Enhancing microbolometer performance at terahertz frequencies with metamaterial absorbers
Kearney, Brian T.
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For Terahertz (THz) imaging to be useful outside of a laboratory setting, inexpensive yet sensitive detectors such as uncooled microbolometers will be required. Metamaterials can improve THz absorption without significantly increasing the thermal mass or using exotic materials because their absorption is primarily dependent on the geometry of the materials and not their individual optical properties. Finite Element (FE) simulations revealed that an array of squares above a ground plane separated by a dielectric is efficient, yet thin. Metamaterials were fabricated and their absorption characteristics were measured using a Fourier Transform Infrared Spectrometer (FTIR) indicating that the FE simulations are accurate. Metamaterial structures tuned to a quantum cascade laser (QCL) illuminator were incorporated into a bi-material sensor, which was used for detection of THz radiation from the QCL source with good sensitivity. In the case of microbolometers, a bolometric layer needs to be embedded in the metamaterial to form a thin microbridge. Simulations indicated that if the bolometric layer was resistive enough or close enough to the ground plane, then absorption would be largely unaltered. Metamaterials with a conductive Titanium (Ti) layer embedded into the dielectric spacer were fabricated and measured with an FTIR, confirming this behavior.
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