EFFECTS OF MILLISECOND SCALE LASER SPIKE ANNEALS ON AMORPHOUS BARIUM TITANATE THIN FILMS
Haber, Lewis Rosevere
Barium titanate is the most widely used dielectric material for ceramic capacitors. The perovskite phase, in particular is prized for its high, stable dielectric constant across a wide temperature range. In addition to the five observed crystalline phases, computational materials science suggest that there exist many more unobserved metastable phases. In this study, amorphous barium titanate films deposited at room temperature on Si substrates via pulsed laser deposition or sputtering were annealed with a CO2 laser in air, achieving peak temperatures from 600-1300 ℃ and dwell times from 250-10000 µs. The samples were then analyzed with synchrotron x-ray diffraction, optical reflectometry and optical microscopy. The laser spike anneal induced surface roughening and delamination in films annealed above 780 ℃. This roughening is consistent with the formation of a low density amorphous phase before crystal nucleation, causing film delamination. Diffraction analysis revealed the onset of crystallization strongly coincided with film damage. Crystallization produced both the equilibrium tetragonal phase and the metastable hexagonal phases. Short anneals near the crystallization threshold produced pure tetragonal regions, while all other anneals above the threshold produced mixed hexagonal and tetragonal regions. These data show that millisecond scale laser spike anneals show promise as a method to stabilize metastable phases in thin films.
Materials Science; Barium Titanate; Laser Spike Anneal
Van Dover, Robert B.
Thompson, Michael Olgar
Materials Science and Engineering
M.S., Materials Science and Engineering
Master of Science
dissertation or thesis