High-frequency characterization and delay-time analysis have been performed for a short channel AlGaN/GaN heterojunction FET. The fabricated device with a short gate length (Lg) of 0.07 µm exhibited an extrinsic current gain cutoff frequency of 81 GHz and a maximum frequency of oscillation of 190 GHz with a maximum stable gain (MSG) of 8.2 dB at 60 GHz. A new scheme for the delay-time analysis was proposed, in which the effects of rather large series resistance RS + RD are properly taken into account. By applying the new scheme to a device with Lg=0.25 µm, we obtained an effective high-field electron velocity of 1.75107 cm/s, which is consistent with our previous results calculated using Monte Carlo simulation.

The DC resistivities of silicon germanium thin films on Si substrates by a non-contact and non-destructive technique using terahertz time domain spectroscopy (THz-TDS) agree with the values obtained by the four-point probe measurement. In the present experiment, the mobility has not been precisely determined owing to the limitation of the frequency range in our equipment (from 0.1 to 1.5 THz). However, when the mobility becomes large enough, this method will be highly useful in evaluating semiconductor thin films, since the method gives the same data as those from Hall measurement without sample processing or electrode contact to sample.

We demonstrated the uniformity and stability as well as the high breakdown voltage of 0.1-µm-gate InP HEMTs with a double recess structure. To overcome the drawbacks regarding the uniformity and stability in the double recess structure, an InP passivation layer that functions as an etch-stopper and a surface passivator was successfully applied to the structure. It was confirmed that there was no degradation in the uniformity and stability of device performance for the double recess HEMTs that had the breakdown voltages in the on-state and off-state improved by a factor of 1.6.

In order to clarify the mechanism of gate leakage in AlGaN/GaN heterostructure field effect transistors (HFETs), temperature (T)-dependent current-voltage (I-V) characteristics of Ni/n-AlGaN Schottky contact were measured in detail. Large deviations from the thermionic emission transport were observed in I-V-T behavior with anomalously large reverse leakage currents. An analysis based on the thin surface barrier (TSB) model showed that the nitrogen-vacancy-related near-surface donors play a dominant role in the leakage through the AlGaN Schottky interface. As a practical scheme for suppressing the leakage currents, use of an insulated gate (IG) structure was investigated. As the insulator, Al2O3 was selected, and an Al2O3 IG structure was formed on the AlGaN/GaN heterostructure surface after an ECR-N2 plasma treatment. An in-situ XPS analysis exhibited successful formation of an ultrathin stoichiometric Al2O3 layer which has a large conduction band offset of 2.1 eV at the Al2O3/Al0.3Ga0.7N interface. The fabricated Al2O3 IG HFET achieved pronounced reduction of gate leakage, resulting in the good gate control of drain currents up to VGS = +3 V. The maximum drain saturation current and transconductance were 0.8 A/mm and 120 mS/mm, respectively. No current collapse was observed in the Al2O3 IG-HFETs, indicating a remarkable advantage of the present Al2O3-based insulated gate and passivation structure.

In this paper, a high-performance pipelining architecture for 2-D inverse discrete wavelet transform (IDWT) is proposed. We use a tree-block pipeline-scheduling scheme to increase computation performance and reduce temporary buffers. The scheme divides the input subbands into several wavelet blocks and processes these blocks one by one, so the size of buffers for storing temporal subbands is greatly reduced. After scheduling the data flow, we fold the computations of all wavelet blocks into the same low-pass and high-pass filters to achieve higher hardware utilization and minimize hardware cost, and pipeline these two filters efficiently to reach higher throughput rate. For the computations of N N-sample 2-D IDWT with filter length of size K, our architecture takes at most (2/3)N2 cycles and requires 2N(K-2) registers. In addition, each filter is designed regularly and modularly, so it is easily scalable for different filter lengths and different levels. Because of its small storage, regularity, and high performance, the architecture can be applied to time-critical image decompression.

InGaP/GaAs HBT with novel ledge coupled capacitor (LCC) structure has been proposed and demonstrated for the first time. The LCC employs an extrinsic InGaP ledge layer as a capacitor parallel to the base resistor. This configuration enables feeding RF signals directly into the base without passing them through the base resistor. With the fabricated HBT, no increase of leakage current between emitter and base electrode was observed. The maximum oscillation frequency (fmax) of the HBT was improved by 10 GHz as compared with an HBT without the LCC.

A distributor of digital contents desires to collect users' attributes. On the other hand, the users do not desire to offer the attributes owing to the privacy protection. Previously, an anonymous survey system for attributes statistics is proposed. In this system, asking trusted third parties' helps, a distributor can obtain the correct statistics of users' attributes, such as gender and age, while no information beyond the statistics is revealed. However, the system suffers from the inefficiency of a protocol to generate the statistics, since the cost depends on the number of all the users registering this survey system. This paper proposes an anonymous survey system, where this cost is independent from the number of all the registering users. In this accomplishment, a group signature scheme with attribute tracing is also proposed. A conventional group signature scheme allows a group member to anonymously sign a message on behalf of the group, while only a designated party can identify the signer. The proposed scheme further enables the party to trace signer's attribute.

This paper describes a method for the fast evaluation of the Sommerfeld integrals for modeling a vertical dipole antenna array in a borehole. When we analyze the antenna inside a medium modeled by multiple cylindrical layers with the Method of Moment (MoM), we need a Green's function including the scattered field from the cylindrical boundaries. We focus on the calculation of Green's functions under the condition that both the detector and the source are situated in the innermost layer, since the Green's functions are used to form the impedance matrix of the antenna. Considering bounds on the location of singularities on a complex wave number plane, a fast convergent integration path where pole tracking is unnecessary is considered for numerical integration. Furthermore, as an approximation of the Sommerfeld integral, we describe an asymptotic expansion of the integrals along the branch cuts. The pole contribution of TM01 and HE11 modes are considered in the asymptotic expansion. To obtain numerical results, we use a fast convergent integration path that always proves to be accurate and efficient. The asymptotic expansion works well under specific conditions. The Sommerfeld integral values calculated with the fast evaluation method is used to model the array antenna in a borehole with the MoM. We compare the MoM data with experimental data, and we show the validity of the fast evaluation method.

We consider a soft-decision iterative bounded distance decoding algorithm for binary linear block codes. In the decoding algorithm, bounded distance decodings are carried out with respect to successive input words, called the search centers. A search center is the sum of the hard-decision sequence of a received sequence and a sequence in a set of test patterns which are generated beforehand. This set of test patterns has influence on the error performance of the decoding algorithms as simulation results show. In this paper, we propose a construction method of a set of candidate test patterns and a selection method of test patterns based on an introduced measure of effectiveness of test patterns. For several BCH codes of lengths 127, 255 and 511, we show the effectiveness of the proposed method by simulation.

When the Alamouti code is applied (as a space-time block code) to an OFDM system with transmit diversity, the simple Alamouti decoding requires that each subchannel is flat-fading and constant over two symbol periods (Alamouti codeword period). The second requirement makes the Alamouti decoding scheme not suitable for time varying channels. In this Letter, we propose a new decision directed receiver to better accommodate time varying channels.

The history of the development of the High Electron Mobility Transistor (HEMT) is an outstanding illustration of how a new device can be successfully marketed. In this paper we discuss a key to successful commercialization of new devices.

Given the importance of the traffic on modern communication networks, advanced error correction methods are needed to overcome the changes expected in channel quality. Conventional countermeasures that use high dimensionality parity codes often fail to provide sufficient error correction capability. We propose a parity code with high dimensionality that is iteratively decoded. It provides better error correcting capability than conventional decoding methods. The proposal uses the steepest descent method to increase code bit reliability and the coherency between parities and code bits gradually. Furthermore, the quantization of the decoding algorithm is discussed. It is found that decoding with quantization can keep the error correcting capability high.

The Earth Simulator (ES), developed by the Japanese government's initiative "Earth Simulator project," is a highly parallel vector supercomputer system. In May 2002, the ES was proven to be the most powerful computer in the world by achieving 35.86 teraflops on the LINPACK benchmark and 26.58 teraflops for a global atmospheric circulation model with the spectral method. Three architectural features enabled these great achievements; vector processor, shared-memory and high-bandwidth non-blocking interconnection crossbar network. In this paper, an overview of the ES, the three architectural features and the result of performance evaluation are described particularly with its hardware realization of the interconnection among 640 processor nodes.

In this paper, we propose an on-line writer recognition method for Thai numeral. A handwriting process is characterized by a change of numeral's shape, which is represented by two features, a displacement of pen-point position and an area of triangle determined from the two adjacent points of pen-point position and the origin. First, the above two features are expanded into Fourier series. Secondly, in order to describe feature of handwriting, FIR (Finite impulse response) system having the above Fourier coefficients as input and output of the system is introduced. The impulse response of the FIR system is used as the feature of handwriting. Furthermore, K-L expansion of the obtained impulse response is used to recognize writer. Writer recognition experiments are performed by using 3,770 data collected by 54 Thai writers for one year. The average of Type I (false rejection) error rate and Type II (false acceptance) error rate were 2.16% and 1.12%, respectively.

Hetero-interface properties of SiO2/4H-SiC on (0001), (11-20), and (03-38) crystal orientations are presented. Epitaxial growth on new crystal orientations, (11-20) and (03-38), is described by comparing with the growth on (0001). Using thermal oxidation with wet oxygen, metal-oxide-SiC (MOS) structure was fabricated. From high-frequency capacitance-voltage characteristics measured at 300 K and 100 K, the interface properties were characterized semi-quantitatively. The interface state density was precisely determined using the conductance method for the MOS structure at 300 K. The new crystal orientations have the lower interface state density near the conduction band edge than (0001). From the characteristics of inversion-type planar MOSFETs, higher channel mobilities were obtained on (03-38) and (11-20) than on (0001). The cause of the difference in the channel mobility is speculated by the difference bond configuration of the three crystal orientations.

Edge detection has been an essential step in image processing, and there has been much work undertaken to date. This paper inspects a fuzzy mathematical morphology in order to reach a higher-level of edge-image processing. The proposed scheme uses a fuzzy morphological gradient to detect object boundaries, when the boundaries are roughly defined as a curve or a surface separating homogeneous regions. The automatic edge detection algorithm consists of two major steps. First, a new version of anisotropic diffusion is proposed for edge detection and image restoration. All improvements of the new version use fuzzy mathematical morphology to preserve the edge accuracy and to restore the images to homogeneity. Second, the fuzzy morphological gradient operation detects the step edges between the homogeneous regions as object boundaries. This operation uses geometrical characteristics contained in the structuring element in order to extract the edge features in the set of edgeness, a set consisting of the quality values of the edge pixels. This set is prepared with fuzzy logic for decision and selection of authentic edge pixels. For experimental results, the proposed method has been tested successfully with both synthetic and real pictures.

In digital content distribution systems, digital watermarking (fingerprinting) technique provides a good solution to avoid illegal copying and has been studied very actively. c-Secure CRT Code is one of the most practical ID coding schemes for such fingerprinting since it is secure against collusion attacks and also secure even though random errors are furthermore added. But its usefulness is decreased in the case that random errors are added because the code length will be longer. In this paper, a new collusion attack with addition of random errors is introduced and show that c-Secure CRT Code is not sufficiently secure against the attack at first. Next, we analyze the problem and propose a new ID coding scheme, Randomized c-Secure CRT Code which overcomes the problem. As a result, this new scheme improves the error tracing probabilities against the proposed attack drastically. This new scheme has the same code length, so this is one of the most responsible fingerprinting codes for content distribution systems.

Schottky gas sensors of CO were fabricated using high quality AlGaN/GaN/Si heterostructures. The CO sensors show good sensitivity in the temperature range of 250 to 300 (530%, at 160 ppm CO in N2) and fast response comparable with SnO2 sensors. A two-region linear regime was observed for the dependence of sensitivity on CO concentration. GaN sensors on Si substrate offer the possibility of integration with Si based electronics. The gas sensors show slow response with time, the change of material properties possibly in the presence of large thermal stress.

We propose an image generation method for an immersive multi-screen environment that contains a motion ride. To allow a player to look around freely in a virtual world, a method to generate an arbitrary direction image is required, and this technology has already been established. In our environment, displayed images must also be updated according to the movement of the motion ride in order to keep a consistency between the player's viewpoint and the virtual world. In this paper, we indicate that this updating process can be performed by the similar method to generate looking-around images and the same data format can be applicable. Then we discuss the format in terms of the data size and the amount of calculations need to consider the performance in our display environment, and we propose new image formats which improve on the widely-used formats such as the perspective, or the fish-eye format.

We describe 150-nm-thick collector InP-based double heterojunction bipolar transistors with two types of thin pseudomorphic bases. The emitter and collector layers are designed for high collector current operation. The collector current blocking is suppressed by the compositionally step-graded collector structure even at JC of over 500 kA/cm2 with practical breakdown characteristics. An HBT with a 20-nm-thick base achieves a high fT of 351 GHz at high JC of 667 kA/cm2, and a 30-nm-base HBT achieves a high value of 329 GHz for both fT and fmax at JC of 583 kA/cm2. An equivalent circuit analysis suggests that the extremely small carrier-transit-delay contributes to the ultrahigh fT.