W. Jutzi

Measured performance parameters of gradiometers with digital output

A planar first-order gradiometer and a DC SQUID (superconducting quantum interference device) comparator have been integrated on the same 6*6 mm/sup 2/ chip in Nb-Nb/sub 2/O/sub 5/-PbInAu technology and operated in a flux-locked loop. Owing to the digital gradiometer output, a very low flux noise of 7*10/sup -7/ phi /sub 0// square root Hz, a coupled noise energy of 34 times Plancks constant h, and a gradient noise of 3.8 pT/m square root Hz have been achieved in the white noise region above about 60 Hz. In spite of the very low flux noise, a maximum slew rate of 1.5*10/sup 5/ phi /sub 0//s at a signal frequency of 4 kHz has been measured. A simple modulation scheme has been developed to cancel Josephson junction critical-current fluctuations, yielding 4.5*10/sup -6/ phi /sub 0// square root Hz at 0.1 Hz. >

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 .

An HTS narrow bandwidth coplanar shunt inductively coupled microwave bandpass filter on LaAlO/sub 3/

Coplanar waveguide bandpass filters with shunt inductively coupled resonators using high-temperature superconductors (HTSs) on LaAlO/sub 3/ substrates were developed for high packing density, narrow bandwidth, and low power applications. The computer-aided design and measurements on resonators to test weak end-coupling are described in this paper. A coplanar three-pole Chebychev bandpass filter with 1.8% 3-dB bandwidth at 10 GHz and 1.3-dB insertion loss at 77 K was fabricated and measured. The maximum superconducting current density of the filter is evaluated.

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.

Experimental SFQ interferometer shift register prototype with Josephson junctions

A shift register prototype has been implemented with lead-alloy technology. Single-flux quanta have been shifted in both directions by local magnetic fields with a maximum repetition frequency of 250 MHz. The absence or presence of a flux quantum at a given position is read out nondestructively. The speed and the miniaturisation potential of the proposed shift register is discussed.

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.

A low power 12 bit flux shuttle shift register with Nb technology

A 12 bit Flux Shuttle shift register with a new write and readout gate has been simulated and fabricated using Nb/Al/sub 2/O/sub 3//Nb Josephson junctions. Write, shift and read operations have been tested successfully at 4.2 K. Drive currents are independent from input bit sequence. Although measurements were disturbed by trapped flux, minimum margins are /spl Delta/I=/spl plusmn/10%. The power dissipation of a shift register cell is 9 nW/GHz. Total power losses caused by terminating resistors are 70 /spl mu/W. The minimum line width may be scaled down to 0.5 /spl mu/m, because power losses per unit area of long Flux Shuttle shift registers are extremely low.

High slew rate gradiometer prototype with digital feedback loop of variable step size

Abstract A gradiometer with two 31 mm 2 pick-up coil areas, a 12 mm baseline and a digital output signal has been built into a NbPb In Au system on a single 6 × 18 mm 2 chip, the measured white magnetic flux and field noise are below 1 μΦ 0 Hz − 1 2 and 0.4 pT m −1 Hz − 1 2 , respectively, at 1 kHz for a clock frequency of 18 MHz in a digital flux locked loop operation with a 12 bit counter of constant step size. With a digital feedback of variable step size and a 50 MHz clock frequency a maximum slew rate of 2 × 10 6 Φ 0 s −1 has been achieved with a signal frequency of 7.5 kHz.