Mikhail Baklanov, IMEC
Jeffery Bielefeld, Intel Corporation
Vincent Jousseaume, CEA-LETI
Eiichi Kondoh, Univ of Yamanashi
Symposium Support Air Products
Aldrich Materials Science
Applied Materials, Inc.
Lam Research Corporation
Tokyo Electron America, Inc.
BB2: Low-K Materials II
Tuesday PM, April 07, 2015
Moscone West, Level 2, Room 2014
2:30 AM - *BB2.01
Block Copolymer Packing Limits and Interfacial Reconfigurability in the Assembly of Periodic Mesoporous Organosilicas
Brett A. Helms 2 Andrew W. Wills 1 Peter Ercius 2 Ethan R. Rosenberg 2 Rory Runser 2
1Lawrence Berkeley National Lab Berkeley United States2The Molecular Foundry, LBNL Berkeley United StatesShow Abstract
Block copolymers are often used as architecture-directing agents during the assembly of periodic mesoporous organosilicas (PMOs). Here, I will describe new architecture-directing agents based on poly(N,N-dimethylacrylamide)-block-poly(styrene) block copolymers (BCPs) that allow PMOs to be generated with independently tunable porosity up to ~64% for pore sizes of 10-25 nm. In our investigation, we identified a universal packing limit of ~64 vol% for spherical BCP porogens in the assembled films. Beyond this limit, porogen packing after thermal processing and, in turn, pore structure showed significant deviations away from simple close-packed lattices. We were able to gain insight into this order-disorder transition above the BCP packing limit using both scattering techniques and high resolution STEM tomography. Notably, and as a result of their well-formed architectures and high porosity, our PMOs gave dielectric constants of 1.2 and 1.5 above and below BCP packing limits, respectively, indicating new avenues for these materials as low-k dielectrics.
3:00 AM - BB2.02
Asymmetric Elastic Behavior in ULK Nanoporous Dielectric Glasses
Joseph Burg 1 Reinhold Dauskardt 1
1Stanford University Stanford United StatesShow Abstract
Considerable effort has gone towards developing PE-CVD organosilicate (OCS) materials for ultra-low-k (ULK) dielectric constant materials. Dielectric constants of 2.0 and lower can be achieved adding nanoporosity into the glass. It is well known that nanoporosity degrades the mechanical properties of these materials resulting in inherently fragile behavior with fracture energies below 5 J/m2 . Additionally, the elastic stiffness decays considerably with reduced dielectric constant. A significant outstanding issue with respect to underlying thermomechanical behavior, however, is the possibility of elastic asymmetry in the material. Accurate experimental techniques to characterize the elastic modulus of thin dielectric films have generally been lacking: nanoindentation provides a measure in compression but suffers from film densification and substrate effects; tension measurements are almost non-existent; and surface acoustic wave (SAW) experiments convolute tension and compression behavior, hence eliminating the detection of any possible asymmetric elastic behavior. However, the existence of asymmetrical elastic behavior would have significant effects on thermomechanical stresses and reliability. To address this challenge, we have developed computational tools to generate a highly accurate molecular model of nanoporous ULK organosilicates. Using NPT molecular dynamic simulations to implement simulated annealing, we obtain the global energy minimum of the high-dimensional configuration space. With a low energy structure, we simulate the bulk modulus under both compressive and tensile hydrostatic pressure. Surprisingly, we report the first indication that ULK nanoporous organosilicates display asymmetric elastic behavior, a rare property for any molecular material. We explore the effects of nanoporosity volume fraction and glass composition. This important result provides insight into the underlying thermomechanical behavior of ULK nanoporous organosilicate glasses and ultimately their reliability as a microelectronic interconnect.
3:15 AM - BB2.03
Adsorption Isobars of Fluorocarbon Compounds Selected for Cryogenic Plasma Etching of Low-K Dielectrics
Askar Rezvanov 2 3 Konstantin P Mogilnikov 1 Oleg P. Gutshin 2 Evgeny S. Gornev 2 3 Gennady Y. Krasnikov 2 3 Liping Zhang 4 Christian Dussarrat 5 Jean-Francois de Marneffe 4 Mikhail R. Baklanov 4
1Rzhanov Institute of Semiconductor Physics Novosibirsk Russian Federation2Molecular Electronics Research Institute Zelenograd, Moscow Russian Federation3Moscow Institute of Physics and Technology Dolgoprudny Russian Federation4IMEC Leuven Belgium5Air Liquide Tokyo JapanShow Abstract
Microelectronic technology is currently studying possibility of introduction of low-k materials with a dielectric constant smaller than 2.5 to sub 10 nm technology nodes. However, their implementation meets considerable difficulties because the porous low-k dielectric films are damaged during plasma processes. The active species of plasma diffuse into pores and modify the pore walls. As a result, the low-k materials become hydrophilic and the k-value increases due to the moisture adsorption. A cryogenic etching method that protects the surface of porous low-k dielectrics against significant plasma-induced damage has recently been developed. When the etching takes place at low temperatures, the reactants and etch by-products condense in the pores and protect it against the penetration of active radicals. The main issue is to develop a standard approach for selection of chemical reagents capable to condense and operate at predetermined temperatures. In this paper we present a theoretical analysis of condensation of selected gases at low temperatures. We developed a method and a program that allow recalculating the adsorption isotherms of toluene or other vapors at room temperature to low temperature adsorption isobars of selected chemical compounds. This method was applied for C6F6, C4F8 for the temperature range from (-200C) to (-700C) and several constant pressures suitable for plasma ignition in CCP and ICP chambers. The data calculated for 100mTorr and 10mTorr compared with experimental data. We found similarity between the calculated and experimental results and proved that this method helps quickly and qualitatively obtains the adsorption isobars of selected gases before the making the etch experiments and the developed program can be efficiently used for selection of chemical compounds for cryogenic etching at the defined temperature range. This method and software also allow to determine polarisability and refractive indices of selected condensates.
3:30 AM - BB2.04
Enhancing Mechanical and Fracture Properties of ULK Materials with Filled Pores
Scott G. Isaacson 1 Krystelle Lionti 2 Willi Volksen 2 Teddie Magbitang 2 Yusuke Matsuda 1 Reinhold H. Dauskardt 1 Geraud Dubois 2 1
1Stanford University Stanford United States2IBM Almaden Research Center San Jose United StatesShow Abstract
Pore filling has emerged as a promising strategy for the protection of ultra-low-κ dielectrics (ULK) against plasma-induced damage [1-3]. In this work we use polymers with a wide range of molecular weights (103 - 106 g/mol) to create filled ULK materials, leading to uniform penetration, a high level of fill (~100%), and confinement of polymer chains to dimensions far smaller than their bulk radius of gyration. This confinement alters the conformations and inter-molecular interactions of the polymer phase, resulting in novel fracture behavior that has important implications for the reliability of pore-filled ULK materials.
Despite its promise as a processing technique, the effects of pore filling on the mechanical properties, fracture strength, and reliability of these backfilled ULK materials remain poorly understood. We show that the mechanical and fracture properties of a nanoporous ULK matrix can be considerably improved by filling the porosity with a polymeric second phase. Importantly, the degree of toughening increases significantly with the polymer molecular weight, and is also found to depend on processing conditions. We show that the mechanism for toughening is based on the pullout of individual confined polymer chains from the ULK matrix, distinct from the more common entanglement-based mechanisms seen in bulk polymers. This mechanism is quantified with a model that describes the nanomechanical processes occurring on the length scale of individual pores.
Nanoindentation measurements demonstrate that pore filling with confined polymers also improves mechanical properties such as Young&’s modulus and hardness. Furthermore, we present subcritical crack growth measurements that highlight the mixed effects of pore filling on the moisture-assisted cracking of ULK materials. This study provides new insight into the mechanical behavior of pore-filled ULK materials and suggests potential routes for increasing the cohesive strength of materials where the traditional bulk toughening mechanisms may be absent.
 T. Frot, W. Volksen, S. Purushothaman, R. Bruce, G. Dubois, Adv. Mater. 2011, 23, 2828-32.
 T. Frot, W. Volksen, S. Purushothaman, RL. Bruce, T. Magbitang, DC Miller, VR. Deline, G. Dubois, Adv. Funct. Mater. 2012, 22, 3043-3050.
 W. Volksen, K. Lionti, T. Magbitang, G. Dubois, Scripta Mater., 2014, 74, 19-24
BB3: Metallization and Emerging Technologies
Tuesday PM, April 07, 2015
Moscone West, Level 2, Room 2014
4:15 AM - *BB3.01
Nanomolecularly Tailored Heterointerfaces for Electronics Device Metallization and Packaging
Ganpati Ramanath 1
1Rensselaer Polytechnic Institute Troy United StatesShow Abstract
Controlling the nanoscale mechano-thermo-chemical integrity and properties of heterointerfaces are crucial for diverse applications in nanoelectronics, e.g., gate metallization, multilevel interconnect scheme, device packaging, and solid-state thermoelectric refrigeration. This talk will describe the use of molecular nanolayers to tailor chemical, mechanical, thermal, and electronic, properties of metal-dielectric and metal-thermoelectric heterointerfaces, and to directly access nanoscale property enhancement mechanisms. The results were obtained from a combination of diffusion studies, fracture tests, electron spectroscopy and microscopy, pump-probe laser thermoreflectance spectroscopy and first-principles theoretical calculations. I will demonstrate the diffusion barrier properties of organic nanolayers, and their attributes to result in several-fold increases in fracture toughness of non-adherent metal-dielectric interfaces. Terminal moieties and water-repelling moieties in the backbone of the molecules forming the nanolayer strongly impact interfacial diffusion and phase formation behavior. Interfacial toughening mechanisms include strong bonding of the nanolayer termini with the non-sticking materials and molecular decomposition into an inorganic layer. These attributes can be adapted to toughen metal-polymer interfaces, e.g., through catalytic activation of molecular moieties and bonding with metals, and tune the interfacial thermal conductance over a wide range by altering the strength of interfacial bonds. In addition to discussing the interfacial thermal conductance-adhesion energy nexus and property enhancement mechanisms, I will highlight the utility of using nanomolecular layers to access atomistic details of nanoscopic interfacial phenomena via macro-experiments.
References:Nature Materials 12, 118 (2013); Nature 447, 299 (2007); Phys. Rev. B. 83, 035412 (2011); Appl. Phys. Lett. 102, 093117 (2013); Appl. Phys. Lett. 105, 081601 (2014); Appl. Phys. Lett. 99, 133103 (2011); Appl. Phys. Lett. 99, 133101 (2011); ACS Appl. Mater. Interf. 2(5), 1275-1280 (2010); J. Appl. Phys. 108, 034317 (2010); J. Phys. Chem. Lett. 1, 336-340 (2010); Appl. Phys. Lett. 96, 143121 (2010); J. Appl. Phys. 106, 054502 (2009); Appl. Phys. Lett. 94, 093502 (2009).
4:45 AM - BB3.02
Contact Metallization for Carbon Nanotube Interconnect Vias
Yusuke Abe 1 Anshul Ashok Vyas 1 Changjian Zhou 2 Richard Senegor 1 Patrick Wilhite 1 Cary Y. Yang 1
1Santa Clara University Santa Clara United States2Hong Kong University of Science and Technology Hong Kong Hong KongShow Abstract
#12288; Carbon-based nanostructures such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), and graphene are candidate materials for next-generation integrated circuit technologies due to their tolerance to electromigration and excellent electrical, thermal, and mechanical properties . However, the key performance-limiting factor remains the high contact resistance at the interface with metal electrodes . High contact resistance inhibits downward device scaling, and is particularly problematic in the nanoscale as in case of vertical CNT in contact with a horizontal metal surface [1, 2]. To mitigate the high contact resistances between these materials and their electrodes, contact metallization becomes the key performance-determining process in functionalizing these materials for potential applications as interconnects in advanced technology nodes.
#12288; We have designed and fabricated CNT vias with widths from 150 nm to 30 nm and measured their current-voltage (I-V) characteristics . Metallization of via top contacts is performed using a point-and-shoot electron-beam induced deposition of tungsten (EBID-W) technique . The deposition conditions are varied to minimize the contact resistance between CNT and W. To extend our previous work on EBID , the SEM electron optics is adjusted to achieve e-beam spot sizes down to 50 nm ' 50 nm for W deposition. Results on test devices with deposited W top contacts show resistance reductions similar to those achieved with only current annealing and without contact metallization. However, to avoid increasing the thermal budget in chip fabrication, the use of EBID-W for via top contact metallization would be preferable.
 2013 International Technology Roadmap for Semiconductors, available online at www.itrs.net.
 P. Wilhite, A.A. Vyas, J. Tan, J. Tan, T. Yamada, P. Wang, J. Park, and C.Y. Yang, “Metal-nanocarbon contacts,” Semiconductor Science and Technology 29, 054006 (16pp), 2014.
 C. Zhou, A.A. Vyas, P. Wilhite, P. Wang, M. Chan, and C.Y. Yang, “Resistance Determination for Sub-100nm Carbon Nanotube Vias,” submitted for publication.
 S.J. Randolph, J.D. Fowlkes, and P.D. Rack, “Focused, nanoscale electron-beam-induced deposition and etching,” Critical Reviews in Solid State and Materials Sciences 31, 55-89, 2006.
 P. Wilhite, H.S. Uh, N. Kanzaki, P. Wang, A. Vyas, S. Maeda, T. Yamada, and C.Y. Yang, “Electron-beam and ion-beam-induced deposited tungsten contacts for carbon nanofiber interconnects,” Nanotechnology 25, 375702 (8pp), 2014.
5:00 AM - BB3.03
All-Carbon Interconnects: Fabrication and Integration
Yihan Chen 1 Changjian Zhou 1 Anshul A. Vyas 2 Mansun Chan 1 Cary Y. Yang 2
1The Hong Kong University of Science and Technology Hong Kong Hong Kong2Santa Clara University Santa Clara United StatesShow Abstract
As the minimum feature size in integrated circuits (IC) continues to shrink, current interconnect materials such as copper (Cu) and tungsten (W) are rapidly approaching their scaling limit due to increasing resistivity and inability to withstand high current densities. Nanocarbons such as carbon nanotubes (CNTs) and graphene are promising materials due to their higher current capacities resulting from strong C-C sp2 bonding. CNT has been investigated extensively as a candidate for on-chip vias due to its excellent current capacity and filling ability in high aspect-ratio structures , and graphene or multi-layer graphene (MLG) as a two-dimensional material has been studied for possible use in horizontal interconnects . However, there are still numerous technical challenges to overcome before nanocarbons can be utilized in future IC technologies. For CNT vias, one of the key challenges is to achieve low contact resistance between CNT and metal electrodes . By choosing graphene as the horizontal interconnect and the growth substrate for vertically aligned CNTs, low contact resistance resulting from a well-matched interface is possible through the covalently bonded graphene-CNT hybrid structure, thus achieving an all-carbon interconnect architecture.
The potential of all-carbon interconnection is demonstrated by successful growth of CNT on graphene presented here. First, single-layer to few-layer graphene is grown by annealing a Ni thin film in H2/CH4 ambient inside a low-pressure PECVD chamber. Then the graphene layer is transferred onto an insulating substrate, prior to deposition of a Fe catalyst film. A thin layer of Al2O3 is deposited on the Fe film to stabilize agglomeration in order to achieve uniform CNT density. CNTs are then grown in the same PECVD system. The effects of substrate material, Fe thickness, and stabilizing layer on CNT areal density, average diameter, and electrical properties are investigated. In general, thinner catalyst film results in smaller CNT diameters and higher densities. Highly uniform vertically aligned CNTs on graphene are obtained, providing the core structure for all-carbon interconnects. Besides excellent electrical properties, such all-carbon structure makes sub-30 nm contact areas possible between CNT vias and a planar interconnect network in advanced technology nodes.
 C. J. Zhou, A. A. Vyas, P. Wang, M. Chan, and C. Y. Yang, IEEE International Conference on Electron Devices and Solid-State Circuits, Chengdu, China (June 2014).
 K.-J. Lee, A. P. Chandrakasan, and J. Kong, IEEE Electron Device Letters 32, 4, 557 (2011).
 P. Wilhite, A. A. Vyas, J. Tan, J. Tan, T. Yamada, P. Wang, J. Park, and C.Y. Yang, Semicon. Sci. Technol. 29, 054006 (2014).
5:15 AM - BB3.04
Time Resolved Observation of Rapid Microstructural Transformation in Narrow Copper Lines
Brendan B OBrien 1 Luke Prestowitz 1 Kathleen A Dunn 1
1State University of New York Polytechnic Institute Albany United StatesShow Abstract
The underlying cause of the polygranular copper microstructure in narrow damascene lines has remained unknown despite multiple attempts to explain an exact mechanism. This work, starting with the Cu seed layer, provides a cradle to grave model for this microstructural transformation specifying differences in the seed layer texture induced by trench geometry as the origin of new driving forces which cause rapid Cu recrystallization in narrow lines.
The seed layer is known to dramatically influence the microstructural transformation of blanket Cu films. This knowledge, however, was difficult to extrapolate to Cu in patterns since the microstructure of the seed layer on patterned substrates was previously unknown. This work uses transmission electron microscopy (TEM)to bridge this gap by examining the seed layer on patterned substrates. We found that the microstructure of the seed on narrow lines differs from the seed on wide lines. The Cu seed on wide lines had a textured, continuous polycrystalline structure similar to blanket films on the field between lines, trench sidewalls, and trench bottoms. The Cu seed on narrow lines also has a textured polycrystalline structure on the field between narrow lines, but differed substantially on other surfaces. In particular, while the trench bottom was still polycrystalline, it showed no preferred crystallographic orientation. Further, the Cu seed on the sidewall of narrow lines had an untextured, irregular heterogeneous structure with isolated grains embedded in an amorphous Cu matrix. Based on this analysis it was hypothesized that the lack of texture, and crystallinity of the seed layer in the narrow lines, led to a high energy structure after plating which in turn could cause rapid trench initiated recrystallization.
Consistent with this hypothesis, a time lapse TEM analysis of the transforming Cu in narrow lines, starting ~1 hour after plating found 1) large subsurface grains growing from the narrow trenches. 2) While the grains inside the lines are larger than the expected as-plated grains, there is only moderate change in grain size inside narrow lines even after 1 week, indicating that the transformation inside the trenches is almost complete in less than an hour, significantly faster that the overburden. 3) The fully transformed grains in the trenches have remarkably few dislocations, whereas the fully transformed grains in the overburden contain many defects, suggesting that the transformation process in narrow lines is a recrystallization process driven by reduction of crystalline defects, whereas the overburden undergoes traditional grain growth.
These results indicate that in narrow lines there is a rapid initiation of recrystallization inside the lines which nucleates randomly and outpaces the surface initiated grain growth in the overburden. With this knowledge, strategies for growing more bamboo like grains will be discussed in terms of crystallographic engineering of the seed layer.
5:30 AM - BB3.05
Low Temperature Interdiffusion of Cu/Ni in Supercritical Fluid Carbon Dioxide Using a New Cu(I) Amidinate Precursor
Md Rasadujjaman 1 Mitsuhiro Watanabe 1 Hiroshi Sudoh 2 Hideaki Machida 2 Eiichi Kondoh 1
1University of Yamanashi Kofu-shi, Yamanashi-ken Japan2Gas-Phase Growth Ltd. Tokyo JapanShow Abstract
We report the interdiffusion of Cu/Ni layer stacks deposited in supercritical carbon dioxide (scCO2) using a new non-fluorinated Cu(I) amidinate precursor. The Cu(I) amidinate precursor was found to disperse well in an acetone/CO2 mixed solution together with H2 as the reducing agent, at very lower temperature (140 °C) than typical values reported for Cu(II)(hfac)2 and Cu(II)(dibm)2. At 140 °C for 60 min deposition, inter- diffusion was predominant which further improved the adhesion strength of Cu/Ni stack interface.
5:45 AM - BB3.06
Tailoring Electrical Contact Resistivity Across Metal-Thermoelectric Interfaces Using a Nanomolecular Monolayer
Thomas John Cardinal 1 . Devender 1 Theo Tasciuc 2 Ganpati Ramanath 1
1Rensselaer Polytechnic Institute Troy United States2Rensselaer Polytechnic Institute Troy United StatesShow Abstract
Tailoring the electrical contact properties of metal-thermoelectric materials interfaces is important to realize high-efficiency solid-state refrigeration for many applications such as cooling hotspots in nanoelectronics devices and solar cells. This is because the energy conversion efficiency of thermoelectric devices fabricated from materials with high thermoelectric figures of merit is often limited by poor electrical transport across metal-thermoelectric interfaces. Here, we report a tenfold increase in electrical contact conductivity Σc upon introducing a molecular monolayer of 1,8-octanedithiol (ODT) monolayer or 1,3-mercaptopropyltrimethoxysilane (MPTMS) at Cu-Bi2Te3 interfaces. For Ni-Bi2Te3 interfaces, introducing an ODT monolayer decreases Σc by 20% while MPTMS results in a threefold Σc increase. Our observations for ODT-modified interfaces are attributable to differences in interfacial bonding and phase formation at the two interfaces. Rutherford backscattering spectroscopy and X-ray diffraction reveals that ODT inhibits interfacial mixing and curtails interfacial Cu2Te formation. Electron spectroscopy of ODT-modified interfaces reveals that the thiol termini of ODT bond more strongly to Cu than Ni. Based upon similar correlations for MPTMS we present a phenomenological model describing the contact conductivity in terms of the chemical bonding and phase formation at metal-thermoelectric interfaces. Our findings show that nanomolecular monolayers could offer new possibilities for devising metallization schemes for efficient thermoelectric devices.
BB1: Low-K Materials I
Tuesday AM, April 07, 2015
Moscone West, Level 2, Room 2014
9:30 AM - *BB1.01
Material Innovations Driving Interconnect Scaling
Zsolt Tokei 1
1IMEC Leuven BelgiumShow Abstract
Moving towards advanced technology nodes of 10, 7, 5nm and beyond, significant material changes are required in order to overcome the interconnect challenges. Innovations are required in the conductor and dielectric materials as well as layout. On one hand, for the past few technology generations, the same type of materials have been reused and served as the workhorse for realizing ever more complex chips in an arena of multiple patterning and shrinking dimensions. On the other hand interconnect parasitics increasingly affect device performance and hence limit the overall technology progress. Time has come for changing our approach. In this talk it will be illustrated which type of materials, methods and approaches are emerging in order to tackle the challenges lying ahead. While aggressive dimensional shrinking remains relevant, emerging materials and processes options, such as for example Mn-based barriers, self assembled monolayers, electroless deposition and carbon based approaches show promise. The implementation of these options has to ensure that interconnect figures of merits for speed, power, noise, bandwidth density and reliability are improved with respect to currently available technologies.
10:00 AM - *BB1.02
Dielectric Material Strategies for Interconnect Layers
David Michalak 1 James Blackwell 1 Arkaprabha Sengupta 2 Jessica Torres 1 Jeffery D. Bielefeld 1 Alan M Myers 1 James S Clarke 1 Daniel Pantuso 2
1Intel Corporation Hillsboro United States2Intel Corporation Hillsboro United StatesShow Abstract
Next generation interconnect layers will need a wide variety of carefully crafted dielectric materials. There are three separate material classes that need to be explored: (1) strong, highly porous interlayer dielectric (ILD) structures having low dielectric constant (k) values, (2) materials that can infiltrate or seal the surface of the porous ILDs, and (3) a range of materials with tunable etch properties.
To address the first material class, we will discuss a strong and chemically stable spin-on material developed at Intel that has a tunable porosity between 0% to 60% volume with corresponding k-values ranging between 3.4 to 1.6. The mechanical properties of this film are stronger than typical PECVD films at matched porosity. We will show how structure can lead to further improvement in the mechanical properties. Finite element modeling was used to accurately model two different porous network systems; further calculations predict which types of structures can give the most mechanical benefit. Selected recent advances will be shown.
Highly porous ILD networks are challenging to integrate on their own because the film needs to be chemically and mechanically preserved throughout the chip manufacturing process. The second material class addresses this need by enabling reversible infiltration, and/or surface sealing, of the porous ILD network.
The third class of materials is currently the least mature and is needed to enable advanced integration schemes. Specifically, there are situations where only one of multiple exposed materials needs to be etched with selectivity greater than 20:1. Etch selectivity values for typical materials (e.g., oxides, nitrides, carbides, amorphous silicon, metal hard masks, and carbon hardmasks) are currently not sufficient. Development of new synthetic materials and/or etch processes that are compatible with current materials are desired to enable next generation integration.
10:30 AM - *BB1.03
MOFs as Low-K Candidates for Future Technology Nodes
Christof Woell 1
1Karlsruhe Institute of Technology Karlsruhe GermanyShow Abstract
Materials with good mechanical properties and low k dielectric constants are of paramount interest for the next generation of electronics, since for the needed increases in clock frequency.low-k materials are a crucial ingredient.It is very difficult to achieve dielectric constants below k = 2 with conventional polymers. Here, we focus on a novel, highly tunable class of materials, metal-organic frameworks (MOFs). MOFs are highly porous hybrid materials consisting of organic linkers connected to inorganic metal (or metal/oxo) clusters. Due to their crystalline, highly ordered, and porous structures, this class of solids exhibits a number of highly interesting properties, including very attractive mechanical properties. The Young&’s modulus of a particular MOF, HKUST-1, amounts to 9.3 GPa Because of the very low mass density of MOFs, the static dielectric constants k is very small and can drop to values far below 2.
We have introduced a novel method to grow thin films of this exciting new class of porous solids by liquid phase epitaxy (LPE) , referred to here as surface-anchored metal-organic frameworks (SURMOFs). The suitability of SURMOFs for investigating solid state elastic and mechanical properties, as well as optical, electrical and electrochemical  properties has recently been demonstrated.
 S. Bundschuh, O. Kraft, H.K. Arslan, H. Gliemann, P.G. Weidler and Ch. Wöll, Appl. Phys. Lett. 101. 101910 (2012)
 O. Shekhah, H. Wang, S. Kowarik, F. Schreiber, M. Paulus, M. Tolan, C. Sternemann, F. Evers, D. Zacher, R. A. Fischer, Ch. Wöll, J. Am. Chem. Soc. 129, 15118 (2007).
 E.Redel, Z. Wang, S.Walheim, J.Liu, H.Gliemann, Ch.Wöll, Applied Physics Letters, 103, 091903 (2013)
 V. Mugnaini, M. Tsotsalas, F. Bebensee, S. Grosjean, A. Shahnas, S. Bräse, J. Lahann, M. Buck, C.
Chem. Comm., 50, 11129-11131 (2014)
 H. Gliemann und Ch. Wöll, Materials Today, 15, 110-116 (2012)
11:30 AM - BB1.04
Nanoscale Measurements of Processing-Induced Changes in the Mechanical Properties of PorousLow-K Dielectric Thin Films and Patterns
Gheorghe Stan 1 2 Richard Gates 1 Jessica Torres 3 David Michalak 3 Canay Ege 3 Jeffery D. Bielefeld 3 Ebony Mays 3 Sean King 3
1National Institute of Standards and Technology Gaithersburg United States2University of Maryland College Park United States3Intel Corporation Hillsboro United StatesShow Abstract
The continuous miniaturization of future integrated circuits (ICs) poses increasing technological challenges for today's nanoscale material property characterization. This is because, in addition to dimensional metrology, material property measurements (e.g. mechanical, electrical, magnetic etc.) were identified as necessary control parameters to achieve the nanoscale material integration and functionality required in the next generations of ICs. It is thus most convincing to demonstrate reliable quantitative mechanical property measurements on specimens of comparable dimensions and structure with those used in fabrication.
In this work, we used contact-resonance atomic force microscopy (CR-AFM) to determine the effect of various fabrication processes on the elastic properties of thin films and narrow patterned lines of low-k dielectric materials. CR-AFM classifies as one of the most versatile AFM-based techniques for nanoscale elastic modulus measurements, with applications to various composites, thin films, and nanostructures. We used load-dependent CR-AFM to detail the change in the elastic properties of porous SiOC:H blanket films at a few important processing stages: SiOC:H with porogen incorporated, porous (porogen-free) SiOC:H, and polymer-filled SiOC:H. While the first two stages are routinely used in today's technology to define porous structures with reduced dielectric constant, the polymer filled structure is a relatively new protective strategy to increase the mechanical stiffness of porous materials during processing. The measurements were used to assess the effect of fabrication processes (UV and ash cures and pore filling) on the elastic modulus of these films and deconvolute the contributions of the constituents to the elastic modulus of each film. Furthermore, the elastic moduli of filled and unfilled porous films were modeled and compared to probe the efficacy of pore filling and analyze the structure-property relationship of these materials. On patterned SiOC:H lines (width from 25 nm to 90 nm), we used intermittent CR-AFM (ICR-AFM) to map the depth and width dependencies of material stiffness into tomographic cross-sections over regions of interest. In these measurements, we demonstrated that, at a spatial resolution of 5 nm, ICR-AFM provides advanced scanning probe capabilities for quantitative 3D mechanical characterization of nanoscale structures.
G. Stan and R. S. Gates, Nanotechnology 25, 245702 (2014).
G. Stan, R. S. Gates, P. Kavuri, J. Torres, D. Michalak, C. Ege, J. Bielefeld, and S. W. King, Appl. Phys. Lett. 105, 152906 (2014).
11:45 AM - BB1.05
Post-Porosity Plasma Protection: A Promising Strategy Against v-UV Damage in Porous, Low-K Materials
Krystelle Lionti 2 Willi Volksen 2 Teddie Magbitang 2 Maxime Darnon 1 Geraud Dubois 2
1CNRS Grenoble France2IBM Almaden Research Center San Jose United StatesShow Abstract
Integration of porous low dielectric constant (k) materials constitutes a major roadblock in the reliable manufacturing of back end of the line (BEOL) wiring for advanced technology nodes . In particular, the low-k materials increasing porosity leads to excessive plasma damage during integration, as the industry adapts procedures developed for dense and microporous insulators to mesoporous materials . Currently, ultra low-k (ULK) materials (k<2.4) cannot be integrated at the most aggressive pitch.
To mitigate plasma damage, we developed and previously reported the P4 (Post Porosity Plasma Protection) integration scheme that takes advantage of the increasing porosity and protects the ULK during BEOL integration [3,4,5,6]. This strategy consists of protecting the fully cured porous ULK material by filling the pores with a sacrificial agent then integrating an apparently non-porous dielectric. The pore filler is finally removed after integration via thermal means, fully restoring the initial properties.
The P4 efficacy was already demonstrated on a wide range of spin-on and PECVD materials: plasma damage is mitigated by the limited physical interactions between the different plasma species and the ULK due to pore-filling. However, unlike ions and free radicals that are known for causing this kind of damage, the interactions between the less energetic v-UV photons and ULK materials are different and not yet fully understood. Therefore, we decided to investigate the protective effect of the P4 against v-UV radiation only on a highly porous k=2.0 low-k material. Fluorocarbon based and oxygen based plasmas mimicking real etching and ashing steps (respectively) during ULK processing were employed. In this presentation, modifications imparted to the ULK upon different plasma or v-UV only exposures as a function of pore filling will be described and discussed. Altogether, the results demonstrate an excellent v-UV resistance of the filler, making the P4 a promising strategy against v-UV damage.
 W. Volksen, R. D. Miller, G. Dubois, Chem. Rev. 2010, 110, 56-110.
 K. Lionti, W. Volksen, T, Magbitang, M. Darnon, G. Dubois, ECS J. Solid State Sci Technol, 2015, in press.
 T. Frot, W. Volksen, S. Purushothaman, R. Bruce, G. Dubois, Adv. Mater. 2011, 23, 2828-2832.
 T. Frot, W. Volksen, T. Magbitang, S. Purushothaman, R. Bruce, S. Cohen, M. Lofaro, G. Dubois, Future Fab Intl 2011, 39, 67.
 T. Frot, W. Volksen, S. Purushothaman, R. Bruce, T. Magbitang, D. Miller, V. Deline, G. Dubois, Adv. Funct. Mater. 2012, 22, 3043-3050.
 W. Volksen, K. Lionti, T. Magbitang, G. Dubois, Scripta Mater. 2014, 74, 19-24.
12:00 PM - BB1.06
Atomic Scale Study of Trap States in Low-K Dielectric Films Studied by Dynamic Tunneling Force Microscopy
Ruiyao Wang 1 Sean King 2 Clayton Williams 1
1Department of Physics and Astronomy, University of Utah Salt Lake City United States2Intel Hillsboro United StatesShow Abstract
Trap states in low-k dielectric films are likely causes of leakage and breakdown. An atomic scale study of these trap states is performed using Dynamic Tunneling Force Microscopy (DTFM) . Two-dimensional mapping of the trap state distribution is performed, revealing each trap state within ~ 1 nm of the surface in low-k dielectric films in ultra-high vacuum. The energy level and depth of each state is measured by differentially subtracting DTFM images acquired at different applied voltages and height. The measured volume density of these trap states near the surface is typically near 1019/cm3. These results are compared with time dependent dielectric breakdown measurements on the same films. Efforts are on-going to determine whether the near surface trap state density is similar to that of the bulk.
 R. Wang, S. W. King, and C. C. Williams, “ Atomic scale trap state characterization by dynamic tunneling force microscopy, “Appl. Phys. Lett. 105, 052903 (2014).
12:15 PM - BB1.07
Atomic Scale Study of the Effect of Electrical Stress in a Low-K Dielectric Film
Ruiyao Wang 1 Sean King 2 Clayton Williams 1
1Department of Physics and Astronomy, University of Utah Salt Lake City United States2Intel Corporation Hillsboro United StatesShow Abstract
To understand the physical processes by which electrical stress causes electrical breakdown in dielectric films, an atomic scale study of individual trap states before and after electrical stress has been performed using Dynamic Tunneling Force Microscopy (DTFM)  and conductive Atomic Force Microscopy (c-AFM). DTFM provides images of the trap state locations in the dielectric surface while the c-AFM images provide images of the local current leakage. Local electrical stress is applied to the dielectric film by a voltage biased AFM probe tip. Individual trap states are observed to both appear and disappear after electrical stressing (> 10 MV/cm) in both DTFM and c-AFM images in ultra-high vacuum. A comparison between DTFM and c-AFM images acquired in the same region of the dielectric sample shows that the location of the trap states measured by DTFM is not well correlated with locations of higher current leakage.
 R. Wang, S. W. King, and C. C. Williams, “ Atomic scale trap state characterization by dynamic tunneling force microscopy, “ Appl. Phys. Lett. 105, 052903 (2014).
12:30 PM - BB1.08
Porous SiOCH Thin Films Obtained by Foaming
Julien El Sabahy 1 Gael Castellan 1 Christophe Licitra 1 Florence Ricoul 1 Vincent Jousseaume 1
1CEA Leti Grenoble FranceShow Abstract
While interconnects are scaled down, many investigations were realized to achieve ultra-low k materials with a dielectric constant lower than 2.5. After modifying chemical composition, the introduction of porosity inside the thin film was studied over the past years. Several strategies were proposed and a porogen approach by Plasma Enhanced Chemical Vapor Deposition (PECVD) was finally chosen in the microelectronic industry.
This approach is based on the co-deposition of an organosilicon precursor and an organic one. The first creates a silicon matrix while the second one creates organic moieties which are removed after an adequate post-treatment to create porosity. Ultra Low dielectric constant thin films are obtained by increasing organic porogen loading and so the film porosity. However, the porogen approach by PECVD presents some limitations. These limitations are related to the percolation of rigidity of low-k matrix for high porogen loading and porogen residues formation. After a critical porogen ratio, the matrix shrinkage observed during the porogen removal treatment induces the loss of the created porosity. Consequently, a maximum porosity of approximatively 50% can be obtained .
In order to overcome this porosity limitation, an attractive alternative approach is to use a foaming process, a well-known technique already used to produce microcellular polymers. In this technique, the porosity is created during a post-deposition step by generation of gas in the film, then nucleation and growth of gas bubbles. When this gas generation occurs, a thin film swelling and a refractive index decrease are observed, assessing the formation of porosity.
In this work, foaming of different SiOCH thin films deposited by PECVD is studied. Several sets of conditions were considered which includes the choice of chemical precursor, deposition temperature, annealing conditions (temperature, duration, UV assisted or not). It is shown that the foaming process is highly dependent on the SiOCH thin films properties, especially on the carbon content and the initial skeleton crosslinking. The use of a barrier layer deposited on top of the SiOCH film is also necessary to maximize the creation of porosity, enhancing the effect of the thin film modification. Then, the porous SiOCH thin films are studied using Fourier Transformed Infrared spectroscopy, Ellipsometry, Ellipso-porosimetry and electrical characterizations.
This work shows that the foaming of low-k allows reaching higher porosity than those obtained by a PECVD porogen approach. The mechanisms and limitations for the creation of porosity in SiOCH thin films are discussed.
 V. Jousseaume et al. "Ultra low-k by CVD: deposition and curing", Advanced Interconnects for ULSI Technology edited by M.R. Baklanov, P.S. Ho et E. Zschech, Wiley (2012), pp 35-78.
12:45 PM - BB1.09
Can Boron Overturn Silicon in the Search for Low-k Dielectric Materials?
Michelle M Paquette 1 Bradley J Nordell 1 Thuong Dang Nguyen 1 Anthony N Caruso 1 Sudhaunshu Purohit 2 William A Lanford 3 Patrick Henry 4 Sean W King 4
1University of Missouri-Kansas City Kansas City United States2University of Missouri-Kansas City Kansas City United States3University at Albany Albany United States4Intel Corporation Hillsboro United StatesShow Abstract
A major challenge facing the semiconductor industry is the development of new low-dielectric-constant (low-k) materials for metal interconnects to mitigate the issues surrounding resistance-capacitance (RC) delays as dimensionality is reduced. Such materials include not only bulk inter-/intra-layer dielectrics (ILDs), but also more specialized layers such as Cu diffusion barriers, etch stop layers, and hard masks. Traditional materials for these purposes have been derived from the Si family; however, it is becoming increasingly challenging to tailor these to meet all of the integration requirements, particularly maintaining mechanical and chemical resilience as k is lowered. Amorphous hydrogenated boron carbide (a-BxC:Hy) is a very intriguing replacement candidate. As a semi-insulating low-density covalent solid with one of the lowest possible average atomic numbers, Z (H = 1, B = 3, C = 4), a-BxC:Hy is expected to feature a low dielectric constant, while also inheriting the appealing properties of crystalline BC, which include extreme hardness, as well as thermal and chemical robustness. We have completed a series of design-of-experiment-based a-BxC:Hy film growths, culminating in the growth and characterization of upwards of 100 films, with the goal of optimizing these toward diffusion barrier/etch stop applications (i.e., slightly higher k than ILDs, but with commensurately higher mechanical and chemical figures of merit). We describe an a-BxC:Hy material composition with dielectric constant (<3.5), leakage current (<10-8 A/cm2 at 2 MV/cm), and mechanical properties (hardness >10 GPa) that meet or surpass those of Si-based materials currently being used for these applications. Further, we demonstrate its suitability for diffusion barrier/etch stop applications through X-ray-diffraction-based Cu diffusion barrier studies, as well as wet and dry etch rate determinations.
Mikhail Baklanov, IMEC
Jeffery Bielefeld, Intel Corporation
Vincent Jousseaume, CEA-LETI
Eiichi Kondoh, Univ of Yamanashi
Symposium Support Air Products
Aldrich Materials Science
Applied Materials, Inc.
Lam Research Corporation
Tokyo Electron America, Inc.
BB6: Barriers, Sealing and CMP
Wednesday PM, April 08, 2015
Moscone West, Level 2, Room 2014
2:30 AM - *BB6.01
Chemically Vapor Deposited (CVD) Polymers for Device Fabrication
Karen K. Gleason 1
1MIT Cambridge United StatesShow Abstract
CVD polymerization represents the intersection of all-dry and scalable microfabrication technology with the chemistry of functional and responsive organic materials. Unique applications enabled by CVD polymers derive from the ability to avoid high substrate temperatures and solvents. Thus CVD polymers are compatible with flexible substrates and roll-to-roll processing. In a single step, vapor-phase monomers undergo selective reactions to produce high purity and durable polymeric layers. Like atomic layer deposition (ALD), CVD polymer deposition can produce coverage which is conformal, pinhole free, and ultrathin (<20 nm thick), the essential requirements for integration into next generation 3D devices and nanostructured devices. The durability of the CVD polymers can be enhanced through in situ grafting to the substrate and crosslinking within the film. Over 70 different CVD polymers have been synthesized, spanning the range of dielectrics, semiconductors and conductors. Some CVD polymer films exhibit responsive behavior, such as a thickness change or change in surface energy, when exposed to an external stimuli such as humidity, temperature, or light. Examples of unique photovoltaics, batteries, ultracapacitors, biosensors, and responsive optical devices fabricated with CVD polymers will be presented. Additionally, use of the CVD polymer process to achieve room temperature passivation of silicon and high resolution lithography will be discussed.
3:00 AM - BB6.02
Formation of Ultra-Thin Pore Seal Layer on Porous Low-K Films
Shoko Sugiyama Ono 1 Yasuhisa Kayaba 1 Hirofumi Tanaka 1 Hiroko Wachi 1 Koji Inoue 1
1Mitsui Chemicals, Inc. Chiba JapanShow Abstract
Future nodes below 16 nm requires interlayer dielectric whose dielectric constant is lower than 2.0. In order to deliver a reduction in dielectric constant, porous low-k film is indispensable and widely studied. However, porous low-k film is sensitive to process-induced stimuli caused by plasma and metallization process, because of the continuous porous structure. Therefore, the pores must be sealed to prevent diffusion of those species. Considerable efforts have been devoted to the development of pore seal layer or metal barrier which suppresses the diffusion of metals into porous low-k film and to tailor the interface between porous low-k films and those thin layers.
We have developed pore sealants which forms ultra-thin (< 3 nm-thick ) layer on top of the surface of porous low-k while the refractive index of the bottom part of the porous low-k is kept which shows that the pore sealant does not diffuse into pores. In this talk, we focus on the formation of the pore seal layer on the surface of porous low-k . The factors which determine thickness of pore seal layer, minimum thickness for sufficient pore seal property and so on will be discussed.
3:15 AM - BB6.03
Transparent Barrier Films with Optimized Adhesion Through Nanoscale Interface Engineering
Can Cai 1 Reinhold H. Dauskardt 1
1Stanford University Stanford United StatesShow Abstract
The development of a cheap, flexible, and reliable packaging and barrier film technology is critical for the integration and commercialization of flexible photovoltaics and organic electronics devices. A promising emerging barrier technology utilizes multiple layers of alternating organic and inorganic laminates that is amenable to roll-to-roll processing while maintaining the desired ultra-low diffusion barrier properties. In operation, the barrier films are subject to effects such as stress cycling, diurnal temperature cycling, moisture and chemical erosion, and UV degradation. The organic to inorganic interfaces are highly susceptible to damage from these degradation sources and delamination often initiates at, and propagates along, these interfaces. This limits the operational lifetime of the barrier film and the device. We demonstrate a novel method to increase the adhesion strength of the organic to inorganic interface in a model system of poly (methyl methacrylate) (PMMA) and silicon oxide through interfacial patterning. An array of nanoscale patterns is etched into the PMMA through the use of nanosphere lithography. A thin layer of silicon oxide is conformally deposited onto the patterned PMMA through plasma enhanced chemical vapor deposition. The patterned interface leverages mechanical adhesion effects and exhibit an order of magnitude increase in adhesion energy (from ~2 J/m2 to ~20 J/m2) over that of a non-patterned interface. The dimensions and aspect ratios of the interfacial features determine the delamination mode and the corresponding adhesion energy. Through XPS, AFM and other surface characterization studies, we show that interfacial structuring can control the delamination pathway to access or avoid the organic to inorganic interface. Through degradation studies, we show that the structuring offers increased adhesion after broadband UV-A and UV-B exposure. By engineering interfacial structures, we can increase the adhesion and durability of organic to inorganic laminate systems.
3:30 AM - BB6.04
Graphene-Based Diffusion Barrier and Its Defect-Dependent Properties
Sooyeoun Oh 1 Janghyuk Kim 1 Jihyun Kim 1
1Korea University Seoul Korea (the Republic of)Show Abstract
High process temperature over 400 #8451; leads to spiking and intermixing of the metal contacts at the interface, which can threaten their long-term reliability. Since the use of diffusion barrier can suppress the creation of trap centers resulted from metal diffusion and reaction of the metals with the underlying semiconductor, an effort is underway on developing novel materials to enhance their the barrier properties. Among promising materials, graphene is an excellent candidate for a diffusion barrier due to its outstanding thermal and chemical stability, and impermeability. It has been reported that the grain size of graphene was one of the main factors to determine its diffusion barrier performance, where the size of graphene grain decreased as increasing its defect density.
We used graphene films grown by chemical vapor deposition method on Cu-foil. We investigated the diffusion barrier performance of defective graphene by annealing as-prepared samples under Ar condition for a min at temperatures ranging from 300 to 500 #8451;. The defects in graphene films were introduced by UV irradiation. And the defect density in graphene was controlled by varying the UV irradiation time. The optical, electrical and diffusion barrier properties of UV-treated and subsequently annealed graphene layers were investigated using 4-point probe measurement, optical transmittance measurement, scanning electron microscopy and micro-Raman spectroscopy to obtain the information of the effects of the defects on the performance of the graphene. The details of the results will be presented at the conference.
3:45 AM -
BB7: Electrodes and Energy
Wednesday PM, April 08, 2015
Moscone West, Level 2, Room 2014
4:30 AM - *BB7.01
Innovation of BEOL Devices for Energy Efficient Computing
M. Tada 1
1Low-Power Electronics Association amp; Project (LEAP) Tsukuba JapanShow Abstract
With the increasing complexity of functions in digital circuit, flexibility and energy-efficiency play important roles in addressing future computing systems. However, scaling transistors to single-nanometer regime are plagued with many challenges of gate leakage, mobility degradation and variations as well as a NRE cost. Soon, scaling will face the limits, requiring alternative devices to enhance the chip performance. BEOL devices are new functional devices embedded in Cu-BEOL and strong candidates potentially improving the chip performance without the CMOS scaling.
Atom switch is an electrochemical resistive-change device categorized in the BEOL devices. The electrochemical phenomenon is based on electrolysis of the Cu electrode to produce a precipitation of Cu at the Ru electrode, which realizing a high ON/OFF current ratio and replacing the TMG. Previously, we reported a replacement of the SRAM-based switch with atom switch integrated in Cu-BEOL.
In this talk, the developed technologies are reviewed and the opportunities and challenges of the BEOL devices including atom switch are discussed especially for low-power programmable logic applications.
Acknowledgement This work was performed as “Ultra-Low Voltage Device Project" funded and supported by METI and NEDO. A part of the device processing was operated by AIST, Japan.
5:00 AM - BB7.02
Role of Indium-Tin-Oxide Interlayer on Ag Reflector in Flexible Top-Illuminated Polymer Solar Cells: Absorption Spectra Tuning by Microcavity Structure
Wan Jae Dong 1 Jong-Lam Lee 1
1POSTECH Pohang Korea (the Republic of)Show Abstract
Recently, flexible polymer solar cells (PSCs)s fabricated on plastic substrate/indium-tin-oxide (ITO) films have attracted much interest. However, there have been distinct problems such as high water permeation rate of plastic film and brittleness of transparent ITO electrode. These problems can be solved by employing a top-illmuniated structure with a reflective metal bottom electrode on the plastic substrate. In the top-illumination configuration, the light incomes from the top transparent electrode and absorbed in the active layer. The small band-gap polymer (PTB7), however, has a small absorption coefficient (α ~ 6 x 103 cm-1 at lambda; = 500 nm), leading to insufficient light absorption. Therefore, the light trapping method is turned out to be crucial component. Although several works have succeeded to demonstrate the light trapping in PSCs with nano-patterns, the drawbacks such as a short-circuiting and complicated processing steps are still remained. Here, we will demonstrate a highly efficient and flexible top-illuminated inverted PSCs with the microcavity structure.
As a reflective eletrode, Silver (Ag) is essential due to high reflectivity. However, Ag reflector suffers from the many problems to be applied in bottom reflective electrode in solution-processed organic electronics. In particular, a few nanometer poly-imine (PEIE) layer cannot be act as a cathode interlayer because the electron-rich Ag layer doesn&’t interact with PEIE, resulting in little interfacial dipole. The surface treatment such as UV-ozone can enhance the wettability of PEIE, but the destructive chemical oxidation of Ag reflector degrades the electrical and optical properties.
In this work, the advantages of the ITO interlayer, deposited on Ag reflector, were used to produce a significantly enhanced efficiency of top-illuminated inverted solar cells. Since the UVO treatment produces the negatively charged oxygen ions on the ITO surface, the PEIE layer was successfully coated on Ag/ITO and strong interfacial dipole is formed without damaging the surface morphology or optical reflectance. This interfacial dipole reduces the work function (3.73 eV) of cathode for use in bottom reflective electrode of inverted PSCs. Simultaneously, the strong light absorption was achieved by employing the ITO layer between Ag reflector and transparent top electrode, leading to the cavity resonance. We optimized micro-cavity structure by FDTD simulation and demonstrated the highest PCE of 6.9% in the top-illuminated inverted PSCs. Moreover, the Ag/ITO reflector exhibits the extremely flexible nature. No change in sheet resistance (0.2 Omega;/sq) was found even after 50,000 bending cycles.
We believe this proposed reflector structure gives a general guideline for demonstrating the chemically robust and mechanically flexible reflector in a highly efficient optoelectronics such as organic light-emitting diodes, polymer solar cells and perovskite solar cells.
5:15 AM - BB7.03
Transfer Printing of Electrodes for Organic Solar Cells - Nanoscale Versus Macroscale Continuity
Timo Jakob 1 Andreas Polywka 1 Luca Stegers 1 Engin Akdeniz 1 Stephan Kropp 1 Michael Frorath 1 Sara Trost 1 Tobias Schneider 1 Thomas Riedl 1 Patrick Goerrn 1
1University of Wuppertal Wuppertal GermanyShow Abstract
Micro- or nanotransfer printing is a powerful tool to manufacture patterned and hence discontinuous thin film devices. On the other hand, the preparation of continuous large-area electrodes by transfer printing has not been reported. Generally, a discontinuity on the nanoscale is required for the successful transfer printing of large-area electrodes. The investigated silver films are formed by physical vapor deposition (PVD) or electro-less deposition (ELD) on an elastomeric PDMS stamp.
We observed that a better nanoscale continuity (lower resistance) leads to a decrease of the successfully transfer printed fraction of the film. In fact, successfully printed PVD films always contain cracks in the nanoscale and ELD printed films show particles that are interrupted by nanoscale voids. The nanoscale discontinuity increases the sheet resistance of transferred films compared to ideal continuous films. On the other hand, the nanoscale discontinuity makes the film slightly stretchable and all successfully transfer-printed films had been stretchable on the stamp before. In general, the nano-voids of ELD silver appear to enable a better stretchability compared to nano-cracks of PVD films, which results in a better transfer printing behavior.
Technologically the transfer of a solution processed ELD silver film appears very promising, as it enables room-temperature processing at atmosphere without the need for any further treatment of the electrode. Hence it is cost-efficient and readily adopted in roll-to-roll fabrication. Moreover, as transfer printing separates film formation from film deposition, harmful chemicals won&’t destroy sensitive subjacent layers (e.g. in an organic device). Based on these findings, we demonstrate transfer printed ELD silver films as top- electrodes for organic solar cells, which reached 85% of the power conversion efficiency compared to the reference devices with vacuum deposited silver electrodes.
5:30 AM - BB7.04
InN/InGaN Quantum Dot Photoelectrode: An Advanced Energy Material for Efficient Water Splitting and Hydrogen Generation at Zero Voltage
Naveed Ul Hassan Alvi 1 Pavel Aseev 1 Soto Rodriguez Paul 1 Gomez Hernandez Jesus Victor 1 Magnus Willander 2 Richard Notzel 3 Calleja Pardo Enrique 1
1Universidad Politeacute;cnica de Madrid Madrid Spain2Linkouml;ping University Sweden Norrkouml;ping Sweden3Universitaacute; di Milano-Bicocca, Milan ItalyShow Abstract
Pollution-free conversion of freely available solar energy into electric power or chemical fuels through photoelectrochemical (PEC) cells has attracted intensive attention of researchers and engineers around the globe. Semiconductor nanostructures have been studied extensively in recent years for PEC cells due to their distinctive properties and promise to offer superior PEC performance. The main requirement of the PEC industry is to find semiconductor materials with the capability of efficient and cost effective conversion of sunlight to H2 by splitting water. Therefore, considering the general requirements for efficient PEC water splitting, InGaN appears to be ideal with a bandgap energy tunable through the whole solar spectrum upon In composition, a large absorption coefficient, high carrier mobility, and good corrosion resistance.
Here we have demonstrated that epitaxial InN quantum dots (QDs) more than double the photoelectrochemical (PEC) water splitting efficiency of an In0.54Ga0.46N photoelectrode. The InN/In0.54Ga0.46N-QDs-photoelectrode reveals a maximum incident-photon-to-current-conversion efficiency (IPCE) of up to 56 % at a wavelength of 600 nm with hydrogen generation rate of 133 µmol h-1 cm-2 at zero applied voltage under white light illumination of a 1000 W Xenon arc lamp. The bare In0.54Ga0.46N-layer-photoelectrode reveals a much lower IPCE of 24% with H2 generation rate of 59 µmol h-1 cm-2.
The photoelectrochemical (PEC) cell based on epitaxial InN/InGaN QDs utilizes the excellent PEC properties of InGaN together with the high surface charge density of the InN QDs for enhanced water splitting and hydrogen generation. The high density of positively charged surface donor states facilitates the oxidation of O2- (oxygen-producing half reaction), i.e., the transfer of electrons to the working electrode. Still, the bandgap energy of the InGaN layer is sufficiently high to drive the redox reaction in the presence of photo-excited electrons and holes under illumination. This is attributed to the zero-dimensional electronic properties of the QDs: The number of positively charged donors accommodated on each InN QD is 40 - 90. Due to the discrete density of states and the Pauli Exclusion Principle the QDs are not accumulating a similar amount of electrons and the donors are not uniformly compensated. This leaves a local positive net charge which actively promotes the electron transfer. Notably, graphene also acts and is used as an electron acceptor and transporter to enhance the PEC activity comparably.
The InN/InGaN-QDs-PEC cell exhibits excellent photocurrent density, high incident-photon-to-current-conversion efficiency (IPCE), and a large hydrogen generation rate, much superior to the PEC cell based on bare a InGaN layer. Our InN/InGaN-QDs-PEC cell has full potential to compete and even outperform other reported PEC cells.
5:45 AM - BB7.05
Flexible Lithium Ion Rechargeable Battery with Large Scale Interdigitated Electrodes
Tae-Hyung Kang 1 2 Ki-Bum Kim 1 2 Avelino Da Costa 2 Kyu Hwan Oh 1 Woong-Ryeol Yu 1 Nam-In Kim 3 In-Suk Choi 4
1Seoul National University Seoul Korea (the Republic of)2Korea Institute of Science and Technology Seoul Korea (the Republic of)3Rocket Electronic Cooperation, LTD. Gwangjoo Korea (the Republic of)4KIST Seoul Korea (the Republic of)Show Abstract
On the advent of flexible devices, developing thin and flexible lithium-ion batteries (FLB) becomes a requisite for full flexible electronic application. Here, we contrived a co-planar type thin and flexible Lithium ion battery by using the design concept of interdigitated electrodes. Whereas a conventional LIB has its components in layer by layer structures, the co-planar type lithium ion battery has the interdigitated structure of positive and negative electrodes on the same plane without a separator, which possibly leads to a thinner battery thickness and stress relieved electrode structure. Unlike previous co-planar type microbatteries, we fabricated pouch cell type batteries with large scale interdigitated electrode structures (~ mm dimension scale) using conventional electrode materials. Our electrochemical tests showed the areal energy density of the co-planar type lithium ion battery of ~ 0.26 mAh/cm2 and the specific capacity of cathode of ~ 90 mAh/g after the cycle test up to 300, which successfully demonstrated the feasibility of a co-planar design pouch cell LIB with the interdigitated electrodes. Furthermore, our mechanical bending test results showed that the co-planar-type battery is mechanically stable during 4000 bending cycles with a bending radius of 1/8 inch.
BB8: Poster Session
Wednesday PM, April 08, 2015
Marriott Marquis, Yerba Buena Level, Salon 7/8/9
9:00 AM - BB8.01
Low-Temperature Curable Conductive Pastes for Electronic Devices
Ho Sun Lim 1 Seong-Dae Park 1
1Korea Electronics Technology Institute Seongnamsi Korea (the Republic of)Show Abstract
We have presented a development of low temperature-curable epoxy-based electrically conductive pastes for flexible substrates. Electrically conductive pastes are composed of a novolac epoxy resin and a trimodal metallic mixture of micron-sized silver flakes, silver microspheres, and silver nanoparticles, followed by curing of epoxy resin at relatively low temperatures. The conductive silver fillers made the pastes electrically conductive due to their metal-to-metal bonding, whereas the epoxy resins used for an improvement of a processability and adhesion between the metal surface and conductive pastes. Silver nanoparticles were also used as a supplementary filler to improve the metallurgical adhesion between conductor traces into the epoxy matrix. In this study, our strategy is to add reactive silver precursors to form the good metallic network of the conductive materials and reduce curing temperatures of the conductive pastes. As a result, we found that volume resistivity and electric conductivity of our epoxy-based conducting pastes containing the reactive silver precursors exhibited high values of 2.5 X 10-5 #8486;middot;cm and 4.0 X 104 S/cm, respectively, even at a low curing temperature of 150 °C. The resulting high conductivity may be used for a fabrication of various electronic devices, which require low temperature process.
9:00 AM - BB8.02
Effects of Titanic Oxide Nanofibers on Electrical and Thermal Properties of Silver Nanowires
Ming-Chih Tsai 1 2 Shang-Jung Yang 2 3 Yu-Hsuan Ho 2 Kai-Yu Peng 2 Wei-Cheng Tian 1 Pei-Kuen Wei 2 3
1Graduate Institute of Biomedical Electronicsamp; Bioinformatics Taipei Taiwan2Research Center for Applied Sciences Taipei Taiwan3Insititue of Optoelectronic Sciences Keelung TaiwanShow Abstract
Low temperature processable silver nanowire/titanic oxide nanofiber composite thin films were prepared by using peroxo-polytitanic (PPT) acid gel and silver nanowire (AgNW) solution. For the practical use of the AgNWs in optoelectronic devices and for the replacement of the conventional ITO films, the optical and electrical characteristics are the main two issues to the AgNW thin films. To increase of conducting property of the AgNWs, the connection between AgNWs played an important role in electrical performance of AgNW thin films. Herein, the PPT acid gel was applied as the precursor for the formation of titanium oxide (TiOx) nanofibers. The as-prepared TiOx nanofiber solution was then used to fuse the AgNWs into efficient conductive networks without any high temperature treatment. The average transmittance for the AgNW/TiOx composite films is ~ 92%. Compared with bare AgNWs, the AgNW/TiOx composite nanofiber thin films possessed better thermal properties which derived from the effects of TiOx coating layer. The AgNW/TiOx composite thin films showed a stable sheet resistance of ~ 20 Omega;/sq which comparable to general ITO electrodes and increased until the operating temperature higher than 300 °C. Also, the AgNW thin films were fragmented after thermal annealing at 250 °C whereas the network of AgNW/TiOx composite thin films remains complete under the annealing temperature of 400 °C. In summary, we believe that such convenient, cost-effective and low temperature processable silver nanowire/titanic oxide nanofiber composite thin films has immense potential use in future electronic devices.
9:00 AM - BB8.03
Crystal Growth of Co Film Fabricated by Electrodeposition with Supercritical Carbon Dioxide Emulsion
Xun Luo 1 Tso-Fu Mark Chang 1 Hideki Hosoda 1 Tatsuo Sato 1 Masato Sone 1
1Tokyo Institute of Technology Yokohama JapanShow Abstract
Electrodeposition is a commonly used method to fabricate components used in electronic devices. However, problems, such as formation of defects in the electrodeposited materials, are crucial problems when the devices are miniturized. Co is a commonly used material in electronic devices, such as random-access memory. Eliminating defects in the electrodeposited Co is more critical when demand of higher memory density is needed. In previous studies, an electrodeposition method with SCE (EP-SCE) was found to be effective in removing defects formed in the electrodeposited materials. In addition, effects of surface smoothening and grain refinement are observed. However, Co material fabricated by EP-SCE has not been well studied. In this study, effects of the surfactants used and the SCE on particles growth of the Co films by EP-SCE was investigated.
Co films with a thickness of about 70 µm were electrodeposited on pure Cu (99.99%) substrates, which is the cathode electrode. Pure Pt (99.99%) was used as the anode electrode. Both substrates have dimensions in 10mm*20mm*0.5mm. The electrodeposited Co films were obtained from an additive-free cobalt sulfate and cobalt chlorate bath. Composition of the bath was CoSO4#12539;6H2O 300 g/L, CoCl2#12539;6H2O 45 g/L and H3BO3 40 g/L. The deposition temperature was 313K, and pressure was 15 MPa. Current density was 4A/dm2. A scanning electron microscope (SEM) was used to observed surface of the films.
For the Co films obtained from the electrodeposition at ambient pressure and without the surfactant, hemi-spherical shaped and size-uniform particles were observed by SEM. After adding the surfactants, polyoxythylene lauvyl ether (C12H25(OCH2)15OH), into the bath, morphology of the particles were still hemi-spherical with uniform size, but average diameter of the particles sharply decreased from roughly 12 µm to 6 µm. We suggested the effect is caused by adsorption of the surfactant on surface of the cathode. When EP-SCE at 15MPa was used, shape of the particles changed. Ridge-liked morphology was observed, and growing orientation of the particles was perpendicular to the substrate surface. This morphology is difference from the results obtained from Ni EP-SCE. Further study is required to clarify the mechanism causing this phenomenon.
9:00 AM - BB8.04
Metallization on Textile by Pd Catalyzation and Ni Electroless Deposition Using Supercritical Carbon Dioxide
Mitsuo Sano 1 Tso-Fu Mark Chang 1 Tatsuo Sato 1 Masato Sone 1 Yuma Tahara 2 Tomoko Hashimoto 2 Hiromichi Kurosu 2
1Tokyo Institute of Technology Yokohama Japan2Nara Women's University Nara JapanShow Abstract
Wearable device is an advanced technology that can be applied in various fields. One of the challenging points in wearable device is deposition of metallic materials on the textile. There are many deposition methods such as sputtering and chemical vapor deposition. Among them, electroless plating is one of the most promising methods. Therefore, study on fabrication of fiber coated with metallic materials by electroless deposition has attracted much attention. However, there are still some problems needed to be improved in electroless plating. First, a pretreatment process is usually needed, and the pretreatment process is performed with toxic substance. In this case, the toxicity raises concerns for practical use of the fibber in clothing. Second, the fibers can be damaged or even lost because the strong acid used in the pretreatment. Third, adherence of the metal coating on the fiber needs to be improved.
In a previous study, we have proposed an electroless plating method with supercritical CO2, which includes a supercritical CO2 catalyzation (SCC) step and a electroless plating step in supercritical CO2 emulsified electrolyte (ELP-SCE), to improve coverage and adherence of Ni on a Kapton® polyimide film. We believe the SCC and ELP-SCE can also be applied in deposition of Ni-P on textile of polyamide to solve the problems of the toxic chemicals used in the pretreatment and improve adhesion of the Ni-P coating on the textile.
The textile used in this study is Nylon 6,6 fiber. No pretreatment was conducted in this study. The catalyzation was either in conventional method with a PdCl2/SnCl2 mixture solution or the SCC with bis (2,4-pentandionato)-palladium. The catalyzation temperature was 353 K, and the pressure for SCC is 15 MPa. After the catalyzation step, either conventional electroless plating (ELP-CONV) or ELP-SCE were performed. The reaction temperature was 353 K for both plating method, and pressure of 15 MPa was used for ELP-SCE. Surface of the Ni-P coatings was observed by an optical microscope and a scanning electron microscope (SEM).
The Ni-P coating by conventional catalyzation and ELP-CONV had many pin-holes. Size of some of the pin-holes was larger than diameter of the fiber. The Ni-P coating by SCC and ELP-CONV showed uniform coverage with no pin-hole on each fiber. However, cracking was observed on the coating. This is an indication of poor adhesion between the coating and the fiber. On the other hand, a uniform coating on the surface of each fiber was obtained by combining SCC and ELP-SCE. These results show the fiber is uniformly impregnated with the Pd catalysts by SCC, and ELP-SCE is effective in minimizing stress accumulated during the plating process and improve adhesion of the Ni-P layer on the fiber. Thus, the proposed method, SCC combined with ELP-SCE, is effective to metallize the surface of Nylon 6,6 fiber and increase functionality of the textiles.
9:00 AM - BB8.05
Fabrication of Silver Nanowire Based Transparent and Conducting Films through Optimization of Synthesis Protocol
Hyunjin Moon 1 Jinhwan Lee 1
1Seoul National University Seoul Korea (the Republic of)Show Abstract
Using Ag nanowires with high aspect ratio is key to fabrication of highly transparent and conductive Ag nanowire films. To control the aspect ratio of Ag nanowires, a series of researches concerning molar ratio of reaction agents, temperature, reaction time, stirring rate and control agent have been conducted for last few decades. Based on these results, some groups modified synthesis protocols and found the way to synthesize very long silver nanowires (>100mu;m), and showed higher conductivity and lower sheet resistance compared to the previous works that used CNT, graphene and copper nanowires as a conductive material. However, in that these films show high haze values over 5%, it is hard to see clear images comparable to ITO film whose haze value is approximately 2%. Therefore, for the fabrication of Ag nanowire films with low haze as well as high transparency and conductivity, it is necessary to synthesize Ag nanowires with thin diameters (~50 nm) as well as high aspect ratios. Although, up to now, there has been many researches on finding experimental conditions for the synthesis of silver nanowires, few study has been done for the synthesis of high performance silver nanowires. In a typical experiment, 50 mL of 0.2 M Glycerol solution of PVP was prepared at 160 #8451; and 5 mg of NaCl was added into the solution. For a parametric study, AgNO3 molar concentration (in a range of 0.022-.0132 M), NaCl molar concentration (in a range of 0.34-10.2 mM), PVP molecular weight (in a range of 29,000-1,300,000) were modulated with other parameters fixed. We found that to reduce the diameter of silver nanowire and maintain high aspect ratios, low AgNO3 molar concentration, balance between AgNO3 and NaCl molar concentration as well as proper selection of PVP molecular weights (MWs) were crucial. From SEM image measurement, synthesized silver nanowires showed 48 nm as an average diameter and aspect ratio of 500. Through Meyer Rod Coating method, we fabricate transparent conducting films with low haze value, 2%, and showed high transparency and low sheet resistance, 95% and 50 ohm/square, respectively, which highly exceed industrial requirements and surpass the performance of typical ITO films. One of the advantage of approach is that we suggests a simple fabrication method of high performance TCF(Transparent Conductive Film), without adopting expensive and cumbersome procedure such as 'Doping', CVD and so on.
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Development of Electro-Deposited Fe-Ni Alloy Sheets for PCB Applications
Jin-Wan Jeon 1 Moon-Sick Hwang 1 Sunyong Kim 1 Dong Jin Lee 1 Yoo Jin Lee 1 Jae Hak Lee 1
1Tgo Tech. Corporation Hwaseong-si Korea (the Republic of)Show Abstract
Recently, the trends of developing for high performance electronic devices such as smart phones and flexible displays focus on small and lightweight exhibiting multi-functional and high thermal resisting properties. To meet these requirements, the copper clad laminate (CCL) substrate of printed circuit boards(PCBs) should have low coefficient of temperature expansion (CTE), high modulus and high thermal conductivity of materials. Especially, the CTE is very important in PCBs that mount large chip packages due to the shearing of the solder balls. The stresses or distortions induced as the PCB expands at a different rate compared to the ceramic package can tear off a chip package.
In this study, we developed an electro-deposited iron-nickel(Fe-Ni) alloy sheets having low thermal expansion and high modulus for CCL applications. The Fe-Ni alloy is well known that it has a very low CTE at room temperature compared to other metallic materials. The machineability of the Fe-Ni alloy is very similar to stainless steels. And, it does not suffer from stress corrosion cracking. These thermal and mechanical characteristics including low CTE of the Fe-Ni alloys are suitable for the metallic materials of the CCL ground and power planes of PCBs.
We fabricated and characterized the Fe-Ni alloy sheets of 10~50mu;m thickness on stainless steel or copper foil substrate by electro-forming method from sulfamate nickel bath, which contained additions of iron chloride, saccharin, and boric acid. The electro-deposition process was carried out at the temperature of 60#8451; and the current density of 60mA/cm2. The characteristics of the electro-deposited Fe-Ni alloy sheets were optimized by adjusting the temperature, current density, stirring speed, and composition ratios of nickel sulfamate solutions and additional chemicals.
The actual electro-deposited sheet size was 470mm #8569;370mm. The composition of the Fe-Ni alloy sheets can be controlled from 42% to 46% of nickel ratio, measuring by X-ray fluorescence(XRF) analysis. The simultaneous electro-deposition of iron and nickel exhibits the phenomenon of anomalous codeposition. The CTE of these sheets was 5.0 ~ 7.0 ppm/#8451; between 30 ~ 220#8451; measuring by thermo mechanical analysis(TMA). The Young&’s modulus of these sheets was 92 GPa at the thickness of 30mu;m. These results are comparable to those of the Fe-Ni alloy sheets fabricated by conventional rolling method.
From the results, the compatibility of low CTE and high modulus of Fe-Ni alloy sheets avoids the warpage and distortion of CCLs. Next, we will apply the Fe-Ni alloy sheet to CCL ground and power planes and evaluate the characteristics of the CCL with the Fe-Ni alloy.
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Electronic Properties of Various B-doped Diamond(111)// Dye Molecule Interfaces
Karin Larsson 1
1Chemistry-Angstrom Laboratory Uppsala SwedenShow Abstract
Diamond is a widely known material for its many excellent properties (e.g., high thermal conductivity, high break down voltage, transparency, chemical intertness and bio-compatability). A B-doped diamond is an excellent p-type material for solar cell usage. Due to some specific properties (e.g., large chemical inertness, very high carrier mobility for both electron and holes, and high transparency), it is considered as one of the strongest candidates for photovoltic electric generation. However, in order to implement the usage of diamond in solar energy applications, properties like the i) electrochemical window, ii) possibility for interfacial charge transfer, and iii) stability of functionalized surface, have to be further studied and optimized.
In the present investigation, the adsorption of different dye molecules onto H-terminated diamond (111) surfaces, have been theoretically studied using Density Functional Theory (DFT) calculations under periodic boundary conditions. The diamond surfaces were B-doped in order to make them p-type semi-conducting. The choice of dyes was based on the match between the electronic structures of these H-terminated B-doped diamond surfaces, and the respective dye molecules. The dye molecules in the present study included C20H13NO3S4 (A), C35H37NO2S3 (B), C34H38OS2(C), C32H36OS2(D), and C31H35S3Br(E). These dyes differ in the various functional groups, which have the role as electron acceptors. The main goal with the present study was thereby to investigate and compare the photovoltaic efficiency of the various dyes when attached to B-doped and H-terminated diamond (111) surfaces. Of a special interest was to study the i) absorption spectra of the dye, ii) degree of electron transfer over the diamond//dye interface, iii) electron transfer rate, iv) electron-hole recombination, and v) diamond//dye bond strength.
The calculated absortion spectra for in principle all of the different dyes were shown to be located in the most intense part of the sunlight spectrum. For the E dye, the spectrum were more positioned towards the UV light range. The usage of a combination of these different dyes would, hence, be an optimal choice in order to improve the light harvesting in a photovoltaic process. Furthermore, the calculations identified the LUMO's for the B, C, and D dyes to be positioned on the upper end of the molecules, which also will be the position of the electron acceptor when being excited by light. For the dyes A and E, there were though certain extentions of the LUMOs to the lower end of the molecules (i.e., towards the diamond surface), which will also increase the electron-hole recombination rates.
Calculation of electron transfer was to ensure that the HOMO of these dyes were positioned at a lower energy compared to the upper edge of the valence band of the B-doped diamond surface. Moreover, all dyes were found to bind with strong C-C covalent bonds to the diamond (111) surface.
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Nitrogen Doped Graphene/Au Nanoparticle Composite Counter Electrode for Dye Sensitized Solar Cells
Sung Ryong Kim 1 Ye-Suel Song 1 Won-Kook Choi 2
1Korea National University of Transportation Chungju Korea (the Republic of)2Korea Institute of Science and Technology Seoul Korea (the Republic of)Show Abstract
An idealized structure of graphene presents numerous extraordinary material properties, including high electrical and thermal conductivity, flexible but high thermo-chemical stability, extremely large surface area. The performance of dye-sensitized solar cell (DSC) can be improved by balancing the electrical conductivityand electrocatalytic activity of the counter electrode. The nitrogen doped graphene was used as a counter electrode of DSC.
Anionic surfactant modified graphene oxide and cyanmide precursor is used for the production of graphene-carbon nitride (G-CN) composites. The addition of cyanamide solution in graphene oxide dispersion with continuous ultra-sonication facilitated the electrostatic interaction between the negatively charged graphene oxide with cyanamide.
The composite of nitrogen doped graphene and Au nanoparticle was effective to tune their electronic characteristics surface structure and local chemical features, and increased the photo-conversion efficiency of DSCs, The nitrogen doped graphene/Au nanoparticle counter electrode showed a conversion efficiency as high as 5.40 %, a value which is 20% higher than the nitrogen-doped grarphene only and its comparable photo conversion efficiency to Pt electrode shows the possibility of Pt-free graphene based electrode in DSC applications.
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Highly Transparent and Stretchable Electrodes using Solvolysis and Anneal Free Silver Nanowires Percolation Network
Jin Hwan Lee 1 Sukjoon Hong 1 Seung Yong Han 1 Jinhyeong Kwon 1 Hyunjin Moon 1 Seung Hwan Ko 1
1Seoul National University Seoul Korea (the Republic of)Show Abstract
As an example of modern technology, transparent conductors have been regarded as an extremely important component in optoelectronics applications such as solar cells, OLED displays, and touch panels. The most common material for transparent conductors is ITO, which has become a market leader due to its high transparency in thin film. However, its brittle ceramic properties and expensive vacuum deposition process are limitations to its further progress. Recently, carbon based materials are intensively investigated as a good candidate for flexible electronics but with limited mechanical and electrical performances. Metal is still the best material for electronics with great electrical properties but with poor transparency and mechanical performance. Here, we developed a novel hybrid approach using commercial polyurethane film and AgNW - to demonstrate a high performance, very large area transparent and stretchable conductor by a simple, low temperature, solution processible nanowire deposition. First, we have developed and synthesized anneal free AgNWs to reduce damage on polymer substrate. Previously, one of challenges for utilizing AgNWs on polymer substrates was thermal annealing which cause polymer‘s melting. Through the various synthesis conditions control, anneal free AgNWs have successfully synthesized. In addition, we adopted solvolysis and re-condensation to enhance adhesion between nanostructures and substrates. Furthermore, through the solvolysis of polymer, surface roughness of electrodes which combined AgNWs have been dramatically decreased. This interesting result can be directly applied to organic devices such as OLED, OPV which required smooth surface for thin film devices. Electrical conductivity of transparent electrodes (over 85% transparency) have been measured on strain conditions (0~30%). We found that fabricated stretchable electrodes combined AgNWs have superior transparency and conductivity for optoelectronic devices. Further, we demonstrated highly flexible and stretchable metal conductor for transparent devices which is composed on polyurethane substrate. The highly flexible and transparent metal conductors can be mounted on any non-planar surfaces and applied for various opto-electronics and ultimately for future wearable electronics.
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Solution Printed, Aligned Silver Nanowire Arrays for High Performance Transparent Electrodes
Saewon Kang 1 Seungse Cho 1 Hyunhyub Ko 1
1UNIST Ulsan Korea (the Republic of)Show Abstract
Transparent electrodes have been regarded as key component in optoelectronics applications including organic light-emitting diodes (OLEDs), touch panel, solar cells and wearable displays. The 1D silver nanowires (AgNWs) have emerged as candidate for the alternative of ITO due to their high conductivity and flexibility. However, the random assembly of AgNWs in traditional solution process has limited the further development of AgNW-based transparent electrodes. Here we demonstrate a cost-effective and one-step approach to aligned AgNW arrays by using a solution-based, nano-patterned polydimethylsiloxane (PDMS) assisted printing technique. With one and two step alignment process, unidirectional and rectangular AgNW arrays were produced over large area regardless of the substrate types. The degree of alignment was determined by the regulation of coating condition including coating speed, contact pressure and NW densities. As a result, exceptional performance (17.8 ohm/sq at 96.7% transmittance at 550 nm wavelength), which is about 4 times lower than those of randomly oriented AgNW networks, was achieved for transparent electrode based on aligned AgNW networks. In addition, aligned AgNW networks possess high stability against mechanical bending and stretching tests, where the conductivity was maintained without significant change in resistance even during 1000 bending test. High-performance transparent electrodes based on aligned AgNW networks would be widely used in various optoelectronics applications.
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Stretchable and Transparent Electrodes Based on Carbon Nanotube Rhombic Networks
Ayoung Choe 2 Sehee Ahn 2 Jonghwa Park 2 Heesuk Kim 1 Jeong Gon Son 1 Sang-Soo Lee 1 Min Park 1 Hyunhyub Ko 2
1Korea Institute of Science and Technology Seoul Korea (the Republic of)2UNIST Ulsan Korea (the Republic of)Show Abstract
Stretchable and transparent electrodes are necessary for the applications in stretchable and wearable displays and solar cells on curved or foldable surfaces. Traditional fabrication approaches are mostly focused on random networks of carbon nanotubes and metal nanowires, in which limited deformability, contact resistance, and light scattering issues deteriorate their performance. In this study, we presented a template-guided self-assembly approach for the integration of carbon nanotubes into two-dimensional (2D) rhombic nanomesh films, where the deformation of rhombic structure accommodates the strain, greatly improving the stretchability. In addition, the regular 2D nanomesh patterns greatly reduce the contact resistance and light scattering. Our rhombic carbon nanotube nanomesh films exhibited significantly lower sheet resistance (~10 times) at a similar optical transmittance (78%), greater stretchability (~8 times less resistance increase at 30% strain), and better mechanical durability (~42 times less resistance increase after 500 stretching cycles at a strain of 30%) than those of random-network carbon nanotube films. We expect that our approach can be generalized to employ other high-quality carbon nanotubes and metal nanowires to greatly improve the properties of transparent and stretchable electrode. This work presents a new technology platform for the fabrication of transparent and stretchable electrodes.
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Room Temperature Processed Electrochromic Smart Windows with Flexible Film
Haekyoung Kim 1 So Hee Lee 1 Jong Deok Park 1
1Yeungnam University Gyeungsan Korea (the Republic of)Show Abstract
Electrochromic devices, which dynamically change colour under applied potential, are widely studied for use in energy-efficient smart windows. To improve the viability of smart windows, many researchers are utilizing nanomaterials, which can provide electrochromic devices with improved colouration efficiencies, faster switching times, longer cycle lives, and potentially reduced costs. We report the synthesis of nanostructured tungsten trioxide (WO3) particles and nanowires. Their electrochromic characteristics will be measured and studied. The thin layers with nanostructured materials were coated with room temperature, solution-processed method. Electrochromic devices were fabricated with various kind of electrolyte, which can be optimized to obtain higher performances.
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Breaking Off the Low-K Death Curve Using a-BxC:Hy and Topological Constraint Theory
Bradley J Nordell 1 Christopher L Keck 1 Thuong Dang Nguyen 1 William A Landford 2 Sudhaunshu Purohit 3 Patrick Henry 4 Sean W King 4 Anthony N Caruso 1 Michelle M Paquette 1
1University of Missouri-Kansas City Kansas City United States2University of Albany Albany United States3University of Missouri-Kansas City Kansas City United States4Intel Corporation Hillsboro United StatesShow Abstract
The discovery and implementation of new amorphous materials in modern day nano-electronic and integrated circuits, specifically low-κ interlayer dielectric and etch stop/diffusion barrier materials, is an essential step to the continuation of Moore&’s law and strengthening its pathway into an undefined future. One such new amorphous material of potential interest for these and other applications is amorphous hydrogenated boron carbide (a-BxC:Hy). Due to strong covalent bonding, high bond stiffness, and low atomic polarizability, a-BxC:Hy is anticipated to exhibit a unique combination of low dielectric permittivity and high thermal and mechanical properties. However, due to a unique B12 icosahedral network bonding, relatively little is known regarding the actual structure-property relationships in a-BxC:Hy materials that could enable this unique combination of properties to be achieved. Therefore, a detailed experimental investigation of the full spectrum of material properties (electrical, thermal, mechanical, and optical) has been performed utilizing plasma-enhanced chemically vapor deposited (PECVD) a-BxC:Hy thin films.
To establish an initial set of structure-property relationships, an empirical power law model was used to correlate the dielectric constant, optical disorder, electrical current density, and Young&’s modulus to the mass density of the PECVD a-BxC:Hy thin films. This scaling theory analysis revealed the existence of critical thresholds in mass density and exponential dependencies above, below, and near the observed critical points that were consistent with those predicted by bond percolation (BP) and topological constraint theories (TCT) for amorphous systems. The application of the BP and TCT theories in turn allowed the a-BxC:Hy structure-property relationships to be extended to the average bond coordination, dimensionality (fractal and Euclidean), and radial distribution function of the a-BxC:Hy icosahedra-hydrocarbon network. Using the developed scaling relations and detailed structure-property relationships, we demonstrate the ability to tune the material properties of a-BxC:Hy for low-κ interlayer dielectric applications and achieve a unique combination of low dielectric permittivity (κ ~ 3) with high Young&’s modulus (>60 GPa).
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High Performance Organic Transistors Using a Metallic Network as Transparent Gate Electrodes
Ke Pei 1 Paddy K. L. Chan 1
1The University of Hong Kong Hong Kong Hong KongShow Abstract
Transparent electrode is a key component in a variety of optoelectronic devices, there is a recent worldwide trend of extending that desirable transparency to non-optoelectronic devices, such as transparent batteries, transparent sensors, transparent capacitors. Indium tin oxide (ITO) is currently the most extensively used transparent electrodes due to its excellent optical transparency and high electrical conductivity. There are, however, some critical drawbacks associated with ITO related to its high cost, chemical stability and brittleness. Here we propose a highly transparent metallic network as gate electrodes, fabricating by a self-forming cracked polymer template, for the first time in organic thin film transistors (OTFT) where Parylene-C (500 nm) and DNTT (50 nm) are employed as gate dielectric and semiconductor, respectively. By applying multiple layers of metallic network as gate electrodes, the obtained OTFT showed a high mobility of 0.291 cm2V-1s-1, on/off ratio of 2.28 x 106, and sub-threshold swing of 285 mV/dec, which is comparable to that of conventional transparent ITO gate control device (mobility of 0.295 cm2V-1s-1 , on/off ratio of 4.97 x 107, and sub-threshold swing of 210 mV/dec). Such a performance is made possible due to high transmittance (~80%) and low sheet resistance (~10 ohm/sq) of the Ag microwire network. The performances of the devices under different silver network density and dimensions are investigated. The current device provides a new approach to replace ITO in diverse thin film devices, especially in organic thin film transistors and memory devices.
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A Novel Concept for Double-Sided Printing of Silver Electrodes for Advanced Printed Electronic Applications
Janghoon Park 1 Sungsik Park 1 Jongsu Lee 1 Dongil Nam 1 Yoonki Min 1 Youngwook Noh 1 Hakyung Jeong 1 Kee-Hyun Shin 1 Dongjin Lee 1
1Konkuk University Seoul Korea (the Republic of)Show Abstract
Printed electronics has been in the spotlight as a potential technology in the next generation for green manufacturing. Green technology is becoming ever more significant in industrial applications. In this manner, printed electronics are a source of technological breakthroughs that are eco-friendly, low-cost, and scalable .
In this study, we present a double-sided silver printing technology for advanced printed electronics applications. Using this technology, a flexible printed circuit board (FPCB) was fabricated using a hybrid printing technique that includes roll-to-roll (R2R) direct gravure printing and via-hole filling processes.
We performed experiments using an R2R large-scale mass-production system and demonstrated that these techniques could be applied in industry. A novel process that includes front- and back-side printing on a polyimide film was investigated. The gravure-printed silver electrode was formed on a sheet and laser drilled for high accuracy with a diameter of 50-500 mu;m. Laser-drilled double-sided electrodes filled with low-viscosity silver ink were used to make interconnections between the front- and the back-side electrodes. Further, to enhance the conductivity of the printed circuit, a chemical copper plating process was utilized. The resistance of the interconnected part showed a few differences (compared with the resistance before the via-filling and the copper plating process at 1-75 mOmega;), which we considered as an excellent result taking into account the initial resistance. To determine the mechanical stability, a reliability test was conducted using cyclic motion equipment. The FPCB showed good electrical properties over 100,000 cycles.
The results obtained in this study suggest that the proposed R2R double-sided printing technology is viable in a mass-production system. To the best of our knowledge, this is the first study to suggest such applicability.
Extending this research, we successfully demonstrated other double-sided printed electronic applications such as a back-gate organic thin film transistor and a back-side heater device for use in gas sensors. The R2R process was partially adopted for the fabrication of these devices, and other printing processes were used (spin coating, screen printing, etc.). This study has significance because such R2R processed double-sided printing logic can be integrated with all future process improvements in various printed applications.
1. J. Perelaer, et al., Journal of Materials Chemistry, vol. 20, pp. 8446-8453, 2010.
This work was supported by the Global Leading Technology Program of the Office of Strategic R&D Planning (OSP) funded by the Ministry of Commerce, Industry and Energy, Republic of Korea (10042421), and by the Leading Foreign Research Institute Recruitment Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (MSIP) (grant number: 2010-00525).
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Performance Enhancement of Metal Nanowire Transparent Conducting Electrodes by Mesoscale Metal Wires
Po-Chun Hsu 1 Shuang Wang 2 Hui Wu 1 Vijay Narasimhan 1 Desheng Kong 1 Hye Ryoung Lee 2 Yi Cui 1 3
1Stanford University Stanford United States2Stanford University Stanford United States3SLAC National Accelerator Laboratory Menlo Park United StatesShow Abstract
For transparent conducting electrodes in optoelectronic devices, electrical sheet resistance and optical transmittance are two of the main criteria. Recently, metal nanowires are demonstrated to be a promising type of transparent conducting electrode for its low sheet resistance and high transmittance. Herein we incorporate the mesoscale metal wire concept (1-5 mu;m in diameter) into metal nanowire transparent conducting electrode and demonstrate at least one order of magnitude reduction in sheet resistance at a given transmittance. We realize experimentally a hybrid of mesoscale and nanoscale metal nanowires with unprecedented excellent performance: sheet resistance of 0.36 Omega;sq-1 and transmittance of92%. In addition, the mesoscale metal wires are applied to a wide range of transparent conducting electrodes including conducting polymers and oxides with improvement up to several orders of magnitude. The metal mesowires can be synthesized by electrospinning methods and their general applicability opens up exciting opportunities for many transparent conducting electrode applications.
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Passivation Coating on Electrospun Copper Nanofibers for Stable Transparent Electrodes
Po-Chun Hsu 2 Hui Wu 2 Thomas Carney 2 Matthew T McDowell 2 Yuan Yang 2 Erik C. Garnett 2 Michael Li 2 Liangbing Hu 2 Yi Cui 2 1
1SLAC National Accelerator Laboratory Menlo Park United States2Stanford University Stanford United StatesShow Abstract
Transparent conducting electrode (TCEs) is generally dominated by indium tin oxide film, but the scarcity and high price of indium have always been an issue. Copper nanowire (CuNW) networks are one of the most promising candidates to replace indium tin oxide films as the premier transparent conducting electrode (TCEs) due to its high sheet resistance (Rs) -transmittance (T) performance, superior mechanical flexibility and low lost. However, the chemical activity of CuNWs causes a substantial increase in the Rs after thermal oxidation or chemical corrosion, which may undermine its applicability. In this work, we utilize atomic layer deposition (ALD) to coat a passivation layer onto electrospun copper nanowires and remarkably enhance their durability. The passivation layer is composed of 20-nm-thick aluminum-doped zinc oxide (AZO) for the inner layer and 1-nm-thick aluminum oxide for the outer layer. Without changing the optical transmittance, the passivated CuNW TCE shows an resistance increase of only 10% after thermal oxidation at 160 °C in dry air and 80 °C in humid air with 80% relative humidity, whereas the bare CuNWs quickly become insulating. In addition, the coating and baking of the acidic PEDOT:PSS layer increases the Rs of bare CuNW by 6 orders of magnitude, while the passivated CuNWs show an 18% increase. Our work demonstrates that this ALD method can greatly enhance the reliability of CuNW TCE and thus provide a practical solution for the degradation problem of metal nanowire TCEs.
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Flexure-Based Roll-to-Roll Platform: A Practical Solution for Realizing Large-Area Nanometer-Resolution Microcontact Printing
Xi Zhou 1 Huihua Xu 1 Jiyi Cheng 1 Ni Zhao 1 Shih-Chi Chen 1
1The Chinese University of Hong Kong Shatin Hong KongShow Abstract
A continuous roll-to-roll microcontact printing (MCP) platform promises large-area nanoscale patterning with significantly improved throughput and a great variety of applications, e.g. precision patterning of metals, bio-molecules, colloidal nanocrystals, etc. Compared with nanoimprint lithography, MCP does not require a thermal imprinting step (which limits the speed and material choices), but instead, extreme precision with multi-axis positioning and misalignment correction capabilities for large area adaptation. In this work, we exploit a flexure-based mechanism that enables continuous MCP with ultrasensitive (0.05N) force control. The fully automated roll-to-roll platform is coupled with a new backfilling MCP chemistry optimized for high-speed patterning of gold and silver. Optical gratings with hundred nanometers line-width at various locations on a 4-inch plastic substrate are fabricated at a speed of 60 cm/min. Our work represents the first example of roll-to-roll MCP with high reproducibility, wafer scale production capability at nanometer resolution. The precision roll-to-roll platform can be readily applied to other material systems such as quantum dots and bio-molecules.
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High Performance Magnetic Sensorics for Printable and Flexible Electronics
Daniil Karnaushenko 1 Denys Makarov 1 Max Stoeber 1 Dmitriy Karnaushenko 1 Stefan Baunack 1 Oliver G. Schmidt 1
1IFW-Dresden Dresden GermanyShow Abstract
Flexible electronics has emerged as a standalone field and matured over past decades offering the unique possibility to adjust the shape of devices at will after their fabrication. Flexible devices strongly benefited from the recent developments of organic as well as inorganic electronics, which are prepared using printing and/or thin film technologies.
To complete the family (transistors, displays, sensors, RFID tags, organic solar cells etc.), there are strong activities towards the fabrication of flexible magnetic field sensorics.[1-3] By now, high performance magnetic sensorics relying on the giant magnetoresistive (GMR) effect are prepared exclusively using expensive and complex thin film fabrication technologies. While the most straightforward solution would be to print magnetic sensing elements at pre-defined locations on flexible circuitry.
To assure applicability of the printed GMR sensors, they should provide stable response in the consumer temperature range from 0°C up to +85°C, which require careful optimization of the polymeric binder solution with respect to the thermal expansion coefficient. Furthermore, accounting for the relatively small amplification coefficient of available printable and flexible transistors, the GMR in the range of several tens of percent under moderate magnetic fields of about 0.5 T, provided by flexible rubber based NdFeB permanent magnets, needs to be demonstrated. Indeed, printable and flexible amplifiers exhibit a DC gain as high as 50 dB and could be coupled with printable magnetoelectronics possessing MR ratios of at least 30%.
Here, we demonstrate the very first high performance printable magnetic field sensorics applicable for flexible electronics. Remarkably, after printing, the GMR sensor elements reveal up to 37% change of the electrical resistance in the magnetic field with a maximal sensitivity of 0.93 T-1 in a field of 130 mT. Furthermore, the developed magneto-sensors are fully operational in the temperature range from -10°C up to +95°C, which fulfills the stringent thermal stability requirements of consumer electronics.
With this performance, printed magnetoelectronic devices could be applied as passive components responding to a magnetic field for flexible electronics. Indeed, the output signal of the sensors can be conditioned using available printed and flexible active electronics. In combination with flexible and printable active electronics as well as wireless communication modules, the high performance magnetic field sensorics enables realization of complex platforms capable of detecting and responding to an external magnetic field. This feature is of great interest to realize smart packaging and