  The method of negative-tone-PMMA electron-beam lithography is investigated to
improve the performance of nanowire-based superconducting detectors. Using this
approach, the superconducting nanowire single-photon detectors (SNSPDs) have
been fabricated from thick 5-nm NbN film sputtered at the room temperature. To
investigate the impact of this process, SNSPDs were prepared by positive-tone
and negative-tone-PMMA lithography, and their electrical and photodetection
characteristics at 4.2 K were compared. The SNSPDs made by negative-tone-PMMA
lithography show higher critical-current density and higher photon count rate
at various wavelengths. Our results suggest a higher negative-tone-PMMA
technology may be preferable to the standard positive-tone-PMMA lithography for
this application.
