Publications

We made numerical calculations of the radiation-induced conductivity by computing current densities, carrier concentrations, and internal electric fields in a disordered sample biased by constant applied voltage under a pulsed or step-function irradiation in a large-signal regime. For this purpose, we used the multiple trapping model featuring an exponential trap distribution with the dispersion parameter α. Calculations of radiation-induced conductivity were done with traditional simplifications (1D-analysis, one-carrier polymer, diffusion currents neglected, and non-injecting electrodes). The nonlinear effects accompanying the large-signal radiation-induced conductivity, such as an internal field variation, the bimolecular recombination, and the charge carrier extraction by electrodes, have been consistently accounted for. Numerical analysis agrees satisfactorily with the results of previously published analytical calculations.

A technique for identifying a model of radiation conductivity of polymeric materials for chip packages of microelectronic equipment has been developed. On the basis of the developed technique, computer simulation of radiation charging of polymer cases of microelectronic equipment with increased conductivity was carried out. The research results are aimed at the development of composite polymeric materials for chip packages of microelectronic equipment with conductivity that ensures the absence of electrostatic discharges and makes it possible to significantly increase the life of spacecraft.

The present research aimed to investigate a charging of the cylindrical insulation layer of wires for space applications under the influence of isotropic electron radiation with an electron injection uniform in the volume of the dielectric. An analytical solution of the first-order differential equation resulting from the proposed charging model is obtained. A software has been developed and received state registration that allows for a complete calculation of the physical parameters of space-application wires resistant to electrification effects. The obtained results are proposed to be used for modeling and testing of wires for space applications to completely exclude the physical possibility of the occurrence of electrostatic discharges (ESR) of the "insulation-core" type during the operation (of the spacecraft) in orbit during geomagnetic disturbances in the Earth's magnetosphere.

A computer simulation of the depth course of the absorbed dose as a function of the electronic irradiation energy of the acting in the range of 30 – 60 keV was performed, and calculations of the dose accumulation factor under these conditions were performed for polyethylene terephthalate, polymethylmethacrylate, polystyrene and low-density polyethylene, as model polymers of microelectronic device housings. It is shown that the electron energy values corresponding to the maximum dose accumulation factor depend on the polymer density. The conducted studies allow us to determine with great accuracy the conductivity of plastic cases of microelectronic devices under conditions of electronic irradiation, which is of particular interest to exclude the physical possibility of the occurrence of electrostatic discharges that lead to failures of the onboard electronics of spacecraft.

The possibility of implementing a modeling of the flight of a small spacecraft in low earth orbit based on a client-server architecture was researched. Issues such as transmitting and displaying the system state, aggregating states at different points in time, and executing user code were discussed. The conducted studies demonstrate the benefits of using a client-server implementation in solving the problem of simulating the flight of a small spacecraft in near-earth orbit in a world of increasing interest in satellite developments.

"Data transfer from satellite to ground station emulator" application has been developed for modelling data transfer between a small spacecraft at low-earth orbit and a control center on Earth. The application takes into account multiple parameters allowing to replace a number of experiments. Additionally, the SGP4 model and models such of parameters such as bit error rate and rain rate attenuation are studied and used in development of the application. Finally, the use cases for the application in education and introduction of school and university students to space-themed projects are considered.

About charge carrier mobility in common insulating polymers

Abstract

We have analyzed the radiation-induced conductivity in polyethyleneterephthalate (PET) and polyimide in terms of the recently developed semi-empirical model whose parameters have been determined numerically by a trial and error method based on our previously published results which have been shown to be correct with respect to such experimental limitations as recombination and current saturation. It has been shown that an application of the Onsager theory in PET meets with serious problems. Numerical and experimental results have been compared with published data.

Radiation-induced conductivity (RIC) of polystyrene has been studied experimentally and numerically mostly in a small-signal regime in a broad time range from some nanoseconds to seconds. It has been established that hole transport is dispersive with a low value of the dispersion parameter α = 0.35. We have suggested a direct method of determination of the frequency factor of the Rose–Fowler–Vaisberg model, which has been parameterized using computer simulations by the trial and error method. The main outstanding concern is the application of the Onsager theory of geminate recombination concerning the field dependence of the free carrier yield and the possible frequency factor increase at high electric fields. The effect of hopping transport on the RIC in this common insulating polymer is still to be understood

In this paper, we consider the problem of reducing the cost of computer time by developing and implementing a method for accelerating the operation of connecting distributed data arrays according to a given criterion. The following tasks were solved: a study was conducted on the architecture of distributed data storages and parallel computing algorithms; on the basis of these studies, limiting stages have been established that slow down the processing process; a method was developed that excludes the established limiting stages; on the basis of the developed method, an algorithm and a utility were created that expand the functionality of the selected software product; experimental studies have been carried out

“Virtual space virtual satellite” (VSVS) software solution has been developed for computing the geomagnetic field and studying the results of modelling small spacecraft flight at low orbit with different parameters. The application will allow to replace a number of experiments. In addition, SGP4 and IGRF models are studied due to their role in development of the solution, as are the possible applications in developing solutions for educating high school and university students as well as introducing them to space-themed projects.

A model and a method of mathematical modeling of radiation charging of polymer cases of microelectronic equipment with increased conductivity are developed, which are based on the application of the approximation function of the experimental dependence of the case conductivity on the irradiation time obtained using parametric identification methods. The research results are aimed at the development of composite polymer materials for the bodies of microelectronic equipment with a conductivity that ensures the absence of electrostatic discharges and allows significantly increasing the active life of spacecraft.

Numerical calculations have been performed on the time of flight transients predicted by a newly developed model describing consistently the radiation-induced conductivity of common insulating polymers under both pulsed and continuous irradiation. The model differs substantially from the conventional multiple trapping formalism based on an exponential trap distribution by the presence of additional deep traps distributed in energy or even external deep traps allowing no thermal detrapping (the so-called sinks). This circumstance complicates the definition of the main transport characteristic, the drift mobility, so familiar in Gaussian (normal) or dispersive transport. An analysis of the current transients has been done in a range of fields (10^7–10^9 V/m), decay times (10^−9 – 10^4 s), and not too thin sample 19 thicknesses (2–20 μm). No operational procedure for the determination of a unique time of flight could be found, and therefore, information about charge carrier transport in common insulating polymers must be obtained through numerical calculations. All previous studies on this subject have been critically reviewed.

The modern state of experimental and theoretical studies of the radiation-induced conductivity and charging of polymeric dielectrics under the action of electron beams is considered. The eff ect of the molecular mobility on the transport of excess charge carriers is discussed.  

Abstract—The electron transport is studied experimentally by measuring pulsed radiation-induced conductivity in polyetheleneterephthalate under bulk irradiation of polymer films by fast electron pulses in a smallsignal regime. Numerical simulation is performed using a multiple trapping model with an exponential energy trap distribution. It is shown that, contrary to the reported interpretation of this phenomenon, there is no electron extraction to electrodes under these experimental conditions. In reality, the electron dispersive transport in PET occurs in the presence of the monomolecular capture of electrons by deep traps of biographic origin.

Abstract: Electrical properties of the thin films of poly(arylene ether ketone) copolymers (co-PAEKs) with the fraction of phthalide-containing units of 3, 5 and 50 mol% in the main chain were investigated by using radiation induced conductivity (RIC) measurements. Transient current signals and current-voltage (I-V) characteristics were obtained under exposing 20÷25 thick films of the co-PAEKs to monoenergetic electron pulses of the energy ranged from 3 to 50 keV in the electric field ranged from 5 to 40 V/μm. The Rose-Fowler-Vaisberg semi-empirical model based on a multiple trapping formalism was used for an analysis of the RIC data and the parameters of the highly dispersive charge carrier transport were evaluated. The analysis revealed that charge carriers moved in isolation from each other and the applied electric fields were below the threshold field triggering the switching effect (a reversible high-to-low resistivity transition) in the co-PAEK films. It was also found that the co-PAEK films due to the super-linear I-V characteristics are highly resistant to electrostatic discharges arising from the effects of ionizing radiation. This property is important for the development of protective coatings for electronic devices.

Abstract: We have performed comparative numerical calculations using a multiple trapping (MT) formalism with an exponential and an aggregate two-exponential trap distributions for describing two mostly used experimental setups for studying the radiation-induced conductivity (RIC) and the time-of-flight (TOF) effects. Computations have been done for pulsed and long-time electron-beam irradiations in a small-signal regime. Predictions of these two approaches differ appreciably in both setups. The classical MT approach proved very popular in photoconductive polymers generally and in molecularly doped polymers in particular, while a newly proposed complex MT worked well in common polymers. It has been shown that the complex MT successfully accounts for the presence of inherent deep traps, which may or may not have an energy distribution.