Influence of the active TaN/ZrO_x/Ni memristor layer oxygen content on forming and resistive switching behavior

The influence of oxygen content in active zirconium oxide layers on the electrophysical properties of TaN/ZrO_x/Ni memristors is investigated. The [O]/[Zr] atomic ratio (x) in the oxide layers was varied in the range from 1.56 to 2.0 by changing the partial oxygen pressure during their deposition by ion-beam sputtering deposition. The ZrO_xfilm compositions were analyzed using x-ray photoelectron spectroscopy and density functional theory simulations. The multiple resistive switching phenomenon in TaN/ZrO_x/Ni memristors was found to occur in a certain range ofx ≥ 1.78. With thexvalue decreasing in the oxide layers, the forming voltage of memristors decreased. Furthermore, at the lower edge ofxvalues the switchable range, they no longer required forming. At the same time, as thexvalue decreased, the memory window (I_ON/I_OFFratio) also decreased from 5 to 1 order of magnitude due to an increase in the memristor conductivity in the high resistance state. In order to identify the underlying conduction mechanism of TaN/ZrO_x/Ni memristors, their current-voltage curves in low and high resistance states were analyzed in the temperature range from 250 to 400 K for the samples withx = 1.78 (forming-free) and 1.97 (which required forming). It was found that, for both samples, the conductivity in the low-resistance state is characterized by the trap-free space-charge-limited current (SCLC) model, whereas the conductivity in the high-resistance state is characterized by the trap-mediated SCLC model. The possible origins of structural defects involved in the memristor conductivity and resistive switching are discussed based on the obtained results.