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The mid- and far infrared are tantalizing regions of the electromagnetic spectrum, containing great information about thermal and chemical properties of objects and materials; however, semiconductor materials that interact with light in this range are often extremely difficult to use, especially at room temperature. Thermal detectors in the form of microbolometers have had great commercial success in the uncooled camera market, but they have significant limitations when speed or spectral selectivity is needed.
This presentation reviews the basic properties and performance of microbolometers and other uncooled thermal detectors. The basic physical limits of thermal detector performance are discussed; these include noise sources, temperature stability, ultimate speeds, ultimate sensitivities, quantum noise effects at far-IR and THz wavelengths, and thermomechanical limits on spectral resolution. With this background, we will explore how the radiation noise limit differs between traditional microbolometers with wide absorption and detectors with narrower spectral pass bands. This can allow improved performance because narrowband microbolometers and thermal detectors can theoretically operate near the performance of cooled detectors. The presentation will discuss some preliminary work at Minnesota showing the highest D* uncooled detectors reported to date as a milestone in our attempt to approach the background limit. The presentation will conclude with some speculations on how research on uncooled detectors will progress in the next 10 years. These speculations will include aspects of pixel design, new materials for optical performance and electrical readout, design for high temperature operation, and other detector characteristics.
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