Composition Control of Barium Strontium Titanate Thin Films Prepared by Chemical Vapor Deposition

Composition control of barium strontium titanate thin films prepared by chemical vapor deposition using Ba(THD)2, Sr(THD)2, and Ti(THD)2(i-OC3H7)2 (THD: 2,2,6,6-tetramethyl-3,5-heptanedionate) has been studied by investigating the effects of deposition temperature and the supply rates of metal sources. Although there were complicated correlations among the deposition rates of Ba, Sr, and Ti under kinetically limited conditions, the deposition rate ratio of Ba/Sr was linearly related to the partial pressure ratio of Ba(THD)2/Sr(THD)2, and the ratio of Ti/(Ba+Sr) spontaneously approaches unity. In order to explain these characteristics, we proposed a model wherein the THD complex of Ba or Sr reacts with the THD complex of Ti and generates a dimer such as (THD)2Ba–O–Ti(THD)2, and this dimer becomes the dominant precursor for chemical vapor deposition (CVD) under kinetically limited conditions.