Epitaxial Bi4Ti3012 (BTO) films with Lao0.5Sr0.5Co03 (LSCO) or Pt bottom electrodes were grown on MgO(OOl) substrates by pulsed laser deposition. Surprisingly, a symmetric Pt/BTO/Pt capacitor showed a highly asymmetric polarization switching and an asymmetric Pt/BTO/LSCO capacitor revealed a nearly symmetric polarization switching. To understand these intriguing phenomena, Auger electron spectroscopy and x-ray photoemission spectroscopy depth-profiles were used. The evidences for interdiffusions at the bottom BTO/Pt interface were found. To get further understanding on the interfacial states, a capacitance-voltage (C-V) measurement was performed on the Pt/BTO/Pt capacitor. By fitting the C-V data with a back-to-back Schottky diode model, built-in voltages at the top and the bottom interfaces were determined to be 1.1 V and 3.2 V, respectively. From the obtained built-in voltages, an asymmetric band diagram for the Pt/BTO/Pt structure was suggested. Therefore, the imprint failure can be explained by existence of asymmetric interracial states.

We show that CSD processing can be optimized in order to achieve columnar structured BaTiO3 and SrTiO3 thin films at elevated temperatures. In addition to these, columnar grain growth was also obtained for films of the solid solution (Ba0.7Sr0.3)TiO3 By controlling the film formation process, polycrystalline and columnar grained thin films were grown on Pt coated Si substrates at temperatures between 750° and 800°. The films were analyzed by glancing incidence X-ray diffraction and scanning electron microscopy. Detailed analysis on the thin films’ microstructure was performed by means of transmission electron microscopy. Based on these data, the film formation process is discussed with respect to process control and precursor chemistry. Differences in the crystallization process of BaTiO3 thin films compared to SrTiO3 films are pointed out.

Bi-based layered perovskites, also called Aurivillius-type phases, are superior to simple perovskite materials with regard to their ferroelectric long-term stability. Another way to alleviate fatigue and aging problems in metal-ferroelectric-metal (MFM) heterostructures is to replace the bottom metallic electrode with a conductive oxide electrode. An attempt to combine the two approaches has been made to investigate whether a further improvement in stability can be achieved. To promote an oriented growth of the ferroelectric films, epitaxial buffer layers (YSZ, Ce02) and epitaxial electrodes of (La0.5Sr0.5 )Co03 (LSC) have been consecutively deposited onto Si (100). Finally a ferroelectric thin film of the layered perovskite Bi4Ti3012 (BiT) has been grown. Rocking curve measurements demonstrate good epitaxial growth of both the buffer and the electrode layers. The ferroelectric thin films show a preferred c-axis orientation. Cross-section TEM images reveal a twinned superstructure in the LSC layer with a tripling of the lattice parameter. EDX line-scans show that a Co-enriched and Bi-depleted layer had formed at the BiT/LSC interface. After deposition of Au electrodes on both the BiT and the LSC layer, a hysteretic behavior could be detected and the ferroelectric properties of the c-oriented BiT film be confirmed.

A unique approach to MOCVD of complex oxides enables deposition of a number of materials of technological importance through the use of liquid delivery of metalorganic precursors. Methodologies for control of composition and exploration of. process space are compared for two film systems, one in a relatively mature state of development ((Ba,Sr)Ti03), the other in an early state of development (Ni-ferrite). In both cases, composition was controlled by mixing metalorganic precursors dissolved in solvents using a liquid delivery system. Films with excellent crystalline quality were deposited in both cases. Polycrystalline BST films displayed properties suitable for DRAM applications: charge storage densities > 80 fF/μm2 and leakage current density < 10−8 A/cm2 for films as thin as 15 nm. Growth mechanisms and rates were determined for the single component oxides of the ferrite films. Epitaxial NiFe204 films were deposited on MgO single crystal substrates at 650°C; x-ray rocking curves yielded FWHM values of 0.046°, commensurate with the substrate.

Domain stabilization in epitaxial potassium niobate films deposited by metalorganic chemical vapor deposition was studied. Stabilization was examined for films deposited on substrates with different coefficients of thermal expansion. X-ray diffraction of KNb03 films deposited on (100) MgAl204, (r) A1203, and (100)pseudocubic YAIO3 substrates shows a mixed domain structure consisting of (110) and (001) domains. However, KNb03 thin films deposited under identical conditions on (100) MgO, (100) SrTi03, and (100)pseudocubic LaA103 substrates exhibited only a single domain variant. A direct correlation between (001) domain volume fraction in the as-deposited KNb03 films and calculated strain resulting from thermal mismatch is observed.

Ferroelectric PbTiO3(FT) and Pb(ZrxTi1−x)03 (PZT) thin films have been deposited on (100) MgO and (111) Pt/SiO2/(100)Si substrates by using a novel single-solid-source metalorganic chemical vapor deposition (MOCVD) technique. The new technique uses a powder delivery system to deliver the mixed precursor powders directly into a hot vaporizer from room temperature, therefore, avoiding any problems associated with polymerization or decomposition of the precursors before evaporation. The technique simplifies MOCVD processing significantly and can improve process reliability and reproducibility. The deposited FT and PZT films have a perovskite structure and are highly oriented with respect to the substrate. With improvement of process control, systematic studies of film evolution under various growth conditions have been carried out. Effects of substrate, substrate temperature, system vacuum, and precursor ratios in the mixture on film microstructure and properties will be presented in this paper.

We have grown epitaxial strontium titanate films on lanthanum aluminate substrates at a range of oxygen pressures and substrate temperatures. The complex dielectric function was measured versus frequency (10 kHz to 1 MHz) and temperature (room temperature to 4.2 K) on coplanar capacitors patterned on the films. Preliminary data from 1.5 to 2.5 GHz is also presented. The dielectric constant εr was as high as 4600 at 65 K, a factor of two greater than previously reported for strontium titanate thin films and a factor of 1.8 greater than the bulk value at the same temperature. Tuning the capacitor by applying a dc bias of ±15 V across the 3 μm coplanar gap at 4.2 K yielded a ratio of maximum to minimum dielectric constant of 2.8. At 101 K this ratio was 2.2. A bulk capacitor does not show tuning over such a large temperature range.

Thin films of SrBiTa2O9, (SBT) were deposited on Si using Sol-Gel technique. The thicknesses of the films are 200 nm (A) and 400 nm (B), respectively. SEM studies show isolated grains in both SBT films with a grain size distribution between 0.1 and 0.5 μ. However, most of the grain size in the film is smaller than 0.1 μ. EDX analysis indicates that the films are inhomogeneous. FTIR external reflectivity measurements of the samples show bands around 1260, 936(for SBT2), 955(for SBT4), 770, 600 cm−1. Micro Raman spectra shows inhomogeneities in the SBT films. Bands corresponding to the SBT materials were found, but frequency shifts and broadening were observed in almost every band. Particularly, the band around 818 cm−1 was found to change from 785 to 827 cm−1. Also, due to the stretching of the Ta06 octahedron, the Alg mode was found to be approximately 163 cm−1. This change seems to be related to the Ta-0 bond length.

The structure of epitaxial BaTiO3 thin films prepared by hydrothermal synthesis on (001) SrTiO3 substrates was studied by transmission electron microscopy (TEM). The growth evolution was followed from initial island formation, through island impingement and fusion. Plan view and cross-section imaging demonstrated that the films grew by an unusual islanding mechanism. Electron diffraction showed the islands and the fully formed film are single crystal with mosaic character and in all cases strain relaxed. Cross-section TEM of the early growth films showed a several monolayer thick interfacial layer and the film/substrate region had no misfit dislocations. In the fully formed films, this interfacial layer was not observed, however a clear misfit dislocation network was observed. Defects analysis shows that the misfit dislocations have pure edge character with <100> Une directions, and <010> Burgers vectors (parallel to the film/substrate interface).

Lead lanthanum titanate thin films have been prepared on MgO and sapphire substrates by sol-gel method. XRD analyses confirm that the PLT films fabricated on MgO(lOO) and c-plane sapphire substrates grow preferentially with (100) and (111) orientations, respectively. The PLT films with a high La content have a low refractive index due to the decrease of the refractive index anisotropy. The propagation losses in PLT films measured, using He-Ne laser light and the prism coupling method decrease as the La content increases. This is due to the reduction of the refractive index anisotropy and the surface scattering by the surface roughness as a function of La content in the film.

The glyme adducts of bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionate)barium, Ba(hfac)2•glyme, are frequently employed as precursors in the MOCVD fabrication of HTSC thin films. The physical properties of these precursors can be modified by changing the glyme ligand in the barium complex. In this study, gas phase concentrations of two barium complexes as a function of purge time and bubbler temperature have been examined by in-situ UV spectroscopy. Also presented are the details of a UV spectrophotometric-based feedback control system designed to maintain constant gas phase concentration of 2,2,6,6-tetramethyl-3,5-heptadionate (thd) precursors, Cu(thd)2 and Y(thd)3, during MOCVD growth of mixed metal oxide films.

The recent experimental results obtained for c-axis oriented YBaCuO thin films deposited at the optimized conditions for the microwave applications are presented and discussed. The emphasis is on the study of the relationship between oxygen profiles, crystallographic structure and electrical and physical properties of the films formed in situ at the same and optimized conditions of sample deposition and further submitted to the different conditions of sample cooling. The studies of the oxygen depth concentration profiles and of the oxygen contents are carried out using the recently developed Nuclear Reaction Analysis (NRA). These results are correlated, on one hand, with the measurements of the atomic composition and structure by RBS, XRD and TEM and, on the other hand, by the measurements of the electrical and physical properties Tc, Jc and microwave surface resistance Rs. All results are consistent with the idea that the fully oxygenated films are formed during in situ growth at T∼ 700°C. For T< 300°C, the oxygen interface transfer coefficient is very small and the oxygen content is practically preserved. However a large room temperature oxidation (corrosion like) takes place in the presence of water vapor. The fundamental and applied consequences of these findings for the mechanism of thin films growth and for the properties of the films in the presence of cathodic plasma or laser plume are analysed.

The anisotropie oxide superconductors YBa2Cu3O7-Dgr; and Sr2RuO4 have been epitaxially combined in various ways (c-axis on c-axis, c-axis on a-axis, and a-axis on a-axis) though the use of appropriate substrates. Phase-pure a-axis oriented or c-axis oriented epitaxial Sr2RuO4 films were grown by pulsed laser deposition. YBa2Cu3O7-δ films were then grown on both orientations of Sr2RuO4 films and the resulting epitaxy was characterized.

We use a near-field scanning optical microscope (NSOM) to investigate microstructural defects at the fusion boundaries of SrTiO3 bicrystal substrates. The optical transmission across the fusion boundary shows circular dark spots with diameters varying from 0.1 to 1 μm that are distributed non-uniformly along the boundary. After detailed characterization of the substrates, a thin YBa2Cu3O7 (YBCO) film (∼ 40 nm) was deposited on a 24° bicrystal. Combining NSOM and scanning force microscopy, we show that these substrate defects can cause the grain boundary of a YBCO thin film grown on the bicrystal to wander up to 0.8 micron in the film. Strain fields associated with these substrate defects are attributed to their influence on YBCO growth. The relation between these structural defects and the electrical characteristics of YBCO grain boundary junctions are also discussed.

Better knowledge of the relationships between YBa2Cu307-δ (YBCO) materials properties and the RF performance of devices made from these materials should lead to improved device performance and yields. A variety of materials tests were performed on our production YBCO films which were patterned into standard microstrip resonators. The materials parameters were then compared with the unloaded Q of the resonators at 77 K. As expected, films with higher Q's tended to have higher Tc, higher Jc, greater film thickness, and better crystallinity. The last was based on narrower YBCO rocking curve peak, lower second phase density (judged by lower resistivity and greater θ-2θ (005) peak area), and a narrower θ-2θ (005) peak. The room temperature sheet resistance was found to be a useful predictor of microwave performance for films that are otherwise similar.

Patterned thin film multilayer structures, consisting of superconducting YBa2Cu3O7-x (YBCO) and insulating PrBa2Cu3O7-x (PrBCO), deposited onto (001) MgO substrates by electron beam co-evaporation, have been examined using Transmission Electron Microscopy (TEM). It is shown that PrBCO films grown over 30° steps in YBCO layers are free of tilt-grain boundaries. The PrBCO is c-oriented everywhere and shows pronounced faceting on the steps. Strain contrast features are present where the PrBCO has to adapt to large variations in the slope angle of the underlying YBCO layer. However, tilt-grain boundaries in YBCO or PrBCO layers are nucleated when depositing over small MgO steps formed by unintentional milling into the substrate. It is shown that grain boundaries associated with milled steps on MgO can be eliminated by the use of a PrBCO buffer layer beneath the superconducting base layer.

We have fabricated numerous magnetometers using our high temperature superconducting (HTS) Josephson junctions. These Josephson junctions are fabricated in a superconducting-normal-superconducting ramp edge configuration1 with silver doped YBa2Cu3O7 (YBCO) for the superconducting electrodes and PrBa2Cu3O7, (PBCO) for the normal layer. Small inductance quantum interference devices (SQUEDs) made from this junction technology have a transfer function exceeding 150 microvolts per flux quanta and a flux noise of 5×10−6flux quanta per root hertz. In addition, we have established that these junctions have identical electrical characteristics after either a year of storage or repeated thermal cycling. We have also examined the trade-off of 1/f noise versus thermal noise that is obtained as we vary the critical current of the devices.

The SQUID magnetometers were made using galvanically coupled input coils. These devices exhibit excellent operational characteristics in the geomagnetic field. They functioned in an unshielded environment for more than 24 hours and operated in a moving dewar (without any feedback fields to compensate the changing applied field) - both without flux trapping. Noise characteristics under these conditions are presented.

We have grown YBa2Cu3O7 (YBCO) and Pr1.85Ce0.15CuO4 (PCCO) polycrystalline films on n-type GaN using pulsed laser deposition. The diodes fabricated out of these heterostructures exhibited a strong rectifying behavior with transport characteristics that were found to fit well to the thermionic emission model. The effective barrier heights for YBCO and PCCO based diodes were found to be 788 meV and 236 meV, respectively. Rutherford Backscattering structural analysis of the heterostructures is also discussed.

A hot-wall type metal organic chemical vapor deposition (MOCVD) apparatus has been developed for the deposition of the YBa2Cu3O7-δ (YBCO) films using liquid metal organic sources on arbitrary shaped substrates. By improving the reactor shape and gas flow of the source materials, we succeeded in fabricating the double-sided YBCO films for electronic and microwave devices and the YBCO-coated conductor on oxide fiber for power applications. Tc(zero)'s of the YBCO film on both sides of the LaAlO3 (100) substrate were 90K and 86K, respectively. The films on the facet of the single crystalline SrTiO3 fiber showed the single phase c-axis orientation with biaxially alignment in the a / b plane.

We incorporate a polarization modulation technique in a near-field scanning optical microscope (NSOM) for quantitative polarimetry studies at the nanometer scale. Using this technique, we map out stress-induced birefringence associated with submicron defects at the fusion boundaries of SiTiO3 bicrystals. The strain fields surrounding these defects are larger than the defect sizes and show complex spiral shapes that break the reflection symmetry of the bicrystal boundary.