High-Frequency Lamb Wave Device Composed of MEMS Structure

2010 IEEE Trans. UFFC Outstanding Paper Award 2564

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control ,

vol. 57, no. 11,

November

2010

High-Frequency Lamb Wave Device Composed of MEMS Structure Using LiNbO3 Thin Film and Air Gap Michio Kadota, Fellow, IEEE, Takashi Ogami, Kansho Yamamoto, Hikari Tochishita, and Yasuhiro Negoro Abstract—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 LiNbO3 thin film deposited by a chemical vapor deposition system (CVD) instead of using a thin LiNbO3 single crystal plate. Lamb wave resonators composed of a interdigital transducer (IDT)/the LiNbO3 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 (SH0) and symmetric (S0) modes.

I. Introduction

I

n recent years, surface acoustic wave (SAW) devices have been key devices in mobile phone systems [1]. A 4th generation system of mobile phones in Japan requires high-frequency devices such as RF filters and duplexers. 10-GHz SAW transversal filters using a Rayleigh wave on an Al-interdigital transducer (IDT)/128°YX-LiNbO3 or a Sezawa wave on a SiO2 film/ZnO film/diamond film/Si substrate structure have been reported [2], [3]. The line and space (L & S) of the IDT of the former filter are as narrow as 0.09 μm to generate high frequency, because the 128°YX-LiNbO3 substrate has a low SAW velocity of 3990  m/s. Because the mobile phones require a high electric power handling capability and reliability, this substrate using this narrow L & S is not suitable for a high-frequency devices for mobile phone applications. The latter filter using a Sezawa wave has a large insertion loss of 22  dB and a narrow bandwidth, because the electromechanical coupling factor k2 is as small as 0.012. Thus,

Manuscript received February 17, 2010; accepted July 16, 2010. The authors are with Murata Mfg. Co., Ltd., Kyoto, Japan (e-mail: [email protected]). Digital Object Identifier 10.1109/TUFFC.2010.1722 0885–3010/$25.00

these SAW waves are not suitable for a high-frequency device with wide bandwidth. There are two kinds of plate waves on a thin plate, Lamb and shear horizontal (SH) waves, as shown in Fig. 1. The Lamb wave has longitudinal and shear vertical displacements. The SH plate wave has mainly an SH displacement. Although the Lamb wave, with the exception of the fundamental (0th) antisymmetric mode (A0), has the feature that high-velocity, very thin crystal plates or films are required to realize a high-frequency Lamb wave device. Lamb waves using piezoelectric films such as ZnO and AlN films and single-crystal plates such as quartz, the LiNbO3 and LiTaO3 were reported [4]–[8]. Their frequencies are not so high; for example, 300 MHz in ZnO-film/ pyrex-glass composite structure [4], 900 MHz in AlN-film/ Si structure [5], 256 to 600 MHz in the quartz single-crystal plate [6], and 100 MHz in LiNbO3 and LiTaO3 crystal plates [7], [8]. Their bandwidths, except LiNbO3 and LiTaO3 single-crystal plate, are also narrow because of their small electromechanical coupling factors, and their frequency characteristics are not sufficiently high. For example, the insertion loss of the ZnO/pylex-glass structure filter is large as 22 dB, a ratio of resonant (fr) and antiresonant (fa) impedances (impedance ratio) of the AlN/ Si structure resonator is smaller than 20 dB, the relative bandwidth is very narrow, 0.04, and the coupling factor is as small as k2 = 0.0034, though the Q factor is as large as 1860. Although the 256-MHz Lamb wave resonator in the quartz crystal plate also has a large Q factor of 5453, it has a small impedance ratio of 7 dB and narrow relative bandwidth of 0.043. For Z-plane LiNbO3 or LiTaO3 crystal plates, the 1st mode A1 of the antisymmetric modes of Lamb wave has high phase velocities and large electro-mechanical coupling factors which are suitable for realization of devices at high frequency and with wide bandwidth. So far, no high-frequency Lamb wave devices have been realized because it is difficult to fabricate a very thin LiNbO3 single-crystal plate. If c-axis highly orientated LiNbO3 or LiTaO3 thin films, with thickness less than 0.5 μm can be obtained, then high-frequency wideband Lamb wave devices operating at frequencies higher than 4 GHz could be realized. It has been reported that a 950-MHz filter using Rayleigh wave on a (012)LiTaO3 film on (012) sapphire substrate deposited by the pulse laser deposition (PLD) method [9]. However, no experimental results for acoustic waves using LiNbO3 thin films and/or Lamb waves using

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Fig. 2. Calculated phase velocity of plate waves on Z-X-LiNbO3 as a function of LiNbO3 thickness. Fig. 1. Schematic views of (a) plate waves and (b) Lamb waves.

LiNbO3 or LiTaO3 films or single crystal plates have been reported so far. Moreover, there have been no reported experiments for SAW devives on LiTaO3 film operating at higher frequency than 1 GHz. In the present study, the authors have attempted to realize a high-frequency device by using this A1 mode. Authors were able to realize high-frequency Lamb wave resonators using a c-axis oriented twinned crystalline epitaxial LiNbO3 thin film deposited by the chemical vapor deposition (CVD) method. One-port resonators composed of an Al-electrode/twinned crystalline epitaxial LiNbO3 thin film/air-gap/base substrate like a micro-electromechanical system (MEMS) resonator were fabricated. The measured resonators have high resonant frequencies of 4.5 and 6.3 GHz, which correspond to very high velocities of 14 000 and 12 500 m/s, large impedance ratios of 52 and 38 dB at resonant and anti-resonant frequencies, respectively, and wide bandwidths of 7.2% and 3.7%, respectively. It has been clarified both theoretically and experimentally that the Lamb wave resonators using the twinned crystalline epitaxial LiNbO3 thin film do not have spurious responses caused by 0th modes of SH (SH0) or symmetric one mode (S0), though the resonators propagating in the x-axis direction, direction of 45° from x-axis and y-axis directions on the Z-plane (Z-X, Z-45°X and Z-Y, respectively) LiNbO3 single crystal plates have spurious responses due to the SH0 or S0 modes. II. Theoretical Analysis Phase velocities and electromechanical coupling factors k2 of the plate waves on a Z-X LiNbO3 plate [Euler angle (0°, 0°, 0°)] were calculated. A finite element method (FEM) was used in this calculation. When the phase velocities on electrically opened and shorted surfaces are defined Vf and Vm, respectively, the electromechanical coupling factor k2 is calculated by k2 = 2 × (Vf − Vm)/Vf. Figs. 2 and 3

Fig. 3. Calculated electromechanical coupling factor of plate waves on Z-X-LiNbO3 as a function of LiNbO3 thickness.

show the calculated phase velocities and electromechanical coupling factors of the plate waves propagating on the thin Z-X LiNbO3 plate as a function of the plate thickness normalized by a plate wavelength (λ), respectively. The A1 mode of Lamb wave has velocities higher than 10 000 m/s and electromechanical coupling factors, k2, larger than 0.1 when the LiNbO3 plate thickness is thinner than 0.2λ. Although the SH0 mode also has large coupling factors, it has velocities too low to be suitable for realization of a high-frequency device. The authors use a Z-cut LiNbO3 thin film to realize the A1 mode of Lamb wave device, because the Z-cut (c-axis orientated) thin LiNbO3 film is relatively suitable for deposition, compared with films oriented at other angles. III. Thin LiNbO3 Film and Device Construction A buffer layer consisting of a c-orientated ZnO film was deposited on a base substrate by RF sputtering before

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IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control ,

Fig. 4. Schematic diagram of chemical vapor deposition (CVD) system.

depositing a LiNbO3 film. The LiNbO3 film was deposited on the ZnO buffer layer/base substrate in the reaction chamber of a CVD shown in Fig. 4; the Ar gas with Li ions and Nb ions and the O2 gas were inserted to a reaction chamber using Li (dipivaloylmethanate: C11H19O2) as solid source for Li and Nb(OC2H5)5 as liquid source for Nb. LiNbO3 thin films with thickness from 340 to 480 nm were deposited on the ZnO buffer layer/base substrate at the substrate temperature from 600 to 700°C using the CVD. The deposition rate was 12 nm/min. Fig. 5(a) shows a morphology of the LiNbO3 thin film measured by an atomic force microscope (AFM). The grain size of 200 nm and a surface roughness of 2.6 nm (RMS) were determined by AFM as shown in Fig. 5(a). Figs. 5(b) and 5(c) show a measured X-ray diffraction (XRD) (2θ − ω) and the rocking curves of the deposited (006) LiNbO3 film with the thickness of 480  nm. The XRD data confirms a (006) axis, which means c-oriented LiNbO3 film. The full-width of half-maximum (FWHM) in Fig. 5(c) is as narrow as 0.2°. This rocking curve provides additional evidence that the LiNbO3 film is highly c-axis orientated.

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Figs. 6(a) and 6(b) show measured pole figures of a Zplane LiNbO3 single-crystal substrate and the c-orientated LiNbO3 thin film at the (0, 1, 14) plane, respectively. The pole figure of a LiNbO3 single-crystal substrate shows the presence of 3 well-defined spots at certain location on the pole figure having [A] type structure, as can be seen in Fig. 6(a). However, the CVD deposited LiNbO3 thin film shows 6 spots in Fig. 6(b) having mixed structures of [A] and [B]. The existence of 6 spots suggests that the deposited thin LiNbO3 film is the twinned crystalline epitaxial film having two types of single crystals of [A] and [B] types which have 180° rotated relation on c-axis to each other as shown in Fig. 6(b). Fig. 7 shows a polarity of thin c-orientated LiNbO3 film measured by a scanning nonlinear dielectric microscopy (SNDM) [10]. The black and white regions show the +c and −c domains, respectively. The +c domain occupies 98.5% of the area as shown in Fig. 7. This LiNbO3 thin film has almost positive polarity. It is considered that a mixture of +c and −c domains causes a degradation of the electromechanical coupling factor. After deposition and patterning of Al-electrodes on the thin LiNbO3 film, the air gap was fabricated by removing the ZnO buffer layer by using the solution of H3PO4 and C2H4O2 at the room temperature. Figs. 8(a) and 8(b) show side and top views of the fabricated Lamb wave resonator, respectively. The membrane with 200-μm squares was warped, so interference fringes were observed as shown in Fig. 8(b). IV. Frequency Characteristics The 4.5- and 6.3-GHz Lamb wave one-port resonators have been fabricated using twinned crystalline epitaxial LiNbO3 thin film/air gap/substrate. They have λ of IDT of 3.2 and 2.0 μm, the LiNbO3 film thickness of 0.15 and 0.17λ (actual thickness of 480 and 340 nm, respectively), the Al-electrode thickness of 0.03λ and 0.07λ, aperture of

Fig. 5. Measurement results for (a) surface morphology, (b) X-ray diffraction curve (2θ − ω), and (c) rocking curve from LiNbO3 thin film.

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Fig. 6. ϕ-Scan pole figures from the (0, 1, 14) plane of (a) LiNbO3 single crystal and (b) LiNbO3 thin film. The former has 3 spots consisting of only [A]-type structure, and the latter has 6 spots consisting of both structures of [A]- and [B]-type.

Fig. 8. Resonator structure: (a) side view and (b) top view. Fig. 7. Polarity of c-domains in LiNbO3 thin film measured by scanning nonlinear dielectric microscopy.

the IDT of 15 and 25λ, for the IDT with 60 and 10 pairs, respectively, and the same number of each grating reflector of 20 fingers. Figs. 9 and 10 show the measured impedance and the phase characteristics of the Lamb wave resonators, respectively. The A1 mode of Lamb wave is observed at 4.5 to 5 GHz in Fig. 9 and at 6.3 to 6.5 GHz in Fig. 10. The A0 mode of Lamb wave is observed at 0.5 GHz in Fig. 9 and at 0.8 GHz in Fig. 10. Though an SH0 mode on a LiNbO3 single-crystal thin plate, which has the coupling factor k2 of about 0.1 as shown in Fig. 3, should be excited at 1 to 2 GHz, the SH0 mode of the resonators composed of the c-orientated twinned crystalline epitaxial LiNbO3 film is not observed in Figs. 9 and 10. The exact reasons are explained in Section V. The A1 modes of Lamb wave resonators have high resonant frequencies of about 4.5 and 6.3 GHz, which correspond to very high phase velocities

of 14 000 and 12 500 m/s, and large impedance ratios of at the resonance and the anti-resonance frequencies of 52 and 38 dB, and wide bandwidths of 7.2% and 3.7%, respectively. As a simulation result, the values of the coupling factor k2 have been estimated to be 0.18 and 0.11, respectively, which are 100% and 72% of theoretical ones shown in Fig. 3, respectively. However, the effective coupling factor k2eff containing the existence of Al-IDT is different from the coupling coefficient k2 shown in Fig. 3 as well as the SAW devices [11]. Therefore, the values of obtained effective coupling factor k2eff are 80% and 62% of the theoretical values of k2eff containing Al-IDT calculated by FEM. The reason of a slight deterioration of the coupling factor is considered that the above-mentioned c-axis polarity of the thin LiNbO3 film is slightly mixed. The 4.5-GHz resonator has larger electromechanical coupling factor, and higher velocity than the 6.3-GHz one, because the normalized thickness of the former LiNbO3 film is thinner than the latter one as can be seen from Figs. 2 and 3, therefore, the

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Fig. 9. Measured impedance and phase characteristics of 4.5-GHz oneport Lamb wave resonator using LiNbO3 film deposited by CVD.

Fig. 11. Calculated coupling factor on various propagation directions (ψ) on Z-LiNbO3 single crystal plate (0, 0, ψ).

using a leaky SAW (LSAW) on a Ta-electrode on a quartz substrate with larger dispersion than this dispersion of the Lamb wave by developing appropriate new approach [1], [15]. Therefore, it is considered that this dispersion is not a significant problem for the actual applications. V. Why Are SH0 and S0 Modes Not Excited? Fig. 10. Measured impedance characteristics of 6.3-GHz one-port Lamb wave resonator using LiNbO3 film deposited by CVD.

4.5-GHz resonator has the wider bandwidth. The 4.5-GHz resonator has a larger impedance ratio at the fr and the fa than the 6.3-GHz resonator one because the 4.5-GHz resonator has more IDT pairs and a larger actual coupling factor than the latter. Their Lamb wave resonators have low Q factor from 140 to 200, but relative wide bandwidth from 3.7% to 7.2%. For SAW resonator applications, the impedance ratio at fr and fa is sometimes more important than the Q factor. Bleustein-Gulyaev-Shimizu wave or Love wave resonators with large impedance ratio of 44 to 68 dB, relative wide band width from 5.1% to 17% and small Q factor from 65 to 150 have been applied to additional traps in TV, to voltage control oscillators (VCOs) and to tunable filters [12]–[14]. Lamb wave resonators could be applied to VCOs, ladder type filters that require wide bandwidth, or tunable filters. The dispersion of the Lamb wave is large, as can be seen in Fig. 2. The authors could succeed in mass production of intermediate frequency (IF) filters for mobile phones

Fig. 11 shows the calculated propagation direction dependency of the coupling factor on the Z-LiNbO3 singlecrystal thin plate with thickness 0.15λ. In addition to the A0 and A1 modes, an SH0 one should be excited in the X propagation, S0 and SH0 modes in the 45°X propagation and an S0 mode in the Y propagation as shown in Fig. 11. However, neither SH0 nor S0 modes are excited in the frequency characteristics of the Lamb wave resonators composed of c-axis twinned crystalline epitaxial LiNbO3 thin film as shown in Figs. 9 and 10. To confirm these frequency characteristics, Lamb wave resonators using Z-cut LiNbO3 single crystal plate were fabricated and measured. It is very difficult to fabricate a very thin single-crystal plate, such as 1 μm or thinner, to realize a high-frequency Lamb wave resonator. The authors tried to thin the normalized single-crystal plate thickness by lengthening the wavelength of IDT instead of thinning the crystal plate even though the operating frequency is low. One-port resonators consisting of the AlIDT with the wavelength of 2000 μm, 10 finger pairs, and the aperture of 20λ, and each grating reflectors with 20 fingers at both sides of the IDT were fabricated on the Z-LiNbO3 single-crystal plate with a thickness of 400 μm. Thus, the normalized plate thickness is 0.2λ. Fig. 12 shows the measured frequency characteristics of the Lamb wave

kadota et al.: high-frequency MEMS Lamb wave device

Fig. 12. Measured frequency characteristics of one-port resonators composed of Z-X and Z-Y LiNbO3 single crystal plates (frequency range: 0 to 10 MHz, velocity range: 0 to 20 000 m/s).

resonators on the Z-X and Z-Y LiNbO3 plates. The vertical axis in Fig. 12 shows impedance and a horizontal axis shows both the frequency (top axis) and the velocity (bottom axis). The velocity of the A1 mode is very high, over 12 500 m/s, though the frequency of 6 MHz is very low, as shown in Fig. 12, because the normalized thickness is thin, even though an actual thickness is thick of 400 μm. The A0, the SH0, and the A1 modes are excited

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on the Z-X-LiNbO3 single-crystal plate, though the S0 is not excited. The A0, the S0, and the A1 modes are excited on the ZY-LiNbO3 single-crystal plate, though the SH0 is not excited. These results have been explained previously in Fig. 3 and are shown in Fig. 11. On the other hand, neither the S0 nor the SH0 modes are excited in the resonators composed of the twinned crystalline epitaxial thin LiNbO3 film as shown in Figs. 9 and 10. It is believed that the reason is that the deposited c-LiNbO3 film is the twinned crystalline epitaxial thin film having the same +c domains. To clarify, the influence of the twinned crystalline epitaxial LiNbO3 thin film is analyzed. Figs. 13(a) and 13(b) show the calculation models. Fig. 13(b) is an enlarged model of Fig. 13(a). Table I shows two types (I) and (II) of the Euler angles used for the calculation. The LiNbO3 single-crystal thin plate and the c-orientated LiNbO3 thin film are divided into 80 regions in 1λ length along the propagation direction as shown in Fig. 13(b), and Euler angle (I) and (II) are applied alternately. The model in Fig. 13 is calculated to explain the twinned epitaxial film effect. When the Euler angle (I) is equal to the Euler angle (II), model (b) shows a LiNbO3 single-crystal plate. When the Euler angle (I) is different from the Euler angle (II), model (b) shows a twinned crystalline epitaxial LiNbO3 film as shown in Table I. The LiNbO3 single-crystal plate or the LiNbO3 film thickness for the calculation is 0.15λ and the Al-electrode thickness is 0.04λ.

Fig. 13. Simulation model diagrams: (a) actual size and (b) enlarged model.

TABLE I. Euler Angle for Calculation Model Used in Fig. 13. Z-X Z-45°X Z-Y

Single crystal Twinned film plate Single crystal Twinned film Single crystal Twinned film

Euler angle I

Euler angle II

(0°, 0°, 0°) (0°, 0°, 0°) (0°, 0°, 45°) (0°, 0°, 45°) (0°, 0°, 90°) (0°, 0°, 90°)

(0°, 0°, 0°) (0°, 0°, 180°) (0°, 0°, 45°) (0°, 0°, 225°) (0°, 0°, 90°) (0°, 0°, 270°)

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Fig. 14. Calculated characteristics of Lamb wave resonators on Z-X, Z45°X, and Z-Y LiNbO3 single crystal plates (thickness 0.15λ).

Impedance characteristics of the plate waves including the Lamb wave on the Z-plane LiNbO3 single-crystal plate and on the twinned crystalline epitaxial c-axis LiNbO3 film are calculated. Fig. 14 shows the calculated impedance characteristics on the Z-X, the Z-45°X, and the Z-Y LiNbO3 single-crystal plates. The horizontal and vertical axes show the velocity and relative impedance of the resonators, respectively. Each mode of the impedance characteristics in the three propagation directions on Z-LiNbO3 single crystal plates has almost same velocity. All responses of the A1 mode in the three propagation directions are almost same, and those of the A0 mode are also same, because they have the same coupling factor, as shown in Fig. 11. However, the characteristics of the SH0 and the S0 modes are different depending on the propagation direction, i. e., those on the Z-X and the Z-45°X ones have a spurious response caused by an SH0 made, but those on the Z-45°Y and the Z-Y ones have a spurious S0 mode. The coupling factors of the SH0 and the S0 modes are different depending on the propagation directions, as shown in Fig. 11. These calculation results are consistent with the measurement results as shown in Fig. 12. On the other hand, Fig. 15 shows the A0 and A1 modes in the X, 45°X, and Y propagation directions on c-orientated twinned crystalline epitaxial LiNbO3 thin films. All of the resonators composed of the twinned crystalline epitaxial thin films have the same characteristics and do not have spurious responses caused by the SH0 and the S0 modes. Those results are different from the results of the LiNbO3 single-crystal plates shown in Figs. 12 and 14. Therefore, the frequency characteristics of the resonator composed of the twinned crystalline epitaxial LiNbO3 film do not depend on the propagation direction of the plate wave, so it is considered that the coupling factor of each mode does not also depend on the propagation direction, i.e., the coupling factor of the A0 and the A1 mode is constant and that of the S0 and the SH0 is nearly zero in the any direction. Because of the expression of any propagation direction on the Z-LiNbO3 film, the Z-∞-LiNbO3 film might be suitable instead of Z-X-LiNbO3.

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Fig. 15. Calculated characteristics of Lamb wave resonators composed of Z-X, Z-45°X, and Z-Y twinned crystalline epitaxial LiNbO3 films (thickness 0.15λ).

The conclusion which the authors can draw so far is that the twinned crystalline epitaxial LiNbO3 films have a merit of not having spurious responses caused by the SH0 and the S0 modes regardless of a propagation direction, though the Z-X, 45°X, and Z-Y-LiNbO3 single-crystal plates have them. These calculated results clarify the previously mentioned measurement results shown in Figs. 9, 10, and 12. VI. Conclusion The authors have attempted to realize a high-frequency device by using Lamb waves on c-orientated LiNbO3 thin films having a high velocity and a large electromechanical coupling factor. The LiNbO3 thin film deposited by CVD was a highly c-axis orientated twinned crystalline epitaxial film. The authors have fabricated one-port Lamb wave resonators composed of an Al-electrode/thin twinned crystalline epitaxial LiNbO3 film/air-gap/substrate structure. As a result, the authors realized 4.5- and 6.3-GHz high-frequency Lamb wave resonators with high velocities of 14 000 and 12 500 m/s, large impedance ratios at resonance and anti-resonance of 52 and 38 dB, and wide bandwidth of 7.2% and 3.7%, respectively, for the first time. Moreover, they have no spurious responses caused by the SH0 and the S0 modes, though the Lamb wave resonators on Y-LiNbO3 single-crystal plate have them. To clarify the reason, the authors measured and calculated the impedance characteristics on the Z-X, Z-45°X, and Z-Y-LiNbO3 single-crystal plates and c-orientated twinned crystalline epitaxial LiNbO3 thin films. It has been confirmed both theoretically and experimentally that the resonators composed of the twinned crystalline epitaxial LiNbO3 films do not have spurious responses caused by the SH0 and the S0 modes, though those composed of the LiNbO3 singlecrystal plates have them. References [1] M. Kadota, “Development of substrate structures and processes for practical applications of various surface acoustic wave devices,” Jpn. J. Appl. Phys., vol. 44, No.6B, pp. 4285–4291, 2005.

kadota et al.: high-frequency MEMS Lamb wave device [2] H. Odagawa and K. Yamanouchi, “10 GHz range extremely low-loss ladder type surface acoustic wave filter,” in Proc. IEEE Ultrason. Symp., 1998, pp. 103–106. [3] H. Nakahata, A. Hachigo, K. Itakuma, and S. Shikata, “Fabrication of high frequency SAW filters from 5 to 10 GHz using SiO2/ ZnO/Diamond Structure,” in Proc. IEEE Ultrason. Symp., 2000, pp. 349–352. [4] A. Tanaka, M. Koike, F. Saito, K. Hashimoto and M. Yamaguchi, “Lamb wave device employing ZnO/Pyrex-glass composite structure on Si,” Inst. Electron. Inf. Commun. Eng. Japan, Tech. Rep. US91–89, 1992, pp. 17–21. [in Japanese] [5] V. Yantchev and I. Katardjiev, “Design and fabrication of thin film Lamb wave resonators utilizing longitudinal wave and interdigital transducers,” in Proc. IEEE Ultrason. Symp., 2005, pp.1580–1583. [6] Y. Nakagawa, S. Tanaka, and S. Kakio, “Lamb-wave-type high frequency resonator,” Jpn. J. Appl. Phys., vol. 42, no. 5B, pt. 1, pp. 3086–3090, 2003. [7] K. Mizutani and K. Toda, “Analysis of Lamb wave propagation characteristics in rotated Y-cut X-propagation LiNbO3 plates,” Trans. Inst. Electron. Inf. Commun. Eng. Japan, vol. J68-A, no. 5, pp. 496–503, 1985. [in Japanese] [8] K. Toda and K. Mizutani, “Propagation characteristics of plate waves in a Z-cut X-propagation LiTaO3 thin plate,” Trans. on Inst. Electron. Inf. Commun. Eng. Japan, vol. J71-A, no. 6, pp.1225–1233, 1988. [in Japanese] [9] Y. Shibata, N. Kuze, K. Kaya, and M. Matsui, “Piezoelectric LiNbO3 and LiTaO3 films for SAW device applications,” in Proc. IEEE Ultrason. Symp., 1996, pp. 247–254. [10] S. Kazuta, Y. Cho, H. Odagawa, and M. Kadota, “Determination of the polarities of ZnO thin films on polar and nonpolar substrates using scanning nonlinear dielectric microscopy,” Jpn. J. Appl. Phys., vol. 39, no. 5, pt. 1, pp. 3121–3124, 2000. [11] M. Kadota and M. Minakata, “Piezoelectric properties of zinc oxide films on glass substrates deposited by RF-magnetron-mode electron cyclotron resonance sputtering system,” IEEE Trans. on Ultrason Ferroelectr. Freq. Contr., vol. 42, no. 3, pp. 345–350, 1995. [12] M. Kadota, J. Ago, H. Horiuchi, and M. Ikeura, “Very small IF resonator filters using reflection of shear horizontal wave at free edges of substrate,” IEEE Trans. on Ultrason Ferroelectr. Freq. Contr., vol. 49, no. 9, pp. 1269–1279, 2002. [13] H. Shimizu, Y. Suzuki, and T. Kanda, “Love-type-SAW resonator of small size with very low capacitance ratio and its application to VCO,” in Proc. IEEE Ultrason. Symp., 1990, pp. 103–108. [14] M. Kadota, T. Kimura, and Y. Ida, “Tunable filters using ultrawideband surface acoustic wave resonator composed of grooved Cu electrode on LiNbO3,” Jpn. J. Appl. Phys., vol. 49, art. no. 07HD26, 2010. [15] M. Kadota, T. Yoneda, K. Fujimoto, T. Nakao, and E. Takata, “Resonator filters using shear horizontal-type leaky surface acoustic wave consisting of heavy-metal electrode and quartz substrate,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control, vol. 51, no. 2, pp. 202–210, 2004.

Michio Kadota (M’97–SM’07–F’09) received the B.S., M.S, and Ph.D. degrees in electrical engineering from the Tohoku University, Sendai, Japan. In 1974, he joined Murata Mfg. Co. Ltd., Nagaokakyo, Kyoto, Japan, where he has engaged in research, development, and production on various bulk wave ceramic devices and various different SAW devices. He has succeeded in the development and the mass-production of various SAW devices such as ZnO TV-VIF SAW filters, small BGS wave

2571 edge-reflection resonators and filters, small IF filters consisting of Taelectrodes/quartz, small SAW duplexers for US-PCS and W-CDMA with excellent temperature stability, and ultra-small RF filters using boundary waves. He received the 41th and 50th Okochi Technical Prize from Okochi Memorial Foundation of Japan in 1995 and 2004, a Minister Award of Science and Technology from the Science and Technology Agency of Japan in 1997, a Medal with Purple Ribbon from the Japanese Government in 2005, and a Fellow award from IEEE in 2009. He was a chairman of Japan for the UFFC Society of IEEE from 2007 to 2008. He was a Fellow from 2005 to 2009, and is now a director in Murata Mfg. Co. Ltd.

Takashi Ogami received the BS and M.S. degrees in electrical engineering from Osaka University, Osaka, Japan. In 1999, he joined Murata Mfg. Co. Ltd., Nagaokakyo, Kyoto, Japan. He has been engaged in development of SAW devices.

Kansho Yamamoto received the B.S. and M.S. degrees in physics from the Tokyo Institute of Technology, Tokyo, Japan. In 2002, he joined Murata Mfg.Co.Ltd., Nagaokakyo, Kyoto, Japan, where he has engaged in research and development of SAW devices and piezoelectric thin film devices.

Hikari Tochishita received the B.S. and M.S. degrees in the Department of Electrical & Electronic Engineering from the Ritsumeikan University, Shiga, Japan. In 1999, he joined Murata Mfg. Co. Ltd., Nagaokakyo, Kyoto, Japan, where he has been engaged in development of various electroluminescence devices, piezoelectric film devices, and SAW devices.

Yasuhiro Negoro received the B.S. degree in engineering science from the Osaka University, Osaka, Japan. In 1981, he joined Murata. Mfg. Co. Ltd., Nagaokakyo, Kyoto, Japan, where he has engaged in research and development on ferrite materials, inorganic electoro-luminescence materials, MEMS devices, and manufacturing methods of thin films.