Electrical and photoelectric properties of MoN/p-CdTe and MoN/n-CdTe heterojunctions

Due to the physical properties of MoN and ITO thin films, it was decided to create MoN/p-CdTe and MoN/n-CdTe heterostructures and investigate their electrical and photoelectric properties. The method of reactive magnetron sputtering was used to create thin MoN and ITO films on single crystal CdTe substrates with different conductivity types. To manufacture test heterostructures, the following CdTe crystal substrates were used: 1) p-type conductivity, grown by Bridgman technique at low cadmium vapor pressures; 2) n-type conductivity, grown by Bridgman technique at high cadmium vapor pressures. During the deposition process, the argon pressure in the vacuum chamber was 0.4 Pa. The power of the magnetron was 30 W, the sputtering process continued 5 min at a substrate temperature of 150°C. I-V characteristics of the heterostructures at different temperatures were measured, the height of the potential barrier, the values of the series and shunt resistance were determined. Electrical and photoelectric properties of the heterostructures were studied, and the dominant mechanisms of current transfer at forward displacements was established. The tunnel-recombination mechanism was found to be the dominant mechanism of current transfer in the MoN/p-CdTe and MoN/n-CdTe heterostructures. It was shown that the photoelectric parameters for the MoN/p-CdTe heterostructure are higher than those for MoN/n-CdTe. MoN/p-CdTe heterojunctions have the following photoelectric parameters: open-circuit voltage Voc = 0.4 V, short-circuit current Isc = 24.6 mA/cm2 at an illumination intensity of 80 mW/cm2. This makes them a promising material for the manufacture of detectors of various radiation types.

Photodetector resistant to background light noise with extended dynamic range of input signals

Measurement of periodic optical information signals in the background light noise with a photodetector with extended dynamic range is an urgent task of modern electronics and thus has become the aim of this study. To increase the dynamic range of the photodetector, a new version of the automatic gain control (AGC) circuit has been developed, which consists of an AGC controller, an output photodetector amplifier and an AGC detector. The authors measured the dynamic range of the photodetector when receiving optical radiation with a wavelength of 1064 nm in the power range from 2.10–8 to 2.10–5 W at a modulation frequency of 20 kHz with the AGC on. Under these conditions, the dynamic range of the photodetector was found to be up to 67 dB. If the AGC was off, the dynamic range did not exceed 30 dB. Thus, the study made it possible to create a photodetector with an extended dynamic range up to 67 dB based on a new version of the AGC circuit. The design of the photodetector allowed choosing a useful signal of a particular modulation frequency in the frequency range from 3 to 45 kHz and effectively suppresses the frequencies caused by optical interference in the low frequency range from the frequency of the input signal of constant amplitude up to 3 kHz inclusive. This compensates the current up to 15 mA, which is equivalent to the power of light interference of about 15 mW. Further research should address the issues of reliability of the proposed photodetector design and optimization of its optical system. The photodetector can be used in geodesy and ambient air quality monitoring.

Quasi-synchronous thermocompensation for ISFET-based ionometric devices. Part 1: Theory and simulation

Solid-state ion selective transducers, as an alternative to the traditional liquid electrolyte-filled glass electrodes, are known for over four decades now, and find their use in various areas of industry and applied science, such as in vivo analysis of the ions activity in biological and medical research, monitoring of toxic and aggressive environments, and biosensors design. However, along with potential advantages — short response time, small size, chemical inertness and durability — solid-state devices also possess certain inherent drawbacks — namely intrinsic noise, drift and instability of sensing properties, and cross-sensitivity to various interfering environmental conditions — that inhibit their widespread acceptance. Further improvement of the fabrication technology and methodology of application of these devices is thus still an important practical task even today. This paper is a first part of the two-part work dedicated to the problem of compensating the temperature dependence of a solid-state ion selective transducer output. Specifically, presented work considers the possibility of using ion-selective field-effect transistors (ISFET) that serve as primary transducers in an ionometric device, as temperature sensors. This allows compensating the temperature dependence of ionometric signal without substantial complication of the ionometer structure, and eliminates the need to include a separate thermometric channel as part of the instrument. Ionometric and thermometric channels are combined into a unified measuring path, with the sensor functions separated in time. The ISFET operation modes are switched by changing polarity of the bias voltage, and thus direction of the current flowing through the sensor. The authors propose a corresponding secondary transducer structure and simplified schematic illustrating the implementation of its key components. The concept’s applicability is supported by the circuit simulation results. Some aspects of the practical implementation of the proposed concept will be presented further in the upcoming second part of the paper.

Synchronization of pulsed and continuous-wave IMPATT oscillators in the millimeter wavelength range. Part 1. Generator designs and a generalized model of their external signal synchronization

Advances in the development of ultrahigh-frequency semiconductor electronics open wide opportunities for developing optimal schemes and designs of microwave power sources in the millimeter wavelength range providing high stability of the frequency and electromagnetic oscillation phase. Synchronized diode generators used in transmit/receive module for active phased array antennas, coherent low-power radar stations, etc. show great promise. The mode of external synchronization of semiconductor generators allows effectively implementing the task of creating output stages of the transmitters with high gain factor, low frequency noise and an output power level corresponding to the maximum power mode. This article presents the first of two parts of the study, which summarizes the results achieved so far in the development of synchronized oscillators based on impact ionization avalanche transit-time (IMPATT) diodes. The first part presents the electrodynamic designs of the oscillators, which are synchronized with an external source of microwave oscillations and contain a resonant oscillating system with a silicon IMPATT diode. The silicon two-drift IMPATT diode was chosen as an active element due to the fact that its use allows reaching significant levels of pulsed microwave power – an order of magnitude higher than those of the most well-known HEMT and pHEMT transistors in the millimeter wavelength range. It is shown that to reduce losses, the oscillating system should be made in the form of a radial resonator with a diode casing, which has distributed parameters. This eliminates the use of additional reactive inhomogeneities in the initial cross-section of the waveguide section of the generator. Due to the low quality factor of the resonant casing of the diode, the generalized quality factor of the microwave circuit takes the minimum value required to implement a stable generator synchronization process in the millimeter wavelength range. The second part of the work will be devoted to synchronized pulse generators with an output power of 20–150 W.

Synchronization of pulsed and continuous-wave IMPATT oscillators in the millimeter wavelength range. Part 2. Stabilizing microwave parameters of synchronized generators

This is the second part of the two-part article, which summarizes the state-of-the-art results in the development of synchronized oscillators based on IMPATT (IMPact ionization Avalanche Transit-Time) diodes. The first part of the paper presented the electrodynamic design of oscillators, which contain a resonant oscillatory system with silicon IMPATT diodes and are synchronized by an external source of microwave oscillations. The second part of the paper considers the methods for stabilizing the parameters of IMPATT oscillators, which make it possible to create coherent power sources in the millimeter wavelength range. The specifics of pulse generators lies in the change in frequency within the microwave pulse relative to the change in temperature, which leads to a change in the impedance of the diode and thus to a phase change with respect to the synchronizing signal. Phase modulation is reduced or completely eliminated (which is necessary to ensure the coherence of the microwave transmitter) by using current compensation, i.e., by using the control current pulse with a special shape. The study demonstrates the expediency of introducing additional heating of the semiconductor structure of the IMPATT diode, which allows the initial temperature of the IMPATT diode in the region of the leading edge of each pulse to remain virtually constant and independent of the ambient temperature. Using these methods on silicon double-drift IMPATT diodes allowed creating synchronized oscillators with high frequency stability and an output power level from 20 to 150 W, which have a high degree of coherence in the synchronization mode with an external signal. The paper also presents the designs and parameters of coherent microwave power sources in the short-wave part of the millimeter wavelength range using the nonlinear properties of the IMPATT diodes in the radio-pulse conversion mode. This mode makes it possible to provide the output power level of the signal at the n-th harmonic Pout ≈1/n, which significantly exceeds the achieved characteristics of the frequency multipliers with charge accumulation, where Pout ≈ 1/n2. The output power of such devices is achieved at the level of 50–20 mW in the 75–180 GHz frequency range with a frequency multiplication factor of 1–15.

Evaluation of metrological characteristics of spectral analysis method for determining erythrocyte morphology

Spectral photometry is currently widely used for quantitative and qualitative analysis of biological molecules in medical biology. The method is based on the ability of molecules to absorb electromagnetic radiation. Modern clinical laboratory diagnostics extensively uses optical methods of analysis that rely on these physical properties of semitransparent objects, such as blood components. Knowing the absorption spectra of blood and its components, it is possible to quantify the concentration of all the components by solving the mathematical system of equations corresponding to these spectra. However, the existing methods of optical analysis of erythrocytes do not allow quantifying their geometric parameters, which may also indicate certain diagnostic signs and be used to analyze the clinical condition of the patient's body. The aim of this work is to evaluate the metrological characteristics of the newly developed method of determining the geometric parameters of erythrocytes, which combines spectral analysis and double annealing. The input data for the 3D imaging of erythrocytes were taken from the images of the sample both made in natural light and illuminated by a coherent light source with different wavelengths. The latter, after some additional image correlation, increases the reliability of the result. The calculation results on the errors and the measuring channel resolution of the digital interference microscope indicate an acceptable accuracy of the method. The accuracy of the three-dimensional image obtained by the proposed method is more than 20% higher than that of other known methods. This allows determining the informative geometric parameters of the structure of erythrocytes more accurately and using them to obtain additional clinical diagnostic characteristics of the patient's body.

Assessment of assembly complexity of electronic units

The article is devoted to the complexity assessment of harvesting systems. The author considers peculiarities of assembly lines as production systems and the reasons for the constant growth of their complexity. Complex assembly systems are expensive to implement, run, control and maintain, while their complexity affects performance, quality and reliability. Thus, when designing any assembly system, one must look for compromises between its future operation features, its cost and its complexity. To do this, you need to be able to quantify the complexity. This study made it possible to classify the methods of complexity analysis and propose a model that allows quantifying, to some extent, the complexity of the assembly of electronic units and can be used to work with complex multi-subject lines. The study considers the complexity indicators for the operator`s work. To numerically assess the complexity indicators, it is proposed to use the Likert scale. It is assumed that further research should take into account the following issues. The assembly should be designed with consideration of the human factor and the interrelation of technological operations, tools and ergonomics. This is due to the fact that in manual and semi-automatic workplaces, the human operator plays the crucial part. The connection between ergonomics and complexity must be established using the utility function, methods of fuzzy logic, and computer experiments with a test dummy.

Using a layer based on materials with a metal to semiconductor phase transition for electrothermal protection of solar cells

One of the main problems in ensuring the reliability of solar electrical power sources is local overheating, when hot spots form in photovoltaic cells of solar arrays. It is currently considered that these negative phenomena are caused, among other things, by overvoltage in the electrical circuits of solar arrays. This leads to the appearance of defective elements and a significant decrease in the functionality of the entire power generation system up to its complete failure. This study considers the possible ways to increase the reliability of solar arrays by using thermistor thermocontacting layers for preventing overvoltage events and overheating. The authors use simulation to study electrical characteristics of a photovoltaic cell in thermal contact with an additional layer based on thermistor materials with a metal to semiconductor phase transition. Vanadium dioxide with a phase transition temperature of ~340 K is considered to be a promising material for this purpose. During the phase transition, electrical resistance sharply decreases from the values characteristic of dielectrics to the values associated with metal conductors. It is shown that such thermistor layers can be used for protecting solar cells from electrical overheating under the following basic conditions: — the layer’s resistance in the «cold» state significantly exceeds that of the lightened forward-biased solar cell; — the layer’s resistance in the «heated» state is sufficiently low compared to those of the reverse-biased photovoltaic cell and of the power source. The current and temperature of the reverse-biased photovoltaic cell are limited and stabilized, and the voltage drop sharply decreases from the moment when the temperature of the thermistor layer reaches the values close to the temperature of its transition to the low-conductivity state. The obtained results substantiate the potntial of the described approach to protect photovoltaic cells of solar modules against electric thermal overloads.

Adaptive algorithm for reducing pulse noise level in images from CCTV cameras

An optical signal is usually converted into an electrical one by using photosensitive matrices with a large number of discrete elements based on charge-coupled device (CCD) technology or CMOS technology. One of the disadvantages of CCD and CMOS technologies is the impulse conversion noise that appears on digitized images, impairing visual perception and significantly reducing the likelihood of correct identification in pattern recognition tasks. Traditionally, impulse noise is removed from images using median filters with a fixed aperture within each iteration of full-format processing. However, such filters reduce the sharpness of the reconstructed image at high noise levels or insufficiently suppress the interference under the same noise conditions. These setbacks call for a need to develop an adaptive median filtering algorithm, which would produce a reconstructed image as a joint result of processing with median filters with different apertures. The essence of this algorithm is to select image areas with different noise levels and process these areas with filters with different apertures. As an objective criterion for assessing the efficiency of the proposed filtering algorithm, the authors used the criterion of the maximum correlation coefficient between noise-free and non-noisy images at various values of the noise variance. The mathematical modeling performed in this study allowed finding that with an increase in the impulse noise variance, the gain of the adaptive median filtering algorithm increases exponentially, in comparison with the algorithms using the filters with a fixed aperture value. The proposed algorithm can be used for pre-preprocessing images intended for recognition by machine vision systems, scanning text, and improving subjective image characteristics, such as sharpness and contrast.

Silicon whisker pressure sensors for noise reduction in silencers

The article contains the results of research and development of a system for active noise damping of an automobile engine. The main source of noise from a running engine is exhaust noise. The frequency spectrum of this sound has a pronounced low-frequency character, which explains its weak absorption when the sound is propagating in open spaces. A possible solution to this problem is to use an active system for suppressing the resonant frequencies of the muffler using strain gauges to read the primary information about the dynamic processes that determine the noise level. It is for such active noise suppression systems that the authors develop a high-temperature pressure sensor based on strain gauges made of silicon whiskers. Such strain gauges have unique mechanical properties, are characterized by high sensitivity and the ability to operate in various amplitude-frequency and temperature ranges up to 500℃. The study of the dynamic characteristics of pressure sensors made it possible to confirm the quality of its electromechanical part and determine that the measurement error of the sensor is ±0.5 in the temperature range of 20 to 500℃. The active noise suppression system is a buffer tank whose volume changes in accordance with signals from pressure sensors. This design makes it possible to dynamically change the resonant frequency of the buffer capacitance depending on the operating modes of the engine, which leads to a decrease in its noise characteristics. Using the developed additional resonator chamber with a variable volume in the exhaust muffler of an internal combustion engine made it possible to reduce resonance phenomena in the zone of low-frequency pulsations of the exhaust gas pressure from 57 to 43 Hz with a frequency drift in the range of 310 to 350 Hz, which significantly improved its noise characteristics.