Large format arrays of kinetic inductance detectors for the TolTEC millimeter-wave imaging polarimeter (Conference Presentation)

Abstract

Microwave Kinetic Inductance Detectors (MKIDs) provide a technological path towards the high-yield, large-format detector arrays needed for the next generation of experiments. The intrinsically integrated readout components of MKIDs generally give rise to high multiplexing factors, simplified assembly, and streamlined experimental integration. We describe the first MKID arrays fabricated and tested on monolithic 150 mm diameter silicon substrates – a crucial scaling in fabrication capacity that is necessary for future large-scale experiments aiming to incorporate hundreds of thousands of detectors in the coming years. The arrays described here are being developed for the TolTEC millimeter-wave imaging polarimeter being constructed for the 50-meter Large Millimeter Telescope (LMT), with observations planned to begin in early 2019. TolTEC uses dichroic filters to define three physically independent focal planes for operation in observational bands centered at 1.1, 1.4, and 2.0 mm. Each focal plane observes in just one wavelength band, allowing the use of simple to produce, direct-absorption pixel designs with each pixel comprising two detectors that are sensitive to orthogonal states of linear polarization. TolTEC comprises approximately 7,000 polarization sensitive MKIDs designed to operate at a base temperature of 100 mK. The primary working material used for these devices are TiN/Ti/TiN multilayer films, which have several advantageous qualities including: low two-level system noise at the TiN-silicon interface; linear responsivity; uniformity in deposition; and tunable transition temperature, sheet resistance and sheet inductance. We describe the detailed pixel and array layout designs, including focal plane integration and optical coupling via spline-profiled, silicon-platelet, feedhorn-coupled waveguide. We present measurements of full arrays and/or prototype small arrays of devices operating in each of the three observation bands and compare the observed noise and optical performance to that predicted from models and simulations. We also describe the fabrication methods used to produce these large-format arrays with high yield and uniformity.