Single-Step Deposition of Gel-Derived Lead Zirconate Titanate Films: Critical Thickness and Gel Film to Ceramic Film Conversion

摘要

PZT thin films were prepared on silica-glass substrates from Pb(CH_3COO)_2·3H_2O-Zr(n-OC_3H_7)_4-Ti(i-OC_3H_7)_4-H_2O-CH_3COOH-CH_3OC_2H_4OH-n-C_3H_7OH solutions containing polyvinylpyrrolidone (PVP) via nonrepetitive dip-coating or spin-coating. The thickness of the gel films was varied by changing the substrate withdrawal and rotation speeds, and the crack formation was examined after firing the gel films at 700℃. The critical thickness, i.e., the maximum thickness achievable without crack formation, was maximized at a PZT/alkoxide mole ratio of ～1, where crack-free PZT films as thick as 2μm could be obtained via single-step deposition. Thermal analysis was conducted on gel films deposited on a glass substrate at ～25℃ and then peeled off the substrate. Infrared absorption spectroscopy and X-ray diffractometry measurements were conducted on films deposited on silicon wafers. These analyses revealed that PVP and CH_3COO~- were thermally decomposed at 250°-320℃, leaving carbonaceous species, followed by the crystallization of Pb_3(CO_3)_2(OH)_2 at ～350℃. The oxidation of the carbonaceous species occurred at ～360°-460℃; perovskite PZT then was formed at ～550℃. The film thickness decreased greatly at 200°-350℃, where thermal decomposition of PVP and CH_3COO~- occurred. The films fired at 700℃ were rather porous and not very transparent. Preheating the gel films at 100°or 200℃ resulted in participate microstructure with gaps between the particles, and, at 350?, caused crack formation, both of which further decreased the optical transmittance.