Capacitor electrodes

The first type of materials, i.e. KOH activated carbons constitute an interesting class of capacitor electrodes due to their highly developed surface area of the order of 3000 m2/g. Especially, inexpensive natural precursors are well adapted for this process. The activation process is strongly affected by the C KOH ratio, temperature and time. The optimal ratio seems to be 4 1 and the temperature for activation ca. 800°C. The total activation process is quite complicated and proceeds via different pathways and by-products. The... 

The pores of the silica template can be filled by carbon from a gas or a liquid phase. One may consider an insertion of pyrolytic carbon from the thermal decomposition of propylene or by an aqueous solution of sucrose, which after elimination of water requires a carbonization step at 900°C. The carbon infiltration is followed by the dissolution of silica by HF. The main attribute of template carbons is their well sized pores defined by the wall thickness of the silica matrix. Application of such highly ordered materials allows an exact screening of pores adapted for efficient charging of the electrical double layer. The electrochemical performance of capacitor electrodes prepared from the various template carbons have been determined and are tentatively correlated with their structural and microtextural characteristics. 

Care is not always sufficiently brought to this electrode. An insoluble redox system, much more capacitive than the working electrode is often a good choice, or possibly a large double layer capacitor electrode, which does not pollute the electrolyte. 

Emmenegger, C., Mauran, P., Sudan, P., Wenger, P., Hermann, V., Gallay, R., and Zuttel, A. Investigation of electrochemical double-layer (EDLC) capacitors electrodes based on carbon nanotubes and activated carbon materials. J. Power Sources 124, 2003 321-329. 

Layers Typical materials for which CMP processes originally have been developed for microelectronic applications include various types of silicon dioxide such as thermal oxide, TEOS, HDP, BPSG, and other B- or P-doped oxide films. These films are used for various isolation purposes including interlevel dielectric (ILD), intermetal dielectric (IMD), or shallow trench isolation (STI). In addition, n- or p-doped poly-Si, which is a semiconducting material used as capacitor electrode material for DRAMS or gate electrode for MOS applications (CMOS as well as power MOS devices), also has to be polished. Metals for which CMP processes have emerged over the last 10-15 years are W for vertical interconnects (vias) and most importantly Cu as a low-resistivity replacement for aluminum interconnects, employed in the damascene or dual-damascene processing scheme. Other metals that are required for future nonvolatile memories are noble metals like Pt or Ir for which CMP processes have been explored. 

Raw materials containing 30% of SWNTs have been also used for the preparation of super capacitor electrodes after mixing with poly(vinyhdene chloride) (PVDC) and pyrolysis of the mixture at 1000 C. The authors attribute the high capacitance value of 180 F/g measured in 7.5 M KOH to the SWNT material [103]. However, in reality, the carbonization of PVDC at 1000°C produces microporous carbon [107], and as a consequence the high capacitance values are certainly because of the carbon obtained from the polymeric binder but not of SWNTs. 

Jiang, Q., Qu, M.Z., Zhou, G.M., et al. (2002). A study of activated carbon nanotubes as electrochemical super capacitors electrode materials. Mater. Lett., 57, 988-91. 

Also shown explicitly in Fig. 6.1.6 is the interconnection resistance Rpm of the movable structure. In sensors with long and skinny mechanical suspensions it is often large and can contribute significant electronic noise. Highly doped substrates and connecting all suspensions electrically in parallel reduce this source of error. Other interconnection resistances are often negligible and omitted from the circuit diagram. Silicon resistivity should be kept sufficiently low also to prevent depletion of the capacitor electrodes. 

Storage condensers are needed to operate the pixel (active-matrix). Some storage capacitors can be constructed by using part of the gate electrode as a storage capacitor electrode (which is called aCs-ongate). Note that... 

Fig. 22a shows SEM pictures of PANT/MWNTs composite electrodes with 20 w1% of MWNTs compared with 100 wt% PANI pellet electrodes (Fig. 22b) [99]. From Fig. 22a, it can be seen that the composite material is porous, keeping the advantage of the entan ed network of the nanotubes, that allows a good access of the electrolyte to the active polymer. There is no doubt that such a texture of the capacitor electrode is optimal for a fast ionic diffusion and migration in the polymer so that the electrode performance should be improved. By contrast, as it can be seen from Fig. 22b, the electrodes which are pressed from pure ECP, are very dense and not porous.

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