Insulating layers aluminium oxide

Growing a quality tunnel barrier on a silicon surface involves cleaning off this oxide and depositing a metal, such as aluminium for example, that is subsequently oxidized to form a thin insulating layer. Two potential difficulties lurk in the process formation of a conducting metal silicide at... 

Concerning the two-layer model, the thickness and properties of each layer depend on the nature of the electrolyte and the anodisation conditions. For the application, a permanent control of thickness and electrical properties is necessary. In the present chapter, electrochemical impedance spectroscopy (EIS) was used to study the film properties. The EIS measurements can provide accurate information on the dielectric properties and the thickness of the barrier layer [13-14]. The porous layer cannot be studied by impedance measurements because of the high conductivity of the electrolyte in the pores [15]. The total thickness of the aluminium oxide films was determined by scanning electron microscopy. The thickness of the single layers was then calculated. The information on the film properties was confirmed by electrical characterisation performed on metal/insulator/metal (MIM) structures. 

The metal oxide silicon field effect transistor (MOSFET) has the basic structure as shown schematically in Figure 10.1 (an n-channel device is shown and will be discussed, although p-channel devices work equally well). The device consists of two n-type diffusions (called the source and the drain) in a p-type substrate separated by a p-type area. This area is covered by a thin (50 nm) insulator layer (generally silicon dioxide or silicon dioxide overlaid with silicon nitride) which is called the gate insulator. On top of the gate insulator there is a metallic contact called the gate electrode, which in conventional devices is made from aluminium. The source and drain diffusions are... 

This occurs in the condensed phase and interferes with heat feedback from the burning gases in the flame to the decomposing polymer beneath. It also promotes the formation of a layer of char which further protects and insulates unbumed material. The smoke suppression effect may be viewed as a consequence of char promotion (that is carbon-rich particulates that would have otherwise become smoke, are locked up in the condensed phase as char). It is also likely that the very high surface area transition aluminium oxides formed during decomposition of ATH will adsorb many volatile species and fragments that could otherwise become smoke. 

One of the emerging technologies that is showing great promise is the use of hydrated mineral fillers such as aluminium and magnesium hydroxides, as such materials can provide high levels of flame retardancy without the formation of smoke or corrosive and potentially toxic fumes. The use of fillers as flame retardants has recently been reviewed by Rothon [23]. Essentially the key features are an endothermic decomposition to reduce the temperature, the release of an inert gas to dilute the combustion gases and the formation of an oxide layer to insulate the polymer and to trap and oxidise soot precursors. 

In thin-film electroluminescence, a transparem front electrode and an opaque back electrode are used. The former may be a thin layer of indium-tin oxide, the latter a thin layer of aluminium. In the early 1970s a MISIM device (metal-insulator-semiconductor-insulator-metal) with a ZnS Mn electroluminescent layer was shown to maintain bright luminescence for thousands of hours. The insulators can be selected from a large groups of oxides. 

Aluminium and A1 alloys react with oxygen and water vapor in the air to produce a thin, conqtact surface oxide film which protects the underlying metal from further attack (Fig. 3.1-80). The surface layer contains mainly amorphous AI2O3 in several layers. The so-called barrier layer has an extremely low conductivity for electrons and ions and thus acts as an insulator in any interfacial electrochemical reactions. It thus affords effective protection against corrosion. If mechanical damage of the protective layer occurs, or if the layer is removed by pickling, it re-forms immediately. Aluminium and A1 alloys thus exhibit good corrosion resistance to chemicals, seawater, and the weather. 

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