Forming mechanism of Te-based conductive-bridge memories

Abstract

International audienceWe investigated origins of the resistivity change during the forming of ZrTe/Al$_2$O$_3$ based conductive-bridge resistive random access memories. Non-destructive hard X-ray photoelectron spectroscopy was used to investigate redox processes with sufficient depth sensitivity. Results highlighted the reduction of alumina correlated to the oxidation of zirconium at the interface between the solid electrolyte and the active electrode. In addition the resistance switching caused a decrease of Zr-Te bonds and an increase of elemental Te showing an enrichment of tellurium at the ZrTe/Al$_2$O$_3$ interface. XPS depth profiling using argon clusters ion beam confirmed the oxygen diffusion towards the top electrode. A four-layer capacitor model showed an increase of both the ZrO$_2$ and AlO$_x$ interfacial layers, confirming the redox process located at the ZrTe/Al$_2$O$_3$ interface. Oxygen vacancies created in the alumina help the filament formation by acting as preferential conductive paths. This study provides a first direct evidence of the physico-chemical phenomena involved in resistive switching of such devices

Chemistry of resistivity changes in TiTe/Al2O3 conductive-bridge memories

“…31 . Furthermore a correlation between oxygen migration and applied voltage on the device has been shown previously for the ZrTe/Al 2 O 3 stack under positive forming 9 .…”

“…This result highlights the additional alumina reduction caused by the top electrode deposition. Similar to the case of a ZrTe top electrode 9 , oxygen scavenging is induced by Ti near the TiTe/Al 2 O 3 interface. Pumping of oxygen by the Ti evidenced in Fig.…”

“…Subquantum CBRAMs based on an Al 2 O 3 electrolyte and an active top electrode of a Te binary alloy such as ZrTe, TiTe and HfTe, are the most promising systems with cell operating current and power as low as 10 µA and 0.01 mW 8 . The origin of resistive switching in Te-based subquantum memories with ZrTe active electrode is attributed to the release of Te following Zr oxidation due to oxygen scavenging from the Al 2 O 3 under the electric field 9 . Note that Te-filaments have also been observed in CBRAMs based on Ge 2 Sb 2 Te 5 (GST) sandwiched between inert electrodes (Ti and Pt).…”

“…It is also necessary to better understand the cycling of the cell. Thus, not only the electroforming step 9 , but also the switching between the LRS to the HRS, known as the RESET step must be investigated. To study the resistive state-dependent chemistry in such Te-based CBRAMs requires advanced characterization techniques.…”

“…This can be used to highlight additional changes of the whole matrix accompanying the filament formation, in particular interface modifications. The technique has already been successfully used to investigate the redox reactions that occurs during the resistive switching of oxide-based resistive memories 21–23 and CBRAMs 9 .…”