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IEICE Transactions on Electronics

Development of Superconducting Devices Supporting Radio Astronomy

Yoshinori Uzawa, M. Kroug, Takafumi Kojima, Masanori Takeda, Kazumasa Makise, Shohei Ezaki, Wenlei Shan, Akihira Miyachi, Yasunori FUJII, Hirotaka Terai

Published Mar 23, 2021• 5 citations
Publisher

Abstract

This paper describes the development of superconductor-insulator-superconductor (SIS) mixers for the Atacama Large Millimeter/submillimeter Array (ALMA) from the device point of view. During the construction phase of ALMA, the National Astronomical Observatory of Japan (NAOJ) successfully fabricated SIS mixers to meet the stringent ALMA noise temperature requirements of less than 230 K (5 times the quantum noise) for Band 10 (787-950 GHz) in collaboration with the National Institute of Information and Communications Technology. Band 10 covers the highest frequency band of ALMA and is recognized as the most difficult band in terms of superconducting technology. After the construction, the NAOJ began development studies for ALMA enhancement such as wideband and multibeam SIS mixers according to top-level science requirements, which are also presented.

DOI
10.1587/transele.2020sui0003

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This paper describes the development of superconductor-insulator-superconductor (SIS) mixers for the Atacama Large Millimeter/submillimeter Array (ALMA) from the device point of view. During the construction phase of ALMA, the National Astronomical Observatory of Japan (NAOJ) successfully fabricated SIS mixers to meet the stringent ALMA noise temperature requirements of less than 230 K (5 times the quantum noise) for Band 10 (787-950 GHz) in collaboration with the National Institute of Information and Communications Technology. Band 10 covers the highest frequency band of ALMA and is recognized as the most difficult band in terms of superconducting technology. After the construction, the NAOJ began development studies for ALMA enhancement such as wideband and multibeam SIS mixers according to top-level science requirements, which are also presented.
Abstract This paper describes the development of superconductor–insulator–superconductor (SIS) receivers in the 787–950 GHz radio frequency (RF) range, which covers the highest frequency band of the Atacama Large Millimeter/submillimeter Array (ALMA) and is recognized as the most difficult band in terms of superconducting technology, because the conventional superconducting material of Nb cannot be used for the circuitry in the mixer devices at the frequencies. The development began at the National Astronomical Observatory of Japan (NAOJ) in 2005, and the manufacturing and testing of all the receivers to be installed in the 66 Cassegrain reflector antennas that compose ALMA was completed in 2013. This enabled the terahertz frequency observations with the highest sensitivity from the ground. To meet the stringent ALMA requirements, terahertz SIS mixers with high‐quality superconducting NbTiN films were developed, which successfully demonstrated an unpreceded noise performance less than 230 K (5 times the quantum noise) for all the receivers. After the construction of ALMA, NAOJ began development studies for ALMA enhancement such as wideband and multibeam SIS receivers according to top‐level science requirements. To increase instantaneous bandwidth of the receivers, a submillimeter‐wave multiband receiver concept with a waveguide multiplexer, wideband intermediate frequency SIS‐mixer‐amplifier, and multifrequency local oscillator (LO) source is presented. The multibeam receiver employs a planar‐integrated SIS mixer circuit that includes all the RF components except the LO distribution network and an SIS‐mixer‐based amplifier of low power consumption, which is expected to enable the wide field‐of‐view observations in the future.
A total of 73 dual polarization superconductor-insulator-superconductor (SIS) receivers for the Atacama Large Millimeter/submillimeter Array (ALMA) have been successfully produced to observe astronomical signals in the 787-950 GHz frequency band. The receivers use two double sideband (DSB) waveguide mixers with Nb/AlOx/Nb tunnel junctions and NbTiN/SiO2/Al microstrip tuning circuits on quartz substrate. The best achieved DSB receiver noise temperature is 125 K, corresponding to about 3 hf/kBfor 4 K operation.
The Atacama Large Millimeter Array (ALMA) is the largest radio astronomical enterprise ever proposed. When completed, each of its 64 constituting radio-telescopes will be able to hold 10 heterodyne receivers covering the spectroscopic windows allowed by the atmospheric transmission at the construction site, the altiplanos of the northern Chilean Andes. In contrast to the sideband-separating (2SB) receivers being developed at low frequencies, double-side-band (DSB) receivers are being developed for the highest two spectroscopic windows (bands 9 and 10). Despite of the well known advantages of 2SB mixers over their DSB counterparts, they have not been implemented at the highest-frequency bands as the involved dimensions for some of the radio frequency components are prohibitory small. However, the current state-of-the-art micromachining technology has proved that the structures necessary for this development are attainable. Here we report the design, modeling, realization, and characterization of a 2SB mixer for band 9 of ALMA (600 to 720 GHz). At the heart of the mixer, two superconductor-insulator-superconductor (SIS) junctions are used as mixing elements. The constructed instrument presents an excellent performance as shown by two important figures of merit: noise temperature of the system and side band ratio, both of them within ALMA specifications.
In this paper, we report on the design and experimental results of a fix-tuned Superconductor-Insulator-Superconductor (SIS) mixer for Atacama Large Millimeter/submillimeter Array (ALMA) band 8 (385-500 GHz) receivers. Nb-based SIS junctions of a current density of 10 kA/cm/sup 2/ and one micrometer size (fabricated with a two-step lift-off process) are employed to accomplish the ALMA receiver specification, which requires wide frequency coverage as well as low noise temperature. Parallel-connected twin junctions (PCTJ) are designed to resonate at the band center to tune out the junction geometric capacitance. A waveguide-microstrip probe is optimized to have nearly frequency-independent impedance at the probe's feed point, thereby making it much easier to match the low-impedance PCTJ over a wide frequency band. In addition, a superconducting magnet fixed onto the compact mixer block to provide efficient magnetic field coupling is designed. The SIS mixer demonstrates a minimum double-sideband receiver noise temperature of 108 K at the band center and temperatures of less than 167 K over the whole band (for an intermediate-frequency range of 4-8 GHz).
We present the design and preliminary experimental results of superconductor-insulator-superconductor (SIS) mixers for Atacama large millimeter array (ALMA) band 10 (780-950GHz) receivers. To achieve wide frequency coverage as well as low noise temperature, we integrated high current density (10 kA/cm2) and small-sized (one micrometer in diameter) Nb/AlOx/Nb SIS junctions with a tuning microstrip line using NbTiN ground plane and Al wiring layers. High quality NbTiN films with Tc reaching 14.5 K and Al films with residual resistivity ratio as large as 15 have been achieved. To minimize the waveguide transmission loss and facilitate the fabrication of mixer block, a full height waveguide was adopted. The waveguide probe was optimized to achieve low input impedance in the frequency range of 780-950 GHz while adopting a backshort cavity of zero depth. Preliminary RF testing with a Nb/Al microstrip tuning circuit demonstrated a DSB receiver noise temperature about 400 K at 832.5 GHz, which promises the accommodation of receiver performance in ALMA specification with low loss NbTiN/Al microstrip lines.
Abstract The Atacama Large Millimetre/Sub-millimetre Array (ALMA) wideband sensitivity upgrade (WSU) project marks the next milestone in the development of millimetre (mm) and sub-mm astronomy. In this paper, we present the design, optimisation, and performance analysis of the ALMA Band-9 superconductor-insulator-superconductor (SIS) mixer for applications in the upcoming WSU programme, and other high-frequency astronomical observations. The mixers feature a niobium radial-rectangular probe antenna integrated with a silicon-on-insulator (SOI) substrate, which ensures minimal RF power leakage and optimised power coupling. We base our mixer design on conventional aluminium oxide (AlO x ) tunnel junction technology, with a critical current density of about 10 kA cm−2. We explore the impact of different junction sizes on the radio frequency (RF) and intermediate frequency (IF) bandwidths. We demonstrate that the new mixer design is capable of meeting the more stringent sensitivity-bandwidth requirements of the ALMA-WSU programme over the original Band-9 frequency range (602–720 GHz), as the IF bandwidth performance reaches up to 20 GHz. The IF bandwidth improvement is approximately double that of the current existing ALMA Band-9 mixers. These results suggest that our mixer designs provide a promising solution for future ALMA upgrades and other high-frequency applications requiring broad RF and IF bandwidth.