New technology of high Tc superconducting hot electron bolometer for terahertz mixing

The recent rise of interest for imaging in the terahertz (THz) domain has started the research to any possible material property that could be useful for detection in this frequency range. Superconducting hot-electron bolometers (HEB) represent a very valuable alternative to the Schottky diode in the detection for frequencies exceeding 1 THz because of their wide bandwidth, high conversion gain, low intrinsic noise level, and for the possibility to use low local oscillator power for heterodyne detection. The high critical temperature materials, with respect to the low critical temperature ones, allow seeking ultra-wide instantaneous bandwidth applications requiring portability and closed-cycle refrigeration. The working principle of such devices require to reduce down to the nanometric scale the dimensions of the sensing bridge, which works as mixing element. To achieve this target, high-performance microelectronic technologies are required for ultrathin film deposition together with a combination of optical and e-beam lithography processes. We report on the fabrication and the characterization of high T_C HEB structures based on ultrathin PrBa₂C₃O_7-δ/YBa₂C₃O_7-δ/PrBa₂C₃O_7-δ films (20–45 nm) patterned in constrictions in the 0.8×0.8 to 0.45×0.45 μm² range.