bluuebunny/crossref_metadata_2025 huggingface dataset:
Tunnel QW-QDs InGaAs-InAs High Gain Medium for All-Epitaxial VCSELs
Authors: Tokranov Vadim , Yakimov Michael , van Eisden Jobert , Oktyabrsky Serge
Published: April 2011

Structures of tunnel-coupled pairs consisting of InGaAs (In composition was varied from 29 to 36%) quantum wells (QW) grown on top of shape-engineered self-assembled InAs quantum dots (QW-on-QDs) were employed to increase the maximum saturated gain of QD-based laser active medium. Room temperature optical properties of tunnel-coupled well-on-dots structures at low excitation were found to be sensitive to energy separation between GS energies of QDs and QW. The spectra also show that QD-related photoluminescence (PL) tends to peak at discrete energy separations from the QW peak, in this case multiples of ∼ 35meV (LO phonon energy). The optimized GS energy separation between QW and QDs was found to be close to the energy of the LO phonon. This structure demonstrated narrowing of the QD PL line down to 21.6 meV at T=77K, indicating efficient resonant tunneling of carriers from QW into QD ensemble states. All-epitaxial vertical cavity surface emitting lasers (VCSELs) with triple-pair tunnel QW-on-QDs as active medium demonstrated continuous wave mode lasing. Tunnel QDs-QW VCSELs exhibited 1.8 mA (Jth ∼ 800 A/cm2) minimum threshold current at QD GS emission wavelength, 1135 nm, with 0.7mW optical power and 12% light-current efficiency.
Multiple modes of laser-induced pattern formation in nanoscopic Co films
Authors: Favazza Christopher , Trice Justin , Sureshkumar Radhakrishna , Kalyanaraman Ramki
Published: April 2011

Dewetting instabilities in nanoscopic Co films, induced by uniform multiple ns pulse laser irradiation, leads to a system of nanoparticles with robust spatial order. On the other hand, irradiation by non-uniform laser intensity, such as with a two beam laser interference pattern generates a quasi two-dimensional pattern of nanoparticles possessing long range order (LRO) and short range order (SRO). Here we discuss the various instabilities that are responsible for the production of these dissimilar patterns and length scales on the basis of their time scales. For the case of single beam irradiation, the film progresses in a manner that can be attributed to classical spinodal dewetting. Pattern formation from interference irradiation is the result of time scale-based selection of competing processes, which can be chosen by controlling the film thickness. This approach promises a simple and cost-effective means to self-assemble various nanostructures.
Vertically Aligned Carbon Nanotubes Growth Using Self-assembled Ni Nanoparticles Produced by Ion Implantation
Authors: Baptista D. L. , Lopes J. M. J. , Morschbacher M. J. , Dalal S. H. , Oei S. P. , Teo K. B. K. , Milne W. I. , Zawislak F. C.
Published: April 2011

An alternative method for seeding catalyst nanoparticles for carbon nanotubes and nanowires growth is presented. Ni nanoparticles are formed inside a 450 nm SiO2 film on (100) Si wafers through the implantation of Ni ions at fluences of 7.5×1015 and 1.7×1016 ions cm−2 and post-annealing treatment at 700, 900 and 1100 °C. After exposed to the surface by HF dip etching, the Ni nanoparticles are used as catalyst for the growth of vertically aligned carbon nanotubes by direct current plasma enhanced chemical vapor deposition.
Novel Nanocarbons: Global Topology and Curvature Perspectives
Authors: Gupta Sanju , Saxena A.
Published: April 2011

Carbon nanotubes (both the single- and multi-walled), in the family of nanostructured carbons, are of great interest because of several unsurpassable physical properties and it needs to be shown that they are physically stable and structurally unaltered when subjected to radiation. In addition to testing them for space applications, when exposed to high energy electron beam from transmission electron microscopy, the results seem quite promising in terms of nano-engineering/ nano-manufacturing for producing novel nanocarbons [1-3]. Experimental studies of effects of electron beam irradiation on carbon nanotubes show that multi-walled ones tend to be relatively more robust than their single-walled kins. The increased exposure on an individual bundle of single-wall nanotubes promoted graphitization, pinching, and cross-linking analogous to polymers forming an intra-molecular junction (IMJ) within the area of electron beam focus, possibly through aggregates of amorphous carbon [2,3]. Formation of novel nanostructures (nano-ring and helix-like) due to irradiation are observed. These studies shed light on the dynamics of nanomanufacturing and a regime of possible relevance of these materials for: (i) short-term space missions; (ii) radiation hard programmable logic circuits; and (iii) radiation pressure sensors. It is suggestive that a local reorganization occurs. Through resonance Raman spectroscopy and related techniques we also elucidate an important notion of global topology and curvature at nanoscale which points to an emergent paradigm of Curvature/Topology → Property → Functionality in these technologically important geometries of carbons: nanotubes, fullerenes, nanorings, nanocones, nanohorns and nanodisks. To this end, we have determined the variation in first order high frequency Raman band which indicates a strong electron-phonon coupling. These concepts also apply to nanostructures of other “topological materials” such as BN nanotubes and nanotori, helical gold nanotubes as well as Möbius conjugated polymers.
Annealing Study of (Co/Pd)N Magnetic Multilayers for Applications In Bit-Patterned Magnetic Recording Media
Authors: Chunsheng E. , Rantschler James , Zhang Shishan , Lee T. Randall , Smith Darren , Weller Dieter , Khizroev Sakhrat , Litvinov Dmitri
Published: April 2011

This work presents an annealing study of high-anisotropy (Co/Pd)N magnetic multilayers designed for bit-patterned medium recording applications. Magnetic multilayers were deposited by magnetron sputtering at 2.5mT argon pressure at room temperature and annealed at different temperatures (up to 250 °C) for up to 2 hours in atmosphere and in vacuum. Depending on the annealing time, the samples annealed in atmosphere exhibited two distinct modes of magnetization reversal. In samples annealed for a time shorter than some critical time, tc, where tc is a function of the annealing temperature, the magnetization reversal occurs by domain wall injection and propagation. In samples annealed for times longer then tc, the magnetization reversal mode switches to magnetization rotation. Using XPS, it is found that the transition is accompanied by the formation of oxidizes at the grain boundaries leading to exchange decoupling of the grains. In samples annealed at higher temperatures, the increases of the coercivity of as high as 30 times the coercivity of as prepared samples are observed. Significantly, annealing in vacuum showed only small modification of magnetic properties as manifested by relatively minor modifications of vertical M-H loops and unchanged morphology of domain patterns in AC demagnetized state.
Nanofabrications for Information Technology
Authors: Choi Kyung
Published: April 2011

Since industry has been seeking for advanced nanotechnology, development of new nano-materials and nanofabrication techniques has been a key contributor to satisfy our growing demands on miniaturization. This will present technological emergences in fabrications of novel optoelectronic devices by developing new materials since nanotechnology is a part of chemical domain. It will cover up as how chemists can contribute to this area to fabricate functional nanofabrications for information technology. For example, we developed a new class of PDMS stamps to overcome the limitations and thus to extend current soft lithography to advanced level for developing nanoscale-devices. Patterns fabricated using functional polymers also have many information technology applications to integrate optoelectronic devices.
Nanopatterning and Nanomachining with Table-top Extreme Ultraviolet Lasers
Authors: Marconi Mario , Wachulak Przemyslaw Wojciech , Capeluto Maria Gabriela , Vaschenko Georgyi , Bravo Herman , Menoni Carmen S , Rocca Jorge , Anderson Erik H , Chao Weilun , Attwood David , Hemberg Oscar , Frazer Bradley , Bloom Scott
Published: April 2011

Nanopatterning and nanomachining of PMMA coated wafers was performed using table top extreme ultraviolet lasers. Features below 100 nm were imprinted with short (50-60 s) exposure times.
Replication of Grating-Based Optically Variable Devices in Polypropylene
Authors: Leech Patrick W.
Published: April 2011

The hot embossing of grating-based optically variable devices has been demonstrated in biaxially-oriented polypropylene (BOPP). The embossing of several types of optically variable device has been examined including portrait, non-portrait and 3 dimensional images. The images embossed into BOPP have displayed a novel optically variable effect when viewed in transmitted light. Embossing of the grating structures was examined over a range of temperatures (80-155 °C) at 135 kN force. High quality replication was achieved over a full embossing area of 80 x 80 mm at temperatures > 120 °C.
Fabrication of Magnetic Nanostructures for MRAM using Electron Beam and Focused Ion Beam Exposure of HSQ
Authors: Chen Chen , Cabral Michael J , Hull Robert , Harriott Lloyd R
Published: April 2011

Giant magnetoresistive (GMR) materials-based magnetic random access memory (MRAM) has become attractive due to non-volatility, speed and density1. The vertical MRAM (VMRAM) design model shows good signal level and high speed and density potential. The memory cell for the VMRAM model is a ring shaped magnetic material multilayer, which ensures high repeatability and low switching energy. This GMR structure, however, is difficult to pattern as it contains materials such as Ni, Fe, Co, and Cu, which are difficult to dry etch because they lack volatile etch products. This work shows that it is possible to overcome the difficulties associated with etching GMR materials by using hydrogen silsesquioxane (HSQ) as an etch mask. We have used HSQ in a direct-write electron-beam lithography system with a dose of 600 μC/cm2, and in a Ga+ ion focused ion beam (FIB) system with a dose of 12 μC/cm2. Both are followed by development and an argon plasma etch at 10mTorr and 100W RIE power. The HSQ layer provides high resolution as well as good etching resistance. Electron-beam exposed HSQ shows a 1:1.5 selectivity over the GMR film stack and the FIB exposed HSQ showed an improved etch selectivity of 1:1. Ring shaped GMR structures with a 75/225 nm (ID/OD) have been fabricated, which corresponds to a memory density of 4Gb/in2.
Novel Anionic Photoacid Generators (PAGs) and Photoresists for sub 50 nm Patterning by EUVL and EBL
Authors: Wang Mingxing , Lee Cheng-Tsung , Henderson Clifford L , Yueh Wang , Roberts Jeanette M , Gonsalves Kenneth E
Published: April 2011

A new series of anionic photoacid generators (PAGs), and corresponding polymers were prepared. The thermostability of PAG bound polymers was superior to PAG blend polymers. PAG incorporated into the polymer main chain may improve acid diffusion compared with the PAG blend polymers, which was demonstrated by Extreme Ultraviolet lithography (EUVL) results: the fluorine PAG bound polymer resist gave 45 nm (1:1), 35 nm (1:2), 30 nm (1:3) and 20 nm (1:4) Line/Space as well as 50 nm (1:1) elbow patterned, showed better resolution than the blend sample.
Application of Novel Base Amplifiers with 3-Nitropentan-2-yl Group to Photoreactive Materials
Authors: Arimitsu Koji , Ito Yusuke , Gunji Takahiro , Abe Yoshimoto , Ichimura Kunihiro
Published: April 2011

In order to enhance the photosensitivity of photoreactive materials utilizing base-catalyzed reactions, we developed base amplifiers that decompose autocatalytically to generate newborn amine molecules. Actually, we reported that the addition of base amplifiers to the photoreactive materials such as photoresists and UV-curing materials resulted in the marked improvement photosensitivity. However, conventional base amplifiers have aromatic rings such as fluorenyl groups and phenyl groups. Consequently, these base amplifiers have strong absorption of UV light which is a trigger of photolysis of a photobase generator. This leads to the hindrance of the photolysis. We report here novel base amplifiers with 3-nitropentan-2-yl group which has no aromatic rings.

The base amplifiers decomposed autocatalytically to generate newborn amine molecules at an elevated temperature in solution and a polystyrene film in the presence of a catalytic amount of amines. Moreover, combining the base amplifiers with UV-curing materials consisting of a photobase generator and liquid epoxy resins resulted in the improvement of curing efficiency. To apply the base amplifier to photopatterning materials, we synthesized novel silicone resins with 3-nitropentan-2-yl groups as base-amplifying polymers. A film of the resin decomposed autocatalytically to generate amino groups in its side chains at an elevated temperature in the presence of a catalytic amount of amines. Furthermore, we demonstrated that the resins sensitized with a photobase generator provided negative- and positive-working photopolymers in the following ways. A thin film of the resin containing 10 wt% of a photobase generator became soluble in an acidic aqueous solution after 254 nm light irradiation of an exposure dose of 1 mJ/cm2 and subsequent baking at 50 oC for 20 min. This is because of formation of amino groups in its side chains. On the other hand, the film became insoluble in organic solvents after 254 nm light irradiation of an exposure dose of 1 mJ/cm2 and subsequent heat treatment at 50 oC for 40 min, this arises from that the photobase-catalyzed hydrolytic condensation of residual ethoxysilyl units of the resin proceeded to form crosslinked networks.
Photoimaging Materials Based on Base-amplifying Silicone Resins Having Phenylsulfonylethyl Groups
Authors: Inoue Satoru , Arimitsu Koji , Gunji Takahiro , Abe Yoshimoto , Ichimura Kunihiro
Published: April 2011

Recently, the large number of investigations concerning acid-catalyzed photopolymer systems such as chemically amplified photoresists and UV-curing materials has been reported. On the other hand, analogous systems utilizing base-catalyzed reactions have received far less attention, because low quantum yields for photobase generation to lead to low photosensitivity of these systems. To improve this problem, we proposed introduction of the concept of base proliferation reactions into the photopolymer systems using base-catalyzed reactions. The concept involves the autocatalytic base-catalyzed decomposition of a compound, referred to as a base amplifier which releases a newborn amine, leading to its autocatalytic decomposition. In fact, the addition of the base amplifiers such as 9-fluorenylmethyl carbamate, phenylsulfonylethyl carbamate, and 3-nitropentane-2-yl carbamate to a photopolymer consisting of an epoxy polymer sensitized and a photobase generator (PBG) resulted in the marked improvement of photosensitivity.

However, these base amplifiers with low molecular weight are not suitable for photopatterning because of the volatility and the excessive diffusion of amines proliferated in polymer films. We report here novel base-amplifying silicone resins tethering phenylsulfonylethyl carbamoyl groups which proliferate primary amino groups or secondary amino groups in their side chains.

Base-catalyzed decomposition behavior of films of these resins containing PBG was evaluated by UV absorption measurements. A film consisting of the resin proliferating primary amino groups and 10 wt% of PBG decomposed immediately in a nonlinear manner by 365 nm irradiation and subsequent heat treatment at 120oC for 6 min. On the other hand, this film without UV irradiation was thermally stable for 18 min at 120oC. These results indicate that photoinduced base proliferation reaction of the resin proceeded. A film consisting of the resin generating secondary amino groups and PBG decomposed in a way similar to that of the resin proliferating primary amino groups. Furthermore, lithographic evaluation of the film comprising the resin to generate secondary amines and PBG obtained 7ÊS positive images with an exposure dose of 75 mJ/cm2 which shows higher sensitivity when compared to conventional base-catalyzed photopolymers.
Modeling Evaporation Driven Self-Assembly Systems for Magnetic Storage Arrays
Authors: Dyreby John , Nellis Greg F. , Turner Kevin T.
Published: April 2011

A modeling methodology based on computational fluid dynamics (CFD) has been developed that is appropriate for the global regime of lithographically directed, evaporation driven self-assembly. The modeling technique has been experimentally verified through comparison with the well-known benchmark case of evaporation driven self-assembly associated with the evaporation of a colloidal, self-pinned droplet. The predicted evolution of the particle distribution during evaporation is compared to optical experimental measurements of the particle distribution within an evaporating droplet containing fluorescing nanoparticles.
Massively Parallel Scanning Probes Microscope with Digital Holographic Readout
Authors: Sache Laurent , Bleuler Hannes
Published: April 2011

Massively Parallel Scanning Probe Microscopy is an obvious path for enhancing the acquisition speed and the imaging range of current based-AFM metrology devices. Current experimental systems, based on active probes array, would reach their limits in density and hardware complexity. This paper presents a new approach with the promise to break several of these barriers. The key idea is readout of a Scanning Probes Microscope (SPM) array by an interferometer technique called digital holography which directly gives the cantilever phase information at each pixel of a CCD array. This means that no contact line to each individual SPM probes is needed, allowing us to reach very high density of probes. The phase information is available in a parallel form in real-time. Moreover, the digital holography optical setup (Digital Holography Microscope or DHM) needs in principle no expensive components, optical (or, to a large extent, mechanical) imperfections being compensated in the signal processing, i.e. in electronics. This gives the system the potential for a low cost device with fast and large readout capability.
Cluster-Assembled Iron-Platinum Nanocomposite Permanent Magnets
Authors: Rui Xiangxin , Sun Zhiguang , Xu Yingfan , Sellmyer David J. , Shield Jeffrey E.
Published: April 2011

Exchange-spring nanocomposite permanent magnets have received a great deal of attention for their potential for improved the energy products. Predicted results, however, has been elusive. Optimal properties rely on a uniformly fine nanostructure. Particularly, the soft magnetic phase must be below approximately 10 nm to ensure complete exchange coupling. Inert gas condensation (IGC) is an ideal processing route to produce sub-10 nm clusters method. Two distinct nanostructures have been produced. In the first, Fe clusters were embedded in an FePt matrix by alternate deposition from two sources. Fe cluster content ranged from 0 to 30 volume percent. Post-deposition multi-step heat treatments converted the FePt from the A1 to L10 structure. An energy product of approximately 21 MGOe was achieved. Properties deteriorated rapidly at cluster concentrations above 14 volume due to uncoupled soft magnetic regions (from cluster-cluster contacts) and cooperative reversal. The second nanostructure, designed to overcome those disadvantages, involved intra-cluster structuring. Here, Fe-rich Fe-Pt clusters separated by C or SiO2 were fabricated. Phase separation into Fe3Pt and FePt and ordering was induced during post-deposition multi-step heat treatments. By confining the soft and hard phases to individual clusters, full exchange coupling was accomplished and cooperative reversal between clusters was effectively eliminated. An energy product of more than 25 MGOe was achieved, and the volume fraction of the soft phase was increased to greater than 0.5 while maintaining a coercivity of 6.5 kOe. The results provide new insight into developing high energy product nanostructured permanent magnets.
Magnetic Anisotropy and Magnetocaloric Effect (MCE) in NiFe2O4 Nanoparticles
Authors: Gass J. , Frey N. A. , Morales M. B. , Miner M. J. , Srinath S. , Srikanth H.
Published: April 2011

Magnetic refrigeration based on the magnetocaloric effect (MCE) has been proposed as an attractive alternative to gas compression technology. Some calculations suggest that MCE can be obtained with higher efficiencies than compressor driven refrigeration. We examine the MCE in a system of nickel ferrite nanoparticles with size range of 6 to 15 nm. A peak in the MCE at 55 K is observed that increases with higher magnetic fields. This gives this system a relatively high peak entropy change compared to other ferrite systems. A sensitive radio-frequency (RF) transverse susceptibility measurement has also been used to study the magnetic anisotropy. We show that the MCE peak is not associated with the blocking temperature and is likely a field-driven surface spin reorientation which also has a signature in the transverse susceptibility. Work supported by NSF-CTS-0408933 and ARO- W911NF-05-1-0354
Synthesis and Magnetic Properties of Co Nanorod Superlattices
Authors: Wetz Fabienne , Soulantica Katerina , Respaud Marc , Falqui Andrea , Chaudret Bruno
Published: April 2011

We present the synthesis and magnetic properties of Co nanorods spontaneously organized in superlattices over a surface of several microns. This material results from the thermal decomposition of a cobalt precursor under hydrogen, in the presence of a long-chain amine and a long-chain acid as shape control agents. These nanorod superlattices are ferromagnetic at room temperature and they are characterized by a strong coercive field as a consequence of their large magnetic anisotropy. This system can be considered as a good candidate for high density magnetic recording.
Interface Morphology of Metallic Multilayers by Means of Deposition Simulation
Authors: Shintani Kazuhito , Kometani Y. , Nakajima T. , Yano Y.
Published: April 2011

Growth of a Co/Cu/Co multilayer is investigated by molecular-dynamics simulation. The interactions between Co and Cu atoms are calculated in terms of the generic-embedded atom method potential. It is confirmed that two-dimensional island growth of Cu atoms on the Co substrate occurs in the simulations. The roughnesses of the surface and the interface are evaluated by means of the standard deviations of the heights of the surface and interface atoms. Intermixing atoms between the layers are also counted. We conclude that there exists an optimum combination of the incident energies of deposited Cu and Co atoms which minimizes both the roughness and intermixing of the interface.
Characterization of Microstructure and Composition of Fe-B Nanobars as Biosensor Platform
Authors: Li Suiqiong , Fu Liling , Wang Chongmin , Lea Scott , Arey Bruce , Engelhard Mark , Cheng Z.-Y.
Published: April 2011

Individual magnetostrictive nanobars and arrays comprised of magnetostrictive nanobars were recently introduced as a high performance biosensor platform. In this paper, we report the fabrication and characterization of magnetostrictive nanobars based on Fe-B alloy. The nanobars were synthesized using a template-based electrochemical deposition method. The composition and microstructure of the Fe-B nanobars are directly related to their performance as a biosensor platform. The Fe-B nanobar arrays and individual nanobar were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), as well as Auger electron spectroscopy (AES). Morphologically, nanobars have a very flat top and a smooth cylindrical surface, which are critical factors for obtaining high performance as sensor platforms. Structurally, electron diffraction reveals that the Fe-B nanobars are amorphous. AES analysis indicates that Fe-B nanobars show no significant compositional variation along the length direction. It is found that the nanobars were covered by an oxidation layer of a typical thickness of ∼ 10 nm. It is believed that this oxidation layer is related to the passivation of nanobars in air. High temperature annealing and subsequent structural analysis indicate that the Fe-B nanobars possess a good thermal stability.
Magnetic and Ferroelectric Properties of YMnO3 Epitaxial Thin Films
Authors: Maeda Kazuhiro , Yshimura Takeshi , Fujimura Norifumi
Published: April 2011

YMnO3, which is one of hexagonal RMnO3 compounds, has antiferromagnetic and ferroelectric properties, simultaneously. Recently, it has been reported that cross-correlation in the magnetic dielectric properties on hexagonal YMnO3 single crystals. However, the cross-correlation in the magnetic-ferroelectric properties has not been understood yet. In this study, we investigated the cross correlation between magnetism and ferroelectricity on YMnO3 epitaxial films with excellent crystallinity. YMnO3 epitaxial films were deposited pulsed laser deposition. The YMnO3 epitaxial films show the dielectric anomalies at around Néel point of the films. It was suggested that the ferroelectric domain switching was suppressed by the magnetic ordering. The relationship between the magnetic structure and the ferroelectric properties are discussed in terms of the temperature dependences of magnetization and dielectric permittivity. Moreover, the ablation plume of YMnO3 was investigated by optical emission spectroscopy. The effect of the ablation conditions on the thin film growth and electrical properties was discussed.
Magnetoelectric Properties of Multiferroic Composites with Pseudo 1-3 Type Structure
Authors: Shi Zhan , Nan Ce-Wen , Zhang Jie , Ma Jing , Li JingFeng
Published: April 2011

A pseudo 1-3 type multiferroic composite consisting of Pb(Zr,Ti)O3 (PZT) rod array (with base) and Terfenol-D/Epoxy matrix was prepared by the dice-and-fill technique. Simple series and parallel mixture rules well described the measured dielectric and piezoelectric constants. Large magnetoelectric coefficients were observed in the pseudo 1-3 type composite, e.g., over 300 mV/cmi×Oe below 40 kHz and over 4500 mV/ cm×Oe at resonant frequency. The ME response strongly depends on the magnetostrictive behavior of the matrix and the volume fraction of PZT rods, which gives us two convenient way to modify their magnetoelectric response. For this pseudo 1-3 type multiferroic composite, the remarkable magnetoelectric response and well-developed fabrication technique are advantageous for their practical applications in piezoelectric-magnetoelectric multifunctional devices and large bandwidth magnetic sensors.
Theory of Spin-charge-orbital States in the Frustrated System RFe2O4
Authors: Ishihara Sumio , Naka Makoto , Nagano Aya
Published: April 2011

Electronic structure in multiferroic compound RFe2O4. is studied theoretically. We suggest that orbital degree of freedom in a Fe2+ ion is active. The effective Hamiltonian for spin, charge and orbital degrees of freedom is derived. Numerical analyses with the multi-canonical Monte-Carlo simulation show that the electric polarization is attributed to the charge order with momentum (1/3, 1/3). A magnitude of the polarization is enhanced around the magnetic ordering temperature due to the coupling between spin and charge. Conventional orbital order is not expected from the numerical calculation. We discuss possible orbital state at low temperatures.
Thermal Stability of Defects in Substrates for Multiferroic Materials
Authors: Jeddy Shehnaz , Zvanut Mary Ellen , Lassiter Brian Einstein , Janowski Gregg M , Brillson Leonard J
Published: April 2011

Strontium Titanate (STO) substrates were studied by electron paramagnetic resonance (EPR) spectroscopy to assess possible changes incurred by deposition of multiferroic thin films. To this effect, STO was vacuum annealed at pressures of 10−5 Torr for one hour at temperatures in the range of 200 – 500 °C. EPR spectra, measured before and after each anneal, revealed changes in the amount of three different defects, Cr3+, Fe3+ and an iron-oxygen vacancy complex, Fe3+Vo. The latter was used to monitor the diffusion of oxygen. EPR analysis showed that Fe3+Vo increases from its as-grown value, suggesting that a charged oxygen species is mobile in the substrate under film deposition conditions. Coupled with a subsequent O2 anneal showing minimal change in the Fe3+Vo signal, the data indicate a loss of oxygen from the sample during vacuum annealing. As charged oxygen vacancies may affect the substrate as well as the substrate/ thin film interface, these results are important for understanding the behavior of multiferroic devices built on STO substrates.
Epitaxial Growth of SrTiO3 Thin Films on TiN/Si Substrates Using RF Sputtering
Authors: Wang Chun , Kryder Mark H
Published: April 2011

Epitaxial SrTiO3 (001) thin films with a TiN template layer have been deposited on Si(001) single crystal substrates by RF sputtering. The deposited SrTiO3 films show a surface with roughness of 0.66nm. The orientation relationship was determined to be SrTiO3(001)[110]∥TiN(001)[110]∥Si(001)[110]. The microstructure and interface of the multilayer was studied using high resolution transmission electron microscopy (TEM). The electron diffraction pattern confirmed the epitaxial relationship between each layer.
Luminescence and Raman Based Real Time Imaging of Ferroelectric Domain Walls
Authors: Dierolf Volkmar , Capek Pavel , Sandmann Christian
Published: April 2011

We studied ferroelectric domain wall regions in lithium niobate using the photoluminescence of intentionally doped rare earth ions (such as Er3+) as well as Raman spectroscopy and present an overview of the current status of our ongoing investigations. We find that the Er emission is a sensitive tool to observe changes in local electric fields as well as reconfiguration of defect dipoles across the domain wall. The Raman spectra, on the other hand can be used to identify charges that accumulate asymmetrically across a domain wall. We further demonstrate that the imaging methods offer sufficient sensitivity to observe the changes associated with a domain in real time while it is moving.
Magneto-Optical Kerr Effect in Multiferroic Nanostructures
Authors: Corbo Matthew T. , Straub Florian , Zheng Haimei , de la Paz Cruz Maria , Suzuki Yuri
Published: April 2011

We report the study of the magneto-optical properties of composite multiferroic thin films composed of CoFe2O4 nanopillars embedded in a BiFeO3 matrix. The magneto-optical Kerr rotation and Kerr ellipticity in these films have been measured and are in good agreement with magnetization measurements. The Kerr signal has been studied as a function of film composition and nanopillar diameter confirming that the magneto-optical signal is due solely to the CoFe2O4 nanopillars.
Surface Reactions of Metal Catalysts for Carbon Nanotubes on an Oxide Thin Layer/Si Substrates Studied by in-situ Micro X-ray Adsorption Spectroscopy using SPELEEM
Authors: Maeda Fumihiko , Hibino Hiroki , Suzuki Satoru , Guo FangZhun , Watanabe Yoshio
Published: April 2011

To clarify the reaction process of Co and Fe with a oxide layer on Si substrates, the annealing processes were analyzed using spectroscopic photoemission and low-energy electron microscopy for a special surface where oxide areas and clean substrate areas (voids) coexist closely in a micrometer-order view. From analyses of XAS spectra and edge jump ratios obtained from the photoemission electron microscopy image, we clarified that Co atoms in the void area remain because of the formation of silicides, but that those on the oxide layer disappear because metallic Co atoms easily diffuse. In contrast, in the case of Fe, we found the formation of various silicides and their gradual diffusion into Si substrate even in the form of silicides.
Thermodynamics and Kinetics of Oxidation of Pure Indium Solders
Authors: Schoeller Harry , Kim Jongman , Park Seungbae , Cho Junghyun
Published: April 2011

MicroElectroMechanical System (MEMS) devices often require low-temperature, fluxless soldering techniques due to their high temperature sensitivity and performance requirements of the components. While seeking the development of a soldering technology using pure indium, the major focus of this study is to assess the thermodynamics and kinetics of indium oxidation at various solder reflow environments that will ultimately provide a processing window for solder reflow and surface oxide cleaning. With a glove box employed to generate reducing environments, oxygen, moisture, and hydrogen contents were varied to examine their effects on oxidation and reduction behavior of indium. We also explored oxidation mechanisms at different regimes of temperature and time. In particular, electron transport from indium to indium oxide is shown to be the rate controlling mechanism under specific oxidizing conditions. For accurate thickness measurements, a spectroscopic ellipsometer was employed. In addition, the effect of indium oxidation on solder joint reliability was observed via wetting angle and interfacial shear strength measurements.
Mechanical Property Measurement of Interconnect Materials by Magnetostrictive Sensors
Authors: Liang Cai , Mathison Leslie , Prorok Barton C.
Published: April 2011

This paper reports on the measurement of elastic modulus for some electronic thin film materials used in electronic interconnects by a magnetostrictive sensor. Thin film materials of Au, Sn, In and Au-rich lead free solder (AuSn) were sputter deposited onto well defined strips of Metglas™. This material possesses magnetostrictive properties whereby it deforms when subjected by a magnetic field and generates a magnetic field when deformed. The MetglasTM strip is driven to resonance via a modulated magnetic field generated by a coil. The elastic modulus of the above materials was determined by measuring the resonant frequency of the sensors before and after film deposition and using the frequency shift, two analytical approaches were employed to extract values. The as sputtered films were examined by X-ray Diffraction (XRD) and Scanning Election Microscope (SEM) to characterize their microstructures. The elastic modulus of Au films was determined by employing two mathematical methodologies that resulted in values of 71.2GPa and 75.9GPa, which exhibit less than 5% divergence. Errors in the different measuring methodologies are discussed. Moreover, elastic modulus values of solder materials of AuSn (80/20 wt%), tin and indium films, which were also measured in their as deposited forms, will be discussed. This method represents a potentially new, non-destructive method to determine critical material properties of as deposited materials.
Evaluation of Void Formation Mechanism in Cu Thin Films; Separation of The Effect of Electron Wind Force and Stress
Authors: Fujii Yousuke , Tsutsumi Masanori , Inoue Junya , Koseki Toshihiko
Published: April 2011

Electromigration (EM) and stress-induced voiding (SIV) in Cu and Cu alloys thin films were studied separately. The characterization of EM was evaluated in a modified interconnect structure where the effect of current density can be observed in the absence of stress disturbance. SIV, on the other hand, is examined in detail by applying a uniform stress to Cu films without electric current. Results of EM tests clearly showed that void and hillock formations were concentrated mainly in the region with high current density gradient without stress disturbance. SIV test performed under the high stress of 1GPa showed that voids were observed to form at grain boundaries and grain boundary triple junctions. Under the high stress, SIV is shown to be generated in the absence of stress gradient. Also, the effect of alloying to EM and SIV was investigated in detail.
Well-Aligned In-situ Formed Open-End Carbon Nanotube for Device and Assembly Applications
Authors: Zhu Lingbo , Wong ChingPing
Published: April 2011

Carbon nanotubes (CNTs) have been proposed for applications in microelectronic applications, especially for electrical interconnects, thermal management, and nanodevices, due to their excellent electrical, thermal, and mechanical properties. In this paper, we reported a simple process to achieve simultaneous CNT growth and opening of the CNT ends, while keeping alignment of the original CNT films/arrays. The addition of relatively low reactivity oxidizing agents (water) into the reaction furnace enables the feasibility. We proposed using novel CNT transfer technology, enabled by open-ended CNTs, to circumvent the high carbon nanotube (CNT) growth temperature and poor adhesion with the substrates that currently plague CNT implementation. The process is featured with separation of high-temperature CNT growth and low-temperature CNT device assembly. Field emission testing of the as-assembled CNT devices is in a good agreement with the Fowler-Nordheim (FN) equation, with a field enhancement factor of 4540.
A Patch-Type Flexible Physiological Monitor on a Non-Woven Material
Authors: Chang Wen-Yang , Chang Jin-Sheng , Chu Chun-Hsun , Ho Tzong-Che , Lin Yu-Cheng
Published: April 2011

The study reported is about an integrated wireless physiological monitor module of the flexible patch type, used on a non-woven material to package this module by a hot press process. The module can monitor the body temperature and heart rate. Experimental results showed that the specification and accuracy should be 25-40 °C ± 0.5 °C and 50-200 bpm ± 2 bpm. The main advantage of the module is that the postural change can be monitored. At the same time, it has also a good adhesion between substrate and components, without crack of conductor trace line after bending the module repeatedly. Thickness is about 2 mm. The aim of this study is to speed up the physiological technology and to create more efficiency by miniaturization. In addition, the acceptance level of wearing it is increased by the small and ergonomic design.
Tailoring Magnetic Microspheres with Controlled Porosity
Authors: Toprak Muhammet S , McKenna Brandon J , Waite Herb , Stucky Galen D
Published: April 2011

The synthesis of organic and inorganic nano- and microspheres has attracted much interest for a variety of applications ranging from drug delivery to chemical storage and catalysis. We recently demonstrated the assembly of magnetic nanoparticles and polycations into hybrid microspheres in a single-step synthesis via complex coacervation. These microspheres showed viability for bio-applications as indicated by toxicity tests, and are therefore potential targeted drug delivery devices, as they can be directed magnetically. This work reports the recent progress on the potential use of these assemblies in drug release by controlling their porosity. Fluorescein tagged dextran molecules with different MW have been infiltrated into these entities to determine critical pore size by confocal fluorescence microscopy. Different physicochemical characterization results are also presented.
Development of Structure-Property Relationships in Disordered Zirconia Thin Films for High Energy Density Mim Capacitors
Authors: Sethi Guneet , Lanagan Michael T. , Furman Eugene , Horn Mark W.
Published: April 2011

Amorphous zirconium oxide thin films were prepared by reactive magnetron sputtering. The dielectric films were characterized by impedance spectroscopy with temperature. The effect of annealing on capacitor performance was studied. Annealing gold electroded thin films at 250°C greatly reduced the losses with little changes in crystallinity. Space charge relaxation started to appear at 190°C. The activation energy for the relaxation was 0.84 eV with a very low relaxation frequency at room temperature (0.23μHz). Electrode effects dominated at very low frequencies at all temperatures. AC conductivity followed the universality behavior for the AC charge transport showing that the films are highly disordered. No DC conductivity regime was observed indicating that DC conductivity is very low. DC conductivity of the films was of the order of 10−13 S/m, which is lesser than the comparable thickness high quality gate oxides.
Studies on Curvature Deformation Control of Bilayer Cantilever Fabricated by Surface Micromachining of SOI Wafer
Authors: Huang Yu-Ming , Sohgawa Masayuki , Noda Minoru , Yamashita Kaoru , Okuyama Masanori , Noma Haruo
Published: April 2011

The Cr/Si bilayer cantilevers for an integrated multi-axis tactile sensor were fabricated by Si surface micromachining process. Among the cantilevers with various shapes, the rectangular and semicircular cantilevers can be deflected upward with good controllability. The maximum deflections are compared with those calculated by finite element method. Calculated deflections of Cr/Si cantilever agree considerably with the measured one. So, it is considered that the analysis by finite element method is useful as optimization of layer thickness and size to obtain the Cr/Si bilayer cantilevers with accurate deflection.
BCB Based Packaging for Low Actuation Voltage RF MEMS Devices
Authors: Peyrou David , PENNEC Fabienne , Achkar Hikmat , PONS Patrick , Coccetti Fabio , Aubert Hervé , Plana Robert
Published: April 2011

This paper outlines the issues related to RF MEMS packaging and low actuation voltage. It is presented an original approach concerning the modeling of the capacitive contact using multi-physics simulation and advanced characterization. A similar approach is used concerning the packaging development where multi-physic simulations are used to optimize the process. A devoted package architecture is proposed featuring very low loss at microwave range.
Power and Radio Frequency Inductors Using a Hybrid Ferrite-Flex Foil Technology
Authors: Gijs Martin , Saidani Menouer
Published: April 2011

We present a hybrid technology for the realization of three-dimensional miniaturized power inductors and RF inductors on silicon. The power inductors consist of planar Cu coils on polyimide substrates, and mm-size ferrite magnetic cores, obtained by three-dimensional micro-patterning of ferrite wafers using powder blasting. The coils are realized using an in-house developed high-resolution polyimide spinning and Cu electroplating process. Winding widths down to 5 μm have been obtained and total device volumes are ranging between 1.5 and 10 mm3. Inductive and resistive properties are characterized as a function of frequency; inductance values in the 100 μH range have been obtained. We also have realized millimetre-size RF inductors on silicon using the same polyimide mould - Cu electroplating coil technology. Subsequently the coils are assembled with magnetic cover plates of commercially available bulk Ni-Zn ferrites of high resistivity. Using the magnetic flux-amplifying ferrite plates, we obtain a 40 % enhancement of the inductance and a 25 % enhancement of the quality factor (Q=10-20) for frequencies up to 0.2 GHz.
Towards the Integration of Barium Ferrite Sputtered Films for Coplanar Isolators and Circulators in the Millimeter Wave Range
Authors: Dehlinger A.-S. , Le Berre M. , Chatelon J.-P. , Benevent E. , Vincent D. , Givord D. , Larrey V. , Rousseau J.J.
Published: April 2011

Signal processing in communication, instrumentation and radar detection requires low cost microwave and millimeter wave devices. The integration of millimeter wave passive components like isolators and circulators is thus a major issue. In these components, the nonreciprocal nature of wave propagation in ferrites plays an essential role. Hexagonal ferrites, such as barium ferrite (BaFe12O19 or BaM), which has a large resistivity and high permeability at high frequency, are of great interest for such applications. The present work deals with the characterization of barium hexaferrite sputtered films and with the device integration for the development of coplanar isolators and circulators working at frequencies around 40 GHz.

The BaM films (in the thickness range of 10μm) were deposited on alumina substrate by RF magnetron sputtering at room temperature and were then crystallized using a 800°C thermal annealing. Structural properties were evaluated by X-ray diffraction and the magnetostatic properties of the film were determined using a Vibrating Sample Magnetometer (VSM) leading to assess a range of deposition conditions appropriate for device integration.

Both coplanar isolators and circulators were implemented using standard lift-off technique. Coplanar circulators were designed by analytical calculation and 3D electromagnetic simulation (HFSS) supposing a saturated material and no losses. The microwave range characterization was performed using a network analyzer and a probing system with a prior OSTL calibration. The coplanar isolators were characterized both at the remanence and under a polarizing field. At the remanence, the gyroresonance occurred at 50 GHz and the nonreciprocal effect - difference between the transmission coefficient in the forward direction and in the reverse direction - was evaluated. When applying a polarizing field, the tunability of the isolator was verified experimentally. Finally first measurements on integrated coplanar circulators are currently under progress.
Development of 3D-Packaging Process Technology for Stacked Memory Chips
Authors: Mitsuhashi Toshiro , Egawa Yoshimi , Kato Osamu , Saeki Yoshihiro , Kikuchi Hidekazu , Uchiyama Shiro , Shibata Kayoko , Yamada Junji , Ishino Masakazu , Ikeda Hiroaki , Takahashi Nobuaki , Kurita Yoichiro , Komuro Masahiro , Matsui Satoshi , Kawano Masaya
Published: April 2011

A 3D packaging technology for 4 Gbit DRAM has been developed. It is targeting to realize 4Gb density DRAM by stacking 8-DRAM chips into one package. Interconnect between stacked chips will be done by through-silicon-via for the requirement of 3Gbps operation. Key process technologies for chip stacking are through-silicon-via formation, wafer back side process and micro-bump bonding. These chip-stacking processes have been developing using TEG, which can evaluate electrical characteristics.
High-Performance Temporary Adhesives for Wafer Bonding Applications
Authors: Puligadda Rama , Pillalamarri Sunil , Hong Wenbin , Brubaker Chad , Wimplinger Markus , Pargfrieder Stefan
Published: April 2011

Myriad structures for stacking chips, power devices, smart cards, and thin substrates for processors have one thing in common: thin silicon. Wafer thinning will soon be an essential process step for most of the devices fabricated and packaged henceforth. The key driving forces for thinned wafers are improved heat dissipation, three-dimensional stacking, reduced electrical resistance, and substrate flexibility. Handling of thin and ultrathin substrates however is not trivial because of their fragility and tendency to warp and fold. The thinned substrates need to be supported during the backside grinding process and through the subsequent processes such as lithography, deposition, etc. Using temporary adhesives to attach the processed device wafer to a rigid carrier wafer offers an efficient solution. The key requirements for such materials are ease of application, coating uniformity with minimal thickness variation across the wafer, good adhesion to a wide variety of surfaces, thermal stability in processes such as dielectric deposition and metallization, and ease of removal to allow high throughput. An additional requirement for these materials is stability in harsh chemical environments posed by processes such as etching and electroplating. Currently available materials meet only a subset of these requirements. None of them meet the requirement of high-temperature stability combined with ease of removal. We have developed adhesives that meet a wide range of post-thinning operating temperatures. Additionally, the materials are soluble in industry-accepted safe solvents and can be spin-applied to required thicknesses and uniformity. Above all, the coatings can be removed easily without leaving any residue. This paper reports on the development of a wide range of temporary adhesives that can be used in wafer thinning applications while applying both novel and conventional bonding and debonding methods.