In operando investigation of resistive switching in electron transparent lamellae of HfOx based RRAM devices

电阻式随机存取存储器（RRAM）开关，也称为忆阻器，是用于快速非易失性存储器的有希望的候选者。在用作功能材料的过渡金属氧化物中，HfOx和TaOx由于它们的性能和与互补金属氧化物半导体（CMOS）技术的经证实的兼容性而引起了高度关注。尽管在这一研究领域做了大量的工作，原子的理解开关过程仍然有很大的争议。这是迄今为止该领域许多科学家尚未实现的梦想，以原子分辨率直接研究在开关操作的不同阶段（形成，设置和重置）发生的功能材料中的结构和电子变化。基于我们最近建立的工艺，以原位电接触和操作从RRAM结构切割的电子透明聚焦离子束（FIB）制备的薄片，我们现在能够提出一组以前不可能的实验。这包括通过扫描透射电子显微镜结合电子能量损失谱来可视化灯丝附近的局部氧化学计量（STEM-EELS），研究薄片的尺寸缩放行为及其在受控氧气气氛中的开关行为，其中接触和操作独立薄片，并作为最危险的部分和最终目标，在操作中，在电偏压下，以原子分辨率直接显示导电丝。如果成功，这将是第一次通过直接成像技术可视化导电细丝。基于所获得的结果，我们打算开发一个模型的电阻开关相关的宏观器件的行为与原子尺度分辨的纳米结构的导电丝。

Resistive random access memory (RRAM) switches, also called memristors, are promising candidates for fast non-volatile memory. Among the transition metal oxides serving as the functional material, HfOx and TaOx have attracted high interest due to their performance and proven compatibility with complementary metal-oxide-semiconductor (CMOS) technology. Despite the huge amount of work done in this research area, an atomistic understanding of the switching process is still much debated. It is a so far an unrealized dream of many scientists in the field, to directly study with atomic resolution the structural and electronic changes in the functional materials occurring in the different stages of the switching operation (formation, set and reset). Based on our very recently established process to in situ electrically contact and operate an electron transparent focused ion beam (FIB) prepared lamella cut from a RRAM structure, we are now in the position to propose a previously not possible set of experiments. This include the visualization of the local oxygen stoichiometry in the vicinity of the filament by scanning transmission electron microscopy in combination with electron energy-loss spectroscopy (STEM-EELS), the study of the size scaling behavior of lamellae and their switching behavior in controlled oxygen atmospheres with contacted and operating free-standing lamellae and as most risky part and ultimate goal, the direct visualization of the conducting filament with atomic resolution under electric bias in operando. If successful, it would be the first time that a conductive filament is visualized by direct imaging techniques. Based on the obtained results, we intent to develop a model for resistive switching that correlates the macroscopic device behavior with the atomic scale resolved nanostructure of the conducting filament.