The magnetic field resolution of the tunnel magneto-resistive (TMR) sensors has been improving and it reaches below 1.0 pT/Hz0.5 at low frequency. The real-time measurement of the magnetocardiography (MCG) and the measurement of the magnetoencephalography (MEG) have been demonstrated by developed TMR sensors. Although the MCG and MEG have been applied to diagnosis of diseases, the conventional MCG/MEG system using superconducting quantum interference devices (SQUIDs) cannot measure the signal by touching the body, the body must be fixed, and maintenance costs are huge. The MCG/MEG system with TMR sensors operating at room temperature have the potential to solve these problems. In addition, it has the great advantage that it does not require a special magnetic shielded room. Further developments are expected to progress to maximize these unique features of TMR sensors.

Fast switching speed, low power consumption, and good stability are some of the important properties of spin transfer torque assisted voltage controlled magnetic anisotropy magnetic tunnel junction (STT-assisted VCMA-MTJ) which makes the non-volatile full adder (NV-FA) based on it attractive for Internet of Things. However, the effects of process variations on the performances of STT-assisted VCMA-MTJ and NV-FA will be more and more obvious with the downscaling of STT-assisted VCMA-MTJ and the improvement of chip integration. In this paper, a more accurate electrical model of STT-assisted VCMA-MTJ is established on the basis of the magnetization dynamics and the process variations in film growth process and etching process. In particular, the write voltage is reduced to 0.7 V as the film thickness is reduced to 0.9 nm. The effects of free layer thickness variation (γtf) and oxide layer thickness variation (γtox) on the state switching as well as the effect of tunnel magnetoresistance ratio variation (β) on the sensing margin (SM) are studied in detail. Considering that the above process variations follow Gaussian distribution, Monte Carlo simulation is used to study the effects of the process variations on the writing and output operations of NV-FA. The result shows that the state of STT-assisted VCMA-MTJ can be switched under -0.3%≤γtf≤6% or -23%≤γtox≤0.2%. SM is reduced by 16.0% with β increases from 0 to 30%. The error rates of writing ‘0’ in the NV-FA can be reduced by increasing Vb1 or increasing positive Vb2. The error rates of writing ‘1’ can be reduced by increasing Vb1 or decreasing negative Vb2. The reduction of the output error rates can be realized effectively by increasing the driving voltage (Vdd).

A non-volatile memory (NVM) employing MTJ has a lot of strong points such as read/write performance, best endurance and operating-voltage compatibility with standard CMOS. However, it consumes a lot of energy when writing the data. This becomes an obstacle when applying to battery-operated mobile devices. To solve this problem, we propose an approach to augment the capability of the precision scaling technique for the write operation in NVM. Precision scaling is an approximate computing technique to reduce the bit width of data (i.e. precision) for energy reduction. When writing image data to NVM with the precision scaling, the write energy and the image quality are changed according to the write time and the target bit range. We propose an energy-efficient approximate storing scheme for non-volatile flip-flops and a magnetic random-access memory (MRAM) that allows us to write the data by optimizing the bit positions to split the data and the write time for each bit range. By using the statistical model, we obtained optimal values for the write time and the targeted bit range under the trade-off between the write energy reduction and image quality degradation. Simulation results have demonstrated that by using these optimal values the write energy can be reduced up to 50% while maintaining the acceptable image quality. We also investigated the relationship between the input images and the output image quality when using this approach in detail. In addition, we evaluated the energy benefits when applying our approach to nine types of image processing including linear filters and edge detectors. Results showed that the write energy is reduced by further 12.5% at the maximum.

We propose a compact magnetic tunnel junction (MTJ) model for circuit simulation by de-facto standard SPICE in this paper. It is implemented by Verilog-A language which makes it easy to simulate MTJs with other standard devices. Based on the switching probability, we smoothly connect the adiabatic precessional model and the thermal activation model by using an interpolation technique based on the cubic spline method. We can predict the switching time after a current is applied. Meanwhile, we use appropriate physical models to describe other MTJ characteristics. Simulation results validate that the model is consistent with experimental data and effective for MTJ/CMOS hybrid circuit simulation.

Gold nanoparticles (GNPs) are often used as island electrodes of single-electron (SE) devices. One of technical challenges in fabrication of SE devices with GNPs is the placement of GNPs in a nanogap between two lead electrodes. Utilization of dielectrophoresis (DEP) phenomena is one of possible solutions for this challenge, whereas the fabrication process with DEP includes stochastic aspects. In this brief paper, we present our experimental results on electric resistance of GNP arrays assembled by DEP. More than 300 pairs of electrodes were investigated under various DEP conditions by trial and error approach. We evaluated the relationship between the DEP conditions and the electric resistance of assembled GNP arrays, which would indicate possible DEP conditions for fabrication of SE devices.

An energy-efficient nonvolatile FPGA with assuring highly-reliable backup operation using a self-terminated power-gating scheme is proposed. Since the write current is automatically cut off just after the temporal data in the flip-flop is successfully backed up in the nonvolatile device, the amount of write energy can be minimized with no write failure. Moreover, when the backup operation in a particular cluster is completed, power supply of the cluster is immediately turned off, which minimizes standby energy due to leakage current. In fact, the total amount of energy consumption during the backup operation is reduced by 66% in comparison with that of a conventional worst-case-based approach where the long time write current pulse is used for the reliable write.

Superconducting tunnel junction (STJ) array detectors can exhibit excellent performance with respect to energy resolution, detection efficiency, and counting rate in the soft X-ray energy range, by which those excellent properties STJ array detectors are well suited for detecting X-rays at synchrotron radiation facilities. However, in order to achieve a high throughput analysis for trace impurity elements such as dopants in structural or functional materials, the sensitive area of STJ array detectors should be further enlarged up to more than 10 times larger by increasing the pixel number in array detectors. In this work, for a large STJ-pixel number of up to 1000 within a 10,mm- square compact chip, we have introduced three-dimensional (3D) structure by embedding a wiring layer in a SiO$_{2}$ isolation layer underneath a base electrode layer of STJs. The 3D structure is necessary for close-packed STJ arrangement, avoiding overlay of lead wiring, which is common in conventional two-dimensional layout. The fabricated STJ showed excellent current-voltage characteristics having low subgap currents less than 2,nA, which are the same as those of conventional STJs. An STJ pixel has an energy resolution of 31,eV (FWHM) for C-K$alpha $ (277,eV).

We have developed a process for the fabrication of high-quality Nb/AlOx/Nb tunnel junctions with small area and high current densities for the heterodyne mixers at millimeter and submillimeter wavelengths. Their dc I-V curves are numerically studied, including the broadening of quasiparticle density of states resulting from the existence of an imaginary part of the gap energy of Nb. We have found both experimentally and numerically that the subgap current is strongly dependent on bias voltage at temperatures below 4.2 K unlike the prediction of the BCS tunneling theory. It is shown that calculated dc I-V curves taking into account the complex number of the gap energy agree well with those of Nb/AlOx/Nb junctions measured at temperatures from 0.4 to 4.2 K. We have successfully built receivers at millimeter and submillimeter wavelengths with the noise temperature as low as 4 times the quantum photon noise, employing those high-quality Nb/AlOx/Nb junctions. Those low-noise receivers are to be installed in the ALMA (Atacama Large Millimeter/Submillimeter Array) telescope and they are going into series production now.

In this paper, it is shown that our fabricated MTJ of 60180 nm2, which is connected to the MOSFET in series by 3 levels via and 3 levels metal line, can dynamically operate with the programming current driven by 0.14 µm CMOSFET. In our measurement of transient characteristic of fabricated MTJ, the pulse current, which is generated by the MOSFET with an applied pulse voltage of 1.5 V to its gate, injected to the fabricated MTJ connected to the MOSFET in series. By using the current measurement technique flowing in MTJ with sampling period of 10 nsec, for the first time, we succeeded in monitor that the transition speed of the resistance change of 60180 nm2 MTJ is less than 30 ns with its programming current of 500 µA and the resistance change of 1.2 kΩ.

In this paper, we have succeeded in the fabrication of high performance Magnetic Tunnel Junction (MTJ) which is integrated in CMOS circuit with 4-Metal/ 1-poly Gate 0.14 µm CMOS process. We have measured the DC characteristics of the MTJ that is fabricated on via metal of 3rd layer metal line. This MTJ of 60180 nm2 achieves a large change in resistance of 3.52 kΩ (anti-parallel) with TMR ratio of 151% at room temperature, which is large enough for sensing scheme of standard CMOS logic. Furthermore, the write current is 320 µA that can be driven by a standard MOS transistor. As the results, it is shown that the DC performance of our fabricated MTJ integrated in CMOS circuits is very good for our novel spin logic (MTJ-based logic) device.

We have developed InGaAs-based VCSELs operating around 1.1 µm for high-speed optical interconnections. By applying GaAsP barrier layers, temperature characteristics were considerably improved compared to GaAs barrier layers. As a result, 25 Gbps 100 error-free operation was achieved. These devices also exhibited high reliability. No degradation was observed over 3,000 hours under operation temperature of 150 and current density of 19 kA/cm2. We also developed VCSELs with tunnel junctions for higher speed operation. High modulation bandwidth of 24 GHz and a relaxation oscillation frequency of 27 GHz were achieved. 40 Gbps error-free operation was also demonstrated.

A normal-distribution-function-shaped superconducting tunnel junction (NDF-STJ) which consists of Nb/Al-AlOx/Al/Nb has been fabricated as an X-ray detector. Current - voltage characteristics were measured at 0.4 K using three kinds of STJs, which have the dispersion parameters σ of 0.25, 0.45 and 0.75. These STJs showed very low subgap leakage current of about 5 nA. By irradiating with 5.9 keV X-rays, we obtained the spectrum of these NDF-STJs. They showed good energy resolution with small magnetic fields of below 3 mT, which is about one-tenth of those for conventional-shaped STJs.

We briefly survey recent developments in the thin film synthesis and junction fabrication of MgB2 toward superconducting electronics. The most serious problem in the thin film synthesis of MgB2 is the high vapor pressure required for phase stability. This problem makes in-situ film growth difficult. However, there has been substantial progress in thin film technology for MgB2 in the past three years. The low-temperature thin-film process in a UHV chamber can produce high-quality MgB2 films with Tc 35 K. Furthermore, technology to produce single-crystal epitaxial MgB2 films has recently been developed by using hybrid physical-chemical vapor deposition. With regard to Josephson junctions, various types of junctions have been fabricated, all of which indicate that MgB2 has potential for superconducting devices that operate at 20-30 K, the temperature reached by current commercial cryocoolers.

Magnetic tunnel junctions (MTJ), i.e., structures consisting of two ferromagnetic layers (FM1 and FM2), separated by a very thin insulator barrier (I), have recently attracted attention for their large tunneling magnetoresistance (TMR) which appears when the magnetization of the ferromagnets of FM1 and FM2 changes their relative orientation from parallel to antiparallel in an applied magnetic field. Using an ultrahigh vacuum magnetron sputtering system, a variety of MTJ structures have been explored. Double Hc magnetic tunnel junction, NiFe/Al2O3/Co and FeCo/Al2O3/Co, were fabricated directly using placement of successive contact mask. The tunnel barrier was prepared by in situ plasma oxidation of thin Al layers sputter deposited. For NiFe/Al2O3/Co junctions, the maximum TMR value reaches 5.0% at room temperature, the switching field can be less than 10 Oe and the relative step width is about 30 Oe. The junction resistance changes from hundreds of ohms to hundreds of kilo-ohms and TMR values decrease monotonously with the increase of applied junction voltage bias. For FeCo/Al2O3/Co junctions, TMR values exceeding 7% were obtained at room temperature. It is surprising that an inverse TMR of 4% was observed in FeCo/Al2O3/Co. The physics governing the spin polarization of tunneling electrons remains unclear. Structures, NiFe/FeMn/NiFe/Al2O3/NiFe, in which one of the FM layers is exchange biased with an antiferromagnetic FeMn layer, were also prepared by patterning using optical lithography techniques. Thus, the junctions exhibit two well-defined magnetic states in which the FM layers are either parallel or antiparallel to one another. TMR values of 16% at room temperature were obtained. The switching field is less than 10 Oe and step width is larger than 30 Oe.

Present status of the development of superconducting tunnel junctions for the detection of X-ray photons and heavy ions is reported. The energy resolution for 5.9 keV X-rays was measured to be 41 eV, 58 eV, 65 eV and 129 eV with STJs of 2020 µm2, 100100 µm2, 200200 µm2 and 500500 µm2, respectively, and a model to describe the phonon-mediated X-ray signals is discussed. Direct voltage switching induced by heavy ions was successfully observed.

We report on the fabrication and operation of all-NbN single flux quantum (SFQ) circuits with resistively shunted NbN/AlN/NbN tunnel junctions fabricated on silicon substrates. The critical current varied by about 5% in 400 NbN/AlN/NbN junction arrays, where the junction area was 88 µm2. Critical current densities of the NbN/AlN/NbN tunnel junctions showed exponential dependence on the deposition time of the AlN barrier. By using the 12-nm-thick Cu film as shunted resistors, non-hysteretic current-voltage characteristics were achieved. From dc-SQUID measurements, the sheet inductance of our NbN stripline was estimated to be around 1.2 pH at 4.2 K. We designed and fabricated circuits consisting of dc/SFQ converters, Josephson transmission lines, and T flip-flop-based SFQ/dc converters. The circuits demonstrated correct operation with a bias margin of more than 15% at 4.2 K.

We report on progress in the development of high current density NbN/AlN/NbN tunnel junctions for application as submillimeter wave SIS mixers. A ultra-high current density up to 120 kA/cm2, roughly two orders of magnitude larger than any reported results for all-NbN tunnel junctions, was achieved in the junctions. The magnetic field dependence and temperature dependence of critical supercurrents were measured to investigate the Josephson tunneling behaviour of critical supercurrents in the high-Jc junctions. We have developed a low-noise quasi-optical SIS mixer with the high-current density NbN/AlN/NbN junctions and two-junction tuning circuits which employ Al/SiO/NbN microstriplines. The tuning characteristics of the mixer were investigated by measuring the response in the direct detection mode by using the Fourier Transform Spectrometer (FTS) and measuring the response in the heterodyne detection mode with the standard Y-factor method at frequencies from 670 to 1082 GHz. An uncorrected double sideband receiver noise temperature of 457 K (12hν/kB) was obtained at 783 GHz.

A 90 GHz band planar-type superconducting mixer using Ba1-xKxBiO3 (BKBO) bicrystal junctions was fabricated on a MgO bicrystal substrate. The mixer is integrated with microwave circuits and two junctions, but we could not operate the mixer in image rejection mode because of process damage to the junction properties. However we confirmed the mixing operation; the intermediate frequency (IF) signal was observed up to 17K (LO87 GHz, RF92 GHz).

Resonant properties of resistance shunted tunnel junctions have been investigated using the RLCSJ model. We found that an increase in dc current resulted from an increase in impedance of the shunted tunnel junctions. The static and dynamic properties of the shunted tunnel junctions were described in detail by numerical simulations and experiments. The simulated and measured results showed good agreement in I-V characteristics. A Josephson array oscillator has been proposed using the resonant properties for increasing oscillator output impedance. We designed and fabricated the oscillator with 20 shunted tunnel junctions. The output power of the oscillator delivered to the load resistor was estimated to be about 0.5µW at 312 GHz.

A Superconductor-Insulator-Superconductor (SIS) mixer using two junctions connected in parallel through a stripline inductance has been studied. The essential point of the two-junctions device is that the capacitance of the junctions was tuned out by the inductance to obtain a broadband operation without mechanical tuning elements. It has been shown by theoretical analysis that the performance of this type of device is excellent and nearly quantum-limited performance of the mixer can be obtained. It has been demonstrated that the double sideband (DSB) noise temperature of a receiver employing this type of device was less than 40 K over the bandwidth of 90-120 GHz and that the lowest receiver noise temperature of 18 K, which is only 3.2 times as large as the quantum limited photon noise was obtained around 118 GHz. Junctions used in the two-junctions device have significantly larger area, i.e. larger capacitance, and smaller normal resistance than conventional ones. In order to obtain a good impedance match between the source and the junctions, an impedance transformer made of a superconductiong stripline was integrated with the junctions. This type of two-junctions device can easily be scaled to submillimeter frequency without using submicron-sized SIS junctions.