DYNAMICS OF RESPONSE OF A SENSOR BASED ON A NANOSTRUCTURED TIN DIOXIDE LAYER EXPOSED TO THE ISOPROPANOL VAPORS

С помощью золь-гель технологии синтезированы наноструктурированные газочувствительные пленки диоксида олова. Исследовано влияние температуры на проводимость сенсора в атмосфере очищенного воздуха, на величину отклика сенсора при воздействии паров изопропанола различной концентрации. На температурной зависимости проводимости плёнки диоксида олова в атмосфере чистого воздуха наблюдается локальный минимум. Уменьшение проводимости с ростом температуры в диапазоне 300...350С может быть связано с диссоциацией молекулярной формы адсорбированного кислорода. При температурах выше 350 °С проводимость возрастает из-за десорбции атомарной формы адсорбированного кислорода с поверхности газочувствительного слоя диоксида олова. Обнаружено, что наибольший отклик к газовым пробам достигается при рабочей температуре сенсора порядка 350°С. Предполагается, что это обусловлено наличием на поверхности атомарной формы хемосорбированного кислорода. Проведен анализ концентрационных и температурных зависимостей времени отклика сенсора при воздействии паров изопропанола. Время отклика сенсора монотонно уменьшается с повышением содержания примеси в газовых пробах, по-видимому, из-за увеличения скорости адсорбции частиц примеси из газовой фазы на поверхность газочувствительного слоя. Установлено, что зависимость времени отклика от рабочей температуры имеет аррениусовский вид, что может быть связано с термоактивированными адсорбционно-десорбционными и гетерогенными химическими процессами на поверхности активного слоя сенсора. Nanostructured gas-sensitive tin dioxide films have been synthesized by sol-gel technology. A conductivity vs temperature dependence of a gas sensor into atmosphere of synthetic air has been investigated. A response vs temperature dependence of a gas sensor into atmosphere of isopropanol vapors with various concentrations has been investigated. Local minimum on the temperature dependence of the tin dioxide film conductivity in clean air atmosphere were observed. A decrease in conductivity with increase temperature in the range of 300...350 °C can be associated with a dissociation molecular form of the adsorbed oxygen. At temperatures above 350 °C, conductivity increases because of desorption of the atomic form of the adsorbed oxygen on the surface of gas-sensitive tin dioxide film. The greatest response value is achieved at a sensor temperature equal to 350 °C. It is proposed that the reason is a domination of the atomic form of the chemisorbed oxygen on the surface. The analysis of response time vs concentration and response time vs temperature of gas sensor has been carried out. Sensor response time decreases monotonically with increase admixture substance in gas-probes, apparently because of increase in adsorption rate admixture particles on the surface of gas-sensitive film. It was found that the dependence of the response time on the operating temperature has an Arrhenius form. This may be associated with thermally activated adsorption-desorption processes and heterogeneous chemical reactions on the surface of sensor active layer.

Role of Slurry Additives on Chemical Mechanical Planarization of Silicon Dioxide Film in Colloidal Silica Based Slurry

Chemical mechanical planarization (CMP) is a critical process for smoothing and polishing the surfaces of various material layers in semiconductor device fabrication. The applications of silicon dioxide films are shallow trench isolation, an inter-layer dielectric, and emerging technologies such as CMOS Image Sensor. In this study, the effect of various chemical additives on the removal rate of silicon dioxide film using colloidal silica abrasive during CMP was investigated. The polishing results show that the removal rate of silicon dioxide film first increased and then decreased with an increasing concentration of K+, pH, and abrasive size. The removal rate of silicon dioxide film increased linearly as the abrasive concentration increased. The influence mechanisms of various additives on the removal rate of silicon dioxide film were investigated by constructing simple models and scanning electron microscopy. Further, the stable performance of the slurry was achieved due to the COO- chains generated by poly(acrylamide) hydrolysis weaken the attraction between abrasives. High-quality wafer surfaces with low surface roughness were also thus achieved. The desirable and simple ingredient slurry investigated in this study can effectively enhance the planarization performance, for example, material removal rates and wafer surface roughness.

­­­­A THZ Tunable Metamaterial Reflective Polarization Converter Based Vanadium Oxide Film

In this paper a simple and tunable reflective polarization converter has been investigated numerically based on metamaterial which composes of a two-corner-cut square patch resonator with a slit embedded into Vanadium dioxide film (VO2) and reflective ground layer. All the results obtained by the CST Microwave Studio show that the polarization conversion ratio (PCR) above 90% is achieved from 2.22-5.42THz at the temperature about 25°C under the linearly and circularly polarized wave incidence normally. In addition, the influences on electromagnetic polarization properties have been demonstrated with the insulator-to-metal phase transition of the Vanadium dioxide film (VO2) film by the method of varying the temperature. At the same time, to be demonstrated, the physical mechanism of changeable polarization conversion has been discussed by the distributions of current densities. According to the results, the designed metamaterial could be applied in the area of temperature-controlled sensing, THz wireless communication, tunable polarized devices.

Capacitive Measurements of SiO2 Films of Different Thicknesses Using a MOSFET-Based SPM Probe

We utilized scanning probe microscopy (SPM) based on a metal-oxide-silicon field-effect transistor (MOSFET) to image interdigitated electrodes covered with oxide films that were several hundred nanometers in thickness. The signal varied depending on the thickness of the silicon dioxide film covering the electrodes. We deposited a 400- or 500-nm-thick silicon dioxide film on each sample electrode. Thick oxide films are difficult to analyze using conventional probes because of their low capacitance. In addition, we evaluated linearity and performed frequency response measurements; the measured frequency response reflected the electrical characteristics of the system, including the MOSFET, conductive tip, and local sample area. Our technique facilitated analysis of the passivation layers of integrated circuits, especially those of the back-end-of-line (BEOL) process, and can be used for subsurface imaging of various dielectric layers.