Chapter 2. Thin film deposition and characterisation technique

Transcription

1 Chapter 2 Thin film deposition and characterisation technique

2 Thin film deposition and Introduction The growth/ deposition processes really begin with selection of a suitable substrate and substrate preparation that would facilitate the deposition of high quality oxide layers or hetrostructures. An appropriate selection of substrate is important since stress (compression / tensile) due to difference in lattice parameters and thermal expansion coefficients cause the deformation of crystalline structure, deteriorating the properties of the thin film. Substrates can be broadly divided into two groups depending on applications; insulating and conducting metal or oxide substrates serving as bottom electrodes. Insulating single crystal substrates such as MgO and SrTiO 3 have been considered as ideal substrates for electro- optic applications, where conducting bottom electrodes are not necessary and at the same time high crystalline quality of thin films is critical for device performance. On the other hand conducting bottom electrodes are necessary for electronic applications and also to improve electrical properties, such as polarization, fatigue, retention and imprint properties. To fabricate high performance devices, the potential electrodes must meet several requirements 1 (i) To achieve high crystalline quality epitaxial ferroelectric films on conductive electrodes, the bottom electrodes must be epitaxial and single crystalline (at least oriented) and have a lattice parameter close to the ferroelectric material, similar crystal structure, and compatible chemistry. At the very least, the bottom electrode must allow the ferroelectric material to assume its own lattice structure during growth 67

3 Chapter 2 if the electrode itself is not of very similar structure. (ii) the bottom electrodes must be impervious to the constituents of the ferroelectric layer and substrate components to prevent interdiffusion during growth and postgrowth annealing. (iii) the electrodes must have a high work function to ensure lower leakage currents. Various types of electrodes have been attempted to meet these requirements and obtain high crystalline quality ferroelectric films and consequently better ferroelectric properties. The bottom electrodes for ferroelectric oxides can be mainly divided into two groups: metal-based and oxide-based electrode structures 1. But from the device point of view the ferroelectric capacitor using oxide based electrodes are considered inferior to Pt based electrode capacitors because of high power consumption and large delay time 2. However, in the present study, conducting oxide bottom electrodes has not been used as the migration of defects between the thin film and bottom electrode would significantly influence the electrical as well as optical characteristics of the films. Platinum electrodes: Platinum (Pt) has been the most widely used bottom and top electrode for PZT thin films in ferroelectric capacitors because Pt has a small lattice mismatch (~3%) with PZT, is relatively inert to oxygen and thus it does not form a stable oxide, and has a high Schottky barrier height leading to low leakage current. The microstructure, preferred orientation, and ferroelectric properties of PZT films grown on Pt bottom electrodes depend strongly on the adhesion layer beneath the Pt layer as well as on 68

4 Thin film deposition and.. preparation conditions of Pt electrodes 3,4. Usually Ti or TiO 2 are used as the adhesion layer between Si/SiO 2 and Pt to form Pt/Ti/ SiO 2 /Si or Pt/TiO 2 /SiO 2 /Si configuration. However, that Ti can diffuse along the Pt grain boundaries and form a TiO x layer on the top Pt surface during heat treatment used for crystallization of PZT films. This results in formation of defects leading to short-circuit between the top and bottom electrodes 5. To avoid this effect some groups used TiO x as an adhesion layer instead of Ti, and the results were quite promising. The use of TiO x layers drastically reduced Ti diffusion in both Pt and Si. 2.2 Processing equipments Dip coater / Spin Coater (a) Dip coater: For the present study we employed a home fabricated dip coating system. The withdrawal speed employed was 6cm/min. (b) Spin coater (Model- KW-4A, Chemat technologies, USA): Spin coater used for the present study had two stage spinning speed. The spinning speed (~3000 rpm) was adjusted so as to get uniform, homogeneous thin film on to substrate Horizontal tube furnace (Model: Indfur, Chennai) Pyrolysis and annealing had to be carried out to get well crystalline thin films. The furnace was employed which can attain a temperature up to C. For this study, depending upon the requirement, the furnace was set to a temperature in the range C. 69

5 Chapter 2 Figure 2.1: Spin coater Figure 2.2: Vacuum coating unit 70

6 Thin film deposition and High vacuum coating unit (Model- 12A4D, Hind High Vacuum, India): This system is employed to deposit gold top electrodes on to thin film. For this a shadow mask is placed on to the film and is placed in the coating chamber. Evaporation method is used to deposit gold on to the film and is carried out under a vacuum ~10-5 mbars. 2.3 Fundamental Characterisation techniques X- ray diffraction- determination of crystalline structure X-ray diffraction technique is usually used for the characterization of crystalline materials based on the Bragg s equation n = 2d sin, where is the monochromatic - X-ray wavelength, is the angle of diffraction from the lattice plane spaced with a distance d and n is an integer indicating order of reflection. The intensity of diffracted X-ray form the sample, which may be a single crystal, powder or a polished surface, is plotted against 2 values. The X-ray diffraction patterns of the samples were obtained from a Bruker (D- 5005), Germany. In the present work Ni filtered CuK radiation-having value 1.54 (A ) was used. The samples prepared in this study are scanned between 20 o to 60 o 2θ values. The recorded curve was matched with the ICDD (International Crystallographers Diffraction Data) to confirm the formation of the desired crystalline phase. 71

7 Chapter 2 Figure 2.3: X- ray Diffractometer UV visible spectrophotometry: determination of fundamental optical constants and film thickness Figure 2.4: UV-Visible spectrophotometer 72

8 Thin film deposition and.. UV- visible Spectrophotometry has been employed to determine the fundamental optical constants of the film. Figure 2.4 shows the image of a UV visible spectrophotometer which consists of dual beam source, sample compartment, optics to focus the beam on to the sample and detectors. Transmittance of the thin film is recorded as shown in figure 2.5(a). A regular ringing interference pattern is the indication of a uniform, homogeneous film surface. From such transmittance spectra, the refractive index and thickness of the film can be determined using the envelope method 6. According to this method the thickness of the film is given by, t 2(n( 1 M 1 2 ) n( 2 2 ) 1 )...(2.1) where, M is the number of oscillations between the two extrima (M = 1 between two consecutive maxima and minima), 1, n( 1 ) and 2, n( 2 ) are the corresponding wavelength and indices of refraction. Also band gap is calculated by plotting hν against (αhν) 2 (Figure 2.5(b)). The intercept with the x-axis of the linear portion gives the band gap of the material. 73

9 Chapter 2 (a) (b) Figure 2.5: (a) Typical transmittance spectrum and (b) determination of optical band gap of thin film 74

10 Thin film deposition and Spectroscopic Reflectometer: determination of film thickness Another method employed to determine the thickness of the film is based on the principle of reflection. In this method, the beam which is being reflected from a film top and bottom surface. The interference pattern thus obtained is then interpreted to determine the thickness of the thin film. Figure 2.6 shows the spectroscopic reflectometer setup. Figure 2.6: Spectroscopic reflectometer Scanning electron microscopy: Microstructural and compositional analysis with EDX A scanning electron microscope (SEM) images a sample by scanning it with a high-energy beam of electrons. The electrons interact with the atoms that make up the sample producing signals that contain useful information about the sample's 75

11 Chapter 2 surface topography and composition. The types of signals produced by an SEM include secondary electrons, back-scattered electrons (BSE), characteristic X-rays, light (cathodoluminescence), specimen current and transmitted electrons. The signals result from interactions of the electron beam with atoms at or near the surface of the sample. In the most common or standard detection mode, secondary electron imaging or SEI, the SEM can produce very high-resolution images of a sample surface, revealing details less than 1 nm in size. Back-scattered electrons (BSE) are beam electrons that are reflected from the sample by elastic scattering. BSE are often used in analytical SEM along with the spectra made from the characteristic X-rays. Because the intensity of the BSE signal is strongly related to the atomic number (Z) of the specimen, BSE images can provide information about the distribution of different elements in the sample. Characteristic X-rays are emitted when the electron beam energy is high leading to removal of inner shell electron from the sample, causing a higher energy electron to fill the shell and release energy. These characteristic X-rays are used to identify the composition and measure the abundance of elements in the sample. The technique is known as energy dispersive x- ray scattering (EDX). For the present study FEI quanta FEG200 HRSEM has been employed. 2.4 Measurement Techniques Measurement of dielectric properties 76

12 Thin film deposition and.. Basic parameters that characterize the dielectric properties of a dielectric material are dielectric constant, loss tangent, dielectric tunability (in the case of tunable dielectrics) and temperature stability 7. Ferroelectric materials are characterized by their high dielectric constants, at temperatures close to curie point (T c ) in both paraelectric and ferroelectric states. Dielectric tunability is defined as ( r0 rv ) Tunability x100..(2.2) r0 where ε r0 and ε rv are dielectric constants at 0 and V applied field, respectively. Dielectric loss tangent (D = tan δ = ε / ε ), ratio of imaginary part to real part of complex permittivity at a given frequency, is another important parameter to characterize the performance of a tunable material. Figure of merit (FOM) is used to describe the suitability of a dielectric for tunable applications. It is defined as the ratio of low frequency tunability to microwave loss tangent, i.e. -...(2.3) where ε r0 and ε rv are the relative dielectric constant at zero and maximum DC bias field at low frequency, tan is the loss tangent at microwave frequency under zero bias). Measurement methods of dielectric properties can be classified into three types: (i) direct methods, (ii) waveguide methods and (iii) resonance methods 8. 77

13 Chapter 2 Figure 2.7: Impedence Analyser for CV determination (Model: 4294A, Agilent, USA) Direct method means that the capacitance and loss tangent of a capacitor constructed using the materials under test can be directly measured by using an impedance analyzer or vector network analyzer (VNA). Waveguide and resonance methods are indirect techniques. Choice of the method depends on the frequency range and the form of the ferroelectric materials. At high frequencies (GHz), the dimensions of the capacitors are comparable with the length of the electromagnetic wave and they are no longer treated as lumped elements. The impedance of a capacitor is small compared to the resolution of any impedance analyser. As a result, waveguide or resonance methods are used. For thin films, parallel plate capacitor or planar model is usually employed. For low frequency measurements, parallel plate model is employed. In this case, the 78

14 Thin film deposition and.. capacitance and loss tangent of the capacitor can be measured directly by a impedance analyzer. Parallel-plate capacitors require bottom and top electrodes. Bottom electrodes are usually platinum (Pt) if silicon (Si) substrates are used. Gold (Au) is used for top electrode. Figure 2.7 shows the set up for CV measurement employing Impedance analyser Measurement of leakage current One of the important factors that deteriorates the performance of a dielectric is the leakage current. The presence of lattice defects giving rise to space charges, injection of electrons into the film due to low work function of the electrode materials etc:- are some of the factors that give rise to this current. For this measurement, a parallel plate capacitor model is constructed. Through the application of the field, the current through the dielectric is studied.. Figure 2.8: Leakage current characteristics of ferroelectric thin film. 79

15 Chapter Measurement of ferroelectric properties Figure 2.9: Typical P-E set up and P-E curve. 80

16 Thin film deposition and.. The polarization is a true measure of the degree of ferroelectricity. Polarization can be measured in various ways: The easiest and the most frequently used approach is the investigation of polarization (P) electric field (E) hysteresis. Figure 2.9 shows the measurement set up and the PE curve measured for a ferroelectric film. To characterize a ferroelectric for its polarization hysteresis, a sinusoidal voltage is applied to the sample and the corresponding polarization, displacement etc are recorded. In the present study Ferroelectric hysteresis (P E) were measured using a TF Analyser (Model: aix ACCT 2000, Germany) Measurement of Piezoelectric properties Transverse piezoelectric coefficient, e 31 Transverse piezoelectric coefficient, e 31 refers to the in- plane stress developed in piezoelectric thin films when an electric field is applied along the film thickness. This is the most important parameter to be determined for actuator applications. According to the theory developed by Smith and Choi 9 for heterogeneous bimorph and considering the approximations applied to it by Kanno et.al. 10, e 31 can be expressed as..(2.4) where, h si is the thickness of the silicon substrate, s s 11 is the compliance of the silicon substrate, L is the length of the cantilever, V the applied voltage and the tip displacement. 81

17 Chapter 2 Different techniques are employed to determine either d 31 or e 31 as discussed below AFM technique: Atomic force microscopy (AFM) based techniques have been extensively used to examine dielectric, piezoelectric, pyroelectric, and ferroelectric properties of thin films 11,12. The AFM technique has the advantage of being able to measure the piezoelectric effect at single points on a sample (in situ nanoscale studies of polarization domain dynamics), and the tip can be rastered to generate piezoelectric images (piezoresponse imaging technique). This technique has also extensively been used to investigate the ferroelectric switching characteristics of submicronscale capacitors, to understand ferroelectric degradation mechanisms, and to store information like in the high-density ferroelectric memory capacitors. The large bending of the substrate puts limitation on this technique Normal Loading method 13 In this method stress T is applied by placing a load on a metallic tip oriented perpendicular to the film s surface as shown in the figure, and charge (Q) of the sample is measured as a function of the applied stress. The drawback of this method is that effect of the substrate also has to be taken into account Cantilever beam method For characterizing the transverse piezoelectric coefficient (d 31 ) of thin films, cantilever beam technique based on the controlled bending of a small (millimetersized) cantilever beam have been developed 14. As shown in Figure

18 Thin film deposition and.. the test chip is fixed at one end to form a cantilever structure and charge induced by strain in the PZT thin film is measured in response to an impulsive shock applied to the free edge of the test tip. Figure 2.10: Typical cantilever mounting Laser interferometric technique: Laser interferometeric method 15 is the most well-established method for the characterization of both longitudinal and transverse piezoelectric coefficients of piezoelectric thin films. Interferometers can be configured as either single or double beam setups and are based upon the interference of monochromatic laser light in response to a piezoelectrically induced strain, which results in a change of the optical path length. This is done by comparing the interference light intensity of a reference laser beam to that of a laser beam striking the surface of the sample before and after strain develops. It has the capability to resolve very small changes in displacement 83

19 Chapter 2 (10 3 A 0 ) and reasonable effective d 33 values have been obtained by a double beam interferometer. Figure 2.11: Schematic illustration of the measurement system for transverse piezoelectric properties 2.5 Nonlinear optical absorption and its measurement techniques Nonlinear optics deals with interaction of matter with electromagnetic fields to generate polarized electric field altered in frequency, phase or other physical properties. The polarization induced can be expressed as P(t) (1) E(t) (2) 2 E (t) (3) 3 E (t)... (i) i E (t) (2.5) where, E i (t) represents the field strength of i th order and (i), nonlinear susceptibility of i th order. 84

20 Thin film deposition and.. (3) Therefore, E 3 (t) represents the third order polarization. The third order polarization provides several nonlinear phenomena such as intensity dependent absorption and refraction which can be utilized for application such as in power stabilizers, all optical switches etc Mechanism of nonlinear absorption Nonlinear absorption refers to the reduction in the intensity of transmitted light as the irradiance increases. Various mechanisms that can lead to nonlinear absorption are discussed below Two -Photon Absorption Two- photon absorption (TPA) involves a transition from the ground state of a system to a higher lying state by the simultaneous absorption of two photons from an incident radiation fields or fields 16. This process involves different selection rules than those of single photon absorption. Two possible situations are illustrated in figure 5-1. In the first, two photons from the same optical field oscillating at the frequency ω are absorbed to make the transition, which is approximately resonant at 2ω. In the second situation, two optical fields at frequencies ω e and ω p are present, and one photon from each field is absorbed for transition, which is approximately resonant at ω e + ω p. In both cases, the intermediate is not real. Hence the system must absorb the two photons simultaneously. This makes the process sensitive to the instantaneous optical intensity. 85

21 Chapter 2 Excited state ω Virtual state ω p ω Ground state ω e Figure 2.12: Schematic diagram of the two photon absorption (TPA) Excited state absorption: When the incident intensity is well above the saturation intensity, then the excited state can become significantly populated. In systems such as polyatomic molecules and semiconductors, there is a high density of states near the state involved in the excitation. The excited electron can rapidly make a transition to one of these states before it eventually makes transition back to the ground state. There are also a number of higher lying states that may be radiatively coupled to the intermediate states, and for which the energy differences are in near-resonance with the incident photon energy. Therefore, before the electron completely relaxes to the ground state, it may experience absorption that promotes it to a higher lying state. This process is called excited state absorption. It is observable when the incident intensity is sufficient to deplete the ground state significantly. a) Saturable and reverse saturable absorption 86

22 Thin film deposition and.. When the absoption cross section of the excited state is smaller than that of the ground state, the transmission of the system will be increased when the system is highly excited. This process is called saturable absorption. When the absorption cross section of the excited state is larger than that of the ground state, then the system will be less transmissive when excited. This gives the opposite result as saturable absorption and is thus called reverse saturable absorption (RSA). b)free- carrier absorpion In semiconductors, the absorption of a photon with energy greater than the bandgap will promote an electron to the conduction band, where it is a free carrier and can contribute to current flow when the field is applied. The excited electron will rapidly thermalise and relax to the bottom of the conduction band (C.B.), from there it will recombine with an excited hole in the valence band after a characteristic recombination time. However, at sufficiently high intensities, it can absorb another photon while still in the conduction band. This process is called free carrier absorption. It has similar qualitative characteristics to RSA. Of the several techniques used to measure third order nonlinearity such as degenerate four wavemixing, nearly degenerate three wave mixing, ellipse roation and beam distortion measurements, Z-scan is a simple and effective tool for determining the nonlinear response and is used widely in material characterization 87

23 Chapter 2 because it provides not only the magnitude of real and imaginary part of third order susceptibility, but also the sign of the real part Z-scan technique Z-scan technique developed by Sheik Bahae 17 and his co-workers, is a single beam method for measuring the sign and magnitude of nonlinear refractive index, n 2, and has sensitivity comparable to interferometric methods. This method can be used to directly measure nonlinear absorption apart from measuring the nonlinear refractive index of materials possessing nonlinear absorption. The technique is based on the principle of spatial beam distortion, but offers simplicity as well as high sensitivity. In the original single beam configuration, the transmittance of the sample is measured, as the sample is moved along the propagation direction of a focused gaussian beam. A laser beam through a nonlinear medium will experience both amplitude and phase variations. If transmitted light is measured through an aperture placed in the far field with respect to focal region, the technique is called closed aperture z- scan. In this case, the transmitted light is sensitive to both nonlinear absorption and nonlinear refraction. In a closed aperture z-scan experiment, phase distortion suffered by the beam while propagating through the nonlinear medium is converted into corresponding amplitude variations. On the other hand, if transmitted beam is measured without an aperture, the mode of measurement is referred to as open aperture z-scan. In this case, the throughput is sensitive only to nonlinear absorption. Z-scan graphs are always normalised to linear transmittance i.e., 88

24 Thin film deposition and.. transmittance at large values of z. Closed and open aperture z-can methods yield the real part and imaginary part of nonlinear susceptibility (3) respectively. In a z-scan measurement, it is assumed that the sample thickness is much less than Rayleigh s range z 0 (diffraction length of the beam), defined as where k is the wave vector and 0 is the beam waist radius given by where f is the focal length of the lens. For ensuring that the beam profile does not vary appreciably inside the sample, the sample thickness should always be kept less than the rayleigh s range. The experimental setup for single beam open aperture Z- scan technique is given in figure below. Figure 2.13: Schematic representation of the experimental setup for open aperture z-scan technique. 89

25 Chapter 2 Figure 2.14: Typical Open aperture Z-scan curve. (a) reverse saturable absorber, (b) saturable absorber (c) linear absorption. Open aperture z-scan technique is employed to measure nonlinear absorption in the sample. If nonlinear absorption such as two photon absorption is present, it is manifested in the measurements as a transmission minimum at the focal point. On the other hand, if the sample is a saturable absorber, transmission increases with increase in incident intensity and results in a transmission maximum at the focal region. It has been shown that the model originally developed by Bahae et.al, for pure two photon absorption can also be applied for excited state absorption (ESA). ESA is a sequential TPA process, where two photons are successively absorbed. 90

26 Thin film deposition and Theory of open aperture Z-scan technique In the case of an open aperture z-scan, the transmitted light measured by the detector is sensitive only to intensity variations. Hence, phase variations of the beam are not taken into consideration. The theory of z-scan experiment discussed here has been developed by M. Sheik Bahae et.al. The intensity dependent nonlinear absorption coefficient (I) can be written in terms of linear absorption coefficient and TPA coefficient as...(2.6) The irradiance distribution at the exit surface of the sample can be written as....(2.7) where..(2.8) L eff is the effective length and is given, in terms of sample length l and by the relation...(2.9) 91

27 Chapter 2 The total transmitted power P(z, t) is obtained by integrating Eq (2.2) over z and r and is given by.. (2.10) P I (t) and q 0 (z,t) are given by the equations (2.6) and (2.7) respectively as,.. (2.11).. (2.12) For a pulse of Gaussian temporal profile, eq. (2.5) can be integrated to give the transmission as..(2.13) Nonlinear absorption coefficient is obtained by fitting the experimental results to equation 2.8. If q 0 <1, eq.(2.4) can be simplified as.....(2.14) Once an open aperture z-scan is performed, nonlinear absorption coefficient can be unambiguously deduced. 92

28 Thin film deposition and Merits and demerits of Z-scan technique This technique has several advantages, some of which are (i) Simplicity: No complicated alignment is needed except for keeping the beam centered on aperture. (ii) Simultaneous measurement of both sign and magnitude of nonlinearity (in the case of nonlinear refraction) (iii) Possibility of isolating the refractive and absorptive parts of nonlinearity unlike degenerate four wave mixing. (iv) High sensitivity, capable of resolving a phase distortion of /300, provided the sample is of high optical quality. (v) Closed similarity between z-scan and the optical power limiting geometry. Some of the disadvantages include, (i) Stringent requirement of high quality Gaussian TEM 00 beam for absolute measurements. (ii) For non-gaussian beams, the analysis is completely different. Relative measurements against a standard sample allows relaxation on requirements of beam shape. (iii) Beam walk-off due o sample imperfections, tilt or distortions. 93

29 Chapter 2 (iv) Not suitable for measurements of off diagonal elements of the susceptibility tensor, except when a second non-degenerate frequency beam is employed. 94

30 Thin film deposition and.. References: [1] N. Izyumskaya, Y.-I. Alivov, S.-J. Cho, H. Morkoe, H. Lee and Y.-S. Kang, Processing, Structure, Properties, and Applications of PZT thin films, Critical Reviews in Solid State and Materials Sciences, 32 (2007) [2] J. L. Wang, Y.-S. Lai, D.-C. Shye, C.-C. Chou, B.-S. Chiou, C.-P. Juan, and H.-C. Cheng, Dependence of Ferroelectric Characteristics on the Deposition Temperature of (Pb,Sr)TiO3 Films, Jap. J. Appl. Phys., 46 (2007) [3] G. J. Willems, D. J. Wouters, and H. E. Maes, Influence of the Pt electrode on the properties of sol-gel PZT-films, Microelectr. Eng. 29 (1995) [4] K. G. Brooks, I. M. Reaney, R. Klissurska, Y. Huang, L. Buzsill, and N. Setter, Orientation of rapid thermally annealed lead zirconate titanate thin films on (111) Pt substrates, J. Mater. Res. 9 (1994) [5] Y. Matsui, M. Hiratani, Y. Kumagai, H. Miura, and Y. Fujisaki, Thermal stability of Pt bottom electrodes for ferroelectric capacitors, Jpn. J. Appl. Phys. 37 (1998) L465-L467. [6] J. C. Manifacier, J. Gasiot, and J. P. Fillard, A Simple Method for the Determination of the Optical Constants n, k and the Thickness of Weakly Absorbing Thin Films, J. Phys. E, 9 (1976) [7] L.B Kong, S. Li, T.S. Zhang, J. W. Zhai, F. Y. C. Boey, J Ma Electrically tunable dielectric materials and strategies to improve their performance, Progress in Materials Science 55 (2010)

31 Chapter 2 [8] A. K. Tagantsev, V. O. Sherman, K. F. Astafiev, J. Venkatesh, N. Setter, Ferroelectric materials for microwave tunable applications, J. Electroceram.,11 (2003) [9] J. G. Smits and W. Choi, The Constituent equations of piezoelectric Heterogeneous Bimorphs, IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 38 (1991) [10] I. Kanno, H. Kotera, and K. Wasa, Measurement of transverse piezoelectric properties of PZT thin films, Sens. Actuators A Phys., 107 (2003) [11] G. Zavala, J. H. Fendler, and S. Trolier-McKinstry, Characterization of ferroelectric lead zirconate titanate films by scanning force microscopy, J. Appl. Phys., 81 (1997) [12] C. S. Ganpule, A. Stanishevsky, Q. Su, S. Aggarwal, J.Melngailis, E. Williams, and R. Ramesh, Scaling of ferroelectric properties in thin films, Appl. Phys. Lett. 75 (1999) [13] K. Lefki, and G. J. M. Dormans, Measurement of piezoelectric coefficients of ferroelectric thin films, J. Appl. Phys., 76 (1994) [14] M. Sakata, S. Wakabayashi, H. Goto, H. Totani, M. Takenchi, and T. Yada, Sputtered high d 31 coefficient PZT thin film for microactuators, Proc. IEEE Micro Electro Mechanical Syst., (1996) [15] 1 Q. M. Zhang, W. Y. Pan, and L. E. Cross, Laser interferometer for the study of piezoelectric and electrostrictive strains, J. Appl. Phys., 63 (1988)

32 Thin film deposition and.. [16] 1 R. L. Sutherland, Handbook of Nonlinear Optics, 2nd ed. Marcel Dekker, New York (2003) [17] 1 M. Sheik-Bahae, A. A. Said, T. H. Wei, D. J. Hagan, and E. W. Van Stryland, Sensitive measurement of optical nonlinearities using a single beam, IEEE J. Quantum Electron., 26, (1990)