title: Position detection and observation of a conducting filament hidden under a top electrode in a Ta₂O₅-based atomic switch.
abstract: Resistive random access memories (ReRAMs) are promising next-generation memory devices. Observation of the conductive filaments formed in ReRAMs is essential in understanding their operating mechanisms and their expected ultimate performance. Finding the position of the conductive filament is the key process in the preparation of samples for cross-sectional transmission electron microscopy (TEM) imaging. Here, we propose a method for locating the position of conductive filaments hidden under top electrodes. Atomic force microscopy imaging with a conductive tip detects the current flowing through a conductive filament from the bottom electrode, which reaches its maximum at a position that is above the conductive filament. This is achieved by properly biasing a top electrode, a bottom electrode and the conductive tip. This technique was applied to Cu/Ta2O5/Pt atomic switches, revealing the formation of a single Cu filament in a device, although the device had a large area of 5 × 5 μm(2). Change in filament size was clearly observed depending on the compliance current used in the set process. It was also found from the TEM observation that the cross-sectional shape of the formed filament varies considerably, which is attributable to different Cu nuclei growth mechanisms.
authors.affiliation: WPI Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan. Japan Science and Technology Agency, CREST, 5 Sanbancho, Chiyoda-ku, Tokyo, 102-0075, Japan.
authors.forename: Alpana
authors.initials: A
authors.lastname: Nayak
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.forename: Yaomi
authors.initials: Y
authors.lastname: Itoh
authors.forename: Tohru
authors.initials: T
authors.lastname: Tsuruoka
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Hasegawa
authors.forename: Liam
authors.initials: L
authors.lastname: Boodhoo
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Mizuta
authors.forename: Masakazu
authors.initials: M
authors.lastname: Aono