- Email: [email protected]
Lead-free piezoelectric BiFeO3-BaTiO3 thin film with high Curie temperature
Current Applied Physics 16 (2016) 1449e1452
Contents lists available at ScienceDirect
Current Applied Physics journal homepage: www.elsevier.com/locate/cap
Lead-free piezoelectric BiFeO3-BaTiO3 thin film with high Curie temperature Myang Hwan Lee a, Da Jeong Kim a, Jin Su Park a, Myong-Ho Kim a, Tae Kwon Song a, b, *, Shalendra Kumar b, Won-Jeong Kim c, Dalhyun Do d, Inrok Hwang e, Bae Ho Park e, Kyu Sang Choi f a
School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam 51140, South Korea Institute of Basic Sciences, Changwon National University, Changwon, Gyeongnam 51140, South Korea Department of Physics, Changwon National University, Changwon, Gyeongnam 51140, South Korea d Department of Advanced Materials Engineering, Keimyung University, Daegu 42601, South Korea e Division of Quantum Phases and Devices, Department of Physics, Konkuk University, Seoul 05029, South Korea f Department of Physics Education, Sunchon National University, Sunchon, Jeonnam 57922, South Korea b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 3 May 2016 Received in revised form 26 July 2016 Accepted 13 August 2016 Available online 15 August 2016
Polycrystalline 0.67Bi1.05FeO3-0.33BaTiO3 (BF33BT) lead-free piezoelectric thin film is fabricated on Pt(111)/Ti/SiO2/Si(100) substrate by using pulsed laser deposition technique. The remnant polarization (2Pr) and coercive field (2EC) observed from polarization hysteresis (P-E) loop are 18 mC/cm2 and 208 kV/ cm, respectively. The local piezoelectric constant (d33,PFM) of BF33BT thin film is 92.5 pm/V which is as high as lead-based piezoelectric thin film results. From the temperature dependent dielectric constant result, the Curie temperature is 405 C. These results show that BF33BT thin film is a promising candidate for lead-free piezoelectric nano- and micro-devices with high Curie temperature. © 2016 Published by Elsevier B.V.
Keywords: BiFeO3 BaTiO3 Ferroelectric Piezoelectric Curie temperature
1. Introduction Piezoelectric Pb(Zr,Ti)O3 (PZT) has been widely used in commercial parts such as actuators and sensors due to its highperformance piezoelectric properties and high phase transition Curie temperature (TC) near the morphotropic phase boundary (MPB) composition [1e3]. Because Pb-based materials have problems to the human health and environment, lead-free piezoelectric materials have been studied extensively recently. Among the leadfree materials, alkali and/or Bi-based perovskite materials, such as (K0.5Na0.5)NbO3 (KNN), (Bi0.5Na0.5)TiO3 (BNT), and (Bi0.5K0.5)TiO3 (BKT) materials have been reported to have good piezoelectric properties with high TC [4e6]. KNN-based materials are, however, very sensitive to moisture and have sintering problems due to the
* Corresponding author. School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam 51140, South Korea. E-mail addresses: [email protected] (M.H. Lee), [email protected] (T.K. Song). http://dx.doi.org/10.1016/j.cap.2016.08.008 1567-1739/© 2016 Published by Elsevier B.V.
volatility of alkali elements. BNT-based materials exhibited a high piezoelectric performance, but they have low depolarization temperatures (Td) lower than 200 C and high coercive fields (EC) [5,6]. BiFeO3 (BF) thin films have been studied intensively in terms of multiferroic properties, but piezoelectric properties have been paid less attention [7]. (Bi1-xSmx)FeO3 thin films have been reported to have a good piezoelectric constants (d33,PFM) of 60 pm/V to 110 pm/V with composition range of x ¼ 0.01 to 0.14 in MPB. But this system has relatively low TC of about 250 C when x ¼ 0.11 [8,9]. With complicated structures with BF, G. Lee et al. reported very high d33,PFM of 331 pm/V for highly strained epitaxial BF/SrTiO3/BF nano-laminates structure [10] and Y. F. Hou et al. showed d33,PFM ¼ 119.5 pm/V for polycrystalline BF/BaTiO3(BT) bi-layer structure [11]. Recently, it was observed that quenched (1-x)BF-xBT(BF-BT) lead-free piezoelectric ceramics had good piezoelectric properties and low leakage currents with high TC [12]. BF-BT solid solutions were observed in the complete compositional range with rhombohedral (x ¼ 0.00e0.33), pseudo-cubic (x ¼ 0.33e0.92), and tetragonal (x ¼ 0.92e1.00) perovskite crystal structures [13,14].
1450
M.H. Lee et al. / Current Applied Physics 16 (2016) 1449e1452
Specifically, the composition around x ¼ 0.33 showed that the rhombohedral and tetragonal phases co-exist with MPB [14e16]. However, the piezoelectric properties and TC of BF-BT thin films have not been reported sufficiently. In this work, 0.67Bi1.05FeO30.33BaTiO3 (BF33BT) solid solution thin film was prepared by using a pulsed laser deposition (PLD) method. Its ferroelectric, piezoelectric properties, and TC were investigated and were compared with those of BF thin film. 2. Experimental The BF and BF33BT thin films were deposited on Pt(111)/Ti/SiO2/ Si(100) substrates. The PLD targets were prepared via a solid-state reaction process using raw powders of Bi2O3 (Aldrich 99.9%), Fe2O3 (Aldrich 99.9%), BaCO3 (Aldrich 99.9%), and TiO2 (Aldrich 99.9%). 5 mol% excess Bi was added to compensate the volatile Bi2O3 during the high temperature sintering and/or deposition [17]. Pellets of 1 inch in diameter and 3 mm in thickness were sintered at 830 C for 2 h for BF and, 980 C for 3 h for BF33BT in air. Then the sintered ceramics were quenched to room temperature in water to avoid the formation of secondary phases [18]. A KrF excimer laser with a wavelength of 248 nm was used to ablate the target materials at a repetition rate of 5 Hz. The laser energy fluence was 2.1 J/cm2 per pulse. The substrate temperature was maintained at 540 C and the oxygen pressure was kept at 30 mTorr during the film deposition. After the deposition for 30 min, the film was rapidly cooled down to room temperature under an oxygen pressure of 760 Torr within 10 min without post-annealing process. Circular Pt top electrodes (170 mm in diameter) were deposited on top surfaces of the films by using ion sputtering with a shadow mask. The crystal structure and the microstructure of the films were determined by using X-ray diffraction (XRD, MiniFlex II, Rigaku) and field-emission scanning electron microscopy (FE-SEM, MIRA II LMH, Tescan), respectively. Ferroelectric hysteresis loops were measured by using a modified Sawyer-Tower circuit. Leakage current densities were measured by using a semiconductor parameter analyzer (HP4145b, Agilent). The surface morphology and local piezoelectric responses were observed with an atomic force microscope (AFM, XE-100, Park Systems) and with a piezoelectric force microscope (PFM, SPH-300HV, Seiko Instruments), respectively. Local piezoelectric coefficient d33,PFM value was calculated from the result of standard material of x-cut quartz single crystal. Temperature dependent dielectric constant (ε) and loss (tan d) were measured at 100 kHz using an impedance analyzer (HP4192A, Agilent).
The oriented ferroelectric thin films were reported to have improved ferroelectric properties and reduced EC [19,20]. The deposition temperature (540 C) of BF and BF33BT thin films was much lower than those of other lead-free piezoelectric thin films; 650 C for KNN, 680 C for BNT, and 700 C for BKT [21e23]. The surface morphologies of the BF and BF33BT thin films were measured by using AFM and film thicknesses were measured from cross-sectional SEM image as shown in Fig. 3. The images showed dense and crack-free surfaces in both BF and BF33BT thin films. It was observed that the BF33BT thin film has a more uniform and smaller grains than those of the BF thin film. From SEM images, the thicknesses of thin films were measured to be ~300 nm. Fig. 4(a) shows a ferroelectric polarization hysteresis (P-E) loops of the Pt/BF/Pt and Pt/BF33BT/Pt capacitors with triangular wave at 10 kHz and at room temperature. The remnant polarization (2Pr) and 2EC values of BF and BF33BT thin films were 150 mC/cm2 and 18 mC/cm2 and 630 kV/cm and 208 kV/cm, respectively. 2Pr of the BF33BT thin film is higher than that of the (001) oriented epitaxial BF30BT thin film [24] and the EC decreased by 60% [25]. The leakage current density (J(E)) characteristics of the BF and BF33BT thin films are presented in Fig. 4(b). Higher leakage current densities were observed in the BF thin film compared to those of the BF33BT thin film. The leakage current density of 7.3 103 A/cm2 at 430 kV/cm for the BF33BT capacitor is approximately two orders of magnitude lower than that of the polycrystalline BF30BT thin film under the same electric field [26]. Fig. 5 shows the local piezoelectric d33,PFM hysteresis loops of the BF and BF33BT thin films. The local piezoelectric behaviors of the BF and BF33BT thin films were measured by using PFM with the infield hysteresis method. This method uses a probing ac voltage 0.7 Vp-p and a frequency of 17 kHz superimposed on a dc bias varied in steps from 0 V to Vmax (10 V) and then decreased down to Vmin (10 V) and increased again up to 0 V in order to measure simultaneously d33,PFM as a function of the applied dc bias voltage [27]. The high EC and poor local piezoelectric properties were observed in the BF thin film compared to those of BF33BT thin film. BF33BT thin film showed good local piezoelectric properties with d33,PFM ¼ 92.5 pm/V (positive d33,PFM ¼ 67 pm/V and negative d33,PFM ¼ 118 pm/V). The observed d33,PFM value is similar to the value reported in other lead-free piezoelectric thin films; 94 pm/V for 0.94(Na0.5Bi0.5)TiO3-0.06BaTiO3 thin film [28], 64 pm/V for [Bi0.5(Na0.7K0.2Li0.1)0.5]TiO3 [23], and 61 pm/V for (K0.5Na0.5)NbO3 [29]. This value is comparable with those of 85e125 pm/V in PZT thin films [30,31]. Compared with other lead-free piezoelectric materials, BF-BT
3. Results and discussion Fig. 1 shows the XRD patterns of the polycrystalline BF and BF33BT ceramic targets for comparison with thin film results. The BF and BF33BT bulk ceramic target peaks were indexed based on the rhombohedral structure and high temperature cubic symmetry, respectively. Silicon (Si) powder was coated in a small part on the sintered ceramic targets surface serving as an internal standard to calibrate the XRD results by reducing height and tilt errors. The BF bulk ceramic target has secondary phases, such as Fe-rich and Birich phases. The secondary phases marked by “-” are related to Fe-rich phases such as Fe2O3 and/or Bi2Fe4O9, and the secondary phases marked by “,” are related to Bi-rich phases, such as Bi2O3. BF33BT bulk ceramic target, however shows a polycrystalline perovskite single phase without secondary phases. The BF and BF33BT thin films showed a single perovskite phase without any secondary phases. The XRD peaks in Fig. 2 were indexed based on high-temperature cubic symmetry. The BF and BF33BT thin films were well crystallized and had the preferred orientation of (111).
Fig. 1. The X-ray diffraction patterns of BF and BF33BT ceramic targets.
M.H. Lee et al. / Current Applied Physics 16 (2016) 1449e1452
1451
Fig. 2. The X-ray diffraction patterns of BF and BF33BT thin films.
Fig. 4. (a) Ferroelectric polarization hysteresis loops and (b) leakage current densities of BF and BF33BT thin films.
Fig. 3. The surface AFM images and cross-sectional SEM images of (a), (c) BF thin film and (b), (d) of BF33BT thin film.
system has high TC [16]. The temperature dependent dielectric constants (ε) and losses (tan d) of the BF33BT thin film and bulk ceramic at 100 kHz are shown in Fig. 6. The thin film has a much smaller grain size (nanometer scale) than bulk ceramic (micrometer scale) has. As a general trend the ferroelectric materials have strong grain size dependence on physical properties. It has been reported that the decreased grain size induces the decreased TC, Pr, piezoelectric coefficient, and magnitude of maximum dielectric constant (εmax) in lead-based and lead-free piezoelectric systems [32e34]. These different physical properties were explained by stress effects, grain boundary (high dielectric constant grains and low dielectric constant grain boundaries), and differences in thermal expansion between thin film and substrate [33e36]. We also observed the decrease of TC with broad peak at TC. The TC of BF33BT thin film and bulk ceramic are about 405 C and 425 C, respectively. Similar results were reported in other lead-free piezoelectric thin films [22]. The TC of the BF33BT thin film is, however, still much higher than those of other lead-free piezoelectric thin films; 175 C (Td) and 330 C (TC) for 0.85(Bi0.5Na0.5)TiO3-0.15(Bi0.5K0.5)TiO3 thin film and 180 C (Td) for [Bi0.5(Na0.7K0.2Li0.1)0.5]TiO3 thin film [22,23].
Fig. 5. The local piezoelectric hysteresis loops of electric field dependent strain and piezoelectric constant (d33,PFM) of (a) BF and (b) BF33BT thin films.
1452
M.H. Lee et al. / Current Applied Physics 16 (2016) 1449e1452
by the MEST (2013R1A1A4A01010612 and 2012-045424) and by the Technology Innovation Program (10047914) funded by the Ministry of Trade, Industry and Energy (MOTIE).
References
Fig. 6. Temperature dependent dielectric constant (ε) and dielectric loss (tan d) of (a) BF33BT bulk ceramic and (b) the thin film.
4. Conclusions In summary, lead-free piezoelectric 0.67Bi1.05FeO3-0.33BaTiO3 (BF33BT) thin film was successfully deposited on Pt(111)/Ti/SiO2/ Si(100) substrate by using a pulsed laser deposition method. The ferroelectric and local piezoelectric properties were investigated at room temperature. The BF33BT thin film has local piezoelectric d33,PFM ¼ 92.5 pm/V and TC ¼ 405 C. These values are much higher than reported values in other lead-free piezoelectric thin films [21,22,29]. Moreover, the d33,PFM value was comparable to those of lead-based thin films. The BF33BT thin film shows a good potential for the application of environment-friendly piezoelectric micro/ nano sensors and actuators. Acknowledgment This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (2012-0009457) and by the Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded
[1] B. Jaffe, W.R. Cook, H. Jaffe, Piezoelectric Ceramics, Academic, London, 1971. [2] K. Kakegawa, J. Mohri, S. Shirasaki, K. Takahashi, J. Am. Ceram. Soc. 65 (1982) 515. [3] G.H.L. Wong, B.W. Chua, L. Li, M.O. Lai, J. Mater. Proc. Technol. 113 (2001) 450. [4] Y. Saito, H. Takao, T. Tani, T. Nonoyama, K. Takatori, T. Homma, T. Nagaya, M. Nakamura, Nature 432 (2004) 84. [5] D.M. Lin, D.Q. Xiao, J.G. Zhu, P. Yu, Appl. Phys. Lett. 88 (2006) 062901. [6] Y.S. Sung, H.M. Lee, W. Du, H.G. Yeo, S.C. Lee, J.H. Cho, T.K. Song, M.H. Kim, Appl. Phys. Lett. 94 (2009) 062901. [7] G. Catalan, J.F. Scott, Adv. Mater 21 (2009) 2463. [8] S. Fujino, M. Murakami, V. Anbusathaiah, S.-H. Lim, V. Nagarajan, C.J. Fennie, M. Wuttig, L. Salamanca-Riba, I. Takeuchi, Appl. Phys. Lett. 92 (2008) 202904. [9] S.B. Emery, C.-J. Cheng, D. Kan, F.J. Rueckert, S.P. Alpay, V. Nagarajan, I. Takeuchi, B.O. Wells, Appl. Phys. Lett. 97 (2006) 152902. [10] G. Lee, E.M.A. Fuentes-Fernandez, G. Lian, R.S. Katiyar, O. Auciello, Appl. Phys. Lett. 106 (2015) 022905. [11] Y.F. Hou, T.D. Zhang, W. Wang, W.P. Cao, X.L. Liu, W.D. Fei, Phys. Chem. Chem. Phys. 17 (2015) 11593. [12] S.O. Leontsev, R.E. Eitel, J. Am. Ceram. Soc. 92 (2009) 2957. [13] I.H. Ismailzade, R.M. Ismailov, A.I. Alekberov, F.M. Salaev, Phys. Stat. Sol.(a) 68 (1981) K81. [14] M.M. Kumar, A. Srinivas, S.V. Suryanarayana, J. Appl. Phys. 87 (2000) 855. [15] H. Yang, C. Zhou, X. Liu, Q. Zhou, G. Chen, W. Li, H. Wang, J. Euro. Ceram. Soc. 33 (2013) 1177. [16] M.H. Lee, D.J. Kim, J.S. Park, S.W. Kim, T.K. Song, M.-H. Kim, W.-J. Kim, D. Do, I.K. Jeong, Adv. Mater 27 (2015) 6976. ~es, L.S. Cavalcante, E. Longo, J.A. Varela, [17] A.H.M. Gonzalez, A.Z. Simo C.S. Riccardi, Appl. Phys. Lett. 90 (2007) 052906. [18] T. Rojac, M. Kosec, B. Budic, N. Setter, D. Damjanovic, J. Appl. Phys. 108 (2010) 074107. [19] F. Bai, J. Wang, M. Wuttig, J.F. Li, N. Wang, A.P. Pyatakov, A.K. Zvezdin, L.E. Cross, D. Viehland, Appl. Phys. Lett. 86 (2005) 032511. [20] A.K. Pradhan, K. Zhang, D. Hunter, J.B. Dadson, G.B. Loutts, J. Appl. Phys. 97 (2005) 093903. [21] J. Wu, J. Wang, J. Appl. Phys. 106 (2009) 066101. [22] C.W. Ahn, S.S. Won, A. Ullah, S.Y. Lee, S.D. Lee, J.H. Lee, W. Jo, I.W. Kim, Curr. Appl. Phys. 12 (2012) 903. [23] D.Y. Wang, D.M. Lin, K.S. Wong, K.W. Kwok, J.Y. Dai, H.L.W. Chan, Appl. Phys. Lett. 92 (2008) 222909. [24] K. Ueda, H. Tabata, T. Kawai, Appl. Phys. Lett. 75 (1999) 555. [25] J.M. Park, T. Kanashima, M. Okuyama, S. Nakashima, K.M. Kim, J.Y. Lee, H.Y. Lee, J. Korean Phys. Soc. 58 (2011) 674. [26] Y. Ito, W. Sakamoto, M. Moriya, T. Yogo, Ceram. Int. 39 (2013) S451. [27] M. Alexe, A. Gruverman, Nanoscale Characterisation of Ferroelectric Materials, Springer, New York, 2004. [28] D.Z. Zhang, X.J. Zheng, X. Feng, T. Zhang, J. Sun, S.H. Dai, L.J. Gong, Y.Q. Gong, L. He, Z. Zhu, J. Huang, X. Xu, J. Alloys Compd. 504 (2010) 129. ~ es, M.A. Ramírez, A. Ries, J.A. Varela, E. Longo, R. Ramesh, Appl. Phys. [29] A.Z. Simo Lett. 88 (2006) 072916. [30] T. Iijima, S. Ito, H. Matsuda, Jpn. J. Appl. Phys. 41 (2002) 6735. [31] S. Yokoyama, Y. Honda, H. Morioka, S. Okamoto, H. Funakubo, T. Iijima, H. Matsuda, K. Saito, T. Yamamoto, H. Okino, O. Sakata, S. Kimura, J. Appl. Phys. 98 (2005) 094106. [32] C.A. Randall, N. Kim, J.-P. Kucera, W. Cao, T.R. Shrout, J. Am. Ceram. Soc. 81 (1998) 677. [33] S. Trolier-McKinstry, P. Muralt, J. Electroceram. 12 (2004) 7. [34] C. Molin, S. Gebhardt, Ferroelectrics 498 (2016) 111. [35] T.M. Shaw, Z. Suo, M. Huang, E. Liniger, R.B. Laibowitz, J.D. Baniecki, Appl. Phys. Lett. 75 (1999) 2129. [36] G.A. Rossetti Jr., L.E. Cross, K. Kushida, Appl. Phys. Lett. 59 (1991) 2524.
Contents lists available at ScienceDirect
Current Applied Physics journal homepage: www.elsevier.com/locate/cap
Lead-free piezoelectric BiFeO3-BaTiO3 thin film with high Curie temperature Myang Hwan Lee a, Da Jeong Kim a, Jin Su Park a, Myong-Ho Kim a, Tae Kwon Song a, b, *, Shalendra Kumar b, Won-Jeong Kim c, Dalhyun Do d, Inrok Hwang e, Bae Ho Park e, Kyu Sang Choi f a
School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam 51140, South Korea Institute of Basic Sciences, Changwon National University, Changwon, Gyeongnam 51140, South Korea Department of Physics, Changwon National University, Changwon, Gyeongnam 51140, South Korea d Department of Advanced Materials Engineering, Keimyung University, Daegu 42601, South Korea e Division of Quantum Phases and Devices, Department of Physics, Konkuk University, Seoul 05029, South Korea f Department of Physics Education, Sunchon National University, Sunchon, Jeonnam 57922, South Korea b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 3 May 2016 Received in revised form 26 July 2016 Accepted 13 August 2016 Available online 15 August 2016
Polycrystalline 0.67Bi1.05FeO3-0.33BaTiO3 (BF33BT) lead-free piezoelectric thin film is fabricated on Pt(111)/Ti/SiO2/Si(100) substrate by using pulsed laser deposition technique. The remnant polarization (2Pr) and coercive field (2EC) observed from polarization hysteresis (P-E) loop are 18 mC/cm2 and 208 kV/ cm, respectively. The local piezoelectric constant (d33,PFM) of BF33BT thin film is 92.5 pm/V which is as high as lead-based piezoelectric thin film results. From the temperature dependent dielectric constant result, the Curie temperature is 405 C. These results show that BF33BT thin film is a promising candidate for lead-free piezoelectric nano- and micro-devices with high Curie temperature. © 2016 Published by Elsevier B.V.
Keywords: BiFeO3 BaTiO3 Ferroelectric Piezoelectric Curie temperature
1. Introduction Piezoelectric Pb(Zr,Ti)O3 (PZT) has been widely used in commercial parts such as actuators and sensors due to its highperformance piezoelectric properties and high phase transition Curie temperature (TC) near the morphotropic phase boundary (MPB) composition [1e3]. Because Pb-based materials have problems to the human health and environment, lead-free piezoelectric materials have been studied extensively recently. Among the leadfree materials, alkali and/or Bi-based perovskite materials, such as (K0.5Na0.5)NbO3 (KNN), (Bi0.5Na0.5)TiO3 (BNT), and (Bi0.5K0.5)TiO3 (BKT) materials have been reported to have good piezoelectric properties with high TC [4e6]. KNN-based materials are, however, very sensitive to moisture and have sintering problems due to the
* Corresponding author. School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam 51140, South Korea. E-mail addresses: [email protected] (M.H. Lee), [email protected] (T.K. Song). http://dx.doi.org/10.1016/j.cap.2016.08.008 1567-1739/© 2016 Published by Elsevier B.V.
volatility of alkali elements. BNT-based materials exhibited a high piezoelectric performance, but they have low depolarization temperatures (Td) lower than 200 C and high coercive fields (EC) [5,6]. BiFeO3 (BF) thin films have been studied intensively in terms of multiferroic properties, but piezoelectric properties have been paid less attention [7]. (Bi1-xSmx)FeO3 thin films have been reported to have a good piezoelectric constants (d33,PFM) of 60 pm/V to 110 pm/V with composition range of x ¼ 0.01 to 0.14 in MPB. But this system has relatively low TC of about 250 C when x ¼ 0.11 [8,9]. With complicated structures with BF, G. Lee et al. reported very high d33,PFM of 331 pm/V for highly strained epitaxial BF/SrTiO3/BF nano-laminates structure [10] and Y. F. Hou et al. showed d33,PFM ¼ 119.5 pm/V for polycrystalline BF/BaTiO3(BT) bi-layer structure [11]. Recently, it was observed that quenched (1-x)BF-xBT(BF-BT) lead-free piezoelectric ceramics had good piezoelectric properties and low leakage currents with high TC [12]. BF-BT solid solutions were observed in the complete compositional range with rhombohedral (x ¼ 0.00e0.33), pseudo-cubic (x ¼ 0.33e0.92), and tetragonal (x ¼ 0.92e1.00) perovskite crystal structures [13,14].
1450
M.H. Lee et al. / Current Applied Physics 16 (2016) 1449e1452
Specifically, the composition around x ¼ 0.33 showed that the rhombohedral and tetragonal phases co-exist with MPB [14e16]. However, the piezoelectric properties and TC of BF-BT thin films have not been reported sufficiently. In this work, 0.67Bi1.05FeO30.33BaTiO3 (BF33BT) solid solution thin film was prepared by using a pulsed laser deposition (PLD) method. Its ferroelectric, piezoelectric properties, and TC were investigated and were compared with those of BF thin film. 2. Experimental The BF and BF33BT thin films were deposited on Pt(111)/Ti/SiO2/ Si(100) substrates. The PLD targets were prepared via a solid-state reaction process using raw powders of Bi2O3 (Aldrich 99.9%), Fe2O3 (Aldrich 99.9%), BaCO3 (Aldrich 99.9%), and TiO2 (Aldrich 99.9%). 5 mol% excess Bi was added to compensate the volatile Bi2O3 during the high temperature sintering and/or deposition [17]. Pellets of 1 inch in diameter and 3 mm in thickness were sintered at 830 C for 2 h for BF and, 980 C for 3 h for BF33BT in air. Then the sintered ceramics were quenched to room temperature in water to avoid the formation of secondary phases [18]. A KrF excimer laser with a wavelength of 248 nm was used to ablate the target materials at a repetition rate of 5 Hz. The laser energy fluence was 2.1 J/cm2 per pulse. The substrate temperature was maintained at 540 C and the oxygen pressure was kept at 30 mTorr during the film deposition. After the deposition for 30 min, the film was rapidly cooled down to room temperature under an oxygen pressure of 760 Torr within 10 min without post-annealing process. Circular Pt top electrodes (170 mm in diameter) were deposited on top surfaces of the films by using ion sputtering with a shadow mask. The crystal structure and the microstructure of the films were determined by using X-ray diffraction (XRD, MiniFlex II, Rigaku) and field-emission scanning electron microscopy (FE-SEM, MIRA II LMH, Tescan), respectively. Ferroelectric hysteresis loops were measured by using a modified Sawyer-Tower circuit. Leakage current densities were measured by using a semiconductor parameter analyzer (HP4145b, Agilent). The surface morphology and local piezoelectric responses were observed with an atomic force microscope (AFM, XE-100, Park Systems) and with a piezoelectric force microscope (PFM, SPH-300HV, Seiko Instruments), respectively. Local piezoelectric coefficient d33,PFM value was calculated from the result of standard material of x-cut quartz single crystal. Temperature dependent dielectric constant (ε) and loss (tan d) were measured at 100 kHz using an impedance analyzer (HP4192A, Agilent).
The oriented ferroelectric thin films were reported to have improved ferroelectric properties and reduced EC [19,20]. The deposition temperature (540 C) of BF and BF33BT thin films was much lower than those of other lead-free piezoelectric thin films; 650 C for KNN, 680 C for BNT, and 700 C for BKT [21e23]. The surface morphologies of the BF and BF33BT thin films were measured by using AFM and film thicknesses were measured from cross-sectional SEM image as shown in Fig. 3. The images showed dense and crack-free surfaces in both BF and BF33BT thin films. It was observed that the BF33BT thin film has a more uniform and smaller grains than those of the BF thin film. From SEM images, the thicknesses of thin films were measured to be ~300 nm. Fig. 4(a) shows a ferroelectric polarization hysteresis (P-E) loops of the Pt/BF/Pt and Pt/BF33BT/Pt capacitors with triangular wave at 10 kHz and at room temperature. The remnant polarization (2Pr) and 2EC values of BF and BF33BT thin films were 150 mC/cm2 and 18 mC/cm2 and 630 kV/cm and 208 kV/cm, respectively. 2Pr of the BF33BT thin film is higher than that of the (001) oriented epitaxial BF30BT thin film [24] and the EC decreased by 60% [25]. The leakage current density (J(E)) characteristics of the BF and BF33BT thin films are presented in Fig. 4(b). Higher leakage current densities were observed in the BF thin film compared to those of the BF33BT thin film. The leakage current density of 7.3 103 A/cm2 at 430 kV/cm for the BF33BT capacitor is approximately two orders of magnitude lower than that of the polycrystalline BF30BT thin film under the same electric field [26]. Fig. 5 shows the local piezoelectric d33,PFM hysteresis loops of the BF and BF33BT thin films. The local piezoelectric behaviors of the BF and BF33BT thin films were measured by using PFM with the infield hysteresis method. This method uses a probing ac voltage 0.7 Vp-p and a frequency of 17 kHz superimposed on a dc bias varied in steps from 0 V to Vmax (10 V) and then decreased down to Vmin (10 V) and increased again up to 0 V in order to measure simultaneously d33,PFM as a function of the applied dc bias voltage [27]. The high EC and poor local piezoelectric properties were observed in the BF thin film compared to those of BF33BT thin film. BF33BT thin film showed good local piezoelectric properties with d33,PFM ¼ 92.5 pm/V (positive d33,PFM ¼ 67 pm/V and negative d33,PFM ¼ 118 pm/V). The observed d33,PFM value is similar to the value reported in other lead-free piezoelectric thin films; 94 pm/V for 0.94(Na0.5Bi0.5)TiO3-0.06BaTiO3 thin film [28], 64 pm/V for [Bi0.5(Na0.7K0.2Li0.1)0.5]TiO3 [23], and 61 pm/V for (K0.5Na0.5)NbO3 [29]. This value is comparable with those of 85e125 pm/V in PZT thin films [30,31]. Compared with other lead-free piezoelectric materials, BF-BT
3. Results and discussion Fig. 1 shows the XRD patterns of the polycrystalline BF and BF33BT ceramic targets for comparison with thin film results. The BF and BF33BT bulk ceramic target peaks were indexed based on the rhombohedral structure and high temperature cubic symmetry, respectively. Silicon (Si) powder was coated in a small part on the sintered ceramic targets surface serving as an internal standard to calibrate the XRD results by reducing height and tilt errors. The BF bulk ceramic target has secondary phases, such as Fe-rich and Birich phases. The secondary phases marked by “-” are related to Fe-rich phases such as Fe2O3 and/or Bi2Fe4O9, and the secondary phases marked by “,” are related to Bi-rich phases, such as Bi2O3. BF33BT bulk ceramic target, however shows a polycrystalline perovskite single phase without secondary phases. The BF and BF33BT thin films showed a single perovskite phase without any secondary phases. The XRD peaks in Fig. 2 were indexed based on high-temperature cubic symmetry. The BF and BF33BT thin films were well crystallized and had the preferred orientation of (111).
Fig. 1. The X-ray diffraction patterns of BF and BF33BT ceramic targets.
M.H. Lee et al. / Current Applied Physics 16 (2016) 1449e1452
1451
Fig. 2. The X-ray diffraction patterns of BF and BF33BT thin films.
Fig. 4. (a) Ferroelectric polarization hysteresis loops and (b) leakage current densities of BF and BF33BT thin films.
Fig. 3. The surface AFM images and cross-sectional SEM images of (a), (c) BF thin film and (b), (d) of BF33BT thin film.
system has high TC [16]. The temperature dependent dielectric constants (ε) and losses (tan d) of the BF33BT thin film and bulk ceramic at 100 kHz are shown in Fig. 6. The thin film has a much smaller grain size (nanometer scale) than bulk ceramic (micrometer scale) has. As a general trend the ferroelectric materials have strong grain size dependence on physical properties. It has been reported that the decreased grain size induces the decreased TC, Pr, piezoelectric coefficient, and magnitude of maximum dielectric constant (εmax) in lead-based and lead-free piezoelectric systems [32e34]. These different physical properties were explained by stress effects, grain boundary (high dielectric constant grains and low dielectric constant grain boundaries), and differences in thermal expansion between thin film and substrate [33e36]. We also observed the decrease of TC with broad peak at TC. The TC of BF33BT thin film and bulk ceramic are about 405 C and 425 C, respectively. Similar results were reported in other lead-free piezoelectric thin films [22]. The TC of the BF33BT thin film is, however, still much higher than those of other lead-free piezoelectric thin films; 175 C (Td) and 330 C (TC) for 0.85(Bi0.5Na0.5)TiO3-0.15(Bi0.5K0.5)TiO3 thin film and 180 C (Td) for [Bi0.5(Na0.7K0.2Li0.1)0.5]TiO3 thin film [22,23].
Fig. 5. The local piezoelectric hysteresis loops of electric field dependent strain and piezoelectric constant (d33,PFM) of (a) BF and (b) BF33BT thin films.
1452
M.H. Lee et al. / Current Applied Physics 16 (2016) 1449e1452
by the MEST (2013R1A1A4A01010612 and 2012-045424) and by the Technology Innovation Program (10047914) funded by the Ministry of Trade, Industry and Energy (MOTIE).
References
Fig. 6. Temperature dependent dielectric constant (ε) and dielectric loss (tan d) of (a) BF33BT bulk ceramic and (b) the thin film.
4. Conclusions In summary, lead-free piezoelectric 0.67Bi1.05FeO3-0.33BaTiO3 (BF33BT) thin film was successfully deposited on Pt(111)/Ti/SiO2/ Si(100) substrate by using a pulsed laser deposition method. The ferroelectric and local piezoelectric properties were investigated at room temperature. The BF33BT thin film has local piezoelectric d33,PFM ¼ 92.5 pm/V and TC ¼ 405 C. These values are much higher than reported values in other lead-free piezoelectric thin films [21,22,29]. Moreover, the d33,PFM value was comparable to those of lead-based thin films. The BF33BT thin film shows a good potential for the application of environment-friendly piezoelectric micro/ nano sensors and actuators. Acknowledgment This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (2012-0009457) and by the Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded
[1] B. Jaffe, W.R. Cook, H. Jaffe, Piezoelectric Ceramics, Academic, London, 1971. [2] K. Kakegawa, J. Mohri, S. Shirasaki, K. Takahashi, J. Am. Ceram. Soc. 65 (1982) 515. [3] G.H.L. Wong, B.W. Chua, L. Li, M.O. Lai, J. Mater. Proc. Technol. 113 (2001) 450. [4] Y. Saito, H. Takao, T. Tani, T. Nonoyama, K. Takatori, T. Homma, T. Nagaya, M. Nakamura, Nature 432 (2004) 84. [5] D.M. Lin, D.Q. Xiao, J.G. Zhu, P. Yu, Appl. Phys. Lett. 88 (2006) 062901. [6] Y.S. Sung, H.M. Lee, W. Du, H.G. Yeo, S.C. Lee, J.H. Cho, T.K. Song, M.H. Kim, Appl. Phys. Lett. 94 (2009) 062901. [7] G. Catalan, J.F. Scott, Adv. Mater 21 (2009) 2463. [8] S. Fujino, M. Murakami, V. Anbusathaiah, S.-H. Lim, V. Nagarajan, C.J. Fennie, M. Wuttig, L. Salamanca-Riba, I. Takeuchi, Appl. Phys. Lett. 92 (2008) 202904. [9] S.B. Emery, C.-J. Cheng, D. Kan, F.J. Rueckert, S.P. Alpay, V. Nagarajan, I. Takeuchi, B.O. Wells, Appl. Phys. Lett. 97 (2006) 152902. [10] G. Lee, E.M.A. Fuentes-Fernandez, G. Lian, R.S. Katiyar, O. Auciello, Appl. Phys. Lett. 106 (2015) 022905. [11] Y.F. Hou, T.D. Zhang, W. Wang, W.P. Cao, X.L. Liu, W.D. Fei, Phys. Chem. Chem. Phys. 17 (2015) 11593. [12] S.O. Leontsev, R.E. Eitel, J. Am. Ceram. Soc. 92 (2009) 2957. [13] I.H. Ismailzade, R.M. Ismailov, A.I. Alekberov, F.M. Salaev, Phys. Stat. Sol.(a) 68 (1981) K81. [14] M.M. Kumar, A. Srinivas, S.V. Suryanarayana, J. Appl. Phys. 87 (2000) 855. [15] H. Yang, C. Zhou, X. Liu, Q. Zhou, G. Chen, W. Li, H. Wang, J. Euro. Ceram. Soc. 33 (2013) 1177. [16] M.H. Lee, D.J. Kim, J.S. Park, S.W. Kim, T.K. Song, M.-H. Kim, W.-J. Kim, D. Do, I.K. Jeong, Adv. Mater 27 (2015) 6976. ~es, L.S. Cavalcante, E. Longo, J.A. Varela, [17] A.H.M. Gonzalez, A.Z. Simo C.S. Riccardi, Appl. Phys. Lett. 90 (2007) 052906. [18] T. Rojac, M. Kosec, B. Budic, N. Setter, D. Damjanovic, J. Appl. Phys. 108 (2010) 074107. [19] F. Bai, J. Wang, M. Wuttig, J.F. Li, N. Wang, A.P. Pyatakov, A.K. Zvezdin, L.E. Cross, D. Viehland, Appl. Phys. Lett. 86 (2005) 032511. [20] A.K. Pradhan, K. Zhang, D. Hunter, J.B. Dadson, G.B. Loutts, J. Appl. Phys. 97 (2005) 093903. [21] J. Wu, J. Wang, J. Appl. Phys. 106 (2009) 066101. [22] C.W. Ahn, S.S. Won, A. Ullah, S.Y. Lee, S.D. Lee, J.H. Lee, W. Jo, I.W. Kim, Curr. Appl. Phys. 12 (2012) 903. [23] D.Y. Wang, D.M. Lin, K.S. Wong, K.W. Kwok, J.Y. Dai, H.L.W. Chan, Appl. Phys. Lett. 92 (2008) 222909. [24] K. Ueda, H. Tabata, T. Kawai, Appl. Phys. Lett. 75 (1999) 555. [25] J.M. Park, T. Kanashima, M. Okuyama, S. Nakashima, K.M. Kim, J.Y. Lee, H.Y. Lee, J. Korean Phys. Soc. 58 (2011) 674. [26] Y. Ito, W. Sakamoto, M. Moriya, T. Yogo, Ceram. Int. 39 (2013) S451. [27] M. Alexe, A. Gruverman, Nanoscale Characterisation of Ferroelectric Materials, Springer, New York, 2004. [28] D.Z. Zhang, X.J. Zheng, X. Feng, T. Zhang, J. Sun, S.H. Dai, L.J. Gong, Y.Q. Gong, L. He, Z. Zhu, J. Huang, X. Xu, J. Alloys Compd. 504 (2010) 129. ~ es, M.A. Ramírez, A. Ries, J.A. Varela, E. Longo, R. Ramesh, Appl. Phys. [29] A.Z. Simo Lett. 88 (2006) 072916. [30] T. Iijima, S. Ito, H. Matsuda, Jpn. J. Appl. Phys. 41 (2002) 6735. [31] S. Yokoyama, Y. Honda, H. Morioka, S. Okamoto, H. Funakubo, T. Iijima, H. Matsuda, K. Saito, T. Yamamoto, H. Okino, O. Sakata, S. Kimura, J. Appl. Phys. 98 (2005) 094106. [32] C.A. Randall, N. Kim, J.-P. Kucera, W. Cao, T.R. Shrout, J. Am. Ceram. Soc. 81 (1998) 677. [33] S. Trolier-McKinstry, P. Muralt, J. Electroceram. 12 (2004) 7. [34] C. Molin, S. Gebhardt, Ferroelectrics 498 (2016) 111. [35] T.M. Shaw, Z. Suo, M. Huang, E. Liniger, R.B. Laibowitz, J.D. Baniecki, Appl. Phys. Lett. 75 (1999) 2129. [36] G.A. Rossetti Jr., L.E. Cross, K. Kushida, Appl. Phys. Lett. 59 (1991) 2524.