Fabrication of Nb Superconducting Nanowires by Nanoimprint Lithography

Abstract

Nanoimprint lithography (NIL) is an attractive nonconventional lithographic technique in the fabrication of superconducting nanowires for superconducting nanowire single-photon detectors (SNSPDs) with large effective detection areas or multi-element devices consisting of hundreds of SNSPDs, due to its low cost and high throughput. In this work, NIL was used to pattern superconducting nanowires with meander-type structures based on ultra-thin (~4 nm) Nb films deposited by DC-magnetron sputtering at room temperature. A combination of thermal-NIL and UV-NIL was exploited to transfer the meander pattern from the imprint hard mold to Nb films. The hard mold based on Si wafer was defined by e-beam lithography (EBL), which was almost nonexpendable due to the application of IPS ® as a soft mold to transfer the pattern to the imprint resist in the NIL process.The specimens fabricated by NIL keep good superconducting properties which are comparable to that by conventional EBL process.

Dimensional crossover and incipient quantum size effects in superconducting niobium nanofilms

“…The 80 nm thick film (#6), being least resistive of those measured, exhibits a room temperature (R.T.) value of ρ ( T ) ≈ 20 μ Ω cm, approaching the Nb bulk value (15 μ Ω cm) 18 , 19 . Lowering of the resistivity with thicker d suggests a gradual reduction of the film defectivity, in accordance with the behavior reported for Nb films by other groups 20 – 22 . For K, the ρ ( T ) shows a plateau, due to the residual defects in the nanofilm (the nature and the influence of which will be discussed later).…”

“…Zhao et al . 20 reported a rapidly rising Δ T C for d < 30 nm, with multiply larger values than those measured in our films with comparable thickness (Fig. 5 ).…”

“…For comparison, we have added data from: Zhao et al . (squares) 20 ; Gubin et al . (diamonds) 22 ; Delacour et al .…”

“…What is then the reason for observed lower T C values for d < 17 nm than was the case in ref. 20 ? This is likely an unwanted contribution from an oxidized Nb (i.e.…”

Substrate induced proximity effect in superconducting niobium nanofilms

“…The width of the superconducting transition, ∆T C , also exhibits an increasing trend from 15 mK at 80 nm to 80 mK for 10 nm films (Figure 2b). While ∆T C in our samples show lower values compared to those reported in the literature, suggesting a relatively higher quality films [21], the transition width of the Nb films on sapphire are relatively lower.…”