This work addresses the need for thick layers of ferroelectric thin films on semiconductors for integrated optics applications. The deposition of BaTiO3 thin films with MgO buffers on patterned GaAs substrates is presented as an approach to achieve crack-free optical waveguiding structures. Cracking and peeling of the thin films are observed on patterns with lateral dimensions exceeding 60 microns and nearly crack-free thin films for patterns with lateral dimensions of a few microns. The cracking and peeling of the thin films is attributed to thermal expansion mismatch during the heating and cooling steps of the deposition process. A thin film stress and fracture model is used to analyze the phenomenon. Reduced cracking and peeling on the patterned features are attributed to strain relief on the patterned features. The inclusion of thick AlxOy buffer layers obtained through wet-oxidation of AlGaAs prior to BaTiO3/MgO deposition are presented as a means of obtaining electro-optic waveguide structures on GaAs.

It is well known that spontaneous polarization of ferroelectric material is an intrinsic property applied for nonvolatile memory devices. Poling direction can be reversed in a nanometer size area using the conductive cantilever of a scanning probe microscope. In order to detect nanodots patterns, scanning nonlinear dielectric microscope (SNDM) is superior to piezore-sponse microscope in terms of resolution. In this paper, a real-time measuring method of a poling direction is proposed. Using this method, the domain reversal process was observed and an unexpected phenomenon was found, namely, that the poling directions were aligned antiparallel to the poling electric field. This antiparallel poling reversal took place when the film thickness was more than 350 nm in the case of lithium tantalate. At present, the reason and mechanism of the antiparallel poling reversal are uncertain, although it might be related to the concentrated electric field near the cantilever tip.

There has been a recent shift towards a tunable phase shifter for microwave antenna design. Barium strontium titanate [BaxSr(1-x)TiO3] thin films are the principal materials of interest in these applications, primarily because of their low loss, high dielectric constant and large tunability. Both magnesium doped and undoped films were made, and they were deposited on MgO or Pt-Si substrates using metal organic solution deposition and pulsed laser deposition. Residual stress within these materials is known to have a drastic effect on the material, electrical, and dielectric properties. This becomes of particular importance in thin film materials, where the residual stress can be several orders of magnitude higher than in bulk materials. The residual stress in the films was measured in three ways. A Tencor stress analysis system was employed to measure the change in the substrate curvature due to the film stress, and a nano-indentation method was used to calculate the residual stress in a system by measuring the maximum penetration, the force at maximum penetration, and the slope of the initial unloading curve. These methods were validated using XRD lattice calculations. Stresses as high as 2 GPa were observed under certain conditions. The results also show that the surface region of the films is not stress free at these thicknesses (∼200 nm) as was mathematically suggested.

Polycrystalline Bi4-xLaxTi3O12 (BLT) thin films were formed on p-Si(100) substrates. Crystallization of the film was investigated quantitatively by X-ray diffraction (XRD) and X-ray reflection (XRR) analyses. The film was crystallized onto bismuth-oxide layered perovskite structure when annealing temperatures became higher than 550°C. The annealing time dependence of diffraction intensity and peak width indicated that grain growth occurred during crystallization. Moreover, it was shown that the average crystal dimension in the BLT film reached ca. 60 nm by 120-min annealing. That value is comparable to the B LT thickness. Film thickness and density were evaluated by XRR analysis. Simulation fitting showed that the BLT film was densified and that an interfacial layer was formed during crystallization. Pole figure measurements also suggested that the c-axis of B LT was preferentially oriented to nearly parallel the surface. Clockwise hysteresis loops were observed at room temperature in capacitance-voltage (C-V) characteristics of Au/BLT/p-Si structures. The coercive field and the dielectric constant of 65 nm-thick BLT films crystallized at 550°C for 60 min were evaluated to be ca. 23 kV/cm and ca. 17, respectively.

We have investigated the structural, chemical and electrical properties of films with Pb0.6Sr0.4TiO3 (PST60) nominal composition grown on well texturized LSCO/SrTiO3 (STO) substrates by RF-Sputtering. The crystal structure and electrical properties of the PST60 films are remarkably influenced by the texture characteristics of the LSCO films. The structural and ferroelectric characteristics of PST60 thin films are determined to evaluate the potential of this heterostructure for non-volatile memory applications. Epitaxy of LSCO films was confirmed before depositing PST60 films on the above mentioned substrates through 4-Circle X-Ray Diffraction analysis (θ/2θ, ω and φ scans). The XRD analysis performed on the ferroelectric PST60 layer showed that the films are textured and entirely perovskite phase. LSCO and PST60, crystallize in the perovskite structure and their lattice parameters are well matched. This fact renders favorable structural and chemical conditions for the growth of PST60 on LSCO. The electrical performance of the Pt/PST60/LSCO/SrTiO3(001) capacitors was evaluated through Polarization-Voltage (P-V), Current-Voltage (I-V) and Fatigue measurements.

We simulate propagation of phonon-polaritons (admixtures of polar lattice vibrations and electromagnetic waves) in ferroelectric LiNbO3 with a model that consists of a spatially periodic array of harmonic oscillators coupled to THz electromagnetic waves through an electric dipole moment. We show that when this model is combined with the auxiliary differential equation method of finite difference time domain (FDTD) simulations, the salient features of phonon-polaritons may be illustrated. Further, we introduce second order nonlinear coupling to an optical field to demonstrate phonon-polariton generation by impulsive stimulated Raman scattering (ISRS). The phonon-polariton dispersion relation in bulk ferroelectric LiNbO3 is determined from simulation.

We introduced high-k Al2O3/Si3N4 buffer layer in MFIS (Metal-Ferroelectric-Insulator-Semiconductor) devices to reduce the leakage current though the buffer (I) layer. We prepared the buffer layer by nitridizing Si substrate by atomic nitrogen radicals and then deposited Al2O3 film using ALD (Atomic Layer Deposition) technique. The interface state density between the ALD-Al2O3/Radical-Si3N4 stacked insulator and a Si substrate is as low as 1011 cm-2eV-1. The current density less than 10-9 A/cm2 is realized under the 1V bias application using films with the capacitance density of 12fF/μm2. The c-axis oriented Bi3.45La0.75Ti3O12 (BLT) ferroelectric films were deposited to make MFIS structure. With this structure, we obtained the retention time as long as 1.5×106 sec (about 17 days). This excellent retention character is attributable to the high insulating property of the ALD-Al2O3/Radical-Si3N4 stacked insulator and also attributable to the perfect elimination of defects at the interfaces in the MFIS structure.

We performed a parametric study to suppress secondary phases in lithium niobate thin films by using pulsed laser deposition (PLD). A KrF excimer laser (λ=248nm) was used as a PLD source and c-oriented sapphire was used as substrates, for waveguide applications. By reducing the growth rate and changing the ambient gas pressure respectively, we found that the main parameter suppressing a secondary phase is controlling the plume strength. To investigate the relation between film phases and the plume strength, extensive parametric studies were performed by changing the oxygen ambient pressure, the target to substrate distance, and also the Li content in the target. The surface morphologies of single phase films and Li-deficient phase mixed films are compared and related to the growth mechanism with a lattice misfit. Deposition parameters to achieve lower loss films are also discussed.

In this work, material compositional design and optimized film processing methods, were employed to simultaneously lower the dielectric loss and enhance the dielectric tunability of Ba0.6Sr0.4TiO3 (BST) based thin films without compromising the device impedance matching (εr<500) and device control voltage (<10 V) requirements. The films compositional design was achieved by Mg doping BST from 3 to 10 mol % via the metalorganic solution deposition (MOSD) technique and post-deposition annealing in an oxygen ambience. The films dielectric loss at these doping levels was identical, tanδ ∼0.007 and the permittivity values ranged from 339 to 220. Device quality values of tunability, 40 and 32 %, for the 3 and 7 mol% doped BST films, respectively, were achieved by elevating the applied bias to 474 kV/cm. This device quality tuning is compatible with voltage requirements of current semiconductor based systems. The results suggest that the low level acceptor doping from 3 to 7 mol%, optimized precursor solution concentration (0.43 M), and oxygenated post-deposition thermal processing were found to work in concert to lower dielectric loss, limit defect density concentration, optimize film microstructure, and eliminate undesirable film/electrode interfacial phases. The enhanced dielectric and insulating properties of the 3–7 mol% Mg doped BST thin films make them excellent candidates for integration into tunable devices.

The employment of judicious substitution on B-sites in the perovskite oxide, BaTiO3, has yielded materials suitable for relatively temperature insensitive electric field tunable microwave devices. The properties, single-phase cubic perovskites with tunabilities as large as 30% at 1 V/μm and room temperature that possess low temperature coefficient of dielectric constant and tunability over the majority of the military specified temperature range, -55 to 125 °C, have been achieved in the charge compensated system Ba1-xSrxTi1–2yCyDyO3 where C is Ho, Er, Tm, Lu, Sc, Y, In and D is Ta, Sb with 0 ≤ X ≤ 0.2, and 0 < y ≤ 0.10.

BaTiO3 and Ba0.9Ca0.1TiO3 thin films were deposited on the p – type Si substrate by pulsed excimer laser ablation technique. The Capacitance – Voltage (C-V) measurement measured at 1 MHz exhibited a clockwise rotating hysteresis loop with a wide memory window for the Metal – Ferroelectric – Semiconductor (MFS) capacitor confirming the ferroelectric nature. The low frequency C – V measurements exhibited the response of the minority carriers in the inversion region while at 1 MHz the C – V is of a high frequency type with minimum capacitance in the inversion region. The interface states of both the MFS structures were calculated from the Castagne – Vaipaille method (High – low frequency C – V curve). Deep Level Transient Spectroscopy (DLTS) was used to analyze the interface traps and capture cross section present in the MFS capacitor. There were distinct peaks present in the DLTS spectrum and these peaks were attributed to the presence of the discrete interface states present at the semiconductor – ferroelectric interface. The distribution of calculated interface states were mapped with the silicon energy band gap for both the undoped and Ca doped BaTiO3 thin films using both the C – V and DLTS method. The interface states of the Ca doped BaTiO3 thin films were found to be higher than the pure BaTiO3 thin films.

In this paper, thin films of La- modified (Bi,La)FeO3-PbTiO3 (BLF-PT) morphotropic phase boundary (MPB) solid solutions have been prepared by using sol-gel processing. A thin Pb(Zr,Ti)O3 (PZT) template layer was introduced to make BLF-PT thin films adhere tightly to the platinized silicon (Pt/Ti/SiO2/Si) substrate. X-ray diffraction (XRD) analysis revealed that BLF-PT thin films were of the perovskite structure without detectable pyrochlore phase annealing at 650–750°C. The cross sectional and plain view images of or our specimen were observed by using the scan electrical microscope (SEM). The room temperature dielectric constant K and tanδ were of ∼800 and 4% respectively, for BLF-PT thin films using a measurement frequency of 1 kHz. Our preliminary experiments indicated that the sol-gel derived BLF-PT thin films have good insulation resistance and measurable dielectric and ferroelectric responses.

A new type of alkoxide precursor was developed to avoid the formation of the oxo-carbonate phase as an intermediate phase during crystallization. The precursors were synthesized from Ba metal, Sr metal and aminoethanol. The new precursors were found to be quite stable and soluble in a number of organic solvents. Films were prepared by depositing the precursor solution on Pt coated Silicon wafers and crystallized between 550 and 700°C. The films were found to crystallize only above 600°C. After crystallization Pt top electrodes were deposited by sputtering and lift off processing. FT-IR studies were performed on the films to check for any oxo-carbonate phase. Microstructural studies involving XRD, SEM and AFM were performed on the films. The films were found to have a dielectric constant of around 400 with a tunability of around 37%. The frequency and temperature dependence of the dielectric constant were also studied. In addition leakage studies were performed on the films at various temperatures.

Temperature dependent performance of ferroelectric non-volatile memories is an important issue, that impacts memory device reliability. In general, the device temperature strongly influences the speed of polarization reversal in ferroelectric capacitors. In particular, the switching speed decreases with the decreasing temperature, which may give rise to incomplete switching. In the present work, the recently proposed Nucleation-Limited Switching model for ferroelectric thin films is extended for description of the temperature dependence of the polarization reversal. The model is shown to be valid for the temperature range important for memory applications. This model enables quantitative prediction of the switching performance of ferroelectric capacitors at different temperatures based upon results obtained at room temperature. The temperature and voltage range where the proposed concept is applicable is discussed in context of limits of validity of the Nucleation-Limited Switching model.

Using first principles calculations, we have investigated the electronic structure of Pb(ZrTiNb)O3 (PZTN), a system with a low leakage current and high reliability in thin films. We proposed that in PZTN, the oxygen vacancy is suppressed due to the addition of a Nb atom at the B site and that this change prevents a bandgap narrowing which would enhance the leakage current. The oxygen vacancy in the perovskite structure reduces the bandgap because it lowers the d orbital energy of the nearest-neighbor transition metal through the Madelung potential; this bandgap narrowing induces the leakage current in conventional Pb(ZrTi)O3 (PZT) systems with the Shottky type Pb-O deficit. In contrast, the PZTN systems, which also have the Pb deficit but lack the oxygen vacancy, can maintain the bandgap, and attain a low leakage current.

This work presents a systematic study of ferroelectric films and multilayers made by a metal-organic chemical liquid deposition method. BaxSr1-xTiO3, Pb(Mg1/3Nb2/3)O3-PbTiO3, and Pb(Zn1/3Nb2/3)O3-PbTiO3 films, as well as multilayers incorporated with these materials have been grown at different conditions. Ultrahigh dielectric constant (∼6700) has been achieved in the PMN/PZN-PT multilayers when the sublayer thickness approached to nanometer scale, where interfaces become dominant. When the sublayer materials with desired Curie temperatures were properly chosen, the temperature dependent dielectric constant of the multilayer structure could be greatly reduced. These nanostructured multilayers may find very important applications where temperature variation is a key concern. Pb doping in BaxSr1-xTiO3 was found very efficient in increasing the dielectric constant and reducing the loss. It is believed that the addition of Pb improved the film density and reduced the grain boundary defects.

Barium strontium titanate (Ba0.60Sr0.40TiO3) thin films are the main materials of interest in tunable phase shifter for microwave antenna applications. Ba0.60Sr0.40Y0.05Ta0.05Ti0.90O3 thin films, of nominal thickness ranging from 1.7 μm to 2.3 μm, were synthesized on MgO (100) substrates, at substrate temperatures ranging from 500°C to 900°C, at oxygen partial pressures 20 and 50 mTorr, at 500 mJ energy fluence on 3 mm x 1 mm spot size and 10 pulses per second using the pulsed laser deposition technique. All film synthesized at temperatures greater than 500°C were crystalline. The effect of the ionic substitution and substrate temperature in conjunction with the effect of the oxygen partial pressure on the microstructure, and mechanical and electrical properties of the thin films have been studied using shallow angle x-ray diffraction, SEM, nanoindentation, atomic force microscopy (AFM), and focused ion beam analysis (FIB) and are reported in detail. We are currently in the process of measuring the capacitance of these films by various methods.

An additive technique for the growth of PZT crystallites in the sub-200 nm range on predefined sites is presented. The method is based on nucleation promotion by TiO2 seeds. Epitaxial (111)-oriented Pt on a SrTiO3 single crystal served as substrate. TiO2 seed sites have been defined by an e-beam lithographic process. The initial Pb flux determines whether (100) or (111) crystallites are obtained. Best results have been obtained with PZT(100) yielding one square grain per site with a narrow size distribution (120 to 150 nm). In this case, the seed collected additional PbO adatoms reaching the seed by diffusion. The sidewalls consist mostly of {110} facets. A model in the frame of classical nucleation theory describes well experimental observations. The piezoelectric response and the ferroelectric switching of the structures have been verified.

Natural-superlattice-structured Bi3TiNbO9–Bi4Ti3O12 (m =2–3) (BTN–BIT) films have been grown on Pt/TiO2/SiO2/Si substrates at 400 °C to 550 °C by pulsed laser deposition (PLD) using BTN–BIT (1 mol:1 mol) target, and were post-annealed in O2 for 45 minutes at 750 °C. BTN–BIT films prepared above 500 °C have single phase whose c lattice parameter is estimated to 8.300 nm in consideration of periodicity of lattice structures. This lattice constant is very close to the value (8.316 nm) of that of two unit cells of BTN and one unit cell of BIT, that is 2–1 superlattice structure of BTN–BIT. The BTN–BIT film with 2–1 superlattice structure has large remanent polarization (2Pr = 50 μC/cm2) and large coercive field (2Ec= 350 kV/cm). La-doped BTN–BIT thin film has also large remanent polarization (2Pr = 52 μC/cm2) and relatively small coercive field (2Ec= 220 kV/cm). The La-doped BTN–BIT film is fatigue-free on Pt electrodes up to 1010 switching cycles.

High-resolution domain studies are performed on Pb(Zr1-xTix)O3 (PZT) films of different thicknesses and compositions (x=0.30, 0.48, and 0.70) by piezoresponse force microscopy (PFM). Depending on the composition, the orientation of the films is varied from purely (111) (related to the orientation of Pt bottom electrode) to a more random texture. Statistical processing of the obtained domain images is used to analyze the correlation between the composition of the films and their nanoscale piezoelectric properties. It is shown that the virgin (unpoled) films possess large piezoelectric activity comparable to that after local poling (self-polarization effect). This corresponds to a clear predominance of the domains with polarization oriented from the free surface of the film to the bottom electrode. Both the average piezoelectric signal and half-width of the piezoelectric histograms depend on the composition and thickness of the films. The largest local piezoelectric coefficient and the broadest distribution are found for tetragonal (x=0.70) films with almost pure (111) texture. The results are discussed in terms of texture and PFM instrumentation effects on local piezoelectric measurements.