Low Temperature Growth of Barium Strontium Titanate Films by Ultraviolet-Assisted Pulsed Laser Deposition
- PDF / 816,220 Bytes
- 6 Pages / 412.92 x 637.2 pts Page_size
- 105 Downloads / 249 Views
LOW TEMPERATURE GROWTH OF BARIUM STRONTIUM TITANATE FILMS BY ULTRAVIOLET-ASSISTED PULSED LASER DEPOSITION V. CRACIUN, J. M. HOWARD, E. S. LAMBERS, R. K. SINGH Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611 ABSTRACT Barium strontium titanate (BST) thin films were grown directly on Si substrates by an in situ ultraviolet (UV)-assisted pulsed laser deposition (UVPLD) technique. With respect to films grown by conventional (i.e. without UV illumination) pulsed laser deposition (PLD), the UVPLD grown films exhibited improved structural and electrical properties. The dielectric constant of a 40-nm thick film deposited at 650 'C was determined to be 281, the leakage current density was approximately 4xl0-8 A/cm 2 at 100 kV/cm, and the density of interface states at the flat-band voltage was found to be approximately 5.6x101 eV- cm:. X-ray photoelectron spectroscopy investigations found that the surface of the grown films exhibited an additional Ba-containing phase, besides the usual BST perovskite phase, which was likely caused by stress and/or oxygen vacancies. The amount of this new phase was always smaller and very superficial for UVPLD grown films, which can explain their better overall properties.
INTRODUCTION Barium strontium titanate, BaSrl_,TiO 3 (BST), possesses a high dielectric constant (r»>> es 0 2) [1-4], which makes it attractive for capacitor applications. Several studies have also suggested that BST could be a potential replacement of Si0 2 thin layers in future MOS circuits [57]. The results obtained so far have shown that thin BST layers usually exhibit much lower dielectric constants than the bulk value [8]. Fine grain microstructure, high stress levels, the presence of oxygen vacancies, the formation of interfacial layers, and the oxidation of the bottom electrode or Si are believed to be factors which can contribute to the degradation of the electrical properties [9-11 ]. In addition to the interfacial layer, which is formed due to the high temperatures (700-800 'C) and oxygen pressures (-200 mTorr) required for growth of high quality BST films, it has been found that Ba atoms on the surface of the film are present in two chemical states [12]. Besides the usual BST perovskite phase, an additional phase was found, most likely caused by the presence of mechanical stresses and/or oxygen vacancies. This phase will also negatively affect the electrical characteristics of the grown structure. One of the most promising methods for the growth of high quality thin BST films, which could alleviate some of the problems mentioned above, is pulsed laser deposition (PLD) [13-17]. In this paper we demonstrate the growth of BST films directly on Si wafers of very low equivalent Si0 2 thickness (
Data Loading...
