Metastable Pyrochlore Structures in Sol Gel Spin Coated Lead Titanate Thin Films on Silicon Substrate
- PDF / 2,791,913 Bytes
- 7 Pages / 420.48 x 639 pts Page_size
- 67 Downloads / 168 Views
METASTABLE PYROCHLORE STRUCTURES IN SOL GEL SPIN COATED LEAD TITANATE THIN FILMS ON SILICON SUBSTRATE JEON-KOOK LEE*, HYUNG-JIN JUNG* AND CHONG-HEE KIM** *Div. Ceramics, Korea Institute of Science and Technology, Seoul 130-650, Korea "**Dept. Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Seoul 130-012, Korea ABSTRACT High quality lead titanate thin films were fabricated by spin coating on a silicon substrate. The resulting dried gel layers were uniform in thickness through 2 X 2 cm' area, and polycrystalline perovskite structures developed almost crack free with a heat treatment above 500'C in films with thickness above 0.36Am. Metastable pyrochlore structures were observed in films with thickness of 0.16,am when heat treated at 500 and' 600 0 C. But these structure did not appear in films with thickness of 0.36Am.The thickness dependencein crystal structure of films was studied by varing the substrate condition and analyzing the interface between the.film and. substrate. In native oxide films on silicon substrates, amorphous dried gel layers were heterogeneously nucleated. Metastable cubic pyrochlore structure could be crystallized in amorphous native oxide (cubic property in random network structure). INTRODUCTION
Much of the recent sol-gel ferroelectric thin film research has been directed to the PbO based perovskite compounds such as PbTiO. 3 , Pb(Zr,Ti)0 3 . The microstructures and crystallizations of lead titanate thin films on a silicon substrate are highly dependent on the sol-gel processing variables such as substrate materials, film thickness, heat treating conditions. The-thickness dependence of several physical properties of ferroelectric films have been documented. The effective dielectric constant of PZT on silicon is very low and depends on the thickness of the PZT film and the annealing conditions [1]. At 500'C, pyrochlore structure grew on glass plate when the thickness of the coated films was below 100 rim [2]. The objective of our work was to study the reason why the pyrochlore structure was formed in films substrate with the thickness of 0.12 Am.
on
the
silicon
EXPERIMENTAL Precursor Solution Stock solutions of complex Pb-Ti alkoxide were prepared by reacting lead acetate trihydrate (99%, Alfa) with titanium isopropoxide (Alfa) in 2-methoxyethanol (99.9% HPLC grade, Aldrich) in a method similar to that reported by Blum (3]. The resulting Pb-Ti stock solution had 0.2 molar concentrations. The stock solutions were handled as moisture sensitive reagents and were stable. Mat. Res. Soc. Symp. Proc. Vol. 230. c1992 Materials Research Society
308
The coating solutions were acidified with concentrated HN03 to a resulting concentration of 0.1 molar concentration. Hydrolysis was initiated by the addition of an aqueous 2-methoxyethanol solution. The total hydrolysis water charge was 2 moles of H*0 per 1 mole of Pb. Coating Coatings were deposited on (100) p-type single crystal silicon wafer. The Pb, Ti coating solution was applied by spin coater utilizing a
Data Loading...
