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

9732847 Sands热辅助和电场驱动的块状铁电陶瓷中自发电偶极矩的排列是众所周知的。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是必不可少的。对于集成铁电薄膜的新兴应用，从非易失性存储器到化学传感器再到压电微阀，目前对极化效应的理解和操作仅限于对1800磁区边界的操作。其他潜在的重要极化效应，包括控制沉积的薄膜织构，热辅助操纵非1800铁弹磁区边界，以及导致形状记忆行为的场驱动相变，都相对较少受到关注。这项研究的主要目标是阐明、模拟和控制铁电薄膜中自发电偶极子的分布，并了解极化行为、铁电和压电性能与器件性能之间的关系。在极化方面，薄膜与块体陶瓷的主要区别是：1)衬底的双向面内机械夹持效应，2)薄膜中的颗粒要小得多，3)薄膜的颗粒形状各向异性和晶体织构，以及4)大多数薄膜的较高的击穿电场。将追求以下科学目标：-评估和模拟温度和电场对操纵铅基钙钛矿型铁电薄膜(例如，PZT或PZT)自发极化的综合影响，作为机械夹紧程度和类型的函数。确定晶体织构对微区结构、极化行为和性能的影响。通过电场驱动的相变和相关的形状记忆效应对极化进行建模和演示。这些目标将通过使用PZT/金属氧化物/模板/衬底组合的实验来解决，这些组合旨在制备具有从名义上的单晶到单轴(纤维)织构到随机多晶的微结构的铁电薄膜。通过比较衬底去除前后相同的原型器件结构，来探索机械夹紧的效果。电场驱动的极化效应将通过滞后测量和原位电子显微镜来研究其随温度的变化。最后，通过这些研究所获得的理解将被应用于原型存储器、传感和驱动器件的设计和制造，重点是初始器件的性能以及微结构对器件可靠性和稳定性的作用。在可制造性的约束下，研究生和本科生参与从基础科学到设备原型的项目，将为学生未来在功能增强的微系统材料集成方面的职业生涯做好准备。首席研究人员和他的学生可以使用必要的设施来进行脉冲激光沉积、溅射、四圈X射线衍射、电学测试、透射电子显微镜(原位、分析和高分辨率)、电子束光刻以及CMOS硅和硅表面微加工所需的所有工艺。这些设施位于首席研究人员的实验室以及综合材料实验室(IML)、伯克利微制造实验室、国家电子显微镜中心(NCEM/LBNL)和伯克利传感器与放大器中心(BSAC)的共用设施中。***

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). ***