Antenna-Coupled Nanowire Thermocouple for Infrared Detection

Humans and animals emit thermal electromagnetic radiation in the long-wave infrared range. The atmospheric absorption in this range is relatively low making this band attractive for application, such as target detection and tracking. Unbiased, uncooled, and frequency-selective antenna-coupled nanowire thermocouples have been designed, fabricated from different metal combinations, and characterized for long-wave infrared detection.

Due to their small size, nanowires exhibit different physical properties from their bulk counterparts. One of these properties, the Seebeck coefficient, specifies how well the thermocouple converts a temperature gradient into an open-circuit voltage. We have developed a characterization platform, with which the Seebeck coefficient of the nanowires was measured. The nanowire thermocouples were calibrated, and their fabrication process was optimized. The characterization platform was co-located on the same chip as the infrared detectors. The area of the hot junction of the nanowire thermocouple was approximately 75 nm x 75 nm. The antenna-coupled thermocouples show polarization dependence with a maximum normalized detectivity (D*) of 5.46?10^5 cm√Hz/W. We also investigated an unexpected and novel effect, namely the antenna-coupled shape-engineered thermocouples. Only one single metal was used for the fabrication of the entire thermocouple. The necessary Seebeck coefficient difference between the two conductors was reached by shape engineering and using the reduction of the Seebeck coefficient in thin films. This phenomena opens the door for possible cheap implementation of these devices as well as the mass production for future application, since the complexity of fabrication is greatly reduced.