Low temperature preparation and properties of calcium-modified lead titanate thin films by laser annealing
| Autor: | Jing-Tang Yang, 楊景棠 |
|---|---|
| Rok vydání: | 2002 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 91 In this study, (Pb,Ca)TiO3 (PCT) thin films were prepared by Sol-Gel route were deposited on Pt/Ti/SiO2/Si(Pt(Si)) and La0.5Sr0.5MnO3/Pt(Si) substrates. The structure of PCT thin films was transformed from the amorphous phase to the perovskite structure via cw-CO2 laser annealing and XeCl excimer pulsed laser annealing technique, respectively. At the same time, ferroelectric and pyroelectric properties were measured. We carefully investigate the discrepancies in different annealing processes including electrical properties, crystallinity and microstructures by different instruments. The experimental results of substrate selectiveness reveal that LSMO/Pt(Si) substrate enhance the nucleation of PCT thin films and improve fatigue properties because of the same perovskite structure and less lattice mismatch. Besides, SIMS figures show that LSMO can decrease diffusion of titanate element effectively. For that reason, LSMO is a suitable buffer layer between metal electrode and ferroelectric thin films. Structural investigations reveal that PCT thin films grew up the (110) plane at 500℃ for 30 minutes using furnace annealing. The relative intensity of XRD patterns increased as the annealing temperature increased. Further,. Electrical properties reveal the remanent polarization (Pr) increased as the laser power density increased using cw-CO2 laser annealing. The Pr；25.42 μC/cm2 could be obtained at 573 W/cm2 for 20 seconds. The value is larger than conventional furnace annealed sample (700℃ for 30 minutes). In other words, cw-CO2 laser annealing can reaches higher Pr within an extremely short period of time and in room temperature. And coercive electric field (Ec) using cw-CO2 laser annealing is 36.79 kV/cm is smaller than 78.40 kV/cm using furnace annealed ones. If PCT thin films are annealed by XeCl excimer pulsed laser annealing, two layers of films crystallized differently are observed because of extremely thin absorbed thickness. The upper film absorbs greater part photon energy. The lower layer of the PCT film relies on the heat conduction from the upper layer, and therefore the bad grain growth situation will be obtained. But, when we annealed in situ substrate heating to provide nucleation energy, the Pr and Ec；25.42 μC/cm2 and 86 kV/cm could be obtained at 4.0 MW/cm2. Pyroelectric properties show that samples annealed by cw-CO2 laser annealing will get higher pyroelectric coefficient than conventional furnace annealing. Above all, 4.25×10-8 C/cm2 K could be obtained at PCT73. In conclusion, excimer pulsed laser annealing is suitable to improve surface quality of thin films or anneal the greatly thin films. And laser annealing can make grains nucleate and grow within short period of time. The grain size, roughness and electrical properties using cw-CO2 laser annealing are better than those using furnace annealing, therefore cw-CO2 laser annealing can be an appropriate low temperature annealing process. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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