Niobium nitride-based normal metal-insulator-superconductor tunnel junction microthermometer

Abstract

We have successfully fabricated micron-scale Cu-AlO${}_x$-Al-NbN normal metal-insulator-superconductor (NIS) tunnel junction devices, using pulsed laser deposition (PLD) for NbN film growth, and electron-beam lithography and shadow evaporation for the final device fabrication. The subgap conductance of these devices exhibit a strong temperature dependence, rendering them suitable for thermometry from $\sim$ 0.1 K all the way up to the superconducting transition temperature of the NbN layer, which was here $\sim 11$ K, but could be extended up to $\sim 16$ K in our PLD chamber. Our data fits well to the single particle NIS tunnel junction theory, with an observed proximised superconducting gap value $\sim$ 1 meV for a 40 nm thick Al overlayer. Although this high value of the superconducting energy gap is promising for potential electronic NIS cooling applications as well, the high value of the tunneling resistance inhibits electronic cooling in the present devices. Such opaque barriers are, however, ideal for thermometry purposes as self-induced thermal effects are thus minimized.

References in corpus (8)

• Micrometre-scale refrigerators
• Tunneling studies in a homogeneously disordered s-wave superconductor: NbN
• Observations and modeling of large area normal-metal/insulator/superconductor refrigerator cooling from 300 mK to below 100 mK
• Phonon cooling of nanomechanical beams with tunnel junctions
• On the correct formula for the lifetime broadened superconducting density of states
• Niobium nitride-based normal metal-insulator-superconductor tunnel junction microthermometer
• Sub-micron normal-metal/insulator/superconductor tunnel junction thermometer and cooler using Nb
• Effects of charging energy on SINIS tunnel junction thermometry

Cited by in corpus (11)

• Tunnel-Junction Thermometry Down to Millikelvin Temperatures
• Superconducting tantalum nitride-based normal metal-insulator-superconductor tunnel junctions
• Efficient thermionic operation and phonon isolation by a semiconductor-superconductor junction
• Fabrication of superconducting tantalum nitride thin films using infra-red pulsed laser deposition
• Niobium nitride-based normal metal-insulator-superconductor tunnel junction microthermometer
• Charge dynamics in quantum-circuit refrigeration: thermalization and microwave gain
• Electrical conductivity in extremely disordered molybdenum oxynitrides thin films
• Applications and non-idealities of submicron Al-AlOx-Nb tunnel junctions
• Optical and transport properties of NbN thin films revisited
• Superconducting tunnel junction fabrication on three-dimensional topography via direct laser writing
• Excess quasiparticles and their dynamics in the presence of subgap states