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

PZT thin films were prepared on silica‐glass substrates from Pb(CH 3 COO) 2 ·3H 2 O–Zr( n ‐OC 3 H 7 ) 4 –Ti( i ‐OC 3 H 7 ) 4 –H 2 O–CH 3 COOH–CH 3 OC 2 H 4 OH– n ‐C 3 H 7 OH 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°C. 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 2 μm could be obtained via single‐step deposition. Thermal analysis was conducted on gel films deposited on a glass substrate at ∼25°C 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 3 COO − were thermally decomposed at 250°–320°C, leaving carbonaceous species, followed by the crystallization of Pb 3 (CO 3 ) 2 (OH) 2 at ∼350°C. The oxidation of the carbonaceous species occurred at ∼360°–460°C; perovskite PZT then was formed at ∼550°C. The film thickness decreased greatly at 200°–350°C, where thermal decomposition of PVP and CH 3 COO − occurred. The films fired at 700°C were rather porous and not very transparent. Preheating the gel films at 100° or 200°C resulted in particulate microstructure with gaps between the particles, and, at 350°C, caused crack formation, both of which further decreased the optical transmittance.