A thermodynamic and kinetic model for nucleation and growth in solution derived thin films.

摘要

Due to the higher cost efficiency, chemical solution deposition (CSD) processes have become an attractive alternative for the fabrication of various electronic applications, including ferroelectric memory chips, pyroelectric and microelectromechanical systems (MEMS) applications, thin film decoupling capacitors, as well as 2nd generation high temperature superconductors (HTS). For chemical solution deposited films it has been reported that microstructural variations that may be induced through changes in chemical precursor, processing route, employment of a seed layer, or heat treatment schedule. In the first part the effects on microstructural evolution and densification behavior of holmium oxide and strontium titanate buffer layers for high temperature superconductor tape products have been studied using various analytical techniques, incl. XRD, SEM, TEM, FTIR, TGA, DSC, and profilometry. The experiments also show the need to control film microstructure, therefore, it is essential to develop a fundamental understanding of the nucleation and growth mechanisms that govern the transformation of the as-deposited amorphous film into the crystalline state. Therefore, in the second part, a model for the prediction of microstructural evolution of solution derived thin films has been developed. The model is based on standard nucleation and growth rate expressions that have been used previously to explain transformation behavior in amorphous materials. A Basic program was written incorporating these standard analytical expressions and known material properties, such as lattice constants, moduli, and melting point, as well as calculated thermodynamic parameters, such as the volume free energy. The output of the model gives a visualization of the thin film microstructure for different boundary conditions, including substrate type, lattice matching with the film, processing temperature, and time. The utility of the model is demonstrated through comparison with experimentally obtained results for a diverse variety of film-substrate systems, including holmium oxide on nickel or platinized silicon, strontium titanate on single crystal or nickel or barium titanate and lead zirconate titanate (PZT) on platinized silicon substrates. The experimental and simulation results of this work have let to a further understanding of the importance of heat treatment conditions, and substrate effects on microstructural evolution and orientation in solution-derived thin films.