E. Crocoll

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. >

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.

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.

Superconductor-to-Semiconductor Interface Circuit for High Data Rates

We present a new kind of rapid-single-flux-quantum (RSFQ) output driver together with a pseudomorphic high electron mobility transistor (p-HEMT) amplifier both operating at liquid helium temperature. The passive interconnect including the interchip connection between the RSFQ output driver and the first transistor stage of the semiconductor amplifier is the key element for signal matching and was optimized for minimizing the reflections to the RSFQ circuit. The RSFQ output driver is based on a single-flux-quantum to dc converter and a voltage doubler. The circuit is realized in the Niobium based 1 kA/cm2 process of FLUXONICS Foundry and provides up to 438-muV output voltage. We demonstrate high-speed experiments of the output driver in combination with two different semiconductor amplifier circuits at liquid helium temperature. The output voltage of a 2-Gb/s data stream was measured to be about 3.5 mV.

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.

Parameter evaluation of asymmetric interferometers with two Josephson junctions

The essential magnetostatic parameters of asymmetric interferometers with two Josephson junctions must often be deduced from measured envelopes of all flux quantum states in the current plane. Diagrams are given for a graphical evaluation of parameters.

Cryogenic Semiconductor Amplifier for RSFQ-Circuits With High Data Rates at 4.2 K

The connection of RSFQ circuits with commercial room temperature electronics and amplifying SFQ pulses with high data rates require cryogenic interface amplifiers. Such amplifiers should provide extremely high bandwidth, low noise and low power consumption at the same time. Various hybrid amplifiers based on commercial p-HEMT transistors in an embedded microwave design were designed and characterized. Towards the p-HEMT transistor characterization at cryogenic temperature the biasing settings according to an optimum between voltage gain and low power consumption were determined. Thus a total power consumption of 2 mW and a voltage gain of 12 dB per single stage were achieved. For a preamplifier and an amplifier concept a multiple number of these stages were implemented in a microstrip and a coplanar transmission line design with a special matched interconnect taper towards the RSFQ components. Measurements of the amplifiers, the combination of an amplifier with a RSFQ circuit at 4.2 K showed their good performances without any disturbance of the RSFQ circuit. Due to the losses between the stages a total gain of 25 dB with a four stage amplifier was achieved; pulse rates went up to 3 Gb/s. The total power consumption was in the range of 8 mW. Further increase of data rates will be achieved by improving the matching between RSFQ output stage and amplifier.

An experimental Josephson interferometer memory cell for nondestructive read out

Abstract An interferometer memory cell with two unequal Josephson junctions for nondestructive read out of single flux quantum states has been implemented and tested successfully. The agreement between the measurements and computer simulations is very satisfactory.

Design and development of a cryogenic semiconductor amplifier for interfacing RSFQ circuits at 4.2 K

There is a great deal of interest in amplifiers with extremely high bandwidth, low noise and low power consumption which interface RSFQ circuits with commercial room temperature electronics or amplifying SFQ pulses. In this special application a hybrid amplifier should interface an RSFQ circuitry with a Josephson junction array quantizer chip (JA-Q) at 4.2 K. The input signal for the amplifier is generated by an RSFQ signal generator and the output signal fed-in to a Josephson array quantizer. A voltage gain of about 104 with a pattern frequency of 2 GHz for a good transfer of the SFQ pulses is required. Additionally, the JA-Q requires a high output current at low power consumption of the amplifier at the same time. Various hybrid amplifiers based on commercially available p-HEMT transistors in an embedded microwave design were designed and characterized. For the p-HEMT transistor characterization at cryogenic temperatures the biasing settings according to an optimum between voltage gain AV and low power consumption PV were determined. Thus a power consumption of PV = 2 mW and a voltage gain of about AV = 4 per stage were achieved. For a preamplifier and an amplifier concept a number of these stages were implemented in a microstrip and a coplanar transmission line design with a special matched interconnect taper towards the RSFQ components. Measurements of the amplifiers and the combination of the amplifiers and the JA-Q at 4.2 K showed their good performance without any disturbances of the quantized voltage steps.

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.