Energy Storage Properties of Sol–Gel-Processed SrTiO3 Films

Dielectric films with a high energy storage density and a large breakdown strength are promising material candidates for pulsed power electrical and electronic applications. Perovskite-type dielectric SrTiO3 (STO) has demonstrated interesting properties desirable for capacitive energy storage, including a high dielectric constant, a wide bandgap and a size-induced paraelectric-to-ferroelectric transition. To pave a way toward large-scale production, STO film capacitors were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by the sol–gel method in this paper, and their electrical properties including the energy storage performance were studied as a function of the annealing temperature in the postgrowth rapid thermal annealing (RTA) process. The appearance of a ferroelectric phase at a high annealing temperature of 750 °C was revealed by X-ray diffraction and electrical characterizations (ferroelectric P-E loop). However, this high dielectric constant phase came at the cost of a low breakdown strength and a large hysteresis loss, which are not desirable for the energy storage application. On the other hand, when the RTA process was performed at a low temperature of 550 °C, a poorly crystallized perovskite phase together with a substantial amount of impurity phases appeared, resulting in a low breakdown strength as well as a very low dielectric constant. It is revealed that the best energy storage performance, which corresponds to a large breakdown strength and a medium dielectric constant, is achieved in STO films annealed at 650 °C, which showed a large energy density of 55 J/cm3 and an outstanding energy efficiency of 94.7% (@ 6.5 MV/cm). These findings lay out the foundation for processing high-quality STO film capacitors via the manufacturing-friendly sol–gel method.