Enhancement of Optical Response in Nanowires by Negative-Tone PMMA Lithography

The method of negative-tone polymethyl methacrylate (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 5-nm-thick NbN film sputtered at 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.