Ultrafast crystallization kinetics in (Pb,La)(Zr_0.30Ti_0.70)O₃ thin films by pulsed excimer laser annealing

Abstract

The crystallization kinetics of laser-annealed Lamodified Pb(Zr,Ti)O₃ (PLZT) thin films on LaNiO₃-coated silicon substrates were investigated for substrate temperatures below 400 °C. A KrF excimer laser having a ~20 ns pulse width and an energy density ~40 mJ/cm² was used to crystallize the films. The perovskite phase developed with cumulative laser pulse exposures; it was found that ~380 to 400 nm thick films could be fully crystallized for a total exposure time of 0.1 to 1 ms. Laser-crystallized films exhibited comparable dielectric and ferroelectric properties to those prepared by rapid thermal annealing at 650 °C for 1 min. The evolution of the dielectric properties as a function of the number of laser strikes suggests that once nuclei are present, they rapidly grow through the depth of the film. This is consistent with the electron microscopy results, which did not show a well-defined planar growth front that proceeds from the top to the bottom of the film. The resulting films showed comparatively large lateral grain sizes (on the order of 250 to 300 nm), with high defect concentrations. The nucleation and growth mechanisms were modeled using Avrami kinetics under rate-dependent and nonisothermal conditions. These results indicate that PLZT crystallization via laser annealing is nucleation-limited.

In situ laser annealing during growth of Pb(Zr0.52Ti0.48)O3 thin films

“…[3][4][5] It also allows development of texture in Pb(Zr 0.52 Ti 0.48 )O 3 (PZT (52/48)) to achieve excellent piezoelectric properties. 6 However, limited thicknesses ($300 nm) can be crystallized in this manner due to the limited thermal diffusion length of the absorbed laser pulse in the film.…”

“…6 However, limited thicknesses ($300 nm) can be crystallized in this manner due to the limited thermal diffusion length of the absorbed laser pulse in the film. 4 On the other hand, some PZT (52/48) thin film MEMS applications require thicknesses >1 lm.…”

“…4,13 Hence, a crystallized seed-layer was utilized to aid nucleation during in situ laser annealing. For the purpose of maintaining a low process temperature throughout, laser crystallization of the seed layer was adopted.…”

Microstructure Evolution of In Situ Pulsed‐Laser Crystallized Pb(Zr0.52Ti0.48)O3 Thin Films

“…On the other hand, direct integration of the piezoelectric thin film with a microchip would improve response times in sensors, potentially coupled with low‐cost manufacturing . Pulsed‐laser treatment is one way to selectively heat the film to achieve the high temperatures required for perovskite phase crystallization, while causing minimal heating of the underlying substrate …”

“…3 Pulsed-laser treatment is one way to selectively heat the film to achieve the high temperatures required for perovskite phase crystallization, while causing minimal heating of the underlying substrate. [4][5][6][7][8][9][10] Moreover, in situ heat treatment of oxide thin films during growth can also benefit from reduced crystallization temperatures compared to a postdeposition thermal processing. 11,12 It has been shown that crystallization of ferroelectric thin films can be achieved by simultaneous laser annealing during growth at substrate temperatures of ≤400°C.…”