Gamma-ray transition edge sensor with a thick SiO2/SixNy/SiO2 membrane

Abstract

Thick membranes of the gamma-ray transition-edge sensor (γ-TES) generally exhibit great mechanical strength and can support a bulk metal absorber typical for γ-TES. However, for conventional silicon-nitride (SixNy) membranes, thermal conductance (G) is proportional to the thickness, indicating that thicker membranes provide larger thermal-fluctuation noise in TESs. We propose a thick-trilayer membrane consisting of the silicon oxide (SiO2), SixNy, and SiO2 layers. The SixNy layer accounts for 5.8 μm of the total 6.9 μm, and thus, it is expected to be hard compared with conventional SixNy membranes with a typical thickness below 1 μm. G of the trilayer membrane is characterized as a function of heat-transport distance (L), and the G-L relation follows that of the intermediate model between ballistic and diffusive transports. Resulting G of the thick-trilayer membrane is 1.1–1.7 nW/K, which is not far from the one reported by conventional SixNy membranes. Gamma-ray spectroscopy around 93 keV is carried out based on series biased 5-pixels TES. The best full-width-half-maximum energy resolution among all pixels under characterization is 43.1 ± 1.6 eV for 93-keV, which is close to the median value of a state-of-the-art 236-pixels γ-TES in the literature. The measured low-frequency noise can be represented by theoretical phonon noise and its excess component with the same order as conventional ones. The thick-trilayer membrane is demonstrated to be able to work without any problems in a γ-TES regime.