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BB3.04 - Comparison of Oxygen Vacancy Creation, Migration, Coalescent and Dispersion Energies for Different Metal Oxides for RRAM 
April 22, 2014   2:30pm - 2:45pm

There is presently an extensive effort to develop non-volatile resistive random access memories (RRAM) based on metal oxides, particularly those made of high K oxides such as HfO2. The general storage processes have been described by Waser et al [1], DeGraeve [2], Bersuker [3], Shiraishi [4] and others. The experimental performance of the different oxides has been compared [5]. It is interesting to understand the detailed atomistic processes in order to understand the best material. The general mechanism is that a conductive filament of oxygen vacancies is formed across the film in a forming step; oxygen vacancies then migrate towards the tip of a partly formed filament, or disperse away from this tip into the oxide, in the SET and RESET processes. The filament in the ON state has a metallic conductivity with small positive temperature coefficient of resistance, but is strongly semiconducting in the OFF state. The partly formed filament acts as a metallic tip, with a high electric field at its tip. Charged oxygen vacancies migrate towards this tip. Inside the tip is metallic, with no electric field, so further increases in vacancy concentration are not needed. The high current density in the filament also creates O vacancy/ O interstitial Frenkel pairs.The energy parameters of these various processes are calculated at the M/MOx oxygen chemical potential (O poor limit). The migration barriers in the different charge states, and the various 0/n+ transition levels with respect to the work functions of the metal electrodes are calculated, for the popular oxides, HfO2, TiO2, Ta2O5, Al2O3. Al2O3 has the largest migration barriers and defect formation energies. Ta2O5 the smallest migration barriers.1. R Waser, et al, Adv Mats 21 2632 (2009)2. R DeGraeve, et al, Tech Digest VLSI (2013)p8.1; Tech Digest VLSI (2012); S Clima et al, APL 100 133102 (2012); L Roux, et al, VLSI (2013) T12-1, S Clima, Microelec Eng (2013)3. G Bersuker, et al, JAP 110 124518 (2011)4. K Shiraishi et al, SSDM (2014) A7-1; K Kamiya et al, APL 100 073502 (2012); PRB 87 155201 (2013)5. J J Yang et al, Nature Nanotechnol 3 429 (2008)

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