The physical properties and the effect of effective surface area (ESA) on the sensing properties of tin dioxide [SnO2] thin films in air and propane [C3H8] atmosphere as a function of operating temperature and gas concentration have been studied in this paper. SnO2 thin films with different estimated thicknesses (50, 100 and 200 nm) were deposited on glass substrates by the chemical spray technique. Besides, they were prepared at two different deposition temperatures (400 and 475 °C). Tin chloride [SnCl4 · 5H2O] with 0.2 M concentration value and ethanol [C2H6O] were used as tin precursor and solvent, respectively. The morphological, and structural properties of the as-prepared films were analyzed by AFM and XRD, respectively. Gas sensing characteristics of SnO2 thin solid films were measured at operating temperatures of 22, 100, 200, and 300 °C, and at propane concentration levels (0, 5, 50, 100, 200, 300, 400, and 500 ppm). ESA values were calculated for each sample. It was found that the ESA increased with the increasing thickness of the films. The results demonstrated the importance of the achieving of a large effective surface area for improving gas sensing performance. SnO2 thin films deposited by spray chemical were chosen to study the ESA effect on gas sensing properties because their very rough surfaces were appropriate for this application.
Chromium and ruthenium-doped zinc oxide (ZnO:Cr) and (ZnO:Ru) thin solid films were deposited on soda-lime glass substrates by the sol-gel dip-coating method. A 0.6 M solution of zinc acetate dihydrate dissolved in 2-methoxyethanol and monoethanolamine was used as basic solution. Chromium (III) acetylacetonate and Ruthenium (III) trichloride were used as doping sources. The Ru incorporation and its distribution profile into the films were proved by the SIMS technique. The morphology and structure of the films were studied by SEM microscopy and X-ray diffraction measurements, respectively. The SEM images show porous surfaces covered by small grains with different grain size, depending on the doping element, and the immersions number into the doping solutions. The sensing properties of ZnO:Cr and ZnO:Ru films in a propane (C3H8) atmosphere, as a function of the immersions number in the doping solution, have been studied in the present work. The highest sensitivity values were obtained for films doped from five immersions, 5.8 and 900, for ZnO:Cr and ZnO:Ru films, respectively. In order to evidence the catalytic effect of the chromium (Cr) and ruthenium (Ru), the sensing characteristics of undoped ZnO films are reported as well.
In the present work the development of an amperometric transducer in order to build a free cholesterol biosensor in planar configuration is reported. The one single use disposable biosensors were constructed by screen printing process which is compatible with automated methodologies of production. Based in the incorporation of tetracyanoquinodimethane (TCNQ), Prussian blue (PB) or ferrite (Fe<sub>3</sub>O<sub>4</sub>) as mediator or electrocatalytic agent, three types of electrochemical transducers were evaluated. The cholesterol biosensors require a sample volume of 7.2 μL, exhibits good reproducibility and selectivity and cover a lineal answer of 2-16 mM with detection limits from 0.3 to 1.6 mM. The characteristics of biosensors are satisfactory for the decentralized analysis of the lipid in blood since enclose the range of clinical interest (3.5-6.5 mM).
Gas sensors based on various principles and configurations have been studied for several years. Some of them are based on resistance variation of sensing layers. On the other hand, floatinggate MOSFETs can modify its threshold voltage by means of a chemical reaction. Here a study is made to prove that the charge produced by such chemical reaction can affect the voltage upon the floating gate. An analysis of a reading circuit with an FG-MOS as the transducer is made, showing this approximation as a promising alternative for gas sensors. A very simple design can be made for fabrication of a monolithic gas sensing system, by using a standard technology, supported in a MEMS structure for thermal isolation purposes. In order to show feasibility of this idea, experimental data is obtained using a conventional MOSFET and an Fe 2 O 3 layer, showing that the system can be used as a gas sensor.
El objetivo de este trabajo es proporcionar a los estudiantes de electrónica, computación y áreas afines, un panorama de la construcción y funcionamiento de los transistores de efecto de campo de aleta (FinFET), los cuales son dispositivos extremadamente diminutos, con longitud de compuerta en el rango de los nanómetros, se fabrican con la técnica de silicio sobre aislante (SOI). Utilizando FinFETs tipo n y p se diseñaron los diagramas esquemáticos y las formas y dimensiones de los materiales utilizando un código de colores (layouts) de las compuertas lógicas básicas, este tipo de compuertas son la base para el diseño y construcción de la mayoría de los dispositivos digitales utilizados en los aparatos electrónicos modernos, principalmente los portátiles. Con los tamaños tan reducidos de los FinFET se fabrican todos los microprocesadores, los DSPs, las memorias, los chips de los teléfonos celulares y tabletas de las compañías electrónicas más importantes del mundo.
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