Tolerance to deformation and flux pinning in superconducting amorphous molybdenum nitride thin films grown on flexible polyimide

Abstract

We investigate the superconducting properties of 80 nm thick amorphous MoNx films fabricated via reactive sputtering on silicon and flexible commercial polyimide substrates. The samples are grown at room temperature using reactive sputtering with a gas mixture of N2 and Ar. The mechanical deformation tolerance for films on polyimide is evaluated by comparing the superconducting critical temperature (Tc) and critical current density (Jc) when the films are attached to cooper surfaces with varying curvatures. The amorphous films exhibit a Tc of 8.2 K on silicon and 7.9 K on polyimide. Our results demonstrate a significant enhancement in flux pinning for the thin films grown on polyimide, with the Jc at self-field and 3 K increasing from approximately 0.5 MA/cm2 to around 1 MA/cm2. Analyses of Jc as a function of the magnetic field, angle, and temperature reveal that the films on polyimide exhibit remarkable resilience to deformation. Interestingly, comparable Jc values are observed when the samples are affixed to both flat and cylindrical surfaces with diameters of 2.5 cm. This observation suggests that vortex dissipation predominantly occurs through flux motion in the region experiencing the maximum Lorentz force. Furthermore, the films maintain Tc without any discernible changes in resistivity when fixed to cylindrical surfaces with 1.2 cm diameters. However, there is a significant drop in vortex pinning, indicating reduced pinning capability in the stressed regions. The high deformation tolerance of amorphous MoNx renders it highly suitable for cryogenic electronics applications, providing a viable alternative to the commonly utilized metallic Nb.