Development of mm-wave sensors for measurements of the Cosmic Microwave Background

In the process of developing superconducting sensor technology for the next generation of Cosmic Microwave Background (CMB) experiments, we have been working on a design that couples the CMB signal from a microstrip antenna to transition edge sensors (TES). In our detector design, the signal from the microstrip antenna is split into passbands centered at 95 GHz, 150 GHz and 220 GHz [1,2], and is then routed to different transition edge sensors. Making this possible in a compact topology requires crossover structures that isolate the high frequency superconducting lines from each other. Here, we will discuss the design optimization that replaces these superconducting cross-over structures with ground layer embedded cross-under structures. This change reduces the number of required depositions and circumvents liftoff issues associated with cross-over structures. In doing so, we had to ensure no cross talk in the high frequency lines, confirmed by HFSS simulation results. [1] C. M. Posada et al., Supercond. Sci. Technol. 28, 94002 (2015), [2] J. Ding et al., IEEE Trans. Appl. Supercond. 27, 2100204 (2017)