Oral Presentation 24th Australian Conference on Microscopy and Microanalysis 2016

Non-local oxygen migration during electrical stressing of silicon oxide (#99)

Manveer S. Munde 1 , Michel Bosman 1 , Anthony J. Kenyon 2 , Alexander Shluger 3
  1. Institute of Materials Research and Engineering, Singapore
  2. Electronic and Electrical Engineering, University College London, London, United Kingdom
  3. Physics & Astronomy, University College London, London, United Kingdom

Through electrical stressing, Metal-Insulator-Metal (MIM) structures can often be made to cycle between low and high resistance states. These two resistive states form the basis of a novel approach to digital, non-volatile memory. This resistive switching based memory or Resistive RAM (ReRAM) has been observed to outperform commercial flash memories in many areas such as programming speed, endurance, and memory density [Waser 2012]. 

Resistive switching is the result of the formation and degradation of a conductive path, which in some oxides is thought to originate from oxygen vacancy migration [Li 2008A][Li 2008B][Yao 2010][Yao 2012][Mehonic 2012][Wang 2013]. So far, the exact mechanism of ReRAM switching in silicon suboxides remains unresolved due to the experimental challenges in observing oxygen vacancies in amorphous compounds.

Here we present an experimental and simulation study of the switching behaviour in silicon suboxide films through the use of Scanning Transmission Electron Microscopy (STEM), Electron Energy-Loss Spectroscopy (EELS), and Hybrid Density Functional Theory calculations (DFT).

We studied electrically stressed and unstressed devices, revealing chemical change not just locally to the conductive path region but—unexpectedly—throughout the insulating layer. EELS measurements show the presence of silicon-rich regions in the unstressed device which act as nucleation zones for further segregation of silicon in the oxide film while oxygen is migrating during electrical stressing [Kenyon 2015].

Our DFT calculations on vacancy clustering in amorphous silicon dioxide have revealed that there do indeed exist sites where vacancy clustering is energetically favoured. This indicates that upon electrical stressing, material-wide changes may occur, eventually leading to the establishment of a local conductive filament. 

Further investigation on the nature of this process will have strong implications not only for the resistive switching memory device application, but also for the understanding of MOSFET failure since silicon suboxide is also a key material in modern logic devices.

  1. [Kenyon 2015] Kenyon, A.J. et al. Nature Communications (under review).
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  4. [Mehonic 2012] Mehonic, Adnan, Sebastien Cueff, Maciej Wojdak, Stephen Hudziak, Olivier Jambois, Christophe Labbe, Blas Garrido, Richard Rizk, and Anthony J. Kenyon. "Resistive switching in silicon suboxide films." Journal of Applied Physics 111, no. 7 (2012): 074507-074507.
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