Design and Fabrication of the KID-Based Light Detectors of CALDER

Abstract

The goal of the Cryogenic wide-Area Light Detectors with Excellent Resolution project is the development of light detectors with large active area and noise energy resolution smaller than 20 eV RMS using phonon-mediated kinetic inductance detectors. The detectors are developed to improve the background suppression in large-mass bolometric experiments such as CUORE, via the double read-out of the light and the heat released by particles interacting in the bolometers. In this work, we present the design and the fabrication process, starting from the silicon wafer arriving to the single chip. The Al thin films (40 nm) are evaporated on high-quality, high-resistivity (>$10\,\mathrm{k \Omega }\,$cm) Si(100) substrates using an electron beam evaporator in a high-vacuum chamber. Detectors are patterned in direct-write mode, using electron beam lithography , positive tone resist poly-methyl methacrylate and lift-off process. Finally the wafer is diced into 20 $\times$ 20 mm$^2$ chips and assembled in a holder OFHC copper (oxygen-free high conductivity) using PTFE supports.