Temperature Effect on Selectivity of HTSC Josephson Junction Detector

The most sensitive THz detection is obtained with superconducting Josephson Junction (JJ) detectors, cooled by liquid helium. These detectors require complex cooling systems. JJ detectors implemented in High Temperature Superconductors (HTSC) are considered a viable and more applicable alternative. The frequency of the detected radiation is directly proportional to the voltage of the Shapiro steps. To investigate temperature dependence of the frequency selectivity, i.e., the accuracy of the measured voltage, we implemented JJs detectors in YBa2Cu3O7 HTSC thin films, patterned on MgO bicrystal substrate. We improved the detector sensitivity and reduced losses by placing the JJ between the ends of two strips integrated with the antenna, reducing the high mismatch between the impedance of the JJ and that of the Au bow-tie planar antenna. The detector parameters were determined by extensive simulations. High correlation was obtained between the simulations and the experimental results. Error in the measured V DC, hence in the radiation frequency, was 3.5-7% at 60-70 K, 3-4 orders of magnitude larger than that measured at 40-50 K, less than 0.01%, showing the very strong influence of temperature on the frequency selectivity of high temperature JJs detectors.