A manmade ferroelectric-paraelectric heterostructure, a BaTiO3 / SrTiO3 superlattice, was studied to explore the effect of strain on ferroelectricity. An atomically abrupt BaTiO3 / SrTiO3 superlattice was grown on a (001) SrTiO3 substrate by reactive molecular beam epitaxy. Both BaTiO3 and SrTiO3 layers were grown with their individual thicknesses less than the critical thickness for the formation of interfacial misfit dislocations, leaving the entire superlattice fully coherent with the substrate. This resulted in a uniformly and highly strained BaTiO3 layer to study the effect of strain on ferroelectricity. Quantitative high-resolution transmission electron microscopy was employed to examine the atomic positions of cations and anions in the strained BaTiO3 layers. It was found that the relative static displacement of cations (Ti4+, Ba2+) to anions (O2−) is larger than that of bulk BaTiO3. Our observation thus illustrates the strain-induced elevation of spontaneous polarization in BaTiO3 thin films.

We have used electrical characterization and secondary ion mass spectroscopy (SIMS) to investigate the influence of hydrogen or deuterium (H/D) on the degradation of the electrical properties of Pt/Ba0.7Sr0.3TiO3/Pt thin film capacitors after forming gas exposure. Deuterium SIMS depth profiling shows that high deuterium concentrations can be incorporated into Pt/BSTO/Pt capacitors after forming gas annealing. The increase in H/D concentration in the film is accompanied by an increase in the leakage and dielectric relaxation current density. Voltage offsets in the capacitance-applied voltage (C-VA) characteristics after forming gas exposure at lower temperatures (20 °C) and a suppression in the capacitance density near zero applied D.C. bias after forming gas exposure at higher temperatures, suggests that one effect of forming gas exposure to Pt/BSTO/Pt thin film capacitors is to introduce positive space charge into the BSTO film. Using an equivalent model for a ferroelectric thin film capacitor, which incorporates lower permittivity interfacial layers and a nonlinear electric field-electric displacement relationship for the film interior, the effects of a uniform distribution of positive space charge on the theoretical C-VA and current density applied voltage (J-VA) characteristics are investigated. It is shown the model can account for many of the observed changes that occur in the experimental C-VA and J-VA characteristics after forming gas exposure.

Near field optical second harmonic microscopy has been applied to imaging of the c/a/c/a polydomain structure of epitaxial PbZrxTi1−xO3 thin films in the 0<x<0.4 range. An uncoated adiabatically tapered fiber tip was employed in our microscope which, according to our previous research [5] could yeild a resolution of up to 80 nm. Experimentally measured nearfield second harmonic images have been compared with the results of theoretical calculations. Good agreement between theory and experiment has been demonstrated. Thus, novel optical technique for nanometer scale ferroelectric domain imaging has been developed.

Anisotropies of the properties of the bismuth-layered perovskite SrBi2Ta2O9 (SBT) have been investigated using epitaxial thin films grown by pulsed laser deposition both on conducting Nb-doped SrTiO3 (STO) single crystal substrates and on Si(100) substrates. It has been found that the three-dimensional epitaxy relationship SBT(001)∥STO(001); SBT [110] ∥STO[100] can be applied to all SBT thin films on STO substrates of (001), (011), and (111) orientations. An about 1.7 times larger remanent polarization was obtained in (103)-oriented SBT films than in that of (116) orientation, while the (001)-oriented SBT films revealed no ferroelectricity along their c-axis. Non-c-axis-oriented SBT films with a well-defined (116) orientation were also grown on silicon substrates for the first time. They were deposited on Si(100) covered with a conducting SrRuO3 (110) bottom electrode on a YSZ(100) buffer layer.

SrRuO3 and CaRuO3 films prepared by MOCVD were compared not only in term of their own properties but for their characteristics as the top electrodes of (Pb, La)(Zr, Ti)O3[PLZT] capacitor, especially for H2 degradation. Resistivity of CaRuO3 and SrRuO3 films increased after heat treatment in H2-containing atmosphere, but was recovered by a heat treatment at 600 °C under O2 atmosphere. When SrRuO3 and CaRuO3 films deposited at 600 °C were used as top electrodes, the remanent polarization(Pr) value of SrRuO3/PLZT/Pt and CaRuO3/PLZT/Pt capacitors were almost the same as the values for capacitors with a Pt top electrode. After a heat treatment in a 3 % H2 atmosphere at 200 °C, followed by one in O2 atmosphere at 450 °C, Pr value was perfectly recovered for both of SrRuO3 and CaRuO3 films. The leakage current become the smallest when using 50 nm-thick CaRuO3 film as a top electrode. Moreover, no degradation was observed for fatigue test up to 1010 cycles when MOCVD-CaRuO3 films were used as top electrodes. These data show that MOCVD-CaRuO3 film with thin thickness is a useful top electrode for PLZT capacitor.

Materials requirements for electrodes and barriers in high density dynamic random access memory (DRAM) and ferroelectric random access memory (FERAM) are reviewed, and some approaches to barrier materials and device geometries are described. Electrode/barrier topics covered in more detail include Pt reactivity with Si-containing barriers and dielectric overlayers, the application of a Bragg-Brentano x-ray diffraction technique to quantitatively probe Pt and Ir electrode morphology and thickness changes during ferroelectric processing, the stability of metal oxide electrode materials in reducing ambients, electrode patterning techniques (including Pt electroplating), and electrical properties of 3-D capacitors in 256k arrays as a function of top electrode annealing treatments.

Ba0.8Sr0.2TiO3 thin films that are suitable for infrared detector applications have been prepared with a sol-gel process using a highly diluted precursor solution. Columnar structure with grain size close to 200 nm was obtained with layer-by-layer homoepitaxy due to a very small thickness of individual layer. The measured pyroelecrtic coefficient is larger than 3.1×10划4 C/m2K at the temperatures ranging from 10 to 26 °C and reaches the maximum value of 4.1×10划4 C/m2K at 16.8 °C. The infrared detectivity of 4.6×107 cmHz1/2W划1 has been obtained at 19 °C and 10 Hz in the Ba0.8Sr0.2TiO3 films deposited on thick (500 μm) platinum coated silicon substrates. The better infrared response can be expected by the improvement in the thermal isolation of pyroelectric element and the electrode materials.

We report on the performance of a planetary multi-wafer MOCVD reactor which handles 5 six inch wafers simultaneously. The reactor is combined with a liquid delivery system which mixes the liquid precursors from three different sources: 0.35 molar solutions of Ba(thd)2 and Sr(thd)2 and a 0.4 molar solution of Ti(O-i-Pr)2(thd)2. The microstructure and the film stress were investigated by X-ray diffraction and the composition of the films was determined by X-ray fluorescence analysis. As a direct consequence of the reactor design we obtain a high uniformity of the films over 6 inch wafers, as well as high efficiencies for the precursor incorporation. Film growth is discussed within a wide parameter field and the finally achieved electrical properties, e.g., permittivity, loss tangent, leakage current, are discussed in relation to the microstructural properties.

Monte Carlo simulations of some typical order-disorder ferroelectrics such as TGS, NaNO2 and DKDP nanocrystals were studied using a Transverse Ising Model Hamiltonian with four-spins interactions. The microscopic parameters corresponding to this Hamiltonian were adjusted to fit the experimental polarization-temperature curves for each one of the materials in the bulk phase. Then the dependences of the ferroelectric-paraelectric phase transition temperatures, Tc, on the sizes of those crystals were studied with Monte Carlo simulations of the order-disorder system. We report a weak dependence of Tc on the size of the crystal (d) for these materials above d∼6nm. The addition of surface effects showed that the expected lowtemperature shift of Tc due to size effects, can be reverted.

The objective of this work was to develop a process to pattern noble metal electrodes. To systematically investigate possible reactive etch process regions, characterized by volatile etch products, we used a reactive ion beam etching (RIBE) tool with a filament free ICP source. This configuration gives us exact control over the beam energy and the current density, and allows to use reactive gases. An energy dispersive quadrupole mass spectrometer is fitted to the chamber for in situ monitoring.

We study the influence of the beam energy and the beam current impinging on the wafer surface as well as it's angular dependence. Several additives to the chlorinated process chemistry are investigated and characterized in terms of their role to help to increase the etch rate, maintain a vertical profile, or to enhance process selectivity.

The main focus of the study is on Platinum. Blanket films were used to describe the influence of the material, and analysis were carried out to characterize the process in terms of etch rate, residues and selectivity.

Thin film capacitors with barium strontium titanate (BST) dielectric layers of 7.5 to 950 nm were fabricated by Pulsed Laser Deposition. XRD and EDX analyses confirmed a strongly oriented BST cubic perovskite phase with the desired cation stoichiometry. Room temperature frequency dispersion (ε100 kHz / ε100 Hz) for all capacitors was greater than 0.75. Absolute values for the dielectric constant were slightly lower than expected. This was attributed to the use of Au top electrodes since the same sample showed up to a threefold increase in dielectric constant when Pt was used in place of Au. Dielectric constant as a function of thicknesses greater than 70 nm, was fitted using the series capacitor model. The large interfacial parameter ratio di / εi of 0.40 ± 0.05 nm implied a significant dead-layer component within the capacitor structure. Modelled consideration of the dielectric behaviour for BST films, whose total thickness was below that of the dead layer, predicted anomalies in the plots of d/ ε against d at the dead layer thickness. For the SRO/BST/Au system studied, no anomaly was observed. Therefore, either (i) 7.5 nm is an upper limit for the total dead layer thickness in this system, or (ii) dielectric collapse is not associated with a distinct interfacial dead layer, and is instead due to a through-film effect.

Ferroelectric random access memories (FeRAMs) are new types of memories especially suitable for mobile applications due to their unique properties such as nonvolatility, small DRAM - like cell size, fast read and write as well as low voltage / low power behavior. Although standard CMOS processes can be used for frontend and backend / metallization processes, FeRAM technology development has to overcome major challenges due to new materials used for capacitor formation. In this paper, advantages and disadvantages of different ferroelectric materials and major development issues for high density applications are discussed. Results of a 0.5μm ferroelectric process using SrBi2Ta2O9 (SBT) as ferroelectric layer, Pt as electrode material, and 2-layer tungsten / aluminum metallization are discussed.

Thin film capacitor structures in which the dielectric is composed of superlattices of the relaxors [0.2Pb(Zn1/3Nb2/3)O3 – 0.8BaTiO3] and Pb(Mg1/3Nb2/3)O3 have been fabricated on MgO {100} substrates by Pulsed Laser Deposition. Structural studies show dielectrics to be 100% perovskite, with strong chemical distinction between individual relaxor layers. The dielectric properties of the superlattices were investigated as a function of periodicity. Significant enhancement of the dielectric constant was observed in relatively fine-scale superlattices, consistent with previous studies. However, unlike previous work, in these relaxor superlattices dielectric enhancement is not associated with increased loss. Rather tan δ is low across the entire superlattice series. Polarisation measurements as a function of temperature suggest that the observed enhancement in dielectric constant is associated with the onset of coupled behaviour. The thickness of the individual layers in the superlattice at which coupled functional behaviour becomes apparent is ∼10nm and is comparable to that found in literature for coupled structural behaviour.

Thin films of ferroelectric ABi2Ta2O9 bismuth-layered structure, where A = Ba, Sr and Ca, were prepared by pulsed laser deposition technique on Pt/TiO2/SiO2/Si(100) substrates. The influence of substrate temperature between 500 to 750°C, and oxygen partial pressure 100-300 mTorr, on the structural and electrical properties of the films was investigated. The films deposited above 650°C substrate temperature showed complete Aurivillius layered structure. Films annealed at 750°C for 1h in oxygen atmosphere have exhibited better electrical properties. Atomic force microscopy study of surface topography shows that the films grown at lower temperature has smaller grains and higher surface roughness. This paper discusses the pronounced influence of A-site cation substitution on the structural and ferroelectric properties with the aid of Raman spectroscopy, X-ray diffraction and electrical properties. The degradation of ferroelectric properties with Ba and Ca substitution at A-sites is attributed to the higher structural distortion caused by changing tolerance factor. A systematic proportionate variation of coercive field is attributed to electronegativity difference of A-site cations.

Sr2(Ta1划x, Nbx)2O7(STN) ferroelectric thin films have been prepared on SiO2/Si(100) substrates by the pulsed laser deposition (PLD) method. Preferential (110) and (151)-oriented STN thin films are deposited at a low temperature of 600°C in N2O ambient gas at 0.08 Torr. A counterclockwise C-V hysteresis was observed in the metal-ferroelectric-insulator-semiconductor (MFIS) structure using Sr2(Ta0.7, Nb0.3)2O7 on SiO2/Si deposited at 600°C. Memory window in the C-V curve spreads symmetrically towards both positive and negative directions when applied voltage increases and the window does not change in sweep rates ranging from 0.1 to 4.0×103 V/s. The C-V curve of the MFIS structure does not degrade after 1010 cycles of polarization reversal. The gate retention time is about 3.0×103 sec when the voltages and time of write pulse are ±15V and 1.0 sec, respectively, and hold bias was -0.5 V.

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.

(BiLa)4Ti3O12 (BLT) films have been fabricated by the sol-gel technique and characterized. It is shown that the partially replacing Bi with La can promote the crystallization, hence can reduce the crystallization temperature of the film. It is also demonstrated that crystalline orientations of sol-gel derived ferroelectric BLT films can be controlled by the growth conditions.

Self-polarization of Pb(Ti1−xZrx)O3 (PZT) thin films is explained on the basis of the formation of a TiO2−x-enriched interlayer close to the bottom electrode. Electrons provided by oxygen vacancies generate a n-type interface layer in the PZT at the electrode. A graded ferroelectric layer is then formed by electron injection from the bottom electrode and electron trapping on Ti4+ ions. A “built-in” difference in free energy forms which acts to pole the ferroelectric. Band bending was observed by contact potential difference measurements at a distance of 70 to 90 nm from the bottom electrode.

We have been proposing YMnO3 with low remanent polarization and permittivity as a ferroelectric gate transistor, and reported that c-oriented YMnO3 films were obtained on (111)Si with (111) oriented Y2O3 buffer layer. The ferroelectricity was confirmed by pulsed C-V measurement. However, the retention property was not satisfied because of its poor crystallinity. To improve the crystallinity of YMnO3 films, deposition conditions of Pulsed Laser Deposition (PLD) were optimized. The laser power, oxygen pressure and introducing Ozone gas are effective for maintaining the stoichiometry during the deposition. Improvement of the crystallinity of the YMnO3 film makes the retention property better. We also demonstrate the use of epitaxially grown Y2O3 buffer layer to improve the crystallinity of the YMnO3 films.

Large scale actuated structures often require piezoelectric elements in the thickness range 10-50μm. For manufacturing purposes, the chemical solution deposition of sol gel composites can create such structures using methods compatible with semiconductor fabrication technology. The piezoelectric characteristics of structures fabricated by patterning methods based on the lapping and dicing of bulk ceramic, spray coating and laser machined and micromolded sol gel composites are compared. Laser interferometer measurements on PZT/PZT composites give d33 = 200 pC/N and d31 = 24 pC/N. The design and fabrication of large area voltage actuated mirrors and annular and linear ultrasonic arrays in the frequency range of 50 MHz are demonstrated.