  www.elsevier.com/locate/procedia Proceedings of the Eurosensors XXIII conference A Simple Fabry-Perot-Based Germanium Bolometer for CO2 Monitoring: Simulation and Measurement J. Mayrwöger a, *, W. Reichl b , C. Krutzler c , B. Jakoby a a Institute for Microelectronics and Microsensors, Johannes Kepler University Linz, Linz, Austria b E+E Elektronik, Engerwitzdorf, Austria c Integrated Microsystems Austria (IMA), Wiener Neustadt, Austria Abstract We report on the design of a simple germanium bolometer designed as a Fabry-Perot absorbing structure, which can be used for monitoring, e.g., CO 2 , where no additional filter is required. CO 2 is absorbs IR radiation in a major band centered around 4.26μm. The selectivity of the whole sensor-configuration is mainly accomplished by the wavelength-response associated with the Fabry-Perot structure involved. The analysis shows, that the designed bolometer has an adequate response-function for the measurement of CO 2 concentration. Combining this analysis for the bolometer with ray tracing simulations for a connected sample chamber yields the response for an entire IR-absorption sensor system, which is in good agreement with measurements. Keywords: gas monitoring, infrared, bolometer 1. Introduction Non-dispersive infrared (NDIR) gas sensors are used in various applications, e.g., monitoring of air quality in office buildings, which is a big market for low cost sensors. Such NDIR gas sensors consist of basic building blocks i.e., an IR-source, an optical path with reflecting walls containing the sample gas, and an IR-detector in combination with a gas-specific filter (see Fig. 1). Commercially available systems use thermopile or pyroelectric detectors fabricated with, e.g., a narrowband interference filter as detecting device. In this paper we present a much simpler design of an absorbing device which requires just a few layers and can be manufactured effortlessly. The main part is the combination of the two mirrors and a germanium dielectric layer, which represent a Fabry-Perot structure. This structure filters the targeted CO 2 -specific absorbtion wavelength 1 (4.26μm) out of the spectrum of the total IR- radiation impinging on the bolometer. The absorbed radiation heats up the structure, which can be measured by the change of the electrical resistance of a defined layer. There are two main advantages of germanium as dielectric layer: at first its high index of refraction (n Ge ≈4 for mid infrared) 2 which allows for a design with a thinner layer. The second advantage lies in the possibility to use this material itself as the active sensing layer because of its high (negative) temperature coefficient of resistance 3 (TCR). * Corresponding author. Tel.: +43-(0)732-2468/9318; fax: +43-(0)732-2468/9316. E-mail address: johann.mayrwoeger@jku.at. 1876-6196/09 © 2009 Published by Elsevier B.V. doi:10.1016/j.proche.2009.07.343 Procedia Chemistry 1 (2009) 1375–1378 Open access under CC BY-NC-ND license. brought to you by CORE View metadata, citation and similar papers at core.ac.uk provided by Elsevier - Publisher Connector