Closed Loop Controlled Ba_xSr_1–xTio₃ Thin Films In Spray Flames

Abstract

Control logic was developed for automated thin film deposition in the combustion chemical vapour deposition (CCVD) process. In situ film thickness and deposition temperature measurements were used as a feedback to control film thickness and optical properties through real-time adjustment of the deposition parameters. The closed loop controller was optimised for the deposition of barium–strontium–titanate (Ba_xSr_1–xTiO₃, BST) films on sapphire but it can be used for other coating/substrate combinations. Besides enabling repeatable depositions of BST films with optimal thickness and optical properties for electronic applications, this control process proved that unique features of the Nanomiser atomiser can be implemented to tune the film deposition rate. Comparison of scanning electron microscopy cross-sections of epitaxial BST films on sapphire substrate with the predicted film thickness suggests that the closed loop controller can be used to control the thickness of the deposited film to within ± 2%