Influence of the microstructure of Pt/Si substrates on textured growth of barium titanate thin films prepared by pulsed
- PDF / 454,522 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 1 Downloads / 193 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Influence of the microstructure of PtyySi substrates on textured growth of barium titanate thin films prepared by pulsed laser deposition Cheol Seong Hwang,a) Mark D. Vaudin, and Peter K. Schenck National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (Received 13 February 1997; accepted 9 July 1997)
Pt-coated silicon substrates with strong (111) Pt texture were annealed in an oxidizing atmosphere at temperatures from 500 ±C to 750 ±C. BaTiO3 thin films were deposited by pulsed laser ablation on the substrates. Observation by transmission electron microscopy showed that the substrate anneal caused the formation of TiO2 in the Pt layer, accompanied by the formation of a high density of faceted protrusions on the Pt surface, particularly at the higher anneal temperatures. The Pt protrusions had (111) facets, parallel to the substrate surface, on which (100)-oriented BaTiO3 grains were observed. BaTiO3 grains with an epitaxial relationship to the Pt lattice were observed on inclined facets of the Pt protrusions [which were not (111) planes], and also on the nonplanar regions of the Pt surface. These epitaxial BaTiO3 grains had (111) preferred orientation relative to the substrate surface. Thus, the BaTiO3 films displayed bimodal growth behavior, with both (100) texture and (111) epitaxy. We propose a model for this behavior based on surface energy considerations.
I. INTRODUCTION
Ferroelectric oxide thin films are now attracting great interest because of their potential usefulness in nonvolatile memory devices (NVRAM) and dynamic random access memory devices (DRAM). Many papers1 and reviews2–4 have been published on the deposition, processing, and electrical and/or structural characterization of ferroelectric thin films, including Pb-based oxide thin films, such as PbTiO3 , (Pb, La)TiO3 , Pb(Zr, Ti)O3 , and (Pb, La) (Zr, Ti)O3 , and other perovskites such as BaTiO3 , SrTiO3 , and Bi4 Ti3 O12 . In most cases the substrates used were Si wafers or single crystal oxide materials, typically MgO, SrTiO3 , or LaAlO3 . For microelectronic applications, Si wafers are the most important substrates. However, it is well known that bare Si wafers react readily with ferroelectric thin films during deposition or postannealing procedures to form interfacial SiO2 and Pb or Ba silicate compounds, with deleterious consequences. Therefore, Pt thin films have been deposited on thermally oxidized Si wafers as a buffer layer prior to ferroelectric thin film deposition because Pt films are chemically very stable and, in addition, can act as a bottom electrode. Some researchers have claimed that thin film Pt is not a suitable electrode for NVRAM or DRAM applications because of a work function mismatch between Pt and oxide ferroelectrics5,6 ; however, Pt thin films still play an important role in the development of new memory materials. a)
Currently at Samsung Electronics Co. Ltd., Kihung, South Korea.
368
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 2, Feb 1
Data Loading...
