bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue Degradation of Nanometer-Scale Silicon Dioxide Reaction Layers on Silicon Structural Films
Authors: Muhlstein C.L. , Stach E.A. , Ritchie R.O.
Published: June 2019

Although bulk silicon is ostensibly immune to cyclic fatigue and environmentally-assisted cracking, the thin film form of the material exhibits significantly different behavior. Such silicon thin films are used in small-scale structural applications, including microelectromechanical systems (MEMS), and display ‘metal-like’ stress-life (S/N) fatigue behavior in room temperature air environments. Fatigue lives in excess of 1011 cycles have been observed at high frequency (∼40 kHz), fully-reversed stress amplitudes as low as half the fracture strength using surface micromachined, resonant-loaded, fatigue characterization structures. Recent experiments have clarified the origin of the susceptibility of thin film silicon to fatigue failure. Stress-life fatigue, transmission electron microscopy, infrared microscopy, and numerical models have been used to establish that the mechanism of the apparent fatigue failure of thin-film silicon involves sequential oxidation and environmentally-assisted crack growth solely within the nanometerscale silica layer on the surface of the silicon, via a process that we term ‘reaction-layer fatigue’. Only thin films are susceptible to such a failure mechanism because the critical crack size for catastrophic failure of the entire silicon structure can be exceeded by a crack solely within the surface oxide layer. The growth of the oxide layer and the environmentally-assisted initiation of cracks under cyclic loading conditions are discussed in detail. Furthermore, the importance of interfacial fracture mechanics solutions and the synergism of the oxidation and cracking processes are described. Finally, the successful mitigation of reaction-layer fatigue with monolayer coatings is shown.
Effect of Moisture and Graded-Layer Mechanical Properties on Deformation and Interfacial Adhesion
Authors: Wang Lorraine C. , Dauskardt Reinhold H.
Published: June 2019

Controlling material properties over nanometer length scales is crucial for current and emerging high-density microelectronic device packages. Miniaturization of devices is increasingly limited by the ability to “connect” to the device, and the required packaging structures must be fabricated where layer thickness and feature sizes approach micron size scales while achieving the required mechanical, thermal and electrical properties. Second phase additions such as sub-micron sized particles are often added to locally adjust the material properties of constituent layers in the complex package structure. This results in significant variation of mechanical properties over sub-micron length scales. Such manipulation of material structure and its effects on mechanical and interfacial fracture behavior are addressed using experimental and modeling studies. Underfill layers consisting of an epoxy matrix with dispersed silica beads are shown to exhibit variations of elastic and flow properties in excess of three-fold across the layer thickness. Mechanical properties are not only affected by the distribution of second-phase fillers, but also by the adhesion properties of the filler/matrix interface. Interfaces are susceptible to stress corrosion cracking associated with moisture which can lead to progressive debond growth at loads much lower than that required to exceed the critical interface fracture energies. Subcritical debonding is affected by temperature, humidity, and the bond chemistry of the interface. The effects of these variations are considered on the adhesive and subcritical debonding behavior of interfaces between model epoxy underfills and SiNxchip passivation. Implications for other constrained complex layered structures are considered.
Multi-Scale Simulations of Interfacial Fracture of Nanoscale Thin-Film Structures: Effect of Length Scales and Residual Stresses
Authors: Strohband Sven , Dauskardt Reinhold H.
Published: June 2019

Plasticity is a significant contributor to the interfacial fracture resistance of multilayer thinfilm structures containing ductile layers. In this study we investigate the effect of a nanoscale elastic barrier layer separating the crack from a plastically deforming layer. The simulation procedure is multiscale in the sense that the simulation zone encompasses only a small region around the crack tip that includes the layers of interest and the bulk of the sample is modeled as applied boundary conditions on that region. The salient parameters governing the plasticity contribution to interfacial fracture energy, GC, including the barrier layer thickness and elastic properties, intrinsic fracture energy G0, and the maximum cohesive stress governing interface separation are reported. In addition, we explore the effect of residual stresses on debonding with particular attention to the the stress state in the ductile layer. It is shown that residual thin-film stresses can alter plasticity in the ductile layer and significantly influence the macroscopic fracture energy.
Plasticity-Related Phenomena in Metallic Films on Substrates
Authors: Legros M. , Dehm G. , Balk T.J. , Arzt E. , Bostrom O. , Gergaud P. , Thomas O. , Kaouache B.
Published: June 2019

Plastic deformation due to thermal stresses has been investigated for different metallic films deposited on Si or α-alumina substrates. We conducted post-mortem TEM and SEM investigations of samples that underwent thermal cycles in order to capture the microstructural changes imposed by thermal stresses. The ultimate goal is to determine the dominant plasticity mechanisms responsible for such changes. In-situ thermal cycles performed inside the TEM allowed direct and real-time observations of dislocation behaviour under stress. It is shown that dislocation density drops in Al/Si, Au/Si and in Cu/α-alumina thin film systems. Except in the case of pseudo-epitaxial Cu on sapphire, the interaction of dislocations with the interfaces (passivation, oxide, adhesion layer) is attractive and leads to the disappearance of interfacial dislocations. In this light, the generalized observation of high tensile stresses that arise in metallic films at the end of cooling is explained in terms of insufficient dislocation sources instead of classic strain hardening. Diffusional processes can substitute for a lack of dislocation, but the low relaxation strain rate that would be excpected should lead to high stresses during the cooling stages of thermal cycles.
Parallel Glide: A Fundamentally Different Type of Dislocation Motion in Ultrathin Metal Films
Authors: Balk T. John , Dehm Gerhard , Arzt Eduard
Published: June 2019

When confronted by severe geometric constraints, dislocations may respond in unforeseen ways. One example of such unexpected behavior is parallel glide in unpassivated, ultrathin (200 nm and thinner) metal films. This involves the glide of dislocations parallel to and very near the film/substrate interface, following their emission from grain boundaries. In situ transmission electron microscopy reveals that this mechanism dominates the thermomechanical behavior of ultrathin, unpassivated copper films. However, according to Schmid's law, the biaxial film stress that evolves during thermal cycling does not generate a resolved shear stress parallel to the film/substrate interface and therefore should not drive such motion. Instead, it is proposed that the observed dislocations are generated as a result of atomic diffusion into the grain boundaries. This provides experimental support for the constrained diffusional creep model of Gao et al.[1], in which they described the diffusional exchange of atoms between the unpassivated film surface and grain boundaries at high temperatures, a process that can locally relax the film stress near those boundaries. In the grains where it is observed, parallel glide can account for the plastic strain generated within a film during thermal cycling. One feature of this mechanism at the nanoscale is that, as grain size decreases, eventually a single dislocation suffices to mediate plasticity in an entire grain during thermal cycling. Parallel glide is a new example of the interactions between dislocations and the surface/interface, which are likely to increase in importance during the persistent miniaturization of thin film geometries.
On the Interaction Between Mg Solute Atoms and Dislocations in Al-Mg Binary Alloys
Authors: Zhang D. , Picu R.C.
Published: June 2019

The interaction between solute atoms and dislocations is known to lead to negative strain rate sensitivity and poor formability. The negative rate sensitivity causes inhomogeneous flow and the Portevin-LeChatelier (PLC) effect. These observations motivate the present study of the solute-dislocation interaction in binary Al-Mg alloys. We report here on three issues. First, we determine the size and shape of stable Mg clusters at stationary dislocations of edge, 60° and pure screw type. We then evaluate the accuracy with which clustering is predicted by the classical pressure field-solute interaction formula, i.e. within the assumption that solute do not interact and the pressure field of the dislocation is unperturbed by the solute. Second, we investigate to what extent the presence of the cluster perturbs the far field of the dislocation. Finally, the effect of the solute on the stacking fault energy is investigated.
Plasticity in Polycrystalline Thin Films: a 2D Dislocation Dynamics Approach
Authors: Nicola Lucia , Giessen Erik Van der , Needleman Alan
Published: June 2019

Thermal stress evolution in polycrystalline thin films is analyzed using discrete dislocation plasticity. Stress develops in the film during cooling from a stress-free configuration due to the difference in thermal expansion coefficient between the film and its substrate. A plane strain formulation with only edge dislocations is used and each grain of the polycrystal has a specified set of slip systems. The film–substrate interface and the grain boundaries are impenetrable for the dislocations. Results are presented for two film thicknesses, with higher hardening seen for the thinner films.
Shape Change in Compressively Loaded Single Crystals
Authors: Bull C.W. , Briant C.L. , Lassila D.A.
Published: June 2019

This paper presents a study of compressively loaded single crystals of tantalum. Strain gauges, interferometry, optical microscopy, and micrometers were employed to measure the deformation caused by loading. All of the measures indicated non-uniform deformation at plastic strains of less than 0.01. By using these measurements we were able to show that surface creation and shape changes of the sample introduce additional components which affected the measurement recorded by the strain gauge.
Application of the 3D X-Ray Crystal Microscope to Study Mesoscale Structure of Materials
Authors: Ice Gene E. , Liu Wenjun , Larson Bennett C. , Walker Fredrick J.
Published: June 2019

The 3D x-ray crystal microscope is an emerging tool for the study of mesoscale structure in polycrystalline materials. With this nondestructive device, local crystalline orientation, phase, elastic and plastic strain tensors can be measured with submicron spatial resolution in three dimensions. A key step in analyzing the Laue patterns from the 3D microscope is indexing the reflections, which determines the orientation of the sub-grain. With current algorithms, the angles between pairs, triplets and quadruplets of reflections are compared to theoretical angles to make guesses as to the reflection indices. The ability to index a pattern can however be compromised by both elastic and plastic deformation of a grain; elastic deformation changes the angles between reflections and plastic deformation increases the uncertainty in the centroid of each reflection. Here we report on the use of an indexing algorithm that simultaneously fits all peaks from a subgrain. This algorithm is more robust than previous methods and allows for indexing of deformed or strained grains. Some applications to studies of mesoscale materials properties are described.
Performance Assessment of Electrodeposited Thin Epoxy Films
Authors: Lopez Agustin Santana , Popa Mihai V. , Drob Paula , Vasilescu Ecaterina , Mirza-Rosca Iulia , Vasilescu Cora , Drob Silviu I.
Published: June 2019

The paper presents the experimental results concerning the performance assessment of electrodeposited epoxy films using electrochemical techniques (electrochemical impedance spectroscopy–EIS and anodic polarization) assisted by microscopical studies. The films were formed during the cathodic and anodic electrodeposition of a modified epoxy resin on carbon steel substrate. The specimens were tested in a normal aerated 3% NaCl solution at room temperature for a total period up to 1500 hours. Analysis of the impedance spectra has established an equivalent electric circuit with two time constants fitted to describe the electrodeposited epoxy film/carbon steel/electrolyte system. The time monitoring of the principal elements from the equivalent electric circuit were used to determine protective properties of the electrodeposited epoxy films. Results show a high performance of electrodeposited epoxy films, characterized by uniformity, insignificant porosity, very low water and ions permeability.
First-Principles Structural Optimization of Cubic Approximant Cd6Ca
Authors: Nozawa Kazuki , Ishii Yasushi
Published: June 2019

First-principles structural optimization is carried out for cubic Cd6Ca crystal with 168 atoms in a unit cell. The unit cell of Cd6Ca involves two four-layered icosahedral atomic clusters and 36 glue Cd atoms. Calculations are performed to determine energy cost owing to different orientations of the Cd tetrahedron, which is the innermost shell of the icosahedral cluster. Energetically favorable ordering of central Cd tetrahedra is such that the nearest neighboring tetrahedra is oriented in an anti-parallel fashion. As a result of the structural optimization, significant changes of atomic positions are observed in the first and second shells. The optimal nearest neighbor interatomic distance between the first and second shells is found to be close to the nearest neighbor distance of pure Cd. It is found that the pseudogap in the total density of states is enhanced as a result of the structural relaxation.
The Effects of Hydrogen Profiling and of Light-Induced Degradation on the Electronic Properties of Hydrogenated Nanocrystalline Silicon
Authors: Halverson A.F. , Gutierrez J.J. , Cohen J.D. , Yan Baojie , Yang Jeffrey , Guha Subhendu
Published: June 2019

The electronic properties of hydrogenated nanocrystalline silicon (nc-Si:H) were studied using junction capacitance methods. Drive-level capacitance profiling (DLCP) measurements revealed significant differences for nc-Si:H layers deposited under constant hydrogen dilution compared to those deposited using hydrogen profiling, with lower DLCP densities in the latter case. Transient photocapacitance (TPC) measurements revealed the mixed-phase nature of these materials. It disclosed spectra that appeared quite microcrystalline-like at lower temperatures, but more similar to a-Si:H at higher temperatures where the minority carrier collection is higher in the nanocrystalline component of these samples. This then suppresses the TPC signal from this component compared to the a-Si:H component. In contrast, because transient photocurrent signals are enhanced by the additional minority carrier collection, those spectra appear microcrystalline like at all temperatures. We also investigated the effects of light-induced degradation in these devices. This caused a dramatic decrease in hole collection, similar to that caused by reducing the measurement temperature of the samples. However, the light exposure did not appear to increase the deep defect density (dangling bonds).
Low Temperature Thin-film Silicon Diodes for Consumer Electronics
Authors: Wang Qi , Ward Scott , Duda Anna , Hua Jian , Stradins Paul , Crandall Richard S. , Branz Howard M. , Jeffrey Frank , Lou Hao , Perlov Craig , Jackson Warren , Mei Ping , Taussig Carl
Published: June 2019

We have developed high current density thin-film silicon n-i-p diodes for low cost and low temperature two-dimensional diode-logic memory array applications. The diodes are fabricated at temperatures below 250°C on glass, stainless steel, and plastic substrates using hot-wire chemical vapor deposition (CVD). The 0.01-mm2 standalone diodes have a forward current-density (J) of near 10 kA/cm2 and a rectification ratio over 107 at ±2 V. The 25 μm2 array diodes have J > 104 A/cm2 and rectification of 105 at ±2V. On plastic substrates, we have also used plasma-enhanced CVD to deposit 10-μm diameter diodes with J ˜ 5 x 104 A/cm2. We found that the use of microcrystalline silicon (μc-Si) i- and nlayers results in higher current-density diodes than with amorphous silicon. Reducing the diode area increases the forward current density by lowering the voltage drop across the external series resistances. A prototype diode array memory based on 10-micron devices was successfully demonstrated by monolithically integrating diodes with a-Si:H switching elements. High current density diodes have potential applications in a variety of large area, thin-film electronic devices, in addition to a-Si:H-based memory. This could widen the application of thin-film silicon beyond its present industrial applications in thin-film transistors, solar cells, bolometers and photo-detectors.
CO2 laser annealing synthesis of silicon nanocrystals buried in Si-rich SiO2
Authors: Lin Chun-Jung , Chueh Yu-Lun , Chou Li-Jen , Kuo Hao-Chung , Lin Gong-Ru
Published: June 2019

Localized synthesis of 3-8 nm Si nanocrystals (nc-Si) in PECVD-grown Si-rich SiO2 (SRSO) film is demonstrated using CO2 laser annealing at an intensity below the ablation-threshold (6.0 kW/cm2). At an optimized surface temperature of 1285°C, the precipitated nc-Si in CO2-laser-annealed SRSO film results in near-infrared photoluminescence (PL) at 806 nm, whereas the ablation damage induced at higher laser intensities as well as temperatures results in blue PL at 410 nm related to structural defects. The refractive index of the laser-annealed SRSO at 633 nm increases from 1.57 to 2.31 as the laser intensity increases from 1.5 to 6.0 kW/cm2. Transmission electron microscopy analysis reveals that the average size and volume density of Si nanocrystals embedded in the SRSO film are about 6 nm and 4.5×1016 cm-3, respectively. The CO2 laser annealing with controlled intensity and spot size can potentially accomplish in-situ, localized annealing of the SRSO film without causing irreversible damage to nearby electronics.
Crystallographic Study of The Initial Growth Region of μc-Si with Different Preferential Orientations
Authors: Sobajima Y. , Sugano T. , Kitagawa T. , Toyama T. , Okamoto H.
Published: June 2019

Growth of microcrystalline silicon (μc-Si) thin films with different preferential orientations has been studied employing XRD measurements versus thickness. The focus of this study is on the influence of preferential orientation on the film growth process. The (220) preferential orientation and randomly oriented μc-Si films studied here were prepared by VHF-PECVD at 180 °C. The thickness evolution revealed that the crystallinity was improved in the μc-Si with (220) preferential orientation μc-Si particularly in the first 0.5-μm of growth, while that in the randomly oriented μc-Si was almost completely unchanged. The difference in the crystallinity in the initial growth region arises from a difference in the growth mechanisms. Specifically, the growth of μc-Si with (220) preferential orientation can be elucidated by a hybrid-phase mode consisting of vapor- and solid-phase growth, whereas the growth of randomly oriented μc-Si can be achieved only by vapor-phase growth as occurs conventionally. Based on the growth mechanisms, the microstructures of μc-Si with both orientations and their influence on the photovoltaic performance are discussed.
Silicon homoepitaxy using tantalum-filament hot-wire chemical vapor deposition
Authors: Teplin Charles W. , Iwaniczko Eugene , Jones Kim M. , Reedy Robert , To Bobby , Branz Howard M.
Published: June 2019

We have studied silicon films grown epitaxially on silicon wafers using hot-wire chemical vapor deposition (HWCVD) with a tantalum filament. Silicon films were grown on (100)-oriented hydrogen terminated silicon wafers at temperatures from 175°C to 480°C, using a Ta filament 5 cm from the substrate to decompose pure SiH4 gas. The progression of epitaxy was monitored using real-time spectroscopic ellipsometry (RTSE). Analysis using RTSE, transmission electron microscopy (TEM), and scanning electron microscopy shows that at a characteristic thickness, hepi all of the films break down into a-Si:H cones. Below 380°C, both hepi and the thickness of the transition to pure a-Si:H increase with increasing temperature. Above 380°C, hepi was not observed to increase further but TEM images show fewer defects in the epitaxial regions. Secondary ion-mass spectrometry shows that the oxygen concentration remains nearly constant during growth (<1018 cm-3). The hydrogen concentration is found to increase substantially with film thickness from 5·1018 to 5·1019 cm-3, likely due to the incorporation of hydrogen into the a-Si:H cones that grow after the breakdown of epitaxy.
Temperature-Dependent Open-Circuit Voltage Measurements and Light-Soaking in Hydrogenated Amorphous Silcon Solar Cells
Authors: Liang Jianjun , Schiff E. A. , Guha S. , Yan B. , Yang J.
Published: June 2019

We present temperature-dependent measurements of the open-circuit voltage VOC(T) in hydrogenated amorphous silicon nip solar cells prepared at United Solar. At room-temperature and above, VOC measured using near-solar illumination intensity differs by as much as 0.04 V for the as-deposited and light-soaked states; the values of VOC for the two states converge below 250 K. Models for VOC based entirely on recombination through deep levels (dangling bonds) do not account for the convergence effect. The convergence is present in a model that assumes the recombination traffic in the as-deposited state involves only bandtails, but which splits the recombination traffic fairly evenly between bandtails and defects for the light-soaked state at room-temperature. Recombination mechanisms are important in understanding light-soaking, and the present results are inconsistent with at least one well-known model for defect generation.
Improved Back Reflector for High Efficiency Hydrogenated Amorphous and Nanocrystalline Silicon Based Solar Cells
Authors: Yan Baojie , Owens Jessica M. , Jiang Chun-Sheng , Yang Jeffrey , Guha Subhendu
Published: June 2019

Ag/ZnO back reflectors (BR) on specular stainless steel substrates are optimized for hydrogenated amorphous silicon germanium alloy (a-SiGe:H) and nanocrystalline silicon (nc-Si:H) solar cells. The BRs are deposited using a sputtering method. The texture of the Ag and ZnO layers is controlled by deposition parameters as well as chemical etching with diluted HCl. The surface morphology is investigated by atomic force microscopy. The scattered light intensity from a He-Ne laser, which illuminates the sample surface perpendicularly, is measured at different angles. Finally, a-SiGe:H and nc-Si:H solar cells are deposited on the BR substrates prepared under various conditions. For a-SiGe:H bottom cells, the improved BR with large micro-features leads to an enhanced open-circuit voltage. For the nc-Si:H solar cells, large micro-features on the improved BR eliminate interference fringes otherwise observed in the quantum efficiency measurement and result in high short circuit current density. The result is consistent with an enhanced scattered light intensity. Hence, the cell performance was improved. We also deposited a-Si:H/a-SiGe:H/nc-Si:H triple-junction cells on the optimized BR and achieved a high initial active-area efficiency of 14.6%.
Metastable Changes in the Photoconductive Properties of Microcrystalline Silicon Upon Heat Treatment
Authors: Brüggemann R.
Published: June 2019

We demonstrate that metastable changes or instabilities in the dark conductivity of microcrystalline silicon upon heat treatment and ambient conditions, which have been reported in the literature, are accompanied by changes in the photoconductivity or the majority-carrier mobility-lifetime product. The minority-carrier mobility-lifetime product and sub-gap absorption appear to be much less affected by different heat treatment procedures and ambient conditions. The observations can be related to Fermi-level induced change in defect occupancy by which the effective density of recombination centres is reduced for electrons but remains the same for holes. Minority carrier properties seem to be better suited as an indicator for sample quality and for comparison of microcrystalline silicon samples from different laboratories.
Light-Intensity Dependence of the Staebler-Wronski Effect in a-Si:H with Various Densities of Defects
Authors: Kumeda Minoru , Sakai Ryohei , Morimoto Akiharu , Shimizu Tatsuo
Published: June 2019

The light-intensity dependence of the photocreation of dangling bonds (DBs) were investigated for a-Si:H films with increasing density of defects before light soaking. Samples in which the density of neutral DBs had been increased by annealing at 400 C for 1 h exhibited a weak light-intensity dependence of the photocreated DBs compared to that for the as-deposited sample. Furthermore, the sample which had been illuminated with a light intensity of 1 W/cm2 for 1 h also showed a weak dependence. The results can be qualitatively explained by using rate equations for the densities of DBs and floating bonds (FBs) based on the FB-mediated photocreation of DBs. When both the densities of DBs and FBs before illumination increase, the light-intensity dependence of the DB density for a moderate value of the illumination time becomes weaker, qualitatively consistent with the observed results.
Charging effect of a nc-Si in a SiO2 layer observed by scanning probe microscopy
Authors: Son J. M. , Kim J. M. , Khang Y. , Lee E. H. , Park S. I. , Kim Y. S. , Kang C. J.
Published: June 2019

Scanning probe microscopy (SPM) with a conducting tip has been used to electrically probe silicon nanocrystals (NCs) on an insulating substrate. NC samples were produced by aerosol techniques followed by a sharpening oxidation. The size of NCs is in the range of 10-50nm and deposited on a silicon substrate with a density of around 1011/cm2. Using a conducting tip, the charge was injected directly into the NCs, and the bias dependent images due to the trapped charges in the NCs were monitored. Charging effects affected by the size of NCs and injection direction were also estimated from the apparent height differences of the NCs with respect to the applied bias.
Application of SC-Simul for Numerical Modeling of the Opto-Electronic Properties of Heterojunction Diodes
Authors: Brüggemann R. , Rösch M. , Tardon S. , Bauer G.H.
Published: June 2019

We apply the publicly available device modeling tool SC-Simul for simulating experiments with user-defined heterojunction diodes to discuss the role of the electric field in solar cells. For amorphous silicon/crystalline silicon heterodiodes, the role of interface defects, an amorphous silicon buffer layer and low-cost crystalline silicon is studied by simulation of current-voltage characteristics and photoluminescence. Photoluminescence is sensitive to the minority carrier density in the volume of the device and can be used to monitor minority carrier properties in these diodes.
A New Technique for the Characterization of the Adhesion in Integrated Circuit Interconnect Structures
Authors: Ocana Ibon , Molina Jon M. , Gonzalez Diego , Elizalde M. Reyes , Sanchez Jose M. , Martinez-Esnaola Jose M. , Gil-Sevillano Javier , Scherban Tracey , Pantuso Daniel , Sun Brad , Xu Guanghai , Miner Barbara , He Jun , Maiz Jose A.
Published: June 2019

A new testing technique for the characterization of the mechanical behavior of the interconnect structures of integrated circuit devices is introduced in this paper. Modified crosssectional nanoindentation (MCSN) is the result of extending cross-sectional indentation (CSN) to patterned structures. As in conventional CSN, a Berkovich indenter is used to initiate fracture in the silicon substrate beneath the interconnect structure. The cracks propagate through this structure, preferentially along the weakest interfaces in the system. A FIB (Focused Ion Beam) is used for sample preparation, machining a trench parallel to the indentation surface. In this way, the crack growth can be better controlled and the problem may be modeled in two dimensions.

The technique has been used to study crack propagation in patterned structures as a function of thin film composition and processing. The results obtained, in terms of crack length along each interface studied, correlate well with the fracture energy measured by four-point bending (4 PB) in blanket films of the same materials. Finite element modeling of the stress fields in the vicinity of the crack tip has been carried out to understand the crack paths observed.
Effects of Bonding Process Parameters on Wafer-to-Wafer Alignment Accuracy in Benzocyclobutene (BCB) Dielectric Wafer Bonding
Authors: Niklaus F. , Kumar R.J. , McMahon J.J. , Yu J. , Matthias T. , Wimplinger M. , Lindner P. , Lu J.Q. , Cale T.S. , Gutmann R.J.
Published: June 2019

Wafer-level three-dimensional (3D) integration is an emerging technology to increase the performance and functionality of integrated circuits (ICs). Aligned wafer-to-wafer bonding with dielectric polymer layers (e.g., benzocyclobutene (BCB)) is a promising approach for manufacturing of 3D ICs, with minimum bonding impact on the wafer-to-wafer alignment accuracy essential. In this paper we investigate the effects of thermal and mechanical bonding parameters on the achievable post-bonding wafer-to-wafer alignment accuracy for polymer wafer bonding with 200 mm diameter wafers. Our baseline wafer bonding process with softbaked BCB (∼35% cross-linked) has been modified to use partially cured (∼ 43% crosslinked) BCB. The partially cured BCB layer does not reflow during bonding, minimizing the impact of inhomogeneities in BCB reflow under compression and/or slight shear forces at the bonding interface. As a result, the non-uniformity of the BCB layer thickness after wafer bonding is less than 0.5% of the nominal layer thickness and the wafer shift relative to each other during the wafer bonding process is less than 1 μm (average) for 200 mm diameter wafers. The critical adhesion energy of a bonded wafer pair with the partially cured BCB wafer bonding process is similar to that with soft-baked BCB.
Pore Structure and Integration Performance of a Porous CVD Ultra Low k Dielectric
Authors: Liu Youfan , Knorr Andreas , Wu Wen-Li , Gidley David , Kastenmeier Bernd
Published: June 2019

A porous ultra low k PECVD dielectric has been evaluated at SEMATECH for 45 nm and beyond technology node applications. Material structure, integration performance, and electrical characteristics were investigated in a one level metal single damascene integrated structure.
Effect of Dielectric Pore Size Distribution on Interfacial Adhesion of the Tantalum-Porous Dielectric Interface
Authors: Saxena R. , Cho W. , Rodriguez O. , Gill W. N. , Plawsky J. L. , Tsui T. , Grunow S.
Published: June 2019

In this work we report the adhesion of a thin Tantalum (Ta) barrier films deposited on nanoporous dielectric substrates (Xerogel and Methyl Silesquioxanes (MSQ)). The high compressive stresses in the Ta barrier layer lead to spontaneous delamination from the underlying substrate resulting in a telephone cord like morphology, which allows the measurement of critical interfacial adhesion (fracture) energy. The fracture energy of Ta barrier films on different porous substrates is evaluated using the above two methods and the resulting differences are explained. Fracture energy varies inversely as a power law with the dielectric pore size indicating pores are essential to delamination in the barrier-dielectric interface. The observed trend of fracture energy is related to other mechanical properties of the porous substrate offering insights into the underlying mechanisms governing fracture of films deposited on porous substrates.
Employing Thin Film Failure Mechanisms to Form Templates for Nano-electronics
Authors: Adelung Rainer , Elbahri Mady , Rudra Shiva Kumar , Biswas Abhijit , Jebril Seid , Kunz Rainer , Wille Sebastian , Scharnberg Michael
Published: June 2019

Recently, we showed that thin film stresses can be used to form well aligned and complex nanowire structures [1]. Within this approach we used stress to introduce cracks in a thin film. Subsequent vacuum deposition of metal leads to the formation of a metal layer on the thin film and of metal nanowires in the cracks of the film. Removal of the thin film together with the excess metal cover finishes the nanowire fabrication on the substrate. As stress can be intentionally introduced by choosing an appropriate thin film geometry that leads to a stress concentration, the cracks and consequently the nanowires can be well aligned. Meanwhile, we have demonstrated how to form thousands of parallel aligned nanowires, x-and y-junctions or nanowires with macroscopic contacts for sensor applications, simply by applying fracture mechanics in thin films. Christiansen and Gösele called this approach “constructive destruction” in a comment in Nature Materials [2]. This gives a hint how to overcome some problems of the approach, arising from the limits of thin film fracture. A generalization of the fracture approach by being “more destructive” can overcome this limitations. For example, it is difficult to form pairs of parallel wires with a nanometer distance of the pair, but a micrometer separation between the individual pairs. Structures like this are useful for many contact applications including sensor arrays or field effect transistors. As well as thin film fracture, thin film delamination can be well controlled by fracture mechanics. Our latest experiments show that the combination of both, fracture and delamination, forms an ideal shadow mask for vacuum deposition. Cracks with delaminated sides were used as templates for the deposition of pairs of parallel wires consisting out of different materials with only a few 10 nm separation. First, a metal was sputter deposited under an angle of approx. 45° through the delaminated crack, which was used as a shadow mask. Afterwards, a second deposition metal is deposited under the opposite 45° angle with respect to the sample normal, having the crack located in the middle between both deposition sources. The angle, the delamination height and the crack width determine the separation of the nanowire contacts. We present several examples which show how these mechanisms of mechanical failure of thin films can be turned into useful templates for various nanostructures. We will focus here on two thin film systems, that can be easily deposited in every lab. These are wet chemically deposited photo-resist and flash evaporated amorphous carbon. These examples are compared with finite element simulations of the thin film stress with the ANSYS program. Moreover, we show how the delamination cracks can be also used as masks for the removal of material. Channals with a width down to 20 nm produced by ion beam sputtering are shown.
Comparison of Line Stress Predictions with Measured Electromigration Failure Times
Authors: Morusupalli Rao R. , Nix William D. , Patel Jamshed R. , Budiman Arief S.
Published: June 2019

Reliability of today's interconnect lines in microelectronic devices is critical to product lifetime. The metal interconnects are carriers of large current densities and mechanical stresses, which can cause void formation or metal extrusion into the passivation leading to failure. The modeling and simulation of stress evolution caused by electromigration in interconnect lines and vias can provide a means for predicting the time to failure of the device. A tool was developed using MathCAD for simulation of electromigration-induced stress in VLSI interconnect structures using a model of electromigration induced stress. This model solves the equations governing atomic diffusion and stress evolution in one dimension. A numerical solution scheme has been implemented to calculate the atomic fluxes and the evolution of mechanical stress in interconnects. The effects of line geometries and overhangs, material properties and electromigration stress conditions have been included in the simulation. The tool has been used to simulate electromigration-induced stress in pure Cu interconnects and a comparison of line stress predictions with measured electromigration failure times is studied. Two basic limiting cases were studied to place some bounds on the results. For a lower bound estimate of the stress it was assumed that the interface can be treated like a grain boundary in Cu. For an upper bound estimate it was assumed that the interface can be treated like a free surface of Cu. Existing data from experimental samples with known structure geometries and electromigration failure times were used to compare the electromigration failure times with predicted stress build-up in the interconnect lines.
Low temperature deposition of Indium tin oxide (ITO) films on plastic substrates
Authors: Singh Vandana , Saswat B. , Kumar Satyendra
Published: June 2019

Organic light emitting diodes (OLEDs) require a transparent conducting oxide (TCO) electrode for injection of charge carriers and the emitted light to come out. In order to exploit the full flexibility of organic semiconductor based large area electronic devices, the deposition of TCO on plastic substrates is essential, which prohibits high temperature processing. Therefore, low temperature deposition of Indium tin oxide (ITO) films is very important for flat panel displays and solar cells. Here we have carried out a systematic study of ITO deposition on plastic substrates using RF magnetron sputtering. For the optimization of structural, electrical and optical properties of ITO, various experiments such as X-ray diffractometer, transmission measurements, sheet resistance and AFM were employed. These properties were investigated as a function of substrate temperature, deposition time and RF power. From these experiments, we obtained a reasonably low sheet resistance (˜ 14;Ω / □) and high transmittance (˜75%) in the visible region on plastic substrates. We also observed that these films are not much affected by atmosphere and does not degrade with time. These ITO films deposited by RF magnetron sputtering on plastic substrates can be use as anode for flexible organic light emitting displays.
Surface Acoustic Wave-Induced Electroluminescence Intensity Oscillation in Planar Light-Emitting Devices
Authors: Cecchini Marco , Piazza Vincenzo , Beltram Fabio , Ward Martin , Shields Andrew , Beere Harvey , Ritchie David
Published: June 2019

Electroluminescence (EL) emission controlled by means of surface acoustic waves (SAWs) in planar light-emitting diodes (pLEDs) is demonstrated. Interdigital transducers (IDTs) for SAW generation were integrated onto pLEDs fabricated following a scheme compatible with SAW propagation [1]. EL in presence of SAW was studied by time-correlated photon-counting techniques. We found intensity oscillation at the SAW frequency (˜1 GHz) demonstrating electron injection into the p-type region synchronous with the SAW wavefronts.
Fabrication of In2O3 Oxide Semiconductor Nano-Particles Using Apoferritin
Authors: Okuda Mitsuhiro , Yamashita Ichiro , Iwahori Kenji , Yoshimura Hideyuki
Published: June 2019

In2O3 nanoparticles were fabricated in the cavity of the cage-shaped protein, apoferritin by utilizing a quick chemical reaction of indium oxide. Horse spleen apoferritin in the solution of indium ions buffered at pH 9.5 was incubated for 30 minutes. The transmission electron microscopy (TEM) observation with aurothioglucose staining showed that cores were formed in the apoferritin cavity. The sizes of cores were regulated by the cavity size and their diameters were below 7nm. Energy dispersion X-ray analysis (EDX) indicated that indium was contained in the cores. The high-resolution TEM (HR-TEM) revealed that cores are single or poly crystalline and the lattice space was consistent with that of In2O3. These results confirmed that the In2O3 cores were successfully formed in the apoferritin cavity.
Magnetite-PLGA Microparticles for Oral Delivery of Insulin
Authors: Cheng Jianjun , H. Yim Christopher , Teply Benjamin A. , Ho Dennis , Farokhzad Omid C. , Langer Robert S.
Published: June 2019

Magnetic responsive particles were designed for use in oral delivery of insulin. Magnetite nanoparticles (12 nm average size) were synthesized and co-encapsulated with insulin into poly(lactide-co-glycolide) (PLGA) microparticles (4.6 ± 2.2 μm average particle size) through the double-emulsion method. The spherical structures of resulting microparticles were well maintained at magnetite content 5 wt % or less. Mice were gavaged with 125I-insulin-magnetitePLGA microparticles and a circumferential trans-abdominal magnetic field was applied forty minutes after administration to retard the transit of the microparticles in the intestinal tract. As control, mice were similarly dosed without the subsequent trans-abdominal magnetic field. Mice were sacrificed, and the intestinal radioactivity was 101% and 145% higher in treated mice versus the control at 6 h and 12 h, respectively. A single administration of 50 unit/kg Humulin Rmagnetite-PLGA microparticles to the fasted mice resulted in 66% reduction of blood glucose level in the presence of external magnetic field at 12 h, compared to 27% reduction in the absence of magnetic field.
Ferromagnetic Mn-Doped GaN Nanowires for Nanospintronics
Authors: Han Doo Suk , Na Chan Woong , Jang Woo Sung , Bae Seung Yong , Park Jeunghee
Published: June 2019

We report Mn-doped GaN nanowires exhibiting ferromagnetism even at room temperature. The growth of single-crystalline wurtzite structured GaN nanowires doped homogeneously with about 5 atomic % Mn was achieved by chemical vapor deposition using the reaction of Ga/GaN/MnCl2 with NH3. The ferromagnetic hysteresis at 5 and 300 K and the temperature-dependent magnetization curves suggest the Curie temperature around 300 K. Negative magnetoresistance of individual nanowires was observed at the temperatures below 100 K.
Formation of 2-D and 3-D Arrays of Colloidal Co Magnetic Nanoparticles
Authors: Chushkin Y. , Chitu L. , Luby S. , Majkova E. , Satka A. , Holy V. , Ivan J. , Giersig M. , Hilgendorff M. , Metzger T. H. , Konovalov O.
Published: June 2019

Ordering of Co nanoparticles (∼11 nm in diameter) into 2-D and 3-D arrays on Si/Si3N4 substrates in external magnetic field and without field is reported. Arrays of particles were studied by TEM, SEM and GISAXS. The GISAXS measurements were performed at the wavelengths 0.155 nm and 0.336 nm and the spectra were simulated using distorted wave Born approximation approach. From results it follows that 2-D ordered monolayers of particles are composed of hexagonal close-packed mosaic blocks. 3-D arrays – rods are formed along magnetic field direction, being parallel or perpendicular to the substrate surface, when the colloid was more concentrated. Distribution of particles in rods was analyzed only by GISAXS and it was described by close packing of hard spheres. Their effective diameter was 14.7 nm.
Self Assembled Iron Nanowires: Morphology, Electrical and Magnetic Properties
Authors: Huelser T.P. , Wiggers H. , Knipping J. , Roth P. , Lorke A.
Published: June 2019

We report on the self-assembled formation of iron nanowires from iron nanoparticles. Nanosized iron particles with a diameter of about 35 nm are synthesized by thermal decomposition of iron pentacarbonyl Fe(CO)5 in a hot wall reactor. This particle size is chosen to produce single domain ferromagnetic particles. As a result, the particles are attracted by magnetic forces, leading to iron nanowires of up to 300 μm in length. HRTEM and EELS investigations give detailed morphological, structural and chemical information. They reveal a big metallic iron core surrounded by an iron oxide shell with a thickness of 3-4 nm, originating from self limiting surface oxidation under ambient conditions. For electrical characterization, single iron wires are thermophoretically sampled on interdigital contacts. Impedance spectroscopy on single nanowires indicates both, capacitive and ohmic contributions to the overall conductivity. Magnetic properties are investigated with SQUID magnetometry. Magnetization measurements reveal a saturation magnetization of 160 emu/g at 5 K, which is more than 70% of the iron bulk value.
Formation and Characterization of Magnetic Multilayer Ni/Cu Nanowires
Authors: Liu R. S. , Chang S. C. , Hu S. F. , Huang C. Y.
Published: June 2019

Highly ordered composite nanowires with multilayer of Ni/Cu, have been fabricated by pulsed electrodeposition into nanoporous alumina membrane. The diameter of wires can be easily controlled by pore size of alumina, ranging from 30 to 100 nm. The applied potential and the duration of each potential square pulse determine the thickness of the metal layers. The nanowires have been characterized by transmission electron microscopy (TEM), magnetic force microscopy (MFM), and vibrating sample magnetometer (VSM) measurements. From the result of MFM analysis, the magnetic multilayer nanowires indicate unique magnetic property. The MFM images indicate that every ferromagnetic layer separated by Cu layer was present as single isolated domain like magnet. This technique has potential for use in the measurement and application of magnetic nanodevices.
Self Seeded ZnO Nanowire Growth by Ultrasonic Spray Assisted Chemical Vapour Deposition
Authors: Wei M. , Zhi D. , MacManus-Driscoll J. L.
Published: June 2019

ZnO, which exhibits a direct bandgap of 3.37 eV at room temperature with a large exciton binding energy of 60 meV,is of considerable technological importance because of its potential use in short-wavelength devices, such as ultraviolet (UV) light-emitting diodes and laser diodes. The fabrication and application of 1-D ZnO nanostructures has attracted considerable interest in recent years. In this work, we produced single crystal nanowires of zinc oxide using a novel self-seeded growth using ultrasonic spray assisted chemical vapour deposition, in which a nanocrystalline seed layer was first deposited onto a glass substrate and the nanowires subsequently grown using a different precursor concentration and substrate temperature. The diameter of the nanowires is in the range of 20-80 nm and the length of the wires is as long as 10 μm. The single crystal nature of the nanowires was revealed by high resolution transmission electron microscopy. The formation of liquid droplets due to the reducing atmosphere and the higher temperature during the nanowire growth was found to be the key step of the ZnO nanowire formation.
Synthesis of Metal Carbides Using Biological Templates
Authors: Shin Yongsoon , Li Xiaohong S. , Samuels William D. , Wang Yong , Pederson Larry R. , Exarhos Greg J.
Published: June 2019

Nanocrystalline metal carbides (MC: M=Si, Ti) have been prepared using cellulose network mineralized with silica and titania by carbothermal reduction at high temperature in Ar. Hierarchical biological structures indigenous to the cellulose precursor were completely replicated after the reaction. Cubic phase MC composites show relative low oxygen content 0.24 wt% and a high lattice parameter of 4.327Å in TiC. The particle sizes of the MC composites are 200-700nm for SiC and 10-50nm for TiC, and high BET surface area, up to 150m2/g.