Comportamiento mecánico y eléctrico de un gel de silicona empleado en el encapsulamiento de transistores de potencia tipo IGBT

Resumen: Los materiales dieléctricos son ampliamente utilizados en el sector energético, estando a veces sometidos a condiciones de alto estrés eléctrico, mecánico y ambiental en general, que los ponen al borde de procesos y mecanismos de degradación que conllevan a una probable falla futura. Los geles dieléctricos han comenzado a ser ampliamente utilizados en aplicaciones de encapsulamiento de transistores de alta potencia tipo IGBTs (del inglés Insulated Gate Bipolar Transistor), donde se manejan tensiones y corrientes considerables. En la mayoría de los casos, se necesita una protección para evitar descargas en fase gaseosa, ingreso de humedad al circuito y amortiguamiento mecánico para vibraciones. En el presente trabajo caracterizamos con diferentes técnicas aspectos destacables de este tipo de encapsulantes a base de un gel bifásico de silicona. Para observar el proceso de curado se empleó la técnica de espectroscopía de absorción infrarroja (FTIR), junto con la reología oscilatoria desde las propiedades mecánicas. A su vez, esta última, sirvió para comparar información provista por un novedoso concepto que implica observar a estas últimas desde el interior, a partir de la evolución de cavidades gaseosas generadas eléctricamente. Se comprobó que el comportamiento de estas cavidades es sensible a la historia previa del material, es decir, mecanismos de curado y envejecimiento previo.

Piezoelectricity Of Zno Films Prepared By Sol-Gel Method

ZnO piezoelectric thin films were prepared on crystal substrate Si(111) by sol-gel technology, then characterized by scanning electron microscopy, X-ray diffraction and atomic force microscopy (AFM). The ZnO films characterized by X-ray diffraction are highly oriented in (002) direction with the growing of the film thickness. The morphologies, roughness and grain size of ZnO film investigated by AFM show that roughness and grain size of ZnO piezoelectric films decrease with the increase of the film thickness. The roughness dimension is 2.188-0.914 nm. The piezoelectric coefficient d(33) was investigated with a piezo-response force microscope (PFM). The results show that the piezoelectric coefficient increases with the increase of thickness and (002) orientation. When the force reference is close to surface roughness of the films, the piezoelectric coefficient measured is inaccurate and fluctuates in a large range, but when the force reference is big, the piezoelectric coefficient d(33) changes little and ultimately keeps constant at a low frequency.

Piezoelectricity of ZnO films prepared by sol-gel method

ZnO piezoelectric thin films were prepared on crystal substrate Si(111) by sol-gel technology, then characterized by scanning electron microscopy, X-ray diffraction and atomic force microscopy (AFM). The ZnO films characterized by X-ray diffraction are highly oriented in (002) direction with the growing of the film thickness. The morphologies, roughness and grain size of ZnO film investigated by AFM show that roughness and grain size of ZnO piezoelectric films decrease with the increase of the film thickness. The roughness dimension is 2.188-0.914 nm. The piezoelectric coefficient d(33) was investigated with a piezo-response force microscope (PFM). The results show that the piezoelectric coefficient increases with the increase of thickness and (002) orientation. When the force reference is close to surface roughness of the films, the piezoelectric coefficient measured is inaccurate and fluctuates in a large range, but when the force reference is big, the piezoelectric coefficient d(33) changes little and ultimately keeps constant at a low frequency.

Manual for starch gel electrophoresis: A method for the detection of genetic variation

The procedure to conduct horizontal starch gel electrophoresis on enzymes is described in detail. Areas covered are (I) collection and storage of specimens, (2) preparation of tissues, (3) preparation of a starch gel, (4) application of enzyme extracts to a gel, (5) setting up a gel for electrophoresis, (6) slicing a gel, and (7) staining a gel. Recipes are also included for 47 enzyme stains and 3 selected gel buffers. (PDF file contains 26 pages.)

Sensitivity to alcohols of a planar waveguide ring resonator fabricated by a sol-gel method

A planar waveguide ring resonator was fabricated by organic-inorganic hybrid sol-gel materials; its sensitivity to ethanol vapor was experimentally investigated. It was found that dips in the transmission spectrum of the device shifted to longer wavelengths with increasing the ethanol concentration, and its sensitivity showed a linear relation with the ethanol concentration, showing a coefficient of 1.13 pm/ppm. In addition, the transmission loss of the ring resonator decreased with increasing the ethanol concentration. The measured characteristics suggest that the device may be considered as one of the candidates of alcohol vapor sensors. (c) 2006 Elsevier B.V. All rights reserved.

Strong visible up-conversion emissions and thermometric applications of Er3+-Yb3+ codoped Al2O3 prepared by the sol-gel method

The Er3+-Yb3+ codoped Al2O3 has been prepared by the sol-gel method using the aluminium isopropoxide [Al(OC3H7)(3)]-derived Al2O3 sols with addition of the erbium nitrate [Er(NO3)(3) center dot 5H(2)O] and ytterbium nitrate [Yb(NO3)(3) center dot 5H(2)O]. The phase structure, including only two crystalline types of doped Al2O3 phases, theta and gamma, was obtained for the 1 mol% Er3+ and 5 mol% Yb3+ codoped Al2O3 at the sintering temperature of 1,273 K. By a 978 nm semiconductor laser diodes excitation, the visible up-conversion emissions centered at about 523, 545, and 660 nm were obtained. The temperature dependence of the green up-conversion emissions was studied over a wide temperature range of 300-825 K, and the reasonable agreement between the calculated temperature by the fluorescence intensity ratio (FIR) theory and the measured temperature proved that Er3+-Yb3+ codoped Al2O3 plays an important role in the application of high temperature sensor.

Formation and characterization of tin oxide aerogel derived from sol-gel process based on tetra(n-butoxy)tin(IV)

Transparent and translucent SnO2 aerogels with high specific surface area (>300m(2)/g) have been prepared by sol-gel process using tetra(n-butoxy)tin(IV) as a starting compound, and supercritical drying technique for solvent extraction. Light scattering measurements reveal that the polymeric cluster size distribution in sol system is gradually broadened during sol-gel transition. SEM images show that the aerogels are made up of the cottonlike oxide agglomerates with a large number of Pores. TEM images show that these aerogels seem to be self-similar at different magnifications. Their pore size distribution is pretty wide ranging, from mesopore to macropore especially for that of translucent aerogel. (C) 2004 Elsevier B.V. All rights reserved.

H-2-sensing characteristics of nanocrystalline La0.8Pb0.2FeO3 prepared by sol-gel method

Nanocrystalline La0.8Pb0.2FeO3 has been prepared by the sol-gel method. XRD patterns show that the nanocrystalline La0.8Pb0.2FeO3 is a perovskite phase with the orthorhombic structure and its mean crystallite size is about 19 nm. The influence of Pb ions which replaced the La ions on A-sites can be directly observed from the electrical and sensing properties to H-2 gas. The conductance of La0.8Pb0.2FeO3-based sensor is considerably higher than that of LaFeO3-based sensor, and Pb-doping can enhance the sensitivity to H2 gas. An empirical relationship of R = KCH2alpha with alpha = 0.668 was obtained.

Structural role of fluoride in aluminophosphate sol-gel glasses: High-resolution double-resonance NMR studies

The local structure of Na-Al-P-O-F glasses, prepared by a novel sol-gel route, was extensively investigated by advanced solid-state NMR techniques. Al-21{F-19} rotational echo double resonance (REDOR) results indicate that the F incorporated into aluminophosphate glass is preferentially bonded to octahedral Al units and results in a significant increase in the concentration of six-coordinated aluminum. The extent of Al-F and Al-O-P connectivities are quantified consistently by analyzing Al-27{P-31} and Al-21{F-19} REDOR NMR data. Two distinct types of fluorine species were identified and characterized by various F-19{Al-27}, F-19{Na-23}, and F-19{P-31} double resonance experiments, which were able to support peak assignments to bridging (Al-F-Al, -140 ppm) and terminal (Al-F, -170 ppm) units. On the basis of the detailed quantitative dipole-dipole coupling information obtained, a comprehensive structural model for these glasses is presented, detailing the structural speciation as a function of composition.

Optical and surface properties of hybrid TiO2/ormosil planar waveguide prepared by the sol-gel process

Two kinds of silanes, 3-glycidoxypropyltrimethoxysilane (GLYMO) and 3-trimethoxysililpropylmethacrylate (TMSPM), were used to prepare ormosil waveguide films by the sol-gel method. Thirty percent Ti(OBu)(4) and 70% silane were contained in the precursor sets. The properties of films were measured by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV/VIS/NIR spectrophotometer (UV-vis), atomic force microscopy (AFM), m-line and scattering-detection method. The films from GLYMO and TMSPM precursors exhibit similar thickness (2.58 mu m for GLYMO, 2.51 mu m for TMSPM) and refractive index (1.5438 for GLYMO, 1.5392 for TMSPM, lambda=632.8 nm), but the film from TMSPM precursor has higher propagation loss (1.024 dB/cm, lambda=632.8 nm) than the film prepared from GLYMO (0.569 dB/cm, lambda=632.8 nm). Furthermore, the film prepared from TMSPM is easy to be opaque and cracks during coating whereas the same phenomenon was not found for the film prepared with GLYMO. It is confirmed that GLYMO is a better precursor than TMSPM for waveguide film preparation. (C) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.