The possibility to increase the responsivity of 4H-SiC p+-n-n+-photodiodes by varying the thickness of the p+-epilayer has been studied. It is shown that the thinning of the upper epilayer by RIE with the use of metal contacts as a mask makes it possible to control both the maximum responsivity and the spectral dependence of the responsivity of photodiodes and does not lead to degradation of dark electrical characteristics. Keywords: 4H-SiC, p+-n-n+-photodiode, UV-range, p+-epilayer, reactive ion etching RIE, responsivity.

A physical and technological analysis of silicon-carbide epitaxial structures as the basic components of betavoltaic converters (BVC) is carried out. The main factors limiting the efficiency of SiC-BVCs are determined. It is shown that in order to provide the required level of electric power for an actually long-term inexhaustible energy source, it is necessary to use series-parallel hybrid circuits of large-area betavoltaic multichip converters.

One of the promising approaches to the creation of a new electronic-component base is the use of multilevel neuromorphic logic structures based on thin film memristive compositions. Experimental prototypes of memristive synapses are implemented. Memristive devices with the effects of multilevel resistance switching based on heterogeneous (consisting of a sequence of dielectric layers) thin-film structures providing analog (multilevel) restructuring between energy-independent states in terms of resistance in the range of seven orders of magnitude are developed. Possible variants of circuit solutions for neuromorphic modules are presented.

A series of poly(o-hydroxy amides) were prepared by polycondensation of 3,3ʹ-methylenebis(6-aminophenol) with isophthaloyl chloride or 2-(4-carboxyphenyl)-1,3-dioxoisoindoline-5-carboxylic acid dichloride, and also by copolycondensation of mixtures of this diamine and 4,4ʹ-diaminodiphenyl ether or 1,3-bis(4-aminophenoxy)benzene with isophthaloyl chloride. The properties of the products obtained were studied. Thermal cyclization of poly(o-hydroxy amides) yielded the corresponding poly(benzoxazoles). A film of the poly(o-hydroxy amide) derived from 3,3ʹ-methylenebis(6-aminophenol) and 2-(4-carboxyphenyl)-1,3-dioxoisoindoline-5-carboxylic acid dichloride with 50% elongation at break remains plastic (the enlongation at break exceeds 6%) even after the heat treatment and closure of benzoxazole rings; the elastic modulus of such film is 1.2 times higher than that of the poly(o-hydroxy amide) film containing 1,3-bis(4-aminophenoxy)benzene and isophthaloyl chloride moieties. Formulations allowing formation of an adhesion-strong highly heat-resistant relief with the micrometer size of elements and high dielectric parameters on semiconductor substrates were prepared by adding a photosensitive component of naphthoquinone diazide type to poly(o-hydroxy amide) reactive solutions in 1 : 5 ratio relative to the dry polymer.

Heterolayer memristive systems with a functional aluminum oxide layer obtained by the method of atomic layer deposition are studied. A method is proposed for the arrangement of a reservoir of oxygen vacancies, which ensures the creation of a wide memory window. The proposed method uses oxygen permeable platinum electrodes in combination with an amorphous-silicon-dioxide adsorption sublayer formed by plasma-chemical deposition under the bottom electrode of the structure. It is shown that an amorphous-silicon-dioxide sublayer can play, under certain conditions, the role of a reservoir of oxygen vacancies for the functional sublayer, which provides a reversible change in the concentration of molecular oxygen in the regions adjacent to the electrodes and reversible readjustment of the resistivity of the structure within the range of seven orders of magnitude.

The results of studies on the development of technological methods for the formation of low-resistivity contact systems to n- and p-SiC based on single and multilayer Ni-, Al- and Ti-compositions for 4H-SiC based bipolar devices are presented. It is shown that the formation of low-resistivity contacts based on Ni to n-4H-SiC (rho c =3.6·10 -4 Ohm·cm 2 ) and Ni/Al to p-4H-SiC (rho c =5.9·10 -5 Ohm·cm 2 ) is possible within a single cycle of vacuum annealing at 1000 o C for 120 s. This technological solution makes it possible to reduce the number of high-temperature processes. Keywords: 4H-SiC, n-type, p-type, ohmic contacts, RTA, TLM, specific contact resistivity.

The results of studies on the development of technological methods for the formation of low-resistivity contact systems to n- and p-SiC based on single and multilayer Ni-, Al- and Ti-compositions for 4H-SiC based bipolar devices are presented. It is shown that the formation of low-resistivity contacts based on Ni to n-4H-SiC (ρс = 3.6∙10-4 Ω∙cm2) and Ni/Al to p-4H-SiC (ρс = 5.9 ∙10-5 Ω∙cm2) is possible within a single cycle of vacuum annealing at 1000 °C for 120 s. This technological solution makes it possible to reduce the number of high-temperature processes.

The possibility to increase the responsivity of 4H-SiC p+– n –n+ - photodiodes by varying the thickness of the p+ - epilayer has been studied. It is shown that the thinning of the upper epilayer by RIE with the use of metal contacts as a mask makes it possible to control both the maximum responsivity and the spectral dependence of the responsivity of photodiodes and does not lead to degradation of dark electrical characteristics.

The article deals with the issues related to the technical implementation of environmental sensing using capacitive sensors. It proposes a design of a capacitive sensor of a planar type, and studies physical principles of its operation. The operation of the sensor in two main modes is analyzed: 1) determination of the distance to the object at known electrophysical characteristics of the object; 2) determination of the electrophysical characteristics of the object at a known distance to it. The article provides data of direct measurements of the sensor capacitance and its output signal level under various conditions.

A comparative study of bipolar resistive switching in thin films of titanium dioxide, fabricated by different techniques, was carried out by analysis of current-voltage characteristics ( I-V ). For this purpose metal-insulator-metal (MIM) structures were formed with 60-nm-thick titanium dioxide layer deposited by atomic layer deposition (ALD) or RF magnetron sputtering. Based on the analysis of resistance switching characteristics, it was found that the deposition technique of titanium dioxide thin films influences the reproducibility of high-resistance state (HRS) at cycling measurements, the on-resistance (low resistance state)/off-resistance (HRS) ratio, the average values of SET [switching the resistance from a HRS to a low resistance state (LRS)] and RESET [switching the resistance from LRS to HRS] voltages and the number of resistive switching cycles. The results of study of the thin film topography performed by atomic force microscopy (AFM) suggest that the difference in resistive switching parameters could be caused by structural properties of titanium dioxide layers deposited by different techniques.

The polycondensation of 5,5-methylene bis(2-aminophenol) and the mixture of diamines 5,5-methylene bis(2-aminophenol) and 4,4-(hexafluoroisopropylidene)dianiline (molar ratio 0.8:0.2) with isophthaloyl dichloride was used to synthesize a new heat resistant binder of the composites for microelectronics: poly(o-hydroxyamide) (POA) and poly(amido-o-hydroxy amide) (POA-F). The thermal stability of synthesized polymer coatings, as well as based on them photosensitive compositions with a naphthoquinondiazide photosensitive component were studied in the temperature range from 100 to 500 °C. Ferroelectric composites with nanodispersed lead titanate zirconate powder filler were formed based on these polymer matrices. By manipulating the conditions of the polymer formation, we obtained matrices with different stiffnesses, which reflected on the properties of the composite. The electrophysical parameters of the synthesized polymer and ferroelectric composite coatings were measured in the frequency range from 0.1 Hz to 1.5 GHz and the temperature range from 0 to 300 °C. The frequency and temperature stability of the dielectric constant of ferroelectric composite coatings up to 10 MHz and 300 °C, respectively, are noted. The influence of the composition and structure of the polymer matrix and the grain/matrix interfaces on the thermal stability of the dielectric parameters of composite films is estimated. The shift of the phase transition region toward higher temperatures in the composite structure, as well as the sufficient rigidity of the poly(benzoxazole) matrix, provide high temperature and frequency stability of the dielectric constant of the studied composites.

Structurally related poly(amido- o- hydroxy amides) derived from 5,5-methylenebis(2-aminophenol) with tetramethylsiloxane and heteroaromatic (benzoxazole and benzotriazole) fragments incorporated in the second amine component or formed by polyheterocyclization of the corresponding prepolymers were prepared. The effect of modifying fragments introduced into the base poly( o- hydroxy amide) on the heat resistance of powders and films and of films of photosensitive compounds based on the synthesized polymers with the naphthoquinone diazide component was analyzed. The electrophysical parameters of the polymer films and film composites with a nanodispersed ferroelectric filler, (PZT: ceramic powder with the composition Pb 0.81 Sr 0.04 Na 0.075 Bi 0.075 (Zr 0.58 Ti 0.42 )O 3 , Russian brand PZT-1), prepared on the basis of modified polymer binders, were determined. Introduction of 20 mol % sulfur-containing fragments into the polymer binder ensures a 50–65˚C increase in the heat resistance for all types of films without increasing the level of the dielectric loss for the composite coatings.

A study of the voltage-controlled phase transition mechanism in vanadium dioxide thin films was performed in the temperature range 65 - 295 K. Temperature-induced variation of I-V characteristics indicates the type of conductivity defined by space-charge limited currents (SCLC). Based on the analysis of the temperature dependence of sample resistivity, it was found that the dominant transport mechanism is a small polaron hopping conduction. The results of modeling together with obtained experimental data justify the influence of the parameters of trap distribution, associated with oxygen vacancies and hydrogen impurities, on the mechanism of the instability development in vanadium dioxide thin films. At relatively low trap density, the phase transition is more likely initiated electronically. At temperatures below 100 K an appearance of switching with memory is observed. An increase in the trap concentration provokes the prevalence of thermal process in the phase transition triggering. (C) 2020 Elsevier Ltd. All rights reserved.

The method of formation of copper oxide / lead zirconate titanate (CuO/PZT) heterostructures using RF magnetron sputtering of chemically pure grade copper oxide powder on prepolarized ferroelectric ceramic substrate is considered; the direction of polarization was parallel with the copper oxide film plane. The short-circuit photocurrent in the CuO/PZT samples with different thicknesses under irradiation in the visible and near IR regions was measured. The spectral dependences of the photocurrent were estimated. The maximum photoresponse of the structures was observed at the wavelength of 515 nm.

Experimental studies were conducted on the effects of lead oxide on the microstructure and the ferroelectric properties of lead zirconate-titanate (PZT) films obtained by the method of radio frequency (RF) magnetron sputtering of a ceramic PZT target and PbO2 powder with subsequent heat treatment. It is shown that the change in ferroelectric properties of polycrystalline PZT films is attributable to their heterophase structure with impurities of lead oxide. It is also shown that, even in the original stoichiometric PZT film, under certain conditions (temperature above 580 °C, duration greater than 70 min), impurities of lead oxide may be formed. The presence of a sublayer of lead oxide leads to a denser formation of crystallization centers of the perovskite phase, resulting in a reduction of the grain size as well as the emergence of a charge on the lower interface. The formation of the perovskite structure under high-temperature annealing is accompanied by the diffusion of lead into the surface of the film. Also shown is the effect of the lead ions segregation on the formation of the self-polarized state of thin PZT films.

The high dielectric constant ferroelectric-polymer nanocomposite was developed for producing the heat-resistant and chemical stable planar layers. According to the composite coatings formation conditions, the following value ranges of dielectric constant and loss factor were received: 30–400 for dielectric constant and 0.04–0.1 for loss tangent, accordingly. Unlike of composite components, the obtained composite material is characterized by thermo-stability of electrical parameters up to 250 °C. The dielectric frequency spectra of the composite exhibit two clearly visible peaks in contrast to the spectra of the polymer and ferroelectric ceramics. The developed composite material can be used as a built-in film capacitors material in microelectronic devices.

Method for forming thin film heterostructures ZnO/CuO in a single technological cycle with vacuum circuit with use RF magnetron reactive sputtering of copper powder and zinc oxide was offered. The resulting film CuO had band gap of 1.6…1.7 eV and possessed stability up to 350°C. ZnO film had a transparency of 85% in the wavelength range of 400…1100 nm. Selection of medium temperatures for forming the heterostructure (200…250°C) allowed to reduce its series resistance, and the addition of the thin heterojunction structure of the intermediate layer i-ZnO allowed to improve nonlinearity voltage characteristics and improve the photoresponse.

We report the results of experimental study of resistive switching effects in heterogeneous oxide systems based on bilayers with different sequences of two oxide layers (TiO2 and Al2O3) by means of tunnelling atomic-force microscopy (AFM). These systems demonstrate a bipolar resistive switching. Moreover, the resistance state of metal-insulator-metal capacitors with TiO2/Al2O3 bilayers can be electrically tuned over seven orders of magnitude. To elucidate a possible influence of nanoscale characteristics of these bilayers on the parameters of both bipolar resistive switching and electrical tuning of the resistance state, electrical properties of TiO2/Al2O3 bilayers with different thicknesses of the top Al2O3 layer and Al2O3/TiO2 bilayers were investigated. The presence of more conductive anatase crystallites in the amorphous phase of TiO2 layer was experimentally observed only for TiO2/Al2O3 bilayers. Measurements of the current distribution justify the reversible formation of conductive areas in the top Al2O3 layer located directly above the anatase crystallites, under the voltage application between the AFM tip and the bottom electrode of the structure. These conductive areas could be switched back into the high resistive state by application of bias voltage of reverse polarity.