Far-Infrared Microbolometer Detectors.

Receivers and imaging systems for the far-infrared (FIR) spectral region (wavelengths between 100 μm and 3 mm) are desired for applications in astronomy, radar, and fusion research. Microbolometer detectors integrated with planar antennas are broad-band devices which work well in the FIR and which can be assembled into arrays for imaging. Radiation captured by the antenna heats and microbolometer detector, causing its temperature to change. With a good microbolometer material, this temperature change will result in a significant change in resistance, which can be measured. Also, a microbolometer has a small thermal mass, which means it can respond rapidly to a modulated FIR signal. This study addresses the theory and operation of microbolometer detectors, and demonstrates the performance of conventional microbolometers using the elements bismuth and tellurium. The application of a bismuth microbolometer as the detector for a twin slot antenna structure is presented. The conventional microbolometer structure is constrained in that the resistance of the detector must match reasonably well with the impedance of the antenna. A composite microbolometer structure is demonstrated which removes this constraint. Finally, the sharp change in resistance at the transition temperature of a superconductor could be utilized to make a very responsible microbolometer. Preliminary results of such a transition edge microbolometer (TREMBOL) are presented using a conventional superconductor (lead) chilled to 7 K.