Modification of the Metallic Magnetic Calorimeter Fabrication Process for High Production Yield

Abstract

We have modified the fabrication processes of metallic magnetic calorimeters (MMCs) to improve production yield. Key modifications include (i) the stress mitigation of the sputtered Nb film by optimizing the Argon deposition gas pressure, (ii) an optimized SiO\(_{\hbox {x}}\) insulator layer fabrication by switching from a lift-off to a wet-etching method and controlling the optimizing the temperature, (iii) the joint electroplating of thick gold structures for persistent current switch leads and a thermalization layer, and (iv) a reduced sputter-deposition time of the Ag:Er sensor material by introducing a new wafer holder. These modifications contribute to increased production yield, reduced fabrication time, and enhanced overall performance. Tests on MMCs fabricated with these modifications demonstrated uniformly improved critical current of the Nb meander coils, enhanced SiO\(_{\hbox {x}}\) insulation properties, strengthened persistent current switch systems, and reduced probability of Ag:Er oxidation. These modified MMC detectors also functioned well in tests for alpha spectrometry measurements, demonstrating good performance.