A Combined Ab Initio and Experimental Study on the Nature of Conductive Filaments in Resistive Random Access Memory

Through ab initio calculations, we propose that the conductive filaments in Pt/HfO₂/Pt resistive random access memories are due to HfO_x suboxides, possibly tetragonal, where x ≤ 1.5. The electroforming process is initiated by a continuous supply of oxygen Frenkel defect pairs through an electrochemical process. The accumulation of oxygen vacancies leads to metallic suboxide phases, which remain conductive even as ultranarrow 1-nm² filaments embedded in an insulating HfO₂ matrix. Our experiments further show that the filaments remain as major leakage paths even in the OFF-state. Moreover, thermal heating may increase the OFF-state resistance, implying that there are oxygen interstitials left in the oxide layer, which may recombine with the oxygen vacancies in the filaments at high temperature.