Vacuum microelectronics is potential technology of building novel electronic devices that cannot be realized by using solid-state electronics. This paper reviews the current status of this technology. Micron-size cold cathodes using field electron emission have been developed for the electron sources of novel vacuum electron devices. Recently field emission displays are getting into the flat panel display market.

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This paper describes surface charging and flashover characteristics of a cylindrical quartz spacer subjected to a ramped DC voltage in vacuum. Flashover along the side surface of a cover glass protecting photovoltaic solar batteryarray causes sever problems for the operation of a high voltage power generation system in space. We have studied the charging and flashover characteristics that depend on quartz thickness and average roughness of the side surface. The thickness is varied from 0.3 mm, which is close to that of practical cover glasses, to 10 mm, and the roughness from 0.03 µm up to 3 µm. As a result, we have found that the flashover strength for the smoothest surface shows a pronounced increase as the thickness decreases bellow 3 mm. The flashover strength also increases with the roughness in particular when it is larger than about 2 µm. The charging has been observed by using a capacitive probe embedded into the cathode and the results are analyzed by a simulation based on the Secondary Electron Emission Avalanche mechanism. The observed and simulated results very well agree with each other for the variety of thicknesses examined. The accumulated charge decreases with the roughness and, at a certain level of the applied voltage, the surface no more acquires charge for an average roughness larger than about 2 µm. These results explain the reason why the flashover strength increases with the roughness. These results are useful for designing a cover glass of the solar power generation system.

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In order to clarify the instability phenomena of a low current vacuum arc, characterized by noise on the current trace prior to the actual current chopping, an analysis of silver cathode spot has been made. For the analysis, cathode spot region is recognized as the collisionless space charge sheath connected with singly ionized collisional plasmas.It is proposed that a current level below that no real solution exists is unstable current and this current corresponds to the point at which a vacuum arc turns into unstable. It is found that there is no real solution when the current is below 19.4A. The physical explanation is considered that the electrons returning to the sheath region from the plasma one dominate over positive ions and, consequently, the electric field at the cathode surface is F₀²<=0 below 19.4A. Similar results have already been obtained for copper cathode. In order to examine the analytical result for its validity, the probe measurements of electron temperature in the diffused arc plasma has been performed. The electron temperature-arc current characteristics were found to be similar between experimental and analytical results.

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The triggered vacuum gap (TVG) is a closing switch for generating large current pulse and can work in the wide range of voltage for several kV to tens kV. Main electrodes are made of Ag-WC. One of main electrode has a hole for trigger electrode (Mo). The switching time is short, if the polarity of the holed-electrode is negative. It is called polarity effect. We devised a crowbar circuit using the polarity effect of the TVGs. The crowbar current of this circuit was investigated experimentally by varying applied voltage, inductance, capacitance, gap length of TVGs, and trigger current duration. A crowbar current, crest of which is 2.4 kA and 4.9/270µs for example, was observed. The probability of generating the crowbar current was more than about 90 %, in the following condition: the trigger current duration of 6.65 µs and the gap length of 2-6 mm.

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In order to identify the long span reliability of vacuum gap insulation under continuous AC voltage application, characteristics of breakdown strength versus breakdown time (long time E-t characteristics) were measured for a uniform and a non-uniform field gap. The breakdown strength of these gaps before the discharge conditioning treatments did not depend on breakdown time. However, after the discharge conditioning treatments, the breakdown strength became describable as an experimental formula E=A·t^-1/n. The value of drop index (life index) n in the formula was a maximum of 75 for the uniform field gap, while a maximum of 25 for the non-uniform field gap. In addition, with repeating the discharge conditioning treatment, the long time E-t characteristics of both gaps shifted to higher electric field. In particular, the value of n for the uniform field gap became larger. Breakdown modes (failure modes) of these gaps before and after the discharge conditioning treatments, evaluated by the value of shape parameter m in Weibull probability distribution function, were classified into decreasing failure rate mode and constant failure rate mode, respectively.

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Time of flight method in the form of ion acceleration by a negative square pulse is investigated for lead ion plasma generated from a short burning time impulse vacuum arc. In the method, lead ions existing between the grid with earth potential and the accelerating grid which is connected to the ion accelerating tube are accelerated into the tube by applying a negative square pulse voltage to the accelerating grid. The ions fly toward the ion collector with a constant velocity dependent on the charge state. The effect of an axial magnetic field in the accelerating tube on the loss of the flying ions and on the obtained rate of the densities of Pb⁺¹ and Pb⁺² ions in the arc plasma is discussed. The relation between the amount of the accelerated ions and the accelerating voltage is also investigated from the viewpoint of time dependent propagation of the ion sheath, which is formed in front of the accelerating grid.

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Preliminary experiments were conducted on Cu wiring or interconnect preparation in semiconductor devices using shielded cathodic arc deposition, comparing with the non-shielded method, normal shielded method, torus-type filtered arc deposition method (Torus-FAD), and T-shape filtered arc deposition method (T-FAD). The magnetically transported-shielded arc plasma was focused on a substrate using an electromagnetic coil and a permanent magnet. The principal results were as follows: (1) the evaporation rate increased with arc current; (2) the number of macrodroplets emitted from the Cu cathode reduced when the shield-substrate distance in the normal shielded method was shorter; (3) the deposition rate of the magnetically transported-shielded cathodic arc deposition (MT-SCAD) was 8 times higher than that of the normal shielded method; and (4) there was an insufficient filled void in the Cu film at the interconnect trench prepared by MT-SCAD, although there were no voids in the film prepared by Torus-FAD and T-FAD.

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The vacuum electrical breakdown characteristics of oxygen-free copper electrodes, which were processed by precision diamond turning machining in a clean room and were heat-treated in hydrogen after that machining, were investigated by applying impulse voltage. These electrodes were carried in mobile vacuum chamber in order to keep them clean. The surface conditions were analyzed by the X-ray Photoelectron Spectroscopy (XPS) before and after the ion-beam sputtering and after the 500 times repetitive breakdowns. These experiments can be performed in in-situ experimental apparatus that are maintained in ultra-high vacuum (10^-7 to 10^-8Pa). As a result, these electrodes showed higher breakdown fields at the first breakdown relative to values obtained in the past studies. In addition, their conditioning achieved with less number of breakdowns. According to the XPS spectra, it was confirmed that organic contaminants were reduced by heat treatment in hydrogen and ion beam sputtering. These shows that heat treatment in hydrogen is effective in reducing contaminants on the electrode surface and improving the breakdown characteristics.

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Oxygen-free copper electrodes stored in the atmosphere were used as test samples. Changes of field emission characteristics with 500 repetitive breakdowns and He ion beam sputtering were investigated in conjunction with analyses of electrode surface conditions by X-ray Photoelectron Spectroscopy (XPS). Experiments revealed that field emission currents were detected from electrodes used as the anode after 500 breakdowns, while for electrodes that were heavily contaminated and the cathode after 500 breakdowns field emission currents were not detected. Although anode and cathode surfaces were cleaned by 500 breakdowns, the cathode surfaces were more completely cleaned than the anode surfaces during repetitive 500 breakdowns. Residual carbon may play a role to dominate field emission characteristics and breakdown characteristics.

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A three dimensional simulation code with the finite difference time domain (FDTD) method combined with the fluid model for electron has been developed for the microwave excited surface wave plasma in the RDL-SWP device. This code permits the numerical analysis of the spatial distributions of electric field, power absorption, electron density and electron temperature. At low gas pressure of about 10 mTorr, the numerical results were compared with the experimental measurements that show the validity of this 3-D simulation code. A simplified analysis assuming that an electron density is spatially uniform has been studied and its applicability is evaluated by the 3-D simulation. The surface wave eigenmodes are determined by the electron density, and it is found that the structure of the device strongly influences to the spatial distribution of the electric fields of surface waves in a low density area (n_e<3.0×10¹¹cm^-3). A method to irradiate a microwave to the whole surface area of the plasma is proposed which is found to be effective to obtain a high uniformity distribution of electron density.

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Numerical simulation model of separating discharge is proposed in order to simulate the separating discharge patterns generated on the back-side of the sheet, which is separated from the grounded metal. As Poisson's equation is solved taking into consideration separating discharge, surface discharge and movement of the sheet, discharge patterns on the backside of the sheet are simulated. The number of the discharge patterns, discharge gap and potential distribution on the back-side of the sheet after separation are calculated and compared with the experimental results. These simulation results show good agreement with the experimental results. These comparisons confirm that this model can be used for the study of preventing separating discharge and reducing the harmful effect of the separating discharge.

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A test insulator with unpenetrated crack was constructed from two insulating blocks on an insulating board: Inner walls of the crack were formed by the surfaces of two blocks. The test insulator with the crack was set in a needle-plane electrode system. When ac (50Hz) high voltage is applied between the electrodes, PD generates from the needle electrode propagating through the crack, and its propagation is restricted at the dead end of the crack. The material of the blocks is PMMA. The crack width (s) ranged from 10µm to 1000µm. The experiments were performed in air controlled at 20-25°C and 40-50%RH. The experimental results show that the magnitude of positive pulse due to ac PD depends on the width of the crack. The maximum magnitude of positive pulse in the area of the width 10µm<s<200µm (narrow area) is 2 times larger than that in the area of width 500µm<s<1000µm (wide area); The larger magnitude of positive pulse >2×10^-8C is observed only in the narrow area. It appears every 3-4 cycles of applied ac. The generation mechanism of the large magnitude of the pulse is discussed focusing on the charge accumulation on the insulating wall in the crack. The dust-figure suggests that the positive accumulated charge on the wall in the narrow area of width restricts the propagation of positive PD along the insulating wall of the crack. The positive pulse of large magnitude may be generated just after the cycle of negative PD where the accumulated positive charge is largely neutralized by the negative PD.

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By dividing a water-treed XLPE sheet sample of 1 mm thickness into a non-degraded region and a water-treed one, relative permittivity ε_r2' and ac conductivity σ_AC2 of the water-treed region have been estimated using an equivalent circuit. The way of changes of ε_r2' and σ_AC2 with the length r of the water-treed region has been discussed based on the Sillars model. It has been concluded that the volume fraction of water in the water-treed layer is in the range of 0.5 % to 1.5 % for the most-degraded XLPE sheet, which depends on the ratio of axes of spheroids to which water-filled voids and channels are compared. It is also concluded that ac conductivity of water in the water-treed region is in the range of 3×10^-3 S/m to 2×10^-2 S/m.

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Data transmission speed in electronic systems has increased steadily as a result of the development of information technologies. The insulation materials used in these systems require a very low dielectric constant (ε_r) and a similarly low dielectric loss (tanδ). Such materials have been developed for satellite communications and high grade computer systems, however, operating speeds in popular electronics such as mobile or personal systems will also exceed 1GHz in the near future. When that happens, cost will become an even more important factor in the selection of high-performance insulation materials. Dicyclopentadiene polymer (Metathene) has a ε_r of 2.51 and a tan δ of 0.0029 at 1GHz. Moreover, Metathene containing air (63% air by volume) measures as low as 1.57 for ε_r and 0.001 for tan δ at the same frequency. This paper presents an assessment of the appropriateness of Metathene for high-frequency applications.

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It has been shown experimentally that the electron density changes periodically when the thickness of the dielectric window changes in wave guide mode discharges, or hybrid surface wave mode discharges. It suggests there is a optimum thickness of the dielectric window.

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In recent years, the color of advertising signboards or vending machines on the streets should be harmonized with the surrounding landscape. In this study, we investigated how the colors (red and white) of the vending machines virtually installed by CG would affect the traditional landscape. 20 subjects estimated landscape samples in Hida-Furukawa by the SD technique. The result of our experiment shows that the vending machines have great influence on the surrounding landscape. On the other hand, we have confirmed that they can harmonize with the circumference landscape by the color to use.

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