National Institute Of Materials Physics - Romania

Publications

885 articles found

681. Spectroscopic ellipsometry study of amorphous SrxBa1-xNb2O6 thin films obtained by pulsed laser deposition

Authors: Ion, V; Galca, AC; Scarisoreanu, ND; Filipescu, M; Dinescu, M

Published: 2008, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 5, NO 5, 5, +, DOI: 10.1002/pssc.200777818

Optical properties of amorphous Strontium Barium Niobate (a-SBN) thin film are investigated using spectroscopic ellipsometry. Since the SBN can be applied to optoelectronic devices, the dispersion of refractive index is desirable. The films are obtained by Pulsed Laser Deposition (PLD) onto MgO and Si substrates by targeting a SBN:60 monocrystal: The dielectric function of a-SBN is approximated using a single Tauc-Lorentz oscillator model. Thicknesses of the films and of their rough layer are in agreement with SEM and AFM results. The dispersion of the refractive index is presented in the 1 - 5 eV range.

682. A HIGH PERFORMANCE PZT TYPE MATERIAL USED AS SENSOR FOR AN AUDIO HIGH FREQUENCY PIEZOELECTRIC SIREN

Authors: Miclea, C; Tanasoiu, C; Iuga, A; Spanulescu, I; Miclea, CF; Plavitu, C; Amarande, L; Cioangher, M; Trupina, L; Miclea, CT; Tanasoiu, T

Published: 2008, CAS: 2008 INTERNATIONAL SEMICONDUCTOR CONFERENCE, PROCEEDINGS, +, DOI: 10.1109/SMICND.2008.4703364

A high quality PZT type material was designed and produced in order to be used as sensor for a high internsity siren. Two disks from this materials were assembled into a parallel bimorph type transducer with an intermediate metallic plate. This assembly behaves like an acoustic resonator in the high frequency audio range. The fundamental of the flexural mode for a free resonator is taken into account Its frequency dependence on the geometry of the system and on its material properties is computed using the results for a circular plate with clamped edges and an observation on the equivalence between the movement of a particular part of a resonator in a stationary state and the movement of that pari separated from the resonator but with the same border conditions. Acoustical and impedance measurements were made in order to appreciate the influence of the metallic plate on the frequency. In order to increase the acoustic emission a frontal cardboard horn was added to the resonator.

683. Ferroelectric/Antiferroelectric Pb(Zr0.8Ti0.2)O3/PbZrO3 Epitaxial Multilayers: Growth and Thickness-Dependent Properties

Authors: Boldyreva, K; Pintilie, L; Lotnyk, A; Misirlioglu, IB; Alexe, M; Hesse, D

Published: 2008, FERROELECTRICS, 370, 146, DOI: 10.1080/00150190802384492

Epitaxial ferroelectric/antiferroelectric PbZr0.8Ti0.2O3/PbZrO3 multilayers were grown on SrTiO3(100) substrates, covered with a SrRuO3 (100) bottom electrode and a thin tetragonal PbZr0.2Ti0.8O3 buffer layer, using pulsed laser deposition. Polarization-field, switching current-voltage and capacitance-voltage curves show a mixed antiferroelectric-ferroelectric behavior of the multilayers with an individual layer thickness above 10 nm, but below 10 nm the multilayers show only ferroelectric behavior. Obviously the PbZrO3 layers thinner than 10 nm underwent a transition into the ferroelectric state. An X-ray diffraction -2 scan showed a corresponding orthorhombic-to-rhombohedral transition of the PbZrO3 layers. The observations are discussed in terms of a strain effect.

684. High-Q BZT ceramics for microwave applications

Authors: Ioachim, A; Toacsan, MI; Nedelcu, L; Mihut, L

Published: 2008, PROCEEDINGS OF THE 6TH WSEAS INTERNATIONAL CONFERENCE ON APPLIED ELECTROMAGNETICS, WIRELESS AND OPTI, DOI:

Ba(Zn1/3Ta2/3)O-3 (BZT) ceramics were prepared by solid-state reaction and sintered in air at temperatures in the range 1550-1650 degrees C, for 2 hours. In order to improve the microwave and millimeter wave properties, annealing treatment at 1400 degrees C for 10 hours was applied. The long-range order with a 2:1 ratio of Ta and Zn ions on the octahedral positions of the perovskite structure and the vibrational modes were investigated by using XRD and Raman spectroscopy as function of sintering temperature. Presence of small amount of secondary phase, Ba8ZnTa6O24, affects Q factor even in the dense, highly ordered samples. The dielectric parameters were measured in the microwave range by Hakki-Coleman method and were correlated with structural and optical properties. Sintering temperature higher than 1600 degrees C are required for BZT ceramics in order to obtain low microwave loss (Q x f similar to 100 THz).

685. Correlation of Structural and MW-MMW Dielectric Properties with Vibrational Modes in BaX1/3Ta2/3O3 Complex Perovskites

Authors: Toacsan, MI; Ioachim, A; Nedelcu, L; Banciu, MG; Mihut, L; Szilagyi, A

Published: 2008, 2008 33RD INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER AND TERAHERTZ WAVES, VOLS 1 AND 2, +, DOI:

Ceramic based Ba(Zn1/3Ta2/3)O-3 materials were prepared by solid-state reaction. Studies on microwave dielectric parameters in correlation with structural and Raman investigations were performed. Sintering temperatures higher than 1600 degrees C are required in order to obtain dielectric properties suitable for millimeter wave applications.

686. Radiation characteristics of a novel compact microstrip patch resonator

Authors: Militaru, N; Banciu, MG; Nedelcu, L; Lojewski, G

Published: 2008, ECCSC 08: 4TH EUROPEAN CONFERENCE ON CIRCUITS AND SYSTEMS FOR COMMUNICATIONS, +, DOI: 10.1109/ECCSC.2008.4611680

In this paper a new type of dual-mode compact resonator for mobile communication systems, in the 900 MHz frequency band, is investigated. This compact planar resonator, developed on a 0.635 mm substrate with a 10.8 dielectric constant, has a square shape with an edge of 20.5 mm. For this dual resonator, several methods of modes coupling were considered. The radiation characteristics of this new resonator were investigated.

687. Combinatorial pulsed laser deposition of thin films

Authors: Craciun, V; Craciun, D; Mihailescu, IN; Socol, G; Stefan, N; Miroiu, M; Galca, AC; Bourne, G

Published: 2008, HIGH-POWER LASER ABLATION VII, PTS 1-2, 7005, DOI: 10.1117/12.782589

Pulsed Laser Deposition (PLD) is an ideal technique to be used for combinatorial approaches. By simply changing the deposition targets one can obtain alternating layers with different periodicities both vertically and laterally, along the substrate surface. By changing the laser impact area location and the number of pulses on each target used for ablation, one can grow films with a continuous variation of the chemical composition, which will be a function of the location on the substrate. To illustrate the advantages and versatility of this Combinatorial PLD (C-PLD) technique, several examples of films used in applications where more than one property should be tailored or optimized are presented. Investigations of thermo-chemical stability, chemical bonding and crystalline structure of thin films of mixtures of HfO2 and Al2O3 that are used as high-k dielectric layers in advanced C-MOS transistors is the first example, followed by a study of structural, mechanical, optical and electrical properties of mixtures of indium tin oxide and doped or pure zinc oxide that are used as transparent and conductive layers. The third example is from the deposition of multilayers of ZrC and ZrN with variable thicknesses to obtain hard coatings.

688. DLTS measurements of radiation induced defects in epitaxial and MCz silicon detectors

Authors: Honniger, F; Fretwurst, E; Lindstrom, G; Kramberger, G; Pintilie, I; Roder, R

Published: DEC 11 2007, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 583, 108, DOI: 10.1016/j.nima.2007.08.202

n-Type epitaxial silicon layers of different thickness and resistivity, grown on highly Sb doped CZ-substrate by ITME (Warsaw), and n-type MCz silicon supplied by Okmetic (Finland) were used for the processing of planar diodes at CiS (Erfurt). For the epi-diodes a standard as well as a diffusion oxygenation process was employed. Irradiations had been performed with 26 MeV protons at the cyclotron of the Karlsruhe University and with neutrons at the TRIGA reactor of the Ljubljana University. Microscopic investigations using the DLTS method were done. The correlation of the IO(2i)-defect and the oxygen concentration was studied by a depth-profile measurement. The annealing behavior of the IO(2i)-defect at different temperatures was investigated and the activation energy extracted. (C) 2007 Elsevier B.V. All rights reserved.

689. Radiation damage studies on MCz and standard and oxygen enriched epitaxial silicon devices

Authors: Fretwurst, E; Honniger, F; Kramberger, G; Lindstrom, G; Pintilie, I; Roder, R

Published: DEC 11 2007, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 583, 63, DOI: 10.1016/j.nima.2007.08.194

N-type epitaxial layers of 72 mu m thickness and a resistivity of 150 Omega cm have been grown on highly Sb-doped Cz-substrates at ITME (Warsaw). The diode processing was performed at CiS-Erfurt. For comparison a batch of 280 mu m thick n-type MCZ wafers with a resistivity of >600 Omega cm from Okmetic (Finland) was added to the process run. Depth profiles of the oxygen and carbon concentration were measured via the SIMS-method on as grown epi-layers and after different device-process steps at CiS including an oxygen enrichment at 1100 degrees C for 24 h. For the MCz material the profiles were measured on untreated samples and after the full device process. Irradiation runs were performed with neutrons at the TRIGA reactor of Ljubljana up to a fluence value of 10(16) cm(-2). The development of the macroscopic device parameters (effective doping concentration and charge collection for a-particles) as function of fluence is presented for the standard and oxygenated epi-devices and compared with the MCz-diodes. The results are discussed in the frame of defect studies resulting from TSC-measurements. (C) 2007 Elsevier B.V. All rights reserved.

690. Electrical characteristics of nano-PbS/SiO2/Si heterostructures obtained by chemical bath method

Authors: Goldenblum, A; Stancu, V; Buda, M; Iordache, G; Botila, T; Negrila, C

Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3802, DOI:

The PbS/SiO2/Si structures show a clockwise hysteresis of capacitance-voltage (C-V) characteristics. The loop width increases with temperature and sweep time. The conductance-voltage (G-V) characteristics also present a hysteresis effect with two bumps. Both characteristics show a strong shift with frequency. We show that these effects are determined by the positive mobile ions injected in the oxide region during the chemical bath deposition of PbS and by the high concentration Of Si/SiO2 interface states. The corresponding C-V and G-V characteristics are simulated and the main peculiarities of the experimental results are well reproduced by the modeled curves.