Excimer (XeCl) laser annealing of PbZ_0.4Ti_0.6O ₃ thin film at low temperature for TFT FeRAM application

In this study, we successfully produced PbZr_0.4Ti _0.6O₃ (PZT (40/60)) thin films with high crystallinity and high remnant polarization (Pr) at low process temperatures using pulsed excimer (XeCl) laser irradiation. In our experiments, amorphous PZT films were prepared on Pt/Ti/SiO₂/Si substrates by a sol-gel method. A two-step process was used to crystallize the amorphous thin films: the films were annealed at 550°C for 10 min to initiate the nucleation of the PZT perovskite phase, and then annealed with an excimer laser heating at 400°C in a 120 Torr nitrogen gas atmosphere. Laser energy density was varied from 150 to 750 mJ/cm ² per pulse, x-ray diffraction (XRD) patterns show that 150-200 mJ/cm² range multi-shot excimer laser irradiation drastically improved the crystallinity of the PZT perovskite phase, and FESEM photographs show that the PZT thin film has uniform-sized crystal grains. The ferroelectric properties were found to depend on the laser energy density and shot number. Before the laser annealing, the films show hysteresis loops with low Pr and the loops do not saturate. After laser annealing, the films show highly saturated hysteresis loops, with the Pr increasing from 2.2 μC/cm² to 23.0 μC/cm². We also propose a new technology for fabrication of thin film transistor (TFT)-driven FeRAM devices on arbitrary insulator substrate such as on glass.