Pulsed laser deposition of strontium titanate thin films for dynamic random access memory applications

Polycrystalline strontium titanate (SrTiO3) films were prepared by a pulsed laser deposition technique on p-type silicon and platinum-coated silicon substrates. The films exhibited good structural and dielectric properties which were sensitive to the processing conditions. The small signal dielectric constant and dissipation factor at a frequency of 100 kHz were about 225 and 0.03 respectively. The capacitance-voltage (C-V) characteristics in metal-insulator-semiconductor structures exhibited anomalous frequency dispersion behavior and a hysteresis effect. The hysteresis in the C-V curve was found to be about 1 V and of a charge injection type. The density of interface states was about 1.79 x 10(12) cm(-2). The charge storage density was found to be 40 fC mu m(-2) at an applied electric field of 200 kV cm(-1). Studies on current-voltage characteristics indicated an ohmic nature at lower voltages and space charge conduction at higher voltages. The films also exhibited excellent time-dependent dielectric breakdown behavior.

Surface barrier effects in non-resonant microwave absorption by superconducting thin films of YBa2Cu3O7??

We present an unusual temperature dependence of hysteresis in the Lion resonant microwave absorption (NRMA) signals from superconducting thin films of YBa2Cu3O7-delta. We observe that the hysteresis increases with increase in temperature till T-c which we interpret as evidence for the presence of Bean-Livingston surface barriers (BLSB) in the single crystalline films.

Chemical and microstructural modifications in LiPON thin films exposed to atmospheric humidity

Lithium phosphorus oxynitride (LiPON), the widely used solid electrolyte for thin film microbatteries, is not compatible with the ambient humid temperatures. The reasons for reduction in ionic conductivity of LiPON thin films from 2.8 x 10(-6) Scm(-1) to 9.9 x 10(-10) Scm(-1) when exposed to air are analyzed with the aid of AC impedance measurements, SEM, XPS and stylus profilometry. Initially, particulate-free film surfaces obtained soon after rf sputter deposition in N-2 ambient conditions becomes covered with microstructures, forming pores in the film when exposed to air. LiPON films are deposited on Ti coated silicon in addition to bare silicon, ruling out the possibility of stress-related rupturing from the LiPON/Si interface. The reduction of nitrogen, phosphorus, and increased presence of lithium, oxygen and carbon over the film surface lowers the ionic conductivity of LiPON films when exposed to air. (c) 2011 Elsevier B.V. All rights reserved.

Thickness-dependent fcc-hcp phase transformation in polycrystalline titanium thin films

Polycrystalline Ti thin films are shown to gradually transform from face-centered cubic (fcc) to hexagonal close-packed structure (hcp) with increasing film thickness. Diffraction stress analysis revealed that the fcc phase is formed in a highly compressive hcp matrix (>= 2 GPa), the magnitude of which decreases with increasing film thickness. A correlation between stress and crystallographic texture vis-a-vis the fcc-hcp phase transformation has been established. The total free energy change of the system upon phase transformation calculated using the experimental results shows that the fcc-hcp transformation is theoretically possible in the investigated film thickness regime (144-720 nm) and the hcp structure is stable for films thicker than 720 nm, whereas the fcc structure can be stabilized in Ti films much thinner than 144 nm. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Sputter deposited LiPON thin films from powder target as electrolyte for thin film battery applications

Lithium phosphorus oxynitride (LiPON) thin films as solid electrolytes were prepared by reactive radio frequency (rf) magnetron sputtering from Li3PO4 powder compact target. High deposition rates and ease of manufacturing powder target compared with conventional ceramic Li3PO4 targets offer flexibility in handling and reduce the cost associated. Rf power density varied from 1.7 Wcm(-2) to 3 Wcm(-2) and N-2 flow from 10 to 30 sccm for a fixed substrate to target distance of 4 cm for best ionic conductivity. The surface chemical analysis done by X-ray photoelectron spectroscopy showed incorporation of nitrogen into the film as both triply, NE and doubly. Nd coordinated form. With increased presence of NE, ionic conductivity of LiPON was found to be increasing. The electrochemical impedance spectroscopy of LiPON films confirmed an ionic conductivity of 1.1 x 10(-6) Scm(-1) for optimum rf power and N-2 flow conditions. (C) 2011 Elsevier B.V. All rights reserved.

Structural and optical properties of RF sputtered Bi2VO5.5 thin films

Thin films of Bismuth Vanadate Bi2VO5.5 (BiV) have been deposited on amorphous quartz and polycrystalline silicon substrates by r.f. sputtering technique and characterised for their structural and optical properties. The os-deposited films at room temperature are found to be amorphous and transparent over the spectral range of 0.55 mu m to 12 mu m. Post-deposition annealing at 400 degrees C in air shows the formation of the BiV crystalline phase. The optical constants namely refractive index. extinction coefficient and optical bandgap of both amorphous and crystalline films have been determined. The refractive index of the as-deposited film is around 2.4 at 0.7 mu m and drops to 2.26 at 1.56 mu m. The optical bandgap of the material has been determined from the computed values of the absorption coefficients.

Enhanced magnetoresistance in as?deposited oxygen?deficient La0.6Pb0.4MnO3-y thin films

The La0.6Pb0.4MnO3(LPMO) thin films were in situ deposited at different oxygen partial pressure and at a substrate temperature of 630 degrees C by pulsed laser deposition. The films grown at lower oxygen partial pressures showed an increase in lattice parameter and resistivity and a decrease in the insulator-metal transition temperature as compared to the stoichiometric LPMO thin film grown at 400 mTorr. Further, these oxygen-deficient thin films showed over 70% giant magnetoresistance (GMR) near the insulator-metal transition temperature against the 40% GMR in the case of stoichiometric thin films. (C) 1995 American Institute of Physics.

Ferroelectric properties of Bi2VO5.5 thin films on LaAlO3 and SiO2/Si substrates with LaNiO3 base electrode

Ferroelectric bismuth vanadate Bi2VO5.5 (BVO) thin films have been grown on LaAlO3 (LAO) and SiO2/Si substrates with LaNiO3 (LNO) base electrodes by the pulsed laser deposition technique. The effect of substrate temperature on the ferroelectric properties of BVO thin films, has been studied by depositing the thin films at different temperatures. The BVO thin films grown on LNO/LAO were textured whereas the thin films grown on LNO/SiO2/Si were polycrystalline. The BVO thin films grown at 450?°C exhibited good ferroelectric properties indicating that LNO acts as a good electrode material. The remanent polarization Pr and coercive field Ec obtained for the BVO thin films grown at 450?°C on LNO/LAO and LNO/SiO2/Si were 2.5 ?C/cm2, 37 kV/cm and 4.6?C/cm2, 93 kV/cm, respectively. © 1995 American Institute of Physics.

Oriented ferroelectric thin films of PbTiO3, (Pb,La)TiO3, and Pb(Zr,Ti)O3 by nebulized spray pyrolysis

Nebulized spray pyrolysis provides a good low?temperature chemical route for preparing thin films of PbTiO3, (Pb0.9,La0.1)TiO3 and Pb(Zr0.52,Ti0.48)O3. The films are a? or c? axis oriented, with spherical grains of ?30 nm and give satisfactory P?E hysteresis loops. © 1995 American Institute of Physics.

Rapid thermal processed thin films of niobium pentoxide (Nb2 O5) deposited by reactive magnetron sputtering

Niobium pentoxide thin films have been deposited on silicon and platinum-coated silicon substrates by reactive magnetron sputtering. The as-deposited films were amorphous and showed good electrical properties in terms of a dielectric permittivity of about 30, and leakage current density of 10(-6) A cm(-2) al a field of 120 kV cm(-1). A rapid thermal annealing process at 800 degrees C further increased the dielectric constant to 90 and increased the leakage current density to 5 x 10(-6) A cm(-2). The current-voltage characteristics observed at low and high fields suggested a combination of phenomena at different regimes of applied electric field. The capacitance-voltage characteristics performed in the metal-insulator-semiconductor configuration indicated good electronic interfaces with a nominal trap density of 4.5 x 10(12) cm(-2) eV(-1), which is consistent with the behavior observed with conventional dielectrics such as SiO2 on silicon surfaces.

Rapid thermal processed thin films of reactively sputtered Ta2O5

Rapid thermal processed thin films of reactively sputtered tantalum pentoxide Ta2O5 thin films have been deposited on silicon and platinum coated silicon substrates by reactive magnetron sputtering. The as-deposited films were amorphous and showed good electrical properties in terms of a dielectric permittivity of about 24 and leakage current density of 9 x 10(-8) A cm(-2). A rapid thermal annealing process at temperatures above 700 degrees C crystallized the films, increased the dielectric relative permittivity, and decreased the leakage current. The dielectric constant for a film rapidly annealed at 850 degrees C increased to 45 and its leakage current density lowered to 2 x 10(-8) A cm(-2). The dielectric measurements in the MIS configuration showed that Ta2O5 might be used as a dielectric material instead of SiO2 or Si3N4 for integrated devices. The current voltage characteristics observed at low and high fields suggested different conduction mechanisms.

Reactive magnetron co?sputtered antiferroelectric lead zirconate thin films

Antiferroelectric lead zirconate thin films were formed on platinum coated silicon substrates by a reactive magnetron co-sputtering method. The films showed (240) preferred orientation. The crystallization temperatures and the preferred orientation were affected by the lead content in the films. The electric field forced transformation from the antiferroelectric phase to the ferroelectric phase was observed at room temperature with a maximum polarization value of 36 mu C/cm(2). The average field to excite the ferroelectric state and that for the reversion to the antiferroelectric state were 267 and 104 kV/cm respectively. (C) 1995 American Institute of Physics.

Surface resistance and residual losses of Ag?doped YBa2Cu3O7?? thin films on sapphire

High?quality Ag?doped YBa2Cu3O7?? thin films have been grown by laser ablation on R?plane ?1102? sapphire without any buffer layer. Thin films have been found to be highly c?axis oriented with Tc=90 K, transition width ?T?1 K, and transport Jc=1.2×106 A?cm?2 at 77 K in self?field conditions. The microwave surface resistance of these films measured on patterned microstrip resonators has been found to be 530 ?? at 10 GHz at 77 K which is the lowest reported on unbuffered sapphire. Improved in?plane epitaxy and reduced reaction rate between the substrate and the film caused due to Ag in the film are believed to be responsible for this greatly improved microwave surface resistance. © 1995 American Institute of Physics.

Variation of Cu-O charge-transfer energies in YBa2Cu3O7-x thin films studied by photoemission spectroscopy

It is pointed out that the change in the oxidation state of Cu in YBa2CU3O7-x with increasing x vitiates the trend in the Cu(2p) satellite intensity and hence the Cu-O charge-transfer energy. When Y is partly replaced by Ca, however, the satellite intensity and T(c) decrease with the increase in Ca content or hole concentration, just as in other cuprates.

LaNiO3: a promising material for contact with YBa2 Cu3O7-x thin films

Epitaxial LaNiO3 metallic oxide thin films have been grown on c-axis oriented YBa2Cu3O7-delta thin films on LaAlO3 substrates by pulsed laser deposition technique and the interface formed between the two films has been examined by measuring the contact conductance of the same. The specific contact conductance of the interface measured using a modified four probe method was found to be 1.4 to 6 x 10(4) ohm(-1) cm(-2) at 77 K, There are indications that contact conductance can be brought closer to that obtained for noble metal-YBCO interface.