Scaling astronomical detectors and quantum devices to larger and larger sizes will require more readout lines. A problem with extra readout lines is the complexity and cost of many coaxial cables in parallel. Furthermore, the thermal loading on the coldest stages via thermal conductivity should be kept at a minimum. Delft circuits provides an eight-channel flexible cabling solution based on stripline technology with Ag or NbTi conductors and polyimide dielectric (flexline) as a solution to these problems. However, a compact and light-tight flex-to-chip interface is lacking, and this would be key to unlocking its full scaling and lightweight potential. Here, we present the design and measurements of a flexline to PCB interface for cryogenic detectors. The flexline is connected securely via a spring-loaded pressing tool, ensuring reliable contact even after thermal contraction. To reduce stray radiation, the chip and connector assembly sits in a light-tight setup. The connector spans a width of 20 mm along one edge of the chip, illustrating the compact design. We show that the flexline connector has an insertion loss of -2 dB at 7 GHz using a probe measurement at room temperature. We also demonstrate the connector with a test chip with kinetic inductance detectors in a dilution refrigerator cooled to 40 mK.

Studying the polarization and spectral distortion of the cosmic microwave background (CMB) in tandem with intensity fluctuations of the cosmic infrared background allows us to verify our assumptions on cosmic inflation and investigate the dynamics and evolution of galaxy clusters in the past 10 billion years. Because of its broadband emission and being an all-sky extended source, observing the entire CMB in detail is a very time-consuming and expensive exercise. Fortunately, in the past few years, the on-chip superconducting spectrometer technology has moved out of the lab and into the telescope. With its compact size and background-limited sensitivity, this family of instruments is particularly well-suited for fast and large area observations in a relatively unexplored range of the electromagnetic spectrum. However, recent examples of this technology do not yet reach the requirements needed for large spectroscopic and polarimetric surveys of the CMB. We formulate several of these requirements and introduce novel on-chip components and fabrication techniques. We introduce a crossover to enable distinguishing signal polarization, minimize signal loss by locally optimized lithography of a coplanar waveguide, lower the spectral resolution of microstrip filters by deposition of a dielectric layer, and increase the yield of the spectrometer array by removing individual line shorts. These together have culminated in the successful fabrication of a 14-spaxel integral field unit.

In this article, the wrong figure appeared as Figures 1 and 2; the figure should have appeared as shown below Figure 1 (right side of the figure only): (Figure presented.) Figure 2: (Figure presented.)