Optical near-field study of ferroelectric tunnel junctions

铁电隧道结的光学近场研究

• 批准号: RGPIN-2019-07023
• 负责人: Ruediger, Andreas
• 金额: $ 2.48万
• 依托单位: Institut national de la recherche scientifique
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=685325
• 关键词: Optical; near; field; study; ferroelectric

This program merges two active research areas of my group as we are deploying tip-enhanced Raman spectroscopy (TERS) to ferroelectric tunnel junctions (FTJs) of HfxZr1-xO2, which are only three to four unit cells thick (approx. 2 nm). In 2017, we were the first to demonstrate the operation of these FTJs for non-volatile memory applications, thus paving the way for a resistance-based readout memory combining the cost efficiency and scaling potential of DRAM with a write speed that considerably exceeds SRAM while at the same time being non-volatile like Flash, all this at an energy consumption about four orders of magnitude inferior to Flash. The discovery of ferroelectricity in HfxZr1-xO2 in 2011 was unexpected, in particular as both HfO2 and ZrO2 had been individually used as dielectrics over several decades. Despite the tremendous interest in this first fully cmos-compatible ferroelectric, all attempts to explain the physical origin of this ferroelectricity are still in their infancy and lack nanoscale information through a direct, non-invasive technique. Tip-enhanced Raman spectroscopy is currently the only non-invasive imaging technique to yield chemical, structural and functional information at a nanometer scale. The technique is based on the enhancement and confinement of an optical near field mediated through a localized surface plasmon resonance in direct proximity of a noble metal tip that scans as part of an atomic force microscope in feedback at a controlled distance above the sample surface. We have chosen a shear-force tuning fork configuration to be compatible with electrochemically-etched gold and silver tips on virtually any Raman active surface, regardless of whether it is conducting or not and we have achieved a spatial resolution of 3 nm for hyperspectral imaging (i.e. a complete Raman and gold luminescence spectrum at each pixel). In HfxZr1-xO2, neither the bulk monoclinic phase nor the thin film tetragonal phase are ferroelectric and neither is susceptible to epitaxial biaxial strain to induce ferroelectricity as e.g. observed in conventional perovskite ferroelectrics. With a typical grain diameter between 10 and 20 nm, the current working model is that an interfacial energy contribution from grain boundaries induces ferroelectricity; the model is however yet to be experimentally verified. The nature of ferroelectricity in HfxZr1-xO2 has tremendous implications for all optimization procedures regarding the material as well as the deposition process. We therefore intend to deploy tip-enhanced Raman spectroscopy and to back up our experiments with DFT perturbation calculations in order to predict the Raman spectra for all phases in a TERS geometry where the local k-vector is complex and where conventional Raman selection rules are violated due to strong local field gradients at the scale of single bonds. This research program relates to two ongoing strategic partnership grants and several other collaborative research projects.

当我们将尖端增强的拉曼光谱（TERS）部署到HFXZR1-XO2的铁电隧道连接（FTJS）中时，该计划将我组的两个主动研究领域融合在一起，该型孔连接（FTJS）只有三到四个单元细胞厚（约2 nm）。在2017年，我们是第一个证明这些FTJ在非挥发性内存应用中的操作的人，从而为基于电阻的基于电阻的读数内存铺平了道路，从而结合了DRAM的成本效率和缩放速度与写入速度相当大于SRAM，同时铺平了道路。同时，像闪光灯一样是非挥发性的，所有这些都以大约四个数量级低于闪光的数量级。 2011年，HFXZR1-XO2中的铁电性发现是出乎意料的，尤其是HFO2和ZRO2在几十年中都被单独用作介电。尽管对第一个完全与CMOS兼容的铁电的兴趣极大，但所有试图解释这种铁电性的物理起源的尝试仍处于其起步阶段，并且通过直接的，非侵入性的技术缺乏纳米级信息。尖端增强的拉曼光谱法是目前唯一以纳米尺度产生化学，结构和功能信息的非侵入性成像技术。该技术基于通过局部表面等离子体共振的光学近场的增强和限制，在贵族金属尖端直接接近，该贵金属尖端是在反馈中，该贵金属尖端是在样品表面上方受控距离的反馈中作为原子力显微镜的一部分。我们选择了剪切力调谐叉构型与几乎任何拉曼活性表面的电化学蚀刻金和银色尖端兼容，无论它是否进行进行，我们都实现了高光谱成像的3 nm的空间分辨率（即每个像素的完整拉曼和金发光光谱。在HFXZR1-XO2中，散装单斜相和薄膜四方相都不是铁电相，并且既不易受外在双轴菌株的敏感，从而诱导铁电性。在常规的钙钛矿铁电脑中观察到。典型的晶粒直径在10到20 nm之间，当前的工作模型是晶界的界面能量贡献会诱导铁电性。但是，该模型尚未经过实验验证。 HFXZR1-XO2中铁电性的性质对有关材料和沉积过程的所有优化程序具有巨大的影响。因此，我们打算部署尖端增强的拉曼光谱法，并通过DFT扰动计算进行备份实验，以预测本地K-vector中所有阶段的拉曼光谱由于在单键的尺度上，由于局部场梯度很强。该研究计划涉及两个正在进行的战略合作伙伴赠款和其他几个协作研究项目。