Low Temperature Fabrication of Capacitance Materials with High Dielectric Constant for Application of Non-Volatile Memory

2003 Fiscal Year Final Research Report Summary

• Project/Area Number: 13555194
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 展開研究
• Research Field: Material processing/treatments
• Research Institution: The University of Tokyo
• Principal Investigator: MITSUDA Yoshitaka The University of Tokyo, Institute of Industrial Science, Professor, 生産技術研究所, 教授 (20212235)
• Co-Investigator(Kenkyū-buntansha): ODA Katuro The University of Tokyo, Institute of Industrial Science, Associate Professor, 生産技術研究所, 助教授 (80177229)
• Project Period (FY): 2001 – 2003
• Keywords: ferroelectric thin film / barium titanate / sputtering / rf bias / ion bombardment / low temperature crystallization / dielectric characteristics / hysteresis loop

Research Abstract

Barium titanate thin films were deposited with rf magnetron sputtering apparatus with rf substrate bias system. Using powder target in place of sintering target, the composition of deposited thin films could be close to the stoichiometric one. In this case, the deposition rate and crystallinity of thin films were less dependent of target materials. To apply the bias on substrate during deposition, the crystallization of thin films was enhanced, although the deposition rate was slightly decreased due to counter sputtering on deposition surface. According to the average negative bias to be applied on substrate and/or the rf power of sputtering target, the Ba/Ti atomic ratio in films were a little larger than the stoichiometric composition.
The capacitor structure of barium titanate film as dielectric layer was fabricated using the powder mixture target, by which the stoichiometry of deposited films was almost satisfied. At low substrate temperature, for example, even 300 degree C, it was confirmed that the crystallization of films proceeded and the dielectric constant of films increased by ion bombardment on growth surface, and that the dielectric constant of films saturated over the given negative bias. However, the excess energy of ion might cause the increase of dielectric loss. In addition, the deposited thin film, which had the high dielectric constant and the (110) orientation, shows the ferroelectric characteristic by the measurement of hysteresis loop.
The obtained films could show the possibility of dielectric material for the electric memory, although they were insufficient at this stage. By the optimization of the deposition process, the deposited films could have both high dielectric constant and low dielectric loss. In the near future, we should try to conduct hard research to increase the number density and decrease the energy of bombarded ion by the enhancement of ionization ratio in plasma.