Compositional Dependence of the Young s Modulus and Piezoelectric Coefficient of (110)-Oriented Pulsed Laser Deposited PZT Thin Films

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1 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS 1 Compositional Dependence of the Young s Modulus and Piezoelectric Coefficient of (110)-Oriented Pulsed Laser Deposited PZT Thin Films Hammad Nazeer, Minh D. Nguyen, Özlem Sardan Sukas, Guus Rijnders, Leon Abelmann, Member, IEEE, andmikoc.elwenspoek Abstract In this contribution,we report on the compositional dependence of the mechanical and piezoelectric properties of Pb(Zr x Ti 1 x )O 3 (PZT) thin films fabricated by pulsed laser deposition (PLD). These films grow epitaxially on silicon with a (110) preferred orientation and have excellent piezoelectric properties, which make them outstanding candidates for application in microelectromechanical system devices. Vibrometric measurements on capacitors showed that the effective longitudinal piezoelectric coefficient (d 33,f ) of 100-nm thick PZT films has amaximumvalueof72pm/vforacompositionofx =0.52. The Young s modulus was determined by measuring the difference in the flexural resonance frequencies of cantilevers before and after the deposition of the PZT thin films. The compositional dependence of the Young s modulus shows an increase in value for the Zr-rich compositions, which is in agreement with the trend observed in their bulk ceramic counterparts. From the obtained dielectric constant and d 33,f, we show that the calculated coupling coefficients of the PLD-PZT thin films have higher values for most of the compositions than their ceramic counterparts. [ ] Index Terms Pb(Zr x Ti 1 x )O 3 (PZT), piezoelectric coefficient, Young s modulus, coupling coefficient. I. INTRODUCTION I NTHEmicro-andnanoindustry,theever-growingdemand for powerful actuators and sensitive sensors is addressed by the use of piezo-based transducers [1], [2]. Pb(Zr x Ti 1 x )O 3 Manuscript received June 28, 2013; revised April 23, 2014; accepted May 2, This work was supported in part by the SmartMix Program, the Netherlands Ministry of Economic Affairs; and in part by the Netherlands Ministry of Education, Culture, and Science. Subject Editor D. DeVoe. H. Nazeer, Ö. Sardan Sukas, and L. Abelmann are with the Transducers Science and Technology Group, MESA+ Research Institute for Nanotechnology, University of Twente, Enschede 7522 NB, The Netherlands ( h.nazeer@utwente.nl; o.sardansukas@utwente.nl; l.abelmann@utwente.nl). M. D. Nguyen is with the Inorganic Materials Science Group, MESA+ Research Institute for Nanotechnology, University of Twente, Enschede 7522 NB, The Netherlands; with SolMates B.V., Enschede 7522 NB, The Netherlands; and also with the International Training Institute for Materials Science, Hanoi University of Science and Technology, Hanoi 10000, Vietnam ( d.m.nguyen@utwente.nl). G. Rijnders is with the Inorganic Materials Science Group, MESA+ Research Institute for Nanotechnology, University of Twente, Enschede 7522 NB, The Netherlands ( a.j.h.m.rijnders@utwente.nl). M. C. Elwenspoek is with the Transducers Science and Technology Group, MESA+ Research Institute for Nanotechnology, University of Twente, Enschede 7522 NB, The Netherlands; and also with the Freiburg Institute for Advanced Studies, Albert-Ludwigs University, Freiburg 79085, Germany ( m.c.elwenspoek@utwente.nl). Color versions of one or more of the figures in this paper are available online at Digital Object Identifier /JMEMS (PZT) thin films are often used as piezo-materials because they have excellent ferroelectric and piezoelectric properties. These properties can be tuned by controlling the composition of the material by changing the Zr/Ti ratio [3], [4]. For instance, the composition Pb(Zr 0.52 Ti 0.48 )O 3 is used in different types of applications due to its higher piezoelectric properties [5]. Recently [4] discussed the use of a Ti-rich composition (x = 0.2) in energy-harvesting devices. They combined the high in-plane transverse piezoelectric coefficient and low dielectric constant of Pb(Zr 0.2 Ti 0.8 )O 3 to obtain a high figure of merit for power and voltage generation. A similar trade-off can be achieved for the longitudinal piezoelectriccoefficient and the Young s modulus of the material, which are analyzed in this paper. If one looks at micro-electromechanical systems (MEMS), it is apparent that with the development of various types and applications, such as sensors and actuators, the requirement for materials with specific properties is getting very strict. It is realized that because of their tunableproperties,pztthin films are very suitable for such micro- and nano systems [6]. However, in order to efficiently use PZT thin films in these systems a better understanding of the piezoelectric and ferroelectric properties, as well as the mechanical behaviour of PZT thin films of various compositions, is necessary. For instance, the compositional dependence of these properties is dissimilar from their ceramic counterparts due to reasons like clamping of the films to the substrates and the different orientation of the films [7], [8]. PZT thin films can be obtained through different processes like sol-gel [9], sputter- [10] and pulsed laser deposition (PLD) [11] techniques. Previously we reported the excellent ferroelectric properties of PLD-PZT with a (110) preferred orientation [12]. In this work, we investigate the compositional dependence of the effective longitudinal piezoelectric coefficient (d 33,f ), the Young s modulus E, dielectricconstantε 33 and coupling coefficient k of these PLD-PZT thin films in order to efficiently use these films as active device layers in MEMS devices. We used micrometer-sized measurement devices to characterize these dependencies. The d 33,f was determined by measuring the out-of-plane displacement of PZT thin film capacitors, as described in section II-A. The Young s modulus of the PZT thin films was determined by measuring the change in the resonance frequency of cantilevers before and after deposition of the IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See for more information.

2 2 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS Fig. 1. Schematic view of a PZT thin film capacitor. Fig. 2. Schematical representation of a cantilever fabricated from a silicon-on-insulator wafer. The difference in resonance frequency of the cantilevers before and after the PZT deposition is used for Young s modulus determination. PZT thin films. The method used for determining the Young s modulus is briefly introduced in section II-B. In sections III-A and III-B, the fabrication of capacitor structures and silicon cantilevers and the deposition of PZT thin films by PLD are explained. The Young s modulus and the d 33,f depend on the orientation of the PZT thin films. Therefore, X-ray diffraction (XRD) measurements were performed. These measurements and the techniques used to measure the Young s modulus and d 33,f are described in sections III-C, III-D and III-E. Finally, the compositional dependence of the d 33,f,theYoung s modulus, the dielectric constant and the coupling coefficient of the PLD-PZT thin films are discussed in section IV. II. THEORY A. Longitudinal Piezoelectric Coefficient d 33,f The d 33,f can be determined by either measuring the charge generated due to an applied external mechanical stress (direct piezoelectric effect) or measuring thedisplacementinthepzt caused by the application of an electric field (converse piezoelectric effect). Homogeneous uniaxial stress is required in the direct piezoelectric effect measurements, which is difficult to apply. Bending in the film due to application of the nonhomogeneous stress results in a large amounts of charge due to the transverse piezoelectric effect [13]. For this reason, we measured the d 33,f using the converse piezoelectric effect. Applying an ac voltage on the top and bottom electrodes of the PZT capacitors, as shown in Fig. 1, results in a piezoelectric displacement. The d 33,f is then determined by measuring the out-of-plane displacement of these capacitors by using this relation [14]: d 33,f = S 3 V/t f. (1) Here d 33,f is the effective longitudinal piezoelectriccoefficient ( effective means that the thin film is clamped to the substrate which reduces d 33 with respect to a system that is not clamped), S is strain, V is the voltage over the capacitor and t f is the thickness of the film. B. Analytical Model for the Young s Modulus of PZT Thin Films The in-plane Young s modulus of PZT thin films can be determined by using micromachined silicon cantilevers as test structures (see Fig. 2). The flexural rigidity and mass of the cantilevers will change due to the addition of the PZT thin films. These changes result in a difference in the resonance frequency of the cantilevers before and after the deposition of the PZT thin films. This difference is measured, after which the Young s modulus of the PZT thin films is calculated using the equations given in [15]. III. EXPERIMENTAL DETAILS A. Fabrication of PZT Capacitors To measure the d 33,f and dielectric constant of PLD-PZT, capacitors were fabricated on (001) silicon wafers. To obtain epitaxial growth of the PZT thin films, a 50 nm thick buffer layer of yttria-stabilized zirconia (YSZ) was first deposited on silicon by PLD. This layer prevents the diffusion of lead into the silicon during PZT deposition and also acts as a crystallization template for epitaxial growth of the PZT thin films. Next, 50 nm of strontium ruthenate (SRO) was deposited as a bottom electrode. The PLD process then continued with the PZT thin film until the desired thickness of 100 nm was achieved. The parameters for the process used are given in [12]. Deposition of the stack was completed with the 50 nm thick top electrode of SRO. The µm 2 capacitors were patterned by astandardphotolithographicprocess, followed by argon-ion beam milling of the top SRO electrodes with an etching rate of 10 nm/minute and a wet etch to remove the PZT layer in the diluted HF:HNO 3 :H 2 Osolution. B. Fabrication of Cantilevers for Young s Modulus Measurement Silicon cantilevers of varying lengths from 250 µm to 350 µm instepsof10µm werefabricatedusingadedicated SOI/MEMS fabrication process, similar to what we reported in [15]. A schematic illustration showing the main steps of the fabrication procedure can be seen in Fig. 3. Scanning electron micrographs (SEM) and optical images were used to characterize these cantilevers; see Fig. 4. After characterization of the fabricated silicon cantilevers, 10 nm thick buffer layers of YSZ and SRO and then 100 nm thick PZT thin films were deposited. In contrast to the capacitor structures, we deposited thin buffer layers of YSZ and SRO to prevent the influence of the additional layer on the resonance frequency. C. XRD Measurements The orientation of the deposited PZT thin films was analyzed by θ 2θ X-ray diffraction (XRD) scans (XRD, Bruker

3 NAZEER et al.: COMPOSITIONAL DEPENDENCE OF THE YOUNG S MODULUS AND PIEZOELECTRIC COEFFICIENT 3 Fig. 3. Illustration of the fabrication process of the cantilevers. (a) Devices etched on the silicon on insulator (SOI) wafer with deep reactive ion etching (DRIE). (b) Application of polyimide pyralin as protective layer on the front side and wafer through etching from the backside of the wafers. (c) Polyimide pyralin and photoresist removal from the front and backsides and subsequent etching of the buried oxide (BOX) layer using vapor hydrofluoric acid (VHF). Fig. 5. XRD patterns of PZT thin films with different compositions grown on: (a) Si cantilevers and (b) Si substrates. Fig. 4. Scanning electron micrograph of fabricated cantilevers. Cantilevers were fabricated from a 3 µm thicksilicondevicelayer.thelengthofthe cantilevers varies from 250 µmto350 µminstepsof10 µm. The cantilevers have a constant width of 30 µm. See-through to substrate shows rough walls due to DRIE from the backside of the wafers. D8 Discover) with a Cu Kα cathode in the Bragg Brentano geometry. The θ 2θ scans were performed for all compositions of the PZT thin films (x = ). Fig. 5 shows the XRD patterns of the PZT thin films deposited on SRO/YSZ buffered Si cantilevers and Si substrates, respectively. The PZT films grown on Si substrates have a pure (110)-orientation (Fig. 5(b)). Due to the various compositions (or Zr/Ti ratios), change in position of (110)-oriented peaks is observed. This peak-position shifts towards a higher angle when the Zr/Ti Fig. 6. X-ray phi-scan profiles of PZT(002) and Si(202) reflections of the (110)-oriented PZT(x = 0.52) thin films grown on Si substrate and Si cantilever. The insets show the glue step of Si substrate and Si cantilever on the heaters. ratio is varied ranging from 80/20 to 20/80 (or x is decreased). The in-plane epitaxial relationships between the films and substrates were estimated by the X-ray phi-scan (φ-scans) measurement, as illustrated in Fig. 6. In the structure of PZT

4 4 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS film/si substrate, four identical sets of peaks of PZT(002) deflections are positioned around the reflections corresponding to Si(202), showing the epitaxial growth of film on substrate. However, instead of a single peak positioned at the Si(202) position, the intensity is divided over two peaks situated at +10 and 10 with respect to Si. Since two PZT(002) peaks are expected in a perfect crystal, this means that twin domains exist in the (110)-oriented PZT thin film. The following relationship in the structure is deduced: PZT(110) SRO(110) YSZ(001) Si(001), since the rotation angle φ of the (002) peak of SRO and the (202) peak of YSZ coincides with those of PZT and Si, respectively [16]. The PZT films grown on Si cantilevers consist of mainly (110)-orientation and minor orientations of (001), (111), (210) and (211), as shown in Fig. 5(a). The mixed orientations in PZT/Si cantilevers, in comparison with pure (110)-orientation in PZT/Si substrates, are due to the less homogeneous temperature of Si cantilevers during deposition (see the insets in Fig. 6). The phi-scan measurement in Fig. 6 shows that the PZT film grown on Si cantilever is not an epitaxial structure due to worse in-plane orientation. Moreover, the (222) diffraction peaks of the pyrochlore phase are observed in PZT/Si cantilevers. The formation of a metastable stoichiometric pyrochlore becomes more significantly in the tetragonal PZT (Ti-rich) films grown on Si cantilevers at low depositedtemperature in relation to the growth of a Ti-rich pyrochlore (Pb 2 Ti 2 O 6 )phase. Fig. 7. The measured resonance frequencies of a cantilever before and after PZT deposition. Normalised amplitude shows a decrease in the resonance frequency of the cantilever measured after deposition of the Pb(Zr 0.2 Ti 0.8 )O 3. This expected decrease is attributed to the addition of the PZT thin film on the cantilever. D. Measurements of the Longitudinal Piezoelectric Coefficient d 33,f The piezoelectric displacement of the PZT thin film capacitors was measured to determine the d 33,f.AMSA-400micro system analyzer scanning laser Doppler vibrometer was used for measuring the displacement of the capacitors. An ac-voltage of magnitude 6 V p-p (peak to peak) was applied to the top and bottom electrodes at a frequency of 8 khz. This voltage actuates the PZT and the resulting displacement of the top electrode was measured. E. Measurements of the Young s Modulus To determine the in-plane Young s modulus of PZT thin films, the resonance frequencies of cantilevers were measured by using a MSA-400 micro system analyzer scanning laser Doppler vibrometer. Thermally excited vibrations of the cantilevers were measured in ambient conditions. Curve fitting with a theoretical expression for a second-order mass spring system with damping was used to calculate the free resonance frequencies. The resonance frequency measurements were conducted both before and after the deposition of the PZT thin films for cantilevers of varying length and for different compositions. As an example, the measurements for a cantilever of length 250 µm, width 30 µm, and thickness 3 µm beforeandafterdepositionofthepb(zr 0.2 Ti 0.8 )O 3 thin film are shown in Fig. 7. The Young s modulus can be calculated from the shift in resonance frequency as described in [15]. To reduce the uncertainty in the calculated value of the Young s modulus, we measured the thickness of the Fig. 8. (a) Polarization hysteresis (P E) loops, and(b) Remnantpolarization (P r )andcoercivefield(e c ), of PZT thin films as a function of composition. cantilevers by using high-resolution SEM. As a result we could measure the Young s modulus with a standard error of less than ±1.8 GPa. F. Measurements of the Ferroelectric Properties The polarization hysteresis (P E) loopmeasurementswere performed using the ferroelectric mode of the aixacct TF-2000 Analyzer. The P E loops were measured with an applied ac-electric field of ±300kV/cm at 1 khz frequency at room temperature. Fig. 8(a) indicates the difference in ferroelectric properties among PZT thin films with different compositions. The tetragonal film with x = 0.2 exhibitsa well saturated rectangular loop with a large remnant polar-

5 NAZEER et al.: COMPOSITIONAL DEPENDENCE OF THE YOUNG S MODULUS AND PIEZOELECTRIC COEFFICIENT 5 Fig. 10. The d 33,f values as a function of Zr content (x) fordifferentpzt compositions. Based on our measurements we find a maximum value of d 33,f at x = The trend of the d 33,f values for PZT thin films is compared with the bulk PZT ceramics [19] in clamped condition. Fig. 9. (a) Dielectric constant-electric field and (b) Dielectric loss-electric field curves of PZT thin film capacitors, as a function of composition. ization (P r )andalargecoercivefield(e c ). Slim ferroelectric P E hysteresis loop was observed in rhombohedral film with x = 0.8. The plots of the average values of the P r and E c are shown as a function of composition (Zr/Ti ratio) of PZT thin films in Fig. 8(b). With increasing Ti-rich composition, larger P r and E c values are observed. ASüssMicroTechPM300manualprobe-stationequipped with a Keithley 4200 Semiconductor characterization system was used for the capacitance measurement. The capacitanceelectric field (C E) curves were measured using a slowly sweeping dc-electric field of ±300 kv/cm and a 1 khz ac-electric field of 10 kv/cm. Thedielectricconstant(ε 33 E) and dielectric loss (tanδ E) versuselectricfield,asshown in Fig. 9, can be calculated from these capacitance electric field (C E)andconductance electricfield(g E), which were obtained from capacitance measurement, as follows [16]: ε 33 = Ct ε 0 A. (2) tanδ = G 2πfC. (3) where t is PZT film thickness, A is the area of capacitor, ε 0 (= F/m) is the vacuum permittivity and f is the measured frequency. A. Crystal Structure IV. RESULTS AND DISCUSSION It is known that the piezoelectric andmechanicalproperties of PZT thin films depend on the crystal orientation [17], [18]. X-ray diffraction (XRD) measurements reveal that all PZT thin films investigated in this study grow with a (110) preferred orientation; see Fig. 5. Therefore, if there are any variations in the d 33,f values and the Young s modulus, then these can not be caused by the crystal orientation but must be due to a difference in composition. B. Piezoelectric Coefficient The composition of PZT has a strong effect on the d 33,f value, as seen in Fig. 10. For a film thickness of 100 nm, a maximum d 33,f value of 72 pm/v was observed at a composition of Pb(Zr 0.52 Ti 0.48 )O 3.Theoptimumcomposition is in agreement with bulk PZT ceramics in unclamped condition [19], but the value is 68% lower. There are two reasons, which can be used to explain the reduction of d 33,f in PZT thin films: substrate clamping and film/electrode interface effects. Clamping of the thin film with the substrate causes a reduction in the d 33,f value as compared to the corresponding bulk material (d 33 )[20],duetothelimitationofdomainwallmotion in films [21]. The relation between the d 33,f and d 33 using the compliance coefficients data of the bulk Pb(Zr 0.52 Ti 0.48 )O 3 ceramic is given in [22] as: d 33,f = d d 31 (4) Since relevant compliance coefficient data are not available for all PZT ceramic compositions, we used Eq. 4 and d 33 and d 31 of the corresponding composition [19] to calculate the d ceramic 33,c values of PZT ceramics in clamped condition (Fig. 10). It is evident from the comparison of the compositional dependence of the PZT ceramics in clamped condition d ceramic 33,c and d 33,f that the d 33,f value of PLD-PZT thin film is 36% lower for x = 0.52, whereas it shows higher values for other compositions.

6 6 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS Fig. 11. Compositional dependence ofyoung smodulusofthepztthin films plotted as a function of Zr content (x) inpb(zr x Ti 1 x )O 3 thin films. The trend is compared with the data published by Jaffe et al. [19] for bulk PZT ceramics. In addition to substrate clamping effects, the presence of athinlayerwithalowdielectricconstantbetweenthefilm and the electrode, a so-called interfacial dead" layer; can also have a large effect on the piezoelectric properties. The interfacial layer may also alter the distribution of the electric field in the PZT film, leading to adecreaseinpiezoelectric coefficient [23]. Nguyen indicated that an interfacial layer thickness of about 6 nm was calculated for the 100-nm-thick epitaxial PZT film on SRO/YSZ/Si substrate [16]. The maximum of d 33,f at x = 0.52 composition is in agreement with the piezoelectric response reported in literature for PZT thin films obtained by a sol-gel method [24], [25]. However, the effect is more pronounced in our PZT thin films, with a shallow maximum at x = C. Young s Modulus The Young s modulus strongly depends on the film composition, as is shown in Fig. 11. The dependence of Young s modulus on the PZT composition shows an increase in value for the Zr-rich compositions, which is in agreement with the published data for bulk PZT ceramics [19], also shown in Fig. 11. The value of the Young smodulusforthecomposition with the maximum d 33,f was found to be GPa with a standard error of ±1.5 GPa at x = This value is 57% higher than for bulk PZT ceramic. It is also much higher than values reported in literature for sol-gel films (Young s modulus: 84 GPa [26]), but have the same order as values reported for sputter deposited PZT (109 GPa [10]). The dip in the Young s modulus lies at a lower Zr content than found for bulk PZT ceramics (x = 0.52, see Fig. 11). This behaviour is under investigation. D. Dielectric Constant and Coupling Factor The compositional dependence of the dielectric constant (ε 33 ) and dielectric loss (tanδ) is shown in Fig. 12(a). Fig. 12. (a) Dielectric constant and dielectric loss of the PZT film capacitors as a function of composition. (b) Compositional dependence of the relative dielectric constant of the PZT film capacitors in compared with the bulk PZT ceramics data obtained from Jaffe et al. [19]. The values of ε 33 and tanδ were defined from ε 33 -E and tanδ-e curves, respectively, and at 0 V point (see more in Fig. 9). It is shown that the film with a Zr/Ti ratio of 52/48 (x = 0.52) exhibits highest dielectric constant. Such dependence was also reported previously [27]. Rhombohedral films show higher dielectric constants than tetragonal films, due to more possible polarization directions in the rhombohedral phase (eight [111] directions) in comparison to the tetragonal phase (six [100] directions). The dielectric loss is slightly increased with increasing Zr/Ti ratio (or increasing x), as 5.3% and 8.1% for x = 0.2 and x = 0.8, respectively. The electromechanical coupling factor (k 33,f ), which is an extremely useful figure of merit, is defined as [28]: k 33,f = d 33,f E33 ε where ε = ε 0 ε r, E 33 is the out-of-plane Young s modulus. The E 33 can be calculated as: E 33 = E/3(1-ν) = E/2.1, where E (in-plane Young s modulus) is the measured Young s modulus in this study, ν(= 0.3) is Poisson s ratio of PZT film. For this calculation, the intrinsic or relative dielectric constant (ε r ) was estimated by constructing a linear fit to the highest electric field (from 200 to 300 kv/cm range) and extrapolating back to zero field, as shown in Fig. 9. This is required to remove the contribution of 180 domain-wall to the dielectric constant, because such domain-wall does not contribute to the electromechanical properties. Similar to the dielectric constant, the film at x = 0.52 also exhibits large relative dielectric constant (Fig. 12(b)). Compared to bulk PZT ceramics, the PZT films show a much broader with lower values of ε r for Ti-rich compositions and higher values for Zr-rich composition. (5)

7 NAZEER et al.: COMPOSITIONAL DEPENDENCE OF THE YOUNG S MODULUS AND PIEZOELECTRIC COEFFICIENT 7 in clamped condition reveals that our PLD-PZT thin films have a much higher coupling factor because of higher Young s modulus values. ACKNOWLEDGMENT The authors also thank the assistance of M.J. de Boer for etching, R.G.P. Sanders for laser Doppler vibrometer measurements, J.G.M. Sanderink and H.A.G.M. van Wolferen for SEM, and L.A. Woldering and N.R. Tas for helpful discussions. Fig. 13. Compositional dependence ofthecouplingfactorofthepztfilm capacitors in compared with the bulk PZT ceramics in clamped condition. Fig. 13 shows the coupling factor of the PZT films and bulk PZT ceramics as a function of the film composition. The k 33,f of the PZT films are higher than those of the corresponding bulk ceramics. It is then expected that the PLD PZT films in this study are more suitable for applications in both sensors and actuators. V. CONCLUSION We report on the compositional dependence of the effective longitudinal piezoelectric coefficient, the Young s modulus, dielectric constant and coupling coefficient of Pb(Zr x Ti 1 x )O 3 thin films with a (110)-preferred orientation, grown on micromachined silicon cantilevers by pulsed laser deposition. The d 33,f shows a maximum value of 72 pm/v at a Zr content of x = 0.52 for a film thickness of 100 nm. The dependence of the piezoelectric coefficient of PLD-PZT on composition is much weaker than in bulk PZT ceramics material, which has a sharp peak at x = When correcting for the clamping effect, the d 33,f in bulk ceramics exceeds the PLD-PZT thin film value by 36% at this composition. At other compositions the PLD-PZT has a substantially higher value. The Young s modulus of films at x = 0.52 composition is GPa with a standard error of ±1.5 GPa. 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S. Saxena, Polarization change in ferroelectric thin film capacitors under external stress, J. Appl. Phys., vol.105,no.6,p ,2009. Hammad Nazeer obtained his Bachelor in 1997 and his Masters in 2000 in electrical engineering from the N.E.D. University of Engineering and Technology, Pakistan. In 2007, he joined the Transducers Science and Technology Group, University of Twente, The Netherlands, and he received his PhD in His research interests focus on the analytical relation to determine the Young s modulus and residual stress of Pb(Zrx,Ti1-x)O3 (PZT) thin films with various Zr/Ti ratios and orientations. Minh D. Nguyen started his studies in chemistry ( ). After his master in Materials Science (2001), he received his PhD in 2010 in Physics from the University of Twente, The Netherlands. His research interests focus on various piezoelectric MEMS devices, concentrates on piezoelectric microdiaphragms and micro-cantilevers for micro-fluidics and micro-biosensors applications. These devices are based on the textured and epitaxial Pb(Zr,Ti)O3 (PZT) and Pb(Mg1/3Nb2/3)O3/PbTiO3 (PMN-PT) thin films, fabricated on Si wafers using pulse laser deposition (PLD) and sol-gel techniques. Özlem Sardan Sukas received her BSc and MSc degrees in mechanical engineering from Middle East Technical University, Turkey, in 2004, and Koç University, Turkey, in 2006, respectively. During her PhD, she worked on "Topology Optimized Electrothermal Microgrippers for Nanomanipulation and Assembly" within the EU project NanoHand. Receiving her PhD degree from Technical University of Denmark in 2010, she started as a Postdoctoral Fellow at University of Twente, The Netherlands. She worked as a MEMS researhcer at SmartTip BV, The Netherlands, for a year in Her research has included development of MEMS actuators for various applications. Her recent research focuses on realization of cantilever-based piezomems bio-sensors. Guus Rijnders finished his PhD work on "Initial Growth of Complex Oxides: Study and Manipulation," in 2001, after which he became an assistant professor at the Low Temperature Division, University of Twente. In 2003 he joined the Inorganic Materials Science Group, University of Twente, where he became an associate professor in Since April 1st 2010, he has been appointed full professor in Inorganic Materials Science. His research focuses on the structure-property relation of atomically engineered complex (nano)materials, especially thin film ceramic oxides. Leon Abelmann (M 08) (1965) is leader of the NanoEngineering group at KIST Europe, and holds aprofessorshipatthemesa+researchinstituteat the University of Twente, as well as the Physics and Mechantronics Department of Saarland University. He started his career on a grant from the Royal Dutch Academy of Sciences and a subsequent Innovation Grant from the Netherlands Organisation for Scientific Research (NWO). He obtained a tenure track at the University of Twente in 2001, and was appointed full professor in In 2014, he accepted a position as group leader at KIST Europe in Saarbrucken, where he strives to strengthen the link between KIST and the EU research community. Miko C. Elwenspoek (born December 9,1948 in Eutin, Germany) worked on liquids, nuclear physics, light scattering, biophysics (at the Free University of Berlin) and in Nijmegen, The Netherlands, on crystal growth, before he joined the University of Twente in In Twente, he took charge of the micromechanics group that was part of the Sensors and Actuators Lab, now MESA+ Research Institute. Since then his research focused on Microelectromechanical Systems. In 1996 he became full professor in transducers science and technology at the Faculty of Electrical engineering, University of Twente. One year later, he became Simon Stevin Master of the Dutch Technology Foundation. He is fellow of the Institute of Physics and of the Freiburg Institute of Advanced Studies. In 2001, 2008 and in 2011 students electedhimasthebestlecturer in their program. He was a co-founder Advanced Technology at the UT and of Master Nanotechnology. Since January 2007, he has been director of the honours programme at the University of Twente, and from 2011 to end 2013, director of the Electrical Engineering program.