Two types of switching memory devices have been made by integrating a ferroelectric layer in a device. A Schottky diode consisting of a ferroelectric semiconductor and a high work function metal was found to show a bistable I-V behaviour. Experimentally an On/Off current ratio of two orders of magnitude was found in a structure consisting of a semiconducting PbTiO3 layer with a gold top contact, grown on a La0.5Sr0.5CoO3 bottom contact layer. The ferroelectric polarization parallel or antiparallel to the internal field of the diode gives rise to a change in the Schottky barrier height and depletion width. This will, depending on the polarization direction of the ferroelectric layer, enhance or diminish the tunnel probability of charge carriers through the Schottky barrier and thereby increase or decrease the current through the device. In the Ferroelectric Field Effect Transistor an insulating ferroelectric gate oxide was brought in close contact to a gated n-type Sb-doped SnO2 semiconducting channel layer. A maximum On/Off Source-Drain current (IsD) ratio at zero gate voltage of 5.7 was found. Gate pulse measurements showed retention of IsD after polarisation reversal of the ferroelectric gate oxide in both polarization directions. After more than 104 switching cycles the device shows a gradual decrease in ISD both in the On and Off state.

Epitaxial PbTiO3 films have been grown on (100) SrTiO3 substrates by pulsed laser deposition. X-ray diffraction analysis indicates pure c-axis oriented PbTiO3 films with a rocking curve FWHM of 0.25° for the 002 reflection. Thicker films (˜ 2000 Å) grown on 4° miscut SrTiO3 show mixed aaxis and c-axis PbTiO3 due to twinning along {1011} planes. The [100] axis of the a-axis domains are misoriented by 3.4° - 3.8° toward <001> substrate directions with respect to the substrate normal. In contrast to growth on well-oriented (100) SrTiO3 surfaces where the four equivalent tilts of the [100] axis of the a-axis domains are equally likely, on vicinal SrTiO3 the a-axis domains are preferentially oriented (˜ 90 vol. %) in an uphill direction with respect to the miscut substrate.

A film of Sr0.35Ba0.65TiO3 (SBT) has been grown in situ by pulsed laser deposition on (001) LaAlO3 single crystal. From X-ray diffraction studies the sample is found to be in single phase and well oriented. Raman spectrum of the SBT film shows bands around 178, 219, 296, 513, 571 and 741 cm”. The spectrum is similar to that found in SBT ceramic material, but the frequencies of the phonons are shifted. This can be explained if the film is under stress due to the presence of defects. The bands at 296 and 741cm−1 correspond to the B1 and A1(LO) normal modes of the BaTiO3 (BT) system, and they are representative of the BT tetragonal phase, which at first glance appears to contradict earlier structural symmetry assignment for SBT(x=0.35) film at room temperature. Micro-Raman measurements from different regions of the film indicate that the SBT film is homogeneous. The bands at 296 and 741 cm−1 are broader in comparison to those in BT single crystal and SBT ceramic material. Temperature dependent halfwidths of these modes suggest strong contribution of defects. Temperature dependent results are discussed in terms of anharmonic contributions involving three and four phonon processes as well as defects. Also, the orthorhombic and rhombohedral phase transitions are discussed. Finally, SEM/EDAX and FT-IR techniques have been used for the structural characterization.

Epitaxial La0.5Sr0.5CoO3/Ba0.4Sr0.6Tio3/La0.5Sr0.5CoO3 heterostructures were grown (650- 750 °C) on yttria-stabilized zirconia (YSZ)-buffered silicon (100) by pulsed laser (Nd:YAG) deposition. A 15-nm-thick YBa2Cu3O7 film was deposited on the YSZ to act as a template layer for epitaxial growth of the subsequent conductive oxide and ferroelectric film layers. The Ba0.4Sr0.6TiO3 film was (h00) oriented normal to the Si-wafer surface. The temperaturedependent resistance curve measured on the La0.5Sr0.5CoO3 top electrode layer was found to indicate to some extent the film quality of the underlying layers. Hundreds of capacitors, fabricated by wet chemical etching from the as-deposited films, exhibited dc leakage current densities in the range of 0.05–0.1 μA/cm2 at 1-volt operation. By increasing the thickness of the dielectric layer, some of them were able to be tested at up to 20 volts before resistive leakage became dominant. To reduce leakage current densities and increase dielectric constants in these film capacitors for dynamic random access memory (DRAM) applications, we have made efforts to incorporate hybrid Pt/La0.5Sr0.5CoO3 bottom electrodes into capacitors. This results in improved dielectric constants (451 at 10 kHz) and P-E hysteresis characteristics (Ec = 58 kV/cm, Pr = 7.5 μC/cm2, and Pg = 25 μC/cm2).

The effect of a post deposition anneal on the structure and dielectric properties of epitaxial Sr1−x, BaxTiO3 (SBT) thin films with x = 0.35, 0.50 and 0.60 has been measured. The films were grown by pulsed laser deposition on LaAlO3(001) substrates at 750°C in 350 mTorr of oxygen. The asdeposited films were single phase, (001) oriented with 0)-scan widths for the (002) reflection between 0.160 and 0.50'. The dielectric properties of the as-deposited films exhibit a broad temperature dependence and a peak which is as much as 50 K below the peak in bulk SBT. Also, the lattice parameter, as measured by x-ray diffraction, of the as-deposited films was larger than the bulk indicating strain in the films. The as-deposited films were annealed for 8 hours at 900°C in oxygen. The dielectric properties of the annealed films were closer to that of bulk SBT and the lattice parameter was closer to the bulk lattice parameter indicating a reduction of strain. Annealing of as-deposited films also resulted in an increased dielectric tuning without increased dielectric loss.

The problem of phase transitions and physical properties of the BaTiO3-type films on the (001) single-crystal substrates of the cubic syngony was solved in the limits of the Landau- Devonshire thermodynamics. The thermoelastic film-substrate interaction caused by the difference between thermal expansion coefficients was strictly taken into consideration. The model was based on the following assumptions: 1) the film is closely conjugated with the substrate; 2) the film is sufficiently “thick”to find itself unstrained at the growth temperature Ts, ( growth stresses were compensated by misfit dislocations ), and 3) the film is sufficiently “thin, and the stresses arising at the temperatures T>Ts may be considered to be uniform.

Sr(RuxSnl-x)O3 is proposed as a new conducting oxide for use in epitaxial multilayer structures. The Sr(Ru0.48Sn0.52)O3 composition exhibits an excellent lattice match with (100)-oriented KTaO3, and films of this composition grown by pulsed laser deposition on KTaO3, SrTiO3, and LaAIO3 substrates have been analyzed by X-ray diffraction, Rutherford backscattering/ion channeling, and resistivity measurements. Epitaxial KNbO3/Sr(Ru0 48Sn0.52)O3 bilayers have been successfully grown.

Ferroelectric oxide thin films show considerable potential as electro-optic and non-linear optical materials. Of particular interest are the niobates such as strontium barium niobate and potassium niobate. The growth of these epitaxial oxide films by metal-organic chemical vapor deposition (MOCVD) has been investigated. This technique has yielded epitaxial thin films with excellent non-linear optical properties. Issues concerning the epitaxy of these thin films and its relationship to their optical and nonlinear optical properties are discussed.

CeO2 thin films were grown on MgO(001) single-crystal substrates by pulsed laser deposition. The CeO2 thin films were used as a cladding layer of a Bi4Ti3O12 thin film waveguide. Structural properties of the BTO/CeO2/MgO heterostructures were investigated using x-ray diffraction techniques. An epitaxial relationship of BTO(001)//CeO2(001)// MgO(001) and BTO[100]//CeO2[100]//MgO[001] was confirmed. From the epitaxial heterostructure, a ridge waveguide was fabricated by photolithographic and ion-milling techniques. An single-mode near-field pattern was observed using an end-fire coupling method.

Epitaxial SBN:61 films have been grown on SBN:75 and MgO substrates by pulsed laser deposition. The optical loss due to absorption is greatly reduced by increasing the oxygen pressure to 1 mbar during the cooling process. In homoepitaxy, X-ray phi scans on the (221) plane of the SBN:61 films indicate that the in-plane grains are rotated 0° or ±28° with respect to single crystalline SBN:75 substrates. Cross-section and plane view high resolution TEM reveals this crystalline relations and microstructure of SBN thin films. Pr doped SBN:61 thin films show sharp transition band at 495 nm and 607 nm in room temperature photoluminescence measurement.

We have grown epitaxial thin films of LiTaO3 on various substrates. LiTaO3 grows epitaxially on (111) GaAs and forms a waveguide with its underlying buffer layer of MgO, providing a desirable structure for monolithic integration. LiTaO3 grows on LiNbO3 with a buffer layer of magnesium niobate or magnesium tantalate to form an optical waveguide structure having good lattice matching and pronounced differences in refractive index. This heterostructure has the potential for reducing crystal imperfection of waveguides and improving optical confinement. We also describe a multilayer structure using an epitaxial conducting layer as a bottom electrode to grow a nonlinear optical waveguide on LiNbO3 for waveguide switching and modulation. Both light-absorbing metals and transparent metallic oxides are employed. Ion channeling and x-ray diffraction reveal high crystalline quality of the hetero-epitaxial structures. The influence of surface polarity, thermal expansion, and lattice matching on waveguiding LiTaO3 thin films is addressed.

Thin films of LiNbO3 and LiTaO3 are grown by off-axis magnetron sputtering on A12O3 and LiTaO3 substrates. When stoichiometry is precisely controlled, the films display excellent crystallographic and morphologic properties and have optical losses that are acceptable for frequency-doubling. LiNbO3/A12O3 samples have rocking curve widths as low as Δω = 76 arc sec and rms surface roughnesses less than 1 nm. Rocking curves performed with a resolution of 12 arc sec in 2θ indicate that there is very little tilt to the grains. Most of the width of the standard rocking curve is associated with variations in the interplanar spacing. The LiTaO3 films have similar characteristics. LiNbO3/LiTaO3 samples have rocking curve widths as low as Δω = 28 arc sec. Again, there is very little tilt misalignment to the grains, and the best samples have rms surface roughnesses less than 1 nm. The LiNbO3/LiTaO3 samples are typically 650 nm thick and many have optical losses less than 5 dB/cm. The LiNbO3/A12O3 samples, typically 250 nm thick, have losses of 5–7 dB/cm. The higher modal intensity at the surface of the thinner films increases surface scattering losses.

We have generated green light by frequency doubling in LiTaO3 and LiNbO3 thin-film planar waveguides. Phase matching was achieved by both modal dispersion and quasi-phase matching.

Integrated lithium niobate (LiNbO3) thin layers show promise for efficient electrooptic, nonlinear optic, and optical amplifier applications. Solution-derived LiNbO3 thin layers have been deposited on sapphire substrates, allowing low temperature processing, control of stoichiometry, uniform doping and heteroepitaxy. Transmission electron microscopy of the LiNbO3/substrate interface suggests the structure consists of highly oriented grains with slight rotational variance to accommodate lattice mismatch. For use of such films as devices, the ability to pattern waveguides and other structures is desired. Modification of the substrate surface with patterns of hydrophobic monolayers allows control of deposition of solution precursors. Ambient, selective deposition of (00.1) oriented LiNbO3 heteroepitaxial strip waveguides with lateral dimensions as small as 4μm is demonstrated.

Thin films and superlattices of LiTaO3 and LiNbO3 were grown on (0001) LiTaO3 and LiNbO3 wafers by molecular beam epitaxy. Solid sources were employed for the evaporation of Li, Ta, and Nb while oxygen was activated in an ECR plasma source. Samples were completely oxidized during the growth as confirmed by quantitative surface analyses. Crystalline films were obtained on both substrates at a growth rate of 0.1 nm/s and substrate temperature of 900°C. Films were caxis oriented but showed in-plane 60° rotational domains. Superlattice structure with a bilayer period of 10 nm was grown on LiNbO3. It showed well defined interfaces and appeared to be strained.

Epitaxial LiNbO3 films were grown on a-cut sapphire, i.e., α-A12O3(0112), substrates by pulsed laser deposition. It is found the oxygen pressure is an important deposition parameter to influence the orientations of the LiNbO3 films. At an oxygen pressure of 10−1 torr, LiNbO3(0001) film was grown epitaxially. And, at a low oxygen pressure (i.e., 5x10−4 torr), LiNbO3(1120) film was grown epitaxially. Due to the anisotropic electro-optic (EO) constants, these films with the different orientations display large differences in their EO properties: the epitaxial LiNb3(0001) film shows little EO effects, but the LiNbO3(1120) film shows a large quadratic EO behavior with an effective coefficient of 2.38×10−5 m2/V2. The dependence of EO effects on the orientations of the epitaxial films was analyzed in terms of the linear and quadratic EO tensors of LiNbO3.

Metalorganic chemical vapor deposition (MOCVD) was used to prepare epitaxial or highly oriented PLT (Pb1-xLaxTiO3) thin films with x in the range of 0.21 to 0.34. The growth of PLT films resulted in three-dimensional epitaxial heterostructures on (100) surface of the MgO and the KTaO3 substrates. The PLT film grown on the KTaO3 (100) substrate has a significantly lower minimum channeling yield compared to that on the MgO (100) substrate because of the smaller lattice mismatch. The thickness and the refractive indices in the wavelength range of 435 to 1,523 nm were measured by the prism coupling method. The measured film thickness of 570 nm was in good agreement with that from RBS measurements. The refractive index of PLT film is smaller than that of PbTiO3, its difference at 632.8 nm is about 2.5 %. The dispersion of the refractive index was well fitted to a Sellmeier dispersion formula.

Thin LINbO3 films are deposited on (001) sapphire and (001) LiTaO3 substrates by using pulsed excimer-laser ablation. These films are evaluated by high-resolution X-ray diffraction (HRXRD) analysis. Strained LiNbO3 films in which the a-axis is longer and the c-axis is shorter than those of LiNbO3 single crystals are deposited on the sapphire substrates. On the other hand, extremely high-quality LiNbO3 films in which the a-axis of the films is the same as that of substrates are grown on the LiTaO substrates. X-ray rocking curves for the (006) reflection showed very narrow full width at half maximum (FWHM) of 208 arcsec for the films on the sapphire substrates, and 9 arcsec for the films on LiTaO3 substrates.

We have investigated the epitaxial growth of Er-doped BaTiO3 films using rf magnetron sputtering. The Er-doped films (0.5 - 1 μm thick) were deposited on MgO (001) single-crystal substrates at various temperatures (500 - 800 °C). The films deposited at 700 °C or above arehighly (001)- oriented with an in-plane epitaxial relationship of BaTiO3[100] ║ MgO[100], as confirmed by X-ray diffraction. The Er doped films were found to be compressively stressed, as-deposited. The amount of stress monotonically decreases as a function of the deposition temperature. The Er-doped epitaxial films show a strong room-temperature photoluminescence at 1.54 μm, which corresponds to intra-transitions of Er3+ ions. Electrical characterizationswere carried out on Er-doped BaTiO3 films that were grown on MgO with a conducting In203 buffer electrode. The measurement shows that the Er-doped BaTiO3 films are ferroelectric with a remanent polarization of 1.5 μC/cm2 and a coercive field of 40 kV/cm.

In this contribution we will discuss the charge transport of ramp-type HTS Josephson junctions with a Ga-doped PBCO barrier layer. It will be demonstrated that in these junctions charge transport takes place via tunneling processes. The Cooper pairs tunnel directly, at least for T ≤ Tc/2, whereas the quasiparticles tunnel indirectly via localized states. By substituting Cu-chain atoms with Ga-atoms the density of localized states appear to be reduced, resulting in an increase in IcRn-product. Another way to increase this product is a reduction in barrier thickness. Growth studies by AFM of PBCO barriers on ramps indicate that below about 10 nm barriers become increasingly less homogeneous, and below about 6 nm pin holes are very likely to occur. This sets a lower limit on the useful barrier thickness. Presently critical-current densities up to 104 A/cm2 at 40 K, and IlR,-products up to 10 mV at 4.2 K are easily obtained.

We have fabricated and tested YBCO step-edge SNS Josephson junctions on silicon substrates. The silicon step edges were patterned photolithographically and reactively ion etched using an SF6 plasma. The structures were fabricated through sequential angled pulsed laser deposition of yttria stabilized zirconia, YBCO, and gold layers, followed by photolithographic patterning and ion milling. The completed devices showed resistively shunted junction (RSJ)-like current voltage characteristics and microwave induced Shapiro steps. Critical currents as large as 84 PA and resistances of order 0.5 Ω were obtained. Measurable critical currents were observed up to 76 K. We report on the fabrication and properties of these junctions.