Piezoelectric properties of zinc oxide films on glass ... - IEEE Xplore

IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 42, NO. 3, MAY 1995

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Piezoelectric Properties of Zinc Oxide Films on Glass Substrates Deposited by RF-Magnetron-Mode Electron Cyclotron Resonance Sputtering System Michio Kadota and Makoto Minakata, Member, IEEE Abstract— There are various types of electron cyclotron resonance (ECR) sputtering systems, DC-mode, RF-mode, etc. We reported that zinc oxide (ZnO) films on glass substrates deposited by DC-mode ECR and RF-mode ECR sputtering systems had shown excellent piezoelectric properties and c-axis orientations. The RF-mode ECR sputtering system was capable of depositing ZnO films on glass substrates without evidence of column and fiber grains in cross section and driving a 1.1 GHz fundamental Rayleigh surface acoustic wave (SAW). In this paper, the properties of ZnO film deposited by an RF-magnetron-mode ECR sputtering system, which has added magnets to the outside of a cylindrical zinc metal (Zn) target of the RF-mode ECR sputtering system, are investigated. It is confirmed that the SAW filters using ZnO films on an interdigital transducer (IDT)/glass substrate deposited by the RF-magnetron-mode ECR sputtering exhibit almost the same effective electromechanical coupling factors ( keff) as the theoretical keff values calculated by finite element method (FEM) using the constants of ZnO single crystal (measured keff values are 97% of the theoretical values) and 0.6 3.7 dB lower insertion loss in comparison with the films deposited by the DC-mode ECR and the RF-mode ECR sputtering system.

I. INTRODUCTION

S

URFACE acoustic wave (SAW) filters using zinc oxide (ZnO) piezoelectric films have been commercialized [1]–[4]. In those conventional sputtering systems, the plasma can not be generated without high gas pressure ( 10 Torr) [5]–[7], the deposited films have the incorporation of gas and usually have a columnar structure in cross section [1], [5], [8]–[10]. Such ZnO films are considered unsuitable for high-frequency SAW devices. An Electron Cyclotron Resonance (ECR) system enables the formation of a high density plasma [11], [12]. We previously reported that DC-mode ECR (DC-mode-ECR) and RF-mode ECR sputtering systems (RF-mode-ECR) were capable of depositing a ZnO film with a good -axis orientation and good piezoelectric properties under low gas pressure and at low temperatures [13]–[16]. In these papers, it was reported that the measured effective electromechanical coupling factors (keff) of ZnO films deposited by the DC-mode-ECR and the RFmode-ECR exhibited almost the same values as the theoretical values calculated by the finite element method (FEM). Further in these same papers, it was reported that the RF-mode-ECR Manuscript received April 29, 1994; revised October 24, 1994; accepted November 10, 1994. M. Kadota is with Murata Manufacturing Co., Ltd., Nagaokakyo-shi, Kyoto 617. M. Minakata is with Tohoku University, Sendai-shi, Miyagi 980, Japan. IEEE Log Number 9409927.

Fig. 1. Schematic view of the RF-magnetron-mode ECR sputtering equipment.

was capable of depositing a dense ZnO film for driving a high-frequency SAW without adsorption of atmospheric gases during deposition, because all of the charged particles in the plasma chamber were modulated in this system by a 13.56 MHz RF power supply. It was also reported that columnar or fibrous grains were not observed in the sidewall structure of the ZnO films on a glass substrate deposited by the RF-modeECR in the scanning electron microscope (SEM) photograph ( 10,000) [14], [15]. They have been observed in those deposited by conventional sputtering systems. In general, such ZnO films are not suitable materials for high-frequency SAW devices because of a large propagation loss due to their polycrystallinity. The ZnO films by the RF-mode-ECR were capable of driving a 1.1 GHz fundamental mode Rayleigh SAW [14], [15]. In this paper the properties of ZnO films deposited by the RF-magnetron-mode ECR sputtering system with the addition of magnets to the outside of the cylindrical zinc metal (Zn) target of the RF-mode ECR sputtering system, are investigated. ZnO films deposited by this sputtering system exhibited good piezoelectric properties, that is 97% of theoretical keff value 3.7 dB lower insertion calculated by the FEM, and 0.6 loss compared with ZnO films by the DC-mode-ECR and the RF-mode-ECR in the previous reported papers [14], [16]. II. OUTLINE OF RF-MAGNETRONMODE ECR SPUTTERING SYSTEM Figure 1 shows the configuration of the RF-magnetron-mode ECR sputtering system. The electrons in the plasma chamber

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TABLE I SPUTTERING CONDITION FOR DEPOSITING ZnO FILMS

experience cyclotron resonance from 2.45 GHz microwaves, introduced through a waveguide, and the 875 gauss magnetic field inside the plasma chamber. Using this phenomenon, a high density plasma can be formed at low gas pressure [11], [12]. Magnets are added to the outside of the cylindrical Zn metal target to the RF-mode ECR sputtering system described in the previous papers (see * in Fig. 1) [14], [15]. The magnetic field strength is 480 Gauss on the surface of the Zn target as the maximum value. In this paper, hereafter, it is called an RF-magnetron-mode ECR sputtering system (RF-magnetronmode-ECR). Second electrons generated from the target are trapped on the surface of the target and move like a cycloid by the magnetic field paralleled to the surface of the target. The trapped electrons come efficiently into collision with gas particles and the plasma density in the chamber is high. The gas used during deposition is a mixture of Ar and O . The total gas pressure was on the order of 10 Torr•ZnO films were deposited on aluminum (Al) interdigital transducers 230 C. The sputtering (IDT’s)/on glass substrates at 200 conditions for depositing ZnO films by RF-magnetron-modeECR and RF-mode-ECR, for reference, are summarized in Table I. The deposition conditions by RF-magnetron-modeECR such as the gas pressure, the deposition rate, and so on, are a little bit different from those by the RF-mode ECR. III. C-AXIS ORIENTATION, LATTICE CONSTANT, AND ETCH RATES OF ZnO FILMS A ZnO film is in general an assembly of polycrystallites and their spatial distribution can be considered as a Gaussian distribution. The physical structure of the deposited ZnO film of the inclination angles, was evaluated by a mean value the standard deviation , and the full width of half maximum (FWHM) of -axis orientation from the measured pole-figure [5]. Fig. 2 shows an example of pole-figure cross sections for

Fig. 2. Measured cross section of pole-figure.

the ZnO film deposited by the RF-magnetron-mode-ECR. This 1.0 , ZnO film shows a good -axis orientation with =0.45 , and FWHM 1.5 even with a film thickness of 2.8 m. The lattice constant is measured by the X-ray diffraction. of the ZnO film by RF-MagnetronThe lattice constant ˚ The obtained value is closer to mode-ECR is 5.225 A. ˚ [17]) of a ZnO single crystal than that value ( 5.1948 A ˚ of the ZnO film by RF-mode-ECR. Table II 5.251 A) ( shows those values. The densities of ZnO films are evaluated by the chemical 2 etching. The etch rates on the surface of ZnO films (1 m) on the glass substrates were measured using a 35-percent nitric acid solution (23 C). The obtained average etch rates are shown in Table II. Thus, it is considered that the ZnO films by RF-magnetron-mode-ECR are denser than those by the other sputtering systems such as DC-mode-ECR, RF-mode-ECR, or conventional RF magnetron. The RF-magnetron-mode-ECR was enable to deposit epitaxial ZnO films on sapphire substrates as has been shown

KADOTA AND MINAKATA: PIEZOELECTRIC PROPERTIES OF ZINC OXIDE FILMS ON GLASS SUBSTRATES

TABLE II PIEZOELECTRIC PROPERTIES OF

THE

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ZnO FILMS

in chemical vapor deposition (CVD) and other sputtering systems. These results will be reported later on. IV. INSERTION LOSS OF SAW FILTERS AND SAW VELOCITIES The SAW filters are composed of deposited ZnO films on the Al-IDTs formed on the glass substrates. Fig. 3 shows a schematic of the SAW filter. Fig. 4 shows an example of the 700 MHz SAW filter characteristic. In this figure, the vertical scale shows the insertion loss, and the horizontal scale shows the frequency sweep. The SAW filter is composed of a set of standard IDT’s with 40.5 pairs of single ( 4) electrodes having a wavelength of 3.6 m ( is the periodic spacing of electrodes or wavelength of the SAW at the synchronism frequency). The main lobe in this figure exhibits an asymmetrical amplitude increasing to the right which is caused by the SAW reflections between the many fingerelectrodes of the IDT’s (fingers represent single electrodes). The SAW filter characteristics were measured under a 50 circuit impedance without electrical tuning. In Fig. 5 minimum insertion losses of SAW filters of ZnO films by the RFmagnetron-mode-ECR are indicated by open triangles ( ) as a function of H/ , where H/ is the normalized ZnO film thickness. The corresponding values for the ZnO films deposited by the DC-mode-ECR and RF-mode-ECR, reported in previous papers [14], [16], are indicated by open circles ( ) and black circles ( ), respectively, for reference. The SAW filters used for the insertion loss measurement have the same IDT’s as the above-mentioned SAW filters. In the 0.4 0.6, where keff are maximized as range of H/ later-mentioned Fig. 8, SAW filters formed by RF-magnetron-

Fig. 3. Schematic figure of a SAW filter of ZnO/IDT/glass structure.

Fig. 4. Example of SAW filter frequency characteristics (IDT: single elec3.6 m and 40.5pairs). trodes with

=

mode-ECR exhibited about 2.9 3.7 dB and 0.6 1.1 dB lower insertion losses in comparison with those respectively formed by the DC-mode-ECR and the RF-mode-ECR. Fig. 6 shows SAW phase velocities measured from characteristics of the SAW filters in the range of 400 MHz as

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Fig. 7. Analysis model for calculating keff by the FEM.

4

Fig. 5. Comparison of insertion losses of SAW filters (IDT: single elec:RF–magnetron-mode ECR; : DC-mode trodes with 3.6 m; ECR; :RF-mode ECR).

=

4

Fig. 8. Comparison of measured coupling factors keff. (IDT: single electrodes with =6.0, 8.0, 12.0 and 18.0 m; : RF-magnetron-mode ECR; : DC-mode ECR; : RF-modeECR).

4

Fig. 6. Comparison of SAW phase velocities (IDT: single electrodes with 6.0 m; : RF-magnetron-mode ECR; : DC-mode ECR; : RF-mode ECR).

=

a function of H/ . The open triangles ( ), open circles ( ), and black circles ( ) represent the same data for SAW filters formed by the same sputtering systems as indicated in Fig. 5. The SAW velocities were obtained by measuring center frequencies of SAW filters composed of normal IDT’s with 20 pairs of single electrodes having a of 6.0 m. SAW velocities of the ZnO films on glass substrates by the RF-magnetron0.5 mode-ECR are a little bit slower (about 5 m/s) at H/ than the values by the DC-mode-ECR. On the other hand they are almost equal to those by RF-mode-ECR. Table II shows SAW properties. V. ELECTROMECHANICAL COUPLING FACTOR OF SAW The values of electromechanical coupling factors and velocities of SAW’s are different depending on the underlying substrate in the ZnO/IDT/substrate structure. In the case of glass substrates, those values are also different depending on the different materials of glass. In general, material constants may also be different depending on the glass manufacturing lots even for the same material of glass [3]. However, in this investigation, the fact that the electromechanical coupling factor is not different, although the SAW velocity may be

different on the glass, has been analyzed and confirmed by the analysis method described later [18]. In the theoretical analysis the constant values of glass substrate, obtained by using an ultrasonic microscope as described in reference [3], is have been used. An electromechanical coupling factor from SAW velocity and calculated by when the IDT boundary the difference in SAW velocity surface is electrically shorted and open [18]. On the other hand, an effective electromechanical coupling factor keff is of a normal IDT measured from the radiation conductance electrode. The value of keff for the single IDT and that for the split IDT is different [16], [20]. The values of those keff are also different from coupling factor ks [16]. The reason is that ks is a material constant of the substrate, but keff exhibits the value contained the existence of IDT electrodes and latermentioned step-like change areas (facets) caused by IDT as shown in Fig. 7. In the SAW filter with a ZnO/IDT/glass substrate structure, the periodic steplike changes caused by the thickness of the aluminum finger electrodes of an IDT are present on the ZnO film surface [1], [16]. The values of keff can be obtained from the FEM considering the step-like change areas and the IDT electrode fingers. In the theoretical analysis, obtained the values of keff obtained from the FEM and are different. Here, the theoretical from analysis also analyzed keff for the single electrode using the from FEM [21], [22], and calculated in reference [23], [24]. Fig. 7 shows an analysis model for calculating keff by the FEM. The thickness of step-like change areas and IDT electrode fingers is 0.4 m in the analysis.

KADOTA AND MINAKATA: PIEZOELECTRIC PROPERTIES OF ZINC OXIDE FILMS ON GLASS SUBSTRATES

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keff values of ZnO films by the RF-magnetron-mode-ECR are almost identical to those by RF-mode-ECR in the measured frequency range. There is a difference between the insertion losses of SAW filters of ZnO films by the RF-magnetron0.4 0.5, in spite mode-ECR and the RF-Mode-ECR at H/ of having the same values of keff in both sputtering systems. This may be explained by the fact that the propagation loss of 1.1 the ZnO films by the RF-magnetron-mode-ECR is 0.6 dB lower than those by the RF-mode-ECR. VI. CONCLUSIONS Fig. 9. Example of motional conductance circle characteristics (IDT: single electrodes with 6.0 m and 20 pairs; center frequency: 430 MHz).

=

The experiment is carried out on keff when the IDT electrode is a single electrode. A radiation conductance of a normal IDT is defined as (1) where is the center frequency of the SAW filter, is the total electrode capacitance of the IDT, and is the number of the electrode pairs in the IDT [25]. Therefore, the value of keff of one IDT based on (1). In is obtained by measuring the Fig. 8, open triangles ( ) indicate values of keff for ZnO films by the RF-magnetron-mode-ECR as a function of H/ . The values of keff are measured with the motional conductance circle of a normal IDT with 20 pairs of single electrodes having 6.0, 8.0, 12.0 and 18.0 m (140 430 MHz range) [16]. In this figure, for reference, open circles ( ) and black circles ( ) indicate the data for ZnO films by the DC-modeECR and RF-mode-ECR, respectively [14], [16]. Fig. 9 shows an example of a motional conductance circle for a normal IDT. As the residual inductance increases in measurement, the trajectory and the circle of motion conductance become tilted. increases Therefore, the apparent motional conductance and the keff obtained is larger than the actual value [16]. It is confirmed that the value of keff obtained in Fig. 9 is not influenced by the residual inductance because the trajectory and the circle of motional conductance do not tilt in. In Fig. 8 the solid curve represents the values of keff which were calculated using the FEM. The broken curve represents calculated from . In the the values of 0.4 0.5 where the keff values curve region of H/ exhibits a maximum, the keff values for the ZnO films by the RF-magnetron-mode-ECR were almost equal to the values calculated from the FEM values. For example, the measured 0.43 is 97% of 0.172, calculated keff value of 0.166 at H/ from the FEM and is equal to 106 % of the value 0.157, . The measured values of calculated from ZnO films by the DC-mode-ECR and the RF-mode-ECR have 0.44) and 96% (at H/ 0.49) of been 94% (at H/ values calculated by the FEM, respectively, and 103% (at 0.44) 106% (at H/ 0.49) of values calculated from H/ , respectively [14]. This shows that the ZnO films by the RF-magnetron-modeECR exhibit excellent piezoelectric properties. Though the

ZnO piezoelectric films deposited by the RF-magnetronmode ECR sputtering system have the characteristics summarized below. 1) The thin ZnO film with 2.8 m thickness exhibited good -axis orientation with 1.0 , 0.45 and FWHM 1.5 . ˚ The 2) The lattice constant of this ZnO film is 5.225 A. ˚ of value ( 5.1948 A) obtained value is closer to ˚ value ( 5.251 A) of a ZnO single crystal than ZnO film by the RF-mode-ECR. 3) These ZnO films are denser than those by the other sputtering systems such as the DC-mode-ECR, the RFmode-ECR, or the conventional RF magnetron. 4) Insertion losses of SAW filters of these ZnO films are 3.7 dB and 0.6 1.1 dB lower than those, 2.9 respectively, of films by the DC-mode-ECR and the RF3.6 m (700 MHz range) in the region mode-ECR at of H/ 0.4 0.5. SAW velocities of these ZnO films are a little bit slower (about 5 m/s) than those by DCmode-ECR. On the other hand they are very closed to those by the RF-mode-ECR. 5) The keff value of these ZnO films is almost equal to the value calculated by the FEM. That is, the measured 0.43 is 97% of the value 0.172 value of 0.166 at H/ calculated from the FEM, and is equal to 106% of the . value 0.157 obtained from ACKNOWLEDGMENT We wish to thank Professor N. Chubachi of Tohoku University for his guidance, Senior Executive Director H. Ariyoshi and Director T. Kasanami of Murata Manufacturing Co., Ltd. for their supporting our study, and Mr. Miura of Murata for his assistance. REFERENCES [1] M. Kadota, C. Kondo, T. Ikeda, and T. Kasanami, “The polishing effect of ZnO thin films on SAW filters,” Japan. J. Appl. Phys., vol. 29, Suppl. 29-1, pp. 159–161, 1990. [2] M. Kadota, C. Kondo, T. Ikeda, and T. Kasanami, “Frequency trimming of ZnO/glass SAW filters,” Japan. J. Appl. Phys., vol. 30, Suppl. 30-1, pp. 179–181, 1991. [3] M. Kadota, T. Kitamura, and T. Kasanami, “Evaluation of glass substrates for SAW filters by acoustic microscopy technique,” Trans. IEE Japan., vol. 111-C, pp. 412–418, Sept. 1991 (in Japanese). [4] M. Kadota, T. Kasanami, and N. Chubachi, “Influences and reduction of the stress caused at edges of ZnO film on glass substrate for SAW device,” Trans. IEE Japan., vol. 113-C, pp. 85–90, May 1993 (in Japanese).

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[5] N. Chubachi, M. Minakata, and Y. Kikuchi, “Physical structure of DC diode sputtered ZnO films and its influence on the effective electromechanical coupling factors,” Japan. J. Appl. Phys., vol. 13, Suppl. 2, Pt. 1, pp. 737–740, 1974. [6] T. Yamamoto, T. Shiosaki, and A. Kawabata, “Characterization of ZnO piezoelectric films prepared by rf planar-magnetron sputtering,” J. Appl. Phys., vol. 51, pp. 3113–3120, June 1980. [7] S. B. Krupanidhi and M. Sayer, “Position and pressure effects in rf magnetron reactive sputter deposition of piezoelectric zinc oxide,” J. Appl. Phys., vol. 56, pp. 3308–3318, Dec. 1984. [8] F. S. Hickernell, “Reactive sputtering of ZnO,” in Proc. 1st Int. Symp. on Sputtering and Plasma Processes, 1991, pp. 57–66. [9] F. S. Hickernell, “ZnO processing for bulk- and surface-wave devices,” in Proc. IEEE Ultrason. Symp., 1980, pp. 785–794. [10] T. Hata, T. Minamikawa, E. Noda, O. Morimoto, and T. Hada, “High rate deposition of ZnO Film using improved DC reactive magnetron sputtering technique,” Japan. J. Appl. Phys., vol. 18, Suppl. 18-1, pp. 219–224, 1979. [11] S. Matsuo and Y. Adachi, “Reactive ion beam etching using a broad beam ECR ion source,” Japan. J. Appl. Phys., vol. 21, pp. L4–L6, Jan. 1982. [12] M. Matsuoka and K. Ono, “Crystal structures and optical properties of ZnO films prepared by sputtering type electron cyclotron resonance microwave-plasma,” J. Vac. Sci. Technol., vol. A7, pp. 2975–2982, Sept./Oct. 1989. [13] M. Kadota, T. Kasanami, and M. Minakata, “Piezoelectric characteristics of ZnO films deposited using an electron cyclotron resonance sputtering system,” Japan. J. Appl. Phys., vol. 31, pp. 3013–3016, Sept. 1992. [14] M. Kadota, T. Kasanami, and M. Minakata, “Characteristics of zinc oxide films on glass substrates deposited by RF-mode electron cyclotron resonance sputtering system,” Japan. J. Appl. Phys., vol. 32, pp. 2341–2345, May 1993. [15] M. Kadota, T. Kasanami, and M. Minakata, “Characteristics of piezoelectric ZnO films deposited by RF mode electron cyclotron resonance sputtering system,” Electron. Lett., vol. 28, pp. 2315–2316, Dec. 1992. [16] M. Kadota, T. Kasanami, and M. Minakata, “Piezoelectric properties of ZnO films deposited by using an ECR sputtering system,” Trans. IEICE Japan., vol. 76-A, pp. 138–144, Feb. 1993 (in Japanese) or Electrics and Communications in Japan, pt. 3, vol. 76, pp. 1–9, Nov. 1993. [17] American Institute of Physics, American Institute of Physics Handbook, Third Edition. New York: McGraw-Hill, 1982. [18] M. Kadota, “Study of surface acoustic wave filters using piezoelectric zinc oxide film,” Ph.D. Dissertation, Tohoku University, Jan. 1994. [19] H. Sasaki, N. Chubachi, and Y. Kikuchi, “Thickness dependence of effective coupling factors of ZnO thin-film surface-wave transducers,” Electron. Lett., vol. 9, pp. 92–93, Feb. 1973. [20] W. R. Smith and W. F. Pedler, “Fundamental- and harmonic- frequency circuit-model analysis of interdigital transducers with arbitrary metallization ratios and polarity sequences,” IEEE Trans. Microwave Theory and Technol., vol. MTT-23, pp. 853–864, Nov. 1975. [21] M. Koshiba and S. Mitobe, “Equivalent networks for SAW gratings,” IEEE Trans. Ultrason. Ferroelec., Freq. Cont., vol. 35, pp. 531–535, Sept. 1988. [22] K. Inagawa and M. Koshiba, “Theoretical determination of equivalent circuit parameters for interdigital surface-acoustic-wave transducers,” Trans. IEICE Japan., vol. J73-C-I, pp. 731–757, Nov. 1990 (in Japanese).

[23] J. J. Campbell and W. R. Jones, “A method for estimating optimal crystal cuts and propagation directions for excitation of piezoelectric surface waves,” IEEE Trans. Sonics and Ultrason., vol. SU-15, p. 209, Oct. 1968. [24] R. V. Schmidt and F. W. Voltmer, “Piezoelectric elastic surface waves in anisotropic layered media,” IEEE Trans. Microwave Theory and Tech., vol. MTT-17, p. 920, Nov. 1969. [25] W. R. Smith, H. M. Gerard, J. H. Collins, T. M. Reeder, and H. J. Shaw, “Analysis of interdigital surface wave transducers by use of an equivalent circuit model,” IEEE Trans. Microwave Theory and Tech., vol. MTT-17, pp. 856–864, Nov. 1969.

Michio Kadota received the B.S., M.S., and Ph.D. degrees in 1971, 1974, and 1994 all from the Tohoku University, Sendai, Japan. In 1974, he joined Murata Mfg. Co. Ltd., Nagaokakyo, Kyoto, Japan, where he was engaged in research and production on bulk wave ceramic filters, and TV and VCR VIF (video intermediate frequency) SAW filters using ceramics (PZT) and ZnO films. His works have made a great contribution to the success in mass production of these SAW filters. His interests include piezoelectric films, SAW devices, and applied ultrasonics. Dr. Kadota is a member of the Institute of Electronics, Information, and Communication Engineers, the Acoustic Society of Japan, and the Institute of Electrical Engineers of Japan.

Makoto Minakata (M’88) received the B.S., M.S., and Ph.D. degrees in 1968, 1971, and 1974, all from the Tohoku University, Sendai, Japan. Through his education, he was engaged in the research of zinc oxide thin film ultrasonic transducers. In this work, he introduced the X-ray pole figure analysis, discovered the Gaussian distribution in caxis orientation of piezoactive ZnO polychrystalline films, and computed the effective electromechanical coupling factor of ZnO polychrystalline film based on the standard deviation and mean-inclination angle of c-axis measured by the pole figure analysis for the first time. High efficient and wide-band ZnO ultrasonic transducers have been developed, and these devices are now widely used in many applications. In 1974, he joined NTT Electrical Communication Laboratories (NTT Fundamental Research Laboratory), Musashino, Japan, where he was engaged in research on LiNbO3 optical waveguide devices and optical integrated circuits, and high speed IIIV semiconductor transistors. Since 1984, he has been an Associate Professor of Optical Communication Engineering at Tohoku University. His current research interests include characterization of LiNbO3 optical waveguides, analysis and fabrication of active waveguide devices, and high speed optical modulation. He has written five books. Dr. Minakata is a member of the IEEE, the Institute of Electronics, Information, and Communication Engineers, the Japan Society of Applied Physics, and the Laser Society of Japan.