Quantum Limited SIS Receiver Technology for the Detection of Water Isotopologue Emission From Comets

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NASA's Planetary Science Decadal Survey has concluded that isotopic measurements of cometary water vapor are a means to unraveling the mysteries involving the origin of Earth's water and the evolution of our solar system. To support this, a recent Jet Propulsion Laboratory internal research program has developed quantum limited superconductor–insulator–superconductor (SIS) receivers in the important 500 $-$ 600 GHz submillimeter frequency band. These instruments can be used to detect the deuterated water (HDO) ground state (1 $_{10}$ –1 $_{01}$ ), H $_2^{16}$ O ortho ground state (1 $_{10}$ –1 $_{01}$ ), and the oxygen isotopologues H $_2^{17}$ O and H $_2^{18}$ O with exquisite sensitivity. To achieve the presented results, we have investigated aluminum oxide (AlO $_x$ ) and aluminum nitride (AlN $_x$ ) barrier SIS tunnel junction mixers on the 6- $\mu$ m silicon-on-insulator substrate. The AlO $_x$ and AlN $_x$ junction mixer blocks utilize diagonal and smooth-profile conical horns, respectively. In both cases, a commercial 4–8-GHz intermediate frequency low-noise amplifier (LNA) has been integrated into the mixer block. The AlO $_x$ (low-current-density) barrier SIS junctions were fabricated with 2- $\mu$ m gold beam-lead technology, whereas in the case of the AlN $_x$ SIS tunnel junction, we use capacitive RF decoupling tabs. The latter approach simplifies fabrication, increases yield, eases the mounting process, and facilitates scaling to higher frequencies. For an actual flight mission, with operation $\leq$ 4.2 K, the allowed heat dissipation of the mixer-integrated LNA needs to be minimized. In this article, we also investigate the receiver sensitivity as a function of the LNA dc power consumption. We find that the dc power consumption of the LNA can be reduced to $\sim$ 1.6 mW with minimal loss in sensitivity. It is anticipated that the continued InP HEMT development for quantum computer applications are likely to reduce the required LNA power dissipation even further.