Sol-Gel deposition processes of thin ceramic films

The development of inorganic functional thin films is driven by applications in electronics, solar technology, optics and other high-tech fields. A wide range of film compositions can be manufactured by gas phase or liquid phase deposition methods. Due to the high apparative costs of gas phase methods, the use of the sol-gel processing offers advantages by sufficiently inexpensive film technologies. Additionally, purity and stability of the precursors, homogeneity of mixed precursors, comparably low processing temperatures to transfer gel films into pure inorganic films can be used to generate high-performance thin films. Generally, the precursors used are highly reactive compounds such as transition metal alkoxides. They tend to cause problems due to precipitations and ageing of the sols. Chelating agents such as beta-diketones and/or carboxylates can be used as key to control and to moderate the reactivity. This leads to only partially hydrolyzable precursors that can form highly stable sols or even completely redissolvable dried powders. Using this approach, a large number of final compositions like titania, zirconia, silica, lead zirconate titanate and others are available. Film deposition using these coating sols with an adjustable viscosity and the final thermal treatment by rapid thermal annealing lead to thin films. The approach will be demonstrated with selected systems in order to explain the principles of sol-gel chemistry and deposition methods used to produce thin films with excellent properties.