Arkady V. Yakimov

The elementary jumps in the electron current through conducting filaments of two nanometer-sized virtual memristor structures consisting of a contact of a conductive atomic force microscope probe to the Si₃N₄ layer with the thickness of 6[ ]nm deposited onto the [ ]-Si(001) conductive substrates are investigated. These structures are: (S1) the Si₃N₄/Si film; (S2) the Si₃N₄/SiO₂/Si stack, a similar structure with 2[ ]nm SiO₂ sublayer between the film and the substrate. Usually, such investigations are performed by the analysis of the waveform of this current with the aim of extracting the random telegraph noise (RTN). Here, we develop a new indirect method, which is based on the measurement of the spectrum of the low-frequency flicker noise in the current without extracting the RTN. We propose that the flicker noise is caused by the motion (drift/diffusion) of nitrogen ions via vacancies within and around the filament. The number of these ions is estimated by taking into account the geometrical parameters of the filament. This allows us to estimate the root mean square magnitude [ ] of the current jumps, which are caused by random jumps of nitrogen ions, and the number M of these ions. This is fundamental for understanding the elementary mechanisms of the electron current flowing through the filament and the resistive switching in memristor devices.

The nature of introduced phase 1/f (flicker) noise in an amplifier of a microwave oscillator that contains an isolating element (directional coupler) is studied. It is shown that noise can be generated due to fluctuations in resistive equivalent parameters of a heterojunction bipolar transistor (HBT) in the amplifier. The spectra of the fluctuations can be estimated using dc measurements. Such an approach allows selection of transistors for fabrication of amplifiers with low introduced 1/f noise and, hence, oscillators with low flicker fluctuations in the frequency.

We theoretically investigate the generation-recombination processes of magnetic monopoles in spin ices. We calculate the spectrum of the relative fluctuations of the numbers of pairs of magnetic monopoles, directly related to that measurable of the magnetic flux noise, using the Langevin approach, previously proposed. Measurements of spectral density of magnetic-flux noise, recently, gave an experimental confirmation of our theoretical results. The agreement with the experimental results is obtained by suggesting a model for the total spectrum of relative fluctuations, which consists in superimposing the spectra of a set of generation-recombination processes, characterized by different time constants and a given probability density function.

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/f^γ 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.

Fluctuations in parameters of light-emitting diode (LED) electromechanical 3D–display are investigated. It is shown, that there are two types of fluctuations in the rotating 3D–display. The first one is caused by a small increment in the rotation angle, which has a tendency to the increase. That occurs in the form of the “drift” without periodic changes of the angle. The second one is the change in small linear increments of the angle, which occurs as undamped harmonic oscillations with constant amplitude. This shows the stability of the investigated steady state because there is no tendency to increase the amplitude of the considered parameter regime. In conclusion we give some recommendations how to improve synchronization of the system.

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.

We have studied the forward current–voltage (I–V) characteristics of Ti–Au /n-type GaAs Schottky barrier diodes. However, we found some anomalies in I–V characteristics. Hence, we have considered a model that incorporates thermionic emission, thermionic-field emission and leakage components. Leakage component is linear and visible at rather small currents. The anomalies observed in the diode parameters were effectively construed in terms of the contribution of these multiple charge transport mechanisms across the interface of the diodes. It is shown that thermionic-field emission and leakage are the sources of low-frequency (1/f) noise in such type of diodes. Various Schottky diode parameters were also extracted from the I–V characteristics and current dependence of spectrum of 1/f voltage noise.