YBCO grain boundary Josephson junction coupled with a slot dipole antenna for terahertz wave detectors

We examined terahertz wave detectors that used YBa₂Cu₃O_7−δ (YBCO) grain boundary Josephson junctions (GBJJs) coupled with a slot dipole antenna (SDA). The detectors consisted of a 220-GHz full-wavelength SDA patterned on a Au layer and a GBJJ patterned on an YBCO/bicrystal MgO film, which were separated by an insulating benzocyclobutene layer. The microbridge of the fabricated junction was 5-μm wide and was trimmed to 2 μm using an ultraviolet laser cutter to modify the junction parameters. The critical current I_C, normal resistance R_N, and I_CR_N product after the trimming at 30 K were 0.62 mA, 1.42 Ω, and 0.88 mV, respectively. The current-voltage characteristics and radio frequency (RF) wave responses of these detectors for a millimeter wave of 180-240 GHz were measured at 30 K. The coupling efficiency between the GBJJ and the SDA and the system sensitivity were obtained as −19.0 dB and 630 V/W, respectively, at 193 GHz. For the RF wave response of 180-240 GHz, the coupling efficiency was relatively flat.