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The switching current of Spin Torque Magnetic Random Access Memory (MRAM) can be reduced significantly by using perpendicularly magnetized materials. The Ta|CoFeB|MgO system provides both high tunneling magnetoresistance and perpendicular anisotropy. Using this materials system we have demonstrated basic write functionality in fully integrated Spin Torque MRAM arrays. Here, we further demonstrate device scaling down to 20 nm diameter, opening up the possibility of ultra-dense Spin Torque MRAM.

This talk will review emerging MRAM technologies, beginning with field-switched MRAMs that have been in product form for several years now, and extending to spin-torque MRAM under development now for higher density applications. Considerations for scaling to very small cell sizes will be discussed; in particular the importance of perpendicular magnetic anisotropy materials. Standard MRAM approaches involve the two-terminal magnetic tunnel junction device, that both stores the information and is used to read it out. A three-terminal magnetic device with potential advantages for speed will also be discussed, along with another approach dubbed "Racetrack" memory, which has the potential for three-dimensional shift-register like storage and very high densities.

Energy consumption is a dominant constraint on the performance of modern microprocessors and systems-on-chip. Dynamic voltage and frequency scaling (DVFS) is a promising technique for performing “on-the-fly” energy-performance optimization in the presence of workload variability. Effective implementation of DVFS requires voltage regulators that can provide many independent power supplies and can transition power supply levels on nanosecond timescales, which is not possible with modern board-level voltage regulator modules (VRMs) [1]. Switched-inductor integrated voltage regulators (IVRs) can enable effective implementation of DVFS, eliminating the need for separate VRMs and reducing power distribution network (PDN) impedance requirements by performing dc-dc conversion close to the load while supporting high peak current densities [2–3]. The primary obstacle facing development of IVRs is integration of suitable power inductors. This work presents an early prototype switched-inductor IVR using 2.5D chip stacking for inductor integration.

In this paper, we report the first demonstration of CMOS-integrated racetrack memory. The devices measured are complete memory cells integrated into the back end of line of IBM 90 nm CMOS. We show good integration yield across 200 mm wafers. With magnetic field-assist, we demonstrate current-driven read and write operations on cells within a 256-cell CMOS-integrated array.

Recently developed magnetic tunnel junctions with full perpendicular magnetization that are spin-torque switchable allow for quantitative comparison of spin-torque switching statistics with a macrospin model. For typical devices above 50 nm in lateral size, the comparison suggests the presence of subvolume magnetic excitations which often dominate the switching process and which degrade the spin-torque switching efficiency. A simple model of subvolume spin-torque-driven magnetic switching is presented to account for the experimental observations. The origin of the subvolume thermal excitation is traced to a competition between the macrospin fluctuation within a simple uniaxial anisotropy potential and that of thermal magnon excitation. The subvolume excitation problem highlights the importance of improving the magnetic exchange stiffness of the junction free layer, and the reduction of junction lateral sizes below 50 nm where an improved spin-torque efficiency is seen as the switching dynamics cross over to a more macrospin-like process.

PMA spin-torque switchable junctions have been demonstrated with lower switching current and faster switching speed compared to IMA devices. They are promising for further technology exploration in solid-state memory applications.

A 28-channel system for neuromagnetic measurements operative at CNR-IESS (Instituto di Elettronica dello Stato Solido) is described. The instrument uses 28 Nb/PbAuIn DC-SQUID (superconducting quantum interference device) sensors coupled with a flux transformer configuration. The detection coils are arranged on concentric circumferences. Sixteen axial first-order gradiometers are arranged in the internal circles, while the external circle consists of 12 first-order planar gradiometers. The vertical gradiometers show a white noise level of approximately=5 fT/ square root Hz, while the planar ones have a noise approximately=6 fT/cm square root Hz, with a 1/f corner at a few hertz. The evoked potentials of normal subjects and patients affected by various kinds of vascular disturbances have been studied. The system has succeeded at one-shot localization of some cortical activity. The instrument has also been used to record the spontaneous brain activity in patients affected by focal epilepsy. >

Josephson edge junctions have been fabricated using thin sputtered films of MgO (8-32 AA) to produce a weak connection between high-T/sub c/ electrodes. The current-voltage characteristics of these junctions can be well modeled by the resistively shunted junction (RSJ) equation, and they possess excellent Josephson properties, exhibiting strong magnetic field modulation and microwave response at 10 and 100 GHz up to 85 K. The best high temperature (T>70 K) operation has been obtained with devices which have critical current densities in excess of 10/sup 5/ A/cm/sup 2/ at 4.2 K, and junction critical current resistance products I/sub c/R/sub n/ equivalent to 0.10 mV at 83 K. Experiments indicate that improvements in device quality are expected as the base electrode junction surface is improved. Preliminary results indicate that the cyclability of these junctions is good. >

We examine the sweep-rate dependence of magnetic switching field, Hs, in submicron magnetic tunnel junctions where shape anisotropy is dominant. Experimental data support the use of a single-domain thermal activation model for description of activated magnetic reversal in junctions 0.2 by 0.5 μm or less in size. A scaling law is obtained for the thermal activation energy which varies as the cube of junction size.

We report data from 4-kbit spin torque MRAM arrays using tunnel junctions (TJs) with magnetization perpendicular to the wafer plane. We show for the first time the switching distribution of perpendicular spin torque junctions. The percentage switching voltage width, σ(V c )/ = 4.4%, is sufficient to yield a 64 Mb chip. Furthermore we report switching probability curves down to error probabilities of 5×10−9 per pulse which do not show the anomalous switching seen in previous studies of in-plane magnetized bits.

This paper reviews the development of magnetoresistive random access memory (MRAM) with an emphasis on recent developments at IBM. MRAM is unique among nonvolatile memory technologies in having high endurance (actually unlimited) and high performance, though it is not the highest density technology. In the emerging form of MRAM that scales the best, spin-torque-transfer MRAM (STT-MRAM), control of distributions will be crucial for transforming promising research results into products. These challenges are discussed, along with some options for meeting them. For lowering write currents and thus improving power and density, perpendicular magnetic anisotropy materials are vital. For helping with margins and also improving performance, a recently proposed new three-terminal device for the cell structure looks attractive.

All-high-${\mathit{T}}_{\mathit{c}}$-material edge junctions consisting of laser-ablated Y-Ba-Cu-O electrodes and an in situ rf-sputter-deposited MgO barrier have been fabricated whose I-V characteristics show tunneling-related effects. These include a junction resistance with an exponential dependence on the nominal-barrier thickness, gaplike structure observed in the conductance curves, and Josephson effects. These properties are very sensitive to the choice of materials-processsing method for the junction interfaces.

We have studied the fluxoid quantization and the critical state of a ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{x}}$ (YBCO) loop, and vortex movement into the loop using a weakly coupled low-${\mathit{T}}_{\mathit{c}}$ superconducting quantum interference device (SQUID). The YBCO loop was made from a low-current-density polycrystalline film so that the critical-state behavior could be observed in modest magnetic fields at 4.2 K. As the magnetic field was swept, we observed a drastic change in the field responsivity of the SQUID when the loop went into and out of the critical state at a certain field ${\mathit{H}}^{\mathrm{*}}$. At fixed magnetic fields above and below ${\mathit{H}}^{\mathrm{*}}$, we measured the flux in the loop as a function of time by operating the SQUID in a flux-locked loop. Above ${\mathit{H}}^{\mathrm{*}}$ we observed flux-creep-like behavior as well as the movement of individual flux quanta into the loop. Below ${\mathit{H}}^{\mathrm{*}}$ we observed negligible dissipation in the form of flux quanta jumping into the loop, but did observe occasional hopping of individual vortices to other pinning sites in the YBCO.

The field-effect mobility, Hall coefficient, and conductivity as functions of the oxygen concentration and temperature are reported for ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathrm{\ensuremath{\delta}}}$ films on the insulating side of the insulator-to-metal transition. The temperature dependence of the conductivity and Hall coefficient indicate that for small \ensuremath{\delta} the excess oxygen introduces acceptor states at about 30 meV above the valence-band edge. The field effect reveals a space-charge layer in which carriers are depleted at the air-${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathrm{\ensuremath{\delta}}}$ interface. The size of the field effect is limited by localized states at the interface.

We report on the deposition and characterization of SrTiO 3 / YBa 2 Cu 3 O 7− δ bilayers with SrTiO 3 thickness up to 0.7 μm. The films were grown by laser ablation onto NdGaO 3 and also onto Nb-doped SrTiO 3 substrates. Investigations by X-ray diffraction revealed very good crystallinity and (100) orientation of the SrTiO 3 films. The relative permittivity was found to increase from 320 at room temperature to 780 at 65 K. The dielectric breakdown of a 4500 A thick SrTiO 3 film at 4.2 K occurred asymmetrically at 6.2×10 4 V/cm and 2.2×10 5 V/cm. The highly oriented YBa 2 Cu 3 O 7− δ films deposited on top of these insulating layers had T c ( R =0) > 90 K and J c (77 K )≳2.7×10 6 A / cm 2 .

We present measurements of the magnitude of Neel “orange-peel” coupling due to interface roughness in a series of magnetic tunneling junction devices. Results from magnetometry and transport measurements are shown to be in good agreement with the theoretical model of Neel. In addition, we have used transmission electron microscopy to directly probe the sample interface roughness and obtain results consistent with the values obtained by magnetometry and transport methods.

We have studied the switching properties of micron-scale magnetic tunnel junctions in two-dimensional magnetic fields. We present data on interlayer magnetic coupling for multiple samples. We interpret these data as the sum of a magnetostatic and a Neel coupling contribution. The data are presented as functions of layer structure. In addition, we have extracted information about interface roughness. We have also studied the area of switching critical curves as a function of device geometry.

The magnetic switching behavior of micron-size magnetic tunnel junctions has been studied in two-dimensional magnetic fields. By measuring junction resistance, we obtain information about the magnetization state of the free ferromagnetic layer. Magnetic properties of this layer are explored using the Stoner–Wohlfarth rotational model as a starting point. We use geometric parameters of the critical curves to obtain information about interlayer coupling and domain structure effects in the free layer.

Measurements have been made of the low-temperature magnetic response of single, isolated, micron-size Au loops. The magnetic response is found to contain a component which oscillates with the applied magnetic flux with a fundamental period of ${\mathrm{\ensuremath{\Phi}}}_{0}$=h/e. The amplitude of the oscillatory component corresponds to a persistent current of \ensuremath{\simeq}(0.3--2.0)${\mathit{ev}}_{\mathit{F}}$/L, 1 to 2 orders of magnitude larger than predicted by current theories.

The authors have designed, fabricated and tested all-refractory DC SQUIDs in Nb-Al/sub 2/O/sub 3/-Nb trilayer technology that have noise performance comparable to the best previously reported for any technology. A variety of SQUID designs were incorporated as part of a trilayer process development test vehicle. SQUID inductance, junction area, and resistive shunt geometry were varied in matrix fashion to give SQUIDs with near-optimum parameter values for a factor of five range in Josephson current density and shunt sheet resistance. The devices were fabricated using a selective niobium anodization with a minimum feature size of 2 mu m. The base electrode and Nb wiring were patterned with dry etching, and the junction areas were defined by anodization: the Ti resistors were patterned with a lift-off process. Current density on different wafers was varied from 400 to 1000 A/cm/sup 2/ with typical junction V/sub m/'s of 60 mV. The shunt sheet resistance was varied in the 1-5- Omega / Square Operator range. The noise was measured with an RF SQUID direct small-signal readout scheme. A 50-pH SQUID with 3- mu m/sup 2/, 16- mu A junctions and 14- Omega shunt resistors was shown to have an ideally low white noise of 1*10/sup -13/ Phi /sub 0//sup 2//Hz, a white to 1/f crossover frequency at 7 Hz, and a noise level less than 6*10/sup -12/ Phi /sub 0//sup 2//Hz at 0.1 Hz.

Progress toward the development of a 28-multichannel system for neuromagnetic measurements is described. A novel hybrid design consisting of 16 first-order axial gradiometers and 12 first-order planar gradiometers was chosen, which optimize the use of the available cylindrical volume of the dewar tail. This configuration maintains the symmetry of the detected pattern with respect to rotation of a biomagnetic source located under the center of the array and features a localization power considerably better than an array of all first-order planar gradiometers. The detecting array permits simultaneous magnitude measurements over a circular scalp region of 16-cm diameter. The magnetic sensors used are Nb/PbAuIn DC SQUIDs fabricated at IBM. The devices incorporate resonant damping resistors shunting the inductance, resulting in smooth flux-voltage characteristics and, consequently, very low noise figures in a flux-locked loop configuration. A simple and low-cost electronic system has been designed and fabricated for the DC SQUID sensors, consisting of a compact head mounted on top of the cryogenic probe and a control unit where all the DC remote controls are performed. The dynamic range of 10/sup 7/ square root Hz and the bandwidth of 50 kHz are specifically designed to work in multichannel DC SQUID instrumentation.

We have studied bias and magnetic field dependence of voltage noise in metallic magnetic tunnel junctions with areal dimensions on the order of 1 μm. We generally observe noise with Gaussian amplitude distribution and pure 1/f power spectra at low frequencies. The 1/f noise scales with bias voltage as V2. Two kinds of deviations from this low frequency behavior have been observed. One is at fixed magnetic field when the junction bias reaches above a critical value, the other occurs at a fixed bias when the external magnetic field brings the sample to certain magnetic configurations. In both cases the noise spectra become dominated by Lorentzian noise and in both cases we have observed two level fluctuators in the time domain. We attribute the bias dependent noise to charge traps in the tunnel barrier. The field dependent noise is associated with the switching of the magnetization direction of portions of the top electrode, which we believe to be reversible.

We have demonstrated a robust magnetic tunnel junction (MTJ) with a resistance-area product RA=8 Omega-mum2 that simultaneously satisfies the statistical requirements of high tunneling magnetoresistance TMR > 15sigma(Rp), write threshold spread sigma(Vw)/

Two obvious applications of high-T/sub c/ superconductors are discussed: the use of Josephson technology at 77 K and the use of high-T/sub c/ lines for interconnects. The difficulties that must be addressed for each of these is discussed, and the prospects for overcoming them are assessed. The need to achieve full compatibility with polymers is stressed. >

This paper reports on the use of lanthanide gallate perovskite-type substrates for the deposition of epitaxial, high-{ital T{sub c}} superconducting Ba{sub 2}YCu{sub 3}O{sub 7{minus}{delta}} (BYCO) films. They were also found to have moderate dielectric constants ({approximately}25 compared to {approximately} 277 for SrTiO{sub 3}). This study was undertaken to further explore the use of LaGaO{sub 3}, NdGaO{sub 3}, SrTiO{sub 3}, MgO, and Y-stabilized ZrO{sub 2} substrates, prepared from single-crystal joules grown by several suppliers using the Czochralski method. Films were prepared by cylindrical magnetron sputtering and laser ablation. Substrate evaluations included measurement of dielectric constant and loss, thermal expansion, and mechanical hardness and toughness. In addition to their moderate dielectric constants, they were found to have satisfactory mechanical properties, except for the twinning tendency of LaGaO{sub 3}. Lattice mismatch strains were calculated for orthorhombic BYCO films on a number of substrates. NdGaO{sub 3} was found to have the best lattice match with BYCO, and is now available twin-free.

Multilayer edge junction SQUIDs have been fabricated using epitaxial, laserablated films of YBaCuO for both elctrodes. The barrier region is defined by a low voltage plasma oxy-flouridation step. The SQUIDs are patterned using photolithography and ion milling and devices have been made with linewidths as small as 2μm. The edge junction SQUIDs have exhibited very low magnetic hysteresis values of ≤ 50 ppm.

Between 1963 and 1987, 131 patients with benign gastrointestinal stromal tumors, primarily leiomyomas, were treated at the Massachusetts General Hospital. Eighty per cent of tumors were located in stomach or small intestine. Two thirds of the tumors were discovered in symptomatic patients before operation by a variety of diagnostic studies. A mitotic index (MI) was determined for each tumor, defined as the number of mitoses per 50 high-power microscopic fields. Only gastric and small intestine tumors had MIs more than 2. Tumors were treated by conservative excision in 67% and radical excision in 33%. At a median follow-up of 6 years there were no local recurrences. No patient with a tumor discovered incidentally has recurred. Three symptomatic patients have died of metastatic liver disease. Each patient with recurrence had a tumor with MI of 2 or more, which represents a recurrence rate of 16% in this group. We conclude that symptomatic gastric and small intestine tumors having two or more mitoses per 50 high-power fields carry a significant risk for recurrence, and that routine pathologic assessment of MI may identify a subset of patients who would potentially benefit from close follow-up and consideration for further therapy.

We have studied systematically the magnetotunneling properties of several metallic magnetictunnel-junction systems (Ni80Fe20–insulator–Ni80Fe20,Ni80Fe20–I–Co,Co–I–Co, Ni40Fe60–I–Co). The room-temperature magnetoresistance MR value at zero-bias ranges between 16% and 27%, depending on the spin polarization of the electrodes. There seems to be a general bias dependence of MR in all of these systems. In particular, it requires a bias in the range of 0.22–0.23 V to suppress the maximum MR value by half. We have also measured the bias dependence of MR as a function of barrier parameters (thickness and oxidation time). At low temperature, a sharp cusplike feature appears near zero bias. In some cases, low-temperature MR values substantially exceed expectations from established spin-polarization.

When injected spin polarized electrons interact with the magnetic moment of a free layer, their angular momentum becomes transferred to the free layer. If sufficient current is applied, the exerted torque switches the free layer either parallel or anti-parallel to the pinned layer depending on the direction of flow of the current. This type of localized current switching is attractive for an MRAM application. This paper focuses on the fabrication and characterization of sub-100nm spin-transfer switching devices. These fabricated tunnel junctions were characterized at room temperature with a quasi-static electrical measurement setup.

We show that shape anisotropy can be used to control the response characteristics of magnetic tunnel junctions. By varying the junction shape, the resistance versus field curve was made to vary from a nonhysteretic linear curve with a high-field sensitivity (0.3%/Oe) to a hysteretic response curve with high squareness.

MRAM technology offers an attractive combination of performance, density, low power, non-volatility, and write endurance. While first stand-alone MRAM products appear poised for introduction, major technology advances are also being reported. In this review, we discuss our work on a 16Mbit demonstrator chip with a 1.42 /spl mu/m/sup 2/ cell in 180 nm technology in the context of recent world wide advances in MRAM technology. These include a cell architecture that resolves the magnetic half select write disturb issue and an advanced tunnel barrier material, MgO, that promises much larger signals for MRAM read operations.

We report on the fabrication of a new class of trilayer epitaxial thin film devices based on the doped perovskite manganates La–Ca–Mn–O and La–Sr–Mn–O. We show that large resistance changes, up to a factor of 2, can be induced by a moderate applied magnetic field below 200 Oe in these trilayers supporting current‐perpendicular‐to‐plane transport. These results show that low‐field spin‐dependent transport in manganates can be accomplished, the magnitude of which is suitable for magnetoresistive field sensors.

Epitaxial thin films of lanthanum‐deficient LaxMnO3−δ (0.67≤x≤1) have been grown on (100) SrTiO3 substrates by pulsed laser deposition. The as‐deposited films exhibit a ferromagnetic transition at temperatures ranging from 115 to 240 K, with the transition temperature (Tc) increasing with higher La deficiency. A sharp drop in resistivity and negative magnetoresistance is observed close to Tc, a behavior similar to that observed in divalent substituted La1−xMxMnO3−δ (M=Ba, Sr, Ca, Pb) films. Postannealing the films in O2 reduces the resistivity and raises the Tc to values close to room temperature. A magnetoresistance value of 130% (Δρ/ρH) has been obtained at 300 K at 4 T for a post‐annealed film with x=0.75.

Record values of colossal magnetoresistance (CMR) have been achieved in the antiferromagnetic phase of the La1−xCaxMnO3 system. At 125 K, the CMR of the La0.5Ca0.5MnO3 reaches nearly 1 000 000%. It increases exponentially to 100 000 000% at 57 K. While the ground state is primarily an antiferromagnet, application of a magnetic field induces a ferromagnetic alignment of spins that is highly beneficial to the electron conduction. Other ferromagnetic samples exhibit very sharp magnetic phase transitions, with which the magnetotransport is closely correlated.

This letter discusses the effects of a moderate magnetic field applied to a SQUID magnetometer and introduces the invention of the ‘‘flux dam.’’ A flux dam is a weak link or Josephson junction in series with the pickup loop which allows magnetic flux to enter and leave the inside of the superconducting loop easily for moderate changes in magnetic field. This largely prevents the flux lines from entering and being pinned in the superconducting parts of the magnetometer which would create extra low frequency noise. SQUID magnetometers with flux dams in the pickup loop can be operated in the Earth’s magnetic field without a significant increase in low frequency flux noise.

We have combined a novel low temperature positioning mechanism with a single‐chip miniature superconducting quantum interference device (SQUID) magnetometer to form an extremely sensitive new magnetic microscope, with a demonstrated spatial resolution of ∼10 μm. The design and operation of this scanning SQUID microscope will be described. The absolute calibration of this instrument with an ideal point source, a single vortex trapped in a superconducting film, will be presented, and a representative application will be discussed.

Films and electronic devices fabricated from high-T/sub c/ superconductors are briefly reviewed. Present work being done in the field is highlighted. Substrate materials, sputtering techniques, oxygen incorporation, and fabrication of the films are covered. >

A superconductor-insulator-superconductor (SIS) mixer is described that has a broadband integrated tuning structure. The mixer is tunable from 85-116 GHz, and a midband has a noise temperature of 6+or-6 K DSB (double-side-band) and unity DSB conversion gain. Referred to the mixer input flange, the receiver noise temperature is 9+or-6 K at midband. The integral tuning structure consists of a short two-wire transmission line stub with a quarter-wave superconducting transmission line as a DC and intermediate frequency (IF) block. Despite the relatively soft I-V curves of the two-junction arrays used in these mixers, low mixer noise temperature and conversion loss were achieved. >

The effects of radio frequency radiation on the dc SQUID are examined. Simulations show how the shape of the SQUID transfer characteristic is distorted by radio frequency interference (RFI). How this affects three commonly used SQUID modulation methods is discussed, and the results explain why we experimentally observe the bias current reversing readout method to be the least susceptible to RFI. The commonly seen increase in the low frequency flux noise power spectrum of dc SQUIDs in unshielded environments is also explained.

All high‐Tc, multilevel edge junction superconducting quantum interference devices (SQUIDs) which now operate at 77 K have been fabricated using laser‐ablated YBaCuO electrodes and in situ laser‐ablated SrTiO3 for the barrier material. Devices with a SQUID inductance of about 70 pH have a peak to peak voltage swing, VΦ, up to 8 μV (dV/dΦ≂25 μV) and a flux noise (SΦ) of about 3×10−10 Φ20/Hz in the white noise region. IcRn, products for these devices are about 35 μV at 77 K with Ic in the range of 3–100 μA and operation to temperatures as high as 84 K observed. Scaling of the junction conductance and critical current with junction size has been measured on many devices and we observe an IcRn product that varies approximately as J0.89c.

Magnetic random access memory (MRAM) offers an alternative approach to fast low-power non-volatile VLSI memory. MRAM has been pursued for more than 10 years as a robust non-volatile memory for space applications. The magnetic tunnel junction (MTJ) MRAM is dramatically different and achieves four orders of magnitude better bandwidth to sense power ratio by utilizing a high resistance and high magneto-resistance (MR) MTJ and including a FET switch in each cell. Non-volatile storage and 10 ns performance are demonstrated in 1 kb arrays. Read and write on-chip power at 2.5 V and 100 MHz are 5 mW and 40 mW respectively.

We have developed a process for the fabrication of YBaCuO high‐Tc junctions based on the step‐edge weak‐link concept. The process emphasizes the creation of sharp and straight step edges on a substrate, and the restoration of oxygen content for superconducting materials at the step edges. A diamond‐like carbon film is used as an ion milling mask for the creation of steps on substrates such as LaAlO3 and SrTiO3. Room‐temperature plasma oxidation is shown to be effective in restoring Tc from processing related degradation for grains residing at the step edge. Using this process, dc SQUIDs were fabricated with 77 K electrical performances matching, and in certain cases exceeding, similar SQUIDs made using bicrystal‐based tilt‐boundary weak‐link junctions.

We have invented a three superconducting quantum interference device (SQUID) gradiometer (TSG) that uses three SQUID magnetometers and a novel feedback method to measure magnetic field gradients. One SQUID, designated the reference SQUID, operates normally except that its feedback loop output is directed to all three SQUIDs through identical nonsuperconducting coils around each SQUID. The feedback loops for the remaining two SQUIDs, the sensor SQUIDs, measure the differences between the magnetic field at the reference SQUID location and those at the sensor SQUID locations. The voltage difference between the two sensor SQUID outputs divided by the gradiometer base line, the distance between the sensor SQUIDs, represents the average magnetic field gradient. We have measured gradient sensitivities of 10−12 and 10−10 T/m√Hz for TSGs made from bare low‐Tc and high‐Tc SQUIDs. An advantage of a TSG is that a sensitive gradiometer, free of hysteresis error, can be made using relatively small substrates.

Josephson edge junctions have been fabricated using thin sputtered films of MgO (8–32 A) to produce a weak connection between high Tc electrodes. The current voltage characteristics of these junctions can be well modeled by the resistively shunted junction (RSJ) equation and they possess excellent Josephson properties, exhibiting strong magnetic field modulation and microwave response at 10 and 100 GHz up to 82 K. The best high‐temperature (T≳70 K) operation has been obtained with devices which have critical current densities in excess of 105 A/cm2 at 4.2 K, and junction critical current resistance products IcRn≂0.15 mV at 60 K. Experiments indicate that improvements in device quality are expected as the base electrode junction surface is improved.

We compare model predictions for 1/f noise in dc SQUIDs with experimental data and show that the 1/f noise in the our devices results from fluctuations in the magnitude of the critical current of the Josephson junctions that form the SQUID. Operating the SQUID while the bias current direction was being alternated canceled the 1/f noise power from these fluctuations and reduced the output noise power by two orders of magnitude. Using this process, we have measured the 1/f noise in several SQUIDs to be 1×10−7 Φ02/Hz at 0.1 Hz and 77 K, the lowest value reported to date.

Background . Isolated heart models separate cardiac characteristics from systemic characteristics with subsequent findings used in cardiac research, including responses to pharmacologic, mechanical, and electrical components. The model objective was to develop the ability to represent in situ physiologic cardiac function ex vivo. Methods . Swine hearts were chosen over rat or guinea pig models due to their notably greater anatomical and physiologic similarities to humans. An in vitro apparatus was designed to work all four chambers under simulated in situ physiologic conditions. Using standard cardiac surgical techniques, 12 porcine hearts (mean weight 331 ± 18 g) were explanted into the apparatus. Preload and afterload resistances simulated in situ input and output physiologic conditions. Hemodynamic characterizations, including cardiac output, max ±dP/dt, and heart rate, were used to determine in situ function leading to explantation (prethoracic operation, postmedial sternotomy, and postperidectomy) and during in vitro function ( t = 0, 60, 120, and 240 minutes). Results . In vitro performance decayed with time, with statistical differences from base line ( t = 0) function at t = 240 minutes ( p > 0.05). Conclusions . An isolation and in vitro explantation protocol has been improved to aid in the study of isolated cardiac responses, and to determine cardiac hemodynamic function during open chest operation, transplantation, and in vitro reanimation with a crystalloid perfusate. The resulting model offers similar working physiologic function, with real-time imaging capabilities. The resulting model is advantageous in representing human cardiac function with regard to anatomic and physiologic functions, and can account for atrial and ventricular interactions.

We have fabricated and tested superconducting first‐order gradiometers made from YBa2Cu3O7−δ (YBCO) thin‐film flux transformers coupled to YBCO dc SQUIDs. The flux transformers consisted of 10‐turn input coils with 5‐μm linewidth and two pick‐up loops with 600‐μm linewidth, each of which surrounded an area of 2.1 by 2.8 mm. All levels were patterned by wet etching. A magnetic field gradient of 1 nT/m resulted in a flux of 5.8×10−4 Φ in the SQUID which corresponds to a responsivity of 1.21×10−9 m3. The 1/f noise level at 77 K and 10 Hz was 0.6 nT/m√Hz and was dominated by SQUID noise.

We have demonstrated a new planarized all‐refractory technology for low Tc superconductivity (PARTS). With the exception of the Nb‐AlOx‐Nb trilayer preparation, the processing is done almost exclusively within an advanced Si technology fabrication facility. This approach has allowed us to leverage highly off of existing state‐of‐the‐art lithography, metal etching, materials deposition, and planarization capabilities. Using chemical‐mechanical polish as the planarization technique we have fabricated Josephson junctions ranging in size from 0.5–100 μm2. Junction quality is excellent with the figure of merit Vm typically exceeding 70 mV. PARTS has yielded fully functional integrated Josephson devices including magnetometers, gradiometers, and soliton oscillators.