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A superconducting quantum magnetometer for high-sensitivity applications has been developed by exploiting the flux focusing of the superconducting loop. Unlike conventional dc SQUID magnetometers that use a superconducting flux transformer or a multiloop design, in this case, a very simple design has been employed. It consists of a bare dc SQUID with a large washer-shaped superconducting ring in order to guarantee a magnetic field sensitivity BΦ less than one nT/Φ0. The degradation of the characteristics of the device due to an inevitable high value of the inductance parameter βL was successfully compensated by damping the inductance of the dc SQUID. The size of the magnetometer, coinciding with that of the washer, is 5 × 5 mm2 and the spectral density of the magnetic field noise is 8 fT/√Hz with a low frequency noise knee of two Hz. The excellent performance of this simple magnetometer makes it usable for all high-sensitivity applications including magnetoencephalography. [ABSTRACT FROM AUTHOR]

In this paper, we conducted the calculation of the critical current of DC SQUID based on the Josephson junction on a multi-band superconductor with frustration effect. It is shown that the critical current of DC SQUID on the frustrated multi-band superconductor with a small geometrical inductance of the loop is determined by the supercurrent amplitude in different channels and by the external magnetic field. In the case of a DC SQUID with high inductance, frustration effects can be ignored. [ABSTRACT FROM AUTHOR]

In this paper, we conducted the calculation of the critical current of DC SQUID based on the Josephson junction on a multi-band superconductor with frustration effect. It is shown that the critical current of DC SQUID on the frustrated multi-band superconductor with a small geometrical inductance of the loop is determined by the supercurrent amplitude in different channels and by the external magnetic field. In the case of a DC SQUID with high inductance, frustration effects can be ignored.

We have proposed a new design of the Josephson traveling-wave parametric amplifier (JTWPA) capable of providing much higher spurious-free dynamic range (SFDR). For this purpose, we substitute dc SQUIDs for bi-SQUIDs in the used artificial signal transmission line driven by external travelling-wave magnetic flux. The increase of SFDR follows from the increased linearity domain of the phase-current relation in bi-SQUID as compared to dc SQUID. Optimal parameters for bi-SQUIDs have been determined. The first version of JTWPA was modeled to be fabricated using niobium process. [ABSTRACT FROM AUTHOR]

It is known that SQUID has three important parameters, namely, Stewart-McCumber parameter βC, Screening parameter βL and thermal noise parameter Γ. They play a very important role in SQUID performance, especially βC. Recently, researchers extended the SQUID operating area to βc > 1 due to a large noise parameter Γ in experiments. When βC > 1, SQUID exhibits a large flux-voltage transfer coefficient ∂V/∂Φ, which is beneficial in reducing the noise contribution of the readout circuit δΦe. From the simulation results, we found that when βC>1, SQUID produces a larger ∂V/∂Φ than βC<1, and there was no hysteresis, at the same time, we also observed that ∂V/∂Φ increases with the decrease of βL. In order to further verify our findings, we selected two groups of SQUIDs for experiments (βC < 1, βC > 1), by changing the value of the shunt resistance on the Josephson junction to adjust the value of changing βC, and then we observe the value of ∂V/∂Φ. Finally, we find that when βL< 1, the flux-to-voltage transfer coefficient ∂V/∂Φ of SQUID increases while βC increasing. A large ∂V/∂Φ will help us to obtain an optimal SQUID measure system. [ABSTRACT FROM AUTHOR]

The development of superconductor integrated circuits (SCIC) places increasing demands on electronic design automation (EDA) tools. Circuit simulation is a crucial step in the design process of superconducting quantum interference devices (SQUID) and single flux quantum (SFQ) circuits. Over the years, there have been many SC circuit simulators, like JSPICE, JSIM, WRspice, JoSIM, PSCAN2, JSICsim, PrimeSim HSPICE, Spectre, and more. The previous studies have compared the differences in results among some simulators for the same circuit cases. However, designers of SC circuits still face challenges when choosing simulators and setting simulation parameters. The performance of these simulators lacks comprehensive and quantitative evaluations to date. To evaluate the performance of the simulators, we focused on three aspects: the differences among the IV results, accuracy, and speed. For characterizing the accuracy of the simulators, we proposed a method that uses the relative error between the numerical and analytical solutions at the L - C resonance point on the IV curve of a dc SQUID. In this article, we have selected five representative simulators JoSIM, JSIM, WRspice, PSCAN2, and JSICsim for our study. By using multiple cases of the bare and coupled dc SQUID, multiple IV curves, and the analytical solution as a reference, we comprehensively compared the performance of these simulators. Additionally, we quantitatively examined the impact of two key simulation parameters, namely, the maximum allowed simulation timestep (max timestep) and relative tolerance (RelTol), on the performance of these simulators. Our results show that the normalized voltage differences in the IV curves of different simulators are relatively small (within 0.06) in regions far from the L - C resonance point, while they increase significantly near the L - C resonance point (maximum is 0.4). PSCAN2 exhibits a significant relative error of approximately 16% when the max timestep is 0.6ps and RelTol is 1 × 1 0 − 1 , which is close to its default RelTol value. Our work provides some insights and references for the designers of SC circuits on how to choose simulators and set simulation parameters. • Comprehensively studied the performance of the five simulators (JoSIM, JSIM, WRspice, PSCAN2, and JSICsim) from three aspects: the differences among the IV results, accuracy, and speed. • Proposed a reliable method to characterize the accuracy of simulators by using the relative error between the numerical and analytical solutions at the L - C resonance point of the dc SQUID's IV curve. • Evaluated and compared the performance of simulators, and quantitatively examined the impact of simulation parameters (max timestep and RelTol) on the simulators' performance. [ABSTRACT FROM AUTHOR]

We carried out the analysis of the return current of dc SQUID based on tunnel Josephson junction with unconventional current-phase relation. We analyzed two cases of current-phase relation with additional terms to the first harmonic sin φ: a case of the second harmonic sin 2φ and the case of the fractional term sin (φ/2). It is shown that the changing of the return current of dc SQUID on junctions with unconventional current-phase relation is determined by the amplitude of the second term in current-phase relation, geometrical inductance, and external magnetic field. [ABSTRACT FROM AUTHOR]

We present a sensitive voltage amplifier suited for measurements of source impedances in the k Ω range at dilution refrigerator temperatures. The circuit is based on a commercial dc SQUID, an impedance matching transformer, and it works on the principle of negative feedback. At 10 mK, the amplifier contribution to the noise is only 17 pV/ Hz , which is negligible in comparison with the fluctuations of the thermal voltage of a 3.25 k Ω metallic source resistor. Various circuit parameters of the amplifier are discussed. [ABSTRACT FROM AUTHOR]

Here we present calculations of the critical current of dc SQUID based on Josephson junction with un-conventional current-phase relation. We analyzed two cases of current-phase relation of junction: with anhar-monic and Majorana term. It is shown that the changing of the critical current in the case of the small geo-metrical inductance of dc SQUID based on Josephson junctions with unconventional current-phase relation is determined by the amplitude of the second term in current-phase relation, the geometrical inductance of dc SQUID and external magnetic field. In the case of the high inductance of dc SQUID unconventional terms can be ignored. [ABSTRACT FROM AUTHOR]

MoRe–Si(W)–MoRe planar Josephson junctions with a hybrid barrier layer made of amorphous silicon doped with tungsten at relatively high tungsten concentrations (~ 11%) are experimentally studied. Small intrinsic (natural) capacitance and shunting by tungsten nanoclusters give an advantage to MoRe–Si(W)–MoRe junctions against traditional superconductor–insulator–superconductor (SIS) planar junctions as candidates for innovative superconducting electronics. It is shown that the use of such junctions with a Si(W) barrier layer thickness of 15–30 nm can substantially enhance the sensitivity of both RF and DC SQUIDs. [ABSTRACT FROM AUTHOR]

By defining the loop inductance for NQUID and considering sinusoidal Fourier series for the current-phase relations of its nanowires and replacing two Langevin equations with one two-dimensional Fokker-Planck equation, we have obtained analytical relations for the characteristics of the asymmetric NQUID. On the other hand for DC SQUIDs and nanoSQUID, we have to consider simultaneously the effects of the deviation of the current-phase relation from Is(θ)α sinθ , the effects of fluctuations and noises and also the effects of asymmetry (usually two junctions have some differences) on the current-voltage characteristic. Therefore various considerations necessitate more accurate analytical formulation and more theoretical predictions .

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Magnetic field fluctuations in our unshielded urban laboratory can reach hundreds of nT in the noisy daytime and is only a few nT in the quiet midnight. The field fluctuation causes the Larmor frequency f L to drift randomly for several Hz during the unshielded ultra-low field (ULF) nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) measurements, thus seriously spoiling the averaging effect and causing imaging artifacts. By using an active compensation (AC) technique based on the spatial correlation of the low-frequency magnetic field fluctuation, the field fluctuation can be suppressed to tens of nT, which is a moderate situation between the noisy daytime and the quiet midnight. In this paper, the effect of the field fluctuation on ULF MRI measurements was investigated. The 1D and 2D MRI signals of a water phantom were measured using a second-order low- T c superconducting quantum interference device (SQUID) in three fluctuation cases: severe fluctuation (noisy daytime), moderate fluctuation (daytime with AC) and minute fluctuation (quiet midnight) when different gradient fields were applied. When the active compensation is applied or when the frequency encoding gradient field G x reaches a sufficiently strong value in our measurements, the image artifacts become invisible in all three fluctuation cases. Therefore it is feasible to perform ULF-MRI measurements in unshielded urban environment without imaging artifacts originating from magnetic fluctuations by using the active compensation technique and/or strong gradient fields. [ABSTRACT FROM AUTHOR]

Abstract: Active electrically small superconductive antennas based on serial arrays of the cells capable of providing highly linear voltage response to magnetic signal were proposed and developed. Two different basic cells were devised. The first one is bi-SQUID, and the second one is the cell consisting of two parallel SQIFs connected in differential way. The antenna prototypes were designed, fabricated and evaluated. The mostly efficient antenna prototype occupied area of 3.3mm×3.3mm was characterized by the transfer factor dV/dB of about 750mV/mT and the transfer function linearity up to 70dB. [Copyright &y& Elsevier]

We fabricated a dc SQUID phase qubit with a sub-\mum Al/AlOx/\rm Al qubit junction and an interdigitated shunting capacitor on a sapphire substrate. The qubit junction had a critical current of 135 nA, and the isolation junction had a critical current of 8.3 \muA. The shunting capacitance was about 1.5 pF. To reduce the unwanted effects of two-level systems and increase the relaxation time T1, we have removed unnecessary dielectrics, used a small qubit junction area (450 nm \times 500 nm), isolated the qubit from the leads with an on-chip LC filter, and fabricated the device on a bare sapphire substrate. However, at a temperature of 20 mK, we found T1\approx 300\ ns and the coherence time T2\approx 110\ ns, which was much lower than one would expect from loss attributed to the leads and to dielectrics in the tunnel junction and substrate. Measurements of T1 versus applied flux (which tuned the qubit frequency) revealed a correlation between the strength of the coupling of the microwave excitation line to the qubit and the rate of energy dissipation in the qubit. This result suggests that the relaxation time was being limited by coupling to the microwave line. [ABSTRACT FROM AUTHOR]

We recently presented a direct readout technique for the dc Superconducting QUantum Interference Device (SQUID) without flux modulation (FM), operated in voltage bias mode, and named it the SQUID Bootstrap Circuit (SBC). The SBC combines additional voltage and current feedbacks to minimize the room-temperature preamplifier noise. The main point of this paper is to compare the flux noise performance of the SBC readout with that of the FM scheme using a sine wave modulation signal. Several liquid-helium-cooled SQUID magnetometers with different layouts and loop inductances were characterized using these two readout schemes. Measured noise was comparable to or even lower than that measured by FM electronics. Furthermore, the SBC noise performance was evaluated as function of resistance which, when properly adjusted, permits us to nearly fulfill the critical noise suppression condition. We believe SBC to be a promising candidate for multi-channel SQUID systems. [ABSTRACT FROM AUTHOR]

Abstract: This paper summarizes both theoretical and experimental studies aimed at synthesis of high-linearity multi-element Josephson structures. Both the dynamic range and the voltage response linearity are two conjugated characteristics that must be improved jointly. Increase in dynamic range is reasonably associated with increase of number of elements N in the Josephson-junction structures. To improve the voltage response linearity one can use special design of the array structures. The other way is based on use novel basic cell with is bi-SQUID capable of providing highly linear voltage response. Both the approaches were used in designs of the reported high-linearity multi-element Josephson structures. [ABSTRACT FROM AUTHOR]

Abstract: We consider an asymmetric two-junction superconducting quantum interference device, whose junctions are assumed to be overdamped, and regard Sin Fourier series for their current–phase relations. We take into account the effects of thermal fluctuations by forming a two-dimensional Fokker–Planck equation for the distribution function. We judge a series expansion of first order with respect to the components of the reduced inductance for distribution function and obtain current–voltage relation. We consider the measured resistance of the superconducting nanowire quantum interference device with mesoscopic leads that Hopkins et al. reported in Hopkins et al. [D.S. Hopkins, D. Pekker, P.M. Goldbart, A. Bezryadin, Science 308 (2005) 1762] and analyzed in Pekker et al. [D. Pekker, A. Bezryadin, D.S. Hopkins, P.M. Goldbart, Phys. Rev. B 72 (2005) 104517], by defining loop inductance, and by considering appropriate relations for resistance of nanowires. In fact we extend Chesca formulation [B. Chesca, J. Low Temp. Phys. 112 (1998) 165] simultaneously in three aspects and give a unified theory for nanowire two-junction devices, low T c and high T c DC SQUIDs, in restricted conditions. [Copyright &y& Elsevier]

We investigate critical current (Ic) modulation of stacked Josephson junctions (SJJs) dc superconducting quantum interference device (dc SQUID) on a Bi2Sr2CaCu2O8+δ (Bi-2212) whisker. A coupled SJJs with a completely perforated hole of 0.1 μm × 0.2 μm were fabricated by using a 3-D focused-ion-beam (FIB) etching method. Those dc SQUIDs exhibited uniform multi-branch structures and clearly oscillated critical current under external magnetic fields (He). With applying He, the clear periodic modulation patterns of Ic are obtained and well fitted to the calculated value from the loop area of 0.02 μm2. [ABSTRACT FROM AUTHOR]

We investigate critical current (Ic) modulation of stacked Josephson junctions (SJJs) dc superconducting quantum interference device (dc SQUID) on a Bi2Sr2CaCu2O8+δ (Bi-2212) whisker. A coupled SJJs with a completely perforated hole of 0.1 μm × 0.2 μm were fabricated by using a 3-D focused-ion-beam (FIB) etching method. Those dc SQUIDs exhibited uniform multi-branch structures and clearly oscillated critical current under external magnetic fields (He). With applying He, the clear periodic modulation patterns of Ic are obtained and well fitted to the calculated value from the loop area of 0.02 μm2. [ABSTRACT FROM AUTHOR]

We developed a multi-chip module (MCM) system of superconducting quantum bits with single-flux quantum (SFQ) interface circuits. The MCM system consists of chips with quantum bits and chips with SFQ circuits mounted on a base chip by flip-chip bonding (FCB) with superconducting solder. We report on a reliability test of the MCM system. The test was done using a resistance measurement of an MCM with 30 μm diameter bumps. Tested samples showed good durability against thermal cycles between room temperature and 4.2 K. At 4.2 K, the resistance measured through more than two hundred bumps in a series was less than 1 mΩ. Along with achieving a high reliability, reducing thermal interference from SFQ circuits to quantum bits is important. We must understand the thermal conductance between and within the chips to design a system with minimum interference. An MCM on-chip thermometer which is based on the Johnson noise thermometry, has been designed and fabricated to achieve this desired level. The preliminary results of the thermal measurement are reported. [ABSTRACT FROM AUTHOR]

We report on the first observation of clear voltage modulation in dc SQUID based on intrinsic Josephson junctions of Bi2Sr2CaCu2Oy. Stacked series array of intrinsic Josephson junctions and dc SQUID based on it have been made from Bi2Sr2CaCu2Oy single crystals using a double-side etching process. The number of junctions in the stack is rather controllable by monitoring the junction resistance at room temperature. The current-voltage characteristics of the SQUIDs with stacks of 20-50 IJJs at 4.2 K exhibit additional closely spaced branches together with typical multiple quasi-particle branches with voltage spacing of ∼20 mV. On applying magnetic field clear periodic modulation of the lowest critical current and voltage of the SQUID are observed and the flux period obtained from the voltage-flux characteristics agrees with one flux quantum. The maximum voltage modulation and transfer function are about 80 μV and 0.75 mV/Φ0 at 26 K, respectively. The property of dc SQUID with shunt resistances is also discussed. [ABSTRACT FROM AUTHOR]

We have fabricated a high-Tc electronic planar gradiometer composed of dc SQUIDs on a 10 mm × 10 mm SrTiO3 bicrystal substrate. The SQUIDs were patterned in a single-layer YBa2Cu3Oτ-δ thin film which is prepared by pulsed laser deposition. The outputs of the magnetometers are added and subtracted by analog electronic circuits to form the gradiometer. These magnetometers could be used to construct two sets electronic planar first-order gradiometers or an electronic planar second-order gradiometer, which could measure the elements ∂Bz/∂x and ∂Bz/∂y or ∂² Bz/∂x∂y, respectively. The noise spectra of each magnetometer and a first-order electronic planar gradiometer were measured. [ABSTRACT FROM AUTHOR]

We report on serial dc superconducting quantum interference devices (dc SQUIDs) arrays of two-stacked intrinsic Josephson junctions (IJJs) on a Bi2Sr2CaCu2O8+δ (Bi-2212) whisker with a submicron hole fabricated by a 3-D focused ion beam (FIB) etching method. The junction area, the number of elementary junctions, and the loop area of the SQUIDs are 3, 20, and 0.42 μm2, respectively. The SQUIDs show typical I–V characteristics of IJJs with a critical current IC of 12 A at 4.2 K. The modulation parameter βL(=2ICL/Φ0) is 6.4, and the inductance L of the SQUID is 1120 pH. That includes the inductances of the elementary junction around a SQUID loop. In a strong magnetic field, the Fraunhofer pattern is obtained and well fitted to the calculated value from the junction size; ΔB=Φ0/tW; t is the interlayer distance; and W is the junction width. In a low magnetic field, modulation depth of approximately 10% of the IC corresponding to the value of βL is observed. The modulation period of 80 G approximately agrees with the value calculated from the SQUID. [Copyright &y& Elsevier]

We present a concept of a broadband IF amplifier based on experimental results obtained with a dc SQUID rf amplifier (SQA). The frequency range is broadened by using several SQAs, each one tuned to its own central frequency at both input and output; the numerical simulations are presented. A possibility of fine adjustment of the input impedance is numerically demonstrated in the range of 1–1000 Ω. The following parameters are expected for a three-channel SQA: central frequency &ap;4 GHz, bandwidth 1 GHz, noise temperature &ap;2 K, input saturation &ap;300 K GHz. [Copyright &y& Elsevier]

A two-stage dc SQUID is strongly coupled to an electrical resonator at 1.6 kHz with quality factor Q=1.1×106 in order to simulate the behaviour of the SQUID on a resonant gravitational wave detector. A capacitive damping network is successfully employed in order to avoid the instabilities due to the real part of the SQUID dynamic input impedance. The coupled energy resolution is 300 ℎ at 4.2 K, scales with temperature, and is not significantly worsened by the coupling to the resonator and by the damping network. [Copyright &y& Elsevier]

An experimental investigation of high-temperature dc SQUID amplifier connected in series with a high-Tc superconductor (HTS) thin-film band-pass filter is presented. The SQUID amplifiers are designed with microstrip input coils and fabricated on bicrystal substrates of zirconia and sapphire with different misorientation angles of 24° and 37°. SQUID parameters are optimized to attain 50-Ω input impedance for the 1500 MHz central frequency range. The maximum power gain of the amplifier with six turn input coil was measured to be 6 dB at 800 MHz and 4.5 dB at 1750 MHz. Thin-film HTS YBCO filters are based on a band-pass quasi-elliptic prototype consisting of a set of parallel tank circuits connected to a shunt and separated by admittance inverters. The central frequency of the band-pass filter was adjusted close to 1750 MHz amplifier frequency with 4% bandwidth. The natural combination of a high-Tc SQUID amplifier with a HTS band-pass filter allows the reduction of out-of-band noise and optimization of amplifier performance, and demonstrates compatibility with practical components of front-end receiver subsystems. [Copyright &y& Elsevier]

It is well known that electromagnetic interferences (EMI) deteriorate the characteristics of dc SQUIDs as well as any other device based on Josephson junctions. In general a dc-SQUID electronics is made by a head, located near the device, and by a control unit, where the user can adjust the setting parameters of the device. The cables connecting the control unit and the head can be a pathway for EMI, unless careful shielding and filtering are provided. This problem is more serious in directly coupled electronics with respect to readout schemes with a cooled transformer. Here we propose an electronics where the connecting cables have been eliminated and the dparameter settings are made by a common infrared remote control (like those used for household appliances). The remote control unit can fully control the device: it is possible to choose the dc-SQUID bias current, the locking point, the operation mode (open loop or flux locked loop), and the feedback parameters. [Copyright &y& Elsevier]

We present a concept of a rf amplifier based on a directly coupled dc SQUID with bicrystal junctions, which have high saturation power and can be used with SIS mixers or possibly for satellite and cellular phone communications. A novel input resonant circuit is proposed using single layer of HTS. Estimated parameters are (per stage): central frequency&ap;11 GHz, bandwidth&ap;400 MHz, noise temperature&ap;10 K, gain&ap;10 dB and input saturation&ap;1000 K GHz. [Copyright &y& Elsevier]

A prototype of SQUID read-out for current measurements at the output of a normal metal hot-electron microbolometer has been developed and tested. The system is based on serial VTT dc SQUID and input μ-metal core solenoid transformer. The achieved current resolution is 300 fA/Hz1/2. Johnson noise of metal resistor and shot noise of tunnel junction were used for current calibration of SQUID read-out. The current noise spectra of 35 kΩ SIN tunnel junction measured at different bias voltages are presented. [Copyright &y& Elsevier]

The dc SQUID based RF amplifier (SQA) looks very attractive as an IF amplifier for integration with a SIS mixer and a flux-flow oscillator (FFO) in a fully superconducting submillimeter wave receiver suitable for space applications. Important advantages of the SQA are its low noise, extremely low power consumption, and complete compatibility with the fabrication process currently used for SIS mixers. Single stage amplifiers with a novel signal coupling circuit have been developed and tested in the frequency range 3.6-4.1 GHz. The 1 /spl mu/m/sup 2/ area Nb-AlO/sub x/-Nb junctions shunted by Ti resistors are grouped in a double washer dc SQUID. Two samples with slightly different designs showed the following gain, noise temperature and 3 dB bandwidth: 10.0/spl plusmn/1 dB, 5.0/spl plusmn/1.5 K, 3.86-3.90 GHz, and 6.8/spl plusmn/1 dB, 22/spl plusmn/7 K, 3.89-4.05 GHz, respectively. [ABSTRACT FROM PUBLISHER]

We present an integrated magnetometer concept that combines inductance matching by a flux transformer with the low inductance of a multiloop pick-up coil. Using ramp-type Josephson junctions with PrBa/sub 2/Cu/sub 3/O/sub 7/ barriers, a 90 pH dc SQUID together with a five turn flux transformer is coupled to a multiloop pick-up coil. The dependence of the effective area of the magnetometer on the temperature is investigated by successively disconnecting the pick-up loops. The 1/f flux noise of the integrated magnetometer is suppressed by operation in a flux-locked loop mode with bias current modulation. This results in a flux density noise of /spl radic/(S/sub B/)(1 Hz,77 K)=100 fT//spl radic/(Hz). Using this magnetometer, different biomagnetic measurements have been performed. [ABSTRACT FROM PUBLISHER]

Low-Temperature Scanning Electron Microscopy (LTSEM) has been successfully applied to the investigation of the local superconducting properties of thin films and Josephson junctions as well as to the study of more complex superconducting circuits. Since many superconducting devices and circuits can be operated successfully only in low ambient magnetic fields, we have built a liquid nitrogen cooled low temperature stage with improved magnetic shielding for the temperature range between 77 and 130 K. For effective magnetic shielding we use a superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// tube in addition to several Mumetall shields. We established further improvements such as an in-vacuum motorized x-y-slide, which allows us to shift the sample with a minimum step width of 1.5 /spl mu/m. We present first test measurements of the transport properties of a high T/sub c/ dc SQUID that demonstrate the functionality of the new stage. [ABSTRACT FROM PUBLISHER]

High-temperature superconducting Josephson junctions and dc SQUIDs were fabricated using a ramp edge-geometry SNS configuration. Ag-doped YBa/sub 2/Cu/sub 3/O/sub 7-x/ was used as electrodes and PrBa/sub 2/Cu/sub 3/O/sub 7-x/ as barrier. The I/sub c/R/sub n/ value of the junctions was in excess of 120 /spl mu/V at 75 K. The dc SQUIDs showed a flux modulation depth, /spl part/V//spl part//spl Phi/, over 150 /spl mu/V//spl Phi/, at 75 K. The flux noise of the devices, measured with dc bias currents operated at 75 K, showed a 1/f dependence at low frequency having values below 100 /spl mu//spl Phi//sub 0/Hz/sup - 1/2 / (the best values in the range of 30/spl sim/40 /spl mu//spl Phi//sub 0/Hz/sup - 1/2 /) at 1 Hz and less than 5 /spl mu//spl Phi//sub 0/Hz/sup - 1/2 / in the white noise region. The voltage modulation and magnetic field noise were 37 /spl mu/V and /spl sim/2 pTHz/sup - 1/2 / at 1 kHz for the directly-coupled dc SQUID magnetometers (with a pick-up loop 6 mm/spl times/ 3.5 mm) based on the ramp edge-geometry SNS configuration. [ABSTRACT FROM PUBLISHER]

We have fabricated HTS Josephson Junctions and DC SQUIDs using MgO bicrystals and YBCO thin films grown by PLD. The electrical and noise properties of the junctions have been measured. The SQUIDs have been designed and fabricated for use in our NDE programme. For this reason, their performance in unshielded environments is discussed here. [ABSTRACT FROM PUBLISHER]