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Experimental evaluation of a thermopile detector with SU-8 membrane, in a carbon dioxide meter setup
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media. (Electronics design division, STC)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media. (Electronics design division)
SenseAir.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media. (Electronics design division)ORCID iD: 0000-0002-3790-0729
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2009 (English)In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 9, no 12, p. 1633-1638Article in journal (Refereed) Published
Abstract [en]

Continuous control of the carbon dioxide levels in the ventilation systems in office buildings and public schools has been shown to increase productivity and save money. However, these measurement systems require further developments in order to be more cost effective. This paper presents an evaluation of an Al/Bi thermopile detector with a 4 µm thin SiO2/SU-8 membrane in a CO2 meter application using the NDIR (Non-Dispersive Infrared Technology). The system consists of an 11 cm aluminum tube, used as the sample chamber and in which a light source and a thermopile detector with a 4.26 µm optical bandpass filter are positioned on its opposite sides. The light source is pulsed with a frequency of 0.5 Hz. The voltage response of the Al/Bi thermopile is measured for different CO2 concentrations, and, as expected according to the Lambert-Beer law, there is an exponential decrease in the measured intensity. The absolute response is about 50 % lower than for a commercial HMS J21 thermopile from Heimann Sensor GmbH. In relative terms, on the other hand, the Al/Bi thermopile is more sensitive for changes in the CO2 concentration. At 7500 ppm, the voltage response has decreased to 40 % of the reference response measured in the nitrogen atmosphere.

Place, publisher, year, edition, pages
2009. Vol. 9, no 12, p. 1633-1638
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:miun:diva-8830DOI: 10.1109/JSEN.2009.2030645ISI: 000271020700003Scopus ID: 2-s2.0-70350637523OAI: oai:DiVA.org:miun-8830DiVA, id: diva2:213818
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STC - Sensible things that communicateAvailable from: 2009-04-29 Created: 2009-04-29 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Design, Fabrication and Optimization of Thermal Radiation Detectors Based on Thin Polymer Membranes
Open this publication in new window or tab >>Design, Fabrication and Optimization of Thermal Radiation Detectors Based on Thin Polymer Membranes
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The number of applications in which infrared radiation sensors are used is increasing. In some applications, the cost of the sensor itself is an issue, and simple solutions are thus required. In this thesis, the investigations have related to the use of thin polymer membranes in thermal infrared sensors, such as bolometers and thermopiles.

Infrared sensors are usually subcategorized into photonic sensors and thermal sensors. For detection of infrared radiation using a photodetector, there is a requirement for low band-gap material. The need of cooling makes infrared photodetectors rather expensive, and not an alternative for low-cost applications. In thermal sensors, the heat generated from the incident infrared radiation is converted into an electrical output by means of a heat sensitive element. Thermal sensors operate at room temperature, which makes them a low-cost alternative. The basic structure of thermal sensors consists of a temperature sensitive element connected to a heat sink through a structure with low thermal conductance. It is common to use thin membranes of Silicon or Silicon Nitride as thermal insulation between the heat sink and the sensitive element. In comparison, polymers have a thermal conductance that is lower than in these materials, and this increases the generated temperature in the sensitive element. A polymer such as SU-8 has a low thermal conductivity and is applied using a spin coater. This reduces the number of complex processing steps. This thesis presents a new application of SU-8 as a closed membrane in a thermal sensor.

The concept was initially demonstrated by fabricating a nickel bolometer and titanium/nickel thermopile structure with a 5 µm SU-8 / SiO2 membrane. However, for the sensor responsivity to be able to compete with commercial thermal sensors the structures, some optimization was required. Since the thermopile generates its own voltage output and requires no external bias, the optimizations were focused on this structure. There exist a number available software tools for thermal simulation of components. However, to the author’s best knowledge, there exist no tool for design optimization of thermopiles with closed membranes. An optimization tool using iterative thermal simulations was developed and evaluated. A new thermopile structure, based on the optimization results, was both fabricated and characterized. Using an infrared laser with a small spot, the measured responsivity of the manufactured thermopile was higher than that of a commercial sensor. In the case of a defocused spot and for longer wavelengths, the infrared absorption in the absorption layer reduces and degrades the responsivity.

The thermopile was further evaluated as a sensor in a carbon dioxide meter application based on the NDIR principle. An increase in the CO2 concentration demonstrated a clear decrease in the thermopile voltage response, as was expected. By normalizing the voltage response and comparing it with a commercial sensor, this showed that the SU-8 based thermopile is relatively more sensitive to changes in the CO2 concentration.

Place, publisher, year, edition, pages
Sundsvall: Kopieringen Mittuniversitetet, 2009. p. 64
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 73
Keywords
Thermal detector, Polymer, Membrane, SU-8
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-9579 (URN)978-91-86073-46-6 (ISBN)
Public defence
2009-09-19, O111, Holmgatan 10, Sundsvall, 13:15 (English)
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Supervisors
Projects
STC
Available from: 2009-08-28 Created: 2009-08-27 Last updated: 2011-02-06Bibliographically approved

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Mattsson, ClaesThungström, GöranNilsson, Hans-Erik

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