A Thermal Kinetic Inductance Detector Pixel Design for CMB Polarization Observations at 90/150 GHz Bands

The highly sensitive millimeter-wave telescope is an important tool for accurate measurement of cosmic microwave background (CMB) radiation, and its core component is a detector array located in a cryogenic focal plane. The feasibility of utilizing thermal kinetic inductance detectors (TKIDs) for CMB observations has been demonstrated. We propose a pixel design of TKIDs for observing CMB through atmospheric windows for observations in the 90/150 GHz bands. The TKIDs are designed to achieve photon noise limited sensitivity with overall noise equivalent power can be less than 20 aW/ \(\sqrt{\textrm{Hz}}\) $\sqrt{\text{Hz}}$ . Silicon-rich silicon nitride is used as the dielectric of TKIDs, and Al is used as the inductance material. Two pairs of probes are designed on the pixel to divide the signal into two polarization directions. Orthogonal transducer and diplexer are used for signal conversion and frequency division. Assuming lossless dielectric, the coupling efficiency of a single pixel is around 90%. This pixel design will be utilized for future large-scale TKIDs array designs for CMB observations.