Radosveta D. Klissurska

Orientation of rapid thermally annealed lead zirconate titanate thin films on (111) Pt substrates

The nucleation, growth, and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated. The effects of pyrolysis temperature, post-pyrolysis thermal treatments, and excess lead addition are reported. The use of post-pyrolysis oxygen anneals at temperatures in the regime of 350-450 degrees C was found to strongly affect the kinetics of subsequent amorphous-pyrochlore-perovskite crystallization by rapid thermal annealing. The use of such post-pyrolysis anneals allowed films of reproducible microstructure and textures [both (100) and (111)] to be prepared by rapid thermal annealing. It is proposed that such anneals and pyrolysis temperature affect the oxygen concentration/average Pb valence in the amorphous films prior to annealing. Such changes in the Pb valence state then affect the stability of the transient pyrochlore phase and thus the kinetics of perovskite crystallization.

Fatigue, rejuvenation and self-restoring in ferroelectric thin films

Abstract The switching, fatigue and rejuvenation phenomena of ferroelectric PZT thin films with differently processed electrode-PZT interfaces and of different thicknesses have been investigated. The ferroelectric contribution to the switching parameters has been isolated from the leakage current contribution, thus allowing the identification of several salient features of the above phenomena. Incorporating our present results with already established properties of PZT thin films, a set of characteristic features of switching, fatigue and rejuvenation is formulated. This set is interpreted using a framework which takes into account the ferroelectric and semiconductor properties of the system. The key issues of the framework are: (i) Strong inhomogeneous built-in electric field exists in virgin films due to contact phenomena. (ii) Extra near-electrode space-charge layers are created during polarization reversal and destroyed by d.c. rejuvenating fields or by the field of fatiguing pulses. (iii) The built-i...

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

Rhombohedral Pb(Zr0.70Ti0.30)O-3 thin films of four different well-defined textures, namely, (100), (111), bimodal (110)/(111), and (100)/(111), were prepared by a sol-gel method. The films were characterized in terms of grain size, presence of second phases, surface roughness, columnarity of grains, and other microstructural features. The dielectric, ferroelectric, and fatigue properties were investigated, with emphasis on the hysteresis switching characteristics. Results are discussed from the reference point of the allowable spontaneous polarization directions available for the different textures. The values of coercive held, remanent and saturation polarization, and slope of the loop at the coercive held, at saturating fields can be qualitatively explained based on the texture, independent of microstructural differences. The occurrence of surface pyrochlore, however, is observed to affect the functionality of the saturation curves, particularly for the samples of bimodal texture. Shearing of the hysteresis curves of the bimodal films is also attributed to surface microstructural features. The occurrence of nonswitching 71 degrees or 109 degrees domains in the (111) and (110)/(111) textured films is hypothesized based on a comparison with the data from the (100) textured film. Corrected saturation polarization values agree with the spontaneous polarization values of rhombohedral PZT single crystals and published calculated Values for rhombohedral PZT ceramics. The fatigue characteristics show increases in the switching component of polarization in the range 10(3)-10(7) bipolar cycles, particularly for the (111) textured sample. Onset of fatigue is observed for all samples between 10(7) and 10(8) switching cycles.

Microstructure of PZT sol-gel films on Pt substrates with different adhesion

The influence of Ta, Ti and TiO2 adhesion layers with Pt bottom electrodes and the deposition temperature of the metallization on the nucleation and growth of sol-gel derived Pb(Zr0.53Ti0.47)O-3 thin films is reported. Several different PZT annealing profiles were simultaneously investigated to determine the role of PZT annealing on resultant PZT film microstructures for a given metallization. The adhesion layer was found to primarily influence PZT grain size. Largest grain sizes were observed for substrate structures with TiO2 adhesion layers. Slower heating rates resulted in rosette type structures and a large volume of residual pyrochlore, particularly in the case of TiO2 adhesion layers, while yielding only a grain size increase on Ti and Ta bonded substrates. These results were correlated to the stability of the adhesion layers in terms of diffusion through Pt and thus changes in the chemistry and structure of the film/Pt interface where the perovskite nucleation was observed to occur. The Pt metallizations were found to be more strongly (111) textured on the purely metallic adhesion layers and independent of the adhesion layer deposition temperature. PZT texture was found to be influenced by adhesion layer deposition temperature and PZT annealing profile. The perovskite texture was altered through annealing conditions only on TiO2 bonded substrates. The above results suggested a reduction of the number of perovskite nucleation sites on metallizations with TiO2 adhesion layer. This result is in agreement with Rutherford backscattering evidence from previous investigations.

Investigation of Pb(Zr 0.70 Ti 0.30 )O 3 thin films of different textures on Ti/Pt electrodes

Pb(Zr0.70Ti0.30)O-3 rhombohedral thin films of (100), (110)/(111) and (111) textures were prepared on Si wafers with Ti/Pt electrodes. Microstructures and textures were characterized by XRD, SEM, TEM, and AFM. Ferroelectric, dielectric and fatigue properties were measured. Dielectric constants of 1050, 880, and 920 were obtained for the (100), (110)/(111), and (111) films. Remanent and saturation polarizations increased in the order (100), (110)/(111), (111) at high fields. Coercive field values of 27, 43 and 31 kV/cm were measured for the (100), (110)/(111), and (111) samples, respectively, at 300 kV/cm. Similar fatigue characteristic were observed for all films at 300kV/cm, showing an initial increase in switched polarization followed by a decline at 10(7) - 10(8) switching cycles. Observed differences in the measured properties are explained based on allowed polarization directions for given textures, and film microstructure.

Acceptor dopant effects on endurance of PZT thin films

Abstract The effect of acceptor (Na, Mg, Fe) and donor (Nb, Ta) dopants on the switching properties of Pb(Zr0.53Ti0. 47)O3 (PZT) thin films with Pt electrodes was investigated for broad dopant concentration ranges. The effect of dopants on endurance was found to be characteristic to type of doping (donor or acceptor) and independent of individual dopant element, microstructural features, or site of doping. All acceptor dopants studied were found to strongly improve the endurance characteristics of PZT thin films. Increasing the acceptor dopant concentration was found to shift the onset of polarization suppression (electrical fatigue) toward a higher number of switching cycles. It is proposed that the origin of endurance degradation in PZT thin films with Pt electrodes is the transition from p to n type stoichiometry with AC-switching, which leads to the formation of Ti3+ defects. Acceptor dopants shift the p to n transition to higher number of switching cycles, thus postponing the formation of Ti3+ defect...

Effect of Nb doping on the hysteresis parameters of sol-gel derived Pb 1.1-x/2 (Zr 0.53 TiO 0.47 ) 1-x Nb x O 3 thin films

The effect of Nb on the hysteresis parameters of sol-gel Pb-1.1-x/2(Zr0.53Ti0.47)(1-x)NbxO3 (x = 0.0 - 0.05, increments of 0.01) thin films is reported. Two sets of (111) textured films, rapid annealed at 600 and 650 degrees C, were studied. The degree of texture and grain size as a function of Nb was analogous for the two sets. Surface coverage by a pyrochlore phase increased with Nb addition, however its quantity and distribution was determined by the annealing temperature, being less for the 650 degrees C set of films. For the two sets a strong continuous decay of the remanent and maximum polarizations, and the slope at the coercive field, (dP/dE)(Ec), was observed with increasing Nb. The remanent polarization was reduced by a scaling factor at any given field, yielding no changes in the saturation profiles as a function of doping. The difference of the maximum minus remanent polarization and the width of the loop were not influenced by Nb at any given field. A linear increase in coercive field asymmetry (up to 40kV/cm) was observed with Nb addition, yet was field independent and thus electrostatic in origin. A methodology for isolation of Nb induced microstructural effects from bulk or defect modifications was developed. The comprehensive set of hysteresis parameters required for such an analysis is presented here.