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Valve metal, Si and ceramic oxides as dielectric films for passive and active electronic devices

: Michaelis, A.

Alkire, R.C. ; International Society of Electrochemistry ISE:
Electrochemical Surface Modification : Thin Films, Functionalzation and Characterization
Weinheim: Wiley-VCH, 2008 (Advances in Electrochemical Science and Engineering 10)
ISBN: 978-3-527-31419-5
ISBN: 3-527-31419-9
Book Article
Fraunhofer IKTS ()
electrochemistry; valve metal oxide; dielectric; electronic device; ceramics

The application of valve metal oxides such as Ti, Zr, Hf, V, Nb and Si oxides in electronics is discussed. Valve metal oxides show outstanding dielectric properties, which make them a key component in many passive and active devices such as capacitors, resistors and IC´s. Nevertheless, the most important oxide system still is Si/SiO2, which can be considered as the bench mark system.
Consequently, one chapter of this book is dedicated to Si/SiO2 with special emphasis on its use in DRAM (dynamic random access memory) microchip fabrication which can be considered the most advanced and demanding technology in microelectronics. Regarding their electronic properties the valve metal oxides are related to another class of oxides, namely the perovskite structured piezoelectrics: BaTiO3, (Ba,Sr)TiO3 (BST), Pb(ZrxTi1-x)O3 (PZT), SrBi2Ta2O9 (SBT). These advanced electroceramics outperform the simple valve metal oxides in many respects, such as, by their exceptional high relative dielectric constant (er) (sometimes also called relative permittivity). Therefore, both the valve metal and the perovskite oxides compete in many applications. For example, in passive component capacitor manufacturing Al/Al2O3 and Ta/Ta2O5 electrolyte capacitors share the market with multilayer ceramic capacitors (MLCC) that are BaTiO3 based. However, due to their more complex chemistry the integration of perovskite layers into devices is difficult when ultra thin nano-dielectric films are needed. Therefore, this treatise focuses on the less complex valve metal oxides as ultra thin nano dielectrics (< 100 nm). For application as a capacitor dielectric material, a high relative dielectric constant er is important but not sufficient. The anodically formed valve metal oxides differ in structure (some are amorphous, some crystalline), electronic behaviour (some oxides behave like an n-type semiconductor), and some oxides show a pronounced texture dependence of oxide growth, that is the oxide properties vary with the crystallographic orientation of the substrate surface. Depending on the desired application of the oxides, an optimum combination of these properties has to be found. For the study of the oxide systems, electrochemical and optical methods are applied.