Cobalt sulfide films by sulfurizing cobalt for resistive switching memory

A cobalt sulfide (CoS x ) film compromising CoS2 and Co9S8 nanograins was formed by sulfurizing the surface of a Co film to use for resistive switching (RS) memory. The work function and band gap of the CoS x film were measured to be 4.78 eV and 2.18 eV, respectively. The CoS x film was used as a resistive layer together with the Co film underneath as a bottom electrode, and a Ag or Cu film as the top electrode. Both Ag/CoS x /Co and Cu/CoS x /Co devices exhibited bipolar RS behavior with the capability of multi-level memory storage. The conduction of both devices in low resistive states was correlated with metallic filamentary paths following ohmic conduction, whereas Schottky emission originated at the Ag/CoS x and Cu/CoS x interfaces dominated in the high resistance state. The performance of Ag/CoS x /Co and Cu/CoS x /Co devices were compared and correlated with the properties of Ag and Cu electrodes.