bluuebunny/crossref_metadata_2025 huggingface dataset:
Innovative Diodes based on Amorphous-Porous Silicon Heterojunction
Authors: Rosa R. De , Ferrara V. La , Francia G. Di , Quercia L. , Roca F. , Tucci M.
Published: April 2011

In this paper we present an innovative diode based on the heterojunction between amorphous silicon and porous silicon grown on crystalline silicon. The device architecture gives several advantages. Deposition of amorphous silicon on porous material realises high performance junction at temperature less than 250°C and it passives the porous layer against the natural oxidation due to ageing in the environment. Porous technology allows to obtain a controlled textured silicon surface independently from crystalline silicon orientation just to give the opportunity to reduce surface reflectivity and the blue shift of the absorption spectra in solar cell application. Solar cells were characterised by I-V dark/light and quantum yield measurements. Under standard AM 1.5 light we obtained photovoltaic conversion efficiency greater than 10%. Change in photoluminescence in different gas environments showed for gas sensor applications give rise encouraging results. In dark condition we found the typical diode behaviour.
Structural and optoelectronic properties of amorphous and microcrystalline silicon deposited at low substrate temperatures by RF and HW CVD
Authors: Alpuim P. , Chu V. , Conde J. P.
Published: April 2011

The structural and optoelectronic properties of silicon thin films prepared by hot wire chemical vapor deposition and radio frequency plasma enhanced chemical vapor deposition are studied in the range of substrate temperatures (Tsub)from 100 °C to 25 °C. The defect density, structure factor and bond angle disorder of amorphous silicon films (a-Si:H) deposited by both techniques are strongly improved by the use of hydrogen dilution. Correlation of these structural properties with important optoelectronic properties, such as photo-to-dark conductivity ratio, is made. Microcrystalline silicon (μc-Si:H) is obtained using HW with a large crystalline fraction for hydrogen dilutions above 85% independently of Tsub. The deposition of μc-Si:H by RF requires increasing the hydrogen dilution and shows decreasing crystalline fraction as Tsub is decreased. The properties of the low Tsub films are compared to those of samples produced at 175 °C and 250 °C in the same reactors.
An Investigation of the Chromaticity of Blue Emitting Yttrium Silicate
Authors: Bosze E. J. , Hirata G. A. , Mckittrick J.
Published: April 2011

This investigation studied the effects of Ho3+ and Er3+ on the luminescence of the blue emitting phosphor yttrium silicate, (Y1−mCem)2SiO5. Yttrium silicate has a large emission tail that extends into the red portion of the visual spectrum. To improve the chromaticity of this phosphor to give it a more saturated blue color, the emission intensity of the tail needs to be decreased. Photoluminscence and low-voltage cathodoluminescence measurements were performed on yttrium silicate phosphors with varying concentrations of Gd3+, Ho3+ and Er3+. It was found that when co-doping with Ho3+ and Er3+, the relative intensity of the emission tail was decreased, but so to was the overall luminescence intensity of this phosphor.
Ultrafast Silicon Based Internal Photoemission Detectors
Authors: Löken M. , Lipinsky Th. , Kappius L. , Mantl S. , Buchal Ch.
Published: April 2011

We have studied different metal-silicon-metal (MSM) Schottky barrier photodiodes for the detection of visible and infrared light. We investigated the different Schottky barriers from Ti, Cr and Pt. At infrared wavelengths, the Schottky contacts provide electrons and holes by “internal photoemission” into the Si. The lowest Schottky barrier determines the long wavelength cutoff and the current noise. The temporal response was measured byultrashort (100 fs) laser pulses from a Ti:A1203 laser, which were converted by an optical parametric oscillator to a wavelength of 1.1 to 1.6 μm. The measurements were performed between 30 K and room temperature. The best detectors show a pulse width of 3.2ps FWHM at 1.25 μm wavelength and room temperature. To our knowledge this is the fastest infrared response for silicon based diodes ever reported.
A Projection-Type Excimer-Laser Crystallization System For Ultra-Large Grain Growth Of Si Thin-Films
Authors: Oh Chang-Ho , Nakata Mitsuru , Matsumura Masakiyo
Published: April 2011

We have proposed a new excimer-laser crystallization system based on an optical projection concept. In the proposed system, a collimated excimer-laser light pulse is irradiated to Si thin-films on a glassy substrate, through a phase-shift mask and an optical lens system. Using oneand two-dimensional phase-shift masks, we have examined feasibility of the proposed method.
Stress and Dopant Activation in Solid Phase Crystalized Si Films
Authors: Kalkan A. Kaan , Fonash Stephen J.
Published: April 2011

Defect creation mechanisms during solid phase crystallization (SPC) of Si thin films were investigated with PECVD amorphous precursor samples produced with various deposition temperatures and thicknesses. These precursor films were implanted with dopant and then crystallized to obtain both SPC and dopant activation. The doping efficiency was found to decrease with the tensile stress level as measured by Raman shift. The stress shows a decrease as the precursor deposition temperature and thickness are lowered. Furthermore, a lower level of stress is induced by rapid thermal annealing when the annealing temperature is high enough to soften the glass substrate on which the films were deposited. We show that by control of stress during the SPC step, intragrain defect density can be lowered and electronic quality of the resulting polycrystalline Si films can be improved. Based on these observations, we propose the following tentative model to explain the defect creation: during SPC, tensile stress evolution is considered to result from the volumetric contraction of Si film when it transforms from the amorphous to crystalline phase. This contraction is retarded by the substrate, which imposes a tensile stress on the film. A high level of stress leads to formation of structural defects inside the grains of the resulting polycrystalline material. These defects trap carriers or complex with the dopant reducing doping efficiency.
Thin-Film Oxide Phosphors as Electroluminescent Materials
Authors: Minami Tadatsugu
Published: April 2011

In this paper, we introduce rare earth- or transition metal-activated oxide phosphor thin films prepared by magnetron sputtering and dip-coated solution deposition. Thin-film electroluminescent (TFEL) devices using these oxide phosphor thin films as the emitting layer were investigated with a single insulating layer device structure using a thick ceramic sheet insulating layer. High-luminance multicolor emissions and high luminous efficiencies were obtained in TFEL devices using various oxide phosphors: binary compound, Ga2O3; ternary compound, Zn2SiO4, CaGa2O4 and ZnGa2O4; and multicomponent oxide, Zn2SiO4-Zn2GeO4 system. Luminances above 2000 cd/m2were obtained in CaGa2O4:Mn and Zn2Si1-XGeXO4:Mn TFEL devices driven at 1 kHz. Maximum luminous efficiencies of 2.53, 1.7 and 1.2 Im/W were obtained in Zn2Si0.7Ge0.3O4:Mn, Ga2O3:Mn and ZnGa2O4:Mn TFEL devices, respectively. Stable long-term operation was obtained in dip-coated and sputtered Ga2O3:Mn phosphor TFEL devices even when driven at 10 kHz. Various thin-film oxide phosphors activated with transition metals are suitable for the emitting layer of full-color electroluminescent displays (ELD) without the use of color filters. In particular, Ga2O3 is very promising as a phosphor host material for ELDs.
Simulations of Passive Matrix Polymer Image Sensors
Authors: Braun D. , Yu G.
Published: April 2011

Two-dimensional passive photodiode matrices are hardly useful for image sensing due to the crosstalk between pixels. This crosstalk makes it difficult to recover information from individual pixels. A switching unit attached to each sensing unit has been the common solution in image sensors (such as in CMOS sensors and in TFT-PiN a-Si photosensors). A novel organic photodiode with voltage-switchable photosensitivity was developed recently. Passive photodiode matrices made with such organic photodiodes can be used for image sensing applications. This circuit simulation study demonstrates an effective scheme to extract images from passive photodiode matrices, concluding that individual photodiode parameters determine the contrast and resolution of N by M image sensors.
The photoluminescence temperature dependence of aluminium tris(8-hydroxyquinoline) as a function of excitation energy
Authors: Curry R.J. , Gillin W.P.
Published: April 2011

The temperature dependence of the photoluminescence as a function of excitation energy has been investigated for aluminium tris(8-hydroxyquinoline) (AlQ). It was observed that the peak position of the photoluminescence is a function of both temperature and excitation energy. The observed photoluminescence spectra can be deconvolved into three peaks, with varying weighting factors, the positions of which do not change with temperature. Using these three peaks the measured photoluminescence data was then modeled using a rate-equation approach.
Characterisation of the physico-chemical properties of surface-treated indium tin oxide anodes for organic light-emitting diodes
Authors: Kima J. S. , Granströma M. , Friend R. H. , Johansson N. , Salaneck W. R. , Cola A. , Gigli G. , Cingolani R. , Cacialli F.
Published: April 2011

We studied the surface properties of indium-tin oxide (ITO) modified by wet (aquaregia, ultrasonication, RCA) and dry (oxygen- and argon-plasma) treatments. The surface modification was investigated by surface energy, surface morphology, sheet resistance, carrier concentration, carrier mobility, and workfunction measurements. We report that the studiedoxygen-plasmatreatment induces: the highest surface energy with the highest polarity, the smoothest surface, the highest carrier density but the lowest mobility, the lowest sheet resistance, and the highest workfunction (stable in air). Polymer light-emitting diodes fabricated with the oxygen plasma treated substrates give the best performance in terms of electroluminescence efficiency and device lifetime. This is attributed to a favorable surface modification of ITO anodes by oxygen-plasma.
The Influence of Oxygen Content On Photoluminescence from Er-Doped SiOx
Authors: Chen W. D. , Liang J. J. , Hsu C.C.
Published: April 2011

SiOx films with oxygen concentrations ranging 13–46 at.% were deposited by plasma enhanced chemical vapor deposition (PECVD) technique using pure SiH4 and N2O mixture. Erbium was then implanted at an energy of 500 KeV with dose of 2×1015 ions/cm2. The samples were subsequently annealed in N2 for 20 sec at temperatures of (300–950°C). Room temperature (RT) photo-luminescence (PL) data were collected by Fourier Transform Infrared Spectroscopy (FTIS) with an argon laser at a wavelength of 514.5 nm and an output power from 5 to 2500 mw. The intense room-temperature luminescence was observed around 1.54 μm. The luminescence intensity increases by 2 orders of magnitude as compared with that of Er-doped Czochralski (CZ) Si. We found that the Er.- luminescence depends strongly on the SiOx microstructure. Our experiment also showed that the silicon grain radius decreased with increasing oxygen content and finally formed micro-crystalline silicon or nano-crystalline silicon. As a result, these silicon small particles could facilitate the energy transfer to Er3+ and thus enhanced the photoluminescence intensity.
The Optical and Crystalline Structure Properties of ZnO Thin Films Grown by Rf Magnetron Sputtering
Authors: Kim K. K. , Park S. J. , Song J.H. , Song J.-H. , Jung H.-J. , Choi W.K.
Published: April 2011

ZnO thin films were epitaxially grown on A12O3 (0001) single crystalline substrate by RF magnetron sputtering. The films were grown at the substrate temperature of 550°C and 600°C for 1 h and at a power of 60–120 W. The crystalline structure of the ZnO films was analyzed by 4-circle X-ray diffraction and backscattering (BS)/channeling. The FWHM of XRD ø -rocking curve increase from 9.45 to 18 arc-min. as the RF power increased from 80 to 120 W at 550°C. In-plane ZnO growth on sapphire.(0001) substrate at 550°C and at 80 W was found to be ZnO [1010] |: A12O3[1120], indicating a 30° rotation of ZnO unit cell about the sapphire (0001) substrate. For a specimen that was grown at an RF power of 120 W, 550°C, 1 h, the FWHM of XRD ø -rocking curve was 7.79 arc-min. In BS/channeling studies, the films deposited at 120 W, 600°C showed good crystallinity with the channeling yield minimum (Xmin) of only 5%, but for films deposited at 550°C the yield was as high as 50-60%, was of lower crystalline qualilty. From the results of the AFM measurement, the grain size gradually increased as the growing temperature and power increased. In case of the film deposited at 120 W and 600°C. the hexagonal shape of the grains were clearly observed. In PL measurement, only the sharp near band edge (NBE) emission were observed at room temperature for the film deposited at 80-120 W and 550°C, but the emission from deep level were also detected in the films deposited at 60 W, 550°C and 120 W, 600°C. The FWFM was decreased from 133 meV to 89 meV as RF power increased from 80 to 120 W at 550°C, and that of film deposited at 120 W and 600°C showed 98 meV respectively. The results were somewhat opposite to those of XRD. In the present study, the relationship between optical properties and crystal structure is discussed in terms of the quality of grains and the defects.
Investigation of Coupling Mechanism between Erbium (Er3+) and Ytterbium (Yb3+) in Alumina (A12O3) Host
Authors: Chryssou C.E. , Kenyon A.J. , Pitt C.W. , Chandler P.J. , Hole D.E.
Published: April 2011

Plasma-enhanced CVD (PECVD) deposited alumina (A12O3) thin films and single sapphire crystals were co-doped with both erbium and ytterbium using ion implantation. Yb3+ and Er3+ concentrations ranged from 2.4At% to 8At% and from 0.4At% to 0.8At%, respectively. The samples show relatively strong, broad, room-temperature photoluminescence (PL) at λ=11.53µm corresponding to the intra-4f transitions between the 4I13/2 (first excited) and the 4I15/2 (ground) state of Er3+. The full width at half maximum (FWHM) of the emission spectrum is as high as 67nm for the A12O3 thin films; for the sapphire crystals it is 45nm. The fluorescence lifetime of the samples has been measured to be as high as 4.2ms at 50mW laser pump power. The indirect pumping of erbium through the transfer of energy from ytterbium has been demonstrated and the PL peak intensity has been studied as a function of the Yb3+/Er3+ concentration ratio when the samples are pumped at 514nm and 850nm; the PL excitation spectrum (PL at 1.53gm as a function of pump wavelength) of an Er3+/Yb3+ co-implanted sample is also presented. Both the PL peak intensity at 1.53µm and the fluorescence lifetime have been studied as functions of annealing temperature. Luminescence spectra attributed to defects in the alumina matrix are presented for as-implanted samples and following thermal annealing.
Effects of Co-Dopants on the Microstrucutre and El Properties of the Zns:Mn Luminescence Materials
Authors: Zhai Qing , Li Jinghong , Lewis Jay , Waldrip Karen , Jones Kevin , Holloway Paul , Puga-Lambers M. , Davidson Mark
Published: April 2011

Thin films of zinc sulfide (ZnS) doped with Mn, were deposited using magnetron sputter source. The electroluminescent properties of the as-deposited films were relatively poor. Post- deposition rapid thermal annealing (RTA) with and without co-dopants was studied. Significant changes in microstructure and EL performance were observed on the samples after post-sputter processing. Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were employed to characterize the microstructure. Both inter-grain and intra-grain distributions of the co-dopants were measured using energy dispersive X-ray spectra (EDX) and the distribution versus thickness was determined by dynamic secondary ion mass spectrometry (SIMS). A correlation between electroluminescent properties and the microstructure is obtained.
The Origin of Luminescence From Cerium Oxide on Silicon
Authors: Choiv Won Chel , Lee Ho Nyung , Kim Yong , Kim Eun Kyu
Published: April 2011

As the ultra-violet/blue luminescent material, we will introduce the thermal treated cerium oxide on silicon. It has been confirmed a violet/blue luminescence ranging from 358 rim to 450 rnm at room temperature from the thermally treated cerium-dioxide thin films on silicon. As a results of AES and HR-TEM measurement, it was confirmed that cerium silicates were generated by thermal treatment. These cerium silicates such as Ce4.667(SiO4)3O and Ce2Si2O7 are the source of the ultra-violet (UV) emission ranging from 358 nim to 450 nm (maximum at 388 rim).
Evidence for Energy Transfer Mechanisms in Er3+-Doped Pmma Paac Copolymer Samples
Authors: F. R. Sosa , Flores M. , Rodríguez T. R. , Muiñoz F. A.
Published: April 2011

The Judd-Ofelt intensity parameters for f-f transitions of Er3+ ions in PMMA:PAAc copolymer samples were determined from optical absorption measurements and their dependence on the erbium content investigated within the range of 0.1 to 3.0 % mol. The densities, refractive indices and emission spectra have been measured. For our Er-PMMA:PAAc samples an effective radiative transfer between the copolymer host and the erbium ions is observed and discussed.
Survey of Recent Research Results for New Fluor Materials
Authors: Hollerman William A. , Glass Gary A. , Allison Steven A.
Published: April 2011

There is worldwide interest in the use of fluor materials that emit visible light when exposed to ionizing radiation. Typically, fluors are used as components in high performance electromagnetic calorimeters, down-hole oil well loggers, temperature sensors for equipment with high speed moving parts, and beam positioning systems for large particle accelerators. A candidate fluor should have a large fluorescence efficiency, small reduction in output as a function of exposure, intense visible fluorescence spectrum, large material density, and small prompt fluorescence decay time.

Over the last few years, new fluor materials have been located by organizations such as Oak Ridge National Laboratory, Lawrence Berkeley National Laboratory, and the Department of Defense. These new fluors, such as YAIO3:Ce, YSiO5:Ce, GdSiO5:Ce, Y2O2S doped with Tb, Pr, and Eu, and Gd2O0S doped with Th, Pr, and Eu, show a great deal of promise for use in the applications listed above.

This paper will present a summary of fluor research completed by the authors over the last ten years. These results will be used to establish a fluor characterization program at the Acadiana Research Laboratory (ARL) that will move it to the front of this developing technology.
Porous Polymer/Ceramic Composites for Luminescence-Based Temperature and Pressure Measurement
Authors: Scroggin A.M. , Slamovich E.B. , Crafton J.W. , Lachendro N. , Sullivan J.P.
Published: April 2011

Porous Polymer/ceramic films were processed via tape casting. Upon doping with luminescent molecules such as platinum(II) octaethylporphine and [Ru(4,7-diphenyl-1,10-phenanthroline)3]C12, the films were used as pressure sensors, yielding a Stern-Volmer constant of A ranging from 0.02 to 0.61. These films also exhibited very fast response times (∼I ms). Tape cast films doped with Rhodamine B were used as temperature sensors under cryogenic conditions. The temperature sensitivity of the doped films increased with increasing Rhodamine B concentration.
Thin-Film Oxide Phosphors as Electroluminescent Materials
Authors: Minami Tadatsugu
Published: April 2011

In this paper, we introduce rare earth- or transition metal-activated oxide phosphor thin films prepared by magnetron sputtering and dip-coated solution deposition. Thin-film electroluminescent (TFEL) devices using these oxide phosphor thin films as the emitting layer were investigated with a single insulating layer device structure using a thick ceramic sheet insulating layer. High-luminance multicolor emissions and high luminous efficiencies were obtained in TFEL devices using various oxide phosphors: binary compound, Ga2O3; ternary compound, Zn2SiO4, CaGa2O4 and ZnGa2O4; and multicomponent oxide, Zn2SiO4- Zn2GeO4 system. Luminances above 2000 cd/m2 were obtained in CaGa2O4:Mn and Zn2Si1−XGeXO4:Mn TFEL devices driven at 1 kHz. Maximum luminous efficiencies of 2.53, 1.7 and 1.2 lm/W were obtained in Zn2Si0.7Ge0.3O4:Mn, Ga2O3:Mn and ZnGa2O4:Mn TFEL devices, respectively. Stable long-term operation was obtained in dip-coated and sputtered Ga2O3:Mn phosphor TFEL devices even when driven at 10 kHz. Various thin-film oxide phosphors activated with transition metals are suitable for the emitting layer of full-color electroluminescent displays (ELD) without the use of color filters. In particular, Ga2O3 is very promising as a phosphor host material for ELDs.
Enhancement of Nonlinear Optical Properties Through Supramolecular Chirality
Authors: Elshocht S. Van , Busson B. , Verbiest T. , Kauranen M. , Snauwaert J. , Hellemans L. , Persoons A. , Nuckolls C. , Katz T.J.
Published: April 2011

We study second-order nonlinear optical properties of enantiomerically pure and racemic Langmuir-Blodgett films of a chiral helicenebisquinone. Supramolecular aggregation of the material enhances the nonlinear efficiency of the enantiomerically pure material. We also show that the material is potentially useful for constructing quasi-phase-matched structures for frequency conversion.
El Behavior of Stylyl Compounds with Benzoxazole and Benzothiazole for Organic Light-Emitting-Diode
Authors: Yamashita Koichi , Imaizumi Kaname , Mori Tatsuo , Mizutani Teruyoshi , Miyazaki Hiroshi
Published: April 2011

We studied the EL behaviors of benzoheterocyclic derivatives as emitting and hole transport layers for organic light-emitting-diodes (OLEDs). First, we studied the benzoheterocyclic derivatives having stylyl group, triphenylamine group and benzoxazole or benzothiazole group as an emission layer. These devices emitted a blue-green light. The current densities of the OLED having these benzoheterocyclic derivatives as an emission layer were higher than that of the Alq3 OLED at same applied voltage. However, these devices did not have a high EL efficiency (maximum 0.1 lm/W). From these results, in these benzoheterocyclic derivatives having a triphenylamine group, we thought that holes could flow out from hole transport to cathode. We newly synthesized dimer-type benzoheterocyclic derivatives without a triphenylamine group, which have benzoheterocycle at both sides. The current densities of the OLEDs having dimer-type benzoheterocyclic derivatives was more strongly suppressed than that of the OLEDs having benzoheterocyclic derivatives with a triphenylamine group at same applied voltage, but the EL efficiency could not be improved by dimerization and eliminating of a triphenyldiamine group obtained. Next, we studied the TPD derivatives having benzoxazole, benzothiazole and stylyl groups as hole transport layer. In new TPD derivatives, the EL efficiency the OLEDs having the TPD derivatives with stylyl groups was the best efficiency of all. The EL efficiency of ITO/a TPD derivative with stylyl groups/Alq3/AlLi is 1. 1 lm/W (max. luminance 12000cd/m2).
Temperature and Field Dependence in Polymer Light Emitting Diodes
Authors: Bozano L. D. , Carter S.A. , Scott J.C. , Malliaras G.G. , Brock P.J.
Published: April 2011

We investigate the electrical properties of Polymer Light Emitting Diodes (LED's). The experimental data consists of steady state current-voltage characteristics and radiance as a function of temperature.

The basic LED structure is Anode/MEH-PPV (2-methoxy,5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene)/Cathode, with a polymer film 120-140 nm thick. We use different anode/cathode pairs to study transport and light emission properties. Measurements of external quantum efficiency of bipolar and monopolar devices are presented from 200 K to 300 K. The electron and hole mobilities are derived in the trap-free limit and at high voltages.
Multifunctional Fullerene Films for Photonics
Authors: Liu Y. , Claus R. O. , Wang Y.X. , Lu H. , Distler T.
Published: April 2011

We report here the preparation of highly homogeneous multifunctional fullerene thin films for photonics using the electrostatic self-assembled monolayer technique at room temperature for the first time. The monolayers and multilayers were characterized via contact angle measurements, UV-vis spectroscopy and atomic force microscopy. These results demonstrated that close-packed, highly uniform fullerene or fullerene/metal cluster films with micron-thickness could be formed on various substrates including silicon, glass, metal and plastics.
The Synthesis of Diphenylpolenes and PPV-Oligomers Incorporating Diphenylphosphino Donor Groups
Authors: Madrigal L. G. , Spangler C.W.
Published: April 2011

Previous studies of the second and third order nonlinear optical properties of organic molecules have shown enhancement of the nonlinear response when second row elements replace first row elements (e. g. S for O) in electron donating groups. Various substituted amino functionalities have been utilized extensively as strong donors in the design of molecules for both second and third order NLO applications. However, to date, no research groups have reported a systematic study of the effect of replacing N (nitrogen) by P (phosphorus) in various chromophore functionalities. We have now synthesized a series of bis(diphenylphosphio)diphenylpolyenes with up to five double bonds, a bis-(diphenylphosphino)-PPV dimer, and a diphenylphosphino DANS equivalent. The absorption characteristics compared to the N equivalents, and the implications for photonics applications will be discussed.
Synthesis and Optical Limiting Characterization of a Porphyrin-Buckminsterfullerene Dyad
Authors: McEwan Kenneth J. , Lewis Keith L. , Ang How-Ghee , Loh Zhi-Heng , Chng Leng-Leng , Lee Yiew-Wang
Published: April 2011

The optical limiting performances of donor-buckminsterfullerene (C60) dyads have hitherto been unreported. The predicted large excited state absorption cross-section of such dyads in their charge-separated states would enable them to exhibit enhanced optical limiting relative to their individual components. We report herein the synthesis and optical limiting characterization of a novel porphyrin-buckminsterfullerene dyad, in which the porphyrin and C60 moieties are held within close proximity of one another by an o-phenylene bridge. The porphyrin-C60 dyad was synthesized via 1,3-dipolar azomethine ylide cycloaddition, and was obtained in 37.0% yield. Optical limiting measurements at 532 nm using 3-ns pulses show that the limiting performance of the dyad is poorer compared to its model compounds. Possible reasons for the worsened performance of the dyad will be discussed.
Electrical Reliability of Giant Magneto-Resistive Recording Sensors
Authors: Tsu I-Fei , Chang C. , Edelman H. S.
Published: April 2011

The electrical reliability of Ta/NiMn/NiFe/Co/Cu/Co/NiFe/Ta top spin valve sensors was studied. Electrical current densities in the range of 20–50 MA/cm2 were applied at 70°C ambient temperature. The combined Joule and ambient heating correspond to peak sensor temperatures of 170–300°C. Resistance and giant magneto-resistive (GMR) amplitude of the sensors were measured with time up to 800 hours. Device reliability was predicted from the Arrhenius plots of time to failure (TTF). Microstructure of sensors after stress was studied by scanning transmission electron microscope (STEM) and energy dispersive X-ray spectroscopy (EDX). The device failure mechanism is discussed on the scope of inter-layer diffusion and electromigration.
Effect of Modified Metal/Passivation Interfaces on Stress Voiding in Interconnects+
Authors: Kalnas C. E. , Keller R. R. , Phelps J. M. , Marieb T. N.
Published: April 2011

Stress and electromigration voids are believed to nucleate at the metal/passivation interface. In this study, modified interfaces were synthesized to experimentally elucidate the role of the interface on stress voiding for comparison with theoretical predictions. Interfaces were modified by depositing photoresist in a controlled manner on Ti/Algfi lines prior to passivation deposition. Stress voiding susceptibility was assessed in as-received lines as well as those subjected to storage anneals for 1, 5, and 25 days at 190°C to accelerate void formation. The global textures of all the lines were <111> fiber and were not significantly affected by the interface modification. Differences in stress voiding were attributed to the different interfaces. Higher ratios of voids in modified regions to voids in unmodified regions were observed both in as-received lines and those given a 1 day storage anneal due to the heterogeneous nucleation sites provided by the photoresist contamination in the modified regions. However, the void ratio appears to decrease exponentially with longer time anneals. Lowered driving force for void formation in the modified regions leads to less voiding with time, while higher driving force and a limited number of nucleation sites in the unmodified regions leads to more voiding with time. Local textures at a limited number of voided sites in modified and unmodified regions were identical to the global texture of the line. In our limited sampling, voids did not form in local regions of weaker <111> texture.
Kinetics of the Tial3 Formation From Al/Ti Thin Films
Authors: Federspiel X. , Ignat M. , Voiron F. , Fujimoto H. , Marieb T.
Published: April 2011

The interfacial reactions that may occur from the ageing of integrated circuits during operation will change their properties and produce failures. It is crucial to understand the phenomena that controls these reactions and their kinetics.

The object of this work was to establish the role of impurities and grain size on the growth rate of TiAI3 from Al/Ti interfaces. The kinetic study consisted of different annealings followed by electrical measurements. These data were correlated with microstructural analysis and composition evolution from Transmission Electron Microscopy (TEM), Secondary Ions Mass Spectroscopy (SIMS).

The kinetic data were fitted using a combination of classical models (parabolic, Avrami, Aronson) and complemented by a simulation, which accounts for the nucleation frequency and the grain boundary diffusion. The growth simulations were compared to microstructures observations using TEM.
Measurement of Toughness for Sin Films on Silicon Using Channel Cracking Technique
Authors: Ma Qing , Tran Quan , Sun Brad , El-Mansy Safaa , Sun Julie , Fujimoto Harry
Published: April 2011

Silicon nitride thin films used for transistor spacer are usually under large tensile residual stresses. When a film is thick enough, it can crack by channel cracking mechanism. The toughness of these films, used in models for failure criteria, can be obtained by determining the critical thickness for channel cracking of blanket films with known residual stresses. However, depositing films of a range of different thickness to determine the critical thickness is tedious, and this process also introduces risks of producing particles in the deposition chamber when the film exceeds the critical thickness. An alternative technique is to deposit films of thickness below critical thickness and then to apply additional tensile stresses to the film by bending the substrate. A critical film stress can be determined for channel cracking from which the film toughness is obtained. This paper describes the experiments performed for a new SiN film and presents the results.
Fatigue of Silane Bonded Epoxy/Glass Interfaces
Authors: Ritter J. E. , Learned J. C. , Jacome G. S. , Russell T. P. , Lardner T. J.
Published: April 2011

Fatigue (slow) crack growth in silane bonded epoxy/glass interfaces was studied under static and cyclic loading at 23°C, 95% RH using the double cleavage drilled compression test. Crack growth rates under cyclic loading were significantly greater than under static loading, in contrast to crack growth results in monolithic glass. In addition, cyclic crack growth rate data after aging up to 94°C in distilled water were not significantly different from unaged samples; however, after aging at 98°C in distilled water and 70°C in a KOH aqueous solution of pH 10, crack growth became cohesive and fractal in nature. These results are discussed in terms of possible mechanisms for fatigue crack growth at silane bonded epoxy/glass interfaces.
Characteristics of Molybdenum Nitride Thin Film by N2+ Ion Implantation
Authors: Kim Dong Joon , Kim Ik-Soo , Kim Yong Tae , Park Jong-Wan
Published: April 2011

Molybdenum nitride thin films were prepared by N2+ implantation with acceleration energy of 20 keV and the ion dose of 3×1017 ions/cm2. The structural property and thermal stability of the films were investigated by XRD, AES, AFM and RBS. The crystal structure of N2+ implanted molybdenum thin films (Mo-N2+) which had microcrystalline state was transformed to γ-Mo2N phase with a preferred (111) orientation after a post-annealing at 500 °C for 30min. However, a silicide reaction was not observed even after the annealing at 700 °C, which is due to the modification of the interface between Mo thin film and Si substrate by N2+ implantation. Also, Cu diffusion did not seem to be induced by the annealing at 700 °C for 30 min. The internal stress of the Mo-N2+ thin films during post-annealing at 600 °C for 30min was found to change from highly compressive stress to low tensile stress.
In-Situ Study of the Oxide Mediated Epitaxy of CoSi2 on Si
Authors: Kleinschmit M. W. , Yeadon M. , Gibson J. M.
Published: April 2011

Oxide Mediated Epitaxy (OME) shows promise as a method to form good quality, thin epitaxial CoSi2 films on most Si surfaces. We have performed an in-situ study of the OME of CoSi2, on the Si (001) surface. Our work was carried out with our specially modified ultra-high vacuum transmission electron microscope (UHV TEM) SHEBA (Surface High Energy Electron Beam Apparatus). With SHEBA we were able to monitor the diffraction pattern and therefore the phase formation throughout the anneal. Our results confirm the suppression of intermediate phases during CoSi2 formation in the OME process. We also see a difference in the as deposited Co film when the oxide coated silicon surface is used rather than a clean substrate. From combined imaging and diffraction studies we will shed some light on the mechanism behind the success of OME.
Modelling the Influence of the Silicon Doping Profile on a Silicide Well Ohmic Contact
Authors: Reeves G. K. , Holland A. S. , Leech P. W.
Published: April 2011

Low values of contact resistance Rc(Ω) and specific contact resistance, ρc(Ωcm2) are essential for ohmic contacts to devices with ULSI dimensions. The incorporation of silicides into contact structures has made a substantial contribution towards this goal. However the modelling and characterisation of these more complex silicide contact structures still requires considerable development. The variation of doping density in the vertical direction will cause a strong local variation in silicon resistivity with depth as well as a pronounced variation in the silicon-silicide barrier layer as a function of depth.

In this paper we use a three dimensional (3-D) finite element analysis of sub-micron silicide contacts to illustrate the influence on Rc of the silicon doping profile in the sourcedrain contact regions. In addition, the influence of the doping profile on the current density distribution at the silicon-silicide interface is presented. A comparison of results is made between a uniform doping profile and two ion-implanted profiles. In order to improve the model's accuracy, the often neglected contribution of the metal-silicide barrier (ρca) to Rc is taken into account. Experimental measurements using a Cross Kelvin Resistor (CKR) test structure, have been used to determine ρca (∼3–5 × 10−9Ω.cm2 ) of the aluminium-TiSi2 interface.
Effect of Nitrogen Content on Interfacial Adhesion of the Ta/SiO2Interface
Authors: Lane Michael , Dauskardt Reiner , Krishna Nety , Hashim Imran
Published: April 2011

With the advent of copper metallization in interconnect structures, new barrier layers are required to prevent copper diffusion into the adjacent dielectrics as well as the underlying silicon. These barriers must not only prevent interdiffusion but also provide adequate adhesion to both the dielectric and copper. Ta and TaN have received considerable attention as barrier layers in copper metallization schemes. While much has been reported on their diffusion properties, little or no quantitative data exists on their adhesive properties. We present data on both the interface fracture energy and the subcritical debonding of ionmetal- plasma sputtered Ta and TaN films on thermal silicon oxide. Data is also presented showing the significant effect of interfacial chemistry, particularly varying nitrogen contents at the TaN/SiO2interface.
TEM Analyses Of Cu-Ta And Cu-Tan Interfaces
Authors: Wang J. Y. Phillip , Zhang Hong , Hashim Imran , Dixit Girish , Chen Fusen
Published: April 2011

This paper reports an extensive interfacial study of Cu deposited on Ta and TaN barrier layers. It has been reported that the Cu/Ta interface develops a uniform and thin amorphous layer at the interface upon thermal treatment[l]. However, our high resolution transmission electron microscopy (HRTEM) analysis shows atomically sharp interfaces for all conditions without any amorphous layer at the interfaces, especially for the ones which underwent one hour annealing at 400°C and 500°C. The “amorphization” effect is only observed if the Cu/Ta TEM specimen is exposed to oxygen. It exists usually at the thinner regions of the TEM specimen or if the specimen is left in air for > 24 hours. Energy dispersion x-ray (EDX) analysis of the “amorphized” region shows that it is a mixture of Cu, Ta, and O.
The Future Of Silicide For CMOS Contacts
Authors: Roy R. A. , Cabral C. , Lavoie C.
Published: April 2011

This paper examines the challenges for silicide contacts in current and future CMOS technologies and assesses the capability of TiSi2 and related materials, as well as CoSi2, to meet the technology requirements. Specific issues such as maintaining low resistance in narrow lines, source/drain silicon consumption, and silicide thermal budget, are discussed. In this regard we evaluate the salient features of the basic titanium salicide process, and variations such as alloying, implantation, selective CVD, and laser silicidation. Data are presented from recent experiments to assess progress in each approach towards meeting the necessary goals. Finally, projections of the future of silicide processing are given.
Microstructural Development of Dispersion Strengthened Cu Thin Films
Authors: Weiss D. , Kraft O. , Arzt E.
Published: April 2011

The internal oxidation method is applied for the first time to produce a fine dispersion of second phase particles in thin films. A processing route is presented which includes ultra-high vacuum magnetron sputtering of about 1 μm thick alloy films onto Si substrates followed by insitu annealing and oxidation. Two different Cu-base alloys are examined, Cu-Y and Cu-Al, in which the extent of miscibilitiy differs significantly. This has considerable influence on the grain growth behavior. Nanoindention and wafer-curvature experiments show a drastic improvement of both room-temperature and high-temperature strength. Phenomena well known from bulk oxide-dispersion strengthened (ODS) alloys are found to appear in the thin films as well: Results on abnormal grain growth and the formation of creep voids are presented and discussed in terms of particle effects.
Bath Additive and Current Density Effects on Copper Electroplating Fill of Cu Damascene Structures
Authors: Mikkola Robert D. , Jiang Qing-Tang , Carpio Ronald , Carpenter Brad
Published: April 2011

Copper electroplating has become the leading technology for gap fill of damascene structures on advanced interconnects. A key to developing a robust electroplating process that produces deposits free of voids and seams is understanding the role of the additive components, i.e., levelers, brighteners and wetting agents, and their relative diffusion/adsorption characteristics. Additionally, obtaining insight about the cathodic current/potential relationship is critical for maximizing the effectiveness of the additive components.

Our results indicate that bath additive composition and the plating parameters (plating pulse frequency, and current density play critical roles in the outcome of the Cu fill. SEM cross sectional analysis of timed partial electroplating fill studies show two types of fill, 1) conformal and 2) bottom-up. Conformal fill of features smaller than 0.25 μm with an aspect ratio (AR) of 4.0 tends to form seam voids in the center of the structure. These seam voids can lead to early electromigration failures. On the other hand, bottom-up fill leads to a void free Cu deposit within the feature.
Room Temperature Self-Annealing of Electroplated and Sputtered Copper Films
Authors: Chen Michelle , Rengarajan Suraj , Hey Peter , Dordi Yezdi , Zhang Hong , Hashim Imran , Ding Peijun , Chin Barry
Published: April 2011

Self-annealing properties of electroplated and sputtered copper films at room temperature were investigated in this study, in particular, the effect of copper film thickness, electrolyte systems used, as well as their level of organic additives for electroplating. Real-time grain growth was observed by transmission electron microscopy. Sheet resistance and X-ray diffraction measurements further confirmed the recrystallization of the electroplated copper film with time. The recrystallization of electroplated films was then compared with that of sputtered copper films.
Facilitated C54-TiSi2 Formation With Elevated Deposition Temperature: A Study of CO-Deposited Layers
Authors: Ohmi S. , Tung R. T.
Published: April 2011

The effect of co-deposition method on the C49- to C54-TiSi2 phase transformation was investigated. Both the co-deposition ratio of TiSix layers and the deposition temperature were found to have a significant effect on the C54 phase transformation. The optimum composition to form C54 TiSi2 phase was x∼l.5 for room temperature deposition, and x∼2.0 for samples deposited at 400°C. The incorporation of a small amount of Mo had a beneficial effect on the C54 transformation in layers deposited at room temperature, but it had little effect in layers deposited at 400°C.
Characterization of Thin Dielectric Films as Copper Diffusion Barriers using Triangular Voltage Sweep
Authors: Cohen S. A. , Liu J. , Gignac L. , Ivers T. , Armbrust D. , Rodbell K. P. , Gates S. M.
Published: April 2011

As technology progresses, the need for thinner Cu diffusion barrier caps is becoming more important, and it is advantageous if these barriers have low dielectric constants (κ). Towards this end, we characterized Cu penetration in several thin (35 nm to 70 nm) dielectrics, including silicon nitrides, silicon oxynitrides, an amorphous hydrogenated carbon film, and a methyl silsesquioxane layer. Metal Insulator Silicon (MIS) structures were used as the test vehicle. The barrier dielectrics were deposited on 100 nm thermal oxide which was grown on 2 Ω-cm, n-type Si wafers. After the deposition of 50 nm TEOS capping layers, both Al and Cu dots were evaporated on each wafer through a mask. Both Al and Cu dot samples were stressed at +2.7 MV/cm at 300°C for 10 minutes. For Cu dots, the applied stress pushed Cu ions into the dielectric stack. Stressing Al dots characterized the effects of the stress on the dielectric stacks and the quantity of Na ions in the films. Since C-V shifts are subject to stress-related instabilities in the interfaces as well as within the dielectrics themselves, triangular voltage sweep (TVS) was used after the applied stress to measure the concentration of Cu which reached the underlying thermal oxide film. The sensitivity of the TVS test with the structures used is about 5×109/cm2. Secondary ion mass spectroscopy (SIMS) analyses were performed on some of these samples to verify the electrical results.
HRTEM Study of the Interfacial Reactions of High-Temperature Sputtered Ti Thin Films on Preamorphized (001)Si
Authors: Chang S. M , Yang H. Y , Huang H. Y , Chen L. J.
Published: April 2011

Interfacial reactions of high-temperature sputtered Ti thin films on preamorphized (001)Si have been investigated by high-resolution transmission electron microscopy in conjunction with auto-correlation function analysis. Simultaneous presence of multiphases was found to occur in the amorphous TiSix layer at the Ti/Si interface. The enhanced transformation of C54-TiSi2 in high-temperature deposited samples is attributed to the more extensive presence of silicide crystallites, which serve as nucleation sites, in the a-TiSix layer than that in samples deposited at room temperature.
Arsenic-Only Preamorphization Process Extension For TiSi2 Formation Down to 65-nm Gate Lengths
Authors: Losavio A. , Sallagoity P.
Published: April 2011

The scalabilty of the titanium self-aligned silicide (Salicide) process is one of the main issues for sub-quarter micron technologies. The major difficulty is to achieve a low sheet resistance for very narrow polysilicon lines and highly doped S/D regions, without degrading the transistor performance. A preamorphization implant (PAl) performed before the titanium deposition, can achieve a low Ti silicide sheet resistance (<10 Ohms/sq) down to 0.1 Vim gate lengths [1]. Nevertheless, it has been recently reported that PAI should not be sufficient to achieve low silicide sheet resistance for narrower gate widths (< 0.1 µm) [2]. In this work, an extension of the PAI process down to 0.065µm poly-Si lines width, by only using an arsenic implant is presented, achieving a very low sheet resistance value (∼5 Ohms/sq). This result has been obtained by optimizing both the arsenic implant conditions and the silicon surface cleaning. Moreover, a large statistical analysis of the arsenic PAI process impact on 0.25µm device performances has been done, showing that a defectivity of the NMOS Ioff leakage current can appear if preamorphization implant conditions are not optimized.
The Influence Of Stress on The Growth of Titanium Silicide Thin Films on (001) Silicon Substrates
Authors: Cheng S. L. , Chang S. M. , Huang H. Y. , Peng Y. C. , Chen L. J. , Tsui B. Y , Tsai C. J. , Guo S. S.
Published: April 2011

The influence of stress on the enhanced formation of C54-TiSi2 phase has been investigated. Tensile stress induced by backside CoSi2 film on the silicon substrate has been found to enhance the growth of C54-TiSi2 on (001)Si. The thickness of amorphous interlayers (a-interlayers) between Ti films and silicon substrates was found to be thicker and thinner in the tensilly and compressively stressed samples, respectively. From auto-correlation function analysis, the thicker a-interlayer was found to consist of a higher density of crystallites. The crystallites provide nucleation sites for C49-TiSi2 and facilitate the formation of C49-TiSi2 of small size. The larger total area of C49-TiSi2 grain boundaries supplies more nucleation sites for the phase transformation of C49- to C54-TiSi2. Therefore, the tensile stress present in the silicon substrate promotes the formation of a-interlayer and decreases the grain size of C49- TiSi2, which increases the nucleation density of the C54-TiSi2 phase. As a result, the transformation of C49- to C54-TiSi2 phase is enhanced.