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
We report the chemical phenomena involved in the reverse forming (negative bias on top electrode) and reset of a TaN/TiTe/Al2O3/Ta memory stack. Hard X-ray photoelectron spectroscopy was used to conduct a non-destructive investigation of the critical interfaces between the electrolyte (Al2O3) and the TiTe top and Ta bottom electrodes. During reverse forming, Te accumulates at the TiTe/Al2O3 interface, the TiOx layer between the electrolyte and the electrode is reduced and the TaOx at the interface with Al2O3 is oxidized. These interfacial redox processes are related to an oxygen drift toward the bottom electrode under applied bias, which may favour Te transport into the electrolyte. Thus, the forming processes is related to both Te release and also to the probable migration of oxygen vacancies inside the alumina layer. The opposite phenomena are observed during the reset. TiOx is oxidized near Al2O3 and TaOx is reduced at the Al2O3/Ta interface, following the O2− drift towards the top electrode under positive bias while Te is driven back into the TiTe electrode.
In this work, the effects of the N2 addition to the SF6 plasma used in the isotropic silicon etching of Microelectromechanical systems (MEMS) with Au components are investigated. A four-variables Doehlert design was implemented for optimizing the etching parameters (power, pressure, gas flow rate, and N2/SF6 ratio) to maximize the lateral etch rate of Si using SF6/N2 gas mixture. The optimized etch condition founded for a lateral etch rate of 1.8 µm/min was: power=143 W, chamber pressure=86 mTorr, flow rate=22 sccm, and N2/SF6 ratio=0.1. Furthermore, it was demonstrated that the established etching process avoids the structure damage of Au components.
HfO-based resistive oxide memories are studied by core-level spectromicroscopy using a laboratory-based X-ray photoelectron emission microscope (XPEEM). After forming, the top electrode is thinned to about 1 nm for the XPEEM analysis, making the buried electrode/HfO interface accessible whilst preserving it from contamination. The results are obtained in the true photoemission channel mode from individual memory cells (5 × 5 µm) excited by low-flux laboratory X-rays, in contrast to most studies employing the X-ray absorption channel using potentially harmful bright synchrotron X-rays. Analysis of the local Hf 4f, O 1s and Ti 2p core level spectra yields valuable information on the chemistry of the forming process in a single device, and in particular the central role of oxygen vacancies thanks to the spectromicroscopic approach.
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