Electrochemistry, Vol. 71. No.10, 2003



p844

Semiconductor Space Charge and Surface Oxide Thin Layers Capacitance by Electrochemical Impedance Spectroscopy

Marius CHEMLA, a Valérie BERTAGNA, b François ROUELLE, a Sébastien PETITDIDIER, c and Didier LEVY c

a Laboratoire d’Electrochimie, LI2C, Université P. & M. Curie (Paris, France)
b Departement Chimie des Matériaux, CRMD, Université d’Orléans (Orleans, France)
c STMicroelectronics R & D Center (38920 Crolles, France)

Received April 16, 2003 ; Accepted July 2, 2003

The aim of the present work is to analyse the specific contribution of the differential capacitance of SiO2 ultra‐thin layers to the impedance diagrams of Si/Oxide/Electrolyte (SOE) structures. In usual techniques dealing with MOS devices, the determination of the capacitance/voltage characteristics in MOS devices is hindered by the high value of the tunneling leakage current. In this work, the difficulty was overcome by careful measurement of the impedance diagrams using a SOE structure, under zero current flow. With this novel technique we obtained one RC equivalent circuit when the bias potential corresponded to the accumulation regime, whereas two well separated RC circuits appeared under the depletion regime. An interesting feature of the method is that both R and C components were derived from the data processing. It is known that the measured value of the oxide layer capacitance is sensitive to the charging process of the space charge layer. We observed that the experimental values of the depletion layer capacitive term were in the range of a few 10-2 μF cm-2. These results were consistent with a theoretical treatment of the charge distribution near the flatband potential. In the case of a thermal oxide insulating layer a few nanometers thick, the capacitance was found equal to a few μF cm-2, in agreement with the computed value from the SiO2 oxide thickness. The local electric field is effective for the full charge of the oxide capacitance only under light radiation, and leads to an accurate method for ultra‐thin insulators characterization excluding tunnel leakage current.



p853

Transition during the Growth of Nanoporous Columns in p‐Type Silicon:the Origin of Macropores

Didier HAMM,Tetsuo SAKKA, and Yukio H. OGATA

Institute of Advanced Energy, Kyoto University (Uji, Kyoto 611‐0011, Japan)

Received April 25, 2003 ; Accepted July 6, 2003

This work studies the evolution of the porous silicon layer growth at two current densities for p‐type wafer. It shows that the porous layer is produced by the nucleation and growth of nanoporous columns. Below a threshold current density, the columns become separated by silicon walls i.e. a transition from a homogeneous nanoporous layer to a filled macropore layer takes place (p‐Si, 10‐15Ω・cm). The nanoporous filling into the macropores shows an anisotropic structure parallel to the current direction. When the nanoporous material of such sample is dissolved, a macroporous structure appears. The transition is accompanied by a decrease in valence of dissolved silicon while the porosity and the porous silicon growth rate are not affected. Finally, taking the benefit of this morphological change, various patterned substrates are produced. They are characterised by a faceted motif and a narrow size distribution.



p860

Decomposition of Chlorinated Aromatics by Microwave‐induced Ar Plasma Generated using SiC Ceramic Trigger under Atmospheric Pressure

Yasuhiro SHIMIZU,Hiromichi INADA, Takeo HYODO, and Makoto EGASHIRA

Department of Materials Science and Engineering, Faculty of Engineering, Nagasaki University (1‐14 Bunkyo‐machi, Nagasaki 852‐8521, Japan)

Received May 26, 2003 ; Accepted July 19, 2003

Decomposition behavior of chlorinated aromatics, such as monochlorobenzene, o‐dichlorobenzene, and o‐chlorophenol by microwave‐induced (MI) Ar plasma generated from SiC ceramics has been investigated under atmospheric pressure, and was compared with that of benzene under the same decomposition conditions. Benzene was decomposed and oxidized almost completely by the MI Ar plasma in the Ar‐based feed gas containing 3.0% O2 and 0.46% H2O with a maximum CO concentration of 22 ppm. Much larger quantities of CO tended to be produced by the decomposition of other chlorinated aromatics under the almost the same feed gas composition. However, co‐addition of H2O in the feed gas was useful for reducing the CO concentration for the decomposition of all the chlorinated aromatics. Therefore, H2O was considered to act as a weak oxidant under the MI Ar plasma decomposition. In addition, it was revealed that an increase in the O2 content to a level of 10% resulted in a decrease of CO concentration in the effluent gas and then promoted complete oxidation of all the chlorinated aromatics, whereas the minimum microwave power to generated MI Ar plasma tended to increase with the O2 content.



p866

Low‐temperature Sinterable Ce0.9Gd0.1O1.95 Powder Synthesized through Newly‐devised Heat‐treatment in the Coprecipitation Process

Eisaku SUDA, Bernard PACAUD, Yvan MONTARDI,a Masashi MORI,b Masakuni OZAWA,c and Yasuo TAKEDAd

R&D Department, ANAN KASEI Co.,Ltd. (210‐51, Ohgata, Anan, Tokushima 774‐0022, Japan)
a Aubervilliers Research Center, Rhodia Electronics and Catalysis (52, rue de la Haie‐coq‐F‐93308 Aubervilliers Cedex, France)
bSmart Materials Science Department, Central Research Institute of Electric Power Industry (2‐6‐1 Nagasaka, Yokosuka, Kanagawa 240‐0196, Japan)
c Ceramics Research Laboratory, Faculty of Engineering, Nagoya Institute of Technology (10‐6‐29 Asahigaoka, Tajimi, Gifu 507‐0071, Japan)
dDepartment of Chemistry, Faculty of Engineering, Mie University (1515 Kamihama, Tsu, 514‐0008, Japan)

Received June 17, 2003 ; Accepted July 24, 2003

The low‐temperature sinterable Ce0.9Gd0.1O1.95 (CGO) powder has been synthesized through a newly‐devised heat‐treatment process in the coprecipitation method. The precipitate obtained by the coprecipitation method, namely cerium‐gadolinium carbonate slurry, was stirred at 80℃ for 3h. After filtrating this slurry, the precipitate was washed using pure water and was calcined at 700℃ for 5 h in air. From the results of transmission electron microscopy and X‐ray diffraction analysis, the CGO powder showed uniform particle size of approximately 100 nm and its crystallite size was calculated to be approximately 20 nm. For the tablet of the powder, the relative densities reached 94% at temperatures 1000℃ for holding time 5 h.



p873

硫酸ナトリウムを添加した硫酸水溶液中における鉛電極の電気化学的振舞い

塩田 匡史a*,亀田  毅a,松井 一真a,平井 信充b,田中 敏宏b,原  茂太b

a株式会社ユアサコーポレーション研究開発DC(〒569‐1115 高槻市古曽部町2‐3‐21)
b大阪大学大学院工学研究科マテリアル応用工学専攻(〒565‐0871 吹田市山田丘2‐1)

Electrochemical Behavior of Lead Electrodes in Sulfuric Acid Solution Containing Sodium Sulfate

Masashi SHIOTA,a* Tsuyoshi KAMEDA,a Kazumasa MATSUI,a Nobumitsu HIRAI,b Toshihiro TANAKA,b and Shigeta HARAb

a Yuasa Corporation, Research & Development Division Company (2‐3‐21, Kosobe‐cho, Takatsuki, Osaka 569‐1115, Japan)
b Department of Materials Science & Processing Faculty of Engineering (Osaka University, 2‐1, Yamada‐oka, Suita 565‐0871, Japan)

Received January 29, 2003 ; Accepted June 2, 2003

Electrochemical behavior of lead electrodes in sulfuric acid solution containing sodium sulfate was investigated by means of cyclic voltammetry (CV) and electrochemical atomic force microscopy (EC‐AFM). In anodic scanning of CV, it is found that the sodium sulfate addition hardly influences both the oxidation capacity of the lead electrode and the morphology of the deposited lead sulfate. In cathodic scanning, however, it is found that the specific oxidation current flows only when the sodium sulfate is added to the solution. EC‐AFM images before and after the specific oxidation don't change, suggesting that this specific oxidation does not occur at the surface of the electrode. XRD results suggest that this specific oxidation corresponds to the electrochemical reaction (from Pb to PbSO4). We considered that the lead sulfate crystals holding at the potential range of specific oxidation contain sodium, resulting in higher electric conductivity of lead sulfate, which causes this specific oxidation.


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