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

阻性随机存取存储器(RRAM)开关，也被称为忆阻器，是快速非易失性存储器的潜在候选者。在作为功能材料的过渡金属氧化物中，HfOx和TaOx由于其性能和与互补金属氧化物半导体(CMOS)技术的兼容性而引起了人们的极大兴趣。尽管在这一研究领域做了大量的工作，但对转换过程的原子论理解仍然存在很大争议。到目前为止，以原子分辨率直接研究功能材料在开关操作的不同阶段(形成、设置和重置)中发生的结构和电子变化是该领域许多科学家尚未实现的梦想。基于我们最近建立的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)的工艺，我们现在可以提出一系列以前不可能进行的实验。这包括通过扫描电子显微镜结合电子能量损失谱(STEM-EELS)显示灯丝附近的局部氧化学计量比，研究在受控氧气气氛中接触和操作的独立薄片的尺寸缩放行为及其开关行为，以及作为最危险的部分和最终目标，直接显示在操作台中具有原子分辨率的导电丝。如果成功，这将是第一次用直接成像技术显示导电丝。基于所获得的结果，我们打算建立一个将宏观器件行为与导电丝的原子尺度分辨纳米结构相关联的阻性开关模型。

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.