T.A. Scherer

Anisotropy on the a, b-plane of c-axis orientated almost twin-free YBCO films on NdGaO3

Abstract Thin YBCO films have been grown epitaxially on twin-free (001) NdGaO 3 substrates with off-axis DC magnetron sputtering at right angle from a stoichiometric target. The films are 200 nm thick and have c -axis orientation. A very small amount of a -axis orientated grains has been achieved. According to diffractometric measurements the a -axis of the major part of the YBCO film has only one common direction in the plane of the substrate. The critical temperature for zero DC resistance is T co = 88 K. The expected anisotropy of the specific resistances in the a , b -plane has been demonstrated with DC measurements. The ratio of the specific resistances in a - and b -direction is almost temperature independent between 110 K and room temperature. Ratios up to ϱ a ϱ b = 2.1 have been achieved. At 100 K the specific resistance in the direction of the b -axis is ϱ b ≈ 50 μΩ cm for a ratio ϱ a ϱ b = 2 .

In-situ low pressure oxygen annealing of YBa2Cu3O7−δ single- and multilayer systems

Abstract Optimized NdGaO 3 /YBa 2 Cu 3 O 7−δ multilayers grown by various techniques usually suffer from reduced superconducting transition temperatures due to oxygen deficiency in the superconducting layer. We examined different post-deposition processes for in-situ and ex-situ oxygen treatment of sputter-deposited YBa 2 Cu 3 O 7−δ single- and NdGaO 3 /YBa 2 Cu 3 O 7−δ bilayers. The only procedure which reproducibly recovered the superconducting properties for YBCO films covered with a dense NdGaO 3 top layer, was found to be a low-pressure procedure (typically T c ⩾ 90 K and values for the ratio of the resistivities at 300 K and 100 K of 3.2.

Measured temperature dependence of the intermodulation product of coplanar waveguides with s- and d-wave superconductors

Abstract The measured intermodulation product is compared with the calculation that follows the interpretation of the BCS-theory according to Dahm and Scalapino in postulating a specific current density and temperature dependence of the London penetration depth: λ(T,j)≈λ LT (T=0) 1−(T/T c ) 4 1−b Θ (T)(j/j c0 ) 2 −0.5 where j c0 is the current density at zero temperature and b Θ ( T ) the nonlinearity factor. A good agreement between calculated and measured values b Θ ( T ) is obtained if the theoretical d-wave temperature dependence is assumed for YBCO and s-wave behavior for niobium.

A NRZ-output amplifier for RSFQ circuits

Interfaces between RSFQ circuits in the Return-to-Zero (RZ) and semiconductor circuits in the Non-Return-to-Zero (NRZ) mode are developed for data transmission at about 10 GHz clock frequencies reducing the errors owing to a finite sampling jitter of conventional room temperature equipment. A prototype of a NRZ output interface with the Nb-Al/sub 2/O/sub 3/-Nb technology has been simulated, implemented and successfully tested at 100 MHz. The interface can easily be combined with a superconducting pulse amplifier for NRZ output signals in the range of several mV. Corresponding simulations and a layout of the amplifier are presented.

Off-axis sputtered Y1Ba2Cu3O7-δ films on NdGaO3

Abstract Y 1 Ba 2 Cu 3 O 7-δ films have been deposited in situ on twin-free NdGaO 3 (100) substrates at ≈ 750°C by off-axis sputtering from a stoichiometric target. Critical temperatures of 89 K, specific resistances at 100 K of ρ n (100) = 80 μ cm and ρ n (300)/ ρ n (100) ratios of ≈ 3.1 have been achieved. The extrapolated zero temperature specific resistance, ρ n (0) = 16 μΩ cm . The full width at half maximum of the (005) rocking curve, δψ = 0.14°. Only a small amount of 45° grain boundaries could be found ( κ 45 −3 ). The 10 GHz surface resistances (not yet optimized) are below 50 μΩ at 4.2 K and 375 μΩ at 77 K.

Normal and superconductor coplanar waveguides with 100 nm line width

High speed high package density integrated circuits require a hierarchy of interconnections with small and large cross sections where the smallest linewidth approaches the 100 nm range. Attenuation and delay of superconducting interconnections down to the order of the London penetration depth for 50 /spl Omega/ and higher characteristic impedances are compared with normal conducting ones near 20 GHz. Symmetrical coplanar waveguides with polycrystalline aluminum and niobium and c-axis oriented Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// on substrates with a dielectric constant of about 12 are chosen to demonstrate basic properties mainly at 77 K and 4.2 K. Simulated quality factors are checked by measurements down to 1000 nm line width.

Quality factor and intermodulation product of superconducting coplanar wave guides with slots in a DC magnetic field

Superconducting coplanar wave guides may easily be fabricated and combined with surface mounted semiconductor devices. The current density distribution is calculated to determine the microwave losses for different miniaturised cross sections and edge shapes. The calculated and measured quality factors are in good agreement at low power and zero external magnetic field perpendicular to the film. The influence of moats or slots in the CPW stripes on the measured quality factor and intermodulation product as a function of the external magnetic field is discussed in terms of critical superconducting current density.

Quality factors of coplanar niobium resonators on LaAlO3 substrates with different cross-sectional geometries

Quality factors of miniaturized 50Ω coplanar resonators with an inner conductor width of 52 μm and with sputtered niobium on low loss substrates in the order of 20,000 are achieved at 1.8 GHz and 4.2 K. They are investigated in dependence of the shapes of the stripe edges and of slots and stems in the inner and outer stripes. A good agreement between simulated and measured results is obtained.

Microwave resonances with partially untwinned YBCO films near 10 GHz

Partially untwinned YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) films on twin-free NdGaO/sub 3/-substrates have been fabricated by off-axis sputtering. The ratio of the a- and b-axis DC resistances is on the same order as untwinned crystals. The film DC resistances values differ by less than a factor of two from those of untwinned crystals. The surface resistance in the a- and b-direction near 10 GHz has been measured with only one parallel plate resonator of rectangular area. The anisotropy ratio of the surface resistance at 4.2 K is on the order of 1.9. The b-axis surface resistance at 10 GHz and 4.2 K is about 25 mu Omega .<<ETX>>

Step edge junctions on NdGaO3 substrates at 77 K

Abstract D.c. SQUIDS for liquid nitrogen operation are implemented with grain boundary Josephson junctions in off-axis sputtered Y 1 Ba 2 Cu 3 O x stripes at step edges in NdGaO 3 substrates. The special properties of the Josephson junctions due to the excellent lattice match between the orthorhombic substrate and the YBCO stripes are described. The SQUID has a flux modulation up to temperatures very close to the critical temperature of the YBCO stripes beyond the edge. At 77 K the maximum slope is d U /d Φ = 80 μ V Φ 0 −1 and the product of the critical current times the tunnel resistance is I C R N ≈ 40 μ V.