bluuebunny/crossref_metadata_2025 huggingface dataset:
Materials Aspects to Consider in the Fabrication of Through-Silicon Vias
Authors: Burkett Susan , Schaper L. , Rowbotham T. , Patel J. , Lam T. , Abhulimen I. U. , Boyt D. D. , Gordon M. , Cai L.
Published: April 2011

The formation of vertical interconnects to create three-dimensional (3D) interconnects enables integration of dissimilar electronic material technologies. These vertical interconnects are metal filled blind vias etched in silicon and are formed by a series of processing steps that include: silicon etch; insulation/barrier/seed layer deposition; electroplating of Cu to fill the via; wafer grinding and thinning; and back side processing to form contacts. Deep reactive ion etching (DRIE) is used to etch silicon vias with attention given to process parameters that affect sidewall angle, sidewall roughness, and lateral etch growth at the top of the via. After etching, vias are insulated by depositing 0.5 μm of silicon dioxide by plasma enhanced chemical vapor deposition (PECVD) at 325°C. A barrier film of TaN is reactively sputtered after insulation deposition followed by a Cu sputtered seed film allowing electroplated Cu to fill the blind via. Reverse pulse plating is used to achieve bottom-up filling of the via. Once void-free electroplated vias are prepared, the process wafer is attached to a carrier wafer for silicon back grinding. Vias on the process wafer are “exposed” from the back side of the wafer with a combination of processes that include mechanical grinding, polishing, and reactive ion etching (RIE). Contact pads are then formed by conventional IC processes. Cu posts are used to connect the electronic devices and to address thermal management issues as well. This paper presents materials aspects to consider when fabricating through silicon vias (TSVs). Modeling of the Cu-filled vias to investigate thermal management schemes and Cu posts to investigate mechanical reliability is also presented.
Tailoring of Metal Borohydrides for Hydrogen Storage Applications
Authors: Nakamori Yuko , Miwa Kazutoshi , Li Hai Wen , Ohba Nobuko , Towata Shin-ichi , Orimo Shin-ichi
Published: April 2011

Recent investigations on thermodynamical stabilities of metal borohydrides were reviewed. The first-principles calculations indicated that the heat of formation normalized by the number of BH4 complexs, ΔHboro, show a good correlation with the Pauling electronegativitiese of M, χp, which is represented by the liner relation, ΔHboro = 252.8χp − 396.4 in the unit of kJ/mol BH4. In order to clarify the correlation between the stability of borohydrides and the electronegativity χp of M, M(BH4)n (M = Mg, Ca, Sc, Ti, V, Cr, Mn, Zn, Zr and Al; n = 2-4) were systematically synthesized by mechanical milling. The thermal desorption analyses indicated that Td correlate with χ p of M; Td decrease with increasing the values of χp, in M(BH4)n. Furthermore, the correlation can be reasonably extended to double cation ones, (ZrLin-4)(BH4)n. For single cation, M(BH4)n (M = Mn, Zn and Al; χp ≥ 1.5) desorb borane besides hydrogen, and M(BH4)n (M = Ti, V and Cr; χp ≥ 1.5) desorbe small amount of hydrogen provably due to desorption reaction during milling. Therefore χp is an indicator to approximately estimate the stability of M(BH4)n, and appropriateχp in M(BH4)n is expected to be smaller than 1.5. The enthalpy change for the desorption reaction, ΔHdes, is estimated using our predicted ΔHboro and the reported data for decomposition product, ΔHhyd/borideboro, which shows a good correlation with the observed Td. These results are useful for exploring M(BH4)n with appropriate stability for hydrogen storage applications
Molecular Simulation Study on Catenation Effects on Hydrogen Uptake Capacity of MOFs
Authors: Jung Dong Hyun , Lee Tae Bum , Kim Daejin , Park Kangsung , Kim Jaheon , Choi Seung-Hoon
Published: April 2011

In order to investigate the reason for the higher capacity of the interpenetrating isoreticular metal-organic frameworks (IRMOFs) at lower temperatures, we performed grand canonical Monte Carlo (GCMC) simulations and molecular dynamics simulations at 77 K for a set of the interpenetrating IRMOF-11 and the non-interpenetrating counterpart IRMOF-12. From the GCMC simulations, we found universal force field (UFF) is better for describing the hydrogen adsorption behavior than DREIDING force field. The results from the molecular dynamics simulations showed the density of adsorbed hydrogen molecules was increased in the various pores created by the catenation of IRMOF comparing to that of the pores in IRMOF-12. Moreover, the adsorbed hydrogen molecules in IRMOF-11 have the smaller diffusion coefficients. It means that their dynamic behavior is more restricted because of the complexity of the interpenetrating network of IRMOF-11. These results of molecular simulations show the small pores created by the catenation are important for the increase of hydrogen adsorption on IRMOF-11 at lower temperatures.
Carbon Membranes: A Viable Technology for the Recovery and Purification of Hydrogen Gas
Authors: Merritt Anna , Rajagopalan Ramakrishnan , Foley Henry C
Published: April 2011

High throughput, asymmetric carbon membranes derived from pyrolysis of polyfurfuryl alcohol (PFA) have been fabricated on a novel support composed of porous stainless steel filled with nanoparticles. Variation of PFA molecular weight was found to have a significant impact on the single gas permeances of the resultant carbon membranes. High molecular weight precursor material yielded the best results; oxygen permeance values for membranes synthesized from high molecular weight resins were on the order of ∼1×10−8 mol m−2s−1Pa−1 with oxygen over nitrogen ideal selectivities greater than 7. Binary separations of hydrogen from nitrogen and hydrogen from carbon monoxide were carried out using a NPC membrane synthesized from high molecular weight precursor material. For both separations, hydrogen purities of better than 99% by volume were obtained in the permeate stream.
Complex Hydrides Studied by Raman Spectroscopy and Thermal Conductivity Measurements under High Pressure
Authors: Sundqvist Bertil , Talyzin Alexandr V. , Andersson Ove
Published: April 2011

The pressure-temperature phase diagrams of alkali metal alanates and borohydrides are of large current interest, and we have recently studied phase transformations under pressure in several of these materials. We here report Raman studies of KBH4 under pressure at room temperature, showing a phase transition near 6 GPa. Although no structural information is yet available, the similarity between KBH4 and NaBH4 suggests the new structure is orthorhombic. We also report studies on LiBH4 showing that the high pressure phase of this material is metastable to zero pressure below 200 K.
Development of Environmental Cell and its Application to Hydrogen Storage Materials
Authors: Okudera Koya , Hamada Koichi , Suda Takanori , Hashimoto Naoyuki , Ohnuki Somei , Kawai Yasuaki , Kojima Yoshitsugu
Published: April 2011

High-resolution and “environmental cell” microscopy were applied for surveying the reaction of hydrides in Vanadium and Magnesium based alloys, which are candidate for hydrogen storage materials of advanced hydrogen energy systems. For clarify the hydrogenation process, in-situ experiment was carried out by using 200 kV TEM equipped with a newly developed environmental cell, which is enable to observe transmitted image and electron-diffraction under gas reaction under hydrogen environment of 0.1 MPa at room temperature. In case of Vanadium, bending fringe was created under hydrogen-gas of 0.1 MPa, which means that hydrogen reaction is not so quick in this case, and the local stress due to the hydrogen solution caused the fringes. In case of Magnesium, the gas reacted with the powders and showed the swelling, where the surface steps with several ten nm become to more straight, and also SADP showed the formation of MgH2. In-situ experiment for hydrogenation reaction by using the environmental cell has started recently, therefore the precise studies will be continued, as well as its improvement, especially in the transparence films.
Synthesis and Electrochemistry of Acicular Silver Vanadium Oxide Nanofibers
Authors: Takeuchi Kenneth J. , Marschilok Amy C. , Leising Randolph A. , Takeuchi Esther S.
Published: April 2011

Silver vanadium oxide (SVO, Ag2V4O11) has demonstrated commercial success as a solid-state cathode material in power sources for implantable biomedical devices. This report describes the synthesis of SVO via a hydrothermal method. This novel synthetic approach allows low temperature production of acicular SVO nanofibers with a high surface area. This material was investigated as a cathode material in primary lithium batteries for high rate pulse applications.
Direct-Write Microfabrication of Single-Chamber Solid Oxide Fuel Cells with Interdigitated Electrodes
Authors: Kuhn Melanie , Napporn Teko , Meunier Michel , Therriault Daniel , Vengallatore Srikar
Published: April 2011

Miniaturized single-chamber solid-oxide fuel cells (SC-SOFC) are a promising class of devices for portable power generation required in the operation of distributed networks of microelectromechanical systems (MEMS) in harsh environments. The single-face configuration, which consists of interdigitated (comb-like) array of electrodes on an yttria-stabilized zirconia (YSZ) electrolyte substrate, is of particular interest because of the ease of high-temperature microfluidic packaging and integration with MEMS. The primary design consideration for this configuration is the minimization of electrode widths and inter-electrode spacings to dimensions on the order of a few micrometers. This is necessary to minimize polarization resistance and increase fuel cell efficiency. Achieving these geometries using standard microfabrication methods is difficult because of the thickness, porosity, and complex chemistries of the electrodes. Here, we report the development of an innovative and rapid method for manufacturing SC-SOFCs with interdigitated electrodes using robot-controlled direct-writing. The main steps consist of: (i) formation of inks (or suspensions) using anode (NiO-YSZ) and cathode (lanthanum strontium manganite) powders, (ii) pressure-driven extrusion of inks through a micronozzle using a robot-controlled platform, and (iii) sequential sintering to form the fuel cell. The first-generation SC-SOFC device, with electrode widths of 130 μm and inter-electrode spacing of 300 μm, has been manufactured using direct-write microfabrication. The electrodes have been extensively characterized using electron microscopy and x-ray diffraction to assess porosity and to confirm phase identity. The primary process parameters in this approach are the particle size and size distribution, rheological properties of the suspension, extrusion pressure, nozzle size, stage velocity, and sintering conditions. As the first step in the development of detailed process-structure-performance correlations for the fuel cells, we have studied the effects of extrusion pressure (in the range 30-40 bar) and stage velocity (in the range 0.2-2.0 mm/s) on the geometry and size of electrodes, for fixed suspension viscosity and nozzle diameter. An optimal combination of speed and pressure has been identified and catalogued in the form of process maps. Similarly, the particle size distribution of the anode and cathode powders is found to have a significant effect on the microstructure, especially porosity, of the sintered electrodes. The implications of these results for the design of the next generation of SC-SOFC, with reduced electrode dimensions and improved electrochemical performance, will be discussed.
Merits of Bi3TiNbO9 for Humidity Sensors
Authors: Avila Ricardo , Castro A. , Serafini Daniel , Ulloa H. E. , Jiménez R. , Cabrera A.
Published: April 2011

The fast and reproducible electrical response of the new, metastable fluorite phase of Bi3TiNbO9 to ambient humidity is reported. Pellets were prepared by high energy mechanochemical activation of the precursor powders, pellet pressing, sintering, and sputter deposition of Pt electrodes. Thermal analysis shows exothermic peaks at 465 and 594 °C. X ray diffraction analysis identifies a metastable fluorite like phase, isomorphous to the δ phase of Bi2O3, between the first and the second peaks, and the stable Aurivillius phase after the second peak.

Over a wide (-40 to 20 °C) dew point (DP) range, at 23 °C ambient temperature, the conductivity increases close to exponentially, from nearly 10−3 to 102 pS/cm. Upon removal of the bias, and under DP cycling, the relaxation current responds to humidity steps, on top of the long term current decay, in a manner similar as under bias. In addition, upon a step into humidity, after a dry spell, the current overshoots (before proceeding to the long term decay) to a maximum value (Im) which depends on the duration of the previous dry spell. If this is short, Im remains below the current value (Iph) at the end of the previous humidity stage. If the dry spell is long, Im overshoots above Iph. This behavior is unlike that of any discharge current through a leaky capacitor. A preliminary model for understanding it proposes the surface transport of a charge carrier, assisted by diffusion of some species from the interior of the ceramic grains.
Structural Characterization and Ionic Conductivity of Metastable Gd2(Ti0.65Zr0.35)2O7 Powders Prepared by Mechanical Milling
Authors: Fuentes Antonio F. , Moreno Karla J. , Santamaria Jacobo , Leon Carlos , Amador Ulises
Published: April 2011

We analyze in this work the influence of ordering on the oxygen ion dynamics in the ionic conductor Gd2(Ti0.65Zr0.35)2O7, prepared by mechanical milling. As-prepared powder phase presents a metastable anion deficient fluorite-type of structure below 800°C becoming a disordered pyrochlore above this temperature. Such phase transformation implies a significant increase in the ionic conductivity of this material as a result of a systematic decrease in the activation energy for the dc conductivity, from 1.23 to 0.78 eV. Electrical conductivity relaxation is well described by the Kohlrausch-Williams-Watts (KWW) stretched exponential function with the fractional exponent n decreasing systematically with increasing sintering temperature (increasing ordering) as a result of decreasing ion-ion interactions in better ordered samples.
Potentiometric Detection of VOCs using Non-Nernstian SmFeO3/Pt/YSZ/Pt Sensors
Authors: Chevallier Laure , Di Bartolomeo Elisabetta , Traversa Enrico , Mori Masami , Sadaoka Yoshihiko
Published: April 2011

Electrochemical sensors for Volatile Organic Compound (VOCs) based on commercial YSZ layers were fabricated using Pt as reference electrode and SmFeO3 perovskite oxide as a sensing electrode, both exposed to the same gas environment. Pt was sputtered on YSZ layers while SmFeO3 p-type semiconducting oxide was deposited by electrophoretic deposition (EPD). Nanometric SmFeO3 oxide powders were selected because they have already shown good sensing performance in semiconducting sensors for oxidizing gases such as NO2 and ozone, and reducing gases, such as VOCs. Potentiometric measurements were performed under exposure to different concentrations of VOCs such as: methyl ethyl ketone (MEK), ethanol (EtOH) and acetic acid (AA). The best gas sensing response was obtained at 400°C.
Preparation of SrFeO3-X Thin Films by the Spin-Coating Method and its Gas Sensing Properties
Authors: Majid Abdul , Gollner Egmont , Matam Mahesh , Tunney Jim , Post Mike
Published: April 2011

Nanostructured coatings have recently attracted increasing interest because of the possibilities of synthesizing materials with unique physical-chemical properties. In this report we describe our efforts at developing a methodology for the fabrication of SrFeO3-X based thin films using a modified Pechini method. Thin films of SrFeO3-X were fabricated using a spin coating and PLD method on Al2O3. The films annealed at 600 °C for one hour show a perovskite phase. The sensors based on SrFeO3-X thin films on alumina were fabricated using spin coating and PLD techniques. The sensing properties were determined using propane and propene as the probing gases. Response characteristics and temperature dependency of spin coated and PLD fabricated samples were compared. The effect of the electrode material, Au and/or Pt, on the gas detection sensitivity of the SrFeO3-X thin films was also investigated.
The Hydrothermal Synthesis of Lithium Iron Phosphate
Authors: Chen Jiajun , Whittingham M. Stanley
Published: April 2011

Well-crystalline LiFePO4 particles were successfully prepared in the temperature range between 120 and 220°C, and complete ion ordering was obtained above 175°C where the unit cell dimensions were identical to high temperature material. The use of a soluble reductant, such as sugar or ascorbic acid, was found to minimize the oxidation of the iron to ferric. The electronic conductivity was enhanced by the deposition of carbon from the sugar, or by the addition of carbon nanotubes to the hydrothermal reactor when over 90% of the lithium could be de-intercalated electrochemically. We have extended the hydrothermal synthesis method to the Mn, Co and Ni analogs as well as to the mixed phosphates, such as LiMnyFe1-yPO4.
Impact of Surface Chemistry on the Electrochemical Performance of LiCoO2
Authors: Pereira Nathalie , Al-Sharab Jafar , Cosandey Frederic , Badway Fadwa , Amatucci Glenn
Published: April 2011

For almost a decade there have been spurious reports that high specific capacity LiCoO2 can be stabilized through modification of the synthesis protocol, however no basis for this improvement was ever proven. In this study, high specific capacity (190 mAh/g) LiCoO2 with good cycling stability was successfully fabricated in this study with the purpose to identify the basis for, and reproduce the high specific capacity. Extensive physical and electrochemical characterization confirmed the improvement was directly related to the surface chemistry as opposed to bulk modification of the crystal chemistry. In particular, high resolution transmission electron microscopy confirmed the thermodynamic growth of a distinct surface phase of 5-10nm on the best materials. In contrast to extrinsically deposited surface coating, the intrinsic approach enabled a one step synthesis and modification using intrinsic constituents to result in a 5-10nm uniform coating of a cubic cobaltite based on fundamental phase stabilities as dictated by the phase diagram of the Li-Co-O system.
Micro- and Nano-instrument Power
Authors: Karanassios Vassili
Published: April 2011

For the last several years, we have been developing and characterizing “mobile” micro- and nano-instruments for use on-site (e.g., in the field). Although such portable, battery-operated instruments are much smaller that their laboratory-scale counterparts, sometimes they provide comparable performance and they often offer improved capabilities. As such, they are expected to cause a paradigm shift in classical chemical analysis by allowing practioners to “bring the lab (or part of it) to the sample”. Two classes of examples will be used as the means with which to illustrate the power of micro- and nano-instruments. One class involves a “patient” as the sample and an ingestible capsule-size spectrometer used for cancer diagnosis of the gastro intestinal tack as (part of) “the lab”. The other involves the “environment” as the sample and a portable, battery-operated, miniaturized instrument that utilizes a PalmPilot™ with a wireless interface for data acquisition and signal processing as (part of) “the lab”. To discuss how to electrically power such miniaturized instruments, mobile energy issues will be addressed. Particular emphasis will be paid to current or anticipated future applications and to the paradigm shifts that may prove essential in powering the next generation of miniaturized instruments.
Synthesis, Characterization, Photocatalytic Activity and Dye-sensitized Solar Cell Performance of Nanorods/nanoparticles TiO2
Authors: Pavasupree Sorapong , Yoshikawa Susumu
Published: April 2011

Nanorods/nanoparticles TiO2 with mesoporous structure were synthesized by hydrothermal method at 150 °C for 20 h. The samples characterized by XRD, SEM, TEM, SAED, HRTEM, and BET surface area. The nanorods had diameter about 10-20 nm and the lengths of 100-200 nm, the nanoparticles had diameter about 5-10 nm. The prepared material had average pore diameter about 7-12 nm. The BET surface area and pore volume of the sample are about 203 m2/g and 0.655 cm3/g, respectively. The nanorods/nanoparticles TiO2 with mesoporous structure showed higher photocatalytic activity (I3- concentration) than the nanorods TiO2, nanofibers TiO2, mesoporous TiO2, and commercial TiO2 (ST-01, P-25, JRC-01, and JRC-03). The solar energy conversion efficiency (η) of the cell using nanorods/nanoparticles TiO2 with mesoporous structure was about 7.12 % with Jsc of 13.97 mA/cm2, Voc of 0.73 V and ff of 0.70; while η of the cell using P-25 reached 5.82 % with Jsc of 12.74 mA/cm2, Voc of 0.704 V and ff of 0.649.
Highly Efficient Solar Cells Using Organic Dyes with Amorphous Moiety
Authors: Kim Sanghoon , Lee Jae Kwan , Jung Il , Song Kyu-Ho , Baik Chul , Choi Hyunbong , Kim Duckhyun , Fantacci S. , De Angelis F. , Yum J -H , Nazeeruddin Md. K. , Graetzel M. , Ko Jaejung
Published: April 2011

Novel organic sensitizers comprising donor; electron-conducting, and anchoring groups were engineered at molecular level and synthesized. The functionalized unsymmetrical organic sensitizers 3-{5-[N,N-Bis(9,9-dimethylfluorene-2-yl)phenyl]-thiophene-2-yl}-2-cyano-acrylic acid (JK-1) and 3-{5'-[N,N-Bis(9,9-dimethylfluorene-2-yl)phenyl]-2,2'-bithiophene-5-yl}-2-cyano-acrylic acid (JK-2), upon anchoring onto TiO2 film exhibit unprecedented incident photon to current conversion efficiency 91 %. The photovoltaic data using an electrolyte having composition of 0.6M M-methyl-N-butyl imidiazolium iodide, 0.04 M iodine, 0.025 M LiI, 0.05M guanidinium thiocyanate and 0.28 M tert.butylpyridine in 15/85 (v/v) mixture of valeronitrile and acetonitrile revealed a short circuit photocurrent density of 14.0 mA/cm2, an open circuit voltage of 753 mV and a fill factor of 0.76, corresponding to an overall conversion efficiency of 8.01 % under standard AM 1.5
MeV Ion Beam Bombardments Effects on the Thermoelectric Properties of Zn4Sb3 / CeFe(4-x)CoxSb12 Nano-Layered Superlattices
Authors: Budak S. , Smith C. C. , Zheng B. , Muntele C. I. , Zimmerman R. L. , ILA D.
Published: April 2011

We prepared multilayers of semiconducting half-heusler β-Zn4Sb3 and skutterudites CeFe(4-x)CoxSb12 compound thin films by ion beam assisted deposition (IBAD) system for the application of thermoelectric (TE) materials. Rutherford backscattering spectrometry (RBS) was used to analyze the composition of thin films. The thin films were then bombarded by 5 MeV Si ions for generation of nanodots in the films. We measured the cross-plane thermal conductivity by a house developed 3ω-method system, cross-plane Seebeck coefficient by a (MMR) Seebeck system, and cross plane electrical conductivity of these nanolayered systems by a (MMR) Hall system before and after bombardment. Both β-Zn4Sb3 and CeFe(4-x)CoxSb12 systems have been identified as promising thermoelectric materials for the application of thermal-to-electrical energy conversion. The nanodots produced by MeV ion beam can cause significant change in both electrical and thermal conductivity of thin films, thus improving the efficiency. The MeV ion-beam bombardment resulted in decrease in the thermal conductivity of thin films and increase in the efficiency of thermal-to-electrical energy conversion.
ADF-STEM Imaging of Strained GaN0.045As0.955 Epitaxial Layers on (100) GaAs Substrates
Authors: Wu X. , Robertson M.D. , Gupta J.A. , Baribeau J.-M. , Bennett J.C. , Kawasaki M. , Aoki T.
Published: April 2011

The annular dark field (ADF) image contrast of a 0.92% tensile strained GaN0.045As0.955 layer on GaAs substrate was studied with a scanning transmission electron microscope (STEM) as a function of ADF detector inner semi-angles ranging from 28 mrad to 90 mrad. The GaN0.045As0.955 layers were brighter than the surrounding GaAs for the values of ADF detector semiangle up to 65 mrad, and the measured contrast decreased with increasing ADF detector inner semi-angle. For a 37 nm thick specimen, the GaN0.045As0.955 intensity is about 13% higher than that of GaAs in the 28 mrad ADF detector inner semi-angle. Multislice simulations show that the displacement around substitutional N atoms plays an important role in the observed ADF-STEM contrast, while the contribution to the contrast due to misfit strain between GaN0.045As0.955 and GaAs is small.
Hot-Wire Chemical Vapor Deposition Epitaxy on Polycrystalline Silicon Seeds on Glass
Authors: Teplin Charles W. , Branz Howard M. , Jones Kim M. , Romero Manuel J. , Stradins Paul , Gall Stefan
Published: April 2011

During the last few years, hot-wire chemical vapor deposition (HWCVD) has been explored as a low-temperature process for epitaxially thickening c-Si seeds layers on low cost substrates. Here, we demonstrate HWCVD epitaxy on thin polycrystalline silicon seed layers on borosilicate glass substrates. The crystal Si seeds are large-grained (~10 µm) polycrystalline silicon that were fabricated by Al-induced crystallization of a-Si. We report the growth of 0.5 µm of epitaxy at ~670°C.
Grain Size Control by Means of Solid Phase Crystallization of Amorphous Silicon
Authors: Farjas Jordi , Roura Pere , Roca i Cabarrocas Pere
Published: April 2011

The grain size of thermally crystallized a-Si films is controlled by the nucleation, rN, and growth, rG, rates according to the standard Avrami's theory. Despite this evidence, most papers devoted to improve the crystallized grain size analyze their results with a qualitative reference to this theory. In this paper, we will show that one can identify the standard set of rN and rG values for a-Si and that experiments show that deviations from this standard values always result in a smaller grain size. It is also shown that one cannot expect any substantial improvement with non-conventional heat treatments. Finally, it is argued that a larger grain size is expected from a-Si films containing, in their as-grown state, a controlled density of embedded nanocrystals.
Reliability of Silicon Nitride Gate Dielectric in Vertical Thin-Film Transistors
Authors: Moradi Maryam , Striakhilev D. , Chan I. , Nathan A. , Cho N. I. , Nam H. G.
Published: April 2011

In this work, we have conducted a systematic investigation of leakage current and electrical breakdown of plasma enhanced chemical vapor deposited (PECVD) silicon nitride, both for planar films and deposited films on the vertical sidewall for the application of the vertical thin film transistors. The thickness evolution of physical properties and electrical characteristics of silicon nitride films in the range of 50 to 300 nm are investigated. Electrical breakdown strength for 150-300nm thick films was approximately 7 MV/cm, whereas the value dropped to ~3MV/cm for 50nm thick films deposited under the same process conditions. It is shown that the early failure of the thin nitride is accompanied by the increase of the pinholes number. For the vertical thin film transistors, the experimental result shows the reliability and leakage current of the gate dielectric depends on the step coverage of the silicon nitride film on the vertical sidewall.
Single Grain Si TFTs Fabricated at 100oC for Microelectronics on a Plastic Substrate
Authors: He Ming , Ishihara R. , Chen T. , Metselaar J.W. , Beenakker C.I.M.
Published: April 2011

Single grain TFTs are fabricated at a maximum temperature of 100oC for macroelectronics on a plastic substrate, as Si channels are fabricated at 100oC by combination of excimer laser crystallization and sputtering. The gate oxide is formed at 80°C by inductively coupled plasma enhanced chemical vapor deposition. These TFTs have shown a smaller threshold swing of 0.49 V/dec. and a higher field-effect mobility of 290 cm2/V·s, which can be used to directly fabricate system circuits or a high quality display on a plastic substrate.
Contact Effects in High Mobility Microcrystalline Silicon Thin-Film Transistors
Authors: Chan Kah Yoong , Bunte Eerke , Stiebig Helmut , Knipp Dietmar
Published: April 2011

Microcrystalline silicon (mc-Si:H) has recently been proven to be a promising material for thin-film transistors (TFTs). We present mc-Si:H TFTs fabricated by plasma-enhanced chemical vapor deposition at temperatures below 200°C in a condition similar to the fabrication of amorphous silicon TFTs. The mc-Si:H TFTs exhibit device mobilities exceeding 30 cm2/Vs and threshold voltages in the range of 2.5V. Such high mobilities are observed for long channel devices (50-200 mm). For short channel device (2 mm), the mobility reduces to 7 cm2/Vs. Furthermore the threshold voltage of the TFTs decreases with decreasing channel length. A simple model is developed, which explains the observed reduction of the device mobility and threshold voltage with decreasing channel length by the influence of drain and source contacts.
Rapid Crystallization of Amorphous Silicon Utilizing the Plasma Annealing at Atmospheric Pressure
Authors: Shirai Hajime , Sakurai Yusuke , Ye Mina , Haruta Koji , Kobayashi Tomohiro , Takemura Yu-ichiro
Published: April 2011

The rapid crystallization of amorphous silicon utilizing the rf inductive coupling thermal plasma jet of argon is demonstrated. Highly crystallized a-Si films were fabricated on th-SiO2 and textured a-Si:H:B/SnO2/glass by adjusting the translational velocity of the substrate stage. The H concentration in the films decreased from 1021 cm-3 to 1019 cm-3 with no marked increases in oxygen and nitrogen impurity concentrations and defect density. The crystallization proceeds from the bottom to front surface in terms of the volume expansion during the solidification and crystallization of liquid Si.
Status of nc-Si:H Solar Cells at United Solar and Roadmap for Manufacturing a-Si:H and nc-Si:H Based Solar Panels
Authors: Yan Baojie , Yue Guozhen , Guha Subhendu
Published: April 2011

This paper reviews the research and development of hydrogenated nanocrystalline silicon (nc-Si:H) solar cells at United Solar Ovonic LLC. We have been studying nc-Si:H solar cells since 2001 and have made significant progress. We have achieved an initial active-area cell efficiency of 15.1% using an a-Si:H/a-SiGe:H/nc-Si:H triple-junction structure, a stable active-area cell efficiency of 13.3% using an a-Si:H/nc-Si:H/nc-Si:H triple-junction structure, and a stable aperture-area (420 cm2) fully encapsulated module efficiency of 9.5% using an a-Si:H/nc-Si:H double-junction structure. Although the cell efficiencies with nc-Si:H in the middle and/or bottom cells have exceeded the corresponding efficiencies achieved using a-Si:H and a-SiGe:H, we still need to address several critical issues before using nc-Si:H in photovoltaic manufacturing plants. First, the cell efficiency needs to be improved further to show a clear advantage over the conventional a-Si:H/a-SiGe:H/a-SiGe:H triple-junction cell structure. Second, we need to increase the deposition rate further to make the nc-Si:H based technology more cost effective. Third, we need to develop a machine design to overcome the large-area uniformity issue, especially for very high frequency glow discharge deposition. Fourth, we need to qualify nc-Si:H based solar cell product, especially with respect to long term reliability. We have been addressing these critical issues, and will discuss the roadmap for manufacturing a-Si:H and nc-Si:H based solar panels using the roll-to-roll technology.
Manufacturing of TFTs with High Deposition Rated Microcrystalline Silicon using Plasma Enhanced Chemical Vapor Deposition
Authors: Park Kyung-Bae , Jung Ji-Sim , Kim Jong-Man , Ryu Myung-kwan , Lee Sang-Yoon , Kwon Jang-Yeon
Published: April 2011

Microcrystalline silicon was deposited on glass by standard plasma enhanced chemical vapor deposition using H2 diluted SiH4. Raman spectroscopy indicated a crystalline volume fraction of as high as 40% in films deposited at a substrate temperature 350oC. The deposition rate in films was as high as 10Å/sec. This process produced ¥ìc-Si TFTs with both an electron mobility of 10.9cm2/Vs, a threshold voltage of 1.2V, a subthreshold slop of 0.5V/dec at n-channel TFTs and a hole mobility of 3.2cm2/Vs, a threshold voltage of -5V, a subthreshold slop of 0.42V/dec at p-channel TFTs without post-fabrication annealing.
Silicon Nanowires: Growth Studies Using Pulsed PECVD
Authors: Parlevliet David , Cornish John C.L.
Published: April 2011

Silicon nanowires with high aspect ratios have been grown at high density using a variation of Plasma Enhanced Chemical Deposition (PECVD) known as Pulsed PECVD (PPECVD). Growth rate and morphology were investigated for a range of catalysts: gold, silver, aluminum, copper, indium and tin. The thickness of the catalyst layer was 100nm. Deposition was carried out in a parallel plate PECVD chamber at substrate temperatures up to 350°C, from undiluted semiconductor grade Silane. A 1 kHz square wave was used to modulate the 13.56 MHz RF power. Samples were analyzed using either a Phillips XL20 SEM or a ZEISS 1555 VP FESEM. The average diameter for nanowires grown using a gold catalyst layer was 150nm and the average length was 4μm although some nanowires were observed with lengths up to 20μm. Back-scattered-electron images clearly show gold present at the tips of the silicon nanowires grown using gold as a catalyst, confirming their growth by the vapor liquid solid (VLS) mechanism. Sporadic growth of nanowires was detected when using copper as a catalyst. Although gold performed best as catalyst for nanowire growth it was, however, closely followed by tin. The other catalysts produced nanowires with properties between these extremes.
Temperature Dependence of Silicon-based Thin Film Solar Cells on Their Intrinsic Absorber
Authors: Sriprapha Kobsak , Yunaz Ihsanul Afdi , Hiza Shuichi , Ahn Kun Ho , Myong Seung Yeop , Yamada Akira , Konagai Makoto
Published: April 2011

The temperature dependence of Si-based thin-film single junction solar cells on the phase of the intrinsic absorber is investigated in order to find the optimal absorber at high operating temperatures. For comparison, hydrogenated amorphous, protocrystalline, and microcrystalline silicon solar cells are fabricated by plasma-enhanced chemical vapor deposition and hot-wired CVD techniques. Photo J-V characteristics are measured using a solar simulator at the ambient temperature range of 25-85°C. It is found that the cells with a higher open-circuit voltage usually show lower temperature-dependent behaviors; the protocrystalline silicon solar cells provide the lowest temperature coefficient of efficiency, while the microcrystalline silicon solar cells are highly sensitive to the temperature. Therefore, protocrystalline silicon solar cells are promising for use in high temperature regions.
Efficient Thin-Film Polycrystalline-Silicon Solar Cells Based on Aluminium-Induced Crystallization
Authors: Gordon Ivan , Carnel Lode , Van Gestel Dries , Beaucarne Guy , Poortmans Jef
Published: April 2011

Efficient thin-film polycrystalline-silicon (pc-Si) solar cells on inexpensive substrates could lower the price of photovoltaic electricity substantially. At the MRS conference in 2006, we presented a pc-Si solar cell with an efficiency of 5.9% that had an absorber layer made by aluminum-induced crystallization (AIC) of amorphous silicon followed by high-temperature epitaxial thickening. The efficiency of this cell was mainly limited by the current density. To obtain higher efficiencies, we therefore need to implement an effective light trapping scheme in our pc-Si solar cell process. In this work, we describe how we recently enhanced the current density and efficiency of our cells. We achieved a cell efficiency of 8.0% for pc-Si cells in substrate configuration. Our cell process is based on pc-Si layers made by AIC and thermal CVD on smoothened alumina substrates. The cells are in substrate configuration with deposited a-Si heterojunction emitters and interdigitated top contacts. The front surface of the cells is plasma textured which leads to an increase in current density. The current density is further enhanced by minimizing the back surface field thickness of the cells to reduce the light loss in this layer. Our present pc-Si solar cell efficiency together with the fast progression that we have made over the last few years indicate the large potential of pc-Si solar cells based on the AIC seed layer approach.
The Impact of Diamond Conditioning on Surface Contact in CMP Pads
Authors: Elmufdi Carolina L , Muldowney Gregory P.
Published: April 2011

Total contact area between a CMP pad and wafer has emerged as a fundamental property that is directly linked to both removal rate and defectivity. Contact area has been shown to depend on surface morphology as it results from pad microstructure and material properties. Pads exhibiting higher contact area, hence imparting lower point stresses to the wafer, are effective in reducing CMP-related defects. The present study quantifies pad-wafer contact characteristics for both hard and soft porous polyurethane pads as a function of the extent of diamond conditioning. An Instron microtester is used to impart controlled quasi-static pad compression against a sapphire cover slip mounted on a Zeiss confocal microscope. Images collected through the microscope at discrete compressive states are analyzed off-line to quantify the total contact area and the size, shape, and distribution of individual contacts. A relationship is then established between these contact measures and the extent of conditioning. Conditioning decreases the mean asperity contact size as expected, but the evolution of contact regions shows non-intuitive features. In particular, total contact area passes through a minimum within the typical conditioning time of commercial CMP processes, then gradually increases. Clustered contact regions observed at short conditioning times spread out to a more uniform lateral spacing at longer conditioning times. These findings are accounted for by considering the texture subdivision achieved by individual diamonds together with bridging by the conditioning disk of higher regions on an unlevel pad surface. Textures produced by different conditioners on the same pad are quantified in terms of total contact area and number and uniformity of contact points. Formation of an ideal texture of abundant, well-spaced and level asperities is expedited by both conditioner type and treatment time. The results illustrate that evolution of pad contact area under compression is an essential measure for understanding polishing metrics such as wafer removal rate, defect count, and pad wear, and indicate clear direction for next-generation pad microstructures to achieve low-stress planarization.
AFM investigations of chemical-mechanical processes on silicon(100) surfaces
Authors: Iomoto Ruiji , Stevens Forrest , Langford Steven , Dickinson Tom
Published: April 2011

Atomic force microscopy (AFM) was used to examine chemical-mechanical processes on Si (100) surfaces. Places where the underlying silicon was exposed etched in basic solution, producing structures 100 nm or less in size. Etching occurs only in the presence of combined mechanical and chemical effects. By performing AFM in basic solution, the entire etching process could be observed directly. High-force scans were used to remove oxide and initiate etching in selected locations, followed by low-force scans which imaged the etching process. Although roughness initially increased during etching, the final surfaces were smooth. The etching was measured for different applied loads, numbers of scans, concentrations of the etching solution, and time. The oxide layer was extremely sensitive to applied stress, and even very light scanning caused the oxide layer to dissolve more rapidly. Once the oxide layer was removed, chemical etching proceeded with or without AFM scanning, but if AFM scanning was continued additional material was removed, probably by a tribochemical mechanism on pure Si.
Particle Metrology in CMP Slurries - Potential and Limitations of Relevant Measuring Methods
Authors: Stintz Michael , Barthel Herbert , Moinpour Mansour
Published: April 2011

The design of nanostructured materials like CMP slurries on an industrial scale requires the control of disperse systems of nanoparticles as well as of single isolated "bad" particles . It is well known that slurry abnormalities resulting from large abrasive particles and abrasive particles agglomeration can cause defects on wafer surfaces during CMP.

Particle-particle interactions generate secondary nanometer structures, clusters or agglomerates, which can dominate the relevant properties of the bulk material. Size and structure of these particle agglomerates/structures are the result of a dynamic equilibrium between agglomeration and desagglomeration. There is still a lack of understanding of these secondary soft nano- up to micro- particles because no adequate characterization methods are established.

Dilution and other preparation treatment to enable analysis by laboratory methods like TEM or AFM will distort the interparticle forces and will generate artifacts. Hence characterization methods are under investigation which can tolerate a high number of particles in the sensing zone. These high concentration methods often deliver ambiguous results. Consequently different physical principles have to be combined to get unambiguous information on the disperse state.

Performance characteristics of ultrasonic spectroscopy, photon correlation spectroscopy, analytical photo-centrifugation method combined with the high spatial resolution as well as special single particle optical counters are discussed on examples.
Advances in the Characterization of Particle Size Distributions of Abrasive Particles used in CMP
Authors: Kamiti Mungai , Popadowski Stacey , Remsen Edward E.
Published: April 2011

The use of density gradient stabilized centrifugal sedimentation (disc centrifugation) for the characterization of abrasive particles in CMP slurries is reported. For slurries prepared with ceria and colloidal silica abrasives, the technique is demonstrated as capable of providing highly repeatable analyses of the abrasive's apparent particle size distribution (PSD). The addition of water soluble organic additives to the slurries is shown to produce large shifts in the apparent PSD relative to the PSD of the pure abrasive particles. Particle-additive interactions driving the shift in apparent PSD could not be interpreted with confidence due to the lack of accurate densities for particle-abrasive complexes formed in the slurry. To address this problem, sucrose density gradients prepared using H2O and D2O were tested as spin fluids of different densities to analyze a colloidal silica standard with a narrow PSD. Preliminary results comparing experimental disc centrifuge data with theoretical simulations of the disc sedimentation pattern suggest that this technique can potentially characterize both the particle diameter and density of abrasive particles in a CMP slurry.
Particles as Transport Carriers in CMP Slurries
Authors: White Daniela , Parker John , Li Shuyou , Dravid Vinayak
Published: April 2011

Nanoparticles provide multiple functionalities to the performance of CMP slurries. These include mechanical surface abrasion, mass transport of slurry chemistries between the pad and wafer surface, or increased chemical reactivity of some key additives by in-situ interactions with the particles surfaces. Since most of the inorganic nanosized oxides used as common abrasives in CMP slurries (silica, alumina, ceria) have chemically reactive hydrophilic surface functionalities in a large pH range (2 – 12), we can assume that significant interactions between the inorganic particles surface and some of the slurry additives (organic surfactants, oxidizers, film-forming ligands, removal rates promoters, etc.) could have a meaningful impact on slurry ultimate performances (removal rates, planarity, defectivity, etc.)

In this presentation we will highlight the significance of slurry abrasives as surface modified nanoparticles/chemical carriers, able to directly participate and control the metal oxidation/removal mechanism, removal rates and other polishing characteristics. We will discuss two relevant examples, both involving fumed silica as the carrier particle in two different low pH slurries of variable complexities in terms of design (with/without particles surface modifiers) and performance requirements for tungsten CMP. We will provide a complex variety of analytical evidence (TEM, SEM, FT-IR, GPC, cyclic voltammetry, MS-TOF) in order to support the proposed mechanism of “chemically activated fumed silica”, in its natural (no interactions with organic additives in the slurry) and surface modified form (in-situ interactions with organic additives), as a carrier of selective slurry components with enhanced chemical activity, that ultimately controls the tungsten CMP mechanism and the ability of the slurry to efficiently and predictably remove the oxidized tungsten film formed at the wafer surface.
An Approach to Modeling Particle-Based and Contact-Based Wear in CMP
Authors: Terrell Elon Jahdal , Kuo Michael , Higgs C. Fred
Published: April 2011

A volume-pixel, or “voxel”-based wear model was developed in order to predict feature-scale wear in chemical-mechanical polishing (CMP), and was compared to the measured evolution of lithographically-patterned features during full-scale CMP tests. In order to conduct this study, a lithographic technique was used in order to pattern a set of raised square features into Cu-coated silicon wafers. A two-dimensional (2D) contact profilometer was used to measure the topography of an isolated feature on the wafer both before polishing and at various intervals throughout the polishing process. For wear modeling, the voxel modeling framework involved the conversion of each of the pre-polished feature topographies into a square matrix of cuboids, which allowed for contact mechanics and wear modeling to take place between the interacting cuboids of the sample and a simulated polishing pad. After the predicted wear of the Cu feature was then compared to experiment.