In situ methods to explore microstructure evolution in chemically derived oxide thin films

Abstract

In situ residual gas analyzer techniques were used to identify process-property relationships that regulate microstructure evolution in chemical solution-deposited BaTiO3 films. In situ analysis of furnace exhaust gasses enabled quantitative exploration of thermolysis and crystallization reactions and an ability to identify processing parameters that influence the temperature ranges over which they occur. The atmospheric analysis was instrumental in identifying heat treatments that produced optimally consolidated precursor gels that crystallized into BaTiO3 layers with optimized structure and properties. Slow ramp rates resulted in higher porosity, larger grain size, and a dramatic drop in the capacitor yield. Fast ramp rates produced similar trends; however, the mechanisms were distinct. The effects of oxygen partial pressure were also explored. BaTiO3 grain size increased with increasing pO2, whereas there was no appreciable influence on density and capacitor yield. Optimal firing parameters, i.e., 20 °C/min ramp rate at a pO2 of 10−13 atm, were identified as those that produced an overlap in the temperature ranges of thermolysis and crystallization reactions and thus a precursor gel with a density and compliance that supports crystallization and densification while tolerating the associated volume contraction. This in situ approach to analyze downstream furnace gas is shown to be a generically applicable means to understand synthesis methods that are complicated by simultaneous mechanisms of precursor decomposition, extraction of volatile components, and crystallization.