Sergio Carella

Ba substituted Pb(Zr x Ti 1-x )O 3 thin films grown by MOCVD

High quality Pb(Zr,Ti)O 3 [PZT] and (Pb 1-x Ba x )(ZryTi 1-y )O 3 (x ≤ 0.15, 0.25 ≤ y ≤ 0.50) [PBZT] thin films were grown on Pt (111) and Ir (111) coated silicon substrates by means of a pulsed liquid injection metal organic chemical vapor deposition (MOCVD) technique. The precursor solutions of Pb(DPM) 2 , Ba(DPM) 2 , Zr(IBPM) 4 , and Ti(O i Pr) 2 (DPM) 2 dissolved in butylacetate were separately injected into an AIX-200 reactor using a TriJet™ vaporizer. Stoichiometric films (0.98 ≤ A/B ≤ 1.06) with thickness between 80 nm and 150 nm were deposited at a susceptor temperature of 615 °C to 660 °C. Pure PZT films grown on platinum coated substrates show a randomly oriented perovskite structure accompanied with formation of a PbPt x alloy at the PZT/Pt interface. On the Ir(111) coated substrates the pure PZT films also exhibit a random orientation possibly due to oxidation of the Ir surface layer during the deposition process. Ferroelectric properties of Pr = 35 µC/cm 2 and Ec = 90 kV/cm were obtained for a PZT (30/70) film of 150 nm thickness grown on Ir/Si. In contrast, PBZT films with a Ba content of about 5 to 15% show lower tendency for formation of a PbPt x interfacial layer, and a preferred (111) texture was observed for PBZT films grown on the Ir (111) substrates under optimized process conditions. Tetragonal and rhombohedral PBZT films with 15% Ba and a Zr-content of about 0.35 and 0.50, respectively, show an orientation dependence of the ferroelectric properties in the way that E c is highest for textured films in comparison to E c determined for textured films. The remanent polarization of 85 nm thick tetragonal PBZT films changes from 17 µC/cm 2 for orientation to 13.5 µC/cm 2 for texture. The relative permittivity changes in the same way from 600 to 540, respectively. The rhombohedral films exhibit a nearly independent P r value of about 11 µC/cm 2 while the switching field changes from 75 kV/cm for an textured film to 46 kV/cm for an (110) textured one. The relative permittivity values of both films are 890 and 715 for the (110) and the (111) textured films, respectively. The trends observed for the textured PBZT films grown on Si substrates reflect the behaviour reported for epitaxial films [2]

MOCVD GROWTH OF (Pb,Ba)(Zr,Ti)O3 THIN FILMS FOR MEMORY APPLICATIONS

ABSTRACT We are reporting on the modification of Pb(Zr,Ti)O3 (PZT) thin films by substitution of Ba for Pb. The (Pb,Ba)(Ti,Zr)O3 (PBZT) films are grown on iridium coated silicon substrates by a liquid delivery MOCVD technique. Four separate solutions of Pb (DPM)2, Ba (DPM)2, Ti (Oi Pr)2 (DPM)2, and a new zirconium precursor Zr (IBPM)4 were used. A PZT(30/70) film of 150 nm thickness shows a Pr value of 35 μ C/cm2, and Ec of 90.4 kV/cm. Ba substitution leads to suppressed tendency for phase separation, more homogeneous surface morphology, smaller grain sizes and easier growth with respect to adjustment of stoichiometry. PBZT films show low dielectric losses of 0.03 and high permittivity values of up to 1000. A decrease of the coercive field could not be observed.