Characterization of narrowband microelectromechanical systems based detectors for integrated mid-infrared gas sensing

Abstract

The underlying project of this work is performed in cooperation with Infineon Technologies Austria AG and the Johannes Kepler University of Linz. Work is done on the development, characterization and optimization of an optical carbon dioxide sensor, based on mid infrared absorption by the gaseous CO2 molecules. The construction of such a sensing system requires the integration of a mid-IR sensitive detector, attached to a waveguide, a radiation source and a wavelength selective filter structure. In this master thesis the experimental characterization of three different detectors will be presented. In addition to a simple bolometer and a P-N diode, a newer concept, a so-called vertical cavity enhanced detector is examined more closely. A big advantage of this detector is that it has an directly integrated wavelength selective filter, in the form of a Bragg mirror, tailored for 4.26 microns, according to the absorption spectrum of CO2. At the end it is demonstrated that the vertical cavity enhanced detector outperforms the other two and the cavity induces an increase in responsivity by a factor 7.1. As such this design can be easily optimized and integrated to specifically enhance the detector response around the design wavelength.8