We outline a number of high temperature superconducting Josephson junction-based devices including superconducting quantum interference devices (SQUIDs) developed for a wide range of applications including geophysical exploration, magnetic anomaly detection, terahertz (THz) imaging and microwave communications. All these devices are based on our patented technology for fabricating YBCO step-edge junction on MgO substrates. A key feature to the successful application of devices based on this technology is good stability, long term reliability, low noise and inherent flexibility of locating junctions anywhere on a substrate.

This paper proposes a new type of compact waveguide directional coupler, which is constructed from two crossed E-plane rectangular waveguide with two metallic posts in the square junction and one metallic post at each port. The metallic posts in the square junction are set symmetrically along a diagonal line to obtain the directivity properties. The metallic post inserted at each input/output waveguide port can realize a matched state. Tight-coupling properties 0.79-6 dB are realized by optimizing the dimension of the junction and the positions/radii of the posts. The design results are verified by an em-simulator (Ansoft HFSS) and experiments.

The comparative analysis of the well known Double Drift Region (DDR) IMPATT diode structure and the n+pvnp+ structure for the avalanche diode has been realized on the basis of the drift-diffusion nonlinear model. The last type of the diode was named as Double Avalanche Region (DAR) IMPATT diode. This structure includes two avalanche regions inside the diode. The phase delay which was produced by means of the two avalanche zones and the drift zone v is sufficient for the negative resistance obtained for the wide frequency region. The numerical model that is used for the analysis of the various diode structures includes all principal features of the physical phenomena inside the semiconductor structure. The admittance characteristics of both types of the diodes were analyzed in very wide frequency region.

In the FDTD simulation of microwave circuits, a device in very small size compared with the wavelength is often handled as a lumped element, but it may still occupy more than one cell instead of a wire structure without volume routinely employed in classical extended FDTD algorithms. In this paper, two modified extended FDTD algorithms incorporating a lumped element occupying more than one cell are developed directly from the integral form of Maxwell's equations based on the assumption whether displacement current exists inside the region where a device is present. If the displacement current exists, the modified extended FDTD algorithm can be represented as a Norton equivalent current-source circuit, or otherwise as a Thevenin equivalent voltage-source circuit. These algorithms are applied in the microwave line loaded by a lumped resistor and an active antenna to illustrated the efficiency and difference of the two algorithms.

The long-term reliability of heterojunction bipolar transistor (HBT) continues to be a subject of great interest due to the increased acceptance of this device in a wide range of applications. The most demanding requirements for long-term reliability include high performance microwave instrumentation, X-band radar, and lightwave communication (OC-192). A significant leap in the long-term reliability performance was observed in HBT as the AlGaAs emitter material was replaced with lattice matched InGaP. A dramatic improvement in the long-term reliability was also observed in AlGaAs emitter HBT's as the turn on voltage (Vbe) was lowered. The typical failure mechanism in HBT devices at high current density and high temperature long-term reliability testing was a dramatic increase in the base current at low current densities. One of the limiting factors in obtaining MTTF in InGaP HBT was the long time required to promote failures in the HBT device. Furthermore, a large sample size is necessary to extract a reliable MTTF. Significant increases in the current density as high as 180 kA/cm2 during reliability testing was used to promote failures in order to obtain an MTTF within a reasonable amount of time. The MTTF at a junction temperature of 334C and at a current density of 180 kA/cm2 was 1159 hours. The extrapolated MTTF at a junction temperature of 150C exceeded 106 hours for all of the tested devices. An attempt to predict the MTTF of AlGaAs and InGaP HBT using a simple model based upon the fitting of the initial Gummel plots of large area devices was made. The model was based upon the estimation of the trap defect density at the base/emitter junction, the hole injection component of the base current, and the turn-on Vbe. Degradation of the HBT was assumed to occur at the base/emitter junction and this corresponded to an increase in the trap density at this heterojunction. A factor of 5 improvement in the MTTF of the reliability of AlGaAs HBT with a lower turn on voltage was estimated based upon the above model, which confirmed the experimental results. These results suggested that the emitter material is primarily responsible in determining the long-term reliability characteristics of HBT. The combination of a high effective hole barrier and a low turn-on Vbe are highly desirable for long-term reliability characteristics.

Heterojunction bipolar transistors (HBTs) are key devices for a variety of applications including L-band power amplifiers, high speed A/D converters, broadband amplifiers, laser drivers, and low phase noise oscillators. AlGaAs emitter HBTs have demonstrated sufficient reliability for L-band mobile phone applications. For applications which require extended reliability performance at high junction temperatures (>250) and large current densities (>50 kA/cm2), InGaP emitter HBTs are the preferred devices. The excellent reliability of InGaP/GaAs HBTs has been confirmed at various laboratories. At a moderate current density and junction temperature, Jc = 25 kA/cm2 and Tj = 264, no device failures were reported out to 10,000 hours in a sample of 10 devices. Reliability testing performed up to a junction temperature of 360 and at a higher current density (Jc = 60 kA/cm2) showed an extrapolated MTTF of 5 105 hours at Tj = 150. The activation energy for AlGaAs/GaAs HBTs was 0.57 eV, while the activation energy for InGaP/GaAs HBTs was 0.68 eV, which indicated a similar failure mechanism for both devices.

Fundamental microwave key devices used in achieving compact mobile/portable telephones (raidio units) are discussed. The historical development flow of the systems and radio units are introduced, with respect to the 800-/900-MHz and 1.5-GHz Japanese cellular radio systems. The design concept of the developed radio units is briefly described. Tehnical requirements for RF circuits are reviewed and the developed key devices are practically applied to the circuits. Key factors in the requirements are also shown. Finally. future trends fro the key devices are surveyed from the stand point of achieving a smaller and more light weight pocket radio unit.

This paper reports on the properties of thin-film thermal switches that are monolithically fabricated on high-Tc superconductive filter. Operating at a wide temperature range of 50-77 K, it was found that the switch could control the center frequency by -10 MHz with an increased insertion loss of less than 0.7 dB. In an on-off switching operation of filter characteristics using thin-film switches, power consumption was approximately 20 mW at 77 K, and the signal decay time as a switching speed was 30 ms at 76 K with a switch current of 70 mA. The decay time decreased exponentially as the switch current or the temperature setting increased.