A Microsystem Based on Porous Silicon-Glass Anodic Bonding for Gas and Liquid Optical Sensing

Luca De Stefano,Krzysztof Malecki,Francesco Della Corte,Ilaria Rea,Luigi Moretti,Lucia Rotiroti,Ivo Rendina

doi:10.3390/s6060680

Luca De Stefano, Krzysztof Malecki + Show 5 more

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https://doi.org/10.3390/s6060680

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Abstract

We have recently presented an integrated silicon-glass opto-chemical sensor forlab-on-chip applications, based on porous silicon and anodic bonding technologies. In thiswork, we have optically characterized the sensor response on exposure to vapors of severalorganic compounds by means of reflectivity measurements. The interaction between theporous silicon, which acts as transducer layer, and the organic vapors fluxed into the glasssealed microchamber, is preserved by the fabrication process, resulting in optical pathincrease, due to the capillary condensation of the vapors into the pores. Using theBruggemann theory, we have calculated the filled pores volume for each substance. Thesensor dynamic has been described by time-resolved measurements: due to the analysischamber miniaturization, the response time is only of 2 s. All these results have beencompared with data acquired on the same PSi structure before the anodic bonding process.

Highlights

The physical and structural properties of porous silicon (PSi), first of all its high surface area matrix, have led many scientific researchers to investigate this material, using it as a transducer in sensing systems
We have recently reported on the optimisation of the standard silicon-glass anodic bonding (AB) parameters, searching for low temperature, low voltage and short time, taking into account the electrode type and thickness of glass wafers [7]
When the PSi layer is exposed to vapors, or dip in the liquid phase of the same substance, the substitution of air in the pores by its molecules causes a fringes shift in wavelength, which corresponds to a change in the optical path nd

Summary

Introduction

The physical and structural properties of porous silicon (PSi), first of all its high surface area matrix, have led many scientific researchers to investigate this material, using it as a transducer in sensing systems. From the optical point of view, this structure is an optical Fabry-Perot interferometer, so that the maxima in the reflectivity spectrum appear at wavelengths λm which satisfy: m = 2nd / λ m where m is an integer, d is the film thickness and n is the average refractive index of the layer [8,9].

Results

Conclusion