W-band Lumped Element Kinetic Inductance Detector Array for Large Ground-Based Telescopes

We describe the development of a W-band lumped element kinetic inductance detector array for application in large ground-based telescopes, like the Sardinia radio telescope. Based on the previous studies, we use a Ti/Al bi-layer film (10 nm thick Ti + 25 nm thick Al) for the resonators, to cover frequencies greater than 65 GHz. Optical simulations have been performed using ANSYS HFSS software suite, to optimize the absorber geometry, the illumination configuration, and the thickness of the dielectric substrate. Simulations suggest that the best geometry of the absorber is a front-illuminated third-order Hilbert curve, with a Si substrate 235μm thick, coupled to a single-mode circular waveguide. Electrical simulations have been performed using SONNET, to complete the design of the detectors by choosing the size of the capacitor, the bias coupling, and the feedline. In addition, the electrical simulations allow us to verify the lumped condition, to tune the feedline impedance and resonant frequencies, to constrain the coupling quality factor, and to minimize the electrical cross-talk between different pixels of the same array.