Microstructural Characterization of Ferroelectric Thin Films for Non-Volatile Memory Applications

Abstract

Ferroelectric thin films are now being used in conjunction with semiconductor CMOS technology to produce non-volatile IC memory devices. Three film compositions across the lead-zirconate-titanate (PZT) phase diagram were examined by transmission electron microscopy (TEM). The films are produced using organo-metallic sol-gels and sintered using standard semiconductor processing techniques. The grain structure of these thin films differ greatly from bulk ceramic crystals and thin films prepared using other deposition techniques. For two compositions, Pb1.1 (Zr0.75Ti0. 25)O3 and Pb1.1 (Zr0.50Ti0.50)O3, the perovskite structure was found in large rosettes surrounded by the polycrystalline pyrochlore phase. In the Pb1.1(Zr0.25Ti0.75)O3 sample, perovskite grains were found with no evidence of the pyrochlore phase. Ferroelectric domains were imaged in all three samples.

Influence of texture on the switching behavior of Pb(Zr0.70Ti0.30)O3 sol-gel derived thin films

“…Typically in rhombohedral (Zr-rich) films, rosette-type microstructures are observed (particularly for sol-gel derived films) due to the higher perovskite nucleation energy and the increased stability of the pyrochlore phase. 9,10 Similar microstructural features have also been observed for rhombohedral Pb(Zr 0.65 Ti 0.35 )O 3 prepared by reactive dc-magnetron sputtering and crystallization ex situ. 8 In sol-gel deposition where ex situ crystallization is required, these two factors strongly influence the PZT microstructure due to the need for efficient nucleation of the perovskite phase (high nuclei density) and the amorphous to pyrochlore to perovskite crystallization sequence.…”

“…Further, it has been reported that the stability of the pyrochlore phase increases with increasing Zr concentration, often leading to rosette type microstructures for rhombohedral compositions. 9,10 The influence of the substrate, and in particular the Ti͞Pt bilayer metallization, further complicates the perovskite nucleation energetics. Numerous papers report that (111) oriented PZT nuclei form at the Pt͞PZT interface due to a close lattice match between the (111) planes of the two materials.…”

Crystal structure and microstructure of lead zirconate titanate (PZT) thin films with various Zr/Ti ratios grown by hybrid processing

“…''Rosettes'' (see Ref. [15]) with diameters of 5-15 mm were observed in the film fabricated using the target with a Zr/Ti ratio of 70/30 ( Fig. 3(a)).…”

Growth and fatigue properties of pulsed laser deposited Pb1 ? x La x (Zr y Ti z )O3 thin films with [0 0 /] preferred orientation

“…The films may contain only a few domains, since the size of the grains (~ 0.4 ~tm) is of the same order as the size of the domains, reportedly of size several hundreds of nanometres [28,29]. In other words, the domain wall movement makes little contribution to the polarization process of PLZT thin films.…”