NDLI: MEMS infrared gas spectrometer based on a porous silicon tunable filter

Content Provider	IEEE Xplore Digital Library
Author	Lammel, G. Schweizer, S. Renaud, P.
Copyright Year	2001
Description	Author affiliation: Inst. of Microsystems IMS, Swiss Federal Inst. of Technol., Lausanne, Switzerland (Lammel, G.)
Abstract	We present a MEMS infrared spectrometer for selective and quantitative chemical gas analysis. Infrared absorption spectroscopy can distinguish gases easily and also detect nonreactive molecules like CO/sub 2/, in contrast to e.g. metal oxide gas sensors. The following new spectrometer concept avoids expensive linear detectors as used for grating spectrometers: A tunable interference filter scans the desired part of the infrared spectrum. A single pixel thermopile detector measures serially the intensify at selected wavelengths. The tunable optical interference filter is fabricated by a new porous silicon batch technology using only two photolithography steps. The refractive index of this filter microplate is gradually modulated in depth to create a Bragg mirror, edge filter or a Fabry-Perot bandpass filter for central wavelengths between 400 nm and 8 /spl mu/m. Two thermal bimorph micro-actuators tilt the plate by up to 90/spl deg/, changing the incidence angle of the beam to be analyzed. This tunes the wavelength transmitted to the detector. The filter area can be chosen between 0.27 mm/spl times/0.70 mm and 2.50 mm/spl times/3.00 mm, its thickness is typically 30 /spl mu/m. The spectral finesse /spl lambda///spl Delta//spl lambda/ of 25 is sufficient for most diagnosis applications. First results showed that CO/sub 2/ and CO can be detected selectively with this system-which is interesting in combustion processes-by measuring their absorption at 4.26 /spl mu/m and 4.65 /spl mu/m respectively. Other wavelength ranges e.g. for liquid analysis or colorimetry of visible light are possible.
Sponsorship	IEEE Robotics & Autom Soc
Starting Page	578
Ending Page	581
File Size	515087
Page Count	4
File Format	PDF
ISBN	0780359984
ISSN	10846999
DOI	10.1109/MEMSYS.2001.906607
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2001-01-25
Publisher Place	Switzerland
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Infrared spectra Micromechanical devices Spectroscopy Silicon Optical filters Band pass filters Infrared detectors Gas detectors Chemical analysis Electromagnetic wave absorption
Content Type	Text
Resource Type	Article
Subject	Condensed Matter Physics Electronic, Optical and Magnetic Materials Mechanical Engineering Electrical and Electronic Engineering

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