Search

The results of 3D modeling in the Comsol Multiphysics software environment and calculation of temperature and thermal deformation fields of GaAs crystals of monolithic integrated circuits (MIS) of microwave amplifiers as part of the submodule of the X-band output power amplifier (VUM) and their contact connections with the substrate in pulse modes of operation with different duty cycles are presented. It is shown that the maximum temperature and thermomechanical stresses in the MIS crystal in the dynamic mode of operation significantly exceed the calculated values for the stationary mode and strongly depend on the pulse duty cycle of the power dissipated by the MIS. Thermomechanical stresses take the maximum value in some narrow region near the boundary of the adhesive connection of the MIS crystal with the mounting plate; this maximum value strongly depends on the temperature coefficient of expansion (TCR) of the adhesive and takes the lowest value when the TCR of the adhesive is equal to the TCR of the GaAs crystal.

A hardware–software complex that has no analogues in Russia and abroad and that is designed to measure the distribution of the cutoff frequency of electroluminescence over the area of a light-emitting heterostructure (LHS) is described. The complex provides a spatial resolution of 0.65 µm, an upper measurement limit of 40 MHz, and a relative error of 2%. The electroluminescence cutoff frequency in local areas of an LHS is determined from the decay of the brightness of pixels of LHS images by 1.19 times obtained using a digital CMOS camera with a step-by-step increase in the pulse repetition rate of the LHS-supplying current with an off-duty factor of 2. The complex and the measurement method were tested on commercial green light-emitting diodes. The results of measuring the cutoff-frequency distribution can be used to assess the homogeneity of LHSs.

The dynamics of the temperature transformation of the emission spectrum of light-emitting diodes using the “running” gate mode of the photodetecting complementary metal oxide semiconductor (CMOS) matrix were investigated. A device has been developed for measuring the parameters of the spectrum shift of LEDs when they are switched on. The device is based on the optical system of the SF-46 spectrophotometer without an exit slit and with a focusing system in front of an SCMOS-00350KPA CMOS photodetector array with a 480 × 640 pixel photosensitive area and 84 μs line-by-line recording time. In terms of speed and wavelength resolution (0.125 nm), the device significantly surpasses the domestic and foreign IS3000-LED, Cary 100/300, Ocean Optic USB2000, etc., spectrometers. The time dependences of the spectrum shift of the red SMD-LED FYLS-3528BURC in the first 40 ms after switching it on at different values of the operating current were obtained experimentally. The obtained dependences can be used to evaluate the thermal parameters of LEDs.

A description of the functional capabilities of the technology of multifraction separation of particles by density and shape in a polydisperse bulk material is given. The technology assumes a consistent and complex use of the effects of quasi-diffusion separation and segregation of particles in a fast shear flow on a gravity slope, as well as the use of traditional technological methods of particle shape calibration. The assessment of the effectiveness of using of multifraction technology for the production of biologically valuable seed material is given.

In this paper, the effect of the substrate surface roughness on the stability of the parameters of thin-film resistive elements is investigated. The surface roughness of the substrates is determined by optical microscopy and atomic-force microscopy (AFM). A technology is developed to produce a smoothing surface coating based on thin Ta2O5 films with an amorphous coherent structure, the application of which reduces the microroughness of the Rz surface profile to 12 nm or less. The coating allows thin nanoscale films to be formed on its surface, while the temperature coefficient of the resistance decreases about twice and the stability of thin-film resistors is increased.

An experimental study was performed of the influence of mixing intensifier-grids on the cooling of a 37-rod electrically heated TVS-2M model with top and bottom reflooding. It is shown that the mixing grids bring about a very small reduction of the maximum temperature of the rods and longer cooling time of the assembly. To cool the TVS-2M model, the starting temperature of the fuel-rod simulators and the power input can be significantly lower in top reflooding than in bottom reflooding. The effect of the flooding rate is similar to that observed in bottom flooding – as the flooding rate increases, the maximum temperature of the rods and the cooling time of the assembly decrease. The experiments showed that with reflooding the mixing grids do not greatly affect the cooling efficiency of TVS-2M.

The parameter homogeneity of dielectrics imposes increasingly stringent requirements, especially when used in micro- and nanoelectronics products. In this paper, we present an automated method for monitoring the electrophysical parameters of planar dielectrics with increased requirements on accuracy and resolution. A brief review and comparative analysis of the known methods for monitoring the parameters of solid dielectrics are performed here. The method of microwave control of the heterogeneities of the parameters of planar dielectrics by the wave characteristics of a scanning microstrip line (MSL) using a Radon transform is described. The phase response of the MSL is shown to be most sensitive to parameter heterogeneities. A mathematical model for processing the MSL wave characteristics and for constructing a map of the parameter heterogeneity distribution is presented. The parameter realizability and the applicability limits of the mathematical model are estimated. The technical implementation of the method is considered using, as an example, the setup for monitoring the parameter homogeneity of planar dielectrics and the results of modeling the measuring part of the setup in the AWR Microwave Office CAD system. The methodological errors of measuring the electrophysical parameters of dielectrics by the described method are estimated, and they are on average ±1 × 10–4 in the case of measuring the permittivity and 0.2 mm in the case of measuring the spatial resolution according to the preliminary calculations. The described control method is designed for use in the production of electronic products using dielectric materials with a high level of parameter repeatability.

We present the description of an automated hardware-software complex intended for measuring the 3 dB frequency of modulation and evaluation of the quantum efficiency of separate spectral components of the full spectrum of electroluminescence of light-emitting diodes, including the range of low levels of excitation. The principle of operation of this complex is based on measuring the spectrum of radiation of a light-emitting diode with the help of an OceanOptics USB2000+ spectrometer in the signal-accumulation mode in the course of transmission of current pulses with given amplitude and repetition frequency through the light-emitting diode with subsequent selection of separate spectral components from the full spectrum of radiation. We present the results of testing the hardware-software complex performed by measuring, as an example, the frequency characteristics of separate spectral components of the full electroluminescence spectrum of commercial InGaN green light-emitting diodes. The analyzed hardware-software complex can be used for the diagnostics of the quality of light-emitting heterostructures with quantum wells.

The electrophysical and noise characteristics of arrays of multiwall carbon nanotubes (MWCNTs) functionalized in various ways were studied. It is demonstrated that the as-prepared and annealed MWCNT arrays have semiconductor-type resistivities and temperature dependences of resistivity, while the arrays of annealed MWCNTs functionalized with acids have metallic properties. Low-frequency 1/f noise in the 0.2‒20 kHz range was observed for all MWCNT arrays. Simple thermal annealing raised the noise level severalfold and annealing with acid treatment resulted in noise reduction and a change in the index of power in its current dependence. The normal amplitude distribution of noise spikes transformed to a lognormal one as the density of as-prepared MWCNT arrays increased. The duration distribution of these spikes became narrower at higher densities.

In this work, preparation of thermal barrier coatings based on zirconium oxide is shown. The phased treatment of the copper substrate is proposed in order to obtain a layered thermal barrier oxide coating on it. The sample surface is nanostructured, titanium is deposited layer-by-layer (by the vacuum-arc method) and then zirconium (by the magnetron method), and then zirconium is converted into zirconium dioxide by the microplasma method. The formed oxide-ceramic coatings contain elements from a solution, according to the results of elemental analysis, and zirconium dioxide in tetragonal and monoclinic modifications, according to the results of X-ray diffraction. A study of thermal cyclic stability was carried out. It is revealed that an increase in the time of microplasma treatment to a certain value has a positive effect on the thermal cyclic properties of the obtained layer material and it is able to sustain more than 90 cycles without serious damage to the surface layer.

The pressure of saturated vapor above solutions of methyl methacrylate in acetonitrile, benzene, hexane, 1,2-dichloroethane and acetic acid is measured tensiometrically at 295–350 K. The composition of the equilibrium phases, the activity coefficients of the components, and the thermodynamic functions of the mixing (HE, GE) of the investigated solutions are calculated from the temperature dependence of the saturated vapor.

We propose an automated measuring complex for the diagnostics of the lateral homogeneity of semiconductor heterostructures by measurements and analysis of the photoelectric and optic responses to their local photoexcitation in static and dynamic modes. The electronic-mechanical and optical positioning systems guarantee the illumination of local region of the investigated structure with a minimum diameter of the spot of 14 μm and a positioning accuracy of 10 μm. It is shown that the measuring complex can be used for the diagnostics of the quality of light-emitting heterostructures, transistors, solar cells, and photodiodes.

The causes and mechanisms of variation in the quantum efficiency and other characteristics of InGaN/GaN heterostructures are actively investigated in various operating modes. The results are presented from an experimental study of the variation in the external quantum efficiency of low-power InGaN/GaN green light-emitting diodes with and without a quantum well in the space–charge region (SCR) of the heterostructure in the accelerated test mode. It is found that after 8 hours of testing at a temperature of 300 K in the pulse mode with a pulse amplitude of 0.5 A, a pulse duration of 100 µs, and a duty cycle of 100, the external quantum efficiency grows for all LEDs without a quantum well in the SCR and diminishes for LEDs with a quantum well throughout the range of operating currents. It is shown that at a low level of injection, the intensity of emission of light emitting diodes without a quantum well in the SCR is determined by recombination processes according to the Shockley–Read–Hall mechanism, while that of LEDs with a quantum well is determined by tunneling–recombination processes. Current training of green LEDs based on InGaN/GaN heterostructures in the forced pulse mode for 4 hours can be used as a technological operation for stabilizing their lighting characteristics, and for identifying potentially unreliable products under conditions of mass production.

Accounting for the production of heat in high-ohmic substrates of heterostructural light-emitting diodes (LEDs) is an important factor, determining their functional properties, limiting operation modes, and reliability. A nonlinear thermoelectric model of the InGaN/GaN LED is presented, taking into account Joule thermal generation in a semiconductor substrate. The potential distribution on structural elements and the dependence on the current of the thermal resistance of a semiconductor structure of the device are obtained. The adequacy of the model is confirmed by comparing the calculated and experimental dependences of the thermal resistance of a high-power LED on the total current. The thermoelectric model of the LED with allowance for Joule heat production allows us to calculate its thermal resistance. The adequacy of the model is confirmed experimentally.

The results of power solar batteries' thermal resistance measurements are described. A distinctive feature of such batteries is the high heat capacity of the semiconductor material, as well as the high total electrical capacity of p-n-junctions. This complicates the thermal resistance of the measuring process, based on heating the object by the heating current pulses and measuring the temperature of the p-n-junction in the pauses between pulses. To measure the thermal resistance of power solar battery the modulation method was used, a device under test (DUT) heated with current pulses with duration modulated harmonically. The response to the heat (a variable component of the p-n-junction temperature) is measured in the pauses between the pulses. To detect the thermal resistance component junction-to-case, the dependence of the thermal impedance on heating power modulation frequency was measured. In the measured dependence, a frequency range is found when the real part of the thermal impedance value remains constant. This allows the determining of the "junction-to-case" thermal resistance component. Were made estimates of the duration of a single measurement of thermal resistance and a conclusion about the possibility of implementing selective technological control of this parameter in the production of powerful solar cells.

The paper describes the results of investigation of thermophysical processes in power modules. Measuring the thermal field caused by dies heating due to flow of heating current shows uniform temperature distribution in the area of dies mount. This indicates that the processes of current localization caused by positive thermal feedback are compensated by the processes of heat transfer between the chips through the DBC board, which has a high thermal conductivity. The modulation method was used to measure the thermal resistance "junction-to-case" of the power module. In this case, the module dies were heated by PWM pulses of the heating current through the antiparallel diodes of the module MOSFETs. The modulation method allows to measure power module thermal resistance, which value is less than 0.1 K/W.

Structure and properties of initial and functionalized multi-walled carbon nanotubes were investigated by physicochemical analysis methods. Effect of the type and size of nanocarbon particles, their percentage, time ultrasonic dispersion on the stability of dispersed carbon systems nanotubes with acrylic monomers were studied. For dispersion into a material matrix the most promising in technological properties are carbon nanotubes functionalized by grafting on the surface of polar carboxyl groups and forming a stable dispersed system with acrylic monomers.

Current work describes the production of multi-component single-layer and multi-layer coatings by pulsed magnetron sputtering. The study scrutinizes the coatings in terms of their composition (X-ray diffraction analysis, XRD) and microstructure (transmission electron microscopy, TEM). The results demonstrate that the multi-component single-layer Al-Si-N coatings have nanocrystalline structure, while all the layers of the multi-layer Al-Si-N/Al-Si-0 coatings are amorphous due to the ingress of oxygen.

The deposition of nanostructured coatings based on Zr-Y-O was carried out by pulsed magnetron methods. The fine structure and phase composition of nanostructured coatings were studied using a high-temperature TEM and X-ray method. Using the method of the high-temperature X-ray, it was shown that heating up to 500°C leads to a sharp increase in the size of coherent scattering regions (CSRs). Starting from 750 degrees, the size of the CSR monotonously decreases down to 260 A. High-temperature electron microscopy (TEM) studies reveal the same trend in the grain size behavior. The maximum grain size increase is observed at a temperature of 500°C. Such behavior of the CSR may indicate the presence of a reversible phase transition of the tetragonal phase to the monoclinic one, which can results in stress relaxation and the closure of surface cracks.

The results of investigation of the surface of a copper substrate modified with titanium ions are presented. Using TEM it has been established that a multi-level micro- and nanoporous nanocrystalline structure is formed due to simultaneous ion etching, heating, radiation-stimulated diffusion in the surface layer of the metal substrate. When bombarded with titanium ions the intermetallic phases of the equilibrium diagram of the Cu-Ti are formed. The penetration depth of titanium into the copper substrate under ion treatment has investigated in detail. It has been found that the phase composition and the surface morphology are dependent on fluence of the ion treatment.

Producing of cutting tools with high sharpness of the cutting edge (characterized by a small conditional inscribed roundness radius) improves the quality of edge cutting processing of hard-to-cut parts. However, existing carbides do not withstand increased contact loads and quickly destroy. This leads to a deterioration of the quality of the processed surface and to failure of the tool. The paper investigates the influence of different types of processing on the wear of carbide plates. It is found that an increase in the grinding speed leads to a decrease in roughness and an increase in tool life. The efficient ways of the improvement of plate wear resistance are the processing of plates with rhenium and argon ions and the application of thin Al–Si–N coatings.

Calculations were carried out to determine the friction welding conditions for thin wall armlene (mineral-filled polypropylene) components. Design studies and the preparation of a prototype...

A model has been developed for the formation of a porous layer of nanoparticles (nanolayers) on the surface of a heater during the boiling of a nanofluid. From a practical point of view, the properties and the process of the formation of a nanolayer on the heater surface are of interest. Modification of the heating surfaces in power equipment via the formation of a porous layer on them is more promising than the use of a nanofluid as a coolant. The study of the formation of a nanolayer during boiling provides insight into its properties and aids in the study of its effect on heat transfer during boiling and boiling crisis. The main goal of theoretical simulation at this stage is to obtain a calculation expression to calculate the time of the formation of a layer of a certain thickness on the surface.

We propose using logic-element time delay as a temperature-sensitive parameter to measure the thermal resistance of digital integrated circuits. We show that the frequency of a ring oscillator constructed using logic elements is inversely proportional to the signal delay time and is a linearly decreasing function of the temperature. We describe a technique for measuring the thermal resistance of a digital integrated circuit as it is heated by its own power consumption.

Two methods for measuring the spatial distribution of the temperature of electrons in a cloud near a polystyrene pellet that ablates in LHD heliotron plasma are described. The first method is based on measuring the ratio of the local emission-coefficient values at wavelengths of 486 ± 5 nm (the Hβ line) and 630 ± 5 nm (continuum). The second (new) method is based on the measurement of radiation distributions of the Hβ line in the direction along the magnetic field. Both the methods use an assumption about the partial local thermodynamic equilibrium in the cloud and show close results. It is shown for the first time that the temperature of cloud electrons increases from 0.8 eV in the immediate vicinity of the pellet surface to 6.0–7.0 eV at a distance of 6–8 mm from the pellet in the direction along the magnetic field, which agrees with the experimentally observed longitudinal distribution of the Hβ radiation in the cloud.

The paper describes the modulation method of measuring the thermal impedance of semiconductor devices as well as its implementation. In contrast to the standard method (JESD51-1 standard) which requires heating the device under test by the stepped power, the modulation method uses heating power modulated harmonically. A pulse sequence of heating current, with the pulse length varying harmonically, is passed through the device under test. The p-n junction temperature is measured through a temperature-sensitive parameter, namely a forward voltage drop on the p-n junction between heating pulses at low measuring current. First harmonic of the p-n junction temperature oscillation is determined by the discrete Fourier transform, which allows to determine thermal impedance absolute value and phase at modulation frequency of heating power. An analysis of the dependence of thermal impedance on modulation frequency allows to determine thermal impedance components corresponding to the structural elements of the device under test. Numerical simulation shows that the thermal resistance components on the Foster's network may be determined at the modulation frequencies corresponding to the first derivative minima of the thermal impedance of the real part of frequency dependence. The main characteristics of the device that implements the method are described.

—In the cutting of four different alloys, the effectiveness of two machining fluids is investigated as a function of their composition and physical properties. An index characterizing the influence of each chemical element in the fluid on its effectiveness is proposed.

Comprehensive analysis of current spreading, temperature distribution, and near-field electroluminescence of high-power “face-up” AlInGaN LEDs and LED Arrays was performed by combination of different experimental methods. Measurement results of thermal impedance and temperature distribution (mapping) of powerful light-emitting diode assemblies are described. A thermal resistance characterization consists in investigations of transient processes of temperature-sensitive parameter under heating by step-form or harmonically pulse-width modulated direct current and analysis using a thermal equivalent circuit (the Cauer and Foster models). By the involved method, thermal resistances of internal elements of the LEDs are determined. At the same time high resolution mapping of EL and thermal radiation was obtained by optical microscope and infrared images technique. It has been established correlation of the thermal resistance with a change in the current distribution (current crowding) at high excitation levels.

The article contains developed by authors model of the porous layer formation. This layer forms on the heated surface during nanofluids boiling. It has a great influence on boiling characteristics, particularly, on critical heat flux value; and it is very important to have clear knowledge about its formation and properties. The main goal of current step of our investigations was to find out correlations: for calculation of porous layer with definite thickness creation time and for its roughness.

A measuring instrument of the frequency and current dependences of the modulus and phase of the thermal impedance of LEDs and LED matrices of 100 W and higher is described. The principle of operation of the measuring instrument is based on the transmission through LEDs of a sequence of impulses of direct current that is pulse-width modulated under the harmonic law, and the determination of the variable component of the temperature of the p–n junction of the LED as the voltage changes during intervals between current impulses. An algorithm is presented to determine the component of full thermal resistance of an LED or an LED matrix from the results of processing the frequency dependences of the modulus and phase of the thermal impedance. Examples of implementation of the algorithm are given.

The paper focuses on the effect of spontaneous electric field emergence in mixtures of cesium nitrate and/or potassium permanganate microparticles with nickel, aluminum and aluminum oxide nanoparticles in the hydrogen atmosphere. It was established that increase in the share of Ni, Al or Al2O3 nanoparticles in the mix with KMnO4 powder from 0 to 0.25 (in terms of weight) leads to gradual decrease in electric field density in the powder to zero (T = 22–250°C). The authors identified the stimulating effect of nickel nanoparticles on hydrogen-initiated electric field emergence in the CsNO3 powder. It was established that spontaneous polarization of powders is caused by dissociative chemisorption of hydrogen molecules on the surface of KMnO4 and CsNO3 particles.

Analytic relationships for use in calculating the viscoelastic parameters from data of tests performed on a tearing machine with constant loading rate are given. A calculation of the viscoelastic parameters for carbon and quartz filaments using the Rzhanitsyn–Koltunov model is presented. The nature of the relaxation processes in filaments capable of forming fabrics from carbon and quartz filaments on a loom is demonstrated.

Core–shell polyaniline–latex particles have been obtained via oxidative polymerization of aniline hydrochloride in the presence of charged polystyrene latex. The polymerization conditions have been determined under which polyaniline is predominantly formed on the surface of latex particles to yield closed shells. The dependence of the electrical conductivity of the resulting particles on the initial concentration of aniline hydrochloride in the polymerization medium has been studied. Stable aqueous dispersions of polyaniline–latex particles have been prepared by modifying the particles with sodium 3-mercaptopropane sulfonate.

We propose a method for determining the parameters of linear thermal circuits of semiconductor devices represented in the form of series-connected RC circuits. As a result of computer modeling, we obtain an estimate for errors in determining the indicated parameters based on the frequency dependence of the modulus of the thermal impedance.