Plasma-assisted pulsed laser deposition of SrBi2Ta2O9 thin films of improved ferroelectric and crystalline properties

Significant effect of the introduction of O-2-plasma discharge during pulsed laser ablative deposition of SrBi2Ta2O9 (SBT) films on improving the crystallite orientation and ferroelectric properties has been described. O-2-plasma assists in the formation of highly crystalline films at a low 700 degrees C temperature over (111) oriented Pt films coated Si(100) single crystal substrates at a nominal pressure of 200 mTorr. Plasma excitation potential, applied at an auxiliary ring electrode placed near the substrate, has a profound effect on surface morphology, crystallite orientation, and remnant polarization, P-r values. At -350 V, SBT growth at 700 degrees C with predominant (a-b) orientation showing high P-r similar to 6.5 mu C/cm(2) in the as-deposited state has been obtained. In comparison, SBT films deposited identically but without the plasma show a low P-r of similar to 1.7 mu C/cm(2). Ionized cationic species along with ionic and atomic oxygen present in the plasma improve thermodynamic stability of the film growth through enhanced chemical reactivity and thus eliminates the need for any severe postgrowth crystallization anneal step in the synthesis of SBT films. Impingement of energetic O-2 ions and atomic oxygen helps lower the nucleation barrier for the growth of (a-b) crystallites and changes the c-axis orientation from normal to near parallel to the film plane. Quality of the film declines with the plasma excitation potential as enhanced kinetic energy of impinging O-2 ions introduce defects and reduce nucleation density by resputtering from the substrate. (C) 1999 American Institute of Physics. [S0003-6951(99)00423-4].