Design of NbN Based Kinetic Inductance Detectors for Polarimetric Plasma Diagnostics

In this article, we present the design of a custom kinetic inductance detector (KID) tailored for polarimetric diagnostics of magnetically confined fusion plasma. The detector is of the lumped elements KID kind and is based on a crossed 2 × 2 pixel design for polarization sensitivity. Simulations have been performed to tune device parameters like resonance frequency, cross-talking and coupling with the microstrip feed line, taking into consideration the requirements of the final instrument and the field of application. The devices have been designed for optimal absorption at 1.3 THz, the chosen probing frequency for the final instrument, and they resonate in a range from 0.8 to 1.1 GHz. The characterization of the thin niobium nitride film and the first S $_{21}$ parameter measurements performed on patterned thin films deposited on 330 μm high resistivity silicon substrates are also presented.