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

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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.