La0.5Sr0.5CoO3 (LSCO) thin films have been deposited using RF magnetron sputterdeposition for use as an electrode material for Pb(Zr, Ti)O3 (PZT) thin film capacitors. The effect of the O2:Ar sputter gas ratio during deposition, on the LSCO film properties was investigated. It was found that the resistivity of the LSCO films deposited at ambient temperature decreases as the O2:Ar ratio was increased for both the as-deposited and annealed films. In addition, it was found that thin overlayers of LSCO tend to stabilize the underlying Pt//Ti electrode structure during subsequent thermal processing. The LSCO//Pt//Ti composite electrode stack has a low resistivity and provides excellent fatigue performance for PZT capacitors. Furthermore, the LSCO//Pt//Ti electrode sheet resistance does not degrade with annealing temperature and the electrode does not display hillock formation. Possible mechanisms for the stabilization of the Pt//Ti electrode with LSCO overlayers will be discussed.

Ruthenium oxide films were deposited on Al2O3 (0001) and (1102) substrates using reactive sputtering under two different target surface conditions. Films grown when the surface of the target was metallic ruthenium (metallic-target) showed a Ru: O ratio of 1: 2.0±0.05 as determined by Rutherford backscattering spectrometry. At elevated deposition temperatures, these films aligned with the substrates as RuO2 (100) ║ A12O3 (0001) and RuO2 (101) ║ Al2O3(1102). Films deposited when the target surface was fully oxidized (oxidized-target) exhibited a Ru: O ratio of 1: 2.5±0.05 and displayed an oriented crystalline structure even at room temperature. The resistivity of the RuO2.5 films was 75 μΩ-cm and was independent of temperature between 5 and 300 K. Possible causes of this behavior are discussed.

Thin films of Lead-Zirconate-Titanate (PZT) have been grown by pulsed-laserdeposition (PLD) onto polished MgO substrates both with and without pre-annealing.

The surface morphology of polished MgO substrates, which are widely used for deposition, is examined by AFM. Commercially available, mechanically-polished substrates are shown to be microscopically very rough and seem unlikely to present a surface suitable for the growth of the highest quality thin films. Annealed MgO substrates, on the other hand, comprise atomically flat terraces. The use of annealed substrates is found to enhance considerably the crystalline quality of PZT films deposited thereon.

The electrical properties and crystallization process of Pb(Zr0.4, Ti0.6)O3 or PZT thin films grown by rf magnetron sputtering, from ceramic target, on fiber-textured (111)Pt/TiN/Ti/SiO2/Si and polycrystalline RuOx/SiO2/Si have been studied. It is found that the amorphous as-deposited thin film, processed by rapid thermal annealing (RTA), is transformed to a perovskite PZT at about 700°C. It is pointed out that the “heating rates” to reach 700°C affect the electrical properties of such films: TEM analysis reveal different grain sizes as a function of the heating rate. The XRD show that an oriented (111) PZT is promoted when the film is annealed to the temperatures of 800°C for 5 secondes. For these annealing conditions, the electrical properties of such structure depend strongly on the deposition conditions of PZT. Our process studies show that a thin film PZT deposited on Pt or RuO1.65 at 200°C and 1 Pa argon pressure gives good hysteresis loop with high values of Ps and Pr (about 20 and 30 μC/cm2 on Pt and RuO1.65 respectively) and low leakage current about 10−11 A/cm2 on Pt and 10−6 A/cm2 on RuO1.65.

Highly (100)-textured thin film of metallic LaNiO3 (LNO) was grown on the Pt/Ti/SiO2/Si substrates by rf magnetron sputtering at ˜300°C, which was used as a bottom electrode to prepare highly (100)-textured ferroelectric films. Examples on the deposition of PbTiO3, (Pbl−xLax)TiO3, Pb(Zr0.53Ti0.47)O3, Pb[(Mg1/3Nb2/3)1−xTix]O3, and (Ba1−xSrx)TiO3 thin films by rf magnetron sputtering or sol-gel method are shown. A reduction of temperature for perovskite phase formation can be achieved, especially for those difficult to crystallize. The surface roughness of the ferroelectric films is also improved as compared to that of films deposited on conventional Pt electrode. Although the electrical properties of the ferroelectric films are affected by the out-diffusion of LNO when a higher temperature was used in the preparation of the films, under an appropriate processing condition, the highly (100)-textured films can have satisfactory electrical characteristics for application. Moreover, the polarization-fatigue property can be also improved by the use of LNO electrode.

Microstructures and interdiffusions of Pt/Ti/SiO2/Si and RuO2/SiO2/Si during annealing in O2 were investigated using x-ray diffraction, Auger electron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The degree of oxidation and the interdiffusion of elements have remarkably increased with increasing temperature above 500 °C for the Pt/Ti/SiO2/Si case. The generation of Pt hillocks commenced at 500 °C. The Pt-silicide phase was also observed near the TiOx/SiO2 interface. The microstructural variations occurred to only a small amount for the RuO2/SiO2/Si case over the temperature range 300 – 700 °C. While there was no hillock formation, the RuO2 film surface was roughened by the thermal grooving phenomenon. A thin interlayer phase was found at the RuO2/SiO2 interface.

We have studied the optimum conditions of the deposition of NiCr-bottom electrode for preparing the ferroelectric PZT(50/50) thin film capacitor. The NiCr(80/20) layer of about 300nm in thickness was deposited on bare Si(111) wafer by rf magnetron sputtering. The surface morphology and crystallinity were investigated by using Atomic force microscope (AFM) and X-ray diffractormeter (XRD). It is found that the size and crystallinity of grains of NiCr or Ni-silicide depend mainly on the rf power. The PZT(50/50) thin films were prepared on NiCr/Si substates by spin-casting of PZT coating sol and then annealing at 520°C in air for crystallization. The undesirable Pb-silicate is found to be grown during post-annealing in case that substrates having NiCr layer deposited by high power above 80 W are used. We suggest that the formation of Pb-silicate is due to the thermal diffusion of Pb or PbO through crystalline NiCr-grain boundaries. The ferroelectric PZT thin films having the perovskite structure can be obtained by using the NiCr-bottom electrodes whose morphologies are in the amorphous-crystalline boundaries, in which the surface roughness and grain size of NiCr layer is minimum. The values of the dielectric constant, εn, were measured in the range 300˜500, the remanent polarization, Pr, in the range 10˜13 C/cm2 and the coercive field, Ec, around 160 kV/cm, depending on the deposition conditions of NiCr layers.

Dry etching is an area that demands a great deal of attention in the large scale integration of ferroelectric thin film capacitors for nonvolatile random access memory applications. In this review, we discuss some of the issues relating to the etching of the ferroelectric films, patterning of the electrodes, device damage caused by the etch process and post-etch residue problems. An etch process that can provide high etch rates and good etch anisotropy for the current candidate ferroelectrics including Pb(Zr, Ti)O3 and layered structure SrBi2Ta2O9 thin films using environmentally benign gases such as hydrochlorofluorocarbons is presented. The etch mechanism for both of these materials was determined to rely substantially on ion bombardment effects. For example, PZT films were etched anisotropically at rates of up to 60 nm/min using CHCIFCF3 gas under high rf power and low gas pressure conditions. Problems remain with respect to the acrosswafer differential etch rates observed when more than one phase is present in the material (e.g., amorphous/pyrochlore + perovskite phases in PZT). Damage caused by the etch process which can lead to changes in device characteristics, including hysteresis and fatigue properties, and the underlying mechanism that causes the damage are discussed. O2 was found to be a suitable etch gas for etching the conductive oxide electrode material RuO2. However, an anomaly in the etch rate was detected upon introduction of a small amount of fluorine containing gas: addition of 2% of CF3CFH2 gas to the O2 plasma increases the etch rate by a factor of four. This can be taken advantage of in obtaining high etch selectivity between the electrode and ferroelectric layers.

Step coverage of PZT grown by MOCVD was influenced by the growth temperature, the reaction pressure and the aspect ratio of the trench. PZT films grown on Si steps at growth temperatures ranging from 500 to 600°C and at reaction pressures ranging from 3 to 10Torr showed a step coverage of 52 to 86%. The step coverage of PZT grown at 600°C and at 5Torr – conditions which were suitable for the growth of perovskite phase – was 75%. The step coverage of Pt on Si and on SiO2 was 20% and 25%, respectively.

We report the successful deposition of single phase c-axis oriented films of lead zirconate (PbZrO3) on a silicon substrate by pulsed laser ablation. The formation of the film at different substrate temperatures was studied using atomic force microscopy and scanning electron microscopy. We also measured the temperature dependence of the dielectric constant of the films and their dielectric hysteresis behavior.

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)

A number of factors have been identified as affecting the gas phase oxidation of cations during pulsed laser ablation of lead zirconate titanate (PZT), by using energy dispersive mass spectrometry (EDMS). These phenomena are known to be critical to the deposition of high quality thin films of PZT. However, to isolate the role of each cation species and the influence of its gas phase properties, we have also looked beyond the ablation of the PZT ceramic. In this paper, we detail our observations during pulsed laser ablation of electroceramic and metallic targets, specifically PZT, Pb and Ti. We have observed the evolution and transport of molecular species during gas phase expansion over a wide range of oxygen pressures (10−7 - 10−1 mbar) and laser fluences (0.3 -10 Jcm−2). The yields of the molecular ion species are strongly dependent upon the number density of the background gas. We propose an interpretation of the relative yields of the species based upon their respective gas phase binding energies and their ease of formation based upon the reaction thermodynamics and reaction cross-section of each species.

Ferroelectric PbZrxT1−xO3 (PZT) thin films have been deposited on Pt coated Si substrates by if magnetron sputtering. The optimized processing condition to obtain proper stoichiometric PZT, the desired ferroelectric perovskite phase, and better dielectric properties was demonstrated using a PZT target with Pb(Zr+Ti) ratio of 1.2 and depositing at 350°C, followed by thermal treatment at 620°C for 30 min. The structural and electrical properties of the PZT layer were further improved by fabricating a novel multilayer structure which combined the PZT with the nanolayer BaTiO3. The leakage current density was reduced from 2×10−7 A/cm2 for the single layer structure to 2×10−9 A/cm2 for the multilayer structure at a field of 4×105 V/cm, while maintaining a high relative effective dielectric constant of 442. The relative dielectric constant of the PZT film in the multilayer structure was calculated to be about 880.

Pb(ZrxTi1−x)O3(PZT) thin films have excellent ferroelectric, optical, piezoelectric and pyroelectric properties. We prepared PZT thin films using the excimer laser ablation technique. A pulsed KrF excimer laser was used to ablate PZT bulk targets. We have studied optimum preparation conditions such as an oxygen pressure, a laser energy fluence and a substrate temperature.

In this paper, we investigated the composition, crystallization and ferroelectric properties of the PZT films prepared under various deposition conditions.

The X-ray diffraction (XRD) patterns showed that the PZT films prepared on MgO(100) substrates at 600°C and with a laser fluence of 2J/cm2 had a perovskite - pyrochlore mixed structure. The condition of 100 mTorr oxygen pressure provided high quality perovskite films. It is found that the stoichiometric composition of the deposited films is obtained in ambient oxygen of 100˜400 mTorr. The ferroelectric properties of the Pt/PZT/Pt/MgO structure were studied. The capacitance-voltage characteristics and the corresponding hysteresis loop of the dielectric-electric field curve were discussed.

We also studied optical emission of the PZT plasma plume to understand quantitative relation between the PZT film quality and the ablation plume plasma. We identified spectral lines originated in Pb, Pb+, Zr, Zr+, Ti, Ti+, PbO and TiO. These spectral intensities have remarkable dependence on the ambient O2 pressure.

Comparatively low temperature growth of Pb(Zr0.52Ti0.48)O3 thin films was accomplished by using rf magnetron sputtering process. Well crystallized PZT thin films (4000Å thickness) were synthesized on Pt/Ti/SiO2/Si(100) substrate at the temperature as low as 5200°C. The polycrystalline PZT perovskite phase formation was confirmed with XRD analysis. Remanent polarization(Pr) and coercive field(Ec) of as-grown film (4000Å) were 8–30 μC/cm2 and 24–64 kV/cm with the applied voltage variation(5–17 V). The post annealing enhances the electrical properties even at 500°C, which is below the as-grown temperature(520°C). The increase of annealing temperature resulted in the consequent increase of remanent polarization and the decrease of coercive field. The values of dielectric constant(ε′ ) and tan δ measured with small signal sign wave(1V, 10kHz) were 1207 and 0.066 in case of as-grown film (4000Å).

An aspect which has hindered the development of ferroelectric memories is dielectric fatigue and to resolve this conducting oxides are promising candidates as an electrode material for lead zirconate titanate thin films. In this work ferroelectric films have been grown by pulsed laser deposition on ruthenium oxide electrodes. The phase distribution, microstructure and the effect of subsequent heat treatment have been studied by grazing angle X ray diffraction and electron microscopy; the results and implications for use of RuO2 as the bottom electrode during vapour phase deposition are discussed.

We review the processes and mechanisms by which voltage offsets occur in the hysteresis loop of ferroelectric materials. Simply stated, voltage shifts arise from nearinterfacial charge trapping in the ferroelectric. We show that the impetus behind voltage shifts in ferroelectric capacitors is the net polarization, with the net polarization being determined by the perovskite and the aligned defect-dipole components. Some common defect-dipoles in the PZT system are lead vacancy-oxygen vacancy complexes. One way to change the net polarization in the ferroelectric is to subject the PZT capacitor to a dc bias at elevated temperature; this process is spectroscopically shown to align defect-dipoles along the direction of the applied electric field. The alignment of defect-dipoles can strongly impact several material properties. One such impact is that it can lead to enhanced voltage shifts (imprint). It is proposed that the net polarization determines the spatial location of the asymmetrically trapped charge that are the cause for the voltage shifts. An enhanced polarization at one electrode interface can lead to larger voltage shifts since it lowers the electrostatic potential well for electron trapping, i.e., more electron trapping can occur. Defect-dipole alignment is also shown to increase the UV sensitivity of the ferroelectric.

Polarization relaxation in PZT and PLZT (with La concentration from 0% to 10%) thin film capacitors was characterized in the time range from 10 ns to 1000 s. It was found that at zero volt the polarization in PZT and PLZT thin films changes logarithmically with time, P(t) = blog(t) + P0, and the polarization current density J(t) = dP(t)/ dt obeys the Curie-von Schweidler Law, J(t) = b. t−x, with n = 1 from 100 ns extending to 10 s. Over 10 s, the exponent n in the J-t relationship becomes less than 1. The coefficient b in the Q-t and J-t relationship at zero volt correlates strongly with the remanent polarization. La doping in PZT reduces remanent polarization and reduces relaxation.

Retention characteristics of various ferroelectric memory cell structures, based on lead zirconate titanate (PZT) capacitors, were investigated under different test conditions. Test of retentivity without any pre-treatment, revealed very high rates of polarization loss with time for partially polarized PZT capacitors. However, when different structures were subjected to a thermal cycle before retentivity study, they indicated significant polarization loss or polarization reversal in FRAM and MFMIS(metal-ferroelectric-metal-insulatorsemiconductor) structures. This thermal cycle dependent retentivity problem was attribute to pyroelectric charges that are developed during the temperature cycle.

For each memory cell structure, the underlying mechanisms for the rapid polarization. loss were discussed. Furthermore, guidelines for improving the memory retention were proposed based on the theoretical interpretation of the phenomena.

The band structure of the Bi layered perovskite SrBi2Ta2O9 (SBT) has been calculated by the tight binding method. We find both the valence and conduction band edges to consist of states primarily derived from the Bi-O layer rather than the perovskite Sr-Ta-O blocks. The valence band maximum arises from 0 p and some Bi s states, while the conduction band minimum consists of Bi p states, with a band gap of 5.1 eV. It is argued that the Bi-O layers largely control the electronic response of SBT while the ferroelectric response originates from the perovskite Sr-Ta-O block. Bi and Ta centered traps are calculated to be shallow, which may account in part for the excellent fatigue properties of SBT.