Materials of Electronics Engineering (E-Journal) / Известия высших учебных заведений. Материалы электронной техники
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ТИПОВАЯ МОДЕЛЬ ГЕТЕРОСТРУКТУРЫ ДЛЯ СВЧ−УСТРОЙСТВ
Get PDFThis paper addresses the need to develop a methodology of choosing initial materials, architecture of heterostructures and their synthesis for specific types of microwave components taking into account the availability of domestic materials and technologies, locates. Moreover, extending the product range significantly increases the requirements to energy consumption, dimensions and weight, frequency range, noise, sizes of working temperatures and other characteristics of microwave components. Specific examples of amplifiers for various applications (wireless communication and location systems) show that the development of these devices requires modern methods of multilevel computer modeling implying various optimization techniques as well as wide use of proven technical solutions. This development results in the fabrication of a number of standard basic physical models of heterostructures which are based on the solution of optimization tasks, e.g. choice of initial material, substrate material, structure of layers, their sequences, thickness of layers, impurity contents in them, impurity distribution in layer thickness, etc. the totality of which allows achieving an acceptable level of mechanical stress and high electrophysical parameters in heterostructure. The availability of a set of source data in the form of a library of standard heterostructure models will significantly speed up the development of various microwave and optoelectronics components within the system of instrument and technological design, and improve the characteristics of the devices and their economic parameters.Обоснована необходимость разработки методологии выбора исходных материалов, архитектуры и синтеза гетероструктур, базирующихся на отечественных материалах и технологиях, с привязкой к конкретным типам СВЧ−компонентов. По мере расширения номенклатуры существенно возрастают требования к энергопотреблению, габаритам и весу, частотному диапазону, шумам, значениям рабочих температур и другим характеристикам СВЧ−компонентов. Рассмотрены конкретные примеры усилителей мощности различного назначения (системы беспроводной связи и системы локации). Показано, что для выполнения подобных разработок требуется применение современных методов многоуровневого компьютерного моделирования с использованием различных методов оптимизации, а также широкое использование проверенных технических решений. Конечным результатом данной разработки является создание ряда типовых моделей гетероструктур, базирующихся, в том числе, на решении оптимизационных задач по выбору исходного материала, материала подложки, состава слоев, их последовательности, толщины слоев, содержания в них примеси, распределения ее по толщине слоя и т. д. Все это в совокупности позволяет сформировать в гетероструктуре допустимый уровень механических напряжений и высокие значения электрофизических характеристик. Набор исходных данных в виде библиотеки типовых моделей гетероструктур позволит заметно ускорить разработку различных СВЧ−компонентов и компонентов оптоэлектроники в системе приборно− технологического проектирования, улучшить характеристики приборов и экономические показатели
ИССЛЕДОВАНИЕ ПРОЦЕССОВ ПАЙКИ КРЕМНИЕВЫХ КРИСТАЛЛОВ МОЩНЫХ ТРАНЗИСТОРОВ В ИХ КОРПУСА
Get PDFThe aim of this work is to find out the possibility to reduce the laboriousness and cost of high−power silicon transistors manufacturing with retention of their low thermal resistance. To this end we carried out experimental research of replacement soldering silicon chips in the housing transistors of Au—Si solder for lead−silver solder and some other solders. This will reduce the consumption of gold and increase the productivity of the high−power transistors silicon chips installation due to the collective technology application. At the same time it was found that different treatments of the reverse side of the silicon wafer and their thinning influence the thermal resistance. To improve the quality of soldering we used preliminary metallization of the reverse side of the silicon wafer — Ti—Ni coating. We performed experimental evaluation of the influence of the outer layer materials of the housings and the back side metallization of the chips. When one utilizes soldering silicon chips with lead−silver solder, the housing with a nickel outer layer has the advantage, rather than the gold−plated one, as far as the resulting thermal resistance was lower and the absence of gold made the technology cheaper. We obtained a thermal resistance of 0.6 K/W for a chip area of 24 mm2
О СОВМЕСТНОМ ДЕЙСТВИИ ТЕМПЕРАТУРЫ И ЭЛЕКТРИЧЕСКОГО ТОКА НА ПЛАСТИЧНОСТЬ МОНОКРИСТАЛЛОВ КРЕМНИЯ
Get PDFIn low−resistance p−type single−crystalline silicon to explored particularities of the behavior deformations features in condition, as joint action electric and temperature, so and apart electric current. Exists the small growing of resistivity p−Si with growing of the attached pressure. The dependence of the change of the electrical conductivity of p−Si on temperature during heating and cooling, both in terms of compression and without it. In condition of the joint action of the temperature and electric current on single−crystalline is discovered increase the resistance on deformations, but in the event of action only electric current at compression single−crystalline is revealed growing of the increase plastic. Studied surface microstructure got deformed sample. They are offered possible physical explanations to observed phenomenas.В монокристаллах кремния p−типа проводимости (p−Si) исследованы особенности поведения деформационных характеристик в условиях совместного действия электрического тока и температуры, а также отдельно электрического тока. Изучена зависимость изменения удельной электрической проводимости p−Si от температуры при его нагреве и остывании как в условиях сжатия, так и без него. Наблюдается небольшой рост удельного сопротивления p−Si с ростом приложенного давления. В условиях совместного действия на монокристалл температуры и электрического тока обнаружено увеличение сопротивления деформированию. В случае действия только электрического тока при сжатии монокристалла обнаружено увеличение пластических свойств. Изучены поверхностные микроструктуры полученных деформированных образцов. Предложены возможные физические объяснения наблюдаемым явлениям
ИССЛЕДОВАНИЕ ПРОЦЕССА ПЛАСТИЧЕСКОГО ФОРМОВАНИЯ ПРИ ПОЛУЧЕНИИ ТЕРМОЭЛЕКТРИЧЕСКОГО МАТЕРИАЛА НА ОСНОВЕ ТЕЛЛУРИДА ВИСМУТА
Get PDFAn experimental and theoretical study of the process of the equal−channel angular pressing (ECAP) was performed to obtain a thermoelectric (TE) material based on bismuth telluride. A brief review of the mathematical modeling of the ECAP process is given. The influence of the ECAP design features and temperature modes on the process of plastic forming is considered. The results of calculations of the thermally stressed state of samples at different stages of the ECAP process are presented. The calculations of the ECAP process were carried out by means of Lagrangian finite element mesh, which adjusted adaptively during the process to the die geometry and became finer or coarser depending on the magnitude of the plastic deformation. It was required for the specified calculation accuracy and the convergence of iterative process. The results of an experimental study of the structure and properties of samples obtained by the ECAP using a set of measuring methods (X−ray diffractometry and electron microscopy) are discussed. The thermoelectric characteristics of the obtained materials were measured by Harman method. Comparative methodical calculations of the ECAP process for TE materials based on bismuth telluride have been made by adjusting parameters determining the grain formation (i.e. the critical plastic deformation as a function of temperature and power−law dependence of its rates). It made possible to adjust the ECAP model on the basis of the measured grain sizes for TE materials . The calculation results of grain creation during the plastic forming, which are compared with the measurement data, are presented. The practical result of this research was the improved geometry of the die and the validated technological regimes of plastic deformation, which allowed obtaining samples with the good TE efficiency
ВЛИЯНИЕ ТЕМПЕРАТУРЫ ЭКСТРУЗИИ НА ФОРМИРОВАНИЕ СТРУКТУРЫ Bi0,5Sb1,5Te3 p–ТИПА ПРОВОДИМОСТИ
Get PDFThis article deals with regularities of defect structure and texture formation for extrusion of thermoelectric materials at different temperatures. The authors consider the influence of competition between deformation processes, return and recrystallization on the structure and properties of extruded materials. The experiment uses X–ray diffraction method, Harman’s method and the method of hydrostatic weighing for thermoelectric samples at different extrusion temperatures. The texture, physical properties and density of thermo electric materials change nonmonotonically depending on the extrusion temperature. The research allows establishing optimum extrusion temperature for thermoelectric materials achieving the greatest thermoelectric figure of merit. The research shows that the thermoelectric material has the best properties after extrusion at 400 °C.На основе изучения закономерностей формирования дефектной структуры и текстуры термоэлектрических материалов при разных температурах экструзии рассмотрено влияние конкуренции между процессами деформации, возврата и рекристаллизации на структуру и свойства экструдированных материалов. Исследования проведены с применением методов рентгеновской дифрактометрии (анализ структуры по уширению пиков) и Хармана (измерение термоэлектрических свойств). Измерения плотности образцов выполнены методом гидростатического взвешивания. На исследованных образцах термоэлектрического материала выявлены немонотонные зависимости изменения текстуры, электрофизических свойств (электро−, теплопроводность, коэффициент термо−ЭДС, термоэлектрическая эффективность) и плотности экструдированного материала от температуры экструзии. Установлена оптимальная температура экструзии для термоэлектрических материалов, при которой наблюдается наибольшее значение термоэлектрической эффективности. Показано, что наилучшими свойствами обладает материал после экструзии при температуре 400 °С. При этом наблюдается оптимальное сочетание коэффициента термо−ЭДС, электро− и теплопроводности, возникающее за счет конкуренции динамической рекристаллизации, при которой образуются активные дефекты за счет движения высокоугловых границ зерен. Кроме того, за счет отжига точечных дефектов повышается подвижность носителей заряда, и снижается плотность за счет образования пор
УПРУГОНАПРЯЖЕННЫЕ СЛОИ И НАНООСТРОВКИ GESISN В МНОГОСЛОЙНЫХ ПЕРИОДИЧЕСКИХ СТРУКТУРАХ
Get PDFThis work deals with elastically strained GeSiSn films and GeSiSn islands. Kinetic diagram of GeSiSn growth at different lattice mismatches between GeSiSn and Si has been established. Multilayer periodic structures with pseudomorphic GeSiSn layers and GeSiSn island array have been obtained. The density of the islands in the GeSiSn layer reaches 1.8 ⋅ 1012 cm−2 at an average island size of 4 nm. Analysis of the rocking curves showed that the structures contain smooth heterointerfaces, and strong changes of composition and thickness from period to period have not been found. Photoluminescence has been demonstrated and calculation of band diagram in the model solid theory approach has been carried out. Luminescence for the sample with pseudomorphic Ge0.315Si0.65Sn0.035 layers in narrow range of 0.71—0.82 eV is observed with the maximum intensity near 0.78 eV corresponding to a 1.59 µm wavelength. Based on a band diagram calculation for Si/ Ge0.315Si0.65Sn0.035/Si heterocomposition, one can conclud that luminescence with a photon energy of 0.78 eV corresponds to interband transitions between the X−valley in the Si and the heavy hole subband in the Ge0.315Si0.65Sn0.035 layer
К вопросу об определении объемного времени жизни по спаду фотопроводимости на непассивированных образцах монокристаллического кремния
Get PDFМагниторезистивный эффект в наноразмерном ферромолибдате стронция с диэлектрическими прослойками
Get PDFSingle phase strontium ferromolybdate nanopowder with a double perovskite structure has been synthesized using the citrate gel technique at pH = 4. A superstructural ordering degree of the iron and molybdenum cations of 88% has been obtained. X−ray diffraction of pressed Sr2FeMoO6−δ pellets subjected to annealing at T = 700 K and p(O2) = 10 Pa has revealed the formation of the SrMoO4 phase at grain boundaries. The temperature dependence of the electrical resistivity in the 4.2 to 300 K range changes from a metal type one in the single phase Sr2FeMoO6−δ to a semiconductor type one in the Sr2FeMoO6−δ – SrMoO4 – Sr2FeMoO6−δ structure containing dielectric interlayers, indicating variable charge hopping in the latter structure. In the applied magnetic fields the temperature dependence does not change qualitatively; however, the resistivity decreases with increasing field, i.e., a negative magnetoresistance of up to 41% at T = 10 K and B = 8 T is observed. The external field forms a collinear spin structure, thus increasing the spin−polarized current through the barriers in the granular Sr2FeMoO6−δ – SrMoO4 – Sr2FeMoO6−δ heterostructure
Буферные слои в гетероструктурах
Get PDFThe problem of choosing the architecture of buffer layers is considered. This is typical problem faced when standard models of different heterostructures with a controlled level of mechanical stresses and low defect density in the bulk and at the layer boundaries are developed. It has been shown that the abovementioned characteristics depend on the quality of the initial substrate surface. They are also dependent on the substrate preparation procedure for epitaxy and the composition of the buffer layers. We note that the quality of the substrate surface is most objectively estimated from the bonding strength of the spliced plates. It has been also shown that if the bonding strength is below 107 Pa (this is the most frequent experimental value), the substrate surface is characterized by noticeable roughness. There are different contaminating elements and chemical compounds, clusters and dust particles, structural defects of different dimensionality on the substrate surface. In addition the substrate surface is restructured so that the «broken» bonds are brought closer to each other. The effect of the real substrate surface structure and the compatibility of the materials on the quality of the epitaxial film has been demonstrated. The analysis provided in this work shows the feasibility of growing a preliminary low−temperature (LT) underlying layer on the substrate for small lattice mismatch. Additional transition layers with changing component ratios in the composition or in the form of superlattices are required for largely differing lattice parameters