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

M Kazar Mendes,N Barrett,M Bernard,E Martinez,R Gassilloud,J P Rueff,O Renault,J M Ablett,M Veillerot

doi:10.1038/s41598-018-36131-7

Abstract

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.

Highlights

Resistive Random Access Memories (RRAM) are candidates for the generation of non-volatile memories (NVMs) thanks to their switching properties[1,2]
Note that Te-filaments have been observed in conductive bridge random access memories (CBRAMs) based on Ge2Sb2Te5 (GST) sandwiched between inert electrodes (Ti and Pt)
The oxidation of the alumina layer deduced from the decrease of the AlOx component after the forming process (− 9%) shown in Fig. 3(b) may be related to the oxidation of the alumina layer near of the Al2O3/Ta interface caused by the diffusion of O−2 driven by the electric field

Summary

Introduction

Resistive Random Access Memories (RRAM) are candidates for the generation of non-volatile memories (NVMs) thanks to their switching properties[1,2]. Conductive bridge random access memories (CBRAMs) are one promising solution to improve the cycling endurance while maintaining good scaling and high operation speed[3,4,5] In these devices, an electrolyte (chalcogenide or a suitable oxide, for instance) is used as a dielectric layer whose resistive state is changed by the diffusion of cations from the active electrode, containing most often Ag or Cu1,4,6 to form a conducting bridge. TiTe features a retention behaviour controlled by a similar critical conductance as that for ZrTe8 The investigation of this memory cell mechanism is important since not all binary alloys of Te favor the formation of a semiconductor filament. Compared to positive forming, the bottom electrode, here Ta, may play a role in addition to the top TiTe electrode

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Discussion

Conclusion