PROPERTIES OF FERROELECTRIC PBTIO3 FILMS GROWN IN AN IONIZED CLUSTER BEAM SYSTEM

Two ionized cluster beam (ICB) sources were used to deposit PbTiO3 films 300 nm thick onto Pt-metallized, oxidized Si wafers 100 mm in diameter. Pb was deposited from one ICB source and Ti from the other. The deposition was carried out in a mixture of O2 and 6% O3 at a total pressure of 5 X 10(-5) Torr. No substrate heating was used during deposition. However, thermal radiation from the ICB sources caused the substrate temperature to reach approximately 100-degrees-C soon after the start of deposition. The as-deposited films were amorphous according to x-ray diffraction patterns. Annealing the films at 550-degrees-C in 1 atm pressure O2 for 1 h led to the formation of a mixture of a perovskite-type phase and possibly some pyrochlore- and PbO-type structures. However, an anneal at 750-degrees-C for 1 h in 1 atm pressure O2 produced the perovskite phase PbTiO3 with no other detectable phases. It was found that a slightly Pb-rich or stoichiometric Pb/Ti ratio in as-deposited films gave the best ferroelectric film properties. A Pb/Ti ratio much higher than stoichiometric (Pb/Ti ratio > 2) led to the formation of pits and pinholes in the films after annealing at 750-degrees-C, whereas a Pb/Ti ratio lower than stoichiometric did not produce the perovskite phase after annealing at 750-degrees-C. The pits and pinholes associated with Pb/Ti ratio larger than stoichiometric were probably caused by the evaporation of excess PbO during annealing. Films were deposited with and without the use of ionization and acceleration to 2 keV. In both cases, the as-deposited films were amorphous. There were no substantial differences between annealed films deposited with or without ionization and acceleration of the Pb and Ti beams. Ferroelectric domains in the annealed films have been observed by transmission electron microscopy. Ferroelectric switching (hysteresis loops) was recorded in annealed PbTiO3 films with stoichiometric Pb/Ti ratios after the films were capped with Pt to form small capacitors.