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

• Published in: Journal of low temperature physics 2018-12, Vol.193 (5-6), p.726-731
• Main Authors: Colantoni, I., Cardani, L., Casali, N., Cruciani, A., Bellini, F., Castellano, M. G., Cosmelli, C., D’Addabbo, A., Di Domizio, S., Martinez, M., Tomei, C., Vignati, M.
• Format: Article
• Language: English
• Subjects: Aluminum; Bolometers; Characterization and Evaluation of Materials; Condensed Matter Physics; Critical temperature; Detectors; Electron beam evaporators; Electron beam lithography; Energy resolution; Inductance; Ion etching; Low temperature physics; Magnetic Materials; Magnetism; Magnetron sputtering; Physics; Physics and Astronomy; Polymethyl methacrylate; Reactive ion etching; Sensors; Silicon substrates; Silicon wafers; State of the art; Thin films
• ISSN: 0022-2291; 1573-7357
• DOI: 10.1007/s10909-018-1905-4

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 (KIDs). The detectors are developed to improve the background suppression in large-mass bolometric experiments such as CUORE, via the double readout of the light and the heat released by particles interacting in the bolometers. In this work we present the fabrication process, starting from the silicon wafer arriving to the single chip. In the first part of the project, we designed and fabricated KID detectors using aluminum. Detectors are designed by means of state-of-the-art software for electromagnetic analysis (SONNET). The Al thin films (40 nm) are evaporated on high-quality, high-resistivity (> 10 kΩ cm) Si(100) substrates using an electron beam evaporator in a HV chamber. Detectors are patterned in direct-write mode, using electron beam lithography (EBL), positive tone resist poly-methyl methacrylate and lift-off process. Finally, the chip is diced into 20 × 20 mm 2 chips and assembled in a holder OFHC (oxygen-free high conductivity) copper using PTFE support. To increase the energy resolution of our detectors, we are changing the superconductor to sub-stoichiometric TiN (TiN x ) deposited by means of DC magnetron sputtering. We are optimizing its deposition by means of DC magnetron reactive sputtering. For this kind of material, the fabrication process is subtractive and consists of EBL patterning through negative tone resist AR-N 7700 and deep reactive ion etching. Critical temperature of TiN x samples was measured in a dedicated cryostat.