Resistive switching and impedance characteristics of M/TiO2-x/TiO2/M nano-ionic memristor

Employing electrochemical impedance spectroscopy (EIS), we demonstrate a novel approach towards characterizing the switching behavior of nano-ionic memristor, M/TiO2-x/TiO2/M where M = Au, fabricated using combined RF/DC magnetron sputtering techniques. The non-linear resistive switching behavior of the device has been investigated using a constant potential sweep technique to observe I-V switching profile (a pinched hysteresis loop) in which ex-situ impedance response has been measured by interrupting the potential sweep (mV s(-1)) over different distinct regimes (pristine device, SET and after zero-crossing). Accordingly, the obtained EIS spectra are corroborated with oxide circuit model and the corresponding numerical fittings of the impedance response reveals distinct RC frequency domains as exemplified in the equivalent circuit models obtained using the simulated impedance response and attributed to the interfacial barrier between the stoichiometric and non-stoichiometric TiO2 respectively. It is evident that the device shows various functional features as memory element owing to the transport of mobile charges in TiO2-x, when the bias potential (V) is applied across the device. It is revealed that EIS studies render a new insight into much acclaimed formation and annihilation of nanofilament like dendrites (magneli phase of titania, TinO2n-1) which are found to be responsible for the change of switching states between low resistance state (LRS) and high resistance state (HRS) respectively. In order to validate the memory retention and endurance characteristics, the reproducible resistive switching is found to occur consistently over 10(4) s and the device endurance has been verified by toggling between HRS and LAS over 1000 cycles.