Potassium Sodium Niobate Thin Films by Chemical Solution Deposition

Abstract

Stable aqueous KNN-based precursor solutions were developed by using simple and cheap starting materials and good wetting of the precursor solution was secured by the addition of small amounts of polyvinylalcohol. The precursor was deposited on single crystal strontium titanate (STO) substrates with different orientations and heat treatment at 700-900 ºC to obtain a 300-400 nm thickness films.

Nominal stoichiometric KNN films, nominal stoichiometric KNN films with NaCl alternating layers and KNN-based films with selected additives (NaCl/KCl, Mn, or both) were prepared in the first series of KNN-based thin films. The second series of KNN-based film addresses the effect of adding alkali excess and the effects of adding NaCl/KCl and Mn to excess alkali films. The third series of films consider the effect of using reducing atmosphere (95N2/5H2) during the heat.

Homogeneous KNN-based thin films with nano-sized grain size were obtained. For almost all the films, the piezoresponse (PR) amplitudes show a typical butterfly shape while the PR phase hysteresis loops display a well squared shape with saturation at high applied field. The films obtained a high degree of orientation along substrate orientation direction and possess an epitaxial layer close to the interface between the film and the substrate with thickness varying in the range 20-100 nm.

This thesis work has successfully developed a simple, cheap and environmental friendly process for deposition of lead-free KNN materials based on spin coating of an aqueous nitrate based precursor solution. The work has demonstrated that this simple method can be used to deposit strongly textured polycrystalline films as well as epitaxial films on single crystal strontium titanate substrates