Anodic oxides porous silicon

Roussel P, Lysenko V, Remaki B, Delhomme G, Dittmar A, Barbier D (1999) Thick oxidised porous silicon layers for the design of a biomedical thermal conductivity microsensor. Sens Actuators A 74 100-103 Sakly H, MUka R, Chaabane H, Beji L, Ben OH (2006) Anodically oxidized porous silicon as a substrate for EIS sensors. Mater Sci Eng C 26 232-235... 

To understand the electrochemical behavior of silicon, however, the formation and the properties of anodic oxides are important The formation of an anodic oxide on silicon electrodes in HF and HF-free electrolytes will therefore be discussed in detail in this chapter. The formation of native and chemical oxides is closely related to the electrochemical formation process and will be reviewed briefly. The anodic oxidation of porous silicon layers is closely related to the morphology and the luminescent properties of this material and is therefore discussed in Section 7.6. 

Table 4 EL charaeteristics of most devices based on partially oxidized porous silicon. D and L mean that anodization ...

Daumengrofes Labor aus Aluminium-Folie, Blick durch die Wirtschafi, June 1997 Heterogeneous gas-phase micro reactor micro-fabrication of this device anodic oxidation of aluminum to porous catalyst support vision of complete small laboratory numbering-up development of new silicon device [225]. 

A schematic view of the cold cathode fabrication process is shown in Fig. 10.18. The cold cathode is fabricated by low pressure chemical vapor deposition (LPCVD) of 1.5 pm of non-doped polysilicon on a silicon wafer or a metallized glass substrate. The topmost micrometer of polysilicon is then anodized (10 mA cnT2, 30 s) in ethanoic HF under illumination. This results in a porous layer with inclusions of larger silicon crystallites, due to faster pore formation along grain boundaries. After anodization the porous layer is oxidized (700 °C, 60 min) and a semi-transparent (10 nm) gold film is deposited as a top electrode. 

Examples of applications of silicon electrochemistry are exploiting the properties of the silicon-electrolyte contact for analytical purposes, e.g., HF tester and pinhole detector, which directly exploit the special properties of the electrochemical reactions at anodically- or cathodically-polarized silicon electrodes, and the preparation of devices based on porous silicon and silicon oxide (formed by anodic processes). 

Porous anodic alumina films were formed by a two-step anodic oxidation of aluminum foil (99.99% purity) (thickness 100 jum) or of thin aluminum film sputtered onto silicon substrate. First step was performed under lOmA/cm constant current density in 40 g/1 aqueous solution of (COOH)2 during 60 min. After first anodization the formed anodic oxide was removed in the aqueous solution of 0.35 M H3PO4 and 0.2 M CrOs at 90°C. The second anodization was performed in the same regimes as the first one. The formed oxide was removed from the specimen after the first anodization. Nanostructured aluminum samples were rinsed in deionized water and dried in an argon flow. 

The complexity of the system implies that many phenomena are not directly explainable by the basic theories of semiconductor electrochemistry. The basic theories are developed for idealized situations, but the electrode behavior of a specific system is almost always deviated from the idealized situations in many different ways. Also, the complex details of each phenomenon are associated with all the processes at the silicon/electrolyte interface from a macro scale to the atomic scale such that the rich details are lost when simplifications are made in developing theories. Additionally, most theories are developed based on the data that are from a limited domain in the multidimensional space of numerous variables. As a result, in general such theories are valid only within this domain of the variable space but are inconsistent with the data outside this domain. In fact, the specific theories developed by different research groups on the various phenomena of silicon electrodes are often inconsistent with each other. In this respect, this book had the opportunity to have the space and scope to assemble the data and to review the discrete theories in a global perspective. In a number of cases, this exercise resulted in more complete physical schemes for the mechanisms of the electrode phenomena, such as current oscillation, growth of anodic oxide, anisotropic etching, and formation of porous silicon. 

A. Bsiesy, F. Gaspard, R. Herino, M. Ligeon, F. Muller, and J. C. Oberhn, Anodic oxidation of porous silicon layers formed on lightly p-doped substrates, J. Electrochem. Soc. 138, 3450, 1991. 

Y. Kato, T. Ito, and A. Hiraki, Initial oxidation process of anodized porous silicon with hydrogen atoms chemisorbed on the inner surface, Jpn. J. Appl. Phys. 27, L1406, 1988. 

Y. Arita, Formation and oxidation of porous silicon by anodic reaction, J. Cryst. Gr owth 45, 383, 1978. 

A. Grosman, M. Chamarro, V. Morazzani, C. Ortega, S. Rigo, J. Siejka, and H. J. von Bardeleben, Study of anodic oxidation of porous silicon Relation between growth and physical properties, /. Lumin. 57, 13, 1993. 

J. L. Cantin, M. Schoisswohl, A. Grosman, S. Lebib, C. Ortega, H. J. von Bardeleben, fi. Vazsonyi, G. Jalsovszky, and J. Erostyak, Anodic oxidation of p and p -type porous silicon Surface structural transformations and oxide formation, Thin Solid Films 276, 76, 1996. 

The mechanism of electrochemical etching to produce porous silicon has been studied by a number of researchers [11-13]. Although it is certain that several different reactions are occurring simultaneously, anodic etching of crystalline silicon ultimately leads to oxidation and dissolution of the surface to silicon hexafluoride (Scheme 16.1). Under these conditions, Si-Si bonds are electrochemically activated and react with fluoride ions to form soluble, molecular perfluoro species solvation of these silicon fluorides by the etching medium yields a physically irregular, high area porous silicon matrix. Visual indicators for the anodization are the appearance... 

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