We have studied weak links and dc–SQUIDs made from pulsed laser deposited YBa2Cu3O7−δ thin films on Y–ZrO2 bicrystal substrates. The transport properties of the weak links were studied as a function of the misorientation angle (θ) between the two halves of the bicrystal and an exponential dependence of the weak link critical current density was observed for angles up to 40° at 77 K. Josephson effects with clear microwave and magnetic field responses were observed. An optimum dc–SQUID performance at 77 K was obtained for θ=32°. At this temperature, we achieved a periodic magnetic field response with a modulation depth of 12 μV.

Electromagnetic resonances along a YBazCu307 -& bicrystal grain boundary junction made it possible to determine the ratio between the barrier/boundary thickness and the relative dielectric constant ts/s" the London penetration depth A, L, and to estimate the surface resistance R, at the interfaces of the grains. From resonances at 256-638 GHz, their Q values, and the Stewart-McCumber parameter, we find ts/c, =0.4 nm, kt, 140+ 30 nm, and R, -20 mQ at f =280 GHz. This indicates that the bound-

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Superconducting Josephson junctions with high characteristic voltages (I c R n larger than 4 mV at 4.2 K) are fabricated by depositing YBa 2 Cu 3 O 7−x on tilted sapphire bicrystal substrates, where the tilting axis is along the grain boundary. The good junction quality and low microwave losses in sapphire gave high frequency response well into the THz region. High quality YBa 2 Cu 3 O 7−x epitaxial films were deposited on tilted sapphire substrates with CeO 2 buffer layers by pulsed laser deposition. YBaCuO films have smaller tilt angles, from 1.0°up to 10.3°, compared to inclination angles of the substrates from 1.5°to 13.6°. X-ray diffraction shows only a single orientation of the films in the a-b plane, as well as an absence of a-axis particles and outgrowths. Critical temperatures as high as T c = 88.5− 89.0 K and ⌬T c ഛ 1.5 K were obtained in all films. The grain boundary in a common high-T c superconducting junction is usually much less straight than in the in-plane rotated bicrystal substrate, depressing Josephson currents. The waviness of the artificial grain boundary in a tilted bicrystal film is three times less than in an in-plane (untilted) bicrystal. Tilted Josephson junctions of widths from 1.5 to 6 µm were tested at temperatures from 0.26 to 77 K. I c R n products as high as 4.5 mV were observed at T = 4.2 K. Shapiro steps were observed at voltages over 3 mV under 300 GHz irradiation. Josephson radiation from the tilted junction was measured at frequencies up to 1.7 THz by a cryogenic bolometer. Suppressing the critical current with a magnetic field can separate Josephson radiation and thermal radiation. A parabolic dependence of the response on bias voltage for thermal radiation corresponds to an increase of junction temperature from 260 mK at zero bias to 3 K at 1 mV bias.