Superconducting Nb DHEB Mixer Arrays for Far-Infrared Spectroscopy

ABSTRACT- We are developing a heterodyne focal plane array with up to eight ele-ments to study lines of the interstellar medium and planetary atmospheres with frequencies of 2 THz and above. Our fabrication process utilizes selective ion milling techniques to pro-duce Nb Diffusion-Cooled Hot Electron Bolometeric (DHEB) mixers from a bi-layer thin film of Au/Nb deposited on a silicon substrate. A micro-bridge of 10 nm thick Nb forms the HEB device. The first generation of devices with lateral dimensions of 100 nm by 80 nm were fabricated at the feed of a broadband spiral antenna with a frequency response de-signed for up to 16 THz. Harmonic multiplier sources becoming available within the next few years should have sufficient power to provide a local-oscillator source for small-for-mat, quasi-optically coupled arrays of these mixers. First generation devices measured at our laboratory have demonstrated a critical temperature (Tc) of 4.8 K with a 0.5 K transition width. These DHEB mixers are expected to have an optimum operational temperature of 1.8-2.0 K. The current four element array mixer block will ultimately be replaced by a dual polarization slot-ring array configuration with up to eight elements. * Publication of the National Institute of Standards and Technology, not subject to copyright. I