Lateral Inverse Proximity Effect in Ti/Au Transition Edge Sensors

Abstract

We report measured T_c of superconducting Ti/Au bilayer strips with a width W varying from 5 to 50 µm. The strips were fabricated based on a Ti/Au bilayer that consists of a 41-nm-thick Ti layer to which a 280-nm-thick Au layer was added. We find that the T_c drops as W decreases and the declining trend almost perfectly follows T_c/ [mK] = - 738.4 [μ m] ²/ W²+ 91.0 , where T_c(W= ∞) of 91 mK is consistent with the intrinsic T_c of the bilayer. The result is interpreted as a consequence of the lateral inverse proximity effect originated in normal-metal microstructures, namely Au overhangs that exist at the edges of the Ti/Au bilayer. The T_c shift from the intrinsic T_c should be anticipated in addition to the longitudinal proximity effect from superconducting Nb leads when one designs Ti/Au TESs.