bluuebunny/crossref_metadata_2025 huggingface dataset:
TiW/TiWN/Pt Ohmic Contacts to n-Type 3C-SiC
Authors: Hofeling Kirk , Rieth Loren , Solzbacher Florian
Published: April 2011

TiW(40 nm)/TiWN(80 nm)/Pt(500nm) was investigated as a new high-temperature compatible contact stack to 3C-SiC for harsh environment applications. Performance of TiW/TiWN/Pt contacts deposited on unintentionally doped (8.85×1018 cm-3) 3C-SiC grown by LPCVD to a thickness of ~1μm on (100) Si are reported. The linear transmission line method was used to determine specific contact resistance (ρc) at room temperature and for long-term tests at 300 °C. As deposited contacts were Ohmic with a ρc range of 1×10-4 to 1×10-3 cm2. These contacts were annealed for five minutes in forming gas (8% H2 92% Ar), at temperatures from 450 to 950 °C and all retained Ohmic character. Annealing samples at 450, 550 and 950 °C decreased ρc while anneling between 650 and 850 °C generally increased ρc.

Auger Electron Spectroscopy (AES) analysis was performed on a sample annealed at 750 °C. The as-received surface was composed of Si and O; after a brief sputter etch a characteristic Pt peak became visible and the O peak decreased substantially. Depth profiles detected Si throughout the Pt capping layer but not in the TiW layers. We suspect that Si diffuses from the SiC substrate into the Pt capping layer and surface Si also reacts with O2 to from an oxide. These reactions, in combination with incomplete SiC/TiW interface reactions, are suspected to cause the increase of ρc for samples annealed between 650 and 850 °C. Annealing at 950 °C gave the lowest contact resistance of 2.3×10-5. Long-term testing at 300 °C for 190 hours, in atmosphere, was performed on contacts annealed at 450 °C. When heated, the contacts initial ρc of 2.1×10-4 cm2 increased to ~4×10-3 cm2 which remained stable for the test duration. After long-term testing the sample ρc measured at room temperature decreased to 9.8×10-5 cm2.
Thermal detection mechanism of SiC-Based Resistive Gas Sensors
Authors: Fawcett Timothy J. , Reyes Meralys , Lloyd Spetz Anita , Saddow Stephen E. , Wolan John T.
Published: April 2011

Silicon carbide-based resistive gas sensors from our laboratory have been previously reported to detect hydrogen at concentrations ranging from less than 1% to 100% H2 in Ar and at temperatures ranging from 50°C to 450°C. The gas sensing mechanism for these devices was not well understood, hindering further improvement in this technology. In this report, resistive devices built on a thin 3C-SiC epitaxial layer grown on 150Å thick Si layer wafer bonded to a polycrystalline SiC substrate were studied. The polycrystalline SiC substrate is insulating, allowing the formation of isolated epitaxy resistors on the 3C-SiC layer. The gas sensing devices consisted of rectangular ohmic NiCr contacts with a Au overlayer fabricated on the 3C-SiC surface. Under a constant dc bias, nominally 10V in this study, these sensors demonstrated a decrease in current of up to ~25.4 mA upon the introduction of 100% H2, relative to 100% N2 in the test gas stream. The time constant for this device, estimated as a first-order exponential decay, was ~16-22 sec, with the full response occurring after ~90-120 sec. Upon the introduction of 100% H2 to the sensing environment, the device temperature, as measured by an resistance temperature detector (RTD) in intimate thermal contact with the device, decreased from 400°C to 237°C (ΔT = ~163°C). This large decrease in device temperature was driven by increased heat transfer coefficient of H2 relative to N2. The sensitivity to CH4 in N2, CO2 in N2 and He in Ar was also tested. Sensitivities, defined as the smallest change in concentration, as low as 300 ppm H2 in N2 were achieved with devices operating at 400°C and 10 V dc. Details of the device performance and a model of the sensing mechanism will be discussed.
Reliability of High Voltage 4H-SiC MOSFET Devices
Authors: Krishnaswami Sumi , Ryu Sei-Hyung , Heath Bradley , Agarwal Anant , Palmour John , Lelis Aivars , Scozzie Charles , Scofield James
Published: April 2011

The commercialization of 4H-SiC MOSFETs will greatly depend on the reliability of gate oxide. Long-term gate oxide reliability and device stability of 1200 V 4H-SiC MOSFETs are being studied, both under the on- and off-states. Device reliability is studied by stressing the device under three conditions: (a) Gate stress - a constant gate voltage of +15 V is applied to the gate at a temperature of 175°C. The forward I-V characteristics and threshold voltage are monitored for device stability, (b) Forward current stress – devices are stressed under a constant drain current of Id = 4 A and Vg = 20 V. The devices were allowed to self-heat to a temperature of Tsink = 125°C and the I-V curves are monitored with time, and (c) High temperature reverse bias testing at 1200 V and 175°C to study the reliability of the devices in the off-state. Our very first measurements on (a) and (b) show very little variation between the pre-stress and post-stress I-V characteristics and threshold voltage up to 1000 hrs of operation at 175°C indicating excellent stability of the MOSFETs in the on-state. In addition, high temperature reverse bias stress test looks very promising with the devices showing very little variation in the reverse leakage current with time.
Nanothick Layer Transfer of Hydrogen-implanted Wafer Using Polysilicon Sacrificial Layer
Authors: Huang C. H. , Chang C. L. , Yang Y. Y. , Suryasindhu T. , Liao W. -C. , Su Y. -H. , Li P. W. , Liu C. -Y. , Lai C. S. , Ting J. -H. , Chu C. S. , Lee C, -S , Lee T. -H.
Published: April 2011

An ion implantation-wafer bonding-layer splitting based 2-D nanostructure material fabrication method using polysilicon sacrificial layer for forming nanothick SOI materials without using post-thinning processes is presented in this paper. Polysilicon layer was initially deposited on the thermal oxidized surface of silicon wafer prior to the ion implantation step to achieve the hydrogen-rich buried layer which depth from the top surface is less than 100 nm in the as-implanted silicon wafer. Before this as-implanted wafer being bonded with a handle wafer, the polysilicon layer was removed by a wet etching method. A nanothick silicon layer was then successfully transferred onto a handle wafer after wafer bonding and layer splitting steps. The thickness of the final transferred silicon layer was 100 nm measured by transmission electron microscopy (TEM).
Damage Effects of Ionizing Radiation in Polymer Film Electrets
Authors: Parada Marco Aurélio , Minamisawa Renato Amaral , Moreira Marcos Vasques , de Almeida Adelaide , Muntele Iulia , Ila Daryush
Published: April 2011

Electret sensors or dosimeters can be used to quantify the ionizing radiation dose from charged particles or waves beams (α, β, -e, p etc… γ, X), and with appropriate converters, from fast and slow neutrons. The electret state is reached, by some insulating materials (electrical conductivity lower than 10−8 (Ω m)−1), when once charged, the incorporated charge is quasi-permanent ≈ 109 s. The charge densities are read (before and after the irradiations) and the radiation dose inferred from the difference between them. PFA (Tetrafluoroethylene-per-fluoromethoxyethylene) and FEP (Tetrafluoroethylene-hexa-fluoropropylene) damage mechanisms were studied bombarding these fluoropolymers with: 1 MeV protons at constant current and fluences from 1×1011 tower 1×1016 ions/cm2, 60Co gamma and X-rays, respectively of 1.25 and 0.106 MeV for absorbed doses of 0.5, 1.0, 8,0 and 100 Gy. The emission of chemical species was monitored with a Residual Gas Analyzer (RGA), during proton bombardment and techniques of Optical Absorption Photospectrometry (OAP), Fourier Transform Infrared (FTIR) and Micro-Raman spectroscopy were used to analyze the virgin, exposed and irradiated films.
Metallurgical and Corrosion Studies of Modified T91 Grade steel
Authors: Kumar Pankaj , Maitra Debajyoti , Roy Ajit K
Published: April 2011

Modified 9Cr-1Mo steels containing different Silicon (Si) content have been tested for evaluation of their metallurgical and corrosion properties. The results of tensile testing indicated reduced failure strain up to 400°C followed by its enhancement at a higher temperature. Stress corrosion cracking tests at constant load did not show any failure in any materials. However, reduced ductility and true failure stress were noted in slow strain rate (SSR) testing, indicating increased cracking susceptibility at elevated temperatures. The corrosion potential became more active with increasing temperature in polarization studies. A combination of intergranular and cleavage failures was observed in specimens tested by the SSR technique.
The Corrosion Behavior of Nickel-base Austenitic Alloys for Nuclear Hydrogen Generation
Authors: Koripelli Rama S , Pal Joydeep , Roy Ajit K
Published: April 2011

Three nickel-base austenitic alloys, namely Alloy C-22, Alloy C-276 and Waspaloy have been tested for evaluation of their corrosion resistance in an acidic solution at ambient and elevated temperatures. The results of stress corrosion cracking studies indicate that none of these materials did exhibit any failure at constant load. The cracking susceptibility determined by the slow strain rate technique was gradually enhanced at higher temperatures showing reduced ductility and true failure stress. The critical potentials determined by the polarization technique, became more active (negative) with increasing temperature. The fractograpic evaluations by scanning electron microscopy (SEM) revealed ductile failure in Alloys C-22 and C-276. However, Waspaloy showed brittle failure at elevated temperature.
Persistent Inhibition of Cell Growth on Silver Implanted Glassy Polymeric Carbon
Authors: Zimmerman Robert L. , Gürhan Ismet , Ozdal-Kurt F. , Sen B. H. , Rodrigues Marcello , Ila Daryush
Published: April 2011

We have shown that silver ion implantation or argon ion assisted surface deposition of silver inhibits cell growth on Glassy Polymeric Carbon (GPC), a desirable improvement of current cardiac implants. In vitro biocompatibility tests have been carried out with model cell lines to demonstrate that near surface implantation of silver in GPC can completely inhibit cell attachment on implanted areas while leaving adjacent areas vulnerable to strong cell adhesion. After cleaning and sterilization and more than one year in physiologic solution, the silver implanted GPC persists in inhibiting cell attachment.
Osteogenic differentiation of ES cell-derived EBs mediated by embedded BMP-2 and TGF-beta-1 in a polyelectrolyte multilayer film
Authors: Hajare Mjahed , Delphine Cortial , Youssef Haikel , Andree Dierich , Jean-Claude Voegel , nadia Benkirane Jessel
Published: April 2011

In recent years, considerable effort has been devoted to the design and controlled fabrication of structured materials with functional properties. The layer by layer buildup of polyelectrolyte multilayer films (PEM films) from oppositely charged polyelectrolytes1 offers new opportunities for the preparation of functionalized biomaterial coatings. This technique allows the preparation of supramolecular nano-architectures exhibiting specific properties in terms of control of cell activation and may also play a role in the development of local drug delivery systems. Peptides, proteins or DNA, chemically bound to polyelectrolytes, adsorbed or embedded in PEM films, have been shown to retain their biological activities. Recently, tissue engineering has merged with stem cell technology with interest to develop new sources of transplantable material for injury or disease treatment. Eminently interesting, are bone and joint injuries disorders because of the low self-regenerating capacity of the matrix secreting cells. We present here for the first time that embedded BMP-2 and TGFβ1 in a multilayered polyelectrolyte film can drive embryonic stem cells to the cartilage or bone differentiation depending on supplementary co-factors. We selected a model system made from layer by layer poly-ℓ-glutamic acid (PℓGA) and poly-ℓ-lysine succinylated (PℓLs) films into which BMP-2 and TGFβ1 have been embedded. Our results demonstrate clearly that we are able to induce osteogenesis in embryonic stem cells mediated by growth factors embedded in a polyelectrolyte multilayer film.
Evaluation of Biological Responses of UMR-106 Cells to Porous PHBV Matrix
Authors: Raghavan Dharmaraj , Liu Hui , Stubbs John
Published: April 2011

This paper compared the results of osteoblast-like UMR-106 cells response to 3-D biodegradable porous with nonporous PHBV (poly (3-hydroxybutyrate-co-3-hydroxyvalerate) films. Nonporous PHBV films were prepared by solvent casting and evaporation. Porous PHBV films were prepared by solute leaching of salt/PHBV cast film. Sieved sodium chloride (∼150 μm) was used to create a matrix with high porosity and then leached out by the solvent. Thermo gravimetric analysis showed that over 99% of the salts were leached out by the solvent. Osteoblast-like UMR-106 cells were seeded onto the nonporous and porous PHBV films, respectively. After 6 and 10 days of incubation, growth rate of UMR-106 cells on porous film was higher than on nonporous film. The viable cell proliferation on the porous and nonporous PHBV film was quantified by (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt) (MTS) assay. The results of this study suggest that the UMR-106 cells proliferate more on the porous PHBV matrix and porous PHBV films are a promising material for bone tissue engineering applications.
Photoluminescence Excitation Dependence in Three-dimensional Si/SiGe Nanostructures
Authors: Lee Eun-Kyu , Kamenev Boris V. , Kamins Theodore I. , Baribeau Jean-Marc , Lockwood David J. , Tsybeskov Leonid
Published: April 2011

We find that in SiGe clusters grown on Si using Stranski-Krastanov (S-K) growth mode, (i) photoluminescence (PL) spectra, (ii) PL lifetime and (iii) PL thermal quench activation energies exhibit strong dependence on the excitation intensity. Under PL excitation intensity increasing from 1 to 104 W/cm2, the PL spectra exhibit blue shift from below Ge bandgap up to ∼970 meV. The PL lifetime shows strong dependence on the excitation wavelength, decreasing from 20 μs at ∼0.8 eV to 200 ns at ∼ 0.9 eV. The process of PL thermal quench has two clearly distinguished activation energies. At low temperature, small (∼15 meV) and excitation-independent activation energy is attributed to exciton thermal dissociation. At higher temperature, excitation-dependent PL thermal quench activation energy (increasing from ∼ 120 to 340 meV as excitation intensity increases) is found, and it is attributed to hole redistribution via tunneling and/or thermal ionization over the Si/SiGe valence band energy barrier.
Nitrogen Influence on the Photoluminescence Properties of Silicon Nanocrystals
Authors: Ferraioli Luigi , Bellutti Pierluigi , Daldosso Nicola , Mulloni Viviana , Pavesi Lorenzo
Published: April 2011

We have performed photoluminescence analysis of silicon rich oxide (SRO) and silicon rich oxynitride (SRON) samples deposited by plasma enhanced chemical vapor deposition (PECVD) and thermally annealed to cause the formation of silicon nanocrystals (Si-nc). Our purpose was to investigate the influence of nitrogen embedded into the oxide matrix on the photoluminescence properties of Si-nc. We found a large incorporation of silicon and a decrease of its diffusivity when the oxide is nitrogen rich. As a consequence the rate of crystallization for Si aggregates is slowed down when nitrogen is present in the oxide matrix.
Time Evolution of Nano-scale Morphology of Silicon Microstructure Surfaces in the Early Phase of Hydrogen Annealing
Authors: Hiruta Reiko , Kuribayashi Hitoshi , Shimizu Ryosuke , Sudoh Koichi , Iwasaki Hiroshi
Published: April 2011

We have examined how the morphology of the trench sidewall evolves in the early phase of hydrogen annealing under the two conditions of hydrogen pressures. A distinguished result was obtained concerning the sidewall surface morphology after 30 s annealing at 1000 °C under 760 Torr hydrogen ambient. The evanescence of chemical Si dioxide formed by RCA cleaning process was clearly observed to initiate in various places on the surface. And in the area without chemical oxide, the appearance of atomic steps was also observed. In contrast under 40 Torr hydrogen ambient, the chemical oxide was completely removed even after 30 s annealing. Our observation shows that not only the rate of trench shape transformation but also the rate of removal of oxide films decreases with increasing hydrogen pressure.
Junctions of Carbon Nanotubes and Silicon Nanowires Synthesized by ethanol-Co Chemical Vapor Deposition
Authors: Yoshida Hideto , Uchiyama Tetsuya , Kikkawa Jun , Takeda Seiji , Homma Yoshikazu
Published: April 2011

Carbon nanotubes (CNTs) have been grown on silicon nanowires (SiNWs) by chemical vapor deposition using Co catalyst nanoparticles. Single-walled CNTs have been grown mainly when a thin Co film (0.1 nm thick) was deposited on SiNWs, while both SWNTs and MWNTs have been grown on SiNWs on which Co 0.5 nm thick was deposited. The correlation between the diameter of catalyst nanoparticles and that of CNTs has been investigated by transmission electron microscopy. The average diameter of CNTs is smaller than that of catalyst nanoparticles.
High Yield Growth of Various CdS Nano-Structures and Their Electron Field Emission Behavior
Authors: Lawrance Juno , Gutu Timothy , McClain Devon , Wu Jianfeng , Jiao Jun
Published: April 2011

Nanostructures are considered the critical component in a wide range of potential nanoscale device applications. Yet a procedure to fabricate them with both controllable results and in bulk quantities must be developed in order to achieve their commercialization at reduced cost. In this report, we introduce an improved vapor-liquid-solid method that is capable of preparing high yield, high quality CdS nanowires and nanobelts in a turf-like configuration. To increase yield, we placed gold-coated substrates in a ceramic boat partially covered with a glass slide to form a gas trap. Only a small opening was provided to allow the CdS vapor to escape from the trap. This arrangement increases catalyst exposure to CdS vapor flow in comparison to conventional CVD methods. This allowed the CdS vapor to deposit densely over the substrate at a predetermined temperature range of 501°C-630°C inside the quartz tube. These conditions results in synthesis of various morphologies on both quartz and tungsten substrates including an intertwined-like structure not previously reported. Electron microscopy and microanalysis techniques were utilized in characterizing these morphologies, internal structures and elemental compositions. Electron field emission properties were investigated in an ultra high vacuum chamber set up with a base pressure of ∼1E-9 torr.
Electronic and Mechanical Properties of Super Carbon Nanotube Networks
Authors: Coluci Vitor R. , Dantas Socrates O. , Jorio Ado , Galvao Douglas s
Published: April 2011

Eletronic and mechanical properties of ordered carbon nanotube networks are studied using molecular dynamics simulations and tight-binding calculations. These networks are formed by single walled carbon nanotubes (SWNT) regularly connected by junctions. The use of different types of junctions (“Y”-, “X”-like junctions, for example) allows the construction of networks with different symmetries. These networks can be very flexible and the elastic deformation was associated with two main deformation mechanisms (bending and stretching ) of the constituents SWNTs. Rolling up the networks, “super” carbon nanotubes can be constructed. These super-tubes share some of the main electronic features of the SWNT which form them but important changes are predicted (e.g. reduction of bandgap value). Simulations of their deformations under tensile stress have revealed that the super-tubes are softer than the corresponding SWNT and that their rupture occur in higher strain values.
Novel Organic Light-Emitting Transistors with PN-Hetero-Boundary Carrier Recombination Sites Fabricated by Lift-off Patterning of Organic Semiconductor Thin Films
Authors: Suganuma Naotoshi , Shimoji Noriyuki , Oku Yoshiaki , Matsushige Kazumi
Published: April 2011

We have devised a novel organic light-emitting transistor (OLET) with PN-hetero-boundary combined with hole and electron transport materials along carrier channels. In this device, a clear modulation of the current and luminance with the gate voltage is observed. The luminance of 100 cd/m2 or more has been observed at the source-source voltage of 15 V with the turn-on voltage of 10 V or less, which is lower than that of OLETs based on a single organic material. We have implemented the horizontal PN-hetero-boundary structure for the first time by using the photolithographic patterning of the organic semiconductor thin-films. This patterning technique can be applied to fabrication of not only organic light-emitting transistors we report in this paper but also organic integrated circuits or organic displays.
Bottom Contact Ambipolar Organic Thin Film Transistors Based on C60/Pentacene Heterostructure
Authors: Kanai Kaname , Wang Suidong , Seki Kazuhiko
Published: April 2011

We report the fabrication and characterization of the bottom contact organic thin film transistors and inverter based on a heterostructure of C60 on pentacene. The transistor shows ambipolar transport characteristics with high electron and hole mobilities of 0.23 cm2V−1s−1 and 0.14 cm2V−1s−1, respectively. After exposure to air, the n-channel in C60 is completely degraded whereas the p-channel in pentacene keeps working. Both the n-channel and the p-channel are stable in N2 atmosphere. The inverter exhibits typical transfer characteristics, which are interpreted by the distribution of the accumulated electrons and holes depending on the bias conditions. These results suggest a potential way to fabricate organic complementary circuits with a single organic heterostructure device.
Fabrication of Ion-Paths for Ionic Liquid Type Quasi-Solid Dye Sensitized Solar Cell
Authors: Kado Takashi , Kato Takehito , kogo Takeshi , Inakazu Fumi , Noma Yusuke , Ogomi Yuhei , Yamaguchi Yoshihiro , Kohno Mitsuru , Hayase Shuzi
Published: April 2011

A direction to increasing photovoltaic performances of dye sensitized solar cells (DSC) is proposed. An interface between TiO2/dye and an electrolyte layer is focused on. It is proved that better coverage of TiO2layers with dye molecules increases photovoltaic performances, where dye staining is carried out in pressurized CO2atmosphere. This is explained by decreases in the amount of surface traps on TiO2nano-particles, which is discussed by thermally stimulated current (TSC). The decrease in the surface trap density increases electron diffusion coefficient and improves electron lifetime in TiO2layers. In addition, the TiO2-staining with dye molecules having the larger dipole moment seems to leave less amount of electron trap. Another crucial research item is solidification. Quasi-solidification is carried out by using surface modified anodically-oxidized Al2O3films filled with ionic liquids, where ion paths are fabricated on the surface-modified Al2O3walls by concentrating iodine and iodide molecules on the walls. Because of the fabrication of the ion path, photovoltaic performances increased even after solidification. Grötthuss type mechanism is introduced to explain the increase in the photovoltaic performances after the solidification.
Microfluidic Devices for Novel Synthesis
Authors: Choi Kyung
Published: April 2011

We demonstrate here functional polymeric particle synthesis by employing a microfluidic approach. The functional polymer is MIP system (molecularly imprinted polymer), which can be produced by “molecular imprinting”, a general protocol for the preparation of “synthetic receptor or binding sites” with specific recognition for targeted organic molecules. The recognition of complex molecules and biological entities is a necessary component for fabricating chemical sensors, diagonostic bio-sensors, and for drug delivery systems. We have obtained homogeneous MIP's microparticles, which may have high affinity receptor sites only by fabricating a microreactor.
Effect of Buffer or Barrier Layer on Bistability for Nonvolatile Memory Fabricated with Al Nanocrystals Embedded in α-NPD
Authors: Seo Sung-ho , Nam Woo-sik , Kim Jae-seok , Shin Chang-hyup , Lim Se-yun , Park Jea-gun , Kim Yoon-joong
Published: April 2011

Recently, low molecular organic non-volatile memories have been developed as a next generation of non-volatile memory because of nano-meter device-feature size and nano-second access and store-time. We developed a non-volatile memory fabricated with the device structure of Al/ α-NPD/Al nano-crystals surrounded by Al2O3/α-NPD/Al, where α-NPD is N,N'-bis(1-naphthyl)-1,1'biphenyl4-4”diamine. One layer of Al nano-crystals with ∼20 nm-width ∼20 nm length was uniform produced between α-NPD layers, confirmed by 1.2MV high voltage transmission-electron-microscope. This device showed Vth of 3.0 V, Vprogram of 4.3 V, and Verase of 6.3 V. Particularly, this device exhibited an excellent non-volatile memory behavior performing the bi-stability (Iprogrm/Ierase) of >1×102, program/erase cycles of >1×105 and multi-levels. In addition, previous reports about low molecular organic non-volatile memories have showed a bad reproducible memory characteristic. However, this issue was completely solved via isolating Al nano-crystals embedded in α-NPD by O2 plasma oxidation. The uniformity of Vth, Vp, and Ve were 9.91%, 6.94% and 7.92%, respectively. Furthermore, the effect of buffer or barrier layer on non-volatile memory characteristics was investigate to examine the control ability for Vth, Vp, and Ve. The 0.5-nm LiF showed a barrier layer behavior suppressing the bi-stability of non-volatile memory. Otherwise, 15-nm CuPc exhibited a buffer layer behavior enhancing the bi-stability of nonvolatile memory.
Effect of Structural Phase Transition on Thermally Activated Time-of-Flight Charge Carrier Mobility and Field Effect Transport in Diindenoperylene Single Crystals
Authors: Tripathi Ashutosh Kumar , Pflaum Jens
Published: April 2011

We report on the growth, the structural and the electronic characterization of semiconducting Diindenoperylene (DIP) single crystals. Temperature dependent x-ray measurements reveal a structural phase transition occurring at around 370 K. Temperature dependent time-of-flight (TOF) hole mobility shows a thermally activated behavior up to the phase transition temperature with an activation energy of ∼ 180 meV. A field effect is successfully demonstrated on transistors based on DIP single crystal and yields a room temperature hole mobility of about ∼ 2×10−5 cm2/Vs. Unlike TOF measurements, no electron transport was observed in field-effect transistors (FETs) geometry which could be attributed to the large injection barrier for electrons at the DIP-Ag-contact interface in contrast to the injection barrier for holes.
Development of Flexible Photo Sensor and Memory Devices Based on Organic Photo FET
Authors: Yoshida Manabu , Kawai Hiroki , Kondoh Takeshi , Kawai Takeshi , Suemori Kouji , Uemura Sei , Hoshino Satoshi , Kodzasa Takehito , Kamata Toshihide
Published: April 2011

The photo FET having a photosensitive insulator layer showed excellent photo-switching properties upon illuminating the gate dielectric layer, because the gate capacitor was rapidly charged up by providing a large amount of photo-generated charges in the dielectric layer to the gate capacitor. In this study, we have tried to give a memory function to the photo FET. Further, we have tried to fabricate flexible photo FETs by using only solution processes in order to utilize the photo FET as flexible photo sensor and photo memory devices. As a result, we have succeeded in observing the memory effect of the photo FET and the photo-switching behavior of the flexible photo FETs
Optically Transparent Conducting Polymers from Fused Heterocycles
Authors: Yavuz Mustafa Selman , Kumar Arvind , Lee Byoungchul , Bokria Jayesh G. , Dey Tanmoy , Seshadri Venkataramanan , Ner Yogesh , Buyukmumcu Zeki , Sotzing Gregory A.
Published: April 2011

Research in the field of optically transparent conducting polymers has been gaining great attention due to their relatively low processing cost, light weight and flexibility as compared to their inorganic counterpart. Besides having found several applications in the field of electronic and optoelectronic devices, optically transparent conducting polymers are primarily used as a hole- injection layers in photovoltaics and light-emitting devices. Herein, we report the electronic and optoelectronic properties of conducting polymers obtained from different fused heterocycles, viz. thieno[3,4-b]furan, thieno[3,4-b]thiophene, and dimers of thieno[3,4-b]thiophene. Aqueous dispersion polymerization in the presence of poly(styrene sulfonic acid) as a template is also performed to make them processable from water. Water soluble conducting polymer was obtained via ring sulfonation of chemically or electrochemically prepared polythieno[3,4-b]thiophene [PT34bT]. The optical properties were tuned by varying sulfonation level or by depositing different number of bilayers via layer-by-layer technique. Stable conjugated polymers with band gaps ranging from 0.8 to 1.6 eV were obtained.
Transition from Non-Dispersive to Dispersive Hole Transport in a Small Molecule Organic Semiconductor Controlled by Molecular Doping
Authors: Fleissner Arne , Schmid Hanna , Melzer Christian , Schmechel Roland , von Seggern Heinz
Published: April 2011

The influence of charge carrier traps on charge carrier transport is studied in a small molecule organic semiconductor model system by means of an optical time-of-flight method. The model system consists of the hole transport material N,N'-di(1-naphtyl)-N,N'-diphenylbenzidine (α-NPD, sometimes denoted as α-NPB) either undoped or doped with various concentrations of the small molecule 4,4',4”-tris-[N-(1-naphtyl)-N-(phenylamino)]-triphenylamine (1-NaphDATA), which is known to create hole traps in α-NPD.

In case of undoped α-NPD, non-dispersive hole transport is observed and the hole mobility is determined as 6·10−4cm2/Vs in the examined electric field range, being in good agreement with published data. Depending on the intensity of the laser light employed for optical charge carrier generation, current transients both in the space-charge regime and in the small signal case are obtained. In the small signal case the current transients do not exhibit the expected flat current plateau before the characteristic kink that marks the transit time, but feature a cusp instead. A tentative mechanism for its formation is proposed.

The influence of the trap concentration on charge carrier transport is studied by introducing 1-NaphDATA as a molecular dopant. It is demonstrated that the hole transport in α-NPD can be controlled by varying the doping concentration of 1-NaphDATA. Increasing the trap concentration, a transition from non-dispersive transport in undoped α-NPD to non-dispersive but trap-controlled transport with reduced mobility and further to dispersive transport is observed.
Process Optimization of UV Curing for Ultra Low-k Dielectrics and High-Stress SiN Liners
Authors: Matsuura Masazumi , Goto Kinya , Hashii Shinobu , Miura Noriko , Miyagawa Yoshihiro , Murata Tatsunori , Tsunemine Yoshikazu , Asai Koyu
Published: April 2011

This paper describes process optimization of UV curing for ultra Low-k SiOC (ULK-SiOC, k=2.65) and High stress silicon nitride (HS-SiN) liner. We have investigated the impact of UV curing using different UV bulbs (UV-X and UV-Y) on BEOL process damages to the ULK-SiOC. The k-value variations of ULK-SiOC modified with UV-X with higher photon energy than UV-Y are greater than those of the pristine ULK-SiOC and the ULK-SiOC modified with UV-Y. These results are consistent with the previously reported FT-IR and NMR analyses that the UV-X generates 3-fold Si-O ring defects and Si-H bonds in the ULK-SiOC. In order to discuss the pore structure in UV-modified ULK-SiOC, the solvent diffusion of toluene and ethanol in ULK-SiOC were measured. The solvent diffusion of the UV-modified ULK-SiOC with UV-X is faster than that of the UV-modified ULK-SiOC with UV-Y. This result indicates that the pore size of UV-modified ULK-SiOC with UV-X is larger than that of UV- modified ULK-SiOC with UV-Y. The dependence of the stress increase in HS-SiN liner on different UV bulbs (UV-X and UV-Y) has been investigated by using stress measurement and FT-IR. The UV-modified HS-SiN liner with UV-Y achieves higher tensile stress, compared to the UV-X. FT-IR results have revealed that UV-Y is more effective for the dehydrogenation and SiN crosslinking, resulting in the greater increase in the tensile stress. In conclusion, UV-Y bulb with medium photon energy yields the desired UV modifications for ULK-SiOC and HS-SiN applications.
Improvement of LDI BUMP Stripping Process by Development of Room Temperature PR Stripper
Authors: Kang Young-Min , Bae Dong Chan , Kim Hyun-Joon , Kim Young- Nam , Kim Young Ho , Kim Tae Sung
Published: April 2011

Bump process using gold bump led to many cleaning problems like polymer residues, metal and polyimide consumption after stripping process. First of all, stripping process of bump photoresist is one of the difficult technologies since thickness of PR pattern of bump is thicker than that of general metal line at least 100 times. We investigated the improvement of LDI BUMP stripping Process at 25 with new chemical. We found that the wettability may be improved when the additive was added to the chemical and it improves the stripping ability. It was found that new chemical was superior to commercial chemical in terms of chemical stability, removal efficiency of polymer residue and decrease in metal and polyimide consumption. Also, we could obtain removal mechanism of photoresist pattern by measured Raman equipment and enhancement of yield in mass production line of semiconductor.
A Study of Tungsten-Titanium Barriers in Silver Metallization
Authors: Bhagat Shekhar , Theodore N. D. , Alford T. L.
Published: April 2011

This work investigated the viability of tungsten-titanium barrier layers for silver metallization. Reactive sputtered W-Ti was deposited on a Si wafer followed by an Ag thin film over layer. These samples were then annealed in vacuum at temperatures up to 700 °C. Characterization of these samples included using x-ray diffractometry, Rutherford backscattering spectrometry, scanning transmission microscopy, secondary ion mass spectroscopy, transmission electron microscopy, and four point probe analysis. The results indicated that the metal/diffusion barrier stack was stable up to 600 °C. Silicon started moving into the tungsten-titanium film at temperatures above 600 °C. Movement of Si resulted in local Si voiding. These results showed the promise of W-Ti as an effective barrier layer for silver metallization for process temperatures below 600 °C.
Potential of Ag Interconnect and Contact Metallization for Various Applications via Cu Additions
Authors: Han Hauk , Zoo Yeongseok , Mayer James W , Alford Terry L
Published: April 2011

The thermal stability of Ag(Cu) alloy thin films on indium tin oxide (ITO) has been investigated and compared to that of pure Ag thin films on ITO. Atomic force microscopy and X-ray diffraction results of annealed films show differences in the evolution of surface morphology and texture with annealing. The presence of Cu atoms in the silver impacts the surface energy and surface diffusion. This results in Ag and Ag(Cu) alloy having very different surface morphology and crystallographic texture. The enhanced texture and thermal stability of the Ag(Cu) alloy constitute its potential use contact as material for MOSFET and for flip-chip light-emitting diodes.
Formation of Ge Nanocrystals in Lu2O3 High-k Dielectric and its Application in Non-Volatile Memory Device
Authors: Chan Mei Yin , Lee Pooi See , Ho Vincent
Published: April 2011

A simple technique for the formation of Ge nanocrystals embedded in amorphous Lu2O3 high-k dielectric was demonstrated by pulsed laser ablation followed by rapid thermal annealing in N2 ambient. The structure and composition of the Ge nanocrystals in the oxide matrix have been studied by transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) analysis. A significant change in the structure and chemical composition of the film was obtained upon annealing. Cross-sectional and plan-view TEM images confirmed the formation of small Ge nanocrystals in amorphous Lu2O3 matrix with a mean size of about 6nm in diameter and a high areal density of 7 × 1011cm−2. The nanocrystals are well-isolated by the amorphous Lu2O3 in between, with almost spherical shape which are favorable for non-volatile memory (NVM) application due to an effective charge confinement. XPS measurements on the as-deposited sample indicate the existence of Ge in its oxidized state, consisting of GeO2 and Ge suboxides. A spontaneous reduction of GeO2 and GeOx was obtained after the annealing treatment, which provides Ge nuclei for nanocrystal formation. It is found that a low annealing temperature of 400oC is sufficient to dissociate the GeO2 and GeOx leading to the formation of Ge nanocrystals. The application of the nanocrystals in NVM devices was demonstrated by C-V characterization of the memory capacitor devices fabricated with Al2O3 control oxide layer. C-V results show a significant effect of the structure and composition of the film on the electrical performance of the device. The annealed device exhibits good memory behavior with a large memory window of 1.2V achieved with a low operation voltage.
Memory Devices Based on Solid Electrolytes
Authors: Kozicki Michael N
Published: April 2011

Current mainstream memory technologies are unlikely to completely fulfill the solid state data storage requirements that will be imposed beyond the 32 nm node of the International Technology Roadmap for Semiconductors. One potential replacement technology is resistance change memory based on solid electrolytes and a number of significant research and development efforts are already underway. The lowering of the resistance is attained by the reduction of ions in a relatively high resistivity electrolyte to form a conducting bridge between the electrodes. The resistance is returned to the high value via the application of a reverse bias that results in the breaking of the conducting pathway. Germanium chalcogenides and Ag-Ge-S ternaries in particular possess good thermal processing characteristics while maintaining the necessary high ion mobility for rapid switching. Thermally diffused copper in deposited SiO2 also is of interest, as thermal stability in excess of 600°C and commonly used constituents makes this material system compatible with the widest range of back-end-of-line processes. This paper details some of the developments in the understanding of the materials used in solid electrolyte resistance change devices and presents a short review of the electrical characteristics of devices based on Ag-Ge-S and Cu-Si-O electrolytes.
Recent Progress in Ferroelectric Random Access Memory Technology
Authors: Ishiwara Hiroshi , Ishiwara Hiroshi
Published: April 2011

In this paper, ferroelectric materials suitable for realizing high-density 1T1C-type (capacitor-type) FeRAM are first reviewed. It is found in BiFeO3(BFO) films formed by chemical solution deposition that leakage current density at a low electric field increases by substitution of Mn and Cr atoms for Fe atoms. But, it is also found that the breakdown characteristic is much improved by substitution of these atoms. Because of the better breakdown characteristic, the leakage current densities in the 3 and 5% Mn-substituted films are lower than that in an undoped BFO film at an applied electric field of 1MV/cm at room temperature, and thus well saturated hysteresis loops in P-E (polarization vs. electric field) characteristics are observed in these films.

Next, recent technological progress in transistor-type FeRAM, in which data are stored in a single ferroelectric-gate FET(field effect transistor), is discussed. It is demonstrated that the data retention time of ferroelectric-gate FETs is much improved by use of HfO2-based buffer layers which are inserted between the ferroelectric film and Si substrate for preventing interdiffusion of constituent elements. Particular attention is paid to FETs with a Pt/SrBi2Ta2O9/HfO2/Si gate structure, in which the data retention time longer than 30 days has been attained. Finally, the cell structure and operation principle of 1T (one transistor)-type FeRAM are discussed.
Investigation of Magnetic Behaviour of Mechanical Activation Derived Multiferroic BiFeO3
Authors: Garg Ashish , Thota Hari Kishan , Pandey Brajesh , Verma H C
Published: April 2011

Here we report on the synthesis of multiferroic BiFeO3 ceramics by mechanical activation and detailed investigation into its magnetic behavior. The mechanically milled ceramic was calcined at temperatures up to 800°C. X-ray diffraction studies show only the pure BiFeO3 phase forms at 700°C. Vibrating sample magnetometer (VSM) measurements were carried out up to 1.5 Tesla and the results show a weak magnetic ordering in the ceramics. The magnetic measurements were also done on the samples heat treated under various cooling conditions. VSM measurements showed pronounced effect of cooling on the Magnetization vs Field curves. Mössbauer measurements show that short range Fe2O3 ordering is still present in the sample that goes undetected by XRD. This component decreases as the calcination temperature is increased. The nature of magnetic ordering improves upon heating from 600 to 700°C, also suggested by pure BiFeO3 phase formation at 700°C. Magnetization vs Temperature measurements conducted on the sample heat treated at 700°C for 1hr followed by cooling in air show an antiferromagnetic transition at ∼370°C.
Sol-Gel Synthesis and Characterization of BiFeO3-PbTiO3 Thin Films
Authors: Garg Ashish , Kar Soumya , Dixit Anju , Agrawal D C
Published: April 2011

In this work, we report on the synthesis and characterization of thin films of (BiFeO3)1−x (PbTiO3)x (BFPT) solid solutions of compositions around morphotropic phase boundary (MPB) grown on platinized silicon (111) Pt/TiO2/SiO2/Si substrate by sol-gel based spin coating technique. The films were post-annealed at 700 and 750°C for 1 h in air. Morphological analysis of the films was carried out by scanning electron microscopy. Grazing incidence X-ray diffractometry revealed the perovskite structure of the films and peaks suggested the presence of rhombohedral structured pure BFPT phase in polycrystalline form. Scanning electron microscopy suggested that films annealed at 750degC had a denser microstructure as compared to those at 700°C. The room temperature dielectric constant of the films with composition of BF:PT :: 75:25 was measured to be ∼1200 at a frequency of 100 kHz.
Ge2Sb2Te5 Film Deposition and Properties
Authors: Ye Mengqi , Tao Rong , Ding Peijun , Bello Abner
Published: April 2011

Magnetron sputter deposition of Ge2Sb2Te5 film is presented. Good thermal control of the wafer is found critical for maintaining process repeatability. In-situ wafer heating conditions have strong impact on as-deposited Ge2Sb2Te5 film properties such as resistivity, density, stress, composition, and microstructure. The effects of wafer bias and sputtering pressure are also discussed.
Room Temperature Growth of Indium Oxide Films by Reactive Ion Beam Assisted Deposition
Authors: Wang Kai , Vygranenko Yuriy , Nathan Arokia
Published: April 2011

Conducting and semiconducting indium oxide thin films have been grown at room temperature by oxygen ion beam assisted e-beam evaporation. We studied an influence of the deposition conditions on thin film properties including the crystal structure, resistivity, optical transmittance, stoichiometry, morphology, and intrinsic stress. X-ray diffraction analysis shows that the crystal structure of indium oxide films changes from amorphous to polycrystalline with preferred (222) orientation when the discharge current increases from 0.5 A to 2.0 A. Film resistivity is tailored in a wide range from 3E-4 ohm-cm to 2E9 ohm-cm by modifying both the evaporation rate of indium and the discharge current of the oxygen ion source. X-ray photoelectron spectroscopy data reveal that the highly-resistive films are more oxygen-enriched than the highly-conductive samples due to electrical activity of the oxygen vacancies. Morphological properties are evaluated using an optical profiler and a measured root-mean-square (RMS) roughness is ~1 nm for produced indium oxide films. All films being studied in this work have compressive stress ranging from 0.4 Gpa to 1.8 Gpa. They are highly transparent with a transmittance up to 90%.

Thus, high-performance indium oxide films can be engineered by the reactive ion beam assisted deposition to meet the requirements of different applications such as solar cells, photodetectors, OLEDs, transparent TFTs, and optical coatings.
Copper-Indium-Boron-Diselenide Absorber Materials
Authors: Ianno Natale J. , Soukup Rodney J. , Santero Tobin , Kamler Chad , Huguenin-Love James , Darveau Scott A. , Olejnicek Jiri , Exstrom Christopher L.
Published: April 2011

Attempts to fabricate new CuIn1-xBxSe2 (CIBS) and CuBSe2 (CBS) thin-film materials have been complicated by the formation of interfering crystallites and by the loss of boron from the magnetron sputtered precursor alloys during the selenization and annealing processes. Raman and Auger spectroscopic analysis as well as x-ray diffraction studies show that the formation of boron selenide may be contributing to the difficulty in creating these new materials.
Nano-scale Observation of Si Trench Sidewall Surface Morphology by AFM Technology
Authors: Hiruta Reiko , Kuribayashi Hitoshi , Shimizu Ryosuke
Published: April 2011

We have developed an atomic force microscopy (AFM) observation technique with which Si trench sidewall surface can be scanned with the tip of cantilever to investigate its nano-scale morphologies. By developing a new technique of cleaving the substrate at the center of a micron-sized trench along its longitudinal direction [011], the sidewall nano-scale morphology of the trench could be observed with the AFM technique. By comparing of cross sections of the images, we also investigated the difference between Si and carbon nanotube (CNT) tips for the AFM observations. According to the results, the CNT tip proved to show a superior signal-to-noise (S/N) ratio compared with the Si tip. The CNT tip enables us to observe the step patterns of the sidewalls of micron-sized trench structures in the various phases of hydrogen annealing.
Localized Ferromagnetic Resonance Force Microscopy of a Continuous Permalloy-Cobalt Film
Authors: Nazaretski Evgueni , Pelekhov Denis V. , Martin Ivar , Cha Kitty C. , Akhadov Elshan A. , Hammel P. Chris , Movshovich Roman
Published: April 2011

We report on the Magnetic Resonance Force Microscopy (MRFM) experiments performed on a 50 nm thick permalloy and a combined 20 nm thick permalloy – cobalt film. We studied the evolution of the MRFM spectra as a function of the vertical probe-sample distance and the lateral position as probe was scanned across the permalloy/cobalt interface. Our numerical simulations of the ferromagnetic resonance (FMR) modes excited in the presence of a non-uniform tip field of the cantilever compare well with experimental findings. This work demonstrates the capability of MRFM to perform local FMR spectroscopy of different materials in continuous ferromagnetic films.