Development of Aluminum LEKIDs for Balloon-Borne Far-IR Spectroscopy

We are developing lumped-element kinetic inductance detectors (LEKIDs) designed to achieve background-limited sensitivity for far-infrared (FIR) spectroscopy on a stratospheric balloon. The spectroscopic terahertz airborne receiver for far-infrared exploration will study the evolution of dusty galaxies with observations of the [CII] 158 μ m and other atomic fine-structure transitions at z=0.5-1.5, both through direct observations of individual luminous infrared galaxies, and in blind surveys using the technique of line intensity mapping. The spectrometer will require large format (∼ 1800 detectors) arrays of dual-polarization sensitive detectors with NEPs of 1 × 10^{-17} W Hz^{-1/2}. The low-volume LEKIDs are fabricated with a single layer of aluminum (20-nm-thick) deposited on a crystalline silicon wafer, with resonance frequencies of 100-250 MHz. The inductor is a single meander with a linewidth of 0.4 μ m, patterned in a grid to absorb optical power in both polarizations. The meander is coupled to a circular waveguide, fed by a conical feedhorn. Initial testing of a small array prototype has demonstrated good yield and a median NEP of 4 × 10^{-18} W Hz^{-1/2}.