Poling of Ferroelectric Thin Films; Application to Integrated Memory, Sensing and Actuation Devices

在块状铁电陶瓷中自发电偶极矩的热辅助和电场驱动排列是很好理解的。 这种“极化”过程实际上是实现宏观可观察的压电效应所必需的。 相对于集成铁电薄膜的新兴薄膜应用，从非易失性存储器到化学传感器到压电微阀，对极化效应的理解和操纵目前仅限于1800畴边界的操纵。 其他潜在的重要极化效应，包括控制沉积膜的纹理，热辅助操纵非1800铁弹域边界，和场驱动的相变导致形状记忆行为，得到了比较少的关注。 这是拟议的研究的主要目标，阐明，建模和操纵自发电偶极子在铁电薄膜中的分布，并了解极化行为，性能（铁电和压电）和设备性能之间的关系。 关于极化，薄膜和块体陶瓷之间的主要区别是1）衬底的双轴面内机械夹紧效应，2）薄膜中的小得多的晶粒，3）薄膜的晶粒形状各向异性和晶体织构，以及4）大多数薄膜的较高电击穿场。 - 评估和模拟温度和电场对Pb基钙钛矿铁电膜中自发极化操纵的综合影响，例如，Pb（Zr，Ti）O3或PZT作为机械夹持的程度和类型的函数。确定晶体学织构对畴结构、极化行为和性能的作用。 通过电场驱动的相变和相关的形状记忆效应来模拟和演示极化。 这些objectiv es将解决实验，采用PZT/金属氧化物/模板/基板的组合设计，以产生铁电薄膜的微结构范围从名义上单晶单轴（纤维）纹理随机多晶。 机械夹持的效果将通过比较相同的原型器件结构之前和之后的基板去除。 电场驱动的极化效应将作为一个函数的温度滞后测量和原位透射电子显微镜进行研究。 最后，通过这些调查所获得的理解将被应用到原型存储器，传感器和驱动设备的设计和制造，重点是初始设备的性能，和微观结构的作用，对设备的可靠性和稳定性。 研究生和本科生参与的项目，跨越基础科学的设备原型的可制造性的约束下，将为学生未来的职业生涯在材料集成功能增强的微系统。 首席研究员和他的学生可以使用进行脉冲激光沉积，溅射，四圆X射线衍射，电气测试，透射电子显微镜（原位，分析和高分辨率），电子束光刻以及CMOS Si和Si表面微加工所需的所有工艺所需的设施。这些设施位于主要研究者的实验室和综合材料实验室（IML），伯克利微加工实验室，国家电子显微镜中心（NCEM/LBNL）和伯克利传感器致动器中心（BSAC）的共享设施。 ***

9732847 Sands Thermally-assisted and electric-field-driven alignment of spontaneous electric dipole moments in bulk ferroelectric ceramics is well understood. This "poling" process is in fact essential to the achievement of a macroscopically observable piezoelectric effect. With respect to the emerging thin-film applications of integrated ferroelectric films ranging from nonvolatile memory to chemical sensors to piezoelectric microvalves, the understanding and manipulation of poling effects is limited at present to the manipulation of 1800 domain boundaries. Other potentially important poling effects, including control of as-deposited film texture, thermally-assisted manipulation of non-1800 ferroelastic domain boundaries, and field-driven phase changes leading to shape memory behavior, have received comparatively scant attention. It is the primary goal of the proposed research to elucidate, model and manipulate the distribution of spontaneous electrical dipoles in ferroelectric films and to understand the relationships between poling behavior, properties (ferroelectric and piezoelectric) and device performance. With regard to poling, the primary differences between thin films and bulk ceramics are 1) the biaxial in-plane mechanical clamping effect of the substrate, 2) the much smaller grains in thin films, 3) the grain-shape anisotropy and crystallographic texture of thin films, and 4) the higher electrical breakdown fields of most thin films. The following scientific objectives will be pursued: - Evaluate and model the combined effects of temperature and electric field on the manipulation of spontaneous polarization in Pb-based perovskite ferroelectric films e.g., Pb(Zr,Ti)03 or PZT as a function of the degree and type of mechanical clamping. Determine the role of crystallographic texture on domain structure, poling behavior and properties. Model and demonstrate poling via electric-field-driven phase transformations and the associated shape memory effects. These objectiv es will be addressed by experiments that employ PZT/metallic oxide/template/substrate combinations designed to yield ferroelectric films with microstructures ranging from nominally monocrystalline to uniaxially(fiber)-textured to random polycrystalline. The effect of mechanical clamping will be explored by comparing the same prototype device structures before and after substrate removal. Electric-field-driven poling effects will be investigated as a function of temperature by hysteresis measurements and in situ transmission electron microscopy. Finally, the understanding attained by these investigations will be applied to the design and fabrication of prototype memory, sensing and actuation devices, with emphasis on both the initial device performance, and the role of microstructure on the reliability and stability of the devices. The involvement of graduate and undergraduate students in projects that span the fundamental science to the device prototype under the constraints of manufacturability will prepare students for future careers in materials integration for functionally-enhanced Microsystems. The Principal Investigator and his students have access to the facilities necessary to perform pulsed laser deposition, sputtering, four-circle x-ray diffraction, electrical testing, transmission electron microscopy (in situ, analytical and high-resolution), electron-beam lithography and all processes required for CMOS Si and Si-surface micromachining. These facilities are located in the Principal Investigator's laboratory and in the shared facilities of the Integrated Materials Laboratory (IML), the Berkeley Microfabrication Laboratory, The National Center for Electron Microscopy (NCEM/LBNL) and the Berkeley Sensor & Actuator Center (BSAC). ***