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We examined a portable cryostat utilizing liquid nitrogen with temperature control function for operation of high-temperature superconducting quantum interference devices (HTS-SQUIDs) to have a higher slew rate. To operate a non-destructive evaluation system with HTS-SQUID in city areas with serious environmental electromagnetic noise, we often need a higher slew rate. A glass Dewar is installed in an outer case made of aluminum, which is sealed hermetically. The temperature of liquid nitrogen is controlled by using a vacuum pump connected to a feedback circuit, which monitors the temperature of liquid nitrogen. The temperature of liquid nitrogen could be controlled in the range between 73 and 77.2 K with a 0.1 K step. For example, the temperature was kept at 75 K with precision of ±0.05 K for 9 hs and SQUID was operated stably for this period. The ΔV and the slew rate of a test SQUID were increased from 22 μV and 3.2 mT/s at 77.2 K to 37 μV and 5.9 mT/s at 73 K, respectively. The white noise was also improved from 48 fT/√Hz at 77.2 K to 32 fT/√Hz at 74 K. We believe that this technology is useful to extend application of HTS-SQUIDs in the fields.

Direct detection of magnetic fields generated by the ion currents in electrolytic cells was performed and the ion currents were mapped during a cyclic voltammetry experiment. A high-Tc superconducting quantum interference device (SQUID) gradiometer with ramp-edge Josephson junctions was used as the detector and thus the first derivative of the magnetic field along the electrolytic cell surface was obtained. The electric potential vs. the reference electrode was measured between −0.3 V and 0.8 V and the hysteresis signals caused by the redox reactions of the electrolyte were observed. The vector component of the ion current during cyclic voltammetry was mapped along the electrolytic cell. As a demonstration of visualization of ion transportation, the magnetic signal was also measured at various positions above the electrolytic cell surface.

We have investigated the fabrication of a high-temperature superconducting (HTS) gradiometer with long baseline for geophysical applications. The proof-of-concept gradiometer using a 1-turn pickup coil made of a GdBa 2 Cu 3 O y coated conductor (GCC) and 5.5-turn input coil integrated on a SQUID was fabricated in our previous work. In this study, we have optimized the device structure to improve the frequency response, gradient field sensitivity and gradiometer balance. The fabricated flux transformer consists of a 6-turn planar gradiometric pickup coil and a 26-turn input coil made of an HTS thin film. A low-melting-point alloy was used to connect polished Ag surfaces of the CGG pickup coil and Au pads of the input coil. An HTS SQUID was formed on another substrate and stacked on the input coil. A mechanical balancing structure using three pieces of GCC as a superconducting shield was also implemented. The fabricated gradiometer showed a gradient field noise of 0.8 fT/cm Hz 1/2 in the white noise regions, a gradiometer balance of 1/142, and a cutoff frequency of 9 Hz corresponding to a 2 mΩ contact resistance between the pickup coil and the input coil.

We have fabricated a large high- T c superconducting (HTS) SQUID gradiometer with a baseline length of 130 mm for geophysical application. It consists of an HTS-SQUID gradiometer chip with an integrated input coil and a large pickup coil made of an HTS coated conductor (CC). In this work, fabrication of the chip containing ramp-edge Josephson junctions and multilayer structures is reported. An MgO(1 0 0) substrate with a size of 15 × 15 mm 2 was used. The half area of the substrate was occupied by gold pads for connection with an HTS-CC. A directly-coupled thin-film gradiometer with a baseline length of 7 mm was prepared in the remained half area. SmBCO and La-doped ErBCO having T c ’s around 90 K were used for base- and counter-electrodes, respectively. A 5.5-turn input coil made of La-doped ErBCO was formed on the thin-film pickup coil made of SmBCO. The fabricated gradiometer chip was operated by supplying electrical current through the input coil, but modulation corresponding to only three flux quanta was observed in the V – Φ curve. We found that the critical current density of the thin-film pickup coil was insufficient. We speculated that the rather wide pickup coil was not fully oxygenated. After longer annealing treatment, the number of modulation peaks in the V – Φ curve was significantly increased.

For accurate and stable monitoring of the oil/gas and fluid distributions in the reservoir during the EOR (Enhanced Oil Recovery) operation even if the well distance exceeds a thousand meter, JOGMEC (Japan Oil, Gas and Metals National Corporation) is developing a crosswell electromagnetic survey system with applying a super-sensitive magnetic sensor "SQUID" (Superconducting Quantum Interference Device). In this study, we have developed the component technologies of borehole SQUID magnetometer and powerful transmitter coil. The SQUID sensor performs in the temperature condition of 77 K, where the liquid nitrogen is available for cooling. To deploy the SQUID sensor in the deep borehole safely, we designed and trial fabricated pressure- and heat-resistant vessel which contains the glass Dewar of liquid nitrogen, release tubes of vaporized nitrogen gas, electrical circuits, and other devices to control the SQUID sensors. The developed transmitter coil has magnetic moment of 27,500 Am2, which will satisfy the intensity for our purpose. We demonstrated the stable operations of the prototype models of borehole SQUID magnetometer and transmitter systems with using the research wells of the JOGMEC field, of which maximum depth is 300 m and cased with conductive tube. The SQUID magnetometer has the ability to be deployed in the environment of 3,000 ~ 4,000 m deep boreholes by the laboratory experiments. At the next stage, we will demonstrate the systems at the actual borehole, whose typical depth is greater than 1,000 m. On the other hand, we have been developing the algorithms to interpret and correct the effects of conductive casing tubes, and three-dimensional modeling of underground structure. For the demonstration of their performance, we will also conduct the crosswell measurement with using the test wells.

Recent developments of electronic devices containing Josephson junctions (JJ) with high-Tc superconductors (HTS) are reported. In particular, the fabrication process and the properties of superconducting quantum interference devices (SQUIDs) with a multilayer structure and ramp-edge-type JJs are described. The JJs were fabricated by re-crystallization of an artificially deposited Cu-poor precursory layer. The formation mechanism of the junction barrier is discussed. We have fabricated various types of gradiometers and magnetometers. They have been actually utilized for several application systems, such as a non-destructive evaluation (NDE) system for deep-lying defects in a metallic plate and a reel-to-reel testing system for striated HTS-coated conductors.

We have studied the fabrication process for high- T c superconducting quantum interference devices (HTS-SQUIDs) containing ramp-edge-type Josephson junctions and multilayer superconducting wiring. Integrated HTS-SQUID magnetometers with a 20-turn input coil were fabricated. SmBCO and La-doped ErBCO were used for base- and counter-electrodes having T c ’s around 90 K, respectively. MgO (1 0 0) substrates with a size of 15 × 15 mm 2 were used. Two types of magnetometers with different washer sizes and different coil widths were fabricated: Type-I had a 2-μm-wide coil on a 200 × 200-μm 2 washer, and Type-II had a 4-μm-wide coil on a 300 × 300-μm 2 washer. Both the magnetometers exhibited rather low white noise level around 25 fT/Hz 1/2 (@77 K, 1 kHz). Peak-to-peak modulation voltage around 16–20 mV was obtained for both the magnetometers. When the external magnetic field increased, the modulation curve was abruptly distorted. Modulation corresponding to 51 flux quanta appeared in the V – Φ curve of a Type-I magnetometer. On the other hand, modulation up to 121 flux quanta could be seen for a Type-II magnetometer. It was likely that the critical current of the superconducting loop consisting of a pickup and an input coil restricted the number of the observed flux quanta. It seems that the wider coil in the Type-II allowed a larger superconducting current in the loop. We succeeded in improving dynamic range of the V – Φ characteristics.

We examined the ability to detect deep-lying defects in multilayer stacks of aluminum plates using an eddy-current testing technique with HTS planar-type SQUID gradiometers. In addition to a previous gradiometer with a baseline of 1 mm, a new gradiometer with a baseline of 8.5 mm and a larger effective area fabricated by HTS multilayer and ramp-edge junction technologies was used. The frequency and depth dependences of the SQUID signal were compared between the two gradiometers. By employing the longer-baseline gradiometer and an excitation frequency of 35 Hz, a slit-like defect located at about 38 mm in depth could be clearly observed with a signal-to-noise ratio larger than 10.

We have studied the fabrication process of HTS-SQUIDs with ramp-edge Josephson junctions (JJs). SmBa2Cu3Oy (SmBCO) and Er0.95La0.1Ba1.95Cu3Oy (L1ErBCO) having Tc's around 90 K were used for base- and counter-electrodes, respectively. SrSnO3 (SSO) was used for insulating layers. A black-colored Pr1.4Ba1.6Cu2.6Ga0.4Oy (P4G4) layer was first grown on MgO substrate via a thin BaZrO3 buffer layer. It was expected to work as a temperature homogenizer over the whole substrate area during deposition of the upper layers. We fabricated planar gradiometers having pickup coils with sizes of 0.5 × 1.0, 1.0 × 1.0 and 3.0 × 3.0 mm2. Their baselines are 1.0, 1.0 and 3.0 mm, respectively. The gradiometers exhibited flux noise at 77 K as low as 3.3 ~ 4.5 μΦ0/Hz1/2 at 1 kHz. Directly and inductively coupled magnetometers having a 13.5 mm square pickup coil were also fabricated. The latter has an integrated 20-turn input coil. They showed field noise levels of 55 and 10 fT/Hz1/2 at 1 kHz, respectively.

We have studied the fabrication process for high- T c superconducting quantum interference devices (HTS-SQUIDs) containing ramp-edge-type Josephson junctions and multilayer superconducting wiring. 5-Channel gradiometer arrays for non-destructive evaluation of striated coated conductors were fabricated. Our previous process contained some problems which often brought about property spreads of the gradiometers and/or degradation in superconducting electrodes. We attempted to improve homogeneity of substrate temperature during barrier preparation. The thickness of a black-colored Pr 1.4 Ba 1.6 Cu 2.6 Ga 0.4 O y embedded at the lowest in the multilayer was increased. The substrate on which bare ramp-surfaces were arranged was heated from the rear side by thermal radiation. A sapphire plate as a temperature homogenizer was inserted between the substrate and the heater. At the final procedure of the process, careful oxygenation containing surface cleaning by dry etching prior to heat-treatment was carried out. By employing them, five HTS-SQUIDs exhibiting the peak-to-peak modulation voltage over 50 μV were successfully fabricated within 6 × 6-mm 2 area in a chip. Their noise levels at 1 kHz and 77 K were as low as 4 μΦ 0 /Hz 1/2 .

We developed a non-destructive evaluation (NDE) system using an HTS SQUID array in order to examine rare-earth (RE)-123 HTS coated conductors striated into multi-filamentary lines. The 5-channel HTS SQUID gradiometer array was composed of ramp-edge junctions with LaErBaCuO and SmBaCuO electrode layers, and fabricated by using an HTS multi layer fabrication technique. The planar gradiometers with 1 × 1 mm 2 pickup loops and a baseline of 1 mm detected the vertical element of magnetic field gradient induced around defects by an eddy current. The gradiometer array cooled by thermal conduction from a liquid nitrogen bath was placed above the coated conductor on the main stage with a lift-off of about 1.5 mm. A coated conductor was fed from a reel to reel, and cooled blow its T c by stages connected to Gifford–Mcmahon (GM) coolers. By employing a 3 kHz induction current generating the maximum field of 0.14 mT, we could identify a distribution of defects in a long-length non-striated conductor. Furthermore, we could detect and distinguish three kinds of defects, existence of a spotty normal-state region, electrical short between striated filaments, and delamination of the superconducting layer from the Hastelloy tape for each filamentary superconducting line at a high speed up to 30 m/h.

We developed a non-destructive testing (NDT) system utilizing multi-channel high-temperature superconductor (HTS) SQUID gradiometers in order to examine rare earth (RE)-123 coated conductors striated into multi-filamentary lines. The 5-channel HTS SQUID gradiometer array was composed of ramp-edge junctions with LaErBaCuO and SmBaCuO electrode layers, and fabricated by using an HTS multilayer fabrication technique. The parallel gradiometers detected the vertical element of magnetic field gradient induced around defects by an eddy current. It was demonstrated that we can detect macroscopic defects in each filamentary superconducting line at high speed up to 30 m/h.

We proposed a novel multilayer structure having a new combination of oxides for integrated high- T c SQUID with ramp-edge Josephson junctions. La 0.1 Er 0.95 Ba 1.95 Cu 3 O y (L1ErBCO) and SmBa 2 Cu 3 O y (SmBCO) were used as counter- and base-electrodes, respectively. An SrSnO 3 (SSO) layer was deposited as an insulating layer. Prior to deposition of SmBCO, Pr 1.4 Ba 1.6 Cu 2.6 Ga 0.4 O y (P4G4) and SSO were deposited on MgO (100) substrate in order to improve film quality of L1ErBCO/SSO/SmBCO layers. The black-colored P4G4 layer was expected to work as a temperature homogenizer over a whole substrate area during deposition of the upper layers. All the layers except L1ErBCO were deposited by an off-axis magnetron sputtering. An L1ErBCO layer was deposited by a pulsed laser deposition method. A thin Cu-poor L1ErBCO layer was initially deposited to form an adequate barrier on the ramp-edge of SmBCO. Gradiometer arrays having multilayered feedback coils and pickup loops were made in a chip and their proper operation at 77 K was confirmed. The present multilayer structure is promising for application to SQUIDs with more complicated designs.

We have succeeded in observing a pico-second current pulse accompanying a single flux quantum (SFQ) using a high- T c superconducting (HTS) sampler. The sampler circuit used in this study, an on-chip sampler, has two pulsers connected to each other at the comparator in one chip. The waveform of an SFQ current pulse from one pulser is measured by using another SFQ pulse from the other pulser as a sampling pulse. We observed a waveform exhibiting two peaks with 5.8 and 1.6 ps widths. Based on these values, we estimated the sampling-pulse width as 2.8 ps, suggesting the potential bandwidth for the HTS sampler of 125 GHz. This value coincides well with the bandwidth expected from the critical current-normal resistance ( I c R n ) product of the Josephson junctions of 1 mV.

We improved the fabrication technology of high-temperature superconducting (HTS) single-flux-quantum (SFQ) circuits by suppression of oxygen loss. Among a lot of difficulties in the HTS circuit fabrication process, loss of oxygen is one of the most significant problems. To understand the oxygen going in and out at each step of the fabrication process, we utilized a room-temperature probing system and a low-temperature probing system. We found that some of the steps after the fabrication of junctions, such as deposition of an insulating layer, ashing of photo-resist, and RF sputtering of an Au wiring layer, cause loss of oxygen from the junctions. We constructed the peripheral fabrication process by combining the annealing process in oxygen and the process with oxygen loss, and obtained controlled I c , sufficiently large I c R n , and T c of the junction.

We have developed a magnetic prospecting system with HTS SQUID gradiometers for exploration of metal resources. The SQUID gradiometer consists of a flux transformer chip made of a YBCO thin film and a SQUID gradiometer chip which is stacked on the transformer chip. The SQUID gradiometer chip was fabricated by using an HTS multilayer and ramp-edge junction technology at ISTEC. Their effective volume and the balance estimated by using a Helmholtz coil were approximately 3 x 10-9 m3 and 1/500, resulting in the gradiometric field noise of 7 pT/m/Hz1/2 at 10 Hz. Two assembled SQUID gradiometers which measure dBz/dx and dBz/dy field gradients were cooled with liquid nitrogen in a cryostat of the magnetic prospecting system. The cryostat was suspended from the frame of the system and its attitude was self-controlled by gravity. The magnetic prospecting system with the HTS SQUID gradiometers, flux-gate sensors, a GPS module, and a gyro sensor was also tested in a field near an old mine.

We have investigated the flux state in high- and low-Tc SFQ circuits having superconducting ground planes with moats by a scanning SQUID microscope (SSM) system. Observation of YBa2Cu3Oy (YBCO) sampler circuits having superconducting ground planes with 5 µm-wide moats confirmed that magnetic flux was excluded from the moat-surrounded area including ramp-edge Josephson junctions. The threshold value for complete flux exclusion was about 0.8 µT slightly depending on chips, which can be achieved readily with dual μ-metal magnetic shielding. Moreover, we have observed the flux state in Nb multilayer structures having a superconducting ground plane with 4 µm wide moats, which was designed and fabricated using the CONNECT cell library. It was confirmed that magnetic flux was trapped selectively into moats with appropriate configuration, which were fabricated within each 40 µm × 40 µm unit cell.

We propose a new ion etching procedure to level the surfaces of lower layers in multilayer structures for HTS SFQ circuits. In order to make a flat lower layer, we have utilized a variation in the etching rate with the ion incident angle in ion etching process. The etching process under the acceleration voltage of 280 V and the ion incident angle as low as 15° for 5 min improved the average surface roughness (Ra) of the SrSnO3 insulating layer from 2.8 nm to 0.8 nm. This procedure was applied just before the La–YBCO base layer growth on the SrSnO3/La–YBCO groundplane bilayer, which resulted in the base layer with Ra much less than 2 nm.

We report on a latching-type driver operated at 30 K for the output interface of single-flux-quantum (SFQ) circuits. Ramp-edge-type high-temperature superconductor (HTS) junctions showed only small inherent hysteresis in current–voltage characteristics at a temperature of 30 K. To have hysteresis large enough for latching operation, we chose La-doped YbBaCuO as a counter electrode of an interface modified junction, and used amorphous LaSrAlTaO to form an additional barrier to the interface modified barrier. The junction shunted with optimized capacitance showed sufficiently large hysteresis of 33%, which is as large as that of a non-shunted junction at 4.2 K. We employed 20 kA cm−2 as the critical current density (Jc) of the junction to fabricate dc/SFQ, Josephson transmission lines (JTLs) and the latching driver on the same chip. It is smaller than the optimum current density that gives the smallest punchthrough probability of the junction, which was calculated to be 10−12 for a 30 Gbps ac bias by using the junction parameters at 30 K. However, the probability for Jc of 20 kA cm−2 is still smaller than that of low-temperature semiconductor junctions because of the larger Jc of the HTS junctions. The fabricated latching driver successfully converted the SFQ pulse, which passed through several JTLs from the dc/SFQ circuit, to a 1 mV level signal at 30 K.

Latching-type driver circuits integrated with high-temperature superconductivity (HTS) junctions and two types of resistor were fabricated. These circuits could successfully perform latching operation by means of a single-flux-quantum (SFQ) signal input. Ramp-edge-type HTS junctions were fabricated by interface engineering and showed a hysteretic current-voltage characteristics under a temperature of 50 K. The critical current (I/sub c/) of these 5-micron-wide junctions was about 0.2 mA and the I/sub c/R/sub n/ product was about 1.7 mV at 4.2 K. The circuits included two types of resistors, which were made of RF-magnetron-sputtered indium-tin-oxide (ITO) and Au films. A driver with a parallel 2-junction-stack could convert an SFQ pulse, which was transformed through several Josephson transmission lines (JTL's) from a DC/SFQ circuit, to a 2.3-mV level signal.

A ramp-edge junction was fabricated with 200-nm-thick YBa 2 Cu 3 O 7− x (YBCO) electrodes and an intermediate insulating layer of 300-nm-thick LaSrAlTaO (LSAT). Extraneous electrode areas are placed on top of their ramps as a result of the fabrication process. The junction exhibited an RSJ-like I–V curve with a swelling or steps depending on the shape of the extraneous electrode areas. The junctions on a 4-mm□ chip were polished and the extraneous electrode areas were removed. We obtained quasi-planar junctions with planarized surfaces and base structures composed of YBCO and LSAT. The swelling and steps were explained as results of the resonance of parasitic inductance and capacitance as they disappeared after polishing. The I c R n product did not decrease, which suggests that the junction was not damaged by polishing. We think that polishing will be important in the fabrication of high- T c superconducting circuits with ramp-edge junctions.

We developed a latching-type driver using capacitively shunted high-temperature superconductivity (HTS) junctions for Single-Flux-Quantum (SFQ)-semiconductor output interfaces and fabricated it using ramp-edge-type HTS junctions. Assuming a junction IcRn product of 2 mV, a circuit simulation shows that the driver can produce an output of about 8 mV from an SFQ input pulse with a sufficiently short rise time for an interface clock operation of several gigahertz. HTS junctions were fabricated using the interface engineering method, and capacitors were made from an Indium oxide insulator (the dielectric constant was about 23 at 20 K) sandwiched by YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) electrodes. The hysteresis of the I-V characteristics of the junctions increased by increasing the area of capacitance. The latching operation of the driver was observed with an output voltage of up to 3 mV.

As a first step toward fabricating transistors to control supercurrent, we fabricated two- and three-terminal devices that have coplanar Nb electrodes coupled with a SrTiO/sub 3/ substrate. In the two-terminal devices, the Nb electrodes were coupled with an Nb-doped SrTiO/sub 3/ substrate with a carrier concentration of 2/spl times/10/sup 19/ cm/sup -3/. Electrode spacing was about 50 nm. The devices showed Josephson effect at 4.2 K. Three-terminal devices were made on a thinly doped surface of a non-doped 0.4-mm-thick SrTiO/sub 3/ substrate with gate electrodes on the non-doped area of the substrate. Resistance of the three-terminal devices was controlled by applying voltages to the gate electrode at 4.2 K. >

We measured the current-voltage characteristics of YBa/sub 2/Cu/sub 3/O/sub 7-x//oxide/n-SrTiO/sub 3/ diodes using NdGaO/sub 3/, LaAlO/sub 3/, CeO/sub 2/, and MgO as the oxide. MgO films had the highest current density. We then fabricated dielectric-base transistors with a YBa/sub 2/Cu/sub 3/O/sub 7-x/(YBCO) emitter/collector on a SrTiO/sub 3/ dielectric base with an MgO barrier. The transistors had both voltage and current gains exceeding unity at 4.2 K. The emitter current density was about 4/spl times/10/sup 3/ A/cm/sup 2/ at a collector-emitter voltage of 10 V and base-emitter voltage 10 V; this is 2 to 3 orders of magnitude larger than that of transistors with NdGaO/sub 3/ emitter-base barrier. We obtained a transconductance of around 0.4 mS at a collector-emitter voltage of 10 V for a device with a 6-/spl mu/m-diameter emitter. >

The dielectric-base transistor (DBT) is expected to be coupled with various functional oxides such as high-temperature superconductors and ferroelectrics. We experimented with lowering the conduction band of the channel to reduce the operating voltage. LaTiO3 deposited on SrTiO3 supplies carriers in the SrTiO3 substrate by displacing Sr2+ and La3+. With this technique, we fabricated a YBa2Cu3O7−x/In2O3/SrTiO3/LaTiO3/SrTiO3 transistor with a partially doped channel. The transistor operates at under 1 V while maintaining a voltage amplification factor of 2, which is one order smaller than the 15 V operating voltage of a transistor with an undoped channel. The base potential relative to the emitter conduction band has been reduced to 0.3 eV.

For the transient electromagnetic (TEM) method using a high-temperature superconducting interference device (HTS-SQUID), we have developed a magnetometer system with a wide dynamic range, a high slew rate, and superior transportability. To achieve high tolerance to a higher excitation magnetic field, we utilized a SQUID magnetometer containing ramp-edge junctions with La0.1Er0.95Ba1.95Cu3Oy and SmBa2Cu3Oy electrode layers, which was fabricated by using an HTS multi-layer fabrication technique. To operate the magnetometer stably in a rapidly changing magnetic field, we chose the proper materials for the RF shield of liquid nitrogen (LN2) glass Dewar and cables. The white noise level and the slew rate of the system were measured to be 30 fT Hz−1/2 and 10.5 mT s−1, respectively. The resultant signal-to-noise ratio was higher than that of the previous system and improved the exploration depth, which was successfully demonstrated in field tests. The weight of the Dewar, which retains the LN2 for 17 h, is 2.5 kg. The total weight of our system including the LN2 Dewar, a probe with a flux-locked loop (FLL) circuit, a battery, a receiver, and a 30 m-long cable between the FLL and the receiver is as low as 25.6 kg.

We have proposed dielectric-base transistors that use high-permittivity oxide semiconductors, such as SrTiO3, for the base layer. To achieve higher current densities and lower operating voltages in our transistors, we need a method of forming a high-mobility thin SrTiO3 base layer with an appropriate amount of donor concentration. We developed a laser ablation technique to deposit conductive, niobium-doped SrTiO3 thin-films. It is known that the donor states created by the niobium doping are compensated for by doubly-ionized strontium vacancies in an oxidizing ambient. We found that an improved mobility and doping efficiency close to unity were achieved by optimizing the oxygen partial-pressure in the after-deposition cooling process. By controlling the oxygen pressure at around 10−6 Torr, we obtained a niobium-doped SrTiO3 conductive thin-film which had a mobility of 110 cm2/Vs at 11 K.

We have developed a new fabrication method for a high-Tc superconducting quantum interference device (SQUID) with an integrated multiturn input coil to improve the fabrication yield. The method consists of a new multi-SQUID layout and an additional patterning process. In this layout, each input coil is shunted by a shunt inductor to avoid an increase in the inductance of the flux transformer. After preliminary evaluation, the shunt inductor connected to the preferred SQUID is cut to activate the input coil. We demonstrated a drastic improvement in fabrication yield to obtain white field noise less than 25 fT/Hz1/2 from 25 to 83%.

To improve the characterisitcs in dielectric-base transistors, a high quality emitter-base junction is required. We calculated emitter-base characteristics for two junction types -one with a tunneling emitter, where electrons are injected through a thin tunnel barrier, and the other with a space-charge-limited emitter, whose barrier is low and whose electron injection is limited by the space charge effect. The space-charge-limited emitters with its barrier mobolity longer than 10 cm2/Vs have a smaller operating voltage and CR time constant than a tunneling emitter, which has a barrier about 1 eV high and current densities below 105 A/cm2. F-doped SrTiO3, which has a low permittivity, prooved to be a suitable candidate for use in space-charge-limited emitters.

We studied In2O3 for use as an intermediate layer between the YBCO emitter electrode and the SrTiO3 base region of dielectric-base transistors (DBT). We fabricated and tested a YBCO(001)/In2O3(100)/SrTiO3(110) hetero-structure by using a laser-ablation deposition technique with high-density targets. Our YBCO/In2O3/n-SrTiO3 diode structure showed a current density that was one order of magnitude larger than with an MgO intermediate layer.

A Nb-InSb-Nb planar junction with a normal layer of InSb thin film was fabricated by a new process. In this report, the details of the fabrication process and properties of the junction are discussed. The Nb-InSb-Nb junction fabricated using the new process showed a supercurrent. This means that there is no notable barrier, such as the Schottky barrier at the interface between Nb and InSb. The InSb film has a mobility of 500∼700 cm2/V·s, which is 17∼23 times larger than that of Si. This makes it possible to realize the superconductor-semiconductor-superconductor junction with a low carrier density of 1017 cm-3.