Millimeter-Wave Polarimeters Using Kinetic Inductance Detectors for TolTEC and Beyond

TL;DR

This paper details the development of large-scale, polarization-sensitive MKID arrays for millimeter-wave astronomy, specifically for the TolTEC polarimeter, enabling advanced cosmological observations with over 7,000 detectors on a 150 mm silicon wafer.

Contribution

It introduces the first deployment of MKID arrays on monolithic 150 mm silicon wafers and describes their design, fabrication, and performance for millimeter-wave polarimetry.

Findings

Successful fabrication of prototype MKID devices operating at 1.1 mm

Measured optical performance matches model predictions

Demonstrated scalable design for large detector arrays

Abstract

Microwave Kinetic Inductance Detectors (MKIDs) provide a compelling path forward to the large-format polarimeter, imaging, and spectrometer arrays needed for next-generation experiments in millimeter-wave cosmology and astronomy. We describe the development of feedhorn-coupled MKID detectors for the TolTEC millimeter-wave imaging polarimeter being constructed for the 50-meter Large Millimeter Telescope (LMT). Observations with TolTEC are planned to begin in early 2019. TolTEC will comprise $\sim$7,000 polarization sensitive MKIDs and will represent the first MKID arrays fabricated and deployed on monolithic 150 mm diameter silicon wafers -- a critical step towards future large-scale experiments with over $10^5$ detectors. TolTEC will operate in observational bands at 1.1, 1.4, and 2.0 mm and will use dichroic filters to define a physically independent focal plane for each passband, thus allowing the polarimeters to use simple, direct-absorption inductive structures that are impedance matched to incident radiation. This work is part of a larger program at NIST-Boulder to develop MKID-based detector technologies for use over a wide range of photon energies spanning millimeter-waves to X-rays. We present the detailed pixel layout and describe the methods, tools, and flexible design parameters that allow this solution to be optimized for use anywhere in the millimeter and sub-millimeter bands. We also present measurements of prototype devices operating in the 1.1 mm band and compare the observed optical performance to that predicted from models and simulations.