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A total of 73 dual polarization superconductorinsulator-superconductor (SIS) receivers for the Atacama Large Millimeter/submillimeter Array (ALMA) have been successfully produced to observe astronomical signals in the frequency band of 787-950 GHz. For the mass production of waveguide SIS mixer chips used in the receivers, we have tested two different compositions of Nb 1−x Ti x N thin films for use in the mixer's superconductor low-loss transmission lines. These components are being fabricated for mass-produced waveguide SIS mixer chips in receivers. One composition was prepared by employing a sputtering target with 20 wt.% Ti and 80 wt.% Nb (x = 0.2), and the other was prepared with a target composed of 30 wt.% Ti and 70 wt.% Nb (x = 0.3). Both films are deposited using dc magnetron sputtering on quartz substrates. We found that the ratio between the superconducting energy gap and the critical temperature (2Δ/k B T C ) of the Nb 0.8 Ti 0.2 N films is larger than that of the Nb 0.7 Ti 0.3 N films. Since we obtained better sensitivities in the SIS mixers using the Nb 0.8 Ti 0.2 N films, they were used to produce all the receivers. These showed excellent performance complying with the stringent ALMA specifications.

Context. The Atacama Large Millimeter/submillimeter Array (ALMA) has been in operation since 2011, but it has not yet been populated with the full suite of its planned frequency bands. In particular, ALMA Band 2 (67-90 GHz) is the final band in the original ALMA band definition to be approved for production. Aims. We aim to produce a wideband, tuneable, sideband-separating receiver with 28 GHz of instantaneous bandwidth per polarisation operating in the sky frequency range of 67-116 GHz. Our design anticipates new ALMA requirements following the recommendations of the 2030 ALMA Development Roadmap. Methods. The cryogenic cartridge is designed to be compatible with the ALMA Band 2 cartridge slot, where the coldest components -the feedhorns, orthomode transducers, and cryogenic low noise amplifiers -operate at a temperature of 15 K. We use multiple simulation methods and tools to optimise our designs for both the passive optics and the active components. The cryogenic cartridge is interfaced with a room-temperature (warm) cartridge hosting the local oscillator and the downconverter module. This warm cartridge is largely based on GaAs semiconductor technology and is optimised to match the cryogenic receiver bandwidth with the required instantaneous local oscillator frequency tuning range. Results. Our collaboration has resulted in the design, fabrication, and testing of multiple technical solutions for each of the receiver components, producing a state-of-the-art receiver covering the full ALMA Band 2 and 3 atmospheric window. The receiver is suitable for deployment on ALMA in the coming years and it is capable of dual-polarisation, sideband-separating observations in intermediate frequency bands spanning 4-18 GHz for a total of 28 GHz on-sky bandwidth per polarisation channel. Conclusions. We conclude that the 67-116 GHz wideband implementation for ALMA Band 2 is now feasible and that this receiver provides a compelling instrumental upgrade for ALMA that will enhance observational capabilities and scientific reach. 1 https://www.almaobservatory.org of construction. Recent technological developments in cryogenic monolithic microwave integrated circuits (MMICs) and optical components, such as wide bandwidth feedhorns, orthomode transducers (OMT), and lens designs -have opened up the opportunity to extend the originally-planned radio-frequency (RF) bandwidth of this receiver, to cover the 67-116 GHz frequency range on-sky with a single receiver. This holds the potential for combining ALMA Band 2 (67-90 GHz) with ALMA Band 3 (84-116 GHz), serving as an upgrade that paves the way for wider bandwidth ALMA operations. As discussed in Mroczkowski et al. 2019a, this approach offers several opera-Article number, page 1 of 23

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