This paper describes small AlGaAs/GaAs HBT's for low-power and high-speed integrated circuits. The device fabrication is based on a new bridged base electrode technology that permits emitter width to be defined down to 1 µm. The new technology features oxygen-ion implantation for emitter-base junction isolation and zinc diffusion for extrinsic base formation. The oxygen-ion implanted emitter-base junction edge has been shown to provide a periphery recombination current much lower than that for the previous proton implanted edgs, the result being a much higher current gain particularly in small devices. The zinc diffusion offers high device yield and good uniformity in device characteristics even for a very thin (0.04 µm) base structure. An HBT with emitter dimensions of 12.4 µm2 yields an fT of 103 GHz and an fmax of 62 GHz, demonstrating that the new technology has a significant advantage in reducing the parasitic elements of small devices. Fabricated one-by-eight static frequency dividers and one-by-four/one-by-five two-modulus prescalers operate at frequencies over 10 GHz. The emitters of HBT's used in the divider are 12.4 µm2 in size, which is the smallest ever reported for AlGaAs/GaAs HBT IC's. These results indicate that the bridged base electrode technology is promising for developing a variety of high-speed HBT IC's.

The stability of a terminated two-port network is investigated, and the stability conditions with only one inequality are obtained. Furthermore, the stability conditions with two inequalities, which are in the same form as those for the passive terminations known at the present time, are also obtained.

This paper presents a new approach to the recovery of 3-D structure from multiple pairs of images from different viewpoints. Searching for the corresponding points between images, which is common in stereopsis, is avoided. Extracted edges from input images are projected back into 3-D space, and their intersections are calculated directly. Many false intersections may appear, but if we have many pair images, true intersections are extracted by appropriate thresholding. Octree representation of the intersections enables this approach. We consider a way to treat adjacent edge piexels as a line segment rather than as individual points, which differs from previous works and leads to a new algorithm. Experimental results using both synthetic and actual images are also described.

In this paper we introduce the Piecewise Linear Radial Basis Function Model (PWL-RBFM), a new nonlinear model that uses the well known RBF framework to build a PWL functional approximation by combining an l1 norm with a linear RBF function. A smooth generalization of the PWL-RBF is proposed: it is obtained by substituting the modulus function with the logistic function. These models are applied to several time series prediction tasks.

In this paper we estimate the number of permutations realizable in fault-tolerant multistage interconnection networks designed to tolerate faults on any switching element. The Parallel Omega network and the INDRA network are representative types of fault-tolerate multistage interconnection networks designed to tolerate a single fault. In order to evaluate the enhancement in the function of network by preparing the hardware redundancy for fault-tolerance, we estimate the number of permutations realizable in fault-tolerant networks. This result enables us to set up a standard to evaluate the hardware redundancy required to tolerate multifaults from the viewpoint of the enhancement of network function. This paper concludes that in the case where the number of inputs is up to 32 the increase ratio of the number of realizable permutations is no more than 1/0.73 even if the tolerance to multifaults is prepared instead of the tolerance to a single fault.

A novel nonlinear directional coupler consisting of tapered and uniform waveguides with self-focusing or self-defocusing nonlinear material is proposed to improve all-optical switching characteristics. Its switching characteristics are analyzed by using a beam propagation method based on the Galerkin's finite element technique (FE-BPM), in which nonuniform sampling spacings along the transverse coordinate are adopted. It is presented that the tapered nonlinear directional coupler shows fairly distinct 'high' and 'low' states of output power with steep transition versus input power. This property is discussed in comparison with conventional nonlinear directional couplers consisting of uniform symmetric and uniform asymmetric coupled waveguides. In addition, the effects of loss on the characteristics of tapered nonlinear directional coupler are examined.

We report the development of high-performance small-scale AlGaAs/GaAs collector-up heterojunction bipolar transistors (C-up HBT) with a carbon (C)-doped base layer. Oxygen-ion (O+) implantation is used to define their intrinsic emitter/base junctions and zinc (Zn)-diffusion is used to lower the resistivity of their O+-implanted extrinsic base layers. The highly resistive O+-implanted AlGaAs layer in the extrinsic emitter region sufficiently suppresses electron injection even under high-forward-bias conditions, allowing high collector current densities. The use of a C-doped base is especially effective for small-scale C-up HBT's because it suppresses the undesirable turn-on voltage shift caused by base dopant diffusion in the intrinsic area around the collector-mesa perimeter that occurs during the high-temperature Zn-diffusion process after implantation. Even in a small-scale trasistor with a 2 µm2 µm collector, a current gain of 15 is obtained. A microwave transistor with a 2 µm10 µm collector has a cutoff frequency fT of 68 GHz and a maximum oscillation frequency fmax of 102 GHz. A small-scale C-up HBT with a 2 µm2 µm collector shows a higher fmax of 110 GHz due to reduced base/collector capacitance CBC and its fmax remains above 100 GHz, even at a low collector current of 1 mA. The CBC of this device is estimated to be as low as 2.2 fF. Current gain dependence on collector size is also investigated for C-up HBT's and it is found that the base recombination current around the collector-mesa perimeter reduces the current gain.

We studied the selective epitaxy of GaAs grown by a technique called pulsed-jet epitaxy. Pulsed-jet epitaxy is a kind of atomic layer epitaxy (ALE) based on low-pressure metalorganic vapor-phase epitaxy (MOVPE). We compared growth behavior and layers grown by ALE and MOVPE. During ALE we supplied trimethylgallium (TMGa) and arsine (AsH3) alternately; however, during MOVPE we supplied TMGa and AsH3 simultaneously. At a growth temperature of 500, we obtained a better growth selectivity using ALE than using MOVPE. The lateral thickness profile of the ALE-grown GaAs layer at the edge of SiO2 mask was uniform. In contrast, the MOVPE growth rate was enhanced near the mask edge. Using ALE, we selectively grew GaAs epilayers even at mask openings with submicron widths. Scanning electron microscopy revealed that the ALE selectively grown structures had an uniform thickness profile, though the facets surrounding the structures depended on the orientation of mask stripes. After MOVPE, however, the (001) surface of the deposited layer was not flat because of the additional lateral diffusion of the growth species from the gas phase and/or the mask surface and some crystal facets. The experimental results show that, using ALE, we can control the shape of selectively grown structures. Selective epitaxy by ALE is a promising technique for fabricating low-dimensional quantum effect devices.

We developed a simple, practical, adaptive data compression algorithm of the LZ78 class. According to the Lempel-Ziv greedy parsing, a string boundary is not related to the statistical history modeled by finite-state sources. We have already reported an algorithm classifying data into subdictionaries (CSD), which uses multiple subdictionaries and conditions the current string by using the previous one to obtain a higher compression ratio. In this paper, we present a practical implementation of this method suitable for any kinds of data, and show that CSD is more efficient than the LZC which is the method used by the program compress available on UNIX systems. The CSD compression performance was about 10% better than that of LZC with the practical dictionary size, an 8k-entry dictionary when the test data was from the Calgary Compression Corpus. With hashing, the CSD processing speed became as fast as that of LZC, although the CSD algorithm was more complicated than LZC.

This paper is concerned with the data compression and interpolation of multi-view image set. In this paper, we propose a novel disparity compensation scheme based on geometric relationship. We first investigate the geometric relationship between a point in the object space and its projection onto view images. Then, we propose the disparity compensation scheme which utilize the geometric constraints between view images. This scheme is used to compress the multi-view image into the structure of the triangular patches and the texture data on the surface of patches. This scheme not only compresses the multi-view image but also synthesize the view images from any viewpoints in the viewing zone. Also, this scheme is fast and have compatibility with 2-D interframe coding. Finally, we report the experiment, where two sets multi-view image were used as original images and the amount of data was reduced to 1/19 and 1/20 with SNR 34 dB and 20 dB, respectively.

This paper addresses a method for constructing surface representation of 3D structures from a sequence of cross-sectional images. Firstly, we propose cell-boundary representation, which is a generalization of PVP method proposed by Yun and Park, and develop an efficient surface construction algorithm from a cell-boundary. Cell-boundary consists of a set of boundary cells with their 1-voxel configurations, and can compactly describe binary volumetric data. Secondly, to produce external surface from the cell-boundary representation, we define 19 modeling primitives (MP) including volumetric, planar and linear groups. Surface polygons are created from those modeling primitives using a simple table look-up operation. Since a cell-boundary can be obtained using only topological information of neighboring voxels, there is no ambiguity in determining modeling primitives which may arise in PVP method. Since our algorithm has data locality and is very simple to implement, it is very appropriate for parallel processing.

A specific signal in most of actual environmental systems fluctuates complicatedly in a non-Gaussian distribution form, owing to various kinds of factors. The nonlinearity of the system makes it more difficult to evaluate the objective system from the viewpoint of internal physical mechanism. Furthermore, it is very often that the reliable observation value can be obtained only within a definite domain of fluctuating amplitude, because many of measuring equipment have their proper dynamic range and the original random wave form is unreliable at the end of amplitude fluctuation. It becomes very important to establish a new signal processing or an evaluation method applicable to such an actually complicated system even from a functional viewpoint. This paper describes a new trial for the signal processing along the same line of the extended regression analysis based on the Bayes' theorem. This method enables us to estimate the response probability property of a complicated system in an actual situation, when observation values of the output response are saturated due to the dynamic range of measuring equipment. This method utilizes the series expansion form of the Bayes' theorem, which is applicable to the non-Gaussian property of the fluctuations and various kinds of correlation information between the input and output fluctuations. The proposed method is newly derived especially by paying our attention to the statistical information of the input-output data without the saturation operation instead of that on the resultantly saturated observation, differing from the well-known regression analysis and its improvement. Then, the output probability distribution for another kind of input is predicted by using the estimated regression relationship. Finally, the effectiveness of the proposed method is experimentally confirmed too by applying it to the actual data observed for indoor and outdoor sound environments.

New circuit techniques were proposed to realize a high-density and high-performance content addressable memory (CAM). A dynamic register which functions as a status flag, and some logic circuits are organically combined and flexibly perform complex search operations, despite the compact layout area. Any kind of logic operations for the search results, that are AND, OR, INVERT, and the combinations of them, can be implemented in every word simultaneously. These circuits are implemented in an experimental 288 kbit dynamic CAM using 0.8 µm CMOS process technology. We consider these techniques to be indispensable for high-density and high-performance dynamic CAM.

We compare interfaces of Nb/AlOx-Al/Nb and Nb/ZrOx-Zr/Nb junctions using secondary ion mass spectroscopy and cross-sectional transmission electron microscopy. We have clarified that an interface of the Nb/AlOx-Al/Nb junction is drastically different from that of the Nb/ZrOxZr/Nb junction. An adsorbed water vapor layer plays an important role in suppressing grain boundary diffusion between Nb and Al at the interface of the Nb/AlOxAl/Nb junction. In depositing Nb and Al at low power and cooling the substrate, it is important to control the formation of the adsorbed water vapor layer for fabricating Nb/AlOx-Al/Nb junctions exhibiting excellent current-voltage characteristics.

We have fabricated Nb/AlOx/Nb Josephson tunnel junctions by a sputtering apparatus with a load-lock system. This sputtering apparatus had the sub chamber for preparation and the main chamber for sputtering. The substrate temperature was confirmed to be kept less than 85 during Nb sputtering at the deposition rate of 1.18 nm/s for 7 minutes. The junctions that had 50µm50 µm area successfully showed the Vm value (the product of the critical current and the subgap resistance at 2 mV) as high as 50 mV at the current density of 100 A/cm2.

The magnitude of low frequency noise is studied in a Nb-(nanoconstrictions)-NbN system with adjustable current-voltage characteristics. We find that the magnitude of low frequency noise decreases sharply with increasing the subgap conductivity of the device. We suggest a qualitative explanation of this observation in terms of gradual build up of the nanoconstriction region by field assisted growth. The decrease of low frequency noise is related to the "cleanliness" of the system as measured by the amount of Andreev reflection-related conductivity. The scaling of the magnitude of low frequency noise with device resistance is also discussed.

We have systematically grown and characterized (Bi, Pb)2Sr2CaCu2Oy (BPSCCO) single crystals, and investigated the tunneling properties and the intrinsic Josephson effects of the single crystals as a function of the nominal composition of Pb, x. It was observed that Pb atoms (ions) were monotonically substituted for Bi atoms (ions) in the (Bi, Pb)-O layers of the crystals with increasing x in a region of 0x0.5, while the modulation structure was maintained in a range of 0x0.3, but disappeared in x0.3, accompanying the decrease of c-lattice parameter and Tc. Moreover, it was found that the energy gaps Δ of BPSCCO depend hardly on x for x0.5, which are about 24 meV, so that the Pb-induced electronic change in the (Bi, Pb)-O layer do not perturb the electronic states in this superconducting system. And it was confirmed that the currentvoltage characteristics of the BPSCCO single crystals had multiple resistive branches corresponding to a series array of several hundreds Josephson junctions, and showed Shapiro steps and zero-crossing steps with the voltage separation of the order of mV resulting from the phase locking of about a hundred Josephson junctions among them under microwave irradiation. The estimated number of junctions gave the concept that the intrinsic Josephson junctions consist of the superconducting block layers and the insulating layers in the BPSCCO single crystals.

Fabrication of all-epitaxial high-Tc SIS tunnel junctions requires an atomically flat superconducting thin film to be grown and a proper insulating material to be selected. First, we study the initial growth mode of YBCO thin films and show that reducing the growth rate results in a very smooth surface. Second, perovskite-related compound oxides, PrGaO3 and NdGaO3, which have a small lattice mismatch with YBCO and good wetability, are shown to be promising insulating materials for all-epitaxial SIS tunnel junctions. We believe that these concepts will be useful in the development of all-epitaxial high-Tc SIS tunnel junctions with good electrical properties.

High temperature superconductors are eminently suitable for use in high frequency devices because of their large energy gap. We fabricated weak link Josephson junctions connected in series. The junctions were constructed of EuBa2Cu3O7-x (EBCO) superconducting thin films on bicrystal MgO substrates. We measured their microwave broadband detection (video detection) characteristics. The responsivity (Sr) of the junctions depended on the bias current and their normal state resistance. The array junctions were effective in increasing normal state resistance. We obtained a maximum Sr of 22.6 [V/W].

This papter proposes a new type of unidirectional error control codes which indicates the location of unidirectional errors clustered in b-bit length, i.e., unidirectional byte error in b (b2) bits. Single unidirectional b-bit byte error locating codes, called SUbEL codes, are first clarified using necessary and sufficient conditions, and then code construction algorithm is demonstrated. The lower bound on check bit length of the SUbEL codes is derived. Based on this, the proposed codes are shown to be very efficient. Using the code design concept presented for the SUbEL codes, it is demonstrated that generalized unidirectional byte error locating codes are easily constructed.