We have developed a dual-polarization receiver for Band 4 of the Atacama Large Millimeter/submillimeter Array (ALMA). Band 4, which covers the 125 to 163 GHz spectral window, is one of the ten bands that form the ALMA Front End. The Band 4 receiver consists of three elements: a warm optics, a cold cartridge assembly, and a warm cartridge assembly. The cold cartridge includes a feed horn, an orthomode transducer, sideband-separating (2SB) superconductor–insulator–superconductor mixers, cold intermediate frequency (IF) amplifiers, IF isolators, bias-protection circuit boards, and component interconnections. The IF bandwidth is 4–8 GHz. The first eight receivers manufactured as preproduction models have demonstrated excellent performance within the stringent ALMA requirements. Stable astronomical fringes and closure phase have been successfully achieved during field performance tests of the Band 4 receivers installed in the ALMA antennas. Our well-established Band 4 receivers will contribute to various fields of astronomical research, such as the detection of high-redshift galaxies, characterization of cold molecular medium in normal field galaxies, and astrochemistry including observations of deuterated species.
A novel flip-chip bonding (FCB) process was developed for improving the packaging of high frequency ICs operating at more than 10 GHz. This process, which uses multi-stacked p-Au bumps, a lower apparatus cost than that of the FCB process using PbSn bumps. Tests have confiied that the new FCB process is sufficiently reliable and that ICs made with this process has satisfactory high-frequency characteristics in IC operation of up to 15 GHz.
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