Parametric Optimization of a Sol-Gel Process for the Synthesis of Highly-Oriented (Pb, Ba)TiO 3 Thin Films
- PDF / 475,474 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 64 Downloads / 254 Views
U12.21.1
Parametric Optimization of a Sol-Gel Process for the Synthesis of Highly-Oriented (Pb, Ba)TiO3 Thin Films Wein-Duo Yang, Suresh C. Pillai, Stacey W. Boland and Sossina M. Haile* Department of Materials Science, California Institute of Technology, Pasadena, California 91125, USA ABSTRACT A sol-gel process incorporating lead acetate trihydrate, barium acetate and titanium isopropoxide as precursors, acetylacetone as a chelating agent, and ethylene glycol as a solvent was used to prepare solid solution (Pb0.5,Ba0.5)TiO3. Water content, annealing temperature and heating rate were varied and the resulting effects on material properties were studied using TGA/DSC, FTIR, FESEM and X-ray diffraction. Crystallization of the perovskite structure occurred at a temperature as low as 450°C. Thin films were prepared by spin coating on (100) MgO using the optimized precursor sol. Pyrolysis and anneal temperatures were varied and the resultant film properties investigated. The pyrolysis temperature used to dry the film was found to strongly affect orientation. Under optimized conditions, highly oriented films were obtained at a crystallization temperature of 600°C. INTRODUCTION It has been recently shown that the ferroelectric tetragonal distortion of BaTiO3, in which the a and c lattice parameters differ by 1.1%, can be utilized for actuation [1]. Strains of ~ 0.9% have been demonstrated. Even greater strain is expected for PbTiO3 which exhibits a tetragonality of 6.3%. Solid solutions of (Pb1-x,Bax)TiO3, or PBT, with intermediate composition will presumably present a compromise between large actuation and likelihood of mechanical failure. In order for PBT to be successfully utilized in microactuation applications and also be integrated into silicon device technology, it is necessary to synthesize high-quality epitaxial thin films at low temperatures. Furthermore, if crystallization is carried out below the Curie temperature, stresses associated with the cubic to tetragonal phase transition can be eliminated. While there are a variety of techniques for fabricating oxide thin films, including physical vacuum deposition, ion beam sputtering, electron beam evaporation, and pulsed laser ablation, the sol-gel method has been selected here because of the potential for meeting the objective of low temperature crystallization and the possibility of low cost fabrication. In the sol-gel process, controlled hydrolysis of dissolved metalorganic precursors followed by a condensation reaction results in the formation of a three dimensional network of particles [2]. Key challenges in the sol-gel synthesis of PBT are the preparation of a sol stable against uncontrolled hydrolysis and the identification of a solvent system in which multiple metalorganic precursors are compatible. Moreover, while sol-gel and other solution techniques have been widely used for the fabrication of ferroelectric films of PbTiO3 and BaTiO3 [3,4], few studies of the solution deposition of PBT thin films have been reported [5]. We report here an optimized sol-ge
Data Loading...
