bluuebunny/crossref_metadata_2025 huggingface dataset:
The Recrystallization Depth Control of the Excimer-Laser-Recrystallized Poly-Crystalline Silicon Film
Authors: Park Kee-Chan , Choi Kwon-Young , Jeon Jae-Hong , Lee Min-Cheol , Han Min-Koo
Published: April 2011

A novel method to control the recrystallization depth of amorphous silicon (a-Si) film during the excimer laser annealing (ELA) is proposed in order to preserve a-Si that is useful for fabrication of poly-Si TFT with a-Si offset in the channel. A XeCl excimer laser beam is irradiated on a triple film structure of a-Si thin native silicon oxide (~20Å)/thick a-Si layer. Only the upper a-Si film is recrystallized by the laser beam irradiation, whereas the lower thick a-Si film remains amorphous because the thin native silicon oxide layer stops the grain growth of the poly-crystalline silicon (poly-Si). So that the thin oxide film sharply divides the upper poly-Si from the lower a-Si.
Novel Amorphous Silicon Solar Cell using a Manufacturing Procedure with a Temporary Superstrate
Authors: Schropp R.E.I. , Werf C.H.M. Van Der , Zeman M. , Sanden M.C.M. Van de , Spee C.I.M.A. , Middelman E. , Jonge-Meschaninova L.V. de , Peters P.M.G.M. , Zijden A.A.M. Van der , Besselink M.M. , Severens R.J. , Winkeler J. , Jongerden G.J.
Published: April 2011

We developed a novel temporary-superstrate concept for SnO2/p-i-n amorphous silicon solar cells. This concept combines roll-to-roll manufacturability, the utilization of light scattering, the conductive properties of SnO2:F, and the possibility of monolithic series connection. To this purpose, the deposition of high quality textured SnO2:F layers on aluminum foil has been developed using APCVD. Layers have been obtained with a transmission of 80 % and a sheet resistance of 12 Ω/□. After definition of the entire p-i-n cell structure including the back contact, the cell is laminated with a permanent carrier foil. By removing the aluminum foil, light can enter the cell through the textured TCO layer. A wide variety of transparent encapsulants can be used to finalize the (flexible or preshaped) product. Preliminary cells made according to this scheme have an efficiency of 6 %.
Effect of Interface Roughness on Light Scattering and Optical Properties of a-Si:H Solar Cells
Authors: Zeman M. , Swaau R.A.C.M.M. Van , Zuiddam M. , Metselaar J.W. , Schropp R.E.I.
Published: April 2011

The effect of interface roughness on the optical properties of amorphous silicon (a-Si:H) solar cells was investigated using rms roughness measurements and computer modeling. We deposited four single junction a-Si:H solar cells on Asahi U type substrate each with a different intrinsic layer thickness. The roughness of the substrate and of the subsequent interfaces of the cells was measured by Atomic Force Microscopy. The relations between the computer input parameters, which describe the diffuse part of reflected and transmitted light at a rough interface, and the rms roughness of the interfaces in a-Si:H solar cell are presented. After obtaining a good matching between the simulated and measured external quantum efficiencies (QE) of the four cells, we investigated the effect of interface roughness on the absorption in all individual layers of the a-Si:H solar cell using the determined scattering parameters.

The rms roughness of the Asahi U-type substrate surface is determined to be 40 nm. Deposition of a 9 nm thick p-type a-SiC:H layer on the substrate has not changed the surface roughness. Due to a high refractive index of n-type a-Si:H the back contact interface acts as a nearly perfect diffuser for the reflected light when the rms roughness of the interface is higher than 25 nm. The rms roughness of the back interface of the four cells is found to be dependent on the intrinsic layer thickness and is larger than 25 nm.
Material Requirements for Buffer Layers Used to Obtain Solar Cells with High Open Circuit Voltages
Authors: Roedern Bolko Von , Bauer Gottfried H.
Published: April 2011

This paper discusses material requirements for junction layers needed to obtain solar cells with highest possible open-circuit voltages (VOC). In a typical a-Si:H-based “p/i/n” solar cell, this includes the transparent conductive oxide (TCO) contact layer, the p-layer, a “buffer layer” inserted at the p/i interface, and the surface portion of the intrinsic layer. In HIT-cells, the i-layer between (n-type) c-Si and (p-type) a-Si:H may be regarded as the buffer. Our suggestion to obtain high values of VOC relies on using materials with high lifetimes and low carrier mobilities that are capable of reducing surface or junction recombination by reducing the flow of carriers into this loss-pathway. We provide a general calculation that supports these approaches and can explain why these schemes are beneficial for all solar cells.
Simulation of Hydrogenated Amorphous Silicon Germanium Alloys for Bandgap Grading
Authors: Schroten E. , Zeman M. , Swaaij R. A. C. M. M. van , Vosteen L. L. A. , Metselaar J. W.
Published: April 2011

Computer simulations are reported of hydrogenated amorphous silicon germanium (a-SiGe:H) layers that make up the graded part of the intrinsic layer near the interfaces of a-SiGe:H solar cells. Therefore the graded part is approached with a ‘staircase’ bandgap profile, consisting of three layers within which the material properties are constant. Calibrated model parameters are obtained by matching simulation results of material properties of intrinsic a-SiGe:H single layers to measurements. Using the obtained model parameter sets subsequent simulations of p-i-n devices with intrinsic material similar to the single layers are matched to measured current-voltage characteristics. The changes in parameter values are evaluated as a function of optical gap.
Application of Thin-Film Micromachining for Large-Area Substrates
Authors: Boucinha M. , Chu V. , Soares V. , Condee J. P.
Published: April 2011

Surface micromachining is used with amorphous silicon, microcrystalline silicon, silicon nitride and aluminum films as structural materials to form bridge and cantilever structures. Low temperature processing (between 110 and 250 °C) allowed fabrication of structures and devices on glass substrates. Two processes involving different materials as the sacrificial layer are presented: silicon nitride and photoresist. The mechanical integrity of the fabricated structures is discussed. As examples of possible device applications of this technology, air-gap thin film transistors and the electrostatic actuation of bridges and cantilevers are presented.
Deposition of High Quality Amorphous Silicon by a New “Hot Wire” CVD Technique
Authors: Morrison Scott , Coates Ken , Xi Jianping , Madan Arun
Published: April 2011

For the “Hot Wire” chemical vapor deposition technique (HWCVD) method to be applicable for photovoltaic applications, certain critical technical issues need to be addressed and resolved such as: lifetime of the filaments, reproducibility, large area demonstration of the material and stable devices. We have developed a new approach (patent applied for) which addresses some of these problems, specifically longevity of the filaments and reproducibility of the materials produced. The new filament material used has so far shown no appreciable degradation even after deposition of >200 μm of amorphous silicon (a-Si). We report that this can produce “state-ofthe-art” a-Si with a dark conductivity of <10-10 (Ohm*cm)-1 and photoconductivity of >10-5 (Ohm*cm)-1 this material can also be doped p- or n-type. We also provide data using XRD as well as the Raman spectra. These materials have been incorporated into simple Schottky barrier structures. The development of microcrystalline silicon materials is also discussed.
Properties of Electron Emitting Diode Fabricated with Single-Crystalline Diamond
Authors: Ito Toshimichi , Nishimura Masaki
Published: April 2011

Highly efficient electron emitting diodes have been fabricated using single-crystalline diamond films epitaxially grown on high-pressure synthesized (100) diamond. These diodes have an internal electrode of a graphitized layer buried below an overgrown diamond layer with a very high resistivity, the structure of which is formed by a combination of heavy ionimplantation and overgrowth techniques. The efficiency of electron emissions from sufficiently hydrogenated p-type diamond surfaces reached 100% in the best case. It is found that H atoms can passivate internal defects created during the ion implantation process. The mechanism of the high efficiency is discussed in relation to electron-hole creations in the thin diamond layer under extremely high electric fields of 107 V/cm.
Fabrication of Planar Diamond Electron Emitters for Flat Panel Displays
Authors: Kawamura H. , Kato S. , Maki T. , Kobayashi T.
Published: April 2011

A planar electron emitter was fabricated employing chemical vapor deposited (CVD) diamond thin films. This device is composed of CVD diamond films selectively deposited on a pair of patterned Au/Cr films separated 2 micrometers from each other. When the driving voltage (Vd) was applied between the Au/Cr films, the extremely low threshold emission from diamond film was observed (Vd ∼ 10 V). Furthermore, by applying high voltage on anode screen placed above this device, part of emitted current was drawn to the anode and the luminescence from phosphors was clearly seen under Vd = 50V. The mechanism of electron emission from the diamond films used in this device was also discussed by comparing with the electron emission from isolated diamond particles. It was found that the effective work functions differ between the isolated particles and the continuous films. This result suggests a difference in the emission site of electrons.
Changes of Contact Potential Difference Induced by Frictional Damage in Ultrahigh Vacuum
Authors: Zhang L. , Nakayama K.
Published: April 2011

The work function is one of the most fundamental properties of a metal surface. To clarify frictional electrification phenomena, the effects of frictional damage on the contact potential difference (CPD), which is defined by the difference between the work functions of two contacting surfaces, were investigated. Au(111) and Si(111) surfaces were scratched in an ultrahigh vacuum under a light load with the Si cantilever tip of an atomic force microscope. The contact potential difference between the scratched surface and the tip whose work function was known was measured using an ultrahigh vacuum scanning Kelvin probe force microscope (SKPM). Simultaneously, the noncontact atomic force microscope (NC-AFM) images were observed in situ. The CPD images showed clear changes between the areas with and without scratching, corresponding to the scratching track on the NC-AFM images.
Ito/A-Si:H Schottky Photodiode With Low Leakage Current And High Stability
Authors: Ma Qinghua , Nathan Arokia , Murthy R.V.R.
Published: April 2011

We report the design, fabrication, and characterization of an indium tin oxide/hydrogenated amorphous silicon (ITO/a-Si:H) Schottky photodiode based on room temperature deposition of ITO. The optical transmittance of the ITO is larger than 80% in the visible light range and its resistivity is less than 6 x 10-4 Ω-cm. The fabricated photodiode exhibits low leakage current and stable I-V characteristics. The leakage current is 7x10-10 A/cm2when biased at -2 V and the shift in leakage current stabilizes to a value less than 9% after 2 seconds of biasing at -2 V. The improvement in performance can be attributed to the high integrity ITO/a-Si:H interface achieved with the low temperature deposition.
Properties of Image Sensor Structure Obtained Below 120°C On The Foil By Reactive Magnetron Sputtering
Authors: Kolodziej A. , Krewniak P. , Tadeusiewicz R.
Published: April 2011

Polyimide substrates are of interest because of their thermal stability, light weight, and good mechanical characteristics. This paper reports thermal control multilayer deposition experiments which have strongly affected the properties of the image sensor structure (TFT + photodiode). Particularly TFT properties have been studied with respect to difficulties of obtaining of good quality a-SiNx:H films at temperature below 120°C. We characterize the structural properties using infrared absorption, refractive index measurements, small angle x-ray diffraction and the optoelectrical measurements of the TFT and PIN diode structure. The linear image sensor consisting of two rows, 40 pixels per row, with dimensions 0.6 mm2was made on the polyimide foil.
Large Area, Full-Color Image Sensors Made with Organic Semiconductors
Authors: Yu G. , Srdanov G. , Wang J. , Heeger A.J.
Published: April 2011

Large area polymer photodiode arrays were designed and fabricated for full-color imaging applications. These sensor arrays are of high photosensitivity, low dark current, large dynamic range and fast response time. The red, green and blue color primaries were achieved by coupling a set of color filters with the polymer sensor pixels with broad response covering entire visible spectrum. Image recovery process from the pixel photocurrent data was developed, which is suitable generally to image arrays with power-law light intensity dependence and with finite pixel dark current. Large sensing length photodiode arrays (2.5”5”) were fabricated with pixel densities from 40 to 100 dot-per-inch. They were used as the sensing elements in page size document scanners. Voltage switchable polymer photodetectors were developed. Their photosensitivity can be switched on and off with external bias. These devices can be used as the sensing elements in x-y addressable two-dimensional sensor matrices. The high on/off switching ratio and high photocurrent/dark-current ratio allow such two-dimensional, passive photosensor matrices be used for image sensing applications.
Fluorescent Hexacatenar Liquid Crystals
Authors: Hoag Ben , Gin Douglas L.
Published: April 2011

A novel family of phasmidic liquid crystals incorporating an oligo(p-phenylenevinylene) core was produced. These compounds exhibit blue luminescence in both solution and the solid state. The emission profiles are influenced by the degree of organization in the solid state. The snthesis and liquid-crystalline behavior of these compounds will be discussed. Their photophysical properties, as studied by c.w. photoluminescence excitation, emission spectroscopy, and site selective spectroscopy, as well as their optoelectronic properties will be presented.
Secondary Electron Emission Studies of Diamond and GaN Materials
Authors: Yater J.E. , Shih A. , Katzer D.S.
Published: April 2011

Secondary electron emission spectroscopy is used to examine the transport and emission of low-energy electrons in several wide bandgap materials. In particular, the secondary emission properties of C(100), C(111), and CVD diamond samples are compared in order to examine the effect of crystallographic orientation on the emission characteristics. Very high yields are obtained from hydrogenated and cesiated negative-electron-affinity surfaces of all three samples, indicating that low-energy electrons are transported and emitted very efficiently in the diamond materials. While the energy distribution of the emitted electrons is found to be sharply peaked at low energy for all three samples, the energy distributions measured from the C(111) surfaces are broader and reveal structure in the energy gap. The different emission processes at the C(100) and C(111) surfaces may account for the energy distributions observed from the polycrystalline CVD diamond. Finally, initial secondary emission measurements are taken from GaN and AlGaN films grown by molecular beam epitaxy. The secondary emission is not as strong as from the diamond samples, and the measurements reveal the impact of interface and surface barriers on the emission process.
Electron Field Emission from Undoped and Doped DLC Films
Authors: Litovchenko V.G. , Evtukh A.A. , Klyui N.I. , Litvin YU.M. , Kudzinovsky S.Yu. , Chakhovskoi A.G. , Felter T. E.
Published: April 2011

Electron field emission and electrical conductivity of undoped and nitrogen doped DLC films have been investigated. The films were grown by the PE CVD method from CH4:H2 and CH4:H2:N2 gas mixtures, respectively. By varying nitrogen content in the gas mixture over the range 0 to 45%, corresponding concentrations of 0 to 8 % (atomic) could be achieved in the films. Three different gas pressures were used in the deposition chamber: 0.2, 0.6 and 0.8 Torr. Emission current measurements were performed at approximately 10−6 Torr using the diode method with emitter-anode spacing set at 20 gm. The current - voltage characteristics of the Si field electron emission arrays covered with DLC films show that threshold voltage (Vth) varies in a complex manner with nitrogen content. As a function of nitrogen content, Vth initially increases rapidly, then decreases and finally increases again for the highest concentration. Corresponding Fowler-Nordheim (F-N) plots follow F-N tunneling over a wide range. The F-N plots were used for determination of the work function, threshold voltage, field enhancement factor and effective emission area. For a qualitative explanation of experimental results, we treat the DLC film as a diamond-like (sp3 bonded) matrix with graphite-like inclusions.
Field Emission from Carbon Films Deposited by VHF CVD on Different Substrates
Authors: Kosarev A.I. , Abramov A.S. , Vinogradov A.J. , Shutov M.V. , Felter T.E. , Andronov A.N. , Robozerov S.V.
Published: April 2011

As previously demonstrated, non-diamond carbon (NDC) films deposited at low temperatures 200-300 °C on silicon tips reduced the threshold of field emission. In this paper we will present the results of the study of field emission from flat NDC films prepared by VHF CVD. Emission measurements were performed in a diode configuration at approximately 10−10 Torr. NDC films were deposited on ceramic and on c-Si substrates sputter coated with layers of Ti, Cu, Ni and Pt. The back contact material influences the emission characteristics but not as a direct correlation to work function. A model of field emission from metal-NDC film structures will be discussed.
Band-Bending Effects on Field Electron Emission From N- and P-Type Silicon Gated Emitter Tips
Authors: Matsukawa T. , Tokunaga K. , Kanemaru S. , Itoh J.
Published: April 2011

Field emission characteristics from n- and p-type silicon gated emitter tips have been investigated in detail by means of experiments and theoretical estimation of band-bending induced by surface states. Single-tip emitters have been fabricated from n- and p-type silicon and their current-voltage characteristics have been evaluated. The field emission from the p-type emitter has been found to occur at lower extraction voltage than that of the n-type emitter. As the theoretical approach to the origin of the phenomena, potential distribution in the emitter tips has been calculated by using device simulation technique. The surface states of the n-type emitter tip are negatively charged and form a potential barrier against the electrons. On the contrary, there is no potential barrier in the p-type tips. The potential barrier in the n-type tip prevents electrons from reaching the tip apex. This is the reason why the emission current of the n-type emitter was suppressed lower than that of the p-type emitter.
Fluorescence line Narrowing Spectroscopy of Germanate Glasses Doped with Eu3+
Authors: Rolli R. , Samoggia G. , Speghini A. , Bettinelli M. , Montagna M. , Ferrari M.
Published: April 2011

In the present paper we report on time-resolved resonant and non-resonant fluorescence line narrowing measurements on a lead germanate glass doped with Eu3+. Site-selective decay curves were measured at low temperature. The results show that energy transfer processes between Eu3+, ions in different sites are not efficient at the doping level under investigation (I mol% Eu2O3). The homogeneous linewidth of the 5D0→47F0transition was measured at room temperature as a function of the excitation energy within the inhomogeneous profile. The linear dependence of the homogeneous linewidth on the excitation energy is discussed.
Using Polymerised Nanocontacts to Improve the Electroluminescence of Porous Silicon
Authors: Chongt A.S.L. , Gan L.M. , Blackwood D.J.
Published: April 2011

A polyaniline contact layer was deposited via microemulsion polymerisation which resulted in nanosize short-chain polymer particles that penetrate deeper into the pores of porous silicon than polymers deposited by other more conventional methods. The microemulsion method gives a contact with higher chemical electroluminescence efficiency due to a larger area of actively emitting porous silicon.
High Field Limitation of Poole-Frenkel Emission Caused by Tunneling
Authors: Ganichev S. D. , Ziemann E. , Prettl W. , Istratov A. A. , Weber E. R.
Published: April 2011

The electric field dependence of emission of carriers from deep impurities in semiconductors has been investigated applying static and terahertz electric fields. It is shown that at high electric field strengths carrier emission is dominated by phonon assisted tunneling which may easily be recognized by plotting the emission rate as a function of the square of the electric field strength in a log-lin plot giving a straight line. For charged impurities the transition from phonon assisted tunneling to Poole-Frenkel effect at low fields can be traced back.
THE EFFECT OF LEVEL MIXING IN Er-DOPED Si
Authors: Federighi M. , Kenyon A.J. , Chryssou C.E. , Pitt C.W.
Published: April 2011

We have studied the effect of level mixing on the optical properties of Er in Si by calculating the radiative cross sections of Er in Si under external pressure, and the possibility of enhancing in this way both the luminescence and the excitation efficiency.
Optical Gain and Ion-Ion Interactions in Er/Yb Co-Doped Glasses
Authors: Federighi M. , Malla A. , Yeo K.-C.
Published: April 2011

We have developed a model of Er/Yb co-doped glasses taking into account upconversion and concentration quenching. We show in this paper that co-doping with Yb does not affect the maximum gain attainable at very high pump power, but significantly enhances the pump efficiency at moderate pump levels.
Electroluminescence and Photoluminescence of Fluorenecarbazole 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.
Fluorescent Hexacatenar Liquid Crystals
Authors: Hoag Ben , Gin Douglas L. , Theissl Udo , Zojer Egbert , Leising Guenther
Published: April 2011

A novel family of phasmidic liquid crystals incorporating an oligo(ρ-phenylenevinylene) core was produced. These compounds exhibit blue luminescence in both solution and the solid state. The emission profiles are influenced by the degree of organization in the solid state. The snthesis and liquid-crystalline behavior of these compounds will be discussed. Their photophysical properties, as studied by c.w. photoluminescence excitation, emission spectroscopy, and site selective spectroscopy, as well as their optoelectronic properties will be presented.
ZnGa2O4 Thin-Film Phosphors Grown by Pulsed Laser Ablation
Authors: Lee Yong Eui , Rouleau Christopher M. , Park Chan , Norton David P.
Published: April 2011

The growth and properties of undoped and Mn-doped ZnGa2O4 thin-film phosphors on (100) MgO and glass substrates using pulsed laser ablation were investigated. Blue-white and green emission were observed for as-deposited undoped and Mn-doped films, respectively. Luminescent properties as well as crystallinity were considerably affected by processing conditions and film stoichiometry. Films with enhanced luminescent characteristics were obtained on single crystal substrates without post-annealing.
Ultrafast Optical Responses of the Squarylium Dye J-Aggregates Films
Authors: Tatsuura S. , Furuki M. , Tian M. , Sato Y. , Pu L.S.
Published: April 2011

Ultrafast optical responses of the organic films containing squaryliurn dye J-aggregates prepared by simple spincoating method were investigated. Some SQ films exhibited a sharp absorption peak originated from J-aggregates and especially the SQ derivative which has dibutylamino bases at the end of benzene rings forms good J-aggregates in the films without any extra treatment. Time-resolved difference absorption spectra were measured about the SQ44 film. Clear bleached absorption peak and its fast recovery were observed. The decay time was determined to be about 220 fs at 50 MW/cm2 excitation intensity. Sample preparations and all the measurements were performed in air at room temperature.
Determination of Crystallite Size and Lattice Strain in Hexaphenyl Thin Films by Line Profile Analysis
Authors: Brandt H.-J. , Resel R. , Keckes J. , Koppelhuber-Bitschnau B. , Koch N. , Leising G.
Published: April 2011

Hexaphenyl thin films (HTF) are widely used as an electro-active organic medium in blue light emitting diodes. The optical parameters of the HTF-based devices significantly depend on their microstructural properties.

HTF of different types are produced by physical vapor deposition on glass substrates applying specific sample preparation conditions. The microstructural properties of HTF are characterized using X-ray diffraction line profile analysis and atomic force microscopy (AFM). Diffraction peaks representing three different types of preferred growth in HTF are analyzed, namely textures with (00λ), (223) and (203) net planes oriented parallel to the substrate. No additional line-broadening (compared to silicon powder used as standard) is observed in the case of a film prepared at high substrate temperature of 170 °C. On the other hand, considerable broadening is detected in a film with the substrate kept at room temperature. Multiple line analysis documents that the crystallite size and lattice strain for the sample is 150 nm and 3×10−4, respectively. Single line analysis performed on the other reflections reveal size-induced broadening for a crystallite size in the range 40 to 50 nm. From AFM data we obtained that the maximum roughness of the surface is about 40 nm. The results indicate that the deposition temperature significantly influences the microstructural properties and that higher substrate temperature promotes a higher mobility of the molecules on the substrate enabling growth of larger crystallites with lower strain.
Nonlinear Optical Films by Alternating Polyelectrolyte Deposition on Hydrophobic and Hydrophilic Substrates
Authors: Roberts M. Joseph
Published: April 2011

The formation of acentric films using alternating polyelectrolyte deposition (APD) has been achieved on hydrophobic and hydrophilic glass substrates. APD is a layer-by-layer technique for the formation of polymer films by alternately immersing a substrate in aqueous solutions of a polyanion and a polycation. APD provides precise control of the overall film thickness that through automated processing may exceed a thousand layers. In this study, APD films were made of an NLO-active polycation, stilbazolium-substituted polyepichlorohydrin (SPECH), and NLO-inactive polyanions. The peak maximum UV-Visible absorbance in transmission through the films was linear as a function of the number of bilayers. Second harmonic generation (SHG) was used as a tool to indicate acentric order of polarizable sidechain chromophores within the APD films. The SHG exhibited the expected quadratic intensity increase with film thickness.
A Study of Group Velocity Dispersion of Single-Mode Optical Waveguide Utilizing Siloxane Polymer
Authors: Ueno Y. , Kaneko K. , Tanahashi S.
Published: April 2011

We have developed a single-mode optical waveguide utilizing siloxane polymer on ceramic substrate for opto-electronic multichip modules (O/E-MCM) to operate Tera bps. In this paper, we describe group velocity dispersion for the optical waveguide utilizing siloxane polymer on ceramic substrate. The group velocity dispersion becomes 0 fs/cm·nm at around 1310 nm and 1530 nm wavelength. There is abnormal dispersion at around 1530 nm. The results showed that the group velocity dispersion of the optical waveguide was significantly related to the absorption spectrum of siloxane polymer. The group velocity dispersion of the optical waveguide is about 0.4 fs/cm·nm at 1550 nm wavelength. When a 500 femto seconds optical pulse, which has 16 nm for spectrum width, pass through the 50 mm long optical waveguide, pulse expansion is estimated 20 fs/cm·nm. This expansion of spectrum is well to distinguish femto seconds optical signals. Thus, the optical waveguide utilizing siloxane polymer is capable for femto seconds optical pulses transmission.
Combined Main- and Side-Chain Azobenzene Polyesters: A Potential For Photoinduced Nonlinear Waveguides
Authors: Sahlén F. , Geisler T. , Hvilsted S. , Holme N. C. R. , Ramanujam P. S. , Petersen J. C.
Published: April 2011

New combined main- and side-chain azobenzene polyesters, which exhibit an intensity dependent refractive index, have been prepared in order to optically fabricate nonlinear waveguides. Novel sulfone azobenzenes, a diester, (4-[[5-(ethoxycarbonyl)pentyl]sulfonyl]-4'-[[5-(ethoxycarbonyl)pentyl]methylamino] azobenzene, and a diol, 4-[[(8-hydroxy-7-methylhydroxy)-octyl]sulfonyl]-4'-N, N-dimethylamino azobenzene, have been used to prepare new polyesters by transesterification in the molten state. The polyesters have been characterized by UV-visible spectroscopy, differential scanning calorimetry (DSC), size exclusion chromatography (SEC), third harmonic generation (THG) and optical anisotropy measurements. The molar masses of the polyesters were in the range of 5000-10000 g mol−1, which was sufficient in order to spin coat thin films. From THG measurements the polymers are shown to possess an offresonance electronic X(3) of the order 10−12 esu corresponding to a nonlinear refractive index of 2.3×10−14 cm2/W.
Design and Synthesis of Dendrimers with Enhanced Two-Photon Absorption
Authors: Elandaloussi E. H. , Spangler C. W. , Dirk C. , Casstevens M. , Kumar D. , Burzynski R.
Published: April 2011

Model dendrimers based on bis-(diphenylamino)stilbene repeat units have been synthesized and shown to have very stable bipolaronic charge states. Calculations at the AM-1 level predict two orders magnitude enhancement in the third-order nonlinearity in going from the neutral to bipolaron state. Measurement of two-photon cross-sections for PPV dimers with attached diphenylamino donor groups show enhanced two-photon cross-sections for ns pulses. Preliminary evaluation of one of the model dendrimers indicates even larger two-photon cross-sections are possible.
Langmuir-Blodgett Films of Squarylium Dye J-Aggregates Exhibiting Femtosecond Optical Responses
Authors: Furuki M. , Kawashima H. , Tani T. , Pu L. S.
Published: April 2011

J-aggregates of squarylium dyes in Langmuir films have been found to exhibit highly efficient and ultrafast nonlinear optical properties. We established a novel method for making Langmuir- Blodgett (LB) films of J-aggregates with a single absorption band at 784 nm. Deposition of the LB-films was carried out under excess compression of the Langmuir films at a constant speed. Coating the surface of the LB-film with a glassy poly-perfluorocarbon was found to enhance and stabilize the formation of J-aggregates. Characterization of morphology using a near-field scanning optical microscope (NSOM) showed that this LB-film has a highly ordered structure comprising 2- dimensional domains of J-aggregates. We also observed nonlinear-optical responses from this LBfilm. Ultrafast decay of absorption change (250 fs) with quite low saturation energy (3.4 μJ/cm2•pulse) was observed in femtosecond pump-probe measurements. These results suggest highly delocalization of excited states in the J-aggregates of this LB-film with the 2-dimensional mono-molecular layer structure which initially formed in the Langmuir film.
In-Situ Electromigration Damage of Al Interconnect Lines and the Influence of Grain Orientation
Authors: Buerke A. , Wendrock H. , KÖtter T. , Menzel S. , Wetzig K. , Glasow A. v.
Published: April 2011

In this work the authors want to report some experiments concerning unpassivated Al interconnect lines of 8 and 1.4 microns width which have been damaged by in-situ electromigration in the SEM (temperature 230°C, current density 2 and 4×106 A/cm2, respectively). The wider line represents a polygrained structure with few blocking grains spanning the whole width, whereas the narrow line shows bamboo structure. Before electromigration, the local orientation and thus the position of all grain boundaries was mapped by EBSD technique along the entire interconnect line. During and after in-situ current loading in the SEM, the damaged sites were correlated with the grain boundary map to locate where the diffusion paths are situated most likely. It was found that not the deviation from <111> fibre texture, but the misorientation class of the grain boundaries is essential for the localization of the fatal defects.
Measurement of Thin Film Mechanical Properties by Microbeam Bending
Authors: Florando J. , Fujimoto H. , Ma Q. , Kraft O. , Schwaiger R. , Nix W. D.
Published: April 2011

An improved microbeam bending technique has been developed for the study of mechanical properties of thin films on substrates. This testing method utilizes a triangular beam geometry and improved micromachining techniques compared to previously used methods. The technique permits the stress-strain law for a metal film on a substrate to be determined. Single crystal Si beams and bi-layer Si/Al beams of lengths 25–100 pgm have been fabricated and tested. The beams are deflected with a nanoindenter, which accurately imposes a load on the beam and measures the corresponding displacement. For the bi-layer beams, a simple numerical model utilizing a Ramburg-Osgood constitutive law the film has been developed to determine the stress-strain behavior of the Al film.
Subcritical Debonding of Multilayer Interconnect Structures: Temperature and Humidity Effects
Authors: Lane Michael , Dauskardt Reiner , Ma Qing , Fujimoto Harry , Krishna Nety
Published: April 2011

Thin film structures may fail by progressive or time-dependent debonding at stresses far below those required for catastrophic failure. Previous work has shown that progressive debonding in a typical interconnect structure occurs either along the TiN/SiO2 interface or parallel to this interface in the SiO2 Such subcritical debonding was found to span several orders of magnitude of debond growth rates and occur at significantly reduced driving forces. The presence of SiO2 at the failure location indicates that the mechanisms which give rise to stress corrosion cracking in bulk glasses may also play a role in the subcritical debonding behavior of multilayer interconnect structures. Accordingly, this work focuses on the effects of temperature and humidity on subcritical debonding and rationalizes them in terms of the relevant chemical reactions taking place at the debond tip.
Thermal Studies on Stress-Induced Void-Like Defects in Epitaxial-CoSi2 Formation
Authors: Ho C. S. , Pey K. L. , Tung C. H. , Tee K. C. , Prasad K. , Saigal D. , Tan Jackie J. L. , Wong H. , Lee K. H. , Osipowicz T. , Chua S. J. , Karunasiri R. P. G.
Published: April 2011

We report experimental findings on the thermal-induced stress-voiding observed during epitaxial CoSi2 formation on patterned Si(100) wafers associated with the Co/Ti-interposing layer scheme [1–6]. The first rapid thermal process (RTP) in a typical SALICIDE process was studied by varying the temperature and the RTP ramp-up rate. Based on ex-situ cross-sectional transmission electron microscopy (XTEM), crystal defects were observed at shallow trench isolation (STI)/Si and gate spacer/Si edges after annealing at temperatures greater than 520°C. In addition, isothermal anneals for various time periods resulted in increased encroachment of an ultra-thin CoSi2-phase at the STI/Si edge. Higher temperature anneals also resulted in a corresponding increase in void size. In addition, higher ramp-up rates led to a thicker CoSi2 “pocket” film at the tensile-stressed STI/Si edge, aligned epitaxially along the {111}-habit planes. Our attempts to bypass the CoSi formation in order to alleviate the anomalous Si diffusion was found to be irrelevant to the voiding issue, due to the inherent nature of this film stack system to nucleate CoSi2 as the first phase. By comparing our experimental observations of voiding with Hu's analysis of the trench isolation stress fields, we found good agreement with the predicted stress field distribution in the active Si and STI/Si edge with the locations of void nucleation. The anomalously large stress induced is still not known, but can be attributed to the encroaching CoSi2 film which tends to realign epitaxially along the STI/Si interface.
Oxide Mediated Epitaxial Growth of CoSi2 in a Single Deposition Step
Authors: Ohmi S. , Tung R. T.
Published: April 2011

A number of modifications of the oxide-mediated epitaxy (OME) technique are presented which have enabled the growth of thick (∼25–40nm) epitaxial CoSi2 layers in a single deposition sequence. The uses of (a) a thin Ti cap, (b) a thin Ti blocking layer, (c) the codeposition of Co-rich CoSix, and (d) the co-deposition of Col−xTix. have all been shown to lead to improved epitaxial quality over the pure Co OME process, for Co thickness greater than 6nm. Essentially uniform, single crystal silicide layers of over 25nm have been grown in a single deposition step. These results are supportive of the proposed role of a diffusion barrier/kinetics retarder on the part of the interlayer in the OME and the Ti-interlayer mediated epitaxy processes.
The Influence of Ti Capping Layers on CoSi2 Formation in the Presence of Interfacial Oxide
Authors: Detavernier C. , Donaton R. A. , Maex K. , Jin S. , Bender H. , Van Meirhaeghe R. , Cardon F.
Published: April 2011

In this work, we will show that a reactive Ti capping layer can reduce oxide layers that are present at the cobalt-silicon interface. We have used a thin, chemically grown oxide to have a well-controlled form of interfacial oxide layer. To study the silicidation reaction, isochronal annealing was done at various temperatures. Different sets of samples were made in order to investigate the influence of the thickness of the Co layer and its Ti cap. Titanium capping strongly influenced the silicidation reaction. We have found that already at moderate temperatures, Ti can diffuse towards the Co/Si interface, and can reduce the interfacial oxide there present, enabling CoSi2 formation. The CoSi2 thus formed has a preferential epitaxial orientation, and the process by which this epitaxy is attained may be explained by a combination of OME (Oxide Mediated Epitaxy) and TIME (Titanium Mediated Epitaxy).
Influence of the as and BF2 Junction Implantation on Stress Induced Defects During Ti- and Co/Ti-Silicidation
Authors: Steegen A. , Bender H. , Wolf I. De , Maex K.
Published: April 2011

When scaling down the MOS technology, the increasing local mechanical stress induced during the Ti- and Co/Ti silicidation can exceed the critical shear stress on the {111}<110> active glide system in the silicon substrate. This results in the heterogeneous nucleation of 60° dislocations in the silicon substrate underneath the silicide line. In the case of an undoped silicon substrate, these dislocations nucleate at the edge of the silicide lines and are parallel with the [110] oriented line edge. This paper will investigate the effects of As and BF2 junction implantation and implantation defects on the stress developed during the silicidation reaction and on the nucleation and growth of the stress induced 60° dislocations in the silicon.
Transamination in Pulsed DC-Plasma Enhanced CVD Of Ti(C,N) From TDMAT
Authors: Driessen J. P. A. M. , Kuypers A. D. , Schoonman J.
Published: April 2011

Favourable gas-phase conditions for deposition of Ti(C,N) from tetrakis(dimethylamine)titanium (TDMAT) in a pulsed DC-plasma have been determined, making use of mass spectroscopy. Decomposition of TDMAT in a pure hydrogen plasma results in the favourable cleavage of dimethylamine from TDMAT but prevents the formation of Ti(C,N) due to the lack of nitrogen and carbon. Addition of N2 to the hydrogen plasma results in the formation of NHx (l<x<4), opening possible transamination pathways. Transamination plays an important role in thermal CVD processes and results in high quality TiN layers. However, an undesired side-effect is the gas-phase particle formation under the conditions used here, possibly due to TDMAT - N2 interactions. The depletion of TDMAT by interaction with nitrogen in a H2(85%) - N2(15%) plasma proceeds in a mechnistic step with a rate constant of k = 4.7 × 10−14 cm3 mol−1sec. Results were compared with those obtained from using ammonia under similar process conditions, and with results from thermal CVD. Seemingly high quality Ti(C,N) coatings were deposited at temperatures between 200°C and 425°C on steel and glass with this simple and, therefore, interesting set-up.
Formation Mechanism of Metal-Oxides on Plasma-Exposed Wsi/Poly Si Gate Stacks
Authors: Liu Ziyuan , Kawashima Y. , Komatsu A. , Hamada T. , Kawano H. , Shiotani K.
Published: April 2011

The formation mechanism of deformed tungsten oxides (WOx, x=2,3) on WSix/poly Si gate stacks has been investigated. It was revealed that plasma etching process introduced oxygen impurity into WSix surface and caused the WOx formation during the subsequent thermal oxidation. WSix films preferred corientation were found to be stable in the oxidation process after plasma etching process.
Copper-Based Ohmic Contacts For The SiGe/Si Heterojunction Bipolar Transistor (HBT) Structure
Authors: Das K. , Alterovitz S. A.
Published: April 2011

A Cu-based metallization scheme has been studied for establishing low resistance contacts for a Si/SiGe/Si heterojunction bipolar transistor (HBT) structure. As-grown doped layers were further implanted with BF2 and As ions for the p-type base and n-type emitter layers, respectively, in order to produce a low sheet resistance surface layer. Contacts were metallized using an e-beam deposited multilayer structure of Ti/Cu/Ti/Al. Specific contact resistances of the order of 10−7 Ω cm2 or lower were obtained.
In Situ XPS Study of Interaction of Thin IVA, VA Metal Films with Native Oxide on Si Substrates
Authors: Sushkova N. M. , Akimov A. G.
Published: April 2011

Phase formation and change in morphology of Ti, V and Nb oxide films on (100)Si and (111)Si, with native oxide layer, have been studied by XPS in situ. The metal oxides were formed by the interaction at room temperature in UHV multistep deposited of Ti, V or Nb with native oxide. The formation of clean silicon regions during the growth of three-dimensional metal oxide islands is discussed. Differences observed in composition of Nb oxides on (100) Si and (111) Si are considered.
Nucleation and Growth of CVD Cu Films
Authors: Kröger R. , Eizenberg M. , Cong D. , Yoshida N. , Chen L. Y. , Chen L.
Published: April 2011

In this work the nucleation and growth of CVD Cu on MOCVD TiN barrier layer as well as on PVD Ta with and without a PVD Cu seed layer on top were studied. Scanning and transmission electron microscopy was used to characterize the dependence of morphology and microstructure on deposition time. XRD measurements were carried out to study the orientation of the polycrystalline films. Atomic force microscopy was applied to investigate the surface topography. A random crystal orientation and an amorphous interlayer between the CVD Cu film and the barrier - leading to a poor adhesion performance of the CVD Cu films - were obtained on Ta and TiN, where island growth can be observed. A CVD Cu film deposited on top of PVD Cu leads to a highly preferred <111> orientation and a significantly improved adhesion of the Cu film. A PVD Cu seed layer as thin as 60 Å was found to produce an epitaxially grown <111> textured Cu film. These results highlight the importance of the initial growth stages for both morphology and adhesion of the CVD Cu films.
CVD Cu Process Development and Integration for sub-0.18 µm Devices
Authors: Zhang Jiming , Denning Dean , Braeckelmann Greg , Hamilton Greg , Lee J. J , Venkatraman Ram , Fiordalice Bob , Weitzman Elizabeth
Published: April 2011

The advent of inlaid Cu interconnects has presented new challenges for the industry to fill high aspect ratio dual inlaid features. CVD Cu offers advantages for excellent step coverage and is a technique extendible for future generations of devices. We have developed a robust CVD Cu process and a CVD/PVD reflow integration scheme. In this paper, we present results of an extensive study on CVD Cu process development and integration. The effects of various precursors, carrier gases (H2, He and N2) and barrier layers including CVD TiN, PVD Ta, PVD TaN, PVD Ta-Si-N, and a hybrid barrier, on the CVD Cu film properties and device electrical properties are discussed. The extendibility and challenges of current CVD Cu processing will also be discussed.
Comparison of Copper CVD Using Cu(FOD)2 and Cu(HFAC)2 Reduction
Authors: Boey J. S. , Griffin G. L. , Maverick A. W. , Fan H.
Published: April 2011

We have measured the growth rate and film properties for the chemical vapor deposition of copper thin films using H2 reduction of Cu(fod)2 [H(fod) = 6,6,7,7,8,8,8-heptafluoro-2,2- dimethyl-3,5-octanedione]. The results are directly compared to deposition using Cu(hfac)2 [H(hfac) = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione]. Higher growth rates are obtained using Cu(fod)2, in part because of differences in reaction order between the two compounds. However, both compounds exhibit significant cluster formation during film nucleation, which leads to residual porosity and film resistivities above 2 µΩ-cm.
Numerical Simulations of Topographic Evolution for Sputter Deposition into Trenches and Vias
Authors: O'Sullivan Peter L. , Baumann Frieder H. , Gilmer George H.
Published: April 2011

We have performed 2D and quasi-3D numerical simulations of physical vapor deposition (PVD) into high aspect ratio trenches and vias used for modem VLSI interconnects. The topographic evolution is modeled using (continuum) level set methods. The level set approach is a powerful computational technique for accurately tracking moving interfaces or boundaries, where the advancing front is embedded as the zero level set (isosurface) of a higher dimensional mathematical function. First, we study the 2D case of long rectangular trenches including 3D out-of-plane target flux. The 3D flux is obtained from molecular dynamics computations for AI(100), and hence our approach represents a hybrid atomistic/continuum model. We obtain good agreement with X-TEM data. Secondly, we report results of axisymmetric 3D simulations of high aspect ratio vias which we then go on to compare with experimental data for Ti/TiN barrier layers. We find that the simulation data (using the cosine angular distribution) overpredict bottom coverage in some cases by approximately 20%-30% for both collimated and uncollimated deposition but in other cases provide a reasonably accurate comparison with experiment.
Reliability Studies of Cu using Wafer Level Joule Heated Electromigration Test
Authors: Low Kia Seng , O'Neill Anthony
Published: April 2011

In this paper, we describe some of the results that we have obtained using Wafer Level Joule Heated Electromigration Test and Current Ramp Test. The results indicate that the Cu we tested is more resistive to open failure due to current ramp than Al-1%Si-0.5%Cu. The value of the activation energy for electromigration of Cu using fixed current under wafer level joule heated electromigration test is 0.59 eV. The activation energy due to the effect of temperature gradient failure mechanism is 0.82 eV.