Thickness-dependent electroforming behavior of ultra-thin Ta₂O₅ resistance switching layer

Electroforming behaviours of Ta₂O₅ resistance switching memory cell with a diameter of 28 nm and different thickness (0.5-2.0 nm) of Ta₂O₅ layer have been examined. The devices showed a constant forming electric field of 0.54 V/nm regardless of Ta₂O₅ thickness. The electroforming with negative bias to top TiN electrode was ascribed to electric field- driven migration of oxygen vacancies, originally residing near the bottom interface, toward the top electrode interface and formation of conducting filaments. The estimated electroforming energy (0.094-0.14 eV) was favourably compared with the hopping energy of electrons from the V_O site to a nearby Ta site.