THz Range Low-Noise SIS Receivers for Space and Ground-Based Radio Astronomy

Abstract

We report on research in the field of low-noise receiving systems in the sub-terahertz (THz) range, carried out in recent years, aimed at developing receivers with quantum sensitivity for implementation in space and ground-based radio telescopes. Superconductor-Insulator-Superconductor (SIS) mixers based on high-quality tunnel junctions are the key elements of the most sensitive sub-THz heterodyne receivers. Motivations and physical background for technology improvement and optimization, as well as fabrication details, are described. This article presents the results of the SIS receiver developments for the 211–275 GHz and 790–950 GHz frequency ranges with a noise temperature in the double sideband (DSB) mode of approximTELY 20 K and 200 K, respectively. These designs and achievements are implemented in the development of the receiving systems for the Russian Space Agency mission “Millimetron”, and for the ground-based APEX (Atacama Pathfinder EXperiment) telescope.

Superconducting Terahertz Receivers for Space and Ground-based Radio Astronomy

“…It can be seen that the value of the Y-factor at the best point reaches 5 dB, which corresponds to a receiver noise temperature of 24 K. The noise temperature values were obtained without corrections for losses in the beam splitter and the cryostat window; they are only twice the value of hf/k B in the range from 240 to 265 GHz. The dependence of the DSB noise temperature of the SIS receiver on the local oscillator frequency was measured [18]; it was shown that the obtained values meet the technical requirements to the 211-275 GHz receiver for the Millimetron space radio-telescope.…”

“…To achieve a low noise temperature, it is necessary to compensate for the significant capacitance of the SIS junction (Cp ≃ 0.085 pF/μm 2 ); for this purpose, the topology of the mixing element was developed and its operation was modeled [18]. To match the impedance of the SIS junction at a high frequency with a waveguide impedance of about 400 Ohm, a planar structure was used, consisting of sections of coplanar and microstrip Nb/SiO2/Nb lines (Fig.…”

“…1). To prevent RF signal leakage the RF rejection filters were used in the design of the mixing element [18]. The receiving element was fabricated on a quartz substrate with a thickness of 125 μm, located perpendicular to the plane of wave propagation in a rectangular waveguide 500 × 1000 μm, it was located at a distance of 230 μm from the end of the waveguide.…”

Fabrication of Superconducting Nb–AlN–NbN Tunnel Junctions Using Electron-Beam Lithography

“…To realize a quantum-limited performance of the SIS mixers at sub-THz frequencies, tunnel junctions with very high tunnel current density are required. To achieve proper matching between such junctions and the receiving antenna, submicron SIS junctions were implemented [28,[30][31][32][33]. SIS mixers have already been successfully used for both space missions and ground-based telescopes (TELIS, CHAMP) [7,[30][31][32].…”

“…Up to now, SIS junctions with an area down to 0.5 µm 2 have been fabricated by conventional photolithography processes. To improve the performance and the yield of SIS mixers and to ensure equality of the SIS junctions in the twin mixer circuits [32,33], implementation of electron-beam lithography is highly desirable. This is especially important for the development of SIS array receivers and the further increase in the SIS operating frequency above 1 THz.…”