Role of dual-laser ablation in controlling the Pb depletion in epitaxial growth ot Pb(Zr_(0.52)Ti_(0.48))O_3 thin films with enhanced surface quality and ferroelectric properties

摘要

Pb depletion in Pb(Zr_(0.52)Ti_(0.48))O_3 (PZT) thin films has remained as a major setback in the growth of defect-free PZT thin films by pulsed laser ablation techniques. At low excimer (KrF) laser fluences, the high volatility of Pb in PZT leads to non-congruent target ablation and, consequently, non-stoichiometric films, whereas, at high laser fluences, the inherent ejection of molten droplets from the target leads to particulate laden films, which is undesirable in heterostructure growth. To overcome these issues, a dual-laser ablation (PLD_(DL)) process that combines an excimer (KrF) laser and CO_2 laser pulses was used to grow epitaxial PZT films on SrTiO_3 (100) and MgO (100) substrates. Intensified-charge-coupled-detector (ICCD) images and optical emission spectroscopy of the laser-ablated plumes in PLD_(DL) revealed a broader angular expansion and enhanced excitation of the ablated species as compared to those for single-laser ablation (PLD_(SL)). This led to the growth of particulate-free PZT films with higher Pb content, better crystallinity, and lower surface roughness as compared to those deposited using PLD_(SL). For FE measurements, PZT capacitors were fabricated in situ using the latticed-matched metallic oxide, La_(0.7)Sr_(0.3)MnO_3, as the top and bottom electrodes. PZT films deposited using PLD_(DL) exhibited enhanced polarization for all driving voltages as compared to those deposited using PLD_(SL). A highest remanent polarization (P_r) of ～ 91 μC/cm~2 and low coercive field of ～ 40 kV/cm was recorded at 9 V driving voltage. Fatigue characterization revealed that PZT films deposited using PLD_(DL) showed unchanging polarization, even after 10~9 switching cycles.