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

铁电薄膜的极化；

• 批准号: 9732847
• 负责人: Timothy Sands
• 金额: $ 23.59万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-07-01 至 2001-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9732847&HistoricalAwards=false
• 关键词: Poling; Ferroelectric; Thin; Films; Application

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). ***

大块铁电陶瓷中自发电偶极矩的热辅助和电场驱动排列已经很好地理解了。事实上，这种“极化”过程对于实现宏观上可观察到的压电效应至关重要。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，目前对极化效应的理解和操纵仅限于对1800个畴边界的操纵。其他潜在的重要极化效应，包括沉积膜织构的控制，热辅助非1800铁弹性畴边界的操纵，以及导致形状记忆行为的场驱动相变，相对较少受到关注。该研究的主要目标是阐明、模拟和操纵铁电薄膜中自发电偶极子的分布，并了解极化行为、性质（铁电和压电）和器件性能之间的关系。在极化方面，薄膜与本体陶瓷的主要区别是：1)衬底的双轴面内机械夹紧效应，2)薄膜中的晶粒小得多，3)薄膜的晶粒形状各向异性和晶体织构，以及4)大多数薄膜的高击穿场。-评估和模拟温度和电场对Pb基钙钛矿铁电薄膜（如Pb(Zr,Ti)03或PZT）自发极化操纵的综合影响，并将其作为机械夹紧程度和类型的函数。确定晶体织构对畴结构、极化行为和性能的作用。模型和演示极化通过电场驱动的相变和相关的形状记忆效应。这些目标将通过采用PZT/金属氧化物/模板/衬底组合的实验来解决，这些实验旨在产生具有从名义上单晶到单轴（纤维）纹理到随机多晶的微结构的铁电薄膜。通过比较去除基板前后的相同原型器件结构，探讨机械夹紧的效果。电场驱动的极化效应将通过迟滞测量和原位透射电子显微镜作为温度的函数来研究。最后，通过这些研究获得的理解将应用于原型存储器，传感和驱动器件的设计和制造，重点是初始器件性能，以及微观结构对器件可靠性和稳定性的作用。研究生和本科生参与的项目涵盖基础科学到可制造性限制下的设备原型，将为学生未来在功能增强微系统材料集成方面的职业生涯做好准备。首席研究员和他的学生可以使用必要的设备进行脉冲激光沉积，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。这些设施位于首席研究员实验室和集成材料实验室（IML）、伯克利微加工实验室、国家电子显微镜中心（NCEM/LBNL）和伯克利传感器和执行器中心（BSAC）的共享设施中。＊＊＊