bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Pad Surface Texture and Slurry Abrasive Concentration on Tribological and Kinetic Attributes of ILD CMP
Authors: Philipossian Ara , Olsen Scott
Published: June 2019

Real-time coefficient of friction (COF) analysis is used to determine the extent of normal and shear forces during CMP and identify the lubrication regimes associated with the process. Pads with different surface textures and slurries with varying abrasive concentrations are used to polish ILD films over a wide range of operating parameters. Results show that by varying abrasive concentration and pad surface texture, one can cause the process tribology to change from ‘boundary lubrication’ to ‘partial lubrication’, to ‘hydrodynamic lubrication’. A two-phase model relating average coefficient of friction and Preston's constant is presented. At abrasive concentrations up to 9 percent, material removal is proportional to the extent of contact between the abrasives and the wafer. At abrasive concentrations between 9 to 25 percent, removal rate is directly influenced by average COF. A new parameter termed the ‘tribological mechanism indicator’ is defined and extracted from the data, which coupled with the information on COF and ILD removal rate, results in a series of ‘universal’ correlations. A qualitative model based on pad storage modulus is used to explain the trends.
Effect of Ceria Particle-Size Distribution and Pressure Interactions in Chemo-Mechanical Polishing (CMP) of Dielectric Materials
Authors: Chandrasekaran Naga , Taylor Ted , Sabde Gundu
Published: June 2019

Effect of ceria particle-size distribution and pressure interactions in CMP of dielectric materials and the subsequent surface generation mechanisms is investigated in detail. The removal rate is observed to correlate primarily with the slurry mean particle-size distribution (D50) and reach early rate saturation with decreasing particle size. Slurries with tighter particlesize distribution exhibit a logarithmic relationship with pressure, while a linear relationship is observed for wider distribution slurries. In contrast to the removal rate, surface roughness and degree of microscratches depend primarily on the tail distribution (D99) and increase with increasing particle size. The addition of a selective component to the slurry increases the rate differential between the slurries.
Planarisation of Patterned Aluminium/Diamond Surfaces for SAWdevices
Authors: Holland Anthony S. , Reeves Geoffrey K. , Leech Patrick W.
Published: June 2019

A novel method for forming interdigitated electrodes for GHz Surface acoustic wave (SAW) devices on diamond using a damascene-like polishing technique is described. Low aspect ratio Al electrodes are recessed into the diamond substrates to create a near planar surface. This allows the deposition of higher quality oriented ZnO. CVD diamond samples were ion-beam etched with groove widths in the range 1-5μm to a depth of 80-120nm. Al (120nm thick) was sputter deposited on to the etched diamond and was polished using either (i) a solution of 0.05μm silica on a neoprene polishing cloth or (ii) using a ∼0.12mm thick PVDF (polyvinylidene difluoride) filter pad with colloidal solutions of silica. Using AFM scans and optical microscopy it was observed that the combination of method (i) with the small sample size resulted in significant hollowing-out of the Al electrodes and complete removal of Al from over 90% of the pad-interconnect area. The alternative technique in (ii) demonstrated far less Al removal and better uniformity in the electrode patterns.
Supramolecular Abrasive-free System for Cu CMP
Authors: Keleher Jason , Rushing Ken , Zhao Joe , Wojtczak Bill , Li Yuzhuo
Published: June 2019

Key issues in CMP today include reduction of surface defectivity and enhancement of planarization efficiency. More specifically, the polished surface should be free of defects such as scratches, pits, corrosion spots, trench copper loss, and residue particles. For copper/low k CMP, one of the most promising strategies to accomplishing these goals is an Abrasive-Free Process (AFP). By eliminating abrasive particles from the process, either free or fixed to the pad, it has been anticipated and realized that defects such as severe scratching, particle contamination and slurry instability via particle aggregation or settling will be significantly reduced. In addition, with proper formulation, an abrasive free process can also yield an excellent over polishing window and desired step function of pressure for material removal rate. Coupled with a supramolecular design, some of the characteristic advantages seen in abrasive containing system such as step height reduction efficiency can be realized without the side effects often introduced from solid particles. In this presentation, some designing principles for an abrasive free system will be first presented. The potential advantages of a supramolecular design for copper CMP will be illustrated. The CMP performance on a set of testing blanket and patterned wafers will be discussed.
Electrochemical Studies of Copper Chemical Mechanical Polishing Mechanism: Effects of Oxidizer Concentration
Authors: Lu J. , Garland J.E. , Petite C.M. , Babu S.V. , Roy D.
Published: June 2019

The process of copper chemical-mechanical planarization (CMP) can be considered as an erosion corrosion process. Such a process can be efficiently studied by in situ and ex situ electrochemical techniques, such as potentiodynamic scan and electrochemical impedance spectroscopy (EIS). Using a copper disk as the working electrode in an electrochemical cell, slurries with different oxidizer concentrations have been investigated with the aforementioned techniques. Corresponding dissolution tests were also studied and compared. It is shown that changing the oxidizer concentration leads to the formation of surface films with different structure and composition on the copper surface during CMP process. The nature of these films controls the rate of copper corrosion. These results could be used to explain the change of copper removal rate in different oxidizer concentration, as well as to understand the copper CMP mechanism.
Mechanisms of Passivation of Copper in CMP Slurries Containing Peroxide and Glycine
Authors: Wang Ling , Doyle Fiona M.
Published: June 2019

Copper has been observed to passivate in CMP slurries containing glycine, when hydrogen peroxide is used as an oxidant, even under acidic conditions where no solid oxidized phases appear on the potential-pH diagram. This passivation behavior is highly desirable for effective CMP. In contrast, passivation is not seen in slurries of similar pH and complexing agent concentration, where the potential is increased electrochemically. In order to model the effects of chemistry on CMP rates, we are endeavoring to better understand the mechanisms responsible for passivation in slurries containing hydrogen peroxide. Here we report tests that characterize the development and degree of passivation seen in slurries with a reasonably wide range of compositions.
The pH Effect On Chemical Mechanical Planarization Of Copper
Authors: Du Tianbao , Desai Vimal
Published: June 2019

This study explores the effect of pH on the chemical mechanical polishing (CMP) characteristics of copper in H2O2 and KIO3 based slurries under various dynamic and static conditions. High purity copper disc was used to study the dissolution and oxidation kinetics at various pH (2 to 10) with 5% H2O2 or 0.1M KIO3. Electrochemical techniques were used to investigate the dissolution/passivation behavior of Cu. The affected surface layers of the statically etched Cu-disc were investigated using X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). In 5% H2O2, the Cu removal rate decreases with an increase in pH and reaches minimum at pH 6, and then increases under alkaline conditions. XPS results indicate that the surface oxide formed at various pH values was responsible for this CMP trend. However, with 0.1M KIO3, the CMP removal rates were found to be lower at pH 2. The maximum was observed at pH 4, then the removal rate decreased with the increase of pH. The lower value of removal rate at pH2 was due to the fast interaction between Cu and KIO3 and the precipitation of CuI on the pad, which makes the pad glassy, resulting in lowered removal rates. This was confirmed by XPS measurements. The decreased CMP removal rates when the pH is higher than 4 might be due to the weaker oxidation power of KIO3 with the increase of pH.
MechanicalModeling of the 2D Interfacial Slurry Pressure in CMP
Authors: Higgs C. Fred , Ng Sum Huan , Yoon Inho , Shan Lei , Yap Lipkong , Danyluk Steven
Published: June 2019

Chemical mechanical polishing (CMP) is a manufacturing process used to remove or planarize metallic, dielectric, or barrier layers on silicon wafers. During polishing, a wafer is pressed against an elastic pad that is flooded with slurry. Prior work has shown that an asymmetrical, subambient pressure develops at the interface between the silicon and the pad during polishing. Since the slurry pressure is on the order of the wafer-on-pad contact stress, the total contact pressure is asymmetrical. This promotes a non-uniform polishing rate, since Preston's equation states that the material removal rate is proportional to the total contact pressure. In order to determine the total contact pressure, experiments were conducted to measure the two-dimensional fluid pressure. A superposition method was then employed to calculate the slurry film thickness by performing an equilibrium analysis of the forces and moments created by the fluid and solid interactions. The film thickness obtained by this method is used to model the slurry pressure using the polar Reynolds' equation. Modeling results qualitatively agree with experiments.
A New Cleaning Technique for Corrosion Protection in Aluminum Metallization
Authors: Kodera Masako , Uekusa Shin-ichiro , Matsui Yoshitaka , Miyashita Naoto , Shigeta Atsushi , Takahashi Shinya , Kawai Murato , Kawamoto Hiroshi , Tsujimura Manabu
Published: June 2019

A new cleaning technique using gas dissolved water has been found to be effective in protecting against corrosion in aluminum metallization, which is also useful in post-cleaning of Cu CMP as already reported. Corrosion can be a significant concern in aluminum as well as in copper metallization. In Al CMP process, corrosion often occurs in contact with DIWbecause of the big potential difference between Al and the barrier metal. In this study, it has been confirmed that gas dissolved water is able to change the potential of various metal films, and that following Al CMP, post-cleaning using gas dissolved water instead of DIW can successfully protect against corrosion.

Furthermore this technique is also effective in the post-cleaning process of Al wiring formed by RIE, which contains a slight amount of Cu. Because segregation of copper at the side-wall of wiring often occurs during RIE and the following processes, Al-Cu wiring is easily corroded during the DIW rinsing step in wet cleaning, which may cause killer defects. Gas dissolved water can remarkably decrease the potential difference between Al-Cu alloy and segregated Cu, as well as Al-Cu alloy and the Ti/TiN used as a barrier metal. Moreover, because it seems that a reaction occurs between cathode water and Ti/TiN, where electrons may be supplied there to corrosive sites, corrosion can be prevented.
Delamination Behavior of Cu-Low-k Stack Under Different Slurries
Authors: Sikder A. K. , Thagella S. , Zantye P. B. , Kumar Ashok
Published: June 2019

Lower mechanical strength, reduced cohesive strength and lack of compatibility with other interconnect materials, are the major challenges involved in chemical mechanical polishing (CMP) of Cu metallization with ultra low-k materials as interlayer dielectrics. In this study we have investigated the polishing behavior of patterned Cu samples with underneath different low-k materials using two different slurries and a wide range of machine parameters. CMP micro tribometer was used to polish the samples with different rotations of platen (50 to 250 RPM) and down forces (1-6 PSI). Friction co-efficient and wear behavior were also investigated at different conditions. Optical and scanning electron microscopy was used to investigate the polished surface. It was observed that the two different Cu slurries used for polishing have marked effects on the polishing of Cu-low-k stack with respect to wear and delamination.
Integration Challenges for Chemical Mechanical Polishing of Cu/Low-κ Interconnects
Authors: Lee Jeffrey A. , Moinpour Mansour , Liou Huey-Chiang , Abell Thomas
Published: June 2019

The drive for improved performance of microelectronic devices has led to the prevalence of copper metallization and the aggressive development of low-permittivity (low-κ) dielectric materials for use as interlayer dielectrics in BEOL interconnect structures. Progressive scaling of metal line widths coupled with the need to incorporate ultra low-κ (ULK) dielectrics, with κ<2.2, presents numerous challenges for integration and reliability. Perhaps the most significant challenge for the 90nm technology node and beyond is successful planarization of Cuinterconnect structures by chemical mechanical polishing (CMP). The present paper will discuss the general integration challenges and key structural reliability issues for chemical mechanical polishing of Cu-interconnects incorporating ULK dielectric materials.
Laser-Crystallized High Quality ITO on Plastic Substrates for Flexible Displays
Authors: Chung Wonsuk , Wickboldt Paul , Toet Daniel , Carey Paul G. , Thompson Michael O.
Published: June 2019

In the study presented here, we successfully demonstrated that high quality ITO films could be obtained on plastic substrates using Excimer laser crystallization. ITO films were first deposited at 10 °C on PEN substrates by DC magnetron sputtering, and then irradiated using a homogenized pulsed XeCl excimer laser beam (308 nm, 35 ns pulse duration) in a vacuum chamber. It was possible to reliably attain Type I ITO films with sheet resistances down to 35 Ω/΢, combined with 80 % optical transmittance in visible range. Well defined 2 μm lines could be obtained using simple HCl etchant at room temperature. We also developed Type II ITO films with a sheet resistance of 15 Ω/΢ and an optical transmittance of 80 % by means of laser annealing on plastic substrates, although these materials were found inferior to Type I in etching properties.
Development of High Permeability Core Materials for Embeddable Inductors in Flexible Organic Substrates
Authors: Liu C. K. , Cheng P. L. , Leung S. Y. Y. , Law T. W. , Lam D. C. C.
Published: June 2019

Capacitors, resistors and inductors are surface mounted components on circuit boards, which occupy up to 70% of the circuit board area. For selected applications, these passives are packaged inside green ceramic tape substrates and sintered at temperatures over 700°C in a co-fired process. These high temperature processes are incompatible with organic substrates, and low temperature processes are needed if passives are to be embedded into organic substrates. A new high permeability dual-phase Nickel Zinc Ferrite (DP NZF) core fabricated using a low temperature sol-gel route was developed for use in embedded inductors in organic substrates. Crystalline NZF powder was added to the sol-gel precursor of NZF. The solution was deposited onto the substrates as thin films and heat-treated at different temperatures. The changes in the microstructures were characterized using XRD and SEM. Results showed that addition of NZF powder induced low temperature transformation of the sol-gel NZF phase to high permeability phase at 250°C, which is approximately 350°C lower than transformation temperature for pure NZF sol gel films. Electrical measurements of DP NZF cored two-layered spiral inductors indicated that the inductance increased by three times compared to inductors without the DP NZF cores. From microstructural observations, the increase is correlated with the changes in microstructural connectivity of the powder phase.
Dielectric Properties of Layer Polymer Films
Authors: Sakai W. , Yoshiji T. , Tsutsumi N. , Chiang C. K.
Published: June 2019

The dielectric and thermal properties of three-layer structured films were studied. The two outer layers were about 1 μm and the thickness of the middle layer was varied. We measured the thickness dependence of the dielectric constant of the three-layer structured films. The dielectric results were evaluated with a simple serial three-capacitance model. Local thermal property of these polymer films were also measured using a micro-tip local thermal analysis method. Local glass transition of the film was compared with the one expected from bulk data.
N- and P-Type Building Blocks for Organic Electronics Based on Oligothiophene Cores
Authors: Facchetti Antonio , Yoon Myung-Han , Katz Howard E. , Mushrush Melissa , Marks Tobin J.
Published: June 2019

Organic semiconductors exhibiting complementary-type carrier mobility are the key components for the development of the field of “plastic electronics”. We present here a novel series of αω- and isomerically pure β,β'-diperfluorohexyl-substituted thiophene and study the impact of fluoroalkyl substitution and conjugation length vìs-à-vìs the corresponding fluorinefree analogues. Trends between the fluorinated and fluorine-free families in molecular packing, HOMO-LUMO gap, and π-π interactions are found to be strikingly similar. TFT measurements indicate that all members of the fluorinated series are n-type semiconductors
Thin Film Transistors on Plastic Substrates Using Silicon Deposited by Microwave ECR-CVD
Authors: Teng Lihong , Anderson Wayne A.
Published: June 2019

The properties of thin film transistors (TFT's) on plastic substrates with active silicon films deposited by microwave ECR-CVD were studied. Two types of plastic were used, PEEK and polyimide. The a-Si:H TFT deposited at 200°C on polyimide substrates showed a saturation field effect mobility of 4.5 cm2/V-s, a threshold voltage of 3.7 V, a subthreshold swing of 0.69 V/dec and an ON/OFF current ratio of 7.9×106, while the TFT fabricated on PEEK at 200°C showed a saturation field effect mobility of 3.9 cm2/V-s, a threshold voltage of 4.1 V, a subthreshold swing of 0.73 V/dec and an ON/OFF current ratio of 4×106. Comparison is made to TFT's with the Si deposited at 400°C on glass.
High Performance Plastic Transistors With Printed Polyaniline Electrodes
Authors: Lefenfeld Michael , Blanchet Graciela , Rogers John A.
Published: June 2019

This article describes the properties of transistors that use organic semiconductors deposited on top of conducting polymer electrodes patterned by thermal transfer printing onto thin plastic sheets. The polymer, dinonylnaphthalene sulfonic acid doped polyaniline (DNNSA-PANI), contains several weight percent of single walled carbon nanotubes (SWNT) to improve its conductivity. Pentacene serves as the p-type organic semiconductor. The good electrical performance of these devices derives directly from the low resistance contacts between the printed DNNSA-PANI/SWNT source/drain electrodes and the pentacene. The measurements presented here quantify the behavior of these contacts and provide some morphological evidence for their low resistance. The excellent characteristics of the transistors and the operational flexibility of the thermal transfer printing technique that is used to pattern them represent results that may be an important step for the development of means to build realistic flexible electronic devices.
Flexible organic field-effect transistors fabricated by the electrode-peeling transfer
Authors: Yasuda Takeshi , Fujita Katsuhiko , Tsutsui Tetsuo
Published: June 2019

We report a simple and mild fabrication of flexible organic field-effect transistors (OFETs) by an electrode-peeling transfer method. Firstly, fine patterns of source-drain metal electrodes were formed on a solid substrate, where a micro-patterning process such as photolithography is applicable. An organic dielectric layer (poly-chloro-p-xylylene) was deposited by a chemical vapor deposition. Then patterned gate electrode was deposited using a shadow mask. On the top surface of the gate electrode, another adhesive flexible substrate was fixed and the stack of the flexible substrate/gate electrode /dielectric layer /source-drain electrode was peeled away from the solid substrate. The peeling-transfer was completed with a help of a self-assembled monolayer of n-decyl mercaptan as a connecting buffer layer between the gold electrodes and the dielectric layer. Then an organic semiconductor material was deposited on the fresh peeled-off surface on the flexible substrate. When pentacene was used as the semiconductor material, the OFETs exhibited a hole mobility of 0.1 cm2/Vs and a current on/off ratio of 105.
Low Temperature Copper-induced Crystallization Technique for Germanium on Flexible PET, by Means of Mechanical Compressive Stress
Authors: Hekmatshoar B. , Shahrjerdi D. , Mohajerzadeh S. , Khakifirooz A. , Akhavan A. , Robertson M.
Published: June 2019

Low temperature copper-induced crystallization of amorphous germanium (a-Ge) has been significantly enhanced by applying mechanical compressive stress during thermal post-treatment. Manipulation of this technique, alongside with proper patterning of the a-Ge layer before thermo-mechanical process, has led to growth of device-quality poly-Ge layer on flexible PET substrate at temperatures as low as 130°C. Flexibility of the substrate allows the efficient application of uniaxial compressive stress by bending the PET sheets inward. Effects of compressive stress and ultimate crystallization of the Ge layer has been verified by electrical sheet resistance and Hall mobility measurements, and analyzed by XRD, SEM, TEM and RAMAN spectroscopy.
A Method for Making Elastic Metal Interconnects
Authors: Jones Joyelle , Lacour Stéphanie Périchon , Wagner Sigurd , Suo Zhigang
Published: June 2019

Stretchable, elastic metal interconnects are a key to the fabrication of 3-D conformal circuits and electrotextiles. The basic concept for reversibly stretchable, elastic metallization is a corrugated stripe of thin-film metal that is expanded by stretching. The maximum elongation is reached when the stripe is stretched flat. We prepared wavy metal stripes by evaporating gold onto pre-stretched strips of the elastomer, poly-dimethyl siloxane (PDMS). We experimented with gold metal line width and thickness and substrate elongation. We measured the film structure, amplitude, and wavelength, as well as electrical resistance in relaxed and various stretched states. So far we have reached elastic strains of 15% while maintaining the initial resistance and 80% with a rise in the resistance. We discovered a rich macroscopic and microscopic film morphology. Presented are the fabrication, electro-mechanical performance, and data on the film structure of these wavy metal interconnects.
Light trapping in amorphous silicon solar cells on plastic substrates
Authors: Terrazzoni-Daudrix Vanessa , Guillet Joelle , Niquille Xavier , Shah Arvind , Morf R. , Tishchenko A. , Brioude V. , Parriaux O. , Fischer D.
Published: June 2019

In order to simultaneously decrease the production costs of thin film silicon solar cells and obtain higher performances, the authors have studied the possibility to increase the light trapping effect within thin film silicon solar cells deposited on flexible plastic substrates. In this context, different nano-structure shapes useable for the back contacts of amorphous silicon solar cells on plastic substrates have been investigated: random textures and gratings.

The optimisation of such back reflectors is so far empirical. Gratings constitute a well-known optical technique and their light trapping effect can be optimised by simulation.

A first conclusion is that neither the traditional “Haze factor” determined in air for a wavelength of 650nm nor the “rms roughness” of the surfaces are sufficient as criteria to optimise the back contact roughness for light trapping in cells. The shape of grains is a further essential criterion. The authors have so far obtained a relative current enhancement of 16% for solar cells deposited on randomly textured polyethylene terephthalate (PET) as compared to a corresponding conventional solar cell co-deposited on a flat mirror (Ag) on glass. Solar cells on PET with 6.3% stabilized efficiency have until now been obtained. Theoretical calculations indicate that gratings can enhance the current of a-Si solar cells by up to 30 percent.
Molecular Dynamics Simulation of Germanium Nanoparticles
Authors: Yang Sang H. , Berry Rajiv J.
Published: June 2019

Nanoparticles are known to melt at temperatures well below the bulk melting point. This behavior is being exploited for the recrystallization of Germanium to form large-grain semiconductor thin films on flexible and low temperature substrates. The melting of Ge nanoparticles as a function of size was investigated using the ab-initio Harris functional method of density functional theory (DFT).

The DFT code was initially evaluated for its ability to predict the bulk properties of crystalline Ge. A conjugate gradient method was employed for minimizing the multiphase atomic positional parameters of the diamond, BC8 and ST12 structures. The computed lattice constants, bulk moduli, and internal atomic positional parameters were found to agree well with other calculations and with reported experimental results.

A constant temperature Nose-Hoover thermostat was added to the DFT code in order to compute thermal properties via molecular dynamics. The simulations were tested on a 13-atom Ge cluster, which was found to melt at 820 K. Further heating resulted in the cluster breaking up into two smaller clusters, which remained stable up to 1300K.
The Characteristics of Silicon Dioxide Deposited by Inductively Coupled Plasma Chemical Vapor Deposition at 150°C
Authors: Kang Su-hyuk , Lee Min-Cheol , Moon Kook-Chul , Han Min-koo
Published: June 2019

An ultra-low temperature processed silicon dioxide film has been fabricated by inductively coupled plasma chemical vapor deposition at 150°C using He/N2O/SiH4 mixture. The deposited silicon dioxide film exhibits a high breakdown field larger than 6MV/cm in case of high ICP plasma condition while the flat band voltage of the oxide film significantly shifted in the negative direction with increasing ICP power. In order to obtain both high electrical breakdown filed and the low flat-band voltage, excimer laser irradiation with the energy density of 430mJ/cm2 is employed. The oxide film irradiated by excimer laser exhibited considerably shifted in the positive direction without scarifying the breakdown characteristics.
Thin Film Morphology and GrowthMechanism of Pentacene Thin Film Using Low-Pressure Organic Vapor Deposition
Authors: Ahn Seong Deok , Kang Seung Youl , Lee Yong Eui , Joung Meyoung Ju , Kim Chul Am , Suh Kyung Soo
Published: June 2019

We have investigated the growth mechanism and thin film morphology of pentacene thin films by the process of low-pressure gas assisted organic vapor deposition (LP-GAOVD). As the source temperature, flow rate of the carrier gas, substrate temperature and chamber pressure were varied, the growth rate, morphology and grain size of the films were differently obtained. The electrical properties of pentacene thin films for applications in organic thin film transistor and electrophoretic displays were discussed
The Electronic Circuit Composition and Structure of Warp and Woof for a Novel Hybrid Opto-Electronic Integrated Systems with Textile Structures
Authors: Kuniyoshi Shigekazu , Tanaka Kuniaki
Published: June 2019

The new integrated circuit concept that forms electronic equipment by the textile structure using the flexible fiber that has equipped the field effect transistor, the light emitting diode, the wiring pattern, etc. is proposed [1]. In this report, the structure of the filamentous body as a basic structure of the cloth with various electronic functions was examined. In order to simplify circuit composition, an active element such as field effect transistors, the electrode pattern for wiring, and the pads for connection are formed on the warp, and the electrode pattern for wiring and the pad for connection are formed on the woof. The circuit composition and a concrete structure of the warp and the woof are discussed.
Inorganic-organic hybrid materials for polymer electronic applications
Authors: Houbertz R. , Schulz J. , Fröhlich L. , Domann G. , Popall M.
Published: June 2019

For applications in polymer electronics, suitable passivation coatings are searched for. Inorganic-organic hybrid polymers (ORMOCER®.s) have proven to be tunable in a wide range with respect to their physical properties. Their synthesis can be controlled such that the resulting materials show very low water vapor transition rates (WVTR) which is one of the most important key properties for passivation applications. Besides, ORMOCER®.s can be patterned by UV lithography due to their organic functional groups thus yielding the possibility of selectively passivate electronic circuits. Typical WVTR values which have been achieved so far for individual thin-film layers range between approximately 1 and 5 g/m2d (calculated for 100 μm layer thickness). The passivation properties will be discussed with respect to variations of the inorganic content and to the network formed upon processing.
Effect of Microcavity Structures on the Photoluminescence of Silicon Nanocrystals
Authors: Spooner Marc G. , Walsh Timothy M. , Elliman Robert G.
Published: June 2019

ptical microcavity structures containing Si nanocrystals are fabricated by plasma enhanced chemical vapour deposition (PECVD) of SiO2, Si3N4 and SiOx layers. The nanocrystals are formed within Si-rich oxide layers (SiOx) by precipitation and growth, and the microcavity structures defined by two parallel distributed Bragg mirrors (DBM) made from either alternate SiO2/Si3N4 layers or alternate SiO2/SiOx layers. In the latter case, Si nanocrystal layers form part of the DBM structure thereby providing a distributed emission source. The optical emission from these and related structures are examined and compared with that from isolated nanocrystal layers.
Electronic and Optical Properties of Silicon Nanocrystals: Structural Effects
Authors: Degoli E. , Ossicini S. , Luppi M. , Luppi E. , Magri R. , Cantele G. , Ninnoc D.
Published: June 2019

The aim of this work is to investigate the structural, electronic and optical properties of hydrogenated Si nanoclusters (H-Si-nc) in their ground and excited state configurations. Structural relaxations have been fully taken into account in all cases through total energy pseudopotential calculations. Recent results about ab-initio calculations of Stokes shift as a function of the cluster dimension and of optical gain will be presented here. A structural model that can be linked to the four level scheme recently invoked to explain the experimental outcomes relative to the observed optical gain in Si-nc embedded in a SiO2 matrix will be suggested too.
High Efficiency Light Emission Devices in Silicon
Authors: Castagna Maria E. , Coffa Salvatore , Monaco Mariantonietta , Muscara' Anna , Caristia Liliana , Lorenti Simona , Messina Alberto
Published: June 2019

We report on the fabrication and performances of the most efficient Si-based light sources. The devices consist of MOS structures with erbium (Er) implanted in the thin gate oxide. The devices exhibit strong 1.54 μm electroluminescence at 300K with a 10% external quantum efficiency, comparable to that of standard light emitting diodes using III-V semiconductors. Emission at different wavelenghts has been achieved incorporating different rare earths (Ce, Tb, Yb, Pr) in the gate dielectric. The external quantum efficiency depends on the rare earth ions incorporated and ranges from 10% (for an Tb doped MOS) to 0.1% (for an Yb doped MOS). RE excitation is caused by hot electrons impact and oxide wearout limits the reliability of the devices. Much more stable light emitting MOS devices have been fabricated using Er-doped SRO (Silicon Rich Oxide) films as gate dielectric. These devices show a high stability, with an external quantum efficiency reduced to 0.2%. In these devices Er pumping occurs part by hot electrons and part by energy transfer from the Si nanostructures to the rare earth ions, depending by Si excess in the film. Si/SiO2 Fabry-Perot microcavities have been fabricated to enhance the external quantum emission along the cavity axis and the spectral purity of emission from the films that are used as active media to realize a Si based RCLED (resonant cavity light emitting diode). These structures are realized by chemical vapour deposition on a silicon substrate. The microcavities are tuned at different wavelengths: 540nm, 980nm and 1540nm (characteristic emission wavelengths respectively for Tb, Yb and Er). The reflectivity of the microcavities is of 97% and the quality factor ranges from 60 (for the cavity tuned at 980nm) to 95 (for the cavities tuned at 540nm and 1540nm).
Near-infrared Ge Photodetectors Fabricated on Si Substrates with CMOS Technology
Authors: Cannon Douglas D. , Jongthammanurak Samerkhae , Liu Jifeng , Danielson David T. , Wada Kazumi , Michel Jurgen , Kimerling Lionel C.
Published: June 2019

We have fabricated the first CMOS process compatible high-responsivity Ge p-i-n diodes for 1.55 μm wavelengths. The thermal expansion mismatch between Ge epilayers and Si substrates was used to engineer tensile strain upon cooling from the growth temperature. This 0.2% tensile strain results in a lowering of the direct transition energy in Ge by 30 meV and extends the responsivity curve to near 1.6μm.
Prospects of Laser Operation in Erbium Doped Silicon
Authors: Huda M. Q. , Ali S. I.
Published: June 2019

Prospects of laser operation in erbium doped silicon has been analyzed by a Shockley-Read-Hall (SRH) model. Erbium atoms have been considered to be introducing strong recombination centers in the silicon lattice. Electron-hole recombination at these sites were considered to be the source of erbium excitation. A two level system was considered for calculation of optical gain and the laser threshold. For a laser cavity of 300 μm with mirror reflectivities of 90%, and an optimistic absorption coefficient of 5 cm-1, a population inversion of 1.4×1018/cm3 was estimated as the threshold value. Achievement of the lasing condition was found feasible, but only for certain conditions of erbium activation. Effects of nonradiative deexcitation routes have been analyzed. On the assumption of 1019/cm3 of active erbium sites, linear increase of optical power in the laser cavity has been estimated for injected carrier densities above 1018/cm3.
Coupling and Cooperative Up-conversion Coefficients in Er-doped Si Nanocrystals
Authors: Pacifici Domenico , Franzò Giorgia , Iacona Fabio , Priolo Francesco
Published: June 2019

In the present work, a quantitative understanding of the Er-doped Si nanocrystals interaction is reported. We present a model based on an energy level scheme taking into account the coupling between each Si nanocrystal and the neighboring Er ions. By fitting the steady state and time resolved luminescence signals at both the 1.54 and 0.98 μm Er lines we were able to determine a value of 3×10-15cm3s-1for the coupling coefficient. Moreover, a strong cooperative up-conversion mechanism, active between two excited Er ions and characterized by a coefficient of 7×10-17cm3s-1, will be shown to be active in the system, demonstrating that each Si nanocrystal can actually excite more than one Er ion.
Effect of Illumination on Organic Polymer Thin-Film Transistors
Authors: Hamilton Michael C. , Martin Sandrine , Kanicki Jerzy
Published: June 2019

We have investigated the effects of white-light illumination on the electrical performance of organic polymer thin-film transistors (OP-TFTs). The OFF-state drain current is significantly increased, while the drain current in the strong accumulation regime is relatively unaffected. At the same time, the threshold voltage is decreased and the subthreshold slope is increased, while the field-effect mobility of the charge carriers is not affected. The observed effects are explained in terms of the photogeneration of free charge carriers in the channel region due to the absorbed photons.
Pyrromethene dye doped optical polymers for amplifiers and lasers
Authors: Ramon M. , Bryden T. , Jones T.S. , Bradley D.D.C.
Published: June 2019

Polymeric, planar waveguides of pyrromethene dye 1,3,5,7, 8-pentamethyl-2, 6-diethylpyrromethene-BF2 (PM567)-doped poly(methylmethacrylate) (PMMA) were prepared by spin coating (SC) and solution diffusion (SD) methods. Both techniques produced films that, under laser illumination, show strong spectral narrowing due to amplified spontaneous emission (ASE). Samples prepared by SD showed higher gain than the SC films. Also, compared to the SC samples, the smooth surface of the SD samples reduced scattering at the surface and therefore guding losses. The high dye concentration present in the SD samples may be responsible for the increased photostability (more than 105 pulses). The SD method appears to offer a simple alternative for the production of planar wave-guides for amplifier devices.
N- and P-Type Building Blocks for Organic Electronics Based on Oligothiophene Cores
Authors: Facchetti Antonio , Yoon Myung-Han , Katz Howard E. , Mushrush Melissa , Marks Tobin J.
Published: June 2019

Organic semiconductors exhibiting complementary-type carrier mobility are the key components for the development of the field of “gplastic electronics” We present here a novel series of α,ω- and isomerically pure ββ'-diperfluorohexyl-substituted thiophene and study the impact of fluoroalkyl substitution and conjugation length vis-a-vis the corresponding fluorinefree analogues. Trends between the fluorinated and fluorine-free families in molecular packing, HOMO-LUMO gap, and π-π interactions are found to be strikingly similar. TFT measurements indicate that all members of the fluorinated series are n-type semiconductors
Oligothiophene Organic Thin Film Transistors and Circuits
Authors: Halik Marcus , Klauk Hagen , Zschieschang Ute , Schmid Gunter , Ponomarenko Sergei A. , Kirchmeyer Stephan
Published: June 2019

We have investigated a series of α,α'-oligothiophenes with chromophore length ranging from four to six units, and with side chains comprised of ten, six, two, and zero alkyl units. We have fabricated top-contact and bottom-contact organic TFTs with thermally evaporated active layers and found that the TFT performance depends critically on the length of the side chains and on the contact configuration (with mobilities ranging from 0.07 to 1.1 cm2 / V-s), but is relatively insensitive to the chromophore length. We have also fabricated ring oscillators with didecylsexithiophene and measured a signal propagation delay of 30 μsec per stage. In addition, we have fabricated oligothiophene-TFTs with ultra-thin self-assembled monolayer (SAM) gate dielectrics, with the intent to evaluate if long alkyl side chains contribute usefully to the effective thickness of a SAM gate dielectric. We have measured carrier mobilities as large as 0.05 cm2 / V-s and subthreshold swing as low as 200 mV / decade.
Energy Transfer Studies of Polyphenylene-Type Polymers to a Series of Dyes.
Authors: Clancy Sean O. , Padmaperuma Asanga B. , Harper Aaron W.
Published: June 2019

Energy transfer from two polyphenylene-type polymers to a series of organic dyes was studied. One of the polymers was synthesized via Suzuki coupling of 1,4-phenyldiboronic acid with 1,4-dibromobenzene to obtain polyphenylene. The other polymer was a polybenzophenone generated by a nickel-mediated coupling of 2,5-dichloro-4'-methylbenzophenone. These polymers were used as the energy donors. A variety of Coumarins and other dyes were used as acceptors. Photophysical data and energy transfer parameters were determined.
White Electroluminescent Devices Using Polymer Blends
Authors: Hwang Do-Hoon , Lee Jeong-Ik , Lee Chang-Hee
Published: June 2019

White light-emitting devices were fabricated using the blends of blue, green, red emissive polymers of poly[9,9-(2'-ethylhexyl)fluorene] (PEHF), poly(9,9-dioctylfluorene-2,7-vinylene) (POFV), poly(2-(3',7'-dimethyloctyloxy)-5-methoxy-1,4-phenylene-1-cyanovinylene) (CNPPV) and poly(2-(2'-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene) (MEH-PPV). Inefficient energy transfers between the blue polymer and the green or the red polymer, which was observed in PL spectra of the blend films, provides a good opportunity to get white light emission due to better blend ratio controllability. The EL devices were fabricated with ITO/PEDOT/blend/Ca/Al configuration and good white light-emission was obtained for a certain blend ratio. The light-emission was observable from 4V and a maximum brightness of 400 cd/m2 was obtained with the device.
Double-Excitation Dynamics in m-LPPP probed with sub-20 fs Time Resolution
Authors: Gadermaier C. , Cerullo G. , Manzoni C. , Scherf U. , List E.J.W. , Lanzani G.
Published: June 2019

In a novel modification of transient differential transmission spectroscopy, the first excited state S1 is reexcited via a second laser pulse towards a higher lying state Sn. The dynamics of the relaxation of this state Sn as well as the states created from Sn are revealed by a broad-band probe pulse.

We find that the charge carrier generation efficiency from Sn is higher compared to S1. The push and probe durations below 20 fs enable the temporal resolution of the ultrafast relaxation of the Sn state and enables us to identify the two main contributions to enhanced charge generation from Sn, energy migration towards sites of high dissociation probability, and exciton dissociation during vibrational relaxation.
High pressure studies on the packing forces and intermolecular interaction in polyphenyls
Authors: Heimel G. , Puschnig P. , Oehzelt M. , Hummer K. , Koppelhuber-Bitschnau B. , Porsch F. , Ambrosch-Draxl C. , Resel R.
Published: June 2019

In this work, we report on pressure induced structural changes in crystalline oligo(paraphenylenes) containing two to six phenyl rings. Revisiting the crystal structures at ambient conditions reveals details in the packing principle. A linear relationship between the density at ambient conditions and the number of phenyl rings is found. Energy dispersive X-ray diffraction has been performed in a systematic study on polycrystalline powders of biphenyl, paraterphenyl, p-quaterphenyl, p-quinquephenyl and p-sexiphenyl under hydrostatic pressure up to 60 kbar. Our investigations not only yield pressure dependent lattice parameters and hints towards pressure induced changes in the molecular arrangement, but also allow for an analysis of the equations of state of these substances as a function of oligomer length. We report the previously unknown bulk modulus of p-quaterphenyl, p-quinquephenyl, and p-sexiphenyl (B0 = 83 kbar, 93 kbar, and 100 kbar respectively) and its pressure derivative (B0' = 6.4, 7.5, and 5.6). A linear dependence of the bulk modulus on the inverse number of phenyl rings in the molecules is found.
Spectroscopic Photovoltage Chracterization of PPV Thin Films Suitable for Pled Applications
Authors: Samal Girija Sankar , Biswas A.K. , Mohapatra Y. N.
Published: June 2019

We have studied photovoltage spectra of PPV thin films using both conventional single layer LED structure (ITO/PPV/Al), and capacitive structure consisting of ITO/Mica/PPV/ITO films. The photovoltage spectra for both types of devices have sharp features and are identical indicating that the features observed are primarily due to PPV material itself. We observed two sharp peaks in the energy range of 2.5 -2.7 eV (i.e. above HOMO-LUMO gap) in photovoltage spectrum. The lineshape of the peaks strongly suggests that the peaks are most probably associated with photoionization of excitons. Temperature dependence of spectral lineshape of photocurrent peaks has been studied in the range of 80K-300K. The magnitudes of photocurrent peaks are weakly dependent on temperature, while other spectral features such as peak position and peak width are nearly independent of temperature. On the basis of absorbance, photovoltage and PL spectra, we conclude that both polarons and photoionization of excitons contribute to steady state photovoltage spectra.
Characterization of Isomers in Solid Aluminum tris-(Quinoline-8-olate) by 27Al NMR
Authors: Nandagopal Magesh , Mathai Mathew , Papadimitrakopoulos Fotios , Utz Marcel
Published: June 2019

Aluminum tris-(quinoline-8-olate) (Alq3) is the most widely used electron transport material for organic light emitting diodes. The Alq3 molecule exists as two different isomers: meridianal and facial, which differ by the symmetry of the arrangement of ligands around the aluminum ion. Various crystalline polymorphs of Alq3 have been identified to contain one of these isomers. In this paper we present experimental results that show that the facial and meridianal isomers of Alq3 can be distinguished in the solid state by 27Al nuclear magnetic resonance (NMR) spectroscopy under magic angle spinning (MAS). Our results prove that the recently discovered δ-phase of Alq3 exclusively contains the facial isomer. The same technique is also used to characterize the amorphous deposit of Alq3 showing that it is the meridianal isomer that predominantly exists in the amorphous state.
Charge carrier lifetimes in a smectic liquid crystalline photoconductor of a 2-phenylnaphthalene derivative
Authors: Iino Hiroaki , Hanna Jun-Ichi
Published: June 2019

We have investigated the charge carrier lifetimes for electrons and holes in smectic mesophases of a 2-phenylnaphthalene derivative, 6-(4'-octylphenyl)-2-dodecyloxynaphthalene (8-PNP-O12) by time-of-flight (TOF) measurement. For the negative charge carriers, we found two transits in different time range, which are attributed to electronic and ionic conduction. With the aid of liquid-like fluidity of the material, we could prepare very thick samples over 500μm, and it enables us to determine the carrier lifetimes, which are governed by different regimes: the hole lifetime is governed by recombination of charge carriers and estimated to be 10-2 sec; on the other hand, the electron lifetime is dominated by trapping at deep states and estimated to be on the order of 10-5 sec for both SmA and SmB phases.
A Novel Strategy for the Solid Phase Synthesis of Ultra Pure Organic Semiconductors
Authors: Turner D. , Spivey A. , Cupertino D. , Mackie P. , Anemian R. , Yeates S.
Published: June 2019

A new solid phase synthetic strategy for the production of organic semiconductors has been developed. The strategy uses a germanium-based linker and Suzuki-type cross-coupling protocols and has been demonstrated for the iterative synthesis of both a regio-regular oligo-3-alkyl-thiophene and an oligoarylamine. The process also incorporates a novel “doublecoupling” after each iteration which minimizes deletion sequences. The key steps exploits the susceptibility of α-silyl- or α-silyloxy- but not germyl-substituted derivatives toward nucleophilic ipso-protodemetalation.
Oriented Luminescent Nanostructures From Single Molecules Of Conjugated Polymers
Authors: Mehta Adosh , Kumar Pradeep , Zheng Jie , Dickson Robert M. , Sumpter Bobby , Barnes Michael D.
Published: June 2019

Dipole emission pattern imaging experiments on single chains of common conjugated polymers (solubilized poly phenylene vinylenes) isolated by ink-jet printing techniques have revealed surprising uniformity in transition moment orientation perpendicular to the support substrate. In addition to uniform orientation, these species show a number of striking differences in photochemical stability, polarization anisotropy,[1] and spectral signatures[2] with respect to similar (well-studied) molecules dispersed in dilute thin-films. Combined with molecular mechanics simulation, these results point to a structural picture of a folded macromolecule as a highly ordered cylindrical nanostructure whose long-axis (approximately collinear with the conjugation axis) is oriented, by an electrostatic interaction, perpendicular to the coverglass substrate. These results suggest a number of important applications in nanoscale photonics and molecular-scale optoelectronics.