Structures and electrical properties of barium strontium titanate thin films grown by multi-ion-beam reactive sputtering technique

The structure and electrical properties of multi-ion beam reactive sputter (MIBERS) deposited barium strontium titanate (BST) films were characterized in terms of Ba/Sr ratio, substrate temperature, annealing temperature and time, film thickness, doping concentration, and secondary low-energy oxygen ion bombardment. Films deposited onto unheated substrates, followed by annealing at 700 °C showed lower dielectric constant (<200), compared to a dielectric constant of about 560 for those deposited at elevated temperatures, probably due to reduced voids. Two types of microstructures (type I and type II) were observed depending on the incipient phase of the as-grown films, which also led to two types of time domain dielectric response, Curie-von Schweidler and Debye type, respectively. The current-voltage (I-V) characteristics of type II films doped with high donor concentration showed a bulk space-charge-limited conduction (SCLC) with discrete shallow traps embedded in a trap-distributed background at high electric fields. The I-V characteristics of bombarded films deposited at higher substrate temperatures showed promising results of lower leakage currents and trap densities.