bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of Cathodoluminescence and Photoluminescence Properties of Pulsed Laser-Deposited Europium-Activated Yttrium Oxide Thin Film Phosphors
Authors: Cho K.G. , Kumar D. , Chen Z. , Holloway P. H. , Singh R. K.
Published: April 2011

Europium-activated yttrium oxide (Eu:Y2O3) thin films were deposited on (100) silicon and (0001) sapphire substrates using 248 nm KrF pulsed laser. To investigate the effect of the Eu:Y2O3 film roughness on cathodoluminescence (CL) and photoluminescence (PL) properties, the substrate surfaces with various roughnesses were used. The roughness was found to play an important role in determining CL and PL brightness of the Eu:Y2O3 films. The improvement in brightness by increasing the film roughness is due to increase in total portion of light that escapes from the surface of the phosphor film. A model has been proposed which supports strongly this explanation. Our results show that depositions with slower growth rate and lower laser energy are more important parameters than increasing the roughness to improve CL brightness of the Eu:Y2O3 thin film phosphors.
A new laser Printing technique for the fabrication of thin film transistors
Authors: Toet D. , Smith P.M. , Sigmon T.W. , Thompson M.O.
Published: April 2011

We present a new technique for the spatially selective deposition, or “printing”, of materials such as Si and Al. This transfer is effected by irradiating a hydrogenated amorphous silicon film deposited on a quartz substrate and coated with the material to be transferred with an excimer laser pulse. The resulting release and accumulation of hydrogen at the film/substrate interface generates pressures sufficient to propel the silicon, as well as any overlying material, onto an adjacent glass receptor wafer. Transient optical transmission measurements performed during the transfer of Si indicate that the amorphous film is melted by the laser pulse and breaks into droplets during ejection. These droplets travel towards the host substrate with a velocity of about 800 m/s and coalesce upon arrival. For fluences above 400 mJ/cm2, the resulting films adhere well to the receptors and can be smoothed using a second laser irradiation. We fabricated thin film transistors (TFTs) in the printed-and-smoothed Si using conventional lithography. The resulting devices show consistent switching behavior. We have also printed Si and Al lines with widths 5 to 15 µm by patterning the laser beam using a reflective grating mask defined on the target substrate. These lines are straight, show few discontinuities, and have sharp edges.
A μc-Si:H P-I-N Imager For 2-D Pattern Recognition
Authors: Martins J. , Fernandes M. , Sousa F. , Louro P. , MaçArico A. , Vieira M.
Published: April 2011

A TCO/ μc-p-i-n Si:H/AI imager is presented and analyzed. The μc-p-i-n Si:H photodiode acts as a sensing element. Contacts are used as an electrical interface. The image is acquired by a scan-out process. Sampling is performed on a rectangular grid, and the read-out of the photogenerated charges is achieved by measuring simultaneously both transverse photovoltages at the coplanar electrodes. The image representation in gray-tones is obtained by using low level processing algorithms. Basic image processing algorithms are developed for image enhancement and restoration.
Investigation of the Role of Chemical-Mechanical Polishing in Improving the Performance of Polysilicon TFTs
Authors: Lee B. , Quinn L.J. , Baine P.T. , Mitchell S.J.N. , Armstrong B.M. , Gamble H.S.
Published: April 2011

Polycrystalline silicon thin-film transistors (TFTs) have been fabricated on glass substrates using a low temperature top-gate self-aligned process. The interface between the polysilicon active layer and the silicon dioxide oxide gate dielectric is of vital importance in order to achieve good thin-film transistor electrical characteristics. Carrier transport takes place within 10nm of this interface, and any roughness in this region, corresponding to the initial surface roughness of the polysilicon layer, causes scattering of the carriers and a higher density of interface traps. Chemical-mechanical polishing has been used to reduce the initial surface roughness of the polysilicon. Electrical parameters of polished TFTs, such as mobility and threshold voltage, show a marked improvement compared to unpolished devices.
Growth Mechanism of thin Film Wide-Gap Semiconductors by Chemical Bath Deposition Technique
Authors: Nair P. K. , Parmananda P. , Nair M. T. S.
Published: April 2011

Chemical bath deposition is a thin film technique in which semiconductor thin films of typically 0.02 – 1 μm thickness are deposited on substrates immersed in dilute baths containing metal ions and a source of sulfide or selenide ions. Many I–VI, II–VI, IV–VI, and V–VI semiconductors are included in the list of materials deposited by this technique, II–VI compounds CdS, CdSe, ZnS and ZnSe being the most investigated. However, a mathematical model describing the growth mechanism of these films still remains to be established. The deposition process consists of a nucleation phase, growth phase, and a terminal phase, each of which depends on the concentration of the ions in the deposition bath, its temperature, dissociation constants of the metal complex ions, etc. In this paper we propose a mathematical model, which can qualitatively account for most of the features of the experimental growth curves of chemically deposited semiconductor films.
Electroluminescence and Photoluminescence of Fluorene-Carbazole Copolymer
Authors: Stephan O. , Vial J.C.
Published: April 2011

Thin layers of poly(dihexylfluorene-co-N-hexylcarbazole) sandwiched between ITO and aluminium electrodes show stable photoluminescence and electro-luminescence at room temperature and ambient atmosphere. I(V) and Electro-luminescence versus voltage curves present a much lower threshold than device made up of poly(dihexylfluorene) homopolymer. When using the copolymer, the barrier height for hole injection is reduced to a value close to 0.17 eV to be compared to 0.83 eV for the homopolymer. This difference in offsets has been confirmed by electrochemical investigations.
Performing Accurate Cathodoluminescence Measurements of Phosphor Powders and Screens
Authors: Shea L. E. , Walko R. J.
Published: April 2011

In the field of display phosphors, the efficiency of the cathodoluminescence process is a characteristic that is often used to assess the potential of a phosphor for use in flat-panel display applications such as field emission displays (FEDs). Cathodoluminescence characterization in a demountable vacuum chamber is important for preliminary evaluation and lifetesting of phosphor powders and screens prior to incorporation into an actual display device. There are many experimental factors that influence accurate measurement and calculation of the cathodoluminescence efficiency. These include electron beam profile (uniform, Gaussian), current density, electron accelerating voltage, secondary electron collection, and optical detection system. This paper will present some methods for achieving improved accuracy of cathodoluminescence measurements in systems at Sandia National Laboratories, using Y2O3:Eu as a representative phosphor.
Energy and Charge Transfer in Electroluminescent Polymer/Porphyrin Blends
Authors: Cleave V. , Yahioglu G. , Barny P. Le , Friend R.H. , Tessler N. , Hwang D.H. , Holmes A.B.
Published: April 2011

We present a study of the effects of blending electroluminescent polymers with platinum (II) octaethylporphyrin (PtOEP). We find that in the case of polymers which are measured to have HOMO and LUMO levels respectively below and above those of the PtOEP, and which have emission spectra overlapping the PtOEP absorption spectra, energy transfer occurs as expected. We find further evidence, in the form of steady state and time-resolved electroluminescence and photoluminescence measurements, which indicates additional transfer of triplet excitons between polymer and porphyrin. Where the polymers have emission spectra overlapping the absorption spectra of PtOEP, but which are measured to have a HOMO or LUMO level between those of the porphyrin, quenching of the photoluminescence efficiency occurs. We propose this is due to charge separation between the porphyrin and the polymer, and show evidence for this in the form of photoinduced absorption measurements.
A Novel Four Terminal Poly-Si Tft Suppressing Kink and Improving Reliability
Authors: Park Cheol-Min , Kang Ji-Hoon , Park Kee-Chan , Han Min-Koo
Published: April 2011

We fabricated a new device, which employs counter-doped lateral body terminal (CLBT) in order to suppress kink effects and improve the device stability. Proposed device also employs a buried channel (BC), which increases ON-current and operating frequency. Although LDD structure is not employed in the proposed device, low OFF-current is successfully obtained due to elimination of minority carrier through CLBT. We have measured the dynamic properties of poly-Si TFT device and circuit. The reliability of TFT and circuits after AC stress is also discussed in our paper.

The proposed poly-Si TFT has high ON-current and low OFF-current compared with conventional 3-terminal poly-Si TFT. The 4-terminal device characteristics were measured with source and CLBT shorted. The proposed device exhibits superior performance to conventional device in ON-current because BC prevents carrier scattering to gate oxide. We have performed bias and high temperature stress test of ring oscillator in order to investigate dynamic reliability between conventional poly-Si TFT and proposed 4-terminal poly-Si TFT. Our experimental results show that BC enables the device to have high mobility and switching frequency (33MHz at VDD=15V). The minority carrier elimination of CLBT suppresses kink effects and makes superb dynamic reliability of CMOS circuit.
Fabrication of a-Si:H Tfts at 120°C on Flexible Polyimide Substrates
Authors: Sazonov Andrei , Nathan Arokia , Murthy R.V.R. , Chamberlain S.G.
Published: April 2011

The fabrication of large-area thin-film transistor (TFT) arrays on thin flexible plastic substrates requires deposition of thin film layers at relatively low temperatures since the upper working temperature of low-cost plastic films should not exceed ∼200°C. In this paper, we report a fabrication process of a-Si:H TFTs at 120°C on flexible polyimide substrates for large-area imaging applications.

Kapton HN (DuPont) films 50 and 125 μm thick and 3 inches in diameter, were used as substrates. Both sides of the polyimide substrate were first covered with 0.5 μm thick a-SiNx. The TFT structure includes: 120 nm thick room-temperature sputtered Al gate, 250 nm thick PECVD deposited a-SiNx for the gate dielectric, 50 nm thick a-Si:H deposited by PECVD from silane-hydrogen gas mixture, 50 nm thick n+ a-Si:H source- and drain contacts, and roomtemperature sputtered Al top contact metallization. We used dry etching for all layers except for the gate and top metal, which were patterned using wet etchants. For purpose of TFT performance comparison, Coming 7059 glass substrates were used.

The performance of the fabricated TFT and its improvement with use of optimized a-Si:H and a-SiNx quality will be presented along with a discussion of the intrinsic mechanical stress in the thin film layers will also be discussed.
a-Si TFTs on Thin Steel Foil Substrates: How Thin Can We Go?
Authors: Ma Eugene , Wagner Sigurd
Published: April 2011

The mechanics of thin film-substrate couples indicates that mechanical stress in the active electronic layer can be reduced when films are deposited onto thinner substrates. To explore the question of just how thin a substrate can be, a-Si:H TFTs are fabricated on thin steel foil substrates of various thickness, and performance metrics from devices on each of the substrates are measured and compared.
Electrical Properties of Ultra Thin Tin Oxide Films
Authors: Matsui Yuji , Goto Yoshio
Published: April 2011

Tin Oxide transparent conductive oxide(TCO) films of less than 20nm in thickness was developed as a substrate for pen touch screens. The films were deposited using APCVD method by hydrolytic decomposition of stannic chloride. Electrical properties and stability to heat treatment were studied in relation to deposition conditions. We found the both properties depends mainly on fluorine concentration in the films. The stability was much improved at reduced fluorine concentration. The film which showed the stability to heat treatment at 600°C heat treatment was attained at the thickness of 20nm.
A Sims Study of Electroluminescent Phosphors: SrS:Cu
Authors: Zhang Lily H. , Wang Larry , Tong Wusheng , Xin YongBao
Published: April 2011

This study has used secondary ion mass spectrometry (SIMS) as a technique for thin film EL material characterization. It has shown that the Cu dopant concentration in the SrS films directly correlates with the luminescent brightness of the EL devices. A series of SrS:Cu, Y were grown using MBE to study the Y co-doping effects. It has been found that Y peak concentration and areal density in the SrS increased as the Y evaporation cell temperature was increased. The maximum PL intensity was found in the sample grown in the middle of the Y cell temperature range used. The Y co-doping has shown to reduce the thermal quenching effects in SrS EL devices. Therefore, in this series of samples, a good correlation has been found between Y and Cu concentration and the EL device performance characteristics.
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)-l,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.
Analysis of High-Current Yield of Diamond-Based Field Emitters
Authors: Zhimov Victor V. , Rinne C. Lizzul , Wojak Gregory , Hren John J.
Published: April 2011

The maximum emission currents of different diamond coatings were measured and compared quantitatively for the first time. Both the maximum current and the transconductance of field emission tips can be increased significantly by diamond coatings. A strong, nearly linear, dependence of Imax, on thickness was found. The relative effectiveness of CVD diamond, natural diamond, and nanodiamond can be characterized by values of ΔImax/ΔD and ΔVth/D. A quantitative estimate of the thermal conductivity of nanodiamond gave 2.71 W/cm K.
Field Emission from Polymers
Authors: Musa Ismail , Amaratunga G.A.J. , Eccleston W.
Published: April 2011

Carbon based materials are considered to be amongst the most promising field emitters for use in displays. Semiconducting polymer (regioregular poly3 octylthiophene) has been found by the authors to have the lowest threshold field reported to date for any carbon based material. The emission process is, we believe, associated with surface irregularities, voids, possibly resulting from solvent evaporation. Field intensification occurs, and as a consequence there is field emission from the top ridges of the voids. The current flowing through these regions is controlled by space charge in traps in the upper half of the energy gap. There is, in addition, current injected from the base of the voids and the two currents mix to give field emission with current IαV1.8 where V is the anode voltage. Measurements on capacitor samples using Aluminium, Gold and Calcium electrodes have been used to examine the conduction processes in the material and these are linked to results of field emission to further illuminate the mechanisms involved and provide a model for the emission process.
Low Phonon Concentration Lasing Glasses for 1.3 μm Amplification
Authors: Mennig M. , Groß F. , Lang I. , Sohling U. , Schmidt H.
Published: April 2011

Ge-Ga-S-glasses doped with 15000 mole-ppm Pr3+ have been developed for applications in optical amplifiers for 1.3 μm. The formation of crystalline phase separations in Ge 25 Ga10 S65could be suppressed by modification of the glass composition with Sb. Samples have been prepared by melting in sealed silica ampoules at 950°C. Ge-Ga-Sb-S-glasses, doped with 15000 mole ppm Pr3+, were synthesized by addition of Sb2S3up to contents of 14.3 mole% to the composition Ge25,Ga10S65. (corresponding to 83,3GeS2-16,7Ga2S3) or by replacing up to 50 mole% of Ga by Sb. Transparent to opaque glasses were obtained which were free from crystalline phase separations. The modification of the glasses with Sb leads to a remarkable decrease of the transformation temperature of the glasses. However, the temperature working range remains almost unaffected. The transparent glasses exhibit with 15 – 18 μs the same fluorescence lifetimes and the same fluorescence maximum position (1340– 1341 nm) and FWHM (63 μm) as the unmodified Ge-Ga-S-glass. The preparation process for both glass systems could be optimized to obtain monoliths with lengths of several centimeters and intrin- sic optical losses of only 0.05 dB/cm at 1.3 μm (after correction of reflection), which is of very high importance for the future development of planar amplifiers with remarkable net gain.
High Resolution Time and Frequency Resolved Spectroscopy for the Study of Photophysical Processes in Luminescent Materials
Authors: Farris Bruce , Smith Anthony , Martoglio Richard , Spangler Lee H.
Published: April 2011

A method for obtaining time and frequency resolved spectra with high spectral and temporal resolution over a broad spectral range is presented. Step – scan Fourier transform spectroscopy permits spectral coverage from UV to mid IR with sub nanosecond resolution making it possible to track emission from multiple manifolds with full temporal resolution in a single experiment. Data for several rare-earth doped crystalline materials exhibiting multiple emission bands and including evidence of energy transfer is shown.
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.
Application of Photoacoustic Spectroscopy to Porous Silicon
Authors: Ohmukai Masato , Kobayashi Akiharu , Uehara Nobutomo , Yamazaki Tetsuya , Fujihara Shinji , Tsutsumi Yasuo
Published: April 2011

We are investigating applicability of photoacoustic (PA) spectroscopy to porous silicon. Since PA spectroscopy is based on a non-radiative relaxation process, the measurement is of importance as a counterpart to photoluminescent spectroscopy. We studied a dependence of a PA amplitude on a chopping frequency and discussed the influence of a PA signal originated in a silicon substrate. The frequency dependence was elucidated with a two-layer model. Differences in PA spectra are correlated with a photoluminescent efficiency. From the correlation, we believe that non-radiative centers quench the efficiency.
Effects of Gas Environments on Porous Silicon Photoluminescence
Authors: Francia G. Di , Ferrara V. La , Lancellotti L. , Quercia L. , Fasolino T.
Published: April 2011

The photoluminescence response of a series of porous silicon samples, obtained by electrochemical etching of n-type CZ-silicon, has been recorded in various gas environments. A quenching is reported when porous silicon is in the presence of an oxidising ambient (dry air or acetone vapours in dry air). Process reversibility depends on the duration of laser illumination. Quenching is also recorded if porous silicon is in the presence of acetone vapours in nitrogen ambient, where complete reversibility is however shown. Moreover, the peak wavelength is red shifted in dry air and blue shifted in acetone vapours. Irreversible quenching is related to the growth of a thin oxide layer on the emitting nanostrucures.
Strong Activator-Host Interaction in Rare Earth Borate Phosphors
Authors: Mordkovich V.Z. , Umnov A.G. , Inoshita T.
Published: April 2011

Ce3+ luminescence in yttrium cerium aluminium borates was studied. A substantial red shift in photoluminescence and low-voltage cathodoluminescence spectra was found to be induced by Ce concentration increase. Complicated concentration dependence of emission intensity and strong influence of cerium content on emission wavelength suggest strong activator-host interaction in rare earth borates.
Color Engineering of Garnet Based Phosphors for Luminescence Conversion Light Emitting Diodes (Lucoleds)
Authors: Batentschuk M. , Schmitt B. , Schneider J. , Winnacker A.
Published: April 2011

For white light generation with LUCOLEDs the phosphors on the base of YAG:Ce are ideally suited. The variation of the phosphor composition were performed. Powder Ga-substituted phosphors as well as Lu,Y,La,Sc- substituted epitaxial films were investigated. The effects on luminescence and excitation spectra, which is relevant for luminescence conversion, are reported.
Energy Transfer in Erbium-Doped Silicon Nanoclusters: A Comparison of Silicon-Rich Silica and Silicon Nanopowders
Authors: Kenyon A.J. , Botti S. , Chryssou C.E. , Trwoga P.F. , Pitt C.W.
Published: April 2011

A number of groups have demonstrated an efficient excitation transfer mechanism in erbium-doped crystalline and porous silicon. It has been postulated that this is a carrier-mediated transfer, which points to the possibility of fabricating efficient silicon-based 1.5 µm emitters.

We have previously reported the existence of a similar transfer mechanism in silicon-rich silica. In this paper we extend this study to include silicon nanopowders and demonstrate the existence of the same mechanism. Comparing the photoluminescence excitation spectra of erbium doped silica, silicon-rich silica and silicon nanopowders we show that the coupling mechanism enables broad-band pumping of the rare-earth ion.

We have also measured carrier lifetimes in the nanoclustered silicon materials using photoinduced free carrier decay. The measured lifetimes are surprisingly long (in the 2-10 millisecond regime), and we discuss the effect of this on the transfer mechanism.
Optimization of Mixed Storage Phosphors of the Type (Ba,Sr)F1+xBr1−x:Eu for Digital X-Ray Radiography
Authors: Batentschuk M. , Hackenschmied P. , Winnacker A. , Moll M. , Fasbender R.
Published: April 2011

The possibility of further improving the sensitivity of the widely used BaFBr:Eu X-ray storage phosphor is investigated. The influence of CsF- and EuF3-doping on the stimulation spectrum is identical to the one of other ways to vary F/Br-ratio of this mixed crystal. The effect of CsF-doping turns out to be not primarily due to a replacement of Ba2+ by Cs1+ and subsequent charge comensation, but rather to the change in the F/Br ratio. Sr doping not only gives rise to FA(Br; Sr2+)-center formation but, at the same time increases the PSL-response in the bands ascribed to F(Br -)-centers.
Film Preparation Conditions and Characterization of Co-Deposited Tungsten Doped Zinc Oxide Phosphor
Authors: Sobti Jasleen Bombra , Bhatia V. , Babuchna P. M. , Weichold Mark H.
Published: April 2011

Need for efficient blue light emitting source for optoelectronic device applications such as flat panel displays has made the research in luminescent material ever so important. Tungsten doped zinc oxide (ZnO:W) has been identified as a blue light emitting phosphor exhibiting cathodoluminescence near 490 tim. This paper details work done on ZnO:W phosphor preparation conditions for efficient light emission from the phosphor. Material characterization to identify the possible source of blue light emission will also be discussed.
Preparation and Luminescence of Europium Doped Zinc Silicate Phosphor
Authors: Zhang H. X. , Zhou Y. , Kam C. H. , Lam Y. L. , Chan Y. C.
Published: April 2011

Europium doped zinc silicate (Eu:Zn2SiO4) phosphors in the forms of nanoscale powder and film has been prepared by sol-gel method. XRD analysis indicz: ed that the powders have willemite structure with a small amount of triclinic structure and the filn has, pure willemite structure. Photoluminescence measurement showed that strong red emission of Eu3+5D0→7 F2transition could be obtained under excitation at both 256 and 393 nm. Luminescence decay of the emission under 393 nm excitation can be fitted by a single exponential, yielding a decay time τ =1.43 ms; and the luminescence under 256 nm excitation shows double exponential decay with a slow decay time τs,=2.13 ms and a fast decay time τf =2.05 ms.
Time-Resolved Transport of Electrons and Holes in Conjugated Polymers
Authors: Pinner D. , Friend R. H. , Tessler N.
Published: April 2011

Detailed experimental and theoretical analysis of the pulsed excitation of polymer light emitting diodes is presented. We find a set of universal transient features for different device configurations which can be reproduced using our phenomenological numerical model. We find that the temporal evolution of the electroluminescence can be characterised by five main features: i) a delay followed by; ii) fast initial rise at turn-on followed by; iii) a slow rise (slower by at least one order of magnitude); iv) fast modulation (<15ns, unresolved) at turn-off followed by v) a long-lived exponential tail. We suggest a method for extracting mobility values which is found to be compatible with CW drive schemes. Mobilities for holes and electrons are extracted for a poly(p-phenylenevinylene) co-polymer and poly(di-octyl fluorene).
Photovoltage in Conjugated Polymer Photovoltaics with a Titanium Dioxide Anode
Authors: Arango A. C. , Brock P. J. , Carter S. A.
Published: April 2011

We study the photovoltaic response of inorganic/organic composite devices containing the conjugated polymer, MEH-PPV, and a semi-transparent layer of titanium dioxide (TiO2) nanoparticles, which is similar to that employed in the Grätzel photoelectrochemical cell. Comparison of the photovoltage obtainable under illumination with either a Au, Ag, Al or Ca back electrode suggests that the built in potential is determined largely by the difference between the quasi Fermi level of the TiO2 under illumination and the work function of the back electrode. A qualitative model for charge generation and transport through the device is presented.
Improving the Crystallization Resistance of Aluminum(III) 8-Hydroxyquinoline-Based Emitting Materials by Entropic Stabilization
Authors: Higginson Keith A. , Yang Baocheng , Papadimitrakopoulos Fotios
Published: April 2011

The morphological stability of evaporated films of aluminum(III) 8-hydroxyquinoline (Alq3) was investigated. Films which were found to be non-crystalline by x-ray diffraction upon deposition, crystallized rapidly upon annealing, especially where defects were present. Blends of Alq3with aluminum(III) 5-methyl-8-hydroxyquinoline were proposed for thermally stable amorphous emitting layers in light-emitting diodes. Films coevaporated at a 1:1 ratio did not show evidence of crystallization or phase separation even after long annealing periods at temperatures as high as 160°C.
Conjugated Poly-P-Phenylene (PPP) From Poly(1,3-Cyclohexadiene) (PCHD) Homo- and Block Copolymers: Controlled Processability and Properties
Authors: Mays J. , Hong K. , Wang Y. , Advincula R.C.
Published: April 2011

Conjugated polymers have been used as solid-state materials for a variety of opto-electronic applications. Thus, their processability in a number of device fabrication protocols is an important consideration. In this report, we indicate our results on the synthesis of conjugated poly-p-phenylene (PPP) materials derived from poly(1,3-cyclohexadiene) (PCHD). The precursor PCHD polymers were synthesized by living anionic polymerization to produce homo-and block copolymer configurations with polystyrene. We have used a variety of initiators, solvent, and temperature conditions to determine the right parameters for obtaining narrow MWD polymers. The conditions for polymerization determined the ratio of 1,2 and 1,4 isomers in the microstructure. We then proceeded with conversion to PPP derivatives using a dehydrogenation reaction with chloranil. Our results indicate a systematic conversion to a conjugated polymer with increased solubility and photoluminescence properties. The microstructure, MW and block copolymer composition affecting the processability and conversion properties dramatically.
Bridged Polysilsesquioxanes with Improved Second Order Nonlinear Optical Properties and Stability
Authors: Hobson S. T. , Zieba J. , Prasad P. N. , Shea K. J.
Published: April 2011

We report the synthesis and sol-gel polymerization of 4-nitro-N,N-bis[(3- triethoxysilyl)propyl]aniline 1. An efficient synthesis of the monomer was developed by the hydrosilylation of N, N-diallyl-4-nitroaniline. Optical quality thin films were synthesized by spin coating an n-butanol solution of 1 using formic acid as catalyst and source of water. We improved the temporal stability of the NLO signal from films prepared from 4-nitro-N,N-bis[(3-triethoxysilyl)propyl]aniline by increasing the intensity of the poling field and extending the heating period during the poling/curing stage. By Maker fringe analysis, a X(2) value of 9 × 10−8 esu was measured for these polysilsesquioxanes. If one assumes that the major component of the NLO effect is along the z-axis, the X(2) value corresponds to a d33 coefficient of 18.9 pm/V and a r33 value of 4.7 pm/V.
Electrical Field Effects on Crystalline Perfection of MBA-NP Crystals by Mapping of Bragg-Surface Diffraction
Authors: Morelhão S.L. , Avanci L.H. , Hayashi M.A. , Cardoso L.P.
Published: April 2011

The interaction of weak electrical field with the molecular dipole of the MBA-NP crystals is investigated. Such interaction affects the misorientation and size of the perfect diffracting regions of the crystal, which is monitored by mapping the Bragg-surface diffraction condition. This diffraction technique has also confirmed that the diffracting regions are large enough to allow primary extinction and the non-uniform mosaicity along the crystal surface.
Synthesis and Characterization of Some New Metal-Containing Polymers for Third Order Nonlinear Optical Applications
Authors: Bader Mamoun M. , Pham Phuong-Truc T. , Molli Angela , Moser Justin , Meyres Kevin , Albright Leslie
Published: April 2011

We report here our preliminary results on the synthesis and characterization of a new family of metal-containing polymers incorporating 8-hydroxyquinoline. These polymers have the following structural features: a metal center, a chromophore, and a flexible spacer group with variable length. These structural features allow us to have an appreciable degree of control over various physical properties of these materials. We report on three different types of polymers: polyethers, polyesters, and polyamides. The chromophores in these polymers were incorporated in the backbone and in one case as a side chain of polyesters.
A Detailed Study of Void Motion In Passivated Aluminum Interconnects
Authors: Doan Jonathan C. , Bravman John C. , Flinn Paul A. , Marieb Thomas N.
Published: April 2011

Void motion can be an important part of electromigration failure in interconnects. Investigating this process is difficult due to the large variation in behavior in identical samples tested under identical conditions. To deal with the large variability, we have tested 50 samples to failure at four different accelerated test conditions. Because our automated, in-situ technique images an entire test structure, the complete history of a test line is recorded. By testing many samples under direct observation, the complex motion of electromigration voids was comprehensively studied.
Cause of the Decrease in Electromigration Resistance in Am/Al3Ti Lines
Authors: Kameyama A. , Masuzaki K. , Okabayashi H. , Sakata T. , Mori H.
Published: April 2011

To investigate the cause of the lower electromigration (EM) resistance in Al/Al3Ti lines compared to that in Al/TiN lines, we studied the Al microstructure and the EM characteristics. Even after fine-grained Al3Ti formation through a reaction of the Al and Ti, the Al microstructure of the unreacted Al on the AI3Ti remained a bamboo grain structure with a high 111 orientation. Thus, the Al grain structure and texture did not affect the EM resistance. The critical current density for voiding was 0.64 MA/cm2. The Al drift velocity in the Al/Al3Ti bamboo lines was two orders of magnitude higher than that for Al/TiN bamboo lines from 180°C to 280°C. This higher Al drift velocity decreased the EM resistance in the lines. The activation energy of Al drift in the AI/AI3Ti lines was 0.6 to 0.7 eV, which is lower than that for Al lattice diffusion. Thus, the Al lattice is not the dominant transport path in Al/Al3Ti lines. The dependence of the Al drift velocity on the line size showed that the Al/Al3Ti interface was the dominant path in the Al/Al3Ti bamboo lines. Thus, we concluded that the rapid Al transport through the Al/Al3Ti interface decreases EM resistance in Al/Al3Ti lines.
Evaluation of Current Ramp Test for In-Line Electromigration Test
Authors: Low Kia Seng , Glasow Alex v. , Poetzlberger Hans
Published: April 2011

Current ramp tests are performed in a number of experiments to check their validity as an in-line monitoring tool for electromigration evaluation. We discuss our various findings from a series of experiments conducted to validate the usefulness of the current ramp test, using the standard NIST test structure. First, we check whether the current ramp test, using breakdown energy of metal (BEM test), shows the effect of a Ti/TiN underlayer on the reliability of A1–0.5wt%Cu unpassivated interconnects. The second experiment compares current ramp testing with fuse testing. Next we check if current ramp testing gives any indication of interconnect quality following different stages of our sputtering process, and in particular different degas temperatures. The last experiment tries to correlate the breakdown energy obtained from current ramp testing with the lifetime obtained from conventional long term electromigration testing of different combinations of line stack and line stack dimensions. From the results of the experiments, we conclude that current ramp testing using the breakdown energy of metals cannot be used quantitatively for electromigration evaluation using conventional NIST test structures.
X-Ray Microbeam Studies of Electromigration
Authors: Cargill III G. S. , Ho A. C. , Hwang K. J. , Kao H. K. , Wang P.-C. , Hu C.-K.
Published: April 2011

The interplay between stress and electromigration has been recognized since I. A. Blech et al. used x-ray topography in 1976 to demonstrate that stress gradients developed during electromigration. Availability of high brightness synchrotron x-ray sources, high stability energy dispersive detectors, high resolution area detectors, and pinholes, capillaries and other optical elements for forming x-ray microbeams, has made possible more quantitative, real time measurements of strains and composition changes which develop in polycrystalline metal conductor lines during electromigration. This paper describes advances made in this area, implications of results which have been obtained, and prospects for further progress.
In-Situ X-Ray Microbeam Cu Fluorescence and Strain Measurements on Al(0.5 AT.% Cu) Conductor Lines During Electromigration
Authors: Kao H.-K. , III G. S. Cargill , Hwang K. J. , Ho A. C. , Wang P.-C. , Hu C.-K.
Published: April 2011

We have used x-ray microbeam fluorescence and diffraction for in-situ measurements of Cu concentration and strain during 36 hours of electromigration with current density 5×105 A/cm2 at temperature 310°C for a passivated 10μm-wide, 200μm-long Al(0.5 at.% Cu) conductor line. These measurements indicate that Cu is quickly depleted at the cathode end of the line and is piled up at the anode end, where the Cu concentration first increases, then decreases, and finally remains constant. A void begins growing at the cathode end of the line about two hours after the start of current flow, with a nearly constant void growth rate of 1 μm/hr for the remainder of the test. The evolution of stresses within the line during electromigration involves changes by 100's of MPa and is more complex than seen previously for electromigration under similar conditions for pure Al conductor lines.
X-Ray Microbeam Measurement of Local Texture and Strain in Metals
Authors: Chung Jin-Seok , Tamura N. , Ice G. E. , Larson B. C. , Budai J. D.
Published: April 2011

Synchrotron x-ray sources provide high-brilliance beams that can be focused to submicron sizes with Fresnel zone-plate and x-ray mirror optics. With these intense, tunable or broadbandpass x-ray microbeams, it is now possible to study texture and strain distributions in surfaces, and in buried or encapsulated thin films. The full strain tensor and local texture can be determined by measuring the unit cell parameters of strained material. With monochromatic or tunable radiation, at least three independent reflections are needed to determine the orientation and unit cell parameters of an unknown crystal. With broadbandpass or white radiation, at least four reflections and one measured energy are required to determine the orientation and the unit cell parameters of an unknown crystal. Routine measurement of local texture and strain is made possible by automatic indexing of the Laue reflections combined with precision calibration of the monochromator-focusing mirrors-CCD detector system. Methods used in implementing these techniques on the MHATT-CAT beam line at the Advanced Photon Source will be discussed.
Effect of a Titanium Interlayer on the Performance of the Titanium Nitride Diffusion Barrier
Authors: Lu K. Y , Chen J. S.
Published: April 2011

We have studied the effect of a Ti interlayer on the behavior of a TiN diffusion barrier for Al and Cu metallizations. Thermal stability of Al/Ti/TiN/ and Al/TiN/ samples annealed at 400–600°C for 30 min was investigated using Auger electron spectroscopy (AES), glancing angle X-ray diffraction and scanning electron microscopy (SEM). Sheet resistance was measured for electrical characterization.

After annealing at 400°C and 500°C, the AI/TiN/ samples exhibited the same sheet resistance as the as-deposited one, while the sheet resistances of the Al/Ti/TiN/ samples increased upon annealing. After annealing at 600°C, pyramidal pits developed on the surface of the Al/TiN/ sample, but not on the Al/Ti/TiN/ sample. Sheet resistance measurements for the 600°C-annealed Al/TiN/ sample resulted in a more scattered distribution and a higher average value than for the Al/Ti/TiN/ sample. The results clearly indicate that the performance of the TiN barrier layer is significantly improved by including a thin Ti film between the TiN and the Al. The Ti interlayer also improves the TiN barrier performance for the Cu metallization system.
Macroscopic Modeling of Fine Line Adhesion Tests
Authors: Volinsky A. A. , Nelson J. C. , Gerberich W. W.
Published: April 2011

Microwedge Indentation (MWIT) and Precracked Line Scratch (PLST) tests have been developed for adhesion measurements of microscale fine lines. In the MWIT a symmetric wedge-shaped probe is driven downward into a thin film line debonding it from the substrate. For the PLST, a precrack is introduced at one end of a thin metal line on a substrate. The line is loaded from the precrack end by an asymmetric diamond wedge until the crack propagates. When the crack reaches its critical length at a certain critical load, the film buckles.

The mechanics of these tests are based on several assumptions of thin line behavior, which are not experimentally observable due to small line sizes and equipment limitations. Testing similar but larger lines allows for the direct observation of line delamination and buckling, which can be used for calculating in-situ crack lengths as well as instantaneous strain energy release rates.

Both MWIT and PLST models [1–4] were experimentally verified on the macroscopic scale using polycarbonate as a line material bonded to a steel substrate with cyanoacrylate. New features such as initial crack growth as well as instantaneous crack growth at buckling were observed. Modified Kic tests were performed for strain energy release rate comparison. Adhesion values ranging from 200 to 1000 J/m2 were measured for this system, and had very strong mode mixity dependence. Connectivity to the microscale is through previous experiments by de Boer, et al using fine line W/SiO2/Si systems [ 1–4].
TiB2as a Diffusion Barrier for Cu/ Metallization
Authors: Wang J. L. , Chen J. S.
Published: April 2011

TiB2, films deposited by co-sputtering from a boron and a TiB, target are evaluated as the diffusion barrier for Cu metallization. Material characteristics of the TiB, films and metallurgical interactions of the Cu/TiB2/ system annealed at 400−700°C for 30 min, in a 80%Ar+20%H2 flow, were investigated by glancing angle X-ray diffraction, Auger electron spectroscopy (AES), and scanning electron microscopy (SEM). Sheet resistance was measured for electrical characterization.

The composition and resistivity of the sputtered TiB1 films varied with the bias applied on the substrate. To obtain a low film resistivity, a negative bias of 200V was applied during sputtering. The resulting TiB2 film is nanocrystalline with a resistivity of 300 μΩcm. After copper deposition, the Cu/TiB2/ samples have a constant sheet resistance after annealing up to 600°C for 30min. The overall sheet resistance of the sample increases by five orders of magnitude after annealing at 700°C, and scanning electron micrographs reveal that the sample surface is severely deteriorated after annealing at 700°C.
Immortal InterConnects—Prevent Cracking and Limit Void Size
Authors: Suo Z. , Ma Q. , Meyer W. K.
Published: April 2011

This paper considers an aluminum line in a multilevel interconnect structure. Upon cooling from the processing temperature, differential thermal contraction causes a triaxial tensile stress state in the aluminum line; voids may initiate and grow to relax the stress. When a direct voltage is applied, the electric current causes aluminum atoms to diffuse. The interconnect will evolve to a state with a high pressure at the anode, and a large void at the cathode. The pressure may crack the surrounding insulator or debond an interface, extruding aluminum. The void may uncover the via contact area, substantially increasing electrical resistance. Provided neither failure mode occurs, aluminum electromigration will stop and the interconnect will function forever. This paper examines the conditions under which the interconnect is immortal.
Interconnect Reliability Study Using a Microscopic Nucleation Model for Electromigration
Authors: Tammaro M. , Setlik B.
Published: April 2011

A microscopic nucleation model for electromigration is proposed. The solution to the master equations for site occupancy produces a variable current exponent with 1 < n < 2. These results disprove previous claims that n = 2 in nucleation models. We also address the long-standing speculation regarding an additional temperature dependence in Black's equation. Under the premise that the activation energy in Black's equation, Ea, should be equal to the energy barrier for atomic hopping, we provide evidence for an additional T2 dependence of the failure time. Microscopic modeling provides an explicit connection between the macroscopic model behavior and the microscopic parameters of the model. A continuum treatment of our model is derived and compared with standard continuum treatments.
Electromigration Voiding in Argon-Implanted Interconnects
Authors: Meier N. E. , Doan J. C. , Marieb T. N. , Flinn P. A. , Bravman J. C.
Published: April 2011

Electromigration is a complex process consisting of the nucleation, growth, and movement of voids. While interconnect microstructure plays a major role in determining void nucleation time and location of void nucleation, recent studies have shown that this is not the only contributing factor. Thermodynamics and kinetics-based calculations by Flinn and Gleixner et al. have shown that electromigration void nucleation by vacancy condensation at both homogeneous and heterogeneous sites will not occur at a reasonable rate without a mechanism for reducing or altogether eliminating the energy barrier for nucleation. By implanting argon ions into the aluminum interconnect lines, we introduce an initial defect population (argon bubbles) of controlled size and location.

Tests were performed in a high-voltage SEM (120 keV), which enables in-situ observation of the voiding process through the passivation layer. Images taken throughout the in-situ tests were analyzed to determine void nucleation times and locations. In the argon-implanted interconnects, ten of the 15 voids that nucleated were within implanted regions. Voids nucleated in the interior of the line within the implanted regions, as well as at the passivation/sidewall interface where voids are typically seen in conventional electromigration tests. In addition, voids in implanted regions nucleated much more quickly than those in unimplanted regions. These observations support the idea of argon bubbles reducing the nucleation barrier. TEM was used to analyze the microstructure of both control and implanted interconnect lines.
A Beem Study of PtSi Schottky Contacts on Ion-Milled Si
Authors: Ru Guo-Ping , Detavernier C. , Donaton R. A. , Blondeel A. , Clauws P. , Meirhaeghe R. L. Van , Cardon F. , Maex K. , Qu Xin-Ping , Zhu Shi-Yang , Li Bing-Zong
Published: April 2011

Ballistic electron emission microscopy (BEEM) and deep level transient spectroscopy (DLTS) have been used to study the effects of substrate damage introduced by an ion-milling process in PtSi/n-Si Schottky contacts. Argon ions with well-defined energies of 300, 500, 700, 1000, 1500 eV were used to sputter n-type Si substrates in an ion beam sputtering system before metal deposition and silicide formation. Histograms of the PtSi/n-Si Schottky barrier height (SBH) measured by BEEM show that the mean SBH decreases with increasing ion energy, which can be explained as a result of donor-like defects that are introduced by the ion milling treatment. From DLTS measurements, we found direct evidence for the presence of such defects.
Growth Kinetics Of SiO2 On (001)Si Catalyzed By Cu3Si At Elevated Temperatures
Authors: Huang H. Y. , Chen L. J.
Published: April 2011

The oxidation of Si catalyzed by 170-nm-thick Cu3Si at elevated temperatures has been investigated by transmission electron microscopy and Auger electron spectroscopy. For wet oxidation at 140–180 °C, the growth rate of the oxide layer was increased with the temperature. On the other hand, as the temperature was increased above 200 °C, the growth rate slowed down. The growth kinetics of oxide was investigated. Controlling mechanisms for the growth of oxide owing to the grain growth of Cu3Si are discussed. The activation energy for the linear growth of oxide was measured to be 0. 19 ± 0.1 eV.