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. Author manuscript; available in PMC: 2011 Dec 6.
Published in final edited form as: IEEE Trans Ultrason Ferroelectr Freq Control. 2011 Oct;58(10):2042–2049. doi: 10.1109/TUFFC.2011.2054

Structure and Electrical Properties of Na0.5Bi0.5TiO3 Ferroelectric Thick Films Derived From a Polymer Modified Sol-Gel Method

Hongfen Ji 1, Wei Ren 2, Lingyan Wang 3, Peng Shi 4, Xiaofeng Chen 5, Xiaoqing Wu 6, Xi Yao 7, Sien-Ting Lau 8, Qifa Zhou 9, K Kirk Shung 10
PMCID: PMC3232039  NIHMSID: NIHMS339021  PMID: 21989868

Abstract

Lead-free Na0.5Bi0.5TiO3 (NBT) ferroelectric thick films were prepared by a poly(vinylpyrrolidone) (PVP) modified sol-gel method. The NBT thick films annealed from 500°C to 750°C exhibit a perovskite structure. The relationship between annealing temperature, thickness, and electrical properties of the thick films has been investigated. The dielectric constants and remnant polarizations of the thick films increase with annealing temperature. The electrical properties of the NBT films show strong thickness dependence. As thickness increases from 1.0 to 4.8 μm, the dielectric constant of the NBT films increases from 620 to 848, whereas the dielectric loss is nearly independent of the thickness. The remnant polarization of the NBT thick films also increases with increasing thickness. The leakage current density first decreases and then increases with film thickness.

I. Introduction

Thus far, the most widely used piezoelectric materials have been lead-based materials, because of their excellent ferroelectric and piezoelectric properties. However, materials containing lead are considered to be a serious threat to the environment and human health. As a result, studies on lead-free piezoelectric films have become important in recent years. Potassium sodium niobate [(K,Na)NbO3 (KNN)] is a promising candidate for lead-free piezoelectric materials because of its excellent piezoelectric properties, high Curie temperature (TC) and low anisotropy [1]. Meanwhile, bismuth sodium titanate [(Na0.5Bi0.5)TiO3 (NBT)] is also considered to be an excellent candidate because of its strong ferroelectricity with relatively large remnant polarization (Pr = 38 μC/cm2) at room temperature [2]. Because of the high cost of KNN films prepared using the precursor solution-based sol-gel process (i.e., niobium ethoxide) [3]–[5], NBT thick films prepared from a low-cost precursor solution are an attractive alternative. At present, the research on NBT-based films is concentrated on thin films. Several methods have been used to prepare NBT thin films, including pulsed laser deposition [6], [7], radio-frequency magnetron sputtering [8], and sol-gel [9]–[12]. However, there are few reports on NBT thick films [13]. The sol-gel process has several advantages over other techniques, such as low cost and low annealing temperature to limit volatilization of compositions. Polymers used in a sol-gel process can help to achieve the desired viscosity of precursor solutions and act as binding agents to metal precursors [14], [15]. By proper control and optimization of processing parameters such as sol concentration, spin coating parameters, heat treatment, and repeat times, thick films with desired thickness and minimum defects can be obtained. In our previous work, fine KNN ceramic powder and NBT precursor solution had been used to prepare 0–3 KNN/NBT composite thick films. A high-frequency ultrasonic transducer with a center frequency of 193 MHz and −6-dB bandwidth of 34% has been successfully fabricated using the composite thick films [16].

In this study, lead-free Na0.5Bi0.5TiO3 (NBT) ferroelectric thick films were prepared by a poly(vinylpyrrolidone) (PVP)-modified sol-gel method. The effect of annealing temperature and thickness on structures, morphologies, and electrical properties of the resulting NBT thick films has been investigated.

II. Experimental

NBT thick films were prepared by a PVP-modified solgel method using bismuth nitrate pentahydrate, sodium acetate, and tetrabutyl titanate as the raw materials. 2-methoxyethanol and acetylacetone were used as the solvent and the chelating agent, respectively. To compensate for the evaporation of sodium and bismuth during the thermal treatment [3]–[6], 10 mol% excess sodium acetate and 2 mol% excess bismuth nitrate pentahydrate were added to the precursor solution. PVP with an average molecular weight of 30 000 was added to the precursor solution. The molar ratio of PVP monomer to tetrabutyl titanate is 1:1 in the experiment [3], [14], [15], [17]. The concentration of the precursor solution was adjusted to 0.45 M. The solution was deposited on (111) Pt/TiO2/SiO2/Si substrates by a spin coating method. Each layer was pyrolyzed in two steps, first at 150°C for 3 min and then at 410°C for 10 min in a rapid thermal process furnace. Then, the deposited films were annealed in the range of 500°C to 750°C for 3 min in air. This procedure was repeated until the desired thickness was reached.

Thermal analyses including differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) for the NBT dry gel were characterized by TA SDT Q600 thermal analyzer in air from room temperature to 800°C with a heating rate of 20°C/min. The phase structures were examined using an X-ray diffractometer (XRD, Rigaku D/Max-2400, Tokyo, Japan) with Cu Kα radiation. The surface and cross-sectional morphologies of the NBT thick films were examined by a field-emission scanning electron microscope (FESEM, JEOL JSM-7000F, Tokyo, Japan). To measure the electrical properties, 0.5-mm-diameter top Au electrodes were sputtered on the surfaces of the films. Polarization-electric field (P-E) hysteresis loops were measured using a ferroelectric standard testing system with an FE module (aixACC T TF analyzer 2000, aixACC T Systems GmbH, Aachen, Germany) at room temperature. The dielectric constant and loss tangent were measured by a precision impedance analyzer (Agilent 4294A, Agilent Technologies Inc., Santa Clara, CA) at an ac oscillation level of 500 mV. The leakage currents were measured using a semiconductor characterization system (4200-SCS/F, Keithley Instruments Inc., Cleveland, OH). The thickness of the films was measured by a stylus surface profiler (Dektak 6M, Veeco Instruments Inc., Plainview, NY).

III. Results and Discussion

The thermal analyses were used to investigate the decomposition and crystallization process of the NBT gel from the precursor solution dried at 80°C in air. Fig. 1 gives the DSC-TG curve of dried NBT gel. There is an endothermic peak at 155.9°C which corresponds to vaporization of residual organic solvents, accompanied by 4.12% weight loss. The three peaks at 263.6°C, 305.4°C, and 345.9°C resulted from combustion of the remaining solvent and organic ligands which are either from the precursor or from the by-product of the decomposition and polycondensation [11]. Subsequently, another exothermic peak at 464.2°C is related to the formation of the perovskite structure, accompanied by 32.85% weight loss to 500°C. There is no significant new peak appearance in the DSC curve as the temperature increases to 800°C. This indicates that the perovskite structure can be formed once the sintering temperature is higher than 465°C. According to the thermal analysis of the NBT dry gel, the pyrolysis temperature was set at 410°C, and the annealing temperature was set in a range of 500°C to 750°C.

Fig. 1.

Fig. 1

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Differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) thermographs of NBT dry gel.

Fig. 2(a) shows the XRD patterns of NBT films annealed at various temperatures ranging from 500°C to 750°C. It is found that the NBT films show a rhombohedral perovskite phase. The crystallization is improved by increasing the annealing temperature because the intensity of the XRD peaks increases with annealing temperature. The NBT thick films prepared by a modified sol-gel process exhibit relatively low crystallization temperatures. The full-width at half-maximum (FWHM) of the (110) peaks decreases with increasing annealing temperature. The average crystallite size is evaluated by a Scherer formula [d = 0.89·λ/(B cos θ)] using the XRD data. The calculated crystallite size increases from 23 to 37 nm as the annealing temperature increases from 500°C to 750°C, as shown in Fig. 2(b).

Fig. 2.

Fig. 2

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X-ray diffraction patterns of NBT thick films annealed at different annealing temperatures.

Because higher annealing temperature can promote the crystallization of the NBT thick films, the films with thickness between 1.0 and 4.8 μm were annealed at 750°C for 3 min. The FESEM morphologies of the surfaces and cross-sections of the NBT films are shown in Fig. 3. The thicknesses of NBT thick films are 1.0, 2.0, 3.4, and 4.8 μm. The surface morphologies indicate that the surfaces of the thick films with various thicknesses are smooth and compact, and the cross-sectional morphologies indicate that the NBT thick films exhibit very dense columnar structures. The grain nucleation starts from the bottom electrode interface. The decomposition of the PVP polymer during the thermal treatment promotes structural relaxation and prevents cracking in the films [14], [15]; however, some cracks in the films can be observed in the FESEM pictures with larger scales (not shown here). The cracks lead to the increase of the leakage currents and deterioration of the electrical properties. Generally, cracking became more serious with increasing film thickness. The particle size of thick films annealed at 750°C is between 50 and 80 nm, and shows no significant change with the film thickness. The particles are clusters of even smaller crystal grains in size of ~37 nm.

Fig. 3.

Fig. 3

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Field-emission scanning electron microscope morphologies of surfaces and cross sections of NBT thick films annealed at 750°C with various thicknesses.

The dielectric properties of the NBT thick films annealed at various temperatures are shown in Fig. 4. The dielectric constant of the NBT films with thickness between 3.1 and 3.4 μm increases from 650 to 900, whereas the dielectric loss slightly decreases when the annealing temperature increases from 650°C to 750°C. The results indicate that the NBT thick films annealed at high temperature exhibit improved dielectric properties because of better crystallization at high annealing temperature [18], [19].

Fig. 4.

Fig. 4

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Dielectric constant and loss tangent as functions of frequency and annealing temperature for NBT thick films.

As shown in Fig. 5(a), the dielectric constant slightly decreases with increasing frequency, whereas the dielectric loss slightly increases. The thickness dependence of the dielectric constant and dielectric loss at 1 kHz are given in Fig. 5(b). When the thickness increases from 1.0 to 4.8 μm, the corresponding dielectric constant increases from 680 to 1050 at 1 kHz, whereas the dielectric loss is nearly independent of the thickness. A similar thickness effect is also reported in ferroelectric PZT thick films [20]–[22].

Fig. 5.

Fig. 5

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Frequency dependence of dielectric constant and loss tangent of NBT thick films annealed at 750°C with thickness from 1.0 to 4.8 μm.

The decrease of the dielectric constant with decreasing film thickness is often attributed to the low dielectric constant of the interface layers between the electrodes and the films [23], [24]. The NBT film sample can be treated as a simple two-capacitor-in-series circuit: one represents the thick films layer and the other represents the interface layer. The measured dielectric constant εr can be expressed as: 1/εr = (di/εri) · (1/d) + (1/εrf), where d is the film thickness, di is the thickness of the interface layer. εr, εri, and εrf are measured dielectric constant, dielectric constant of the interface layer, and dielectric constant of the NBT thick film, respectively. There should be a linear relationship between 1/εr and 1/d; however, there is an obvious difference between the experimental data and the linear relationship, as shown in Fig. 6. This means that, except for the electrode-film interface layer, other factors such as stress [25], [26] and domain structure effect [27] may also strongly affect the thickness dependence of the dielectric constant in the NBT films [28].

Fig. 6.

Fig. 6

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Reciprocal of dielectric constant as a function of reciprocal of thickness for NBT thick films.

The influence of annealing temperature on the ferroelectric properties of the NBT films is shown in Fig. 7. The voltage available from the ferroelectric test system is not high enough to measure the saturation polarization for the NBT films thicker than 2 μm. However, the values of polarization do increase from 7.3 to 17.5 μC/cm2 with annealing temperature increasing from 650°C to 750°C at the same applied electric field of 350 kV/cm (below saturation). This indicates that the NBT films annealed at higher temperature exhibit improved ferroelectric properties resulting from the improved crystallization of the films [29]. The results are consistent with the XRD results. It can be seen in Fig. 7(b) that the coercive field also increases with annealing temperature. The grain size of the films increases with increasing annealing temperature. This decreases the volume fraction of the grain boundaries and domain walls, resulting in the increase of the domain alignment and the remanent polarization [30]. However, the volatility of Bi and Na also increases with annealing temperature; hence, the concentration of the charged carriers such as bismuth vacancies, sodium vacancies and oxygen vacancies increases. These charged carriers would act as pinning centers to pin domains nearby [31]. Thus, Pr and Ec of the films increase with annealing temperature.

Fig. 7.

Fig. 7

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Ferroelectric properties as a function of annealing temperature for NBT thick films.

The polarization-electric field (P-E) response was measured with a variable applied field for NBT thick films with different thickness, however, the available maximum voltage from the ferroelectric test system is 120 V—not high enough to measure the saturation polarization for NBT films thicker than 2 μm. Therefore, Figs. 8(a)–8(c) present the P-E hysteresis loops under different applied fields for the NBT thick films with different thickness. For NBT films of thicknesses 1.0, 2.0, 3.4, and 4.8 μm, the values of remnant polarization, Pr, are 18.0, 17.8, 17.5, and 14.6 μC/cm2, respectively. The corresponding coercive fields, Ec, are 99.5, 96.7, 73.6, and 59.0 kV/cm, respectively, as shown in Fig. 8(a). It can be seen in Figs. 8(b) and 8(c) that the remnant polarization increases with film thickness, but the Pr value of the 4.8-μm-thick films decreases because of the lower electric field on the film. It is well known that many factors affect the ferroelectric properties of the films, such as interfacial layer [32], residual stress, substrate pinning, domain wall motion [33], and depolarization field.

Fig. 8.

Fig. 8

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(a) Ferroelectric E-P loops of NBT thick films with various thicknesses at different electric fields. (b) Ferroelectric E-P loops of NBT thick films with various thickness at approximately 280 kV/cm. (c) Thickness dependence of the polarization and coercive field of NBT thick films with the electric field at about 280 kV/cm.

The relationship between the current density and the applied electric field of NBT thick films with various thicknesses ranging from 1.0 to 4.8 μm is shown in Fig. 9. The leakage current density first decreases with increasing film thickness because the effect of substrate on the electric properties of NBT films [34], then it increases as the film thickness increases from 2.0 to 4.8 μm, because the defects increase with thickness. The 2.0-μm-thick NBT film has the minimum leakage current density, which is less than 1.0 × 10−10 A/cm2 at zero field. As the electric field increases to 60 kV/cm, the leakage current density increases to 10−8 A/cm2. As the film thickness further increases to 4.8 μm, the leakage current densities of the film increase to 10−7 A/cm2 at 0 kV/cm and 10−4 A/cm2 at 60 kV/cm, respectively. An asymmetric current behavior between the negative field region and the positive field region, as shown in Fig. 9, is contributed by the interfaces between the different electrodes and the films [35], [36].

Fig. 9.

Fig. 9

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J-E characteristics of NBT thick films annealed at 750°C with thickness from 1.0 to 4.8 μm.

The fabrication of high-frequency ultrasonic transducers using the NBT thick films is under way and will be reported elsewhere.

IV. Conclusions

NBT thick films have been successfully prepared on (111) Pt/TiO2/SiO2/Si substrates by a PVP-modified solgel method. The thick films annealed between 500°C and 750°C exhibit a pure perovskite structure. The crystallite size increases with annealing temperature. The NBT thick films with thicknesses in the range of 1.0 to 4.8 μm show compact and smooth structure. The particle size of the films annealed at 750°C is between 50 and 80 nm. As the film thickness increases from 1.0 to 4.8 μm, the dielectric constant of the NBT thick films increases from 620 to 848, whereas the dielectric loss is nearly independent of the thickness and less than 6%. The remnant polarization increases with film thickness. I-V characteristics indicate that the leakage current of the thick films first decreases and then increases as the film thickness increases from 1.0 to 4.8 μm.

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 90923001 and U0634006), by the International Science & Technology Cooperation Program of China (Grant No. 2010DFB13640), by the Shaanxi Province International Collaboration Program (Grant Nos. 2009KW-12 and 2010KW-09), and by NIH Grant P41-EB2182.

Biographies

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Hongfen Ji was born in Datong City, Shanxi, China, in 1982. Currently she is working on her Ph.D. degree in the Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education & International Center for Dielectric Research at the Xi’an Jiaotong University. Her current research interests include lead-free piezoelectric and ferroelectric composite thin/thick films.

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Wei Ren (SM’98) is the Changjiang chair professor in the Department of Electronic Science and Engineering, Xi’an Jiaotong University, the director of Electronic Materials Research Laboratory, Key Laboratory of the State Education Ministry, and the executive director of the International Center for Dielectric Research, Xi’an Jiaotong University.

Dr. Ren received B.S. and Ph.D degrees from Xi’an Jiaotong University in 1984 and 1992, respectively. He joined Xi’an Jiaotong University in 1987 and was promoted to professor in 1997. He has held visiting appointments at the Heinrich Hertz Institute in Berlin, Germany (1992–1993), the Materials Research Laboratory of The Pennsylvania State University, University Park, PA (1998–1999), and Department of Physics of the Royal Military College of Canada (1999–2004). Dr. Ren has published more than 140 papers and held 9 Chinese and U.S. patents.

Dr. Ren is a senior member of the IEEE and a member of the Ferroelectric Committee of the IEEE UFFC Society. He is also a member of the International Advisory Committee of Ferroelectricity, and an executive member of the Asian Ferroelectric Association. He is a chair of the Dielectric Physics Committee, Chinese Physics Society. He was a co-general chair of the 2009 18th IEEE International Symposium on Applications of Ferroelectrics. His current research interests include piezoelectric and ferroelectric materials and sensors, and transducers.

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Lingyan Wang received her B.Eng. and M.Eng. degrees in 2003 and 2006, respectively, both from the Xi’an University of Science and Technology, Shaanxi, China. She received her Ph.D. degree in electronics science and technology from Xi’an Jiaotong University, Shaanxi, China, in Mar. 2011. During Nov. 2007 to Nov. 2008, she worked in the Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), Singapore.

Currently, she is a lecturer in the Department of Electronic Science and Technology and the Electronic Materials Research Laboratory, Xi’an Jiaotong University, Shaanxi, China. Her main research interests are in dielectric, ferroelectric and piezoelectric films, and ceramics.

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Peng Shi was born in October 1973 in Xi’an, China. He received his Ph.D. degree in 2005 in electronic science and technology from Xi’an Jiaotong University, China. He began his career and joined the Electronic Materials Research Laboratory (EMRL) as a staff researcher in Xi’an Jiaotong University from 2005. Currently, he works as Associate Professor in the Department of Electronic Science and Technology and the Electronic Materials Research Laboratory (EMRL) at Xi’an Jiaotong University, China.

His main research interests are in the development of ferroelectric and dielectric thin films and composites, MEMs technology, and functional devices based on ferroelectric and dielectric materials. He has published more than 20 international journal publications and holds 2 Chinese patents.

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Xiaofeng Chen received his B.Eng. degree from Shanghai Jiaotong University, China, in 1988 and his Ph.D. degree from Nanyang Technological University, Singapore, in 2001. He is a professor in the School of Electronic and Information Engineering, Xi’an Jiaotong University. His current research interests are the metal oxide dielectrics and semiconductors for electronic devices and environmental applications.

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Xiaoqing Wu was born in 1955 in Shaanxi Province, China. She received a Ph.D. degree in microelectronics and solid electronics from Xi’an Jiaotong University, Xi’an, China. She holds a research position in the Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education, Xi’an Jiaotong University. Her research interests are in functional thin films and integrated devices, and electronic ceramics and devices.

She was a Member of the Executive Board of the Xi’an Society of Nanotechnologies. She has received the 2nd Prize of the 2001 Technological Invention Award of China Universities, Ministry of Education, and the 2nd Prize of the 1999 Progress Awards of Sciences and Technologies, Ministry of Education, China.

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Xi Yao is a professor of Xi’an Jiaotong University, chair of the International Center for Dielectric Research (ICDR), Xian, China. He is a member of the Chinese Academy of Sciences and a foreign associate of the US National Academy of Engineering (NAE). His major research interests are dielectric materials and devices; ferroelectric, piezoelectric, and pyroelectric materials and devices; oxide and compound semiconductors and devices; functional nanocomposite materials and devices; smart sensors and actuators; integrated ferroelectrics; and ferroelectric micro electromechanical systems.

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Sien-Ting Lau received the B.Sc. with 1st Class Honors, M.Phil., and Ph.D. degrees in 1998, 2001, and 2004, respectively, all from the Hong Kong Polytechnic University. From 2004 to 2009, she was with the Department of Applied Physics at the Hong Kong Polytechnic University, first as a Postdoctoral Fellow, then as a Research Associate working on ferroelectric materials characterizations and ultrasonic transducer and array fabrication.

Currently, she is a Research Associate at the NIH Resource Center for Medical Ultrasonic Transducer Technology and the Department of Biomedical Engineering at the University of Southern California, Los Angeles, CA.

Her main research interests are in the development of ferroelectric polymers and composites, MEMs technology, and design and fabrication of high-frequency ultrasonic transducers for medical applications. She has published more than 50 international journal publications, with a number of papers published in Applied Physics Letters, Journal of Applied Physics, Advanced Materials, etc.

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Qifa Zhou received his Ph.D. degree from the Department of Electronic Materials and Engineering at Xi’an Jiaotong University, China in 1993. He is currently a Research Professor at the NIH Resource on Medical Ultrasonic Transducer Technology and the Department of Biomedical Engineering at the University of Southern California, Los Angeles, CA. Before joining USC in 2002, he worked in the Department of Physics at Zhong-shan University of China, the Department of Applied Physics at Hong Kong Polytechnic University, and the Materials Research Laboratory at The Pennsylvania State University.

Dr. Zhou is a senior member of IEEE and a member of the Ferroelectric Committee of the IEEE UFFC Society. He is also a member of the technical program Committee of the IEEE International Ultrasonics Symposium. He is an Associate Editor of the IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. His current research interests include the development of ferroelectric thin films, MEMS technology, nano-composites, modeling and fabrication of high-frequency ultrasound transducers and arrays for medical imaging applications, and photoacoustic imaging. He has published more than 100 papers in this area.

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K. Kirk Shung obtained a B.S. degree in electrical engineering from Cheng-Kung University in Taiwan in 1968, an M.S. degree in electrical engineering from the University of Missouri, Columbia, MO in 1970, and a Ph.D. degree in electrical engineering from the University of Washington, Seattle, WA, in 1975. He had taught at The Pennsylvania State University, University Park, PA, for 23 years before moving to the Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, as a professor in 2002. He has been the director of the NIH Resource on Medical Ultrasonic Transducer Technology since 1997.

Dr. Shung is a life fellow of IEEE and a fellow of the Acoustical Society of America and the American Institute of Ultrasound in Medicine. He is a founding fellow of the American Institute of Medical and Biological Engineering. He received the IEEE Engineering in Medicine and Biology Society Early Career Award in 1985 and was the coauthor of a paper that received the best paper award for the IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control (UFFC) in 2000. He was elected an outstanding alumnus of Cheng-Kung University in Taiwan in 2001. He was selected as the distinguished lecturer for the IEEE UFFC society for 2002–2003. He received the Holmes Pioneer Award in Basic Science from the American Institute of Ultrasound in Medicine in 2010. He was selected to receive the academic career achievement award from the IEEE Engineering in Medicine and Biology Society in 2011.

Dr. Shung has published more than 400 papers and book chapters. He is the author of the textbook Principles of Medical Imaging, published by Academic Press in 1992, and the textbook Diagnostic Ultrasound: Imaging and Blood Flow Measurements, published by CRC Press in 2005. He co-edited the book Ultrasonic Scattering by Biological Tissues, published by CRC Press in 1993. Dr. Shung’s research interest is in ultrasonic transducers, high-frequency ultrasonic imaging, ultrasound microbeams, and ultrasonic scattering in tissues.

Contributor Information

Hongfen Ji, Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an, China.

Wei Ren, Email: wren@mail.xtju.edu.cn, Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an, China.

Lingyan Wang, Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an, China.

Peng Shi, Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an, China.

Xiaofeng Chen, Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an, China.

Xiaoqing Wu, Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an, China.

Xi Yao, Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an, China.

Sien-Ting Lau, NIH Transducer Resource Center and Department of Biomedical Engineering, University of Southern California, Los Angeles, CA.

Qifa Zhou, NIH Transducer Resource Center and Department of Biomedical Engineering, University of Southern California, Los Angeles, CA.

K. Kirk Shung, NIH Transducer Resource Center and Department of Biomedical Engineering, University of Southern California, Los Angeles, CA.

References

  • 1.Shrout TR, Zhang SJ. Lead-free piezoelectric ceramics: Alternatives for PZT? J Electroceram. 2007;19(1):111–124. [Google Scholar]
  • 2.Smolensky GA, Isupov VA, Agranovskaya AI, Krainik NN. New ferroelectrics of complex composition. Sov Phys Solid State. 1961;2(11):2651–2654. [Google Scholar]
  • 3.Wang LY, Yao K, Ren W. Piezoelectric K0.5Na0.5NbO3 thick films derived from polyvinylpyrrolidone-modified chemical solution deposition. Appl Phys Lett. 2008;93(9):art. no. 092903. [Google Scholar]
  • 4.Wang LY, Ren W, Yao K, Goh PC, Shi P, Wu XQ, Yao X. Effect of pyrolysis temperature on K0.5Na0.5NbO3 thick films derived from polyvinylpyrrolidone-modified chemical solution. J Am Ceram Soc. 2010;93(11):3686–3690. [Google Scholar]
  • 5.Wang LY, Ren W, Shi P, Chen XF, Wu XQ, Yao X. Enhanced ferroelectric properties in Mn-doped K0.5Na0.5NbO3 thin films derived from chemical solution deposition. pApl Phys Lett. 2010;97(7):art. no. 072902. [Google Scholar]
  • 6.Duclère JR, Cibert C, Boulle A, Dorcet V, Marchet P, Champeaux C, Catherinot A, Députier S, Guilloux-Viry M. Lead-free Na0.5Bi0.5TiO3 ferroelectric thin films grown by pulsed laser deposition on epitaxial platinum bottom electrodes. Thin Solid Films. 2008;517(2):592–597. [Google Scholar]
  • 7.Bousquet M, Duclère J-R, Champeaux C, Boulle A, Marchet P, Catherinot A, Wu A, Vilarinho PM, Députier S, Guilloux-Viry M, Crunteanu A, Gautier B, Albertini D, Bachelet C. Macroscopic and nanoscale electrical properties of pulsed laser deposited (100) epitaxial lead-free Na0.5Bi0.5TiO3 thin films. J Appl Phys. 2010;107(3):art. no. 034102. [Google Scholar]
  • 8.Zhou ZH, Xue JM, Li WZ, Wang J, Zhu H, Miao JM. Ferroelectric and electrical behavior of Na0.5Bi0.5TiO3 thin films. Appl Phys Lett. 2004;85(5):804–806. [Google Scholar]
  • 9.Tang XG, Wang J, Wang XX, Chan HLW. Preparation and electrical properties of highly (111)-oriented (Na0.5Bi0.5)TiO3 thin films by a sol-gel process. Chem Mater. 2004;16(25):5293–5296. [Google Scholar]
  • 10.Yu T, Kwok KW, Chan HLW. Preparation and properties of sol-gel-derived Bi0.5Na0.5TiO3 lead-free ferroelectric thin film. Thin Solid Films. 2007;515(7–8):3563–3566. [Google Scholar]
  • 11.Rémondière F, Malič B, Kosec M, Mercurio JP. Study of the crystallization pathway of Na0.5Bi0.5TiO3 thin films obtained by chemical solution deposition. J Sol-Gel Sci Technol. 2008;46(2):117–125. [Google Scholar]
  • 12.Rémondière F, Wu A, Vilarinho PM, Mercurio JP. Piezoforce microscopy study of lead-free perovskite Na0.5Bi0.5TiO3 thin films. Appl Phys Lett. 2007;90(15):art. no. 152905. [Google Scholar]
  • 13.Suzuki M, Noguchi YJ, Miyayama M, Akedo J. Polarization and leakage current properties of bismuth sodium titanate ceramic films deposited by aerosol deposition method. J Ceram Soc Jpn. 2010;118(10):899–902. [Google Scholar]
  • 14.Kozuka H, Kajimura M, Hirano T, Katayama K. Crackfree, thick ceramic coating films via non-repetitive dip-coating using polyvinylpyrrolidone as stress-relaxing agent. J Sol-Gel Sci Technol. 2000;19(1–3):205–209. [Google Scholar]
  • 15.Wang LY, Yao K, Goh PC, Ren W. Volatilization of alkali ions and effects of molecular weight of polyvinylpyrrolidone introduced in solution-derived ferroelectric K0.5Na0.5NbO3 films. J Mater Res. 2009;24(12):3516–3522. [Google Scholar]
  • 16.Lau ST, Ji HF, Li X, Ren W, Zhou QF, Shung KK. KNN/BNT composite lead free films for high frequency ultrasonic transducer applications. IEEE Trans Ultrason Ferroelectr Freq Control. 58(1):249–254. doi: 10.1109/TUFFC.2011.1793. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 17.Wang ZY, Liu JS, Ren TL, Liu LT. Fabrication of organic PVP doping-based Ba0.5Sr0.5TiO3 thick films on silicon substrates for MEMS applications. Sens Actuators A. 2005;117(2):293–300. [Google Scholar]
  • 18.Zhu XH, Zheng DN, Zeng H, Peng W, Zhu JG, Yuan XW, Yong LP, Miao J, Li J, Tian HY, Xu XP. Effects of growth temperature and film thickness on the electrical properties of Ba0.7Sr0.3TiO3 thin films grown on platinized silicon substrates by pulsed laser deposition. Thin Solid Films. 2006;496(2):376–382. [Google Scholar]
  • 19.Kim KT, Kim CI, Lee SG, Kim HM. Correlation between dielectric properties and strain in Pb0.5Sr0.5TiO3 thin films prepared by using the sol–gel method. Surf Coat Tech. 2005;190(2–3):190–194. [Google Scholar]
  • 20.Tu YL, Milne SJ. Processing and characterization of Pb(Zr, Ti)O3 films, up to 10 μm thick, produced from a diol sol-gel route. J Mater Res. 1996;11(10):2556–2564. [Google Scholar]
  • 21.Chen HD, Udayakumar KR, Gaskey CJ, Cross LE, Bernstein JJ, Niles C. Fabrication and electrical properties of lead zirconate titanate thick films. J Am Ceram Soc. 1996;79(8):2189–2192. [Google Scholar]
  • 22.Kurchania R, Milne SJ. Characterization of sol-gel Pb(Zr0.53Ti0.47)O3 films in the thickness range 0.25–10 μm. J Mater Res. 1999;14(5):1852–1859. [Google Scholar]
  • 23.Larsen PK, Dormans JM, Taylor DJ, van Veldhoven PJ. Ferroelectric properties and fatigue of PbZr0.51Ti0.4903 thin films of varying thickness: Blocking layer model. J Appl Phys. 1994;76(4):2405–2413. [Google Scholar]
  • 24.Sakashita Y, Segawa H, Tominaga K, Okada M. Dependence of electrical properties on film thickness in Pb(ZrxTi1−x)O3 thin films produced by metalorganic chemical vapor deposition. J Appl Phys. 1993;73(11):7857–7863. [Google Scholar]
  • 25.Newnham RE, Udayakumar KR, Trolier-McKinstry S. In: Chemical Processing of Advanced Materials. Hench LL, West JK, editors. New York, NY: Wiley; 1982. pp. 379–393. [Google Scholar]
  • 26.Chen HD, Li KK, Gaskey CJ, Cross LE. Thickness-dependent electrical properties in lanthanum-doped PZT thick films. Materials Research Society Symp Proc. 1996;433:325–332. [Google Scholar]
  • 27.Ren SB, Lu CJ, Shen HM, Wang YN. In situ study of the evolution of domain structure in free-standing polycrystalline PbTiO3 thin films under external stress. Phys Rev B. 1997;55(6):3485–3489. [Google Scholar]
  • 28.Xu BM, Ye YH, Wang QM, Cross LE. Dependence of electrical properties on film thickness in lanthanum-doped lead zirconate titanate stannate antiferroelectric thin films. J Appl Phys. 1998;85(7):3753–3758. [Google Scholar]
  • 29.He HY, Huang JF, Cao LY. Effects of annealing schedule on orientation of Bi3.2Nd0.8Ti3O12 ferroelectric film prepared by chemical solution deposition process. Mater Sci Eng B. 2006;133(1–3):132–135. [Google Scholar]
  • 30.Shaw TM, Mckinstry S, Mcintry PC. The properties of ferroelectric films at small dimensions. Annu Rev Mater Sci. 2000;30(1):263–298. [Google Scholar]
  • 31.Wu Y, Wang X, Zhong C, Li L. Effect of anneal conditions on electrical properties of Mn-doped (Na0.85K0.15)0.5Bi0.5TiO3 thin films prepared by sol-gel method. J Am Ceram Soc. 2011;94(6):1843–1849. [Google Scholar]
  • 32.Kim DJ, Park JH, Shen D, Lee JW, Kingon AI, Yoon YS, Kim SH. Thickness dependence of submicron thick Pb(Zr0.3Ti0.7)O3 films on piezoelectric properties. Ceram Int. 2008;34(8):1909–1915. [Google Scholar]
  • 33.Xu F, Trolier-McKinstry S, Ren W, Xu B, Xie ZL, Hemker KJ. Domain wall motion and its contribution to the dielectric and piezoelectric properties of lead zirconate titanate films. J Appl Phys. 2001;89(2):1336–1348. [Google Scholar]
  • 34.Goh PC, Yao K, Chen ZY. Titanium diffusion into (K0.5Na0.5)NbO3 thin films deposited on Pt/Ti/SiO2/Si substrates and corresponding effects. J Am Ceram Soc. 2009;92(6):1322–1327. [Google Scholar]
  • 35.Pabst GW, Martin LW, Chu YH, Ramesh R. Leakage mechanisms in BiFeO3 thin films. Appl Phys Lett. 2007;90(7):art. no. 072902. [Google Scholar]
  • 36.Sudhama C, Campbell AC, Maniar PD, Jones RE, Moazzami R, Mogab CJ, Lee JC. A model for electrical conduction in metal-ferroelectric-metal thin-film capacitors. J Appl Phys. 1994;75(2):1014–1022. [Google Scholar]

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