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.

In this paper, we theoretically investigate the fluctuations in the number of emergent magnetic monopoles in spin ice. The Langevin equation for these fluctuations is deduced. This allows us to calculate the spectrum of relative fluctuations, which can be measured experimentally.

Spectrum SiD of the white current noise iD(t) in p–n junction with the ideality factor η of the current–voltage characteristic, which is greater than one, is investigated here. It is shown, that the Van der Ziel relation, SiD = 2q(ID + 2Is), intended for η = 1, is inapplicable if η > 1; here q is the elementary charge, ID is the current through the junction, and Is is the saturation current. As the first step, the simplest case is considered, η = 2. That is the main recombination of injected electrons and holes takes place in the middle of the junction depleted region. Such junction may be modeled by two identical junctions with η = 1, which are connected in series. The current noise iD(t) is determined by noise sources of both junctions. Obtained result is generalized by the use of the Gupta theorem for the thermal noise spectrum in nonlinear resistive systems. The current noise spectrum is found, SiD = (2q/η) · (ID + 2Is). This result is the modification of the Van der Ziel relation extended to η ≥ 1. Experimental proof of the modified relation is made by analysis of the white noise spectrum in Schottky diode with δ-doping (having η = 2.2) in the vicinity of thermodynamical equilibrium.

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