Retention loss is a significant issue for an application of ferroelectric thin films to high-density non-volatile memory devices. We investigated the polarization retention characteristics of ferroelectric Pb(Zr,Ti)O3 (PZT) thin films which were fabricated on Pt/IrO2/Ir substrates by different deposition methods. In thermally-accelerated retention failure tests, Pb(Zr,Ti)O3 (PZT) films which were prepared by a chmeical solution deposition (CSD) method showed rapid decay of retained polarization charges as the films became thinner down to 1000 Å, while the films which were grown by metal organic chemical vapor deposition (MOCVD) showed relatively large nonvolatile charges at the same thickness. We concluded that in the CSD-grown films, the relatively large interfacial passive layer compared with the MOCVD-grown films had an unfavorable effect on retention behavior. We observed the existence of such interfacial layers by extrapolation of the total capacitance with thickness of the films and the capacitance of this layer was larger in MOCVD-grown films. It means that the possibility of the accumulation of space charges at the interface was reduced, so that less imprint and less retention loss could be observed in the MOCVD-grown films.

PZT thin films with a thickness of 70 nm were successfully fabricated using a modified solution combined with PbTiO3 seed layer. Throughout various approaches, we found that the microstructure of PZT thin film plays an important role in determining the electrical properties such as hysteretic properties and leakage currents, particularly when the thickness is below 100 nm. We modified the precursor system to improve the microstructure in PZT thin film. In addition, we also adopted a thin PbTiO3 seed layer to enhance the initial nucleation density. Finally, we could obtain good electric properties similar to those obtained from 240 nm thick PZT film. The hysteretic properties is excellent enough to operate at a low voltage (2V) for a high density FRAM application.

A new chemical solution for the deposition of SrBi2Ta2O9 (SBT) thin films using crown ether is proposed. Crown ether enhances the solubility of bismuth acetate in acetic acid, which makes a solvent solution possible. A metal acetate-based SBT precursor solution was prepared in acetic acid using 18-crown-6, strontium acetate, bismuth acetate and tantalum ethoxide. (115)-preferentially oriented ferroelectric SBT thin films were formed on Pt/TiO2/SiO2/Si substrates by spin-coating with the new solution. After post-annealing at 800°C, a hysteresis loop obtained from a 2000Å thick SBT film with Pt electrodes showed a remanent polarization of ∼3μC/cm2 and a coercive voltage of ∼50kV/cm. It was shown from SIMS depth profiles that excess bismuth atoms in the SBT thin film diffused towards the Pt electrodes during post-annealing.

Ferroelectric lead zirconate titanate (PZT) thin films have been successfully prepared on a RuOx/Pt multilayered electrode by Metal Organic Chemical Vapor Deposition (MOCVD). The multilayered electrode was introduced to enhance device reliability for FRAM and DRAM applications. The variations in the microstructure and ferroelectric properties of the PZT thin films were investigated as a function of substrate thickness. The microstructure of the PZT thin films was found to have a strong dependence on the surface morphology of the substrate. The control of microstructure resulted in improved ferroelectric properties. The endurance of the Pt/RuOx/PZT/RuOx/Pt capacitor was also maintained up to 1010 cycles without any serious degradation. The ferroelectric capacitors on 4” wafer were integrated by using Inductively Coupled Plasma Reactive Ion Etching (ICP RIE) system and the fully processed MOCVD PZT capacitors showed good ferroelectric properties (Vc=0.57V, ργ=22μC/cm2 respectively).

It was shown that Pb(ZrxTi1−x)O3 thin films (PZT) can be successfully deposited by metalorganic chemical vapor deposition (MOCVD) in a wide deposition temperature range starting from 400°C to 600°C. Variations in texture, morphology and grain size of the films as a function of process parameters were systematically investigated by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The deposition temperature and gas composition in the reactor are the two key parameters that control the film microstructure. The accompanying changes in the ferroelectric properties with respect to the variations of the process parameters will also investigated. In addition, we found an interrelationship between the grain orientation and surface roughness of the films. Films with (111) preferred orientation are significantly smoother than the films with other preferred orientations. We also demonstrate, for the first time, fine grained PZT films with very low surface roughness, which show excellent electrical properties can be obtained by lowering the deposition temperature (e.g. 430°C)

Pb(THD)2 is one of the most popular CVD precursors for lead. It was found in this study that the volatility of Pb(THD)2 can be considerably improved by using ammonia as a carrier gas. An adduct between Pb(THD)2 and NH3 is generated in-situ, when the NH3 carrier gas is passed through the bubbler containing Pb(THD)2. The ammoniated precursor was isolated and its molecular structure was characterized by elemental analysis, infrared and NM.R. PbO thin films could be prepared with this precursor system while maintaining the bubbler temperature at 110° C, which is considerably lower than the temperature used with the Pb(THD)2 precursor in the commonly used carrier gas.