Unipolar resistive switching and mechanism in Gd-doped-TiO2-based resistive switching memory devices

Gd-doped-TiO2-based resistive switching random-access memory (RRAM) devices with MOM structure of top metal electrode (W, Ti)/Gd-doped-TiO2/Pt/Ti/SiO2/Si were fabricated, and resistive switching characteristics were investigated. The W/Gd-doped-TiO2/Pt RRAM device showed typical unipolar resistive switching behavior irrespective of the bias polarity on the W top electrode. However, no unipolar switching was observed in the Ti/Gd-doped-TiO2/Pt devices when positive bias was applied on the Ti top electrode. A new resistive switching model was proposed to explain the unipolar switching behavior in the W/Gd-doped-TiO2/Pt RRAM device, based on the formation and destruction of conducting filaments which result from pinning and unpinning effects of surface trap states of oxide film on the Fermi level of metal electrode. The model clearly elucidates the mechanism of the low resistance state (LRS) and the high resistance state (HRS) as well as the switching behavior between LRS and HRS in the W/Gd-doped-TiO2/Pt RRAM device. The model also indicates the important role of the metal electrode material in unipolar resistive switching of oxide-based RRAM devices