Exchange of Ions across the TiN/TaO_x Interface during Electroformation of TaO_x-Based Resistive Switching Devices

Abstract

The valence change model describes the resistive switching in metal oxide-based devices as due to electroreduction of the oxide and subsequent electromigration of oxygen vacancies. Here, we present cross-sectional X-ray energy-dispersive spectroscopy elemental maps of Ta, O, N, and Ti in electroformed TiN/TaO2.0/TiN structures. O, N, and Ti were exchanged between the anode and the functional oxide in devices formed at high power (∼1 mW), but the exchange was below the detection limit at low power (<0.5 mW). All structures exhibit a similar Ta-enriched and O-depleted filament formed by the elemental segregation in the functional oxide by the temperature gradient. The elemental interchange is interpreted as due to Fick’s diffusion caused by high temperatures in the gap of the filament and is not an essential part of electroformation.

Multimode Synaptic Operation of a HfAlOx-Based Memristor as a Metaplastic Device for Neuromorphic Applications

“…Figure a shows the typical DC current–voltage ( I – V ) resistance switching (RS) curves of a Pt (top electrode)/HfAlO x /TiN/Pt (bottom electrode) device and its schematic (inset image) integrated on a crossbar device structure with a line width of 5 μm. The bottom Pt and TiN layers act as a conductive wire and oxygen scavenging layer (OSL) providing oxygen vacancies, respectively. − The atomic-layer-deposited HfAlO x layer acts as the active resistive switching layer. More detailed process conditions can be found in the Section .…”

“…It shows an oxygen-deficient oxide layer (red) near the TiN electrode, acting as an oxygen vacancy reservoir. The oxygen scavenging capability of the TiN electrode is responsible for the formation of high-density oxygen vacancies at the HfAlO x /TiN interface. − Also, the oxygen-deficient layer acts as a series resistor ( R S ) in a circuit. In addition, it shows an insulating oxide layer (blue) near the Pt electrode, where the memristive switching predominantly occurs.…”

Temperature Distribution in TaOx Resistive Switching Devices Assessed In Operando by Scanning Thermal Microscopy

“…Most of the research efforts in oxide ReRAM have been focused on correlating materials and device design with the electrical characteristics of devices. A few studies, based on transmission electron microscopy (TEM) − and X-ray microscopy (XRM), − have attempted to image the structure and composition of the electroformed devices, leading to a generally accepted model of the switching involving a conducting filament created during electroformation. The filament has a small gap that opens and closes for the high-resistance (HRS) and low-resistance states (LRS) as a result of oxygen vacancy migration. − Both TEM and XRM are limited in sensitivity, however, since they can only detect changes in compositions above about 5 atom %.…”

“…Devices formed with the top electrode as an anode are expected to form a gap in the filament at the top of the oxide near the interface. Similarly, devices formed with the bottom electrode as an anode would have a gap near the bottom of the oxide . We also compare the temperature distribution of a device in the HRS and LRS, observing changes in the gap caused by switching between these two states.…”

“…Similarly, devices formed with the bottom electrode as an anode would have a gap near the bottom of the oxide. 11 We also compare the temperature distribution of a device in the HRS and LRS, observing changes in the gap caused by switching between these two states.…”