| AVS 59th Annual International Symposium and Exhibition | |
| Thin Film | Wednesday Sessions |
| Session TF+AS-WeA |
| Session: | Thin Films: Growth and Characterization-I |
| Presenter: | C. Vallee, LTM (CNRS / UJF-Grenoble1 / CEA), France |
| Authors: | C. Vallee, LTM (CNRS / UJF-Grenoble1 / CEA), France C. Mannequin, LTM (CNRS / UJF-Grenoble1 / CEA), France P. Gonon, LTM (CNRS / UJF-Grenoble1 / CEA), France L. Latu-Romain, LTM (CNRS / UJF-Grenoble1 / CEA), France A. Salaün, CEA, LETI, MINATEC Campus, France H. Grampeix, CEA, LETI, MINATEC Campus, France V. Jousseaume, CEA, LETI, MINATEC Campus, France |
| Correspondent: | Click to Email |
ReRAM device is a non-volatile memory based on resistive switching phenomena in a dielectric in a MIM (Metal Insulator Metal) structure. Depending on the nature of the oxide and the metallic electrode, the switching is based on a unipolar thermochemical mechanism (TCM), a bipolar valence change mechanism (VCM), as well as a bipolar electrochemical metallization mechanism (ECM). For all these devices, the choice of the oxide (nature, crystallization, density, doping, vacancies), the metal (inert electrode, its free energy formation of the oxide) as well as the interfacial layer (role of the electrode, role of the process) are impacting the operation sets and reliability of the device. For example, it has been shown that electrode reaction is one of the major factors determining the functionality of ECM cells [1].
This work is focused on HfO2 based ReRAMs which are good candidates for embedded non-volatile memories [2-4]. For this material, forming/set and reset processes are correlated with the respective generation of oxygen vacancies and recombination of Vo2+ positive charges with oxygen ions (O2-). It has been recently proposed that during the negative reset the passivation occurs by the back-diffusion of oxygen ions stored in the oxide portion near the conductive filaments and at the electrode, which serve as oxygen reservoir [5].
With this work we propose to discuss on the reservoir effect by studying HfO2 memories obtained with top electrodes of different chemical compositions and morphologies. The HfO2 dielectric (10 nm) is deposited by Atomic Layer Deposition on Pt and TiN. X-ray Photoelectron Spectroscopy and Transmission Electron Microscopy characterization have been used to investigate the chemical composition, morphology and crystalline structure of the oxide and metallic layers. It is hence demonstrated that devices with gold deposited by a PVD process give better results than those obtained with gold deposited by evaporation. This can be related to a modification of oxygen diffusion through the top electrode via a difference in the electrode morphology (roughness, thickness…) induced by the process. Moreover, it is shown that alloying the gold target of the PVD process with a suitable metal considerably helps to improve the reliability of the memory. This is discussed in terms of catalytic effect and modification of the electrode morphology and reservoir effect.
[1] I. Valov et al, Nanotech.22 (2011) 254003
[2] P. Gonon et al, J. Appl. Phys. 107 (2010) 074507
[3] J.J. Yang et al, Appl. Phys. A102 (2011) 785
[4] Ch. Walczyk et al, J. Vac. Sci. Technol. B29 (2011) 01AD02-1
[5] S. Yu et al, IEDM (2011) 17.3.1