High-quality schottky and ohmic contacts in planar 4H-SiC metal semiconductor field-effect transistors and device performance

We have fabricated planar 4H-SiC, metal-semiconductor field-effect transistors (MESFETs) with high-quality metal/SiC contacts. To eliminate potential damage to the gate region caused by etching and simplify the device fabrication process, gate Schottky contacts were formed without any recess gate etching, and an ideality factor of 1.03 was obtained for these gate contacts. The interface state density between the contact metal and SiC was 5.7×10¹² cm⁻²eV⁻¹, which was found from the relationship between the barrier height and the metal work function. These results indicate that the interface was well controlled. Thus, a transconductance of 30 mS/mm was achieved with a 3-μm gate length as the performance figure of these MESFETs with high-quality metal/SiC contacts. Also, a low ohmic contact resistance of 1.2×10⁻⁶ Θcm² was obtained for the source and drain ohmic contacts by using ion implantation.     

Thresholding algorithm for local and parallel processing

In this paper, we propose a thresholding algorithm. This algorithm works under a severe constraint: each pixel in a processed image must be derived from only information of its neighboring pixels. This constraint is very important for a low‐cost device such as a mobile camera, because it makes it possible to process each pixel in parallel. The proposed algorithm deals with gray‐scale images, and determines the threshold based on edge information. The proposed algorithm is represented by local and parallel image processing and has been tested using 104 scenery images. The result shows that the proposed algorithm can binarize images. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(2): 50–56, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20267     

Effect of Organic Binder Segregation on Sintered Strength of Dry-Pressed Alumina

The influence of binder systems on the structure and properties of alumina ceramics was examined. Two types of binders were used to prepare alumina granules by spray drying: poly-acrylic acid (PAA) and poly-vinyl alcohol (PVA). PVA segregated to the surface and subsurface of the granules, whereas PAA was homogeneously distributed. Compaction tests on a single granule showed that the PAA binder provides lower yield stress of granules than PVA. In the die compaction process, the relative density of the compact body started to increase at a lower pressure, and a more homogeneous internal structure was observed in the green compact prepared with the PAA binder than PVA. The homogeneous structure resulted in a sintered body with a strength of 580 vs 485 MPa when PVA was used.     

Performance of automatic gain adjustment in a shunt active filter intended for installation on power distribution systems

This paper discusses automatic gain adjustment in a fully‐digital‐controlled shunt active filter intended for installation on power distribution systems. This is the first step in cooperative control of multiple shunt active filters based on voltage detection for harmonic damping throughout power distribution systems. In general, an optimal control gain is equal to the characteristic impedance of a distribution line. However, it is difficult to know the circuit parameters of a real distribution line, which depend strongly on feeder connections, shunt capacitors, and loads. Therefore, the main purpose of the gain adjustment is to help the active filter to damp out harmonic propagation without considering the circuit parameters. Moreover, the gain adjustment can reduce the compensating current and losses in the active filter. The active filter having the function of automatic gain adjustment is experimentally compared to that with a constant gain. Experiment results verify the effectiveness of the active filter having the function of automatic gain adjustment. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 142(4): 56–65, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10094     

Microwave dielectric properties of mixed phase ceramics, Ba(Zn1/3Ta2/3)O3–xCaTiO3 and xMgTiO3–yCaTiO3–z(Nd2O3,wTiO2)

The effect of different chemical compositions on the microwave dielectric properties of Ba(Zn_1/3Ta_2/3)O₃–xCaTiO₃ and xMgTiO₃–yCaTiO₃–z(Nd₂O₃,wTiO₂) was studied. High fQ dielectrics were designed by optimizing composition and firing conditions. Adding up to 1 mol % CaTiO₃ to Ba(Zn_1/3Ta_2/3)O₃ increased ε_r from 25 to 30 at a firing temperature of 1450 °C, and produced very high fQ values of more than 100 000 GHz at a firing temperature of 1550 °C. EPMA and XRD suggested that ceramics based on Ba(Zn_1/3Ta_2/3)O₃ with CaTiO₃ had mixed phases of Ba(Zn_1/3Ta_2/3)O₃ and Ca–Ti–Zn–O. Addition of CaTiO₃ increased the Ba(Zn_1/3Ta_2/3)O₃ peak observed in XRD and decreased the Ba₃Ta₂O₈ peak. Prolonged sintering of Ba(Zn_1/3Ta_2/3)O₃ with CaTiO₃ increased the fQ value but kept ε_r constant. 0.5MgTiO₃–0.5CaTiO₃–z(Nd₂O₃,wTiO₂) showed a high dielectric constant ε_r>40 and fQ>20 000 GHz. When w=1, τ_f decreased linearly with z around 0 ppm/ °C in 0.5MgTiO₃–0.5CaTiO₃–z(Nd₂O₃,TiO₂) (0.25≤z≤0.5). X-ray and EDX analysis revealed a mixed phase matrix of MgTiO₃ and (Ca_1?αNd_2α/3)Ti_βO₃. It was concluded that ε_r of the high fQ materials Ba(Zn_1/3Ta_2/3)O₃–xCaTiO₃ and xMgTiO₃–yCaTiO₃–z(Nd₂O₃,wTiO₂) would be increased by varying their chemical compositions, x, y, z, and w, and that their fQ value would be improved by appropriate choices of heating temperature and time.     

A method of gene selection that decreases the number of fitness value calculations

This paper proposes a new selection method of a gene from a population for reducing the number of fitness value calculations in genetic algorithms. The proposed method effectively reduces the computation time required to search for a solution to the optimization of a process involving a large number of such calculations as in robot behavior decisions and neural network learnings. In the proposed method, the use of a special buffer for storing a gene and its associated fitness value is introduced. The gene in the buffer is used as a candidate for the solution to the optimization problem. This gene is compared with a gene selected from the population, and one of the values is used in the next generation depending on the results of the comparison. The proportion of suitable genes in the population is increased in the possible shortest time. The convergence speed of our buffer depends on the population topology, which is introduced for choosing a gene from the population to compare with the buffer gene. Three kinds of topology are applied to our algorithm and they are compared and evaluated. The proposed method is applied to a robot control problem to demonstrate the validity of the technique. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(4): 42–49, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10148     

Evaluation of long-term durability in high temperature resistant CFRP laminates under thermal fatigue loading

Thermal fatigue tests were conducted on high temperature resistant carbon fiber reinforced plastics cross-ply laminates to evaluate microscopic damage progress which affects macroscopic mechanical behavior of the laminates. Materials system used were thermoplastic polyetheretherketone based, AS4/PEEK and thermoset bismaleimide based, G40-800/5260. Several types of laminate configuration were used to clarify the effect of ply thickness on microscopic damage progress. Microscopic damages were observed using optical microscopy and soft X-ray radiography. Energy release rate associated with transverse cracking was calculated using variational analysis. The modified Paris law was used to predict transverse cracking. From comparison to mechanical fatigue test results, it is clarified that transverse crack accumulation rate was larger under thermal fatigue loading at same energy release rate range due to the dependence of the fracture toughness on temperature.