【作者】 刘子铃；

【导师】 谢中；

【作者基本信息】 湖南大学 ， 凝聚态物理， 2009， 硕士

【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_0.76Ca_0.24)TiO₃（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/SiO₂/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_0.76Ca_0.24)TiO₃（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。更多还原

【Abstract】 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_0.76Ca_0.24)TiO₃ （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.更多还原