Pulsed laser deposition technique was used to fabricate Ba0.5Sr0.5TiO 3 (BST) thin-films on Pt/TiO 2/SiO2/Si substrates. The influence of thin interfacial layers of Ta2O5, TiO2, and ZrO2, on the structural and electrical properties of BST thin films was investigated. Insertion of interfacial layers does not affect the perovskite phase formation of BST thin films. Buffer layers helped to make uniform distribution of grains and resulted in a relative increase in the average grain size. The dielectric tunability of BST thin films was reduced with the presence of buffer layers. A BST thin film having a dielectric permitivity of 470 reduced to 337, 235 and 233 in the presence of Ta2O5, TiO2, and ZrO2 layers, respectively. The reduction of the relative dielectric permittivity of BST films with the insertion of interfacial layers was explained in terms of a series capacitance effect, due to the low dielectric constant of interfacial layers. The TiO2 layer did not show any appreciable change in the leakage current density. Deposition of thin Ta2O5 and ZrO2 interfacial layer on top of Pt reduced the leakage current density by an order of magnitude.

Structures and electrical properties of newly synthesized vinylidene fluoride (VDF) oligomer [CF3(CH2CF2)17I] films evaporated onto various substrates around liquid nitrogen temperature were investigated. As a result, the VDF oligomer films were mainly formed with ferroelectric phase (form I) crystals and the molecular chains were oriented parallel to the substrate surfaces regardless of both the kind of the substrates and the thickness of the VDF oligomer films. In addition to these properties, the VDF oligomer films showed polarization reversal due to 180° rotation of the polar VDF oligomer molecules according to the applied voltages. This ferroelectric behavior was verified by local poling and piezoresponse measurements with an atomic force microscope, and by measurements of D-E hysteresis curves.

Longitudinal Pockels cell as a vertical ferroelectric Pb(Zr0.53Ti0.47)O3 (PZT) thin film capacitor was fabricated by pulsed laser deposition technique onto the both side polished YAlO3 + 1% Nd2O3 single crystal substrate. At first, conducting La0.5Sr0.5CoO3 (LSCO) 100 nm thick layer was deposited as an atomic template for 1 m thick PZT film. Epitaxial quality (exceptional c-axis orientation and coherent in-plane texture) of PZT/LSCO/Nd:YAlO3 (001) heterostructure has been confirmed by x-ray diffraction. On the top, semitransparent 100 nm thick Au electrode was deposited by thermal evaporation. Intensity of the chopped 670 nm polarized laser radiation transmitted through the Au/PZT/LSCO/Nd:YAlO3 cell was measured using lock-in amplifier. Special precautions were employed to get reproducible transmittance vs. temperature scans up to 400 °C. Phenomenon of critical opalescence (scattering of the light with critical fluctuations of polarization) was observed in the vicinity of Curie temperature at 208 °C. Modulation of the transmitted light as high as 3% was achieved applying 20 V (200 kV/cm) across the capacitive cell, whereas the voltage tunability measured at 1 kHz from C-V characteristics was about 70%.

Bismuth titanate (Bi4Ti3O12; BIT) -based ferroelectric thin films fabricated from a view point of “the site-engineering technique” have been expected to improve the fatal disadvantage of a ferroelectric BIT film, i.e., its low spontaneous polarization; here, Bi- and Ti-site ions in the BIT crystal are cosubstituted by lanthanoid ions and cations with a higher charge valence, respectively, In the present study, we have mainly focused on Ti-site substitution of bismuth titanate (Bi4Ti3O12; BIT)-based thin films using some ions with higher charge valences (V5+, Nb5+, Ta 5+ and W6+; in this study) to enhance the ferroelectric properties of those materials. The BIT-based films with various chemical compositions were fabricated on a (111)Pt/Ti/SiO2/(100)Si substrate by a chemical solution deposition method.

Ti-site substitution of BIT films by the higher-valent ions, Bi3.99(Ti2.97V0.03)O12, Bi3.99(Ti2.97Nb0.03)O12, Bi3.99(Ti2.97Ta0.03)O12 and Bi3.98(Ti2.97W0.03)O12, reduced the leakage current density of BIT films from ∼ 10-6 down to ∼ 10-7 A/cm2 at an applied field of 50 kV/cm, while the substitution by the same-valent cation, e.g., Bi4.00(Ti2.97Zr0.03)O12, did not affect the behavior of leakage current. Whereas polarization (P) - electrical field (E) hysteresis loops of non-substituted and Zr-substituted BIT films were distorted due to the leakage current, non-distorted P-E loops were obtained at V5+-, Nb5+-, Ta5+- and W6+-substituted BIT films.

Also, Ti-site substitution was effective for improving the ferroelectric properties in lanthanoid-substituted BIT films. In the case of La3+-substituted BIT film (BLT), remanent polarization (Pr) of V5+- and W6+-substituted BLT films, (Bi3.24La0.75)(Ti2.97V0.03)O12 and (Bi3.23La0.75)(Ti2.97W0.03)O12 (13 and 12 μC/cm2, respectively), were larger than those of Zr4+- and non-substituted BLT films, (Bi3.25La0.75)(Ti2.97Zr0.03)O12 and (Bi3.25La0.75)(Ti3.00)O12 (8 and 9 μC/cm2, respectively), while those films had similar coercive field (Ec) of approximately 120 kV/cm. Also in the case of Nd3+-substituted BIT film (BNT), Pr and Ec values of V5+-substituted BNT film, (Bi3.24Nd0.75)(Ti2.98V0.02)O12, were 37 μC/cm2 and 119 kV/cm, respectively, which were comparable with those of conventional Pb-based ferroelectrics such as lead zirconate titanate, Pb(Zr,Ti)O3. We concluded that enhancement of the Pr value was achieved by the charge compensation of oxygen vacancies in BIT-based ferroelectrics using higher-valent cations than Ti4+ ion whereas no obvious differences were found in the crystal orientation and or microstructure of these films.

(Bi,La)4Ti3O12 (BLT) thin films with various Bi2O3 template layers were prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method. Both of the BLT films with a thin Bi2O3 template layer and those without a Bi2O3 layer had a highly c-axis oriented growth, while both of the BLT films with a thin Bi2O3 bottom layer and those with a Bi2O3 intermediate layer were highly c-axis oriented. It was found that the use of Bi2O3 template layers improved significantly the ferroelectric properties of BLT thin films. In addition, the thin films with a thin Bi2O3 template layer showed good dielectric properties. All the capacitors with Bi2O3 template layers showed high polarization fatigue resistance and good retention properties.

Numerical simulation studies were performed in order to shed light on the controlling mechanism for the steady state leakage current through metal/insulator/metal capacitors with high permittivity dielectric or ferroelectric materials such as SrTiO3, (Ba,Sr)TiO3 or Pb (Zr,Ti)O3. As a model we used an extension of the combined injection-diffusion model, i.e. we have solved the Poisson and continuity equations inside the dielectric assuming thin, low permittivity (“dead”) layers at the electrode interfaces. As “new” boundary conditions we used injection / recombination terms at both electrodes, also taking into account the barrier lowering due to the coulomb mirror potential.

The simulation data are presented in dependence on several extrinsic and intrinsic parameters (voltage, temperature, film thickness, barrier height, dead layer properties, etc.) for symmetrical electrodes together with first results on asymmetrical ones. The most important result is that for nearly all parameter sets the leakage current is (film) bulk-limited, mostly due to the low carrier mobilities in these insulating materials. Only for very special conditions the interface-limited current, e.g. thermionic injection at the cathode for electrons, is a good approximation. The numerical data are compared to experimental true leakage current results on STO and BST.

PbZr0.53Ti0.47O3 (PZT) films on La0.5Sr0.5CoO3 (LSCO) /Pt electrodes crystallize in the perovskite phase at 550°C. Cross section SEM shows a columnar grain structure of PZT films on fine-grained LSCO. The ferroelectric response of the heterostructures depends on the annealing temperature of the LSCO layer. The remanent polarization and coercive field of the PZT annealed at 550 °C deposited on LSCO annealed at 800 °C are 25 μC/cm2 and 99 kV/cm respectively, comparable to the values obtained for PZT films on platinized silicon substrate.

Dielectric properties of SrTiO3 (STO) thin films in Au/Pt/STO/Pt/TiO2/SiO2/Si structure are studied at microwave frequencies. STO films with thickness of 300 nm were grown by laser ablation at different temperatures on templates of Pt/TiO2/SiO2 on Si with resistivity of 5 kQ-cm. XRD measurements reveal highly textured (111)STO films with small amount of (100) and (110) domains. The full with at half maximum of the rocking curve of (11 1)STO domains is about 2 degrees. Circular Au/Pt top electrodes with diameters in the range of 10–60 μm were formed by e-beam evaporation and lift-off process. The on chip microwave impedance of devices was measured in the frequency range of 45 MHz-45 GHz as a function of DC electric field in the range of 0–800 kV/cm. The loss tangent is less than 0.06 in the whole frequency range. Application of DC bias results in resonant absorption of microwave power at frequencies of 1.3, 3.0, 4.7, 6.4, and 9.7 GHz. The relative change of the dielectric permittivity under 800 kV/cm DC field is more than 20% in the whole frequency range. The results indicate that the varactors based on these STO films are suitable for tunable microwave applications.

We investigated ferroelectric properties of 20nm-thick epitaxial Pb(Zr,Ti)O3 (PZT) ultrathin films prepared on SrRuO3 (SRO)/SrTiO3 (STO) by metalorganic chemical vapor deposition (MOCVD). When SRO with terrace ledges was used as a bottom electrode, 20nm-thick PZT ultrathin films with ferroelectricity were successfully obtained. These PZT films exhibited saturated hysteresis loops with remanent polarizations (Pr) of 29–33 μC/cm2 and coercive electric fields (Ec) of 340–370 kV/cm. On the other hand, when PZT films were grown on SRO without terrace ledges, PZT films showed no saturated hysteresis loops because of large leakage current. The 15nm-thick PZT ultrathin film exhibiting unsaturated hysteresis loop was also obtained.

Photoelectron spectra by X-ray photoelectron spectroscopy (XPS) and UV-photoyield spectroscopy (UV-PYS) have been analyzed to study O2-annealing effects on band diagrams of ferroelectric SrxBiyTa 2O9 (SBT) thin films deposited by pulsed laser deposition (PLD) and metalorganic dcecomposition (MOD) methods. XPS studies on the annealed PLD-SBT film has shown a rapid shift in its Bi 4f core peaks from the oxidized to the metallic ones, as the film suffer Ar+ bombardment. Surface of the annealed film has exhibited lower Fermi level than the as-deposited one in UV-PYS. The result suggests O2-annealing can suppress leakage current through PLD-SBT films. The UV-PYS studies on MOD-SBT have shown almost the intrinsic Fermi levels before and after the additional annealing. The XPS studies have shown that the additional annealing is not effective to improve stabilities of (Bi2O2)2+ layers, once the film is baked and crystallized.

We have performed experiments on steady state leakage currents through insulating thin films of high permittivity dielectrics such as strontium-titanate (STO) and barium-strontium-titanate (BST) in order to contribute to the understanding of the mechanism limiting the current. Furthermore, as BST is a candidate as a dielectric in the capacitor of future Gb-generation DRAM cells, the absolute value of the current in dependence of external parameters is interesting for the application.

Besides external parameters such as applied voltage and temperature we have investigated the dependence on dielectric film thickness between 20 nm and 150 nm with symmetrical Pt electrodes. For some selected films the influence of asymmetric electrodes has also been investigated: While the bottom electrode was always Pt, the top electrodes were Pt, Au and Al. An epitaxial STO film with oxide electrode bottom electrode has also been tested.

The main results are as follows:

The field dependence of the leakage current quite often shows a linear behavior in a “Schot-tky”-plot, i.e. log (current density) vs. sqrt (applied field). At constant applied field the thinner films show much lower leakage currents than the thicker ones. The leakage currents increase using Pt, Au and Al as cathode, respectively. The leakage in the epitaxial STO film is much smaller with an oxide electrode (SrRuO3) as cathode than with a platinum one.

All these results will be discussed within a modified model, in which the current is bulk-limited, and compared to numerical simulation results of this model.

Multi-layered epitaxial Pb(Zrx,Ti1-x)O3 (PZT) films of x=0.2–0.5 were deposited on La0.5Sr0.5CoO3-x (LSCO)/ (001)STO and LSCO/CeO2/YSZ/(001)Si substrates with buffer layers. It was investigated how the 90° domain structure and the P-E hysteresis character depend on the difference of the thermal expansion coefficient by changing the Zr/Ti composition and the substrates, using HRTEM and XRD methods. XTEM analysis showed that usual lamella configuration of 90° domains of 8–30nm in width penetrated the columnar grain and the PZT layer in the PZT stacked film of Zr/Ti=20/80, 30/70, 40/60. On the other hand, the close-packed 90° domains of 4–5nm in width existed in a epitaxial columnar grain in the PZT50/50 stacked film. The P-E hysteresis loops of PZT20/80 stacked films deposited on STO and Si substrates show the remanent polarization of 2Pr=136μC/cm2, 2Pr=80μC/cm2, respectively. On the other hands, those of PZT50/50 stacked films deposited on STO and Si substrates show the polarization of 2Pr=125μC/cm2, 2Pr=36μC/cm2, respectively. Thus, the P-E hysteresis loop of PZT50/50 has remarkable difference of 2Pr between the substrates.

Scanning Nonlinear Dielectric Microscopy (SNDM) is the method for observing ferroelectric polarization distribution, and now, its resolution has become to the sub-nanometer order, which is much higher than other scanning probe microscopy (SPM) methods for the same purpose. Up to now, we have studied high-density ferroelectric data storage using this microscopy. In this study, we have conducted fundamental experiments of nano-sized inverted domain formation in LiTaO3 single, and successfully formed inverted dot array with the density of 1.5 Tbit/inch2.

The tunability of epitaxial barium strontium titanate films is analyzed theoretically for the first time using a modified phenomenological Landau-Devonshire approach taking into account the formation of unusual ferroelectric phases that cannot form in bulk and single-crystal ceramics. It is shown that enhanced tunability can be achieved by adjusting the misfit strain especially in the vicinity of a structural phase transformation. The internal stresses in epitaxial films as characterized by the misfit strain can be controlled by changing the substrate material and/or varying the film thickness. The latter is due to the possibility of stress relaxation by formation of misfit dislocations that relieve epitaxial stresses at film growth temperature. Based on the thermodynamic model, we provide quantitative estimations of tunability of (001) Ba0.5Sr0.5TiO3 films on (001) LaAlO3 (LAO) and SrTiO3 (STO) as a function of film thickness. The analysis indicates that films on STO substrates should be as thick as possible in order to achieve optimum tunability. To obtain maximum tunability on LAO substrates, the thickness of films should be as close as possible to a critical film thickness (∼120 nm).

For high density FeRAM devices small cell sizes are essential. The combination of the capacitor on plug (COP) structure with the Chain FeRAM™ cell design is used to develop a 32Mb FeRAM. Based on a 0.2 μm standard CMOS process a silicide capped polysilicon plug is used to contact the bottom electrode of the ferroelectric capacitor to the transistor. The barrier contact to the plug is formed by IrO2/Ir and a sputter deposited PZT (40/60) is used as ferroelectric material. The function of SrRuO3 (SRO) layers at the electrode/PZT interfaces is described in more detail. Double sided SRO results in slightly lower coercive voltage and imprint behavior compared to capacitors without SRO. Double sided SRO is essential to achieve excellent fatigue behavior measured up to 1×1011 switching cycles.

Bismuth titanate thin films have been grown by liquid injection MOCVD using Bi(mmp)3 in combination with the new Ti precursors Ti(OPri)2(mmp)2 and Ti(mmp)4 (mmp = OCMe2CH2OMe). Films were grown on Si(100) substrates over the temperature range 300 – 600°C, and were shown to consist predominantly of the Bi4Ti3O12 phase at substrate temperatures > 500°C.

Recently, there has been growing interest in Ca modified BaTiO3 structures due to their larger electro-optic coefficients for their use in optical storage of information over conventional BaTiO3 crystals. Barium Calcium Titanate (BCT) shows promising applications in advanced laser systems, optical interconnects and optical storage devices. BaTiO3 thin films of varied Ca (3 at. % - 15 at. %) doping were deposited using pulsed laser ablation (KrF excimer laser) technique over Pt/Si substrates. The stoichiometric and the compositional analysis were carried out using EDAX and SIMS. The dielectric studies were done at the frequency regime of 40 Hz to 100 kHz at different ambient temperatures from 200 K to 600 K. The BCT thin films exhibited diffuse phase transition, which was of a typical non lead relaxor behavior and had high dielectric constant and low dielectric loss. The phase transition for the different compositions of BCT thin films was near the room temperature, showing a marked departure from the bulk phase transition. The C - V and the hysteresis behavior confirmed the ferroelectric nature below the phase transition and paraelectric at the room temperature.

The local electromechanical properties of relaxor 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 (PMN-PT) films are investigated by Scanning Force Microscopy (SFM) in a piezoelectric contact mode. The domain contrast is observed only in some grains (∼20 % of the entire surface), which showed clear ferroelectric behavior. Thus on the microscopic level the material behaves as a composite with ferroelectric regions embedded in the non-polar matrix. This was attributed to the relaxor-to-ferroelectric phase transition induced by the internal bias field. The local hysteresis loops are found to depend on the size of the grains. A distinct correlation between the values of the effective piezoelectric coefficients, deffi and the size of the respective grains is observed. Small grains exhibit slim piezoelectric hysteresis loops with low remanent deff while relatively strong piezoelectric activity is characteristic of larger grains. In addition, large grains exhibit longer relaxation time after poling with an effective time constant increasing with the grain size. The nature of size effect is discussed taking in terms of dynamics of nanopolar clusters and SFM instrumentation.

The optical and electro-optical properties of epitaxially grown thin films of ferroelectric BaTiO3 on MgO substrates have been established and high quality Mach-Zehnder waveguide modulators have been demonstrated. As a next step towards the integration of ferroelectric thin films on different substrates, we have modified the growth conditions by lowering the growth temperature to study polycrystalline, but still highly transparent BaTiO3 (BTO) films. Polycrystalline BTO on MgO substrates has been grown by pulsed laser deposition (PLD). The growth temperature was reduced from 800 °C to 400 °C at an oxygen pressure of 2×10-3 mbar. Although polycrystalline, the BTO is still birefringent with no= 2.32 and ne = 2.30. Ridge waveguides have been formed by ion beam etching. The estimated waveguide propagation loss is 4 dB/cm at 633 nm. Electro-optic Mach-Zehnder modulators have been realized. Using 3 mm long electrodes with a spacing of 10 μm, a Vπ voltage of 14 V was obtained at 633 nm wavelength. This is half of the observed effective electro-optic coefficient measured at epitaxial BTO films. At 1.5 μm wavelength similar results were observed.

Arrays of mesoscopic ferroelectric PZT structures with lateral sizes from several micrometers down to below 300 nm were prepared applying nanoimprint lithography. The ferroelectric properties of the mesoscopic structures were investigated by scanning force microscopy in piezoresponse mode. The best chemical route to obtain ferroelectric structures was found to be the sol-gel method. Using Nb-doped SrTiO3 single crystals as bottom electrodes, the crystallization into the ferroelectric phase was uniform with grain sizes in the 35 nm range. The best ferroelectric properties of individual 300 nm structures were obtained if an intermediate, continuous ferroelectric layer was present on the bottom electrode.