Sensitivity Optimization of Millimeter/Submillimeter MKID Camera Pixel Device Design

Abstract

We are using Microwave Kinetic Inductance Detectors in a sub/millimeter camera for the Caltech Submillimeter Observatory. These detectors are microwave resonators that rely on submillimeter and millimeter-wave photons to break Cooper pairs, changing the surface impedance. This changes the resonator frequency and quality factor, Q, and is measured by probe signals sent through a feedline coupled to the detectors. The camera will be divided into 16 independent readout tiles, each of which will fit 144 resonators at different frequencies into 360 MHz of bandwidth. We discuss the effect of readout power and single pixel frequency responsivity on the NEP of the detectors. Finally, we consider the mapping speeds of a full tile as a function of Q, which is controlled through the detector volume. A lower Q at fixed optical power implies greater responsivity, while a higher Q decreases the collision probability - the likelihood that any two resonators will have close enough resonant frequencies for crosstalk to be unacceptably high. We find the optimal design based on these constraints, and the corresponding mapping speeds expected at the telescope.