Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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  • Publication
    Towards nanoreliability of sensors incorporating interfaces between single-walled carbon nanotubes and metals: Molecular dynamics simulations and in situ experiments using electron microscopy
    ( 2016)
    Hartmann, S.
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    Hermann, S.
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    Bonitz, J.
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    Heggen, M.
    ;
    Hölck, O.
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    Shaporin, A.
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    Mehner, J.
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    Schulz, S.E.
    ;
    Gessner, T.
    ;
    Wunderle, B.
    In this paper we present results of our recent efforts to understand the mechanical interface behaviour of single-walled carbon nanotubes (SWCNTs) embedded in metal matrices. We conducted experimental pull-out tests of SWCNTs embedded in Pd and found maximum forces in the range F ≈ (10 to 65) nN. These values are in good agreement with forces obtained from molecular dynamics simulations taking into account surface functional groups (SFGs) covalently linked to the SWCNT material. The dominant failure mode in experiment is a SWCNT rupture, which can be explained with the presence of SFGs. For further in depth investigations, we present a tensile actuation test system based on a thermal actuator to perform pull-out tests inside a transmission electron microscope with the objective to obtain in situ images of SWCNT-metal interfaces under mechanical loads at the atomic scale. First experiments confirmed the presence of suspended thin metal electrodes to embed SWCNTs. These suspended thin metal electrodes are electron transparent at the designated SWCNT locations. Actuator movements were evaluated by digital image correlation and we observed systematic actuator movements. Although significant image drifts occured during actuation, we achieved atomic resolution of the metal electrode and stable movement in the focal plane of the electron microscope.
  • Publication
    Experimental and computational studies on the role of surface functional groups in the mechanical behavior of interfaces between single-walled carbon nanotubes and metals
    ( 2016)
    Hartmann, S.
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    Sturm, H.
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    Blaudeck, T.
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    Hölck, O.
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    Hermann, S.
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    Schulz, S.E.
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    Gessner, T.
    ;
    Wunderle, B.
    To study the mechanical interface behavior of single-walled carbon nanotubes (CNTs) embedded in a noble metal, we performed CNTmetal pull-out tests with in situ scanning electron microscope experiments. Molecular dynamics (MD) simulations were conducted to predict forcedisplacement data during pull-out, providing critical forces for failure of the system. In MD simulations, we focused on the influence of carboxylic surface functional groups (SFGs) covalently linked to the CNT. Experimentally obtained maximum forces between 10 and 102 nN in palladium and gold matrices and simulated achievable pulling forces agree very well. The dominant failure mode in the experiment is CNT rupture, although several pull-out failures were also observed. We explain the huge scatter of experimental values with varying embedding length and SFG surface density. From simulation, we found that SFGs act as small anchors in the metal matrix and significantly enhance the maximum forces. This interface reinforcement can lead to tensile stresses sufficiently high to initiate CNT rupture. To qualify the existence of carboxylic SFGs on our CNT material, we performed analytical investigation by means of fluorescence labeling of surface species and discuss the results. With this contribution, we focus on a synergy between computational and experimental approaches involving MD simulations, nano scale testing, and analytics (1) to predict to a good degree of accuracy maximum pull-out forces of single-walled CNTs embedded in a noble metal matrix and (2) to provide valuable input to understand the underlying mechanisms of failure with focus on SFGs. This is of fundamental interest for the design of future mechanical sensors incorporating piezoresistive single-walled CNTs as the sensing element.
  • Publication
    Quantitative in-situ scanning electron microscope pull-out experiments and molecular dynamics simulations of carbon nanotubes embedded in palladium
    ( 2014)
    Hartmann, S.
    ;
    Blaudeck, T.
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    Hölck, O.
    ;
    Hermann, S.
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    Schulz, S.E.
    ;
    Gessner, T.
    ;
    Wunderle, B.
    In this paper, we present our results of experimental and numerical pull-out tests on carbon nanotubes (CNTs) embedded in palladium. We prepared simple specimens by employing standard silicon wafers, physical vapor deposition of palladium and deposition of CNTs with a simple drop coating technique. An AFM cantilever with known stiffness connected to a nanomanipulation system was utilized inside a scanning electron microscope (SEM) as a force sensor to determine forces acting on a CNT during the pull-out process. SEM-images of the cantilever attached to a CNT have been evaluated for subsequent displacement steps with greyscale correlation to determine the cantilever deflection. We compare the experimentally obtained pull-out forces with values of numerical investigations by means of molecular dynamics and give interpretations for deviations according to material impurities or defects and their influence on the pull-out data. We find a very good agreement of force data from simulation and experiment, which is 17 nN and in the range of 10-61 nN, respectively. Our findings contribute to the ongoing research of the mechanical characterization of CNT-metal interfaces. This is of significant interest for the design of future mechanical sensors utilizing the intrinsic piezoresistive effect of CNTs or other future devices incorporating CNT-metal interfaces.
  • Publication
    Developments trends in the field of wafer bonding technologies
    ( 2008)
    Wiemer, M.
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    Haubold, M.
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    Jia, C.
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    Wünsch, D.
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    Frömel, J.
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    Gessner, T.
    One well established technology for the fabrication of 3D devices in microelectronics and micro system technology is wafer bonding. After an overview about the existing bonding techniques the presentation will address aspects like bonding with plasma pretreatment to reduce the bond temperature below 200°C, use of nanostructures for bonding, metal to metal bonding and integration of new materials to form special SOI substrates.
  • Publication
    Mikrofluidische Schnittstellen durch Laserstrukturierung
    ( 2008)
    Baum, M.
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    Keiper, B.
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    Hänel, J.
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    Otto, T.
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    Gessner, T.
  • Publication
    Copper(I) Carboxylates of Type [(nBu3P)mCuO2CR] (m = 1, 2, 3) - Synthesis, Properties, and their Use as CVD Precursors
    ( 2008)
    Jakob, A.
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    Shen, Y.
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    Wächtler, T.
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    Schulz, S.E.
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    Gessner, T.
    ;
    Riedel, R.
    ;
    Fasel, C.
    ;
    Lang, H.
    Copper(I) carboxylates of type [(nBu3P)mCuO2CR] (m = 1: 3a, R = Me; 3b, R = CF3; 3c, R = Ph; 3d, R = CH=CHPh. m = 2: 4a, R = Me; 4b, R = CF3; 4c, R = Ph; 4d, R = CH=CHPh. m = 3: 8a, R = Me; 8b, R = CF3; 8c, R = CH2Ph; 8d, R = (CH2OCH2)3H; 8e, R = cC4H7O) are accessible by following synthesis methodologies: the reaction of [CuO2CR] (1a, R = Me; 1b, R = CF3; 1c, R = Ph; 1d, R = CH=CHPh) with m equivalents of nBu3P (2) (m = 1, 2, 3), or treatment of [(nBu3P)mCuCl] (5a, m = 1; 5b, m = 2) with [KO2CCF3] (6). A more straightforward synthesis method for 8a - 8e is the electrolysis of copper in presence of HO2CR (7a, R = Me; 7b, R = CF3; 7c, R = CH2Ph; 7d, R = (CH2OCH2)3H; 7e, R = cC4H7O) and 2, respectively. This method allows to prepare the appropriate copper(I) carboxylate complexes in virtually quantitative yield, analytically pure form, and on an industrial scale. IR spectroscopic studies reveal that the carboxylic units in 4, 5, and 8 bind in a unidentate, chelating or ?-bridging fashion to copper(I) depending on m and R. The thermal properties of 4, 6, and 8 were determined by TG and DSC studies. Based on TG-MS experiments a conceivable mechanism for the thermally induced decomposition of these species is presented. Hot-wall Chemical Vapor Deposition experiments (CVD) with precursor 4b showed that copper could be deposited at 480 °C onto a TiN-coated oxidized silicon substrate. The copper films were characterized by SEM and EDX studies. Pure layers were obtained with copper particles of size 200 - 780 nm.
  • Publication
    Controlling the formation of nanoparticles for definite growth of carbon nanotubes for interconnect applications
    ( 2008)
    Hermann, S.
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    Ecke, R.
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    Schulz, S.
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    Gessner, T.
    Our interest is the integration of carbon nanotubes (CNT) in electronic devices (IC, NEMS). In the scope of this work, we present a study on the preparation of the catalyst Ni particles from ultrathin films and the synthesis of carbon nanotubes by the chemical vapour deposition method. For the preparation, we use a cold-wall CVD reactor especially designed for handling samples up to a size of a 4"" wafer. We show the influence of different process conditions like temperature, initial layer thickness of catalyst and substrate on particle formation characterized by scanning electron microscopy (SEM). We show that the optimization of process conditions in the catalyst preparation phase is constitutive for dense CNT films. Regarding the application of CNTs as electrical interconnects, we studied the arrangement of nanoparticles on Al and TiN supporting layer. Furthermore, we fabricated the first test structures for the selective growth of CNTs out of contact holes on a Cu/TiN metallization layer system. The growth of multi-walled nanotubes (MWNTs) was performed with thermal CVD with ethylene as a precursor gas and hydrogen as supporting gas mixed in a nitrogen gas flow. The effects of growth condition on the quality and morphology of the CNTs were characterized by scanning electron microscopy, transmission electron microscopy (TEM) and Raman spectroscopy. The influence of temperature, gas composition and substrate on CNT growth will be presented. We managed to grow dense CNTs even at temperatures as low as 500 °C.
  • Publication
    Micro Actuators based on Structured Water
    ( 2008)
    Nestler, J.
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    Hiller, K.
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    Otto, T.
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    Gessner, T.
  • Publication
    Fabrication and characterization of a force coupled sensor-actuator system for adjustable resonant low frequency vibration detection
    ( 2008)
    Forke, R.
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    Scheibner, D.
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    Hiller, K.
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    Gessner, T.
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    Doetzel, W.
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    Mehner, J.
  • Publication
    Phosphane copper(I) complexes as CVD precursors
    ( 2007)
    Roth, N.
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    Jakob, A.
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    Waechtler, T.
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    Schulz, S.E.
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    Gessner, T.
    ;
    Lang, H.