MgO Bicrystal Substrates Research Articles

Millimeter Wave Mixing Properties of EuBa 2Cu 3O 7-δ Bicrystal Grain Boundary Junction Arrays

We report the millimeter wave mixing properties of high-T c superconductor Josephson junction arrays using a waveguide-to-microstrip converter in the 100 GHz frequency range. The junction arrays consist of 3 weak links fabricated from EuBa2Cu3O7-δ thin films grown on an MgO bicrystal substrate. In these junction arrays, Shapiro steps are observed in the presence of 100 GHz irradiation at intervals of 3 times the fundamental step voltage. Millimeter wave mixing with an input local oscillator frequency of 99.142 GHz and an input signal frequency of 99.880 GHz is detected as the IF output at 738 MHz. The IF output power peaks at voltages corresponding to those of the dynamic resistance dV/ dI. A mixing conversion efficiency of -24.1 dB is obtained for a 3-junction array.

Josephson transport and crystallographic properties of Bi2Sr2CaCu2Oy junctions on (100) MgO bicrystal substrates

We report the Josephson effects of the grain boundary Bi2Sr2CaCu2Oy(2212) bicrystal junctions formed on (100)MgO bicrystal substrates with a misorientation angle of 24° by in situ coevaporation growth technique using molecular beam epitaxy (MBE). It is found that the 2212 film on MgO bicrystal substrate consists of the a−b twin structures by reflection high-energy electron diffraction (RHEED) observation. The atomic force microscope (AFM) observation at the 2212 bicrystal junction interface suggests that the actual junction boundary strongly deviates from the straight line geometry. These microscopic geometry effects are discssed with the observed Josephson effects.

Investigation of YBa/sub 2/Cu/sub 3/O/sub 7/ Josephson junctions on MgO bicrystal substrates

We report on the characterization of the dynamic (ac) properties of YBa/sub 2/Cu/sub 3/O/sub 7/ Josephson junctions on MgO bicrystal substrates with 24/spl deg/ angle. Shapiro steps have been measured in the frequency range 80-95 GHz. Measured current-voltage characteristics, as well as the dependence of Shapiro step height on microwave power, were compared to numerical simulations within the RSJ model including thermal noise. At 77 K, the junctions showed ideal RSJ behavior. The occurrence of half-integer Shapiro steps at lower temperatures could be explained by an inhomogeneous critical current density of the junctions yielding a dc SQUID-like behavior. A nonsinusoidal current-phase relation could be ruled out because of the periodicity of the half-integer steps.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Broadband detection properties of EuBa/sub 2/Cu/sub 3/O/sub 7-δ/ array junctions

We have fabricated EuBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// Josephson junction arrays of two different sizes to improve detection output and microwave coupling between junctions and an rf source. The arrays contain three weak link grain boundary junctions made on an MgO bicrystal substrate. It is demonstrated that both the junction array configuration and smaller junction size are effective in improving microwave coupling and hence in increasing the responsivity. The best responsivity obtained is 1085 V/W for broadband detection at 11.9 GHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Josephson effects in YBa2Cu3Oy grain boundary junctions on (100)MgO bicrystal substrates

The grain boundary YBa2Cu3Oy(YBCO) Josephson junctions are fabricated on (100)MgO bicrystal substrates with a misorientation angle of 24° and the microwave properties of Josephson effects are studied up to millimeter-wave range. Strong [100]//[010] and [010]//[100] in-plane orientations are observed at the junction interface of a YBCO film, whose microscopic geometries are discussed in connection with the observed Josephson effects. The directly observed maximum Josephson microwave self-radiation powers from the junction at receiver frequencies of fREC=22 GHz and 47 GHz are 3.2×10−12 W and 5.6×10−14 W, respectively. The observed characteristic voltage (Vc) is 4.4 mV, corresponding to the frequency of about 2 THz at 4.2 K.

YBCO DC SQUID on MgO bicrystal substrate with flux transformer

A superconducting quantum interference device (SQUID) was fabricated from a YBCO thin film on MgO