（Pb_（0.76）Ca_（0.24））TiO_3薄膜的压电力显微镜研究
|
摘要
铁电薄膜具有铁电性、压电性、介电性、热释电性、光折射效应、电光效应和非线性光学效应等一系列特殊的物理性质,在非易失性铁电存储器(FeRAMS)、微机电系统(MEMS)、现代微电子等领域有着广泛的应用前景。有关铁电薄膜材料的研究是目前高新技术研究的热点之一。随着铁电器件尺寸的减小,铁电材料的纳米尺度微区物理特性,包括铁电畴结构的形成、铁电畴极化和退极化行为等方面的研究吸引了该领域众多研究人员的关注。
现有的铁电畴检测手段,如偏光显微镜、化学腐蚀法、透射电镜、扫描电子显微镜等存在诸如制样繁琐、对样品和原始电畴结构有破坏性、电畴成像分辨率不够高等一些缺点。近年来在AFM基础上发展起来的压电力显微镜(Piezoresponse-SFM,PFM)为铁电畴的研究提供了一种强有力的手段。
(Pb_(0.76)Ca_(0.24))TiO_3(PCT)薄膜是一种具有很强各向异性的铁电/压电材料,其薄膜压电系数值接近其块材值。我们运用溶胶-凝胶法在(Pt/Ti/SiO_2/Si)衬底制备了PCT多晶薄膜,它具有致密、平整的膜面。
本论文运用压电力显微镜(PFM)研究了纳米尺度下(Pb_(0.76)Ca_(0.24))TiO_3(PCT)薄膜的电畴结构、极化反转和退极化行为。对比形貌图和压电响应图,研究了电畴结构和晶粒尺寸之间的关系。
我们以探针作为移动上电极对样品上选择的区域施加电压进行极化,在极化后,利用压电响应模式扫描进行压电力成像,研究了与极化电压相关的畴反转行为。我们发现畴的反转与外加极化电压有关,随着极化电压的增大,反转畴逐渐扩张。不同的畴极化反转所需的极化电压也不相同,有些畴在较小的极化电压作用下就可以反转,而有些畴的反转则需要较大的极化电压。研究还发现当探针施加的极化电压足够大,由边沿效应在非扫描区域产生的场强大于该区域的矫顽场时,也会诱导该区域的畴发生反转。
我们用探针施加电压对样品上选择区域进行极化后,还在不同的时间对样品同一区域进行压电力成像,研究了电畴的退极化行为及电畴结构、畴壁、晶界对退极化过程的影响。
Current interest in ferroelectric thin film results from the numerous potential applications in nonvolatile ferroelectric random access memory (FeRAMS), Micro Electro-Mechanical System (MEMS) and micro-electronics that utilize the unique ferroelectric, piezoelectric, dielectric, pyroelectric, photorefractive, electro-optic and non-linear optic properties of the material. As the dimension of ferroelectric devices reduced, physical properties of ferroelectric materials in nanometer scale which including the formation of domain structure, polarization and depolarization of ferroelectric domain attract attention of many researchers in this area.
There are many methods to investigate domains such as polarizing microscopy, chemical etching, transmission electron microscopy, scanning electron microscopy and so on. However, these methods suffer from some serious disadvantages involving complex sample preparation, damage to sample, low resolution. PFM developed from AFM has provided a powerful tool for the research of ferroelectric domains.
(Pb_(0.76)Ca_(0.24))TiO_3 (PCT) film is a ferroelectric & piezoelectric material with high anisotropy. When prepared in thin-film form it can have a large d33, comparable to bulk material. Using the Sol-gel method, pure teragonal PCT films have been successfully prepared on platinized Si substrates. The films have a dense structure with a relatively smooth surface.
Piezoresponse scanning force microscopy was used to observe the nanoscale ferroelectric domain structure, switching and back-switching processes. The relation between domain structure and the size of the grains were obtained.
In this paper, we present direct observations of local domain switching. Domain switching is performed on the selected area by applying a bias voltage through the probing tip, and thereafter the piezoresponse image is obtained. With the increase of the polarization voltage, the domain switching expands the whole grain. The ferroelectric films were polarized in nanometer scale under positive or negative voltages applied by the probing tip. The reversing of different domains of the PCT films requires different polarization voltages. Some domains can reverse at low polarization voltage, but others reverse at high polarization. This thesis also reveals that when electric field produced by edge effect in non-scan area was larger than coercive field of this area, domains would reverse.
This thesis studies back-switching process through observe piezoresponse images measured in different times after a bias voltage polarization, and the effect of domain structure, domain wall, grain boundaries to back-switching processes.
现有的铁电畴检测手段,如偏光显微镜、化学腐蚀法、透射电镜、扫描电子显微镜等存在诸如制样繁琐、对样品和原始电畴结构有破坏性、电畴成像分辨率不够高等一些缺点。近年来在AFM基础上发展起来的压电力显微镜(Piezoresponse-SFM,PFM)为铁电畴的研究提供了一种强有力的手段。
(Pb_(0.76)Ca_(0.24))TiO_3(PCT)薄膜是一种具有很强各向异性的铁电/压电材料,其薄膜压电系数值接近其块材值。我们运用溶胶-凝胶法在(Pt/Ti/SiO_2/Si)衬底制备了PCT多晶薄膜,它具有致密、平整的膜面。
本论文运用压电力显微镜(PFM)研究了纳米尺度下(Pb_(0.76)Ca_(0.24))TiO_3(PCT)薄膜的电畴结构、极化反转和退极化行为。对比形貌图和压电响应图,研究了电畴结构和晶粒尺寸之间的关系。
我们以探针作为移动上电极对样品上选择的区域施加电压进行极化,在极化后,利用压电响应模式扫描进行压电力成像,研究了与极化电压相关的畴反转行为。我们发现畴的反转与外加极化电压有关,随着极化电压的增大,反转畴逐渐扩张。不同的畴极化反转所需的极化电压也不相同,有些畴在较小的极化电压作用下就可以反转,而有些畴的反转则需要较大的极化电压。研究还发现当探针施加的极化电压足够大,由边沿效应在非扫描区域产生的场强大于该区域的矫顽场时,也会诱导该区域的畴发生反转。
我们用探针施加电压对样品上选择区域进行极化后,还在不同的时间对样品同一区域进行压电力成像,研究了电畴的退极化行为及电畴结构、畴壁、晶界对退极化过程的影响。
Current interest in ferroelectric thin film results from the numerous potential applications in nonvolatile ferroelectric random access memory (FeRAMS), Micro Electro-Mechanical System (MEMS) and micro-electronics that utilize the unique ferroelectric, piezoelectric, dielectric, pyroelectric, photorefractive, electro-optic and non-linear optic properties of the material. As the dimension of ferroelectric devices reduced, physical properties of ferroelectric materials in nanometer scale which including the formation of domain structure, polarization and depolarization of ferroelectric domain attract attention of many researchers in this area.
There are many methods to investigate domains such as polarizing microscopy, chemical etching, transmission electron microscopy, scanning electron microscopy and so on. However, these methods suffer from some serious disadvantages involving complex sample preparation, damage to sample, low resolution. PFM developed from AFM has provided a powerful tool for the research of ferroelectric domains.
(Pb_(0.76)Ca_(0.24))TiO_3 (PCT) film is a ferroelectric & piezoelectric material with high anisotropy. When prepared in thin-film form it can have a large d33, comparable to bulk material. Using the Sol-gel method, pure teragonal PCT films have been successfully prepared on platinized Si substrates. The films have a dense structure with a relatively smooth surface.
Piezoresponse scanning force microscopy was used to observe the nanoscale ferroelectric domain structure, switching and back-switching processes. The relation between domain structure and the size of the grains were obtained.
In this paper, we present direct observations of local domain switching. Domain switching is performed on the selected area by applying a bias voltage through the probing tip, and thereafter the piezoresponse image is obtained. With the increase of the polarization voltage, the domain switching expands the whole grain. The ferroelectric films were polarized in nanometer scale under positive or negative voltages applied by the probing tip. The reversing of different domains of the PCT films requires different polarization voltages. Some domains can reverse at low polarization voltage, but others reverse at high polarization. This thesis also reveals that when electric field produced by edge effect in non-scan area was larger than coercive field of this area, domains would reverse.
This thesis studies back-switching process through observe piezoresponse images measured in different times after a bias voltage polarization, and the effect of domain structure, domain wall, grain boundaries to back-switching processes.
引文
[1]钟维烈.铁电物理学.北京:科学出版社, 1996,1-297
[2] Scott J F, Paz de Araujo C A. Ferroelectric memories. Science, 1989,246 (4936):1400-1405
[3] Lancaster M J, Powell J, Porch A. Thin-film ferroelectric microwave devices. Supercond Sci Technol, 1998,11(11):1323-1334
[4] Shaw T M, Trolier-McKinstry S, Mclntyre P C. The properties of ferroelectric films at small dimensions. Annu Rev Mater Sci, 2000,30(1):263-298
[5] Paz de Araujo C A, Cuchiaro J D, McMillan L D, et al. Fatigue-free Ferroelectric capacitors with platinum electrodes. Nature, 1995,374(6523):627-629
[6]曾慧中.纳米尺度铁电电畴结构及其运动的扫描力显微镜研究:[电子科技大学硕士学位论文].成都:电子科技大学, 2005,1-47
[7]陈志武.电疲劳过程中PLZT铁电陶瓷畴变的原位观测及点疲劳机理研究:[厦门大学博士学位论文].厦门:厦门大学, 2003,104-105
[8] Loge R E, Suo Z. Nonequilibrium thermodynamics of ferroelectric domain evolution. Acta Mater, 1996,44(8):3429-3438
[9] Merz W J. Domain Formation and Domain Wall Motions in Ferroelectric BaTiO3 Single Crystals. Phys Rev, 1954,95(3):690-698
[10] Stadler H L, Zachmanidis P J. Polarization retention in SrBi2Ta2O9 thin films investigated at nanoscale. J Appl Phys, 1964,35(10):2895-2899
[11] Fu D, Suzuki K, Kato K, et al. Effect of built-in bias fields on the nanoscale switching in ferroelectric thin films. Appl Phys A, 2005,80(5):1067-1070
[12] Fu D, Suzuki K, Kato K. Dynamics of nanoscale polarization backswitching in tetragonal lead zirconate titanate thin film. Appl Phys Lett, 2003, 82(13):2130-2132
[13] Hooton J A, Merz W J. Etch Patterns and Ferroelectric Domains in BaTiO3 Single Crystals. Phys Rev, 1955,98(2):409-413
[14] Xu F, Trolier M S, Ren W, et al. 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
[15] Binning G, Rohrer H, Gerber Ch, et al. Tunneling through a controllable vacuum gap. Appl Phys Lett, 1982,40(2):178-180
[16] Binning G, Quate C F, Gerber C. Atomic Force Microscope. Phys Rev Lett, 1986,56(9):930-933
[17]白春礼,田芳.扫描力显微镜.现代科学仪器, 1998,(Z1):79-83
[18] Harnagea C. Local piezoelectric response and domain structures in ferroelectric thin films investigated by voltage-modulated force microscopy:[dissertation]. Halle:Martin Luther Universitat Halle Wittenberg, 2001,12-51
[19] Birk H, Glatz-Reichenbach J, Jie L, et al. The local piezoelectric activity of thin polymer films observed by scanning Tunneling microscopy. J Vac Sci Tech B, 1991, 9(2):1162-1165
[20] Guthner P, Dransfeld K. Local poling of ferroelectric polymers by scanning force microscopy. Appl Phys Lett, 1992,61(9):1137-1139
[21] Franke K, Besold J, Haessler W, et al. Modification and detection of domains on ferroelectric PZT films by scanning force microscopy. Surface science letters, 1994, 302(1-2):283-288
[22] Hidaka T, Maruyama T, Saitoh M, et al. Formation and observation of 50 nm polarized domains in PbZr1-XTiXO3 thin film using scanning probe microscope. Appl Phys Lett, 1996,68(17):2358-2359
[23] Gruverman A, Tokumoto H, Auciello O, et al. Nanoscale imageing of domain dynamics and retention in ferroelectric thin films. Appl Phys Lett, 1997,71(24): 3492-3494
[24] Gruverman A, Kholkin A. Nanoscale ferroelectrics: processing, characterization and future trends. Rep Prog Phys, 2006,69(8):2443-2474
[25]李松霞.铁电畴的扫描力显微镜检测方法研究:[电子科技大学硕士学位论文].成都:电子科技大学, 2003,1-59
[26] Kholkin A L, Calzada M L, Ramos P, et al. Piezoelectric properties of Ca-modified PbTiO3 thin films. Appl Phys Lett, 1996,69(23):3602-3604.
[27] Kholkin A L, Seifert A, Setter N. Electromechanical properties of sol-gel derived Ca-modified PbTiO3 films. Appl Phys Lett, 1998,72(25):3374 -3376
[28] Guo H Y, Xu J B, Wilson I H, et al. Study of domain stability on (Pb0.76Ca0.24)TiO3 thin films using piezoresponse microscopy. Appl Phys Lett, 2002,81(4):715-717.
[29] Guo H Y, Xu J B, Xie Z. Ferroelectric relaxation of (Pb0.76Ca0.24)TiO3 thin thin film. Solid State Communications, 2002,121(11):603-607
[30] Ren S B, Lu C J, Shen H M, et al. Size-related ferroelectric-domain-structure transition in a polycrystalline PbTiO3 thin film. Phys Rev B, 1996,54(20): 14337-14340
[31] Gruverman A, Kholkin A, Kingon A. Asymmetric nanoscale switching in ferroelectricthin films by scanning force microscopy. Appl Phys Lett, 2001,78(18):2751-2753
[32] Zeng H R, Yu H F, Tang X G. Piezoresponse force microscopy studies of nanoscale domain structures in ferroelectric thin film. Materials Science and Engineering B, 2005, 120(1-3):104-108
[33] Roelofs A, Schneller T, Szot K, et al. Piezoresponse force microscopy of lead titanate nanograins possibly reaching the limit of ferroelectricity. Appl Phys Lett, 2002, 81(27):5231-5233
[34] Sarrazin P, Thierry B, Niepce J C. Forming pressure dependence of the ferroelectric domain structure in green barium titanate pellets. J Eur Ceram Soc, 1995,15(7): 623-629
[35] Gruverman A, Auciello O, Tokumoto H. Imaging and control of domain structures in ferroelectric thin films via scanning force microscopy. Annu Rev Mater Sci, 1998, 28(1):101-123
[36] Gruverman A, Auciello O, Tokumoto H. Scanning Force Microscopy for the Study of Domain Structure in Ferroelectric Thin Films. J Vac Sci Technol B, 1996,14(2): 602-605
[37] Asada H, Udaka M, Kawano H. Explosive vaporization of crystal water on temperature programmed heating of a thin film of hydrated calcium nitrate. Thin Solid Films, 1994, 252(1):49-53
[38] Warren W L, Dimos D, Tuttle B A, et al. Electronic domain pinning in Pb(Zr,Ti)O3 thin films and its role in fatigue. Appl Phys Lett, 1994,65(8):1018-1020
[39]曾华荣.纳米尺度铁电畴的扫描力显微术:[上海硅酸盐研究所博士学位论文].上海:上海硅酸盐研究所, 2003,1-109
[40] Anbusathaiah V, Nagarajan V, Aggarwal S. Nanoscale polarization relaxation kinetics in polycrystalline ferroelectric thin films. J Appl Phys, 2007,101(8):084104-1-084104-6
[41] Miller R C, Weinreich G. Mechanism for the sidewise motion of 180°domain walls in barium titanate. Phys Rev, 1960,117(6):1460-1466
[42] Gruverman A, Tanaka T. Polarization retention in SrBi2Ta2O9 thin films investigated at nanoscale. J Appl Phys, 2001,89(3):1836-1843
[43]关振铎,张中太,焦金生.无机材料物理性能.北京:清华大学出版社, 1992, 354-355
[44] Ganpule C S, Nagarajan V, Li H, et al. Role of 90°domains in lead zirconate titanate thin films. Appl Phys Lett, 2000,77(2):292-294
[2] Scott J F, Paz de Araujo C A. Ferroelectric memories. Science, 1989,246 (4936):1400-1405
[3] Lancaster M J, Powell J, Porch A. Thin-film ferroelectric microwave devices. Supercond Sci Technol, 1998,11(11):1323-1334
[4] Shaw T M, Trolier-McKinstry S, Mclntyre P C. The properties of ferroelectric films at small dimensions. Annu Rev Mater Sci, 2000,30(1):263-298
[5] Paz de Araujo C A, Cuchiaro J D, McMillan L D, et al. Fatigue-free Ferroelectric capacitors with platinum electrodes. Nature, 1995,374(6523):627-629
[6]曾慧中.纳米尺度铁电电畴结构及其运动的扫描力显微镜研究:[电子科技大学硕士学位论文].成都:电子科技大学, 2005,1-47
[7]陈志武.电疲劳过程中PLZT铁电陶瓷畴变的原位观测及点疲劳机理研究:[厦门大学博士学位论文].厦门:厦门大学, 2003,104-105
[8] Loge R E, Suo Z. Nonequilibrium thermodynamics of ferroelectric domain evolution. Acta Mater, 1996,44(8):3429-3438
[9] Merz W J. Domain Formation and Domain Wall Motions in Ferroelectric BaTiO3 Single Crystals. Phys Rev, 1954,95(3):690-698
[10] Stadler H L, Zachmanidis P J. Polarization retention in SrBi2Ta2O9 thin films investigated at nanoscale. J Appl Phys, 1964,35(10):2895-2899
[11] Fu D, Suzuki K, Kato K, et al. Effect of built-in bias fields on the nanoscale switching in ferroelectric thin films. Appl Phys A, 2005,80(5):1067-1070
[12] Fu D, Suzuki K, Kato K. Dynamics of nanoscale polarization backswitching in tetragonal lead zirconate titanate thin film. Appl Phys Lett, 2003, 82(13):2130-2132
[13] Hooton J A, Merz W J. Etch Patterns and Ferroelectric Domains in BaTiO3 Single Crystals. Phys Rev, 1955,98(2):409-413
[14] Xu F, Trolier M S, Ren W, et al. 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
[15] Binning G, Rohrer H, Gerber Ch, et al. Tunneling through a controllable vacuum gap. Appl Phys Lett, 1982,40(2):178-180
[16] Binning G, Quate C F, Gerber C. Atomic Force Microscope. Phys Rev Lett, 1986,56(9):930-933
[17]白春礼,田芳.扫描力显微镜.现代科学仪器, 1998,(Z1):79-83
[18] Harnagea C. Local piezoelectric response and domain structures in ferroelectric thin films investigated by voltage-modulated force microscopy:[dissertation]. Halle:Martin Luther Universitat Halle Wittenberg, 2001,12-51
[19] Birk H, Glatz-Reichenbach J, Jie L, et al. The local piezoelectric activity of thin polymer films observed by scanning Tunneling microscopy. J Vac Sci Tech B, 1991, 9(2):1162-1165
[20] Guthner P, Dransfeld K. Local poling of ferroelectric polymers by scanning force microscopy. Appl Phys Lett, 1992,61(9):1137-1139
[21] Franke K, Besold J, Haessler W, et al. Modification and detection of domains on ferroelectric PZT films by scanning force microscopy. Surface science letters, 1994, 302(1-2):283-288
[22] Hidaka T, Maruyama T, Saitoh M, et al. Formation and observation of 50 nm polarized domains in PbZr1-XTiXO3 thin film using scanning probe microscope. Appl Phys Lett, 1996,68(17):2358-2359
[23] Gruverman A, Tokumoto H, Auciello O, et al. Nanoscale imageing of domain dynamics and retention in ferroelectric thin films. Appl Phys Lett, 1997,71(24): 3492-3494
[24] Gruverman A, Kholkin A. Nanoscale ferroelectrics: processing, characterization and future trends. Rep Prog Phys, 2006,69(8):2443-2474
[25]李松霞.铁电畴的扫描力显微镜检测方法研究:[电子科技大学硕士学位论文].成都:电子科技大学, 2003,1-59
[26] Kholkin A L, Calzada M L, Ramos P, et al. Piezoelectric properties of Ca-modified PbTiO3 thin films. Appl Phys Lett, 1996,69(23):3602-3604.
[27] Kholkin A L, Seifert A, Setter N. Electromechanical properties of sol-gel derived Ca-modified PbTiO3 films. Appl Phys Lett, 1998,72(25):3374 -3376
[28] Guo H Y, Xu J B, Wilson I H, et al. Study of domain stability on (Pb0.76Ca0.24)TiO3 thin films using piezoresponse microscopy. Appl Phys Lett, 2002,81(4):715-717.
[29] Guo H Y, Xu J B, Xie Z. Ferroelectric relaxation of (Pb0.76Ca0.24)TiO3 thin thin film. Solid State Communications, 2002,121(11):603-607
[30] Ren S B, Lu C J, Shen H M, et al. Size-related ferroelectric-domain-structure transition in a polycrystalline PbTiO3 thin film. Phys Rev B, 1996,54(20): 14337-14340
[31] Gruverman A, Kholkin A, Kingon A. Asymmetric nanoscale switching in ferroelectricthin films by scanning force microscopy. Appl Phys Lett, 2001,78(18):2751-2753
[32] Zeng H R, Yu H F, Tang X G. Piezoresponse force microscopy studies of nanoscale domain structures in ferroelectric thin film. Materials Science and Engineering B, 2005, 120(1-3):104-108
[33] Roelofs A, Schneller T, Szot K, et al. Piezoresponse force microscopy of lead titanate nanograins possibly reaching the limit of ferroelectricity. Appl Phys Lett, 2002, 81(27):5231-5233
[34] Sarrazin P, Thierry B, Niepce J C. Forming pressure dependence of the ferroelectric domain structure in green barium titanate pellets. J Eur Ceram Soc, 1995,15(7): 623-629
[35] Gruverman A, Auciello O, Tokumoto H. Imaging and control of domain structures in ferroelectric thin films via scanning force microscopy. Annu Rev Mater Sci, 1998, 28(1):101-123
[36] Gruverman A, Auciello O, Tokumoto H. Scanning Force Microscopy for the Study of Domain Structure in Ferroelectric Thin Films. J Vac Sci Technol B, 1996,14(2): 602-605
[37] Asada H, Udaka M, Kawano H. Explosive vaporization of crystal water on temperature programmed heating of a thin film of hydrated calcium nitrate. Thin Solid Films, 1994, 252(1):49-53
[38] Warren W L, Dimos D, Tuttle B A, et al. Electronic domain pinning in Pb(Zr,Ti)O3 thin films and its role in fatigue. Appl Phys Lett, 1994,65(8):1018-1020
[39]曾华荣.纳米尺度铁电畴的扫描力显微术:[上海硅酸盐研究所博士学位论文].上海:上海硅酸盐研究所, 2003,1-109
[40] Anbusathaiah V, Nagarajan V, Aggarwal S. Nanoscale polarization relaxation kinetics in polycrystalline ferroelectric thin films. J Appl Phys, 2007,101(8):084104-1-084104-6
[41] Miller R C, Weinreich G. Mechanism for the sidewise motion of 180°domain walls in barium titanate. Phys Rev, 1960,117(6):1460-1466
[42] Gruverman A, Tanaka T. Polarization retention in SrBi2Ta2O9 thin films investigated at nanoscale. J Appl Phys, 2001,89(3):1836-1843
[43]关振铎,张中太,焦金生.无机材料物理性能.北京:清华大学出版社, 1992, 354-355
[44] Ganpule C S, Nagarajan V, Li H, et al. Role of 90°domains in lead zirconate titanate thin films. Appl Phys Lett, 2000,77(2):292-294