The low-frequency noise in a nanometer-sized virtual memristor consisting of a contact of a conductive atomic force microscope (CAFM) probe to an yttria stabilized zirconia (YSZ) thin film deposited on a conductive substrate is investigated. YSZ is a promising material for the memristor application since it is featured by high oxygen ion mobility, and the oxygen vacancy concentration in YSZ can be controlled by varying the molar fraction of the stabilizing yttrium oxide. Due to the low diameter of the CAFM probe contact to the YSZ film (∼10 nm), we are able to measure the electric current flowing through an individual filament both in the low resistive state (LRS) and in the high resistive state (HRS) of the memristor. Probability density functions (Pdfs) and spectra of the CAFM probe current in both LRS and HRS are measured. The noise in the HRS is found to be featured by nearly the same Pdf and spectrum as the inner noise of the experimental setup. In the LRS, a flicker noise 1/fγ with γ ≈ 1.3 is observed in the low-frequency band (up to 8 kHz), which is attributed to the motion (drift/diffusion) of oxygen ions via oxygen vacancies in the filament. Activation energies of oxygen ion motion determined from the flicker noise spectra are distributed in the range of [0.52; 0.68] eV at 300 K. Knowing these values is of key importance for understanding the mechanisms of the resistive switching in YSZ based memristors as well as for the numerical simulations of memristor devices.

We have applied Conductive Atomic Force Microscopy (CAFM) to study the microscopic mechanism of resistive switching in the ultrathin (3 -5 nm) yttria stabilized zirconia (YSZ) films. Using CAFM, we were able to trace the growth of the individual conductive filaments, which are considered now to be responsible for the resistive switching effect in the transition metal oxides. The growth of the filaments has been proven to be initiated by the defects in the film material including the ones, which are the concentrators of the electric field, in particular, by the roughness (hillocks) of the film/substrate interface. The electron transport via individual filaments has been studied. Besides the butterfly-type hysteresis in the current-voltage (I-V) curves of the probeto-sample contact typical for the bipolar resistive switching, we have observed the I-V curves with resonant peaks attributed to the resonant electron tunneling via the localized electron states in the filaments.

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A mechanism of effect of optical excitation on resistive switching of dielectric films with embedded metal nanoparticles (MNPs) has been proposed. The mechanism is related to a charging of the MNPs due to internal photoemission of electrons from the MNPs, which results in an increasing of the electric field strength at the MNP surfaces that, in turn, promotes the rupture and restoring of the conductive filaments in the dielectric film. The increasing of the electric filed strength due to the MNP charging as a function of the MNP sizes and positions inside the dielectric films was evaluated using a simple model taking into account the mirror charges on the conductive electrodes of a memristor stack. The single electron charging was found to be essential at small MNP radii (∼1 nm). The proposed mechanism was confirmed experimentally by studying the photoexcitation-induced charging of Au MNPs (with average radius 1.6-1.8 nm) embedded into a 10 nm thick ZrO 2 (Y) film by Kelvin probe force microscopy.