Implementação de sensores ópticos integrados para aplicações em análises químicas e ambientais. / Implementation of integrated optical sensors for chemical analysis and environment aplications.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The aim of this work is the development of optical chemical sensors based on Mach-Zehnder Interferometer (MZI) for chemical and environmental analysis applications. Such devices were implemented with waveguides fabricated on a silicon substrate. The waveguides were obtained using silicon nitride (Si3N4) and silicon oxide (SiO2) films obtained by CVD (Chemical Vapor Deposition) and thermal oxidation of the silicon substrate. The waveguides and the optical sensors were fabricated using conventional lithograph and etching processes. The developed chemical sensors are based on the evanescent field interaction in a waveguide exposed to a liquid or gaseous phase of a chemical compound. Such optical sensor were designed, simulated and implemented for the following applications: Glucose concentration; Humidity measurement by scattering effect; Volatile organic compounds (VOCs) vapors detection. The process steps for the optical chemical sensor fabrication were defined during the integrated optical simulations and the films were characterized after the fabrication process steps. The Si3N4 and SiO2 films used in the optical sensor fabrication are uniform and homogenous (thickness and refractive index), with low surface roughness and low levels of water incorporation and OH bonds. However, the roughness values increased significantly after the etching process for the optical sensor structures definition. The implemented waveguides were singlemoded (TE0), with experimental attenuation values between 2 and 20 dB/cm, depending on the surface and sidewall roughness of the waveguide and of the films uniformity. The operation principle and the sensitivity of the optical chemical sensor were verified by glucose concentration measurements, by measuring the MZI output variation intensity as a function of the refractive index of the glucose standard solutions (dn/dc). As the light scattering depends of the roughness and the of refractive index difference between the exposed interface and the atmosphere, its possible to measure the humidity or the amount of water in the interaction window. Afterwards, the detection of volatile organic compounds (VOCs) was done using a HMDS (Hexamethyldissilazane) layer to adsorb the VOCs. The VOCs vapor was applied on the optical chemical sensors and the results obtained for n-Hexane and 2-Propanol showed a good reproducibility and high sensitivity.

ASSUNTO(S)

sensor óptico thin films análise química mach-zehnder interferometer interferômetro mach-zehnder optical sensor filmes finos chemical analyse

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