Spectrally selective high detectivity uncooled detectors for the long wave infrared

Abstract

Long wave infrared is an important region of the electromagnetic spectrum due to strong thermal emission in this region by room temperature blackbodies and good atmospheric transparency which enables transmission of electromagnetic energy over large distances. Detectors for this spectral region, especially ones that can operate at room temperature, have been an active area of research due to applications in surveillance, remote sensing and chemical detection. Of particular interest is the integration of spectral and spatial filtering directly with the detector to incorporate multispectral capabilities with reduced hardware complexity.This thesis explores several aspects of spectral selectivity in infrared detectors operating at room temperature. The effects of spectral selectivity on the fundamental photon noise limit are first explored using the formalism of an ideal resonant optical cavity. It is shown that the photon noise limit of such a detector is higher than that of a broadband detector. The theoretical performance of this detector architecture is investigated for the specific application of passive standoff detection of gases. Some practical aspects and trade-offs involved in optical and electrical design of such detectors is discussed in detail. A process for fabrication of these detectors using standard silicon micromachining techniques is described. Various optical and electrical characterization techniques are used to demonstrate spectrally selective high sensitivity detectors operating at room temperature. These detectors have amongst the highest sensitivities reported in the literature.Finally, a thermal model for detector responsivity is developed for the particular case of spatially non-uniform absorption. An approximate expression for detector absorbing area is derived from this model, which can be directly substituted in standard equations to estimate responsivity to good accuracy. Detailed derivation and experimental verification of this model is described.