Non-selective NDIR array for gas detection

R. Rubio; J. Santander; S. Marco; L. Fonseca; J. Fonollosa; M. Moreno

doi:10.1117/12.607350

1 July 2005 Non-selective NDIR array for gas detection

R. Rubio, J. Santander, S. Marco, L. Fonseca, J. Fonollosa, M. Moreno

Proceedings Volume 5836, Smart Sensors, Actuators, and MEMS II; (2005) https://doi.org/10.1117/12.607350
Event: Microtechnologies for the New Millennium 2005, 2005, Sevilla, Spain

Abstract

A micro component for a non-selective NDIR (non dispersive infrared) gas detection system is presented in this work. This device consist of an IR detection module composed of a thermopile and a thin film filter array. The thermopile arrays (up to 4x4) are built on a silicon substrate by bulk micro-machining processes. The whole matrix is built on a thin freestanding silicon oxide/silicon nitride membrane of 2100x2100μm2 defined by anisotropic wet etching. To ensure the existence of hot and cold junctions for each detector we define on the insulating membrane absorbers and ribs, 6μm thick, by heavy boron doping of the silicon underneath. The ribs crisscross the membrane contacting the silicon bulk acting as a heat sink. Absorbers are located in the centre of each individual pseudo-membrane defined by the ribs intersection. Incident radiation heats up the absorber creating a temperature difference that is measured by the thermocouples that are placed between the absorber and the ribs. On a second chip, the elements of the filter array are fabricated in a matching configuration. The filters are built on a silicon substrate alternating thin films of different refraction index acting like a Fabry-Perot structure with 2-8μm silicon oxide cores. The transmitted filter peaks are not tuned for the detection of any specific substance: they configure a non selective general purpose filter array (400-4000 cm^-1), making signal processing and pattern recognition techniques necessary. Both dies have been fabricated and characterized and have been successfully attached using flip-chip techniques. The measurements on these devices have been used to build an optical simulation tool that allows the assessment of the whole NDIR system behaviour in operating conditions.

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R. Rubio, J. Santander, S. Marco, L. Fonseca, J. Fonollosa, and M. Moreno "Non-selective NDIR array for gas detection", Proc. SPIE 5836, Smart Sensors, Actuators, and MEMS II, (1 July 2005); https://doi.org/10.1117/12.607350

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KEYWORDS

Silicon

Sensors

Absorption

Optical filters

Filtering (signal processing)

Mirrors

Carbon monoxide

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