Controllable growth of conductive filaments in sandwiched CBRAM cells using self-assembled Cu/W multilayer thin films as the electrodes

Self-assembled Cu/W multilayer thin films are fabricated and used as the top electrodes (TEs) in conductive-bridge random access memory (CBRAM) devices. The modulation period (λ) of the Cu/W multilayer structure can be well controlled by changing the substrate rotation speed during magnetron sputtering. For the λ value of 3.2 nm, the Al₂O₃ based CBRAM devices exhibits significantly improved resistive switching (RS) performances with effectively narrowed switching parameters and substantially increased OFF/ON ratio up to 10⁴ at 0.10 V. Good reliability after 600 cycles is demonstrated and the retention time of 10 years at 85 °C is estimated through Arrhenius plot. In essential, the growth of conductive filaments (CFs) in Al₂O₃ layers is well controlled owing to the W-rich layer as the diffusion barrier. As a result, both the number and the size of CFs in Al₂O₃ layer are reduced if the λ value is increased. Especially, volatile RS behavior is evidenced due to the extremely slow diffusion of Cu ions across the TE/Al₂O₃ interface and thus the formation of tiny CFs if the λ value is up to 7.0 nm. A physical model is proposed to describe the controllable formation of CFs by using Cu/W multilayer TEs.