µm and 1.3 µm were fabricated on 26°YX LN using Al for IDTs. Strong excitation of high harmonic SAW was confirmed. The SAW resonator with λ of 1.3 µm generated the 3rd harmonic SAW at 8.1 GHz with an impedance ratio of 32 dB.

This paper reports a low velocity hetero acoustic layer (HAL) surface acoustic wave (SAW) resonator using a combination of 11°YX lithium niobate (LN) thin plate and YX quartz (Qz) substrate with copper (Cu) interdigital transducers (IDTs). The fabricated one-port (1-port) SAW resonator attained a low effective velocity of 2416 ms-1 at resonance with an impedance ratio (Z-ratio) of 80 dB and a relative bandwidth (BW) of 11%. The resonator has temperature coefficient of frequency (TCF) of -129 ppm°C-1 at resonance frequency (f r ) and -117 ppm°C-1 at antiresonance frequency (f a ). The resonator has a roughly 30% lower velocity compared with the previously developed LT/ Qz HAL SAW resonator and a roughly 40% slower than the metallized SH-SAW velocity on 11°YX LN, indicating its potential for low-band filter applications.

Acoustic wave devices utilizing plate waves in thin lithium tantalate (LiTaO3) have the potential of achieving high resonance frequency with a suitable electromechanical coupling factor and a relatively small temperature coefficient of frequency (TCF). The influence of Euler angle and plate thickness on the characteristics of plate waves has been investigated. High-frequency resonators using first antisymmetric Lamb wave mode (A1) in (0°, 42°, 0°) LiTaO3 thin plates have been fabricated and optimized. The resonance frequency is as high as 5 GHz, with a relative bandwidth of 7.3% and an impedance ratio of 72 dB. Finally, the TCF of (0°, 42°, 0°) LiTaO3 has been evaluated. Therefore, it is proved that A1 Lamb wave mode propagating in LiTaO3 at a Euler angle close to (0°, 42°, 0°) is suitable for high-frequency devices.

This paper describes a high-frequency bulk acoustic wave resonator (BAWR) with a solidly-mounted (SM) structure using single crystal LiTaO3 (LT) thin plates. A Bragg reflector solidly supports the LT thin plate, which is fragile if self-suspended. The two kinds of BAWRs use a strip-type thickness shear mode in 0.56 μm thick X37°Y LT and X127°Y LT. The Bragg reflector is made of 5 pairs of Al and Ta films, i.e. 10 layers in total. The X37°Y LT SM structure BAWRs exhibited a resonance frequency (f r) of 3.250 GHz, an anti-resonance frequency (f a) of 3.463 GHz, a bandwidth (BW) of 6.6%, and an impedance (Z) ratio of 48 dB. The X127°Y LT BAWR has a similar characteristic with f r of 3.153 GHz, f a of 3.367 GHz, a BW of 6.8%, and a Z ratio of 46 dB. The X37°Y LT BAWR showed an advantage of 2 dB compared with the X127°Y LT one. The Al film acts as a low acoustic impedance film, but an acoustic impedance layer combination of Al and Ta films is not suitable and that of SiO2 and W films suitable among the four combinations, Al/Ta. SiO2/Ta, Al/W, and SiO2/W films. Although the acoustic impedance layer combination, the acoustic film quality, the structure, electrode design, and fabrication process of the fabricated BAWRs were not optimized yet, this result suggests the high potential of this device.

In this study, the solidly mounted resonators (SMRs) using the thickness expansion (TE) mode of LiNbO3 (LN) single crystal thin plate were investigated. The dispersion curves of the rotated Y-LN plate were drawn by plotting the admittance calculated by FEM. From the calculated dispersion curves, the vibration mode and the energy trapping were confirmed. An SMR composed of an Al electrode, a 1 µm thick 20°Y-LN single crystal plate, an acoustic multilayer and a Si substrate was fabricated. TE mode with 7.1% bandwidth and 34.3 dB impedance ratio was observed at 3.2 GHz. 1.7 GHz thickness shear (TS) mode response was also excited since the fabricated 20°Y-LN SMR was not optimized in terms of the Euler angle of LN. The frequency characteristics could be improved by optimizing the Euler angle and electrode structures.

The common materials of bulk acoustic wave (BAW) resonators are AlN and ScAlN. For a wider bandwidth, the Sc to Al ratio in ScAlN is increased up to 40%, but the Q factor often deteriorates and the impedance (Z) ratio does not improve significantly. For better filter performance, this study investigated monocrystalline LiTaO 3 (LT) as a piezoelectric material for a high frequency strip type thickness shear mode (TS) solidly mounted resonator (SMR). We selected the SMR instead of a film BAW resonator (FBAR) with a cavity, because the suspended ultrathin LT plate is fragile. The strip type TS mode SMR is composed of two Al electrodes, a 2.0 µm thick X LT plate, an Al electrode, eight layers of SiO 2 and Ta film (4+4 layers) and a 350 µm thick Si substrate from the top. The fabricated SMR shows a center frequency of 1 GHz, a bandwidth of 6.7% and an $Z$ ratio of 62 dB. The temperature coefficients of frequency (TCF) at series and parallel resonance are as good as - 17 and -34 ppm/°C, respectively.

Ultrathin lithium niobite (LN) and lithium tantalate (LT) have opened a new era of acoustic wave devices. The performances such as impedance ratio, bandwidth and temperature stability of new types of devices are incredibly high compared with those of conventional ones. The R&D is showing a kind of boom in both industry and academia. In this paper, plate wave devices and HAL (Hetero Acoustic Layer) SAW (surface acoustic wave) devices using ultrathin LN or LT developed by the authors' group are described.

A Hetero Acoustic Layer (HAL) surface acoustic wave (SAW) device is a new class of SAW device using a thin LT or LN layer rigidly mounted on a substrate. In the past reports, the LT layer was as thin as 0.13-0.221 ( 80 dB), but this range of thickness is not easy to control in mass-production. In this study, we investigated the design space at larger LT thickness by FEM simulation. In the design space near the conventional one, in-band ripples and/or out-of-band spurious responses are generated. If a 1.4 times thicker Al or Cu electrode is combined with a LT layer thicker than a specific value (1λ for Al and 4λ for Cu), however, the ripples and spurious responses almost disappear and the deterioration of impedance ratio is limited. On the other hand, by using further thicker electrodes, a higher mode of SAW is excited preferentially at 2-2.6 times higher frequency than the fundamental mode.

Acoustic wave devices utilizing plate waves in thin lithium tantalate (LiTaO

This paper reports hetero acoustic layer (HAL) surface acoustic wave (SAW) resonators using a thin LiTaO 3 (LT) plate with negative TCF and a quartz substrate with positive TCF. In the previous study, a high impedance (Z) ratio (82 dB), an excellent temperature coefficient of frequency (TCF: 2 ppm/°C), and spurious-free characteristic up to 14 GHz were demonstrated. In this study, two kinds of LT/ quartz HAL SAW resonators with different wavelengths of interdigital transducer (IDT) were fabricated, and measured results were compared with simulated ones. The measured bandwidths (BWs) roughly agreed with the simulated ones. Although many measured values of Z ratios are lower than the simulated ones, the best Z ratios among them are similar to the simulated ones. This result is reasonable taking account of the imperfectness of laboratory-level fabrication, and suggests that the simulation in this study well predicts the performance of real devices.

This paper describes a bulk acoustic wave (BAW) high-frequency resonator with a solidly mounted structure using a single crystal LiTaO3 (LT) thin plate. A Bragg reflector solidly supports the LT thin plate, which is fragile if self-suspended. The BAW resonator uses a thickness shear mode in 1.5 μm thick X-LT. The Bragg reflector is made of four pairs of SiO2 and Ta films, i.e. eight layers in total. The fabricated device works at a resonance frequency of 1.14 GHz and an antiresonance frequency of 1.23 GHz, showing a bandwidth of 7.9% and a low-temperature coefficient of frequency of −16 ppm °C−1 and −26 ppm °C−1 at the maximum and minimum admittances, respectively. The measured impedance ratio is 61 dB, although the structure and fabrication process are not optimized yet, suggesting a high potential for this device.

This paper reports the spurious characteristics of Hetero Acoustic Layer (HAL)SAW resonators at high frequency. Spurious-free characteristic is important for carrier aggregation etc. in addition to high impedance ratio, high Q and small temperature coefficient of frequency (TCF). Four types of LT / quartz HAL SAW resonators were fabricated and evaluated up to 14 GHz. All devices show no significant spurious responses. By contrast, a reference HAL SAW resonator with a structure of LT / SiO 2 / Si shows strong spurious responses near the main response. The spurious responses get closer to the main response using a thinner SiO 2 layer, which is inconvenient for TCF compensation. In addition, the TCF of the HAL SAW resonators are discussed in detail.

This article discusses the possibility of tunable RF surface-acoustic-wave (SAW) and bulkacoustic-wave (BAW) filters using varactors (VCs) integrated by the skillful use of micro-electromechanical system (MEMS) technologies. First, the reasons that RF tunable filters are in demand for current wireless communications are explored, and various RF tunable filters are surveyed and compared. Next comes a discussion of tunable RF SAW/BAW filters combined with MEMS technologies, showing that high performance can be expected, provided that some key technologies are developed. Finally, the article introduces tunable SAW filters, which the authors developed in a research project called "heterointegration" to demonstrate what is possible by combining MEMS technologies with RF SAW/BAW technologies.

A cognitive radio terminal using vacant frequency bands of digital TV (DTV) channels, i.e., TV white space, strongly requires a compact tunable filter covering a wide frequency range of the DTV band (470 to 710 MHz in Japan). In this study, a T-type ladder filter using ultra-wideband shear horizontal mode plate wave resonators was fabricated, and a low peak insertion loss of 0.8 dB and an ultra-large 6 dB bandwidth of 240 MHz (41%) were measured in the DTV band. In addition, bandpass filters with different center frequencies of 502 and 653 MHz at 6 dB attenuation were numerically synthesized based on the same T-type ladder filter in conjunction with band rejection filters with different frequencies. The results suggest that the combination of the wideband T-type ladder filter and the band rejection filters connected with variable capacitors enables a tunable filter with large tunability of frequency and bandwidth as well as large rejection at the adjacent channels of an available TV white space.

A Hetero Acoustic Layer (HAL) SAW device is a new type of SAW device with a solidly mounted monocrystalline piezoelectric thin plate, which can obtain very high impedance ratio (ZR) and small temperature coefficient of frequency (TCF) at the same time. In this study, HAL SAW resonators using a LiTaO 3 (LT) thin plate and a quartz substrate were investigated numerically and experimentally. The resonator fabricated using 20°YX LT and 40°Y90°X quartz exhibited a bandwidth (BW) of 5.0%, a ZR of 82 dB and a Bode Q of 3,000, which have been significantly improved from our previous report. The performance is better by a factor of 1.2 times in BW, 31 dB in ZR and 6.4 times in Bode Q compared with a standard SAW resonator on 42°YX LT, which was fabricated in the same facility. Further improvement in performance is expected after optimizing wafer cut angles, electrode metal and fabrication process.

Surface acoustic wave (SAW) resonators with a moderate bandwidth and a large impedance ratio are obtained by Hetero Acoustic Layer (HAL) structure combing a LiTaO 3 (LT) thin plate and the substrate, which has a high velocity of leaky SAW and a small frequency temperature coefficient (TCF). In this study, a new type of HAL SAW resonators were fabricated using 0.5-1 μm thick 42oYX or 20oYX LT and 42o45'YX or 40oY90oX quartz bonded together. An impedance ratio of 65–70 dB and a TCF of −26 ppm/oC were measured. Those impedance ratios are 13–21 dB better than that of a standard 42oYX LT SAW resonator fabricated in the same facility.

Leaky surface acoustic wave (LSAW) devices on Al-electrode/36–48° YX-LiTaO3 substrates have seen wide use as filters and duplexers in cell phones because they possess a suitable electromechanical coupling factor and reflection coefficient, and a good Q factor for cell phones. In this paper, a new LSAW structure consisting of upper Al electrodes stacked on lower grooved Cu electrodes in LiTaO3 is proposed and compared with Al electrodes (0.1 λ)/42° YX-LiTaO3, which have been considered the best structure. We have been able to improve the characteristics of the LSAW. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(2): 25–31, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10409

A cognitive radio system, which is being investigated in order to use limited frequency resources effectively, requires a tunable filter with a wide variable frequency range. A wideband resonator is required to realize a tunable filter. It was reported that a resonator composed of a Cu electrode/15° YX-LiNbO3 had a large bandwidth of 12%. We attempted to fabricate a one-port resonator composed of a grooved Cu electrode/4° YX-LiNbO3. This resonator was applied to a tunable filter, and a tunable filter having a tunable range of 6.8% in the center frequency was experimentally realized using a bandpass-type filter circuit, and one having a tunable range of 9 to 12% was theoretically realized using a ladder-type filter circuit. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(2): 32–40, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10408

QCM sensor coated by a sensing film has been studied as a gas-sensing device with high gas selectivity and high sensor sensitivity. One of the problems to be solved for practical applications is that a resonance frequency of QCM sensor drifts due to the influence of humidity. In this study, we investigated a compensation method of the humidity drift of QCM sensor for NH3 gas by using the element coated by the reference film, that was prepared by modifying the phosphate group of zirconium phosphate of the sensing film with sodium hydroxide. The response properties of the reference element were measured. The results showed good agreement with the humidity response of the sensor element without reacting to ammonia gas. It was found that the compensation of the humidity drift was successfully accomplished by calculating the frequency difference between the sensor element and the reference element. The application to small QCM (1.3×0.9 mm) was also presented.

The 0-th shear horizontal (SH 0 ) mode plate wave has an electromechanical coupling factor k2 larger than 50% in a (0°, 120°, 0°) LiNbO 3 (LN) plate thinner than 0.1λ, where λ is a pitch of an intergidital transducer (IDT). In the previous study, ultra-wide-band ladder filters composed of cavity type resonators recorded 6 dB bandwidth from 41% to 51% in a digital TV band. However, the structure is fragile, because the LN plate as thin as 0.5–0.6 µm is self-suspended. Inspired by solidly mounted (SM) type film bulk acoustic resonators (FBAR), the authors have come up with SM type SH wave devices. The SM type SH wave resonator has an ultra-wide bandwidth of 20% similar to that of SH0 plate wave resonators. In this study, the SM type ladder filter with an insertion loss of 0.5 dB was developed.

A 0-th shear horizontal (SHo) mode plate wave has an electromechanical coupling factor k2 larger than 50% in a (0°, 120°, 0°) LiNbOs (LN) plate thinner than 0.1λ (λ is a pitch of interdigital transducer). However, the structure is fragile, because the plate thickness is as thin as 0.5∼0.6 μm for devices working in several hundred MHz range. To address this issue, a solidly mounted resonator (SMR) structure was applied to SH mode plate resonators. The materials and layer thicknesses of a Bragg reflector, the Euler angle and thickness of a LN plate, and the thickness and material of electrodes were investigated to obtain large k2 and spurious-free response by finite element method (FEM) simulation. The designed Bragg reflector is composed of 6 layers of SiO2 and AlN. The best Euler angle is (0°, 90°, 0°) and the suitable thickness of a LN plate is 0.3 to 1 λ. Also, heavy and thick electrodes are better for interdigital transducers (IDT). This design is significantly different from that of the cavity type. A SMR type plate wave resonator of several hundred MHz was fabricated using 2 μm thick LN, and a wide bandwidth of 20% was measured.

First anti-symmetric (Ai) mode Lamb wave propagating in a LiTaO 3 thin plate at an Euler angle around (0°, 45°, 0°) has a high velocity. Both phase velocity and electromechanical coupling factor have been evaluated at different propagation angles (0°, 45°, ψ°). A1 mode Lamb wave at (0°, 45°, 0°) offers the highest velocity and largest electromechanical coupling factor, thus proving suitable for high frequency devices. Leaky Lamb waves' velocities have been measured for A0 and zero-th symmetric (S0) modes at different propagation angles by ultrasonic microscopy and are almost similar to the calculated Lamb wave velocities. Whereas Ai mode Lamb wave response has been evaluated at (0°, 42°, 0°), (0°, 42°, 45°) and (0°, 42°, 90°) using a network analyzer. The influence of Al-interdigital transducers' (IDT) thickness on the reflection coefficient has been evaluated for thin (0°, 39°, 0°) LiTaO 3 . An IDT's thickness larger than 0.03λ (λ is the wavelength) is needed to fabricate A1 mode Lamb wave resonators.

Ultra-wide band ladder filters with bandwidth of 41 to 51%, which fully cover the digital TV band, were fabricated using 0-th shear horizontal (SH 0 ) mode plate wave in a (0°, 117.5–120°, 0°) LiNbO 3 (LN) ultra-thin plate. A LN/cavity/Si wafer with a number of devices must be separated into chips as they can be mounted on a printed circuit board (PCB). When the wafer is separated using a dicing machine, the wafer must be protected from strong water showers because the LN ultra-thin plate of 0.5 to 0.6 µm thickness on a cavity is fragile. In this study, the authors developed a new separating (plasma half dicing) method using the micro-loading effect instead of the conventional blade dicing. This method enjoys the advantages of dry process, and no additional etching is needed, because the half dicing grooves are fabricated simultaneously with the device cavities. A chip filter mounted on a PCB after separation shows a good frequency characteristic similar to the one measured using a prober system before separation.

An electric field distribution in a top electrode plane/periodical poled (PP) plate/bottom electrode plane looks like a cross-field model (by Smith) of an interdigital transducer (IDT) to generate a surface acoustic wave (SAW). Therefore, this structure has the possibility to generate an acoustic wave. This structure generates a SAW when the plate is thick, and a plate wave when the plate is thin. Although SAW resonators and resonator filters require grating reflectors at both sides of the IDT, previously reported devices composed of PP-plate on thick substrate don't include any grating reflectors, because they don't have electrode fingers. Therefore, their frequency responses are very weak. Proposing and applying effective edge reflections on the PP-plate instead of grating reflectors, authors fabricated Lamb wave resonators and resonator filters in PP Z-LiTaO 3 plates. As a result, resonators with impedance ratio of 34 dB and resonator filters with a low loss of 2.4 dB and 3 dB bandwidth of 2.2% were obtained.

The Lamb waves and horizontal shear waves' propagation in LiTaO 3 thin plate is investigated as a function of Euler angles. Both velocity and electromechanical coupling factor largely depend on the plate's thickness. Around (0°, 30°, 0°), LiTaO 3 thin plate has a high velocity and a suitable coupling factor for a high frequency filter. Authors fabricated A 1 mode Lamb wave resonators in (0°, 39°, 0°) LiTaO 3 's thin plate. Lamb waves' velocities and leaky Lamb wave' velocities were measured by network analyzer and ultrasonic microscopy. Measured velocities correspond to the ones calculated by FEM. Velocities higher than 20,000 m/s were obtained. It is then shown that A 1 mode Lamb wave close to (0°, 30°, 0°) LiTaO 3 thin plate is suitable for high frequency devices.

Currently, a high frequency device more than 3 GHz is required. High frequency resonators with resonant frequencies of 4.5 and 6.3 GHz were fabricated by utilizing an anti-symmetric first mode (A ; ) of a Lamb wave having a high velocity consisting of a thin LiNbO 3 Sim deposited by a chemical vapor deposition (CVD) system. By measuring polarities of their LiNbO 3 films, it was clarified that the thinner film had a large mixture of +c and ―c domains, and the occupation ratio of main polarity influenced their frequency characteristics.

A CaTiO3-doped (K,Na)NbO3 (KNN-CT) film is a lead-free piezoelectric film that is expected to substitute Pb(Zr,Ti)O3 (PZT) film in piezoelectric micro electro mechanical systems (MEMS). However, the full set of the material constants (elastic constants, piezoelectric constants and dielectric constants) of the KNN-CT film have not been reported yet. In this study, all the material constants of a sputter-deposited blanket KNN-CT film were investigated by the resonance responses of MEMS-based piezoelectric resonators and the phase velocities of leaky Lamb waves on a self-suspended membrane. The phase velocities measured by a line-focus-beam ultrasonic material characterization (LFB-UMC) system at different frequencies were fitted with theoretical ones, which were calculated from the material constants, including fitting parameters. A genetic algorithm was used to find the best-fitting parameters. All the material constants were then calculated. Although some problems arising from the film quality and the nature of deliquescence are observed, all the material constants were obtained exhibiting accuracy within 16 m/s in the phase velocity of leaky Lamb wave.

A oriented polycrystal ZnO film is deposited on many types of substrate. However, an epitaxial ZnO film is deposited on only specific substrates, because it depends greatly on the lattice constant of the substrate. An epitaxial ZnO film with the c-axis oriented horizontally on some types of substrate has been reported. In this study, a orientated epitaxial ZnO film has been deposited on a pre-heat-treated Y-plane (0110) LiNbO3 substrate for the first time. A oriented polycrystal ZnO film has also been deposited on this substrate without pre-heat-treatment. Thus, two orientation directions can be controlled by pre-heat-treatment for the first time. Moreover, their applications to shear bulk wave transducers and surface acoustic wave devices are discussed.

We report the application of an acoustooptic tunable filter (AOTF) to the wavelength monitor in a fiber-optic sensing system with fiber Bragg gratings (FBGs). The system requires good temperature characteristics. A system with good temperature characteristics has been realized using two light wavelengths as references. The accuracy of the measured wavelength was approximately 0.63 pm in the temperature range of the AOTF device from -20 to 70 °C. This accuracy corresponds to strain of about 10-6.

Currently, some duplexers are required to have a good temperature coefficient of frequency (TCF). An Al electrodes/36–48° YX-LiTaO3 substrate, which is used for most surface acoustic wave (SAW) duplexers, does not have a good TCF. Its TCF can be improved by depositing a SiO2 film with a positive TCF on a transversal SAW filter consisting of a substrate with a negative TCF such as LiTaO3 and LiNbO3. However, resonator-type SAW devices combining a SiO2 film, Al electrodes, and a LiTaO3 substrate do not show good frequency characteristics because of their small reflection coefficient and so on. It is considered as a countermeasure that a resonator using the reflection of a shear horizontal (SH) wave at substrate edges will show good frequency characteristics because its reflection coefficient is very large regardless of the Al electrode and SiO2 films thicknesses. It has been difficult to obtain a high-frequency edge reflection resonator using ordinary machining techniques because it requires extremely fine substrate edges. However, a high-frequency edge reflection resonator with a good TCF and excellent frequency characteristics has been realized using our newly developed method of obtaining fine edges.

A small surface acoustic wave (SAW) duplexer for a wide-band code-division multiple access (W-CDMA) system with a good temperature coefficient of frequency (TCF) has been required. However, the conventional SAW duplexer for W-CDMA using Al electrode/50–70° YX-LiNbO3 is large (3.8×3.8 mm2) and its TCF is not good (-80 ppm/°C). When a SiO2 film is deposited on this substrate to improve its TCF, good frequency characteristics cannot be realized. Thus, by using a new structure such as a flattened SiO2 film/Cu electrode/substrate structure to improve the TCF, YX-LiNbO3 substrate to obtain a large coupling factor, and flip-chip bonding to miniaturize the duplexer, a small (3×2.5 mm2) SAW duplexer having a low insertion loss and a good TCF has been realized for the first time.

Currently, cognitive radio using a white space of digital TV (DTV) channels is receiving a lot of attention. One of the key devices of a cognitive radio handset is a tunable filter capable of adjusting frequency and bandwidth (BW) throughout DTV band. The authors developed ultra-wideband resonators in a DTV band and ultra-wideband filters fully covering all DTV channels using 0th shear horizontal mode plate wave (SH 0 ) in a (0°, 120°, 0°) LiNbO 3 plate. However, they are fabricated on a self-suspended ultra-thin LiNbO 3 plate of only 0.5–0.6 µm in thickness, which is mechanically fragile and difficult to fabricate at high yield. A much higher phase velocity than that of SH 0 is required to make the plate practically thicker. The objective of this study is to explore a different mode of plate wave showing much higher phase velocity and wide BW. By FEM simulation, it is clarified that a first SH mode (SH 1 ) plate wave propagating in two kinds of new proposed structures, which are different from suitable SH 0 mode structures for wide BW, has higher velocity than 20,000 m/s and wide BW of 24%.

A cognitive radio terminal using vacant frequency bands of digital TV channels, i.e. TV white space, strongly requires a compact tunable filter covering a wide frequency range of the digital TV band. The authors proposed a new bandwidth- and frequency-tunable filter combining an ultra-wideband ladder filter and tunable band rejection filters. T-type and ρ-type ladder filters composed of ultra-wideband 0th shear horizontal mode (SH 0 ) plate wave resonators were fabricated on a submicron thick LiNbO 3 plate supported by a Si substrate. The wavelength ratio of the parallel/series resonators in the ladder filters was changed as a design parameter. As a result, ultra-large 6 dB bandwidths of 41 to 51%, which fully cover the digital TV band, were measured. The lowest peak insertion loss was low as 0.8 dB. The ultra-wideband ladder filter is useful for the above-mentioned new tunable filter for digital TV cognitive radio communication.