Fabrication of high-Tc superconducting hot electron bolometers for terahertz mixer applications

Abstract

Superconducting Hot Electron Bolometer (HEB) mixers are a competitive alternative to Schottky diode mixers or other conventional superconducting receiver technologies in the terahertz frequency range because of their ultrawide bandwidth (from millimeter waves to the visible), high conversion gain, and low intrinsic noise level, even at 77 K. A new technological process has been developed to realize HEB mixers based on high temperature superconducting materials, using 15 to 40 nm thick layers of YBa 2 Cu 3 O 7-(YBCO), sputtered on MgO (100) substrates by hollow cathode magnetron sputtering. Critical temperature values of YBCO films were found in the 85 to 91 K range. Sub-micron HEB bridges (0.8 µm × 0.8 µm) were obtained by combining electronic and UV lithography followed by selective etching techniques. Realization of YBCO HEB coupling to planar integrated gold antennas was also considered.

Fabrication and Characterization of Ultrathin PBCO/YBCO/PBCO Constrictions for Hot Electron Bolometer THz Mixing Application

“…This process, detailed in [14], has been utilized to make devices with YBCO films of various thickness values (12 to 40 nm), with nano-bridges exhibiting both width and length in the 0.5 to 1 range. It comprises the main following steps: -Initial patterning of the PBCO-YBCO-PBCO tri-layers using e-beam lithography to form narrow lines, in order to define the length of the nanobridge; -Xenon ion beam milling of these features; -Regular optical lithography to complete the definition of the micro-bridge structure.…”

Superconducting high-Tc hot electron bolometers used as THz mixers: Predicted performance by hot spot modeling

“…Villégier et al reported on YBCObased small constrictions [2], further characterized at 2.5 THz in direct detection [3]. In the meantime, first modeling of YBCO HEBs was performed with "0-D" or "point bolometer" thermal models (no spatial coordinate introduced) [4].…”