High-density photon-noise-limited multi-octave submillimeter kinetic inductance detectors for the Prime-Cam 850 GHz module

The Prime-Cam instrument is a first generation instrument under development for the 6-m Fred Young Submillimeter Telescope (FYST), which will be sited on Cerro Chajnantor in the Chilean Atacama Desert at an elevation of 5600 m. Among the instrument modules planned for the Prime-Cam instrument, the 850 GHz module is the highest frequency and of particular importance to the astronomical community due to the absence of near-future proposals for instruments at similar wavelengths and at equivalent sites. Success of the 850 GHz module hinges on the development of state-of-the-art detector arrays. The 850 GHz module will consist of approximately 45,000 titanium-nitride, polarization-sensitive, lumped-element kinetic inductance detectors, meaning the module will field more microwave kinetic inductance detectors than any other millimeter-wave receiver to date. The detectors are being designed to be read out using a multi-octave readout architecture, allowing for approximately double the multiplexing of other CCAT modules. We present the parameter space explored in the development of these detectors, including testing a means of shorting inductors to modify the resonance with minimal changes to the absorber architecture and testing different volumes of the inductor. Results and optical characterization of the prototype pixels for the 850 GHz instrument module are presented. The 850 GHz module is expected to be observing in 2026.