Photonic sensors that operate in the mid-infrared spectral range are an emerging field for photonic microsystems. In this paper, we present a photonic gas sensor concept based on silicon waveguides using infrared evanescent field absorption. The waveguides were specifically designed for CO ₂ sensing at a wavelength of λ = 4.26μm as possible application for the proposed sensor platform. The waveguide cross section as well as the substructure were investigated using finite-element simulations and the devised structures were fabricated using mass fabrication processes exclusively. In order to evaluate the potential for long interaction path lengths using polysilicon strip waveguides, a study on the intrinsic losses of polysilicon waveguides was conducted. The lowest intrinsic damping that was obtained for polysilicon strip waveguides was 3.98 dB/cm. Furthermore, the sensing capability of the devised waveguides was tested with quantitative CO ₂ measurements down to a concentration of 500 ppm CO ₂ . From the quantitative measurements, the evanescent field ratio was estimated and was in the range between η = 14%-16%.

The detection of infrared radiation is of great interest for a wide range of applications, such as absorption sensing in the infrared spectral range. In this work, we present a CMOS compatible pyroelectric detector which was devised as a mid-infrared detector, comprising aluminium nitride (AlN) as the pyroelectric material and fabricated using semiconductor mass fabrication processes. To ensure thermal decoupling of the detector, the detectors are realized on a Si₃N₄/SiO₂ membrane. The detectors have been tested at a wavelength close to the CO₂ absorption region in the mid-infrared. Devices with various detector and membrane sizes were fabricated and the influence of these dimensions on the performance was investigated. The noise equivalent power of the first demonstrator devices connected to a readout circuit was measured to be as low as $5.3\times {10}^{-9}\mathrm{W}/\sqrt{\mathrm{Hz}}$ .