薄膜与小尺度材料及力学性能研究组

Scripta Materialia - Volume 60, Issue 5, Pages 269-358 (March 2009)

Steven — Mon, 29 Dec 2008 09:13:08 +0800

Thermomechanical properties of gold nanowires supported on a flexible substrate
Pages 273-276
Sven Olliges, Stephan Frank, Patric A. Gruber, Vaida Auzelyte, Karsten Kunze, Harun H. Solak, Ralph Spolenak

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Microelectronics Reliability - Article in Press, Corrected Proof

Steven — Mon, 29 Dec 2008 09:10:41 +0800

A new on-chip test structure for real time fatigue analysis in polysilicon MEMS

G. Langfelder^a, A. Longoni^a, F. Zaraga^a, A. Corigliano^b, A. Ghisi^b and A. Merassi^c

^aElectronics and Information Department, Politecnico di Milano, via Ponzio 34/5, Milano, Italy

^bDepartment of Structural Engineering, Politecnico di Milano, piazza Leonardo Da Vinci 32, Milano, Italy

^cMAHRS Unit, STMicroelectronics, Cornaredo (Milano), Italy

Received 21 May 2008;

revised 19 November 2008.

Available online 27 December 2008.

Abstract

Fatigue test results on 15 μm thick polysilicon specimens are presented and discussed, both quantitatively and qualitatively. The test structure is a newly designed, electrostatically actuated, MEMS device that allows the execution of on-chip fatigue and fracture tests on polysilicon specimens. The experiments have been carried out through a new analog, low-noise and low-perturbing electrostatic position measurement system for capacitive MEMS sensors. The setup allows for a real time monitoring of MEMS position, from which a macroscopic quantity, the elastic stiffness of the specimen, can be continuously evaluated, provided that the applied force is known.

The results obtained in the present research put in evidence the decrease of the elastic stiffness during fatigue life before rupture. In addition, the stress amplitude during the load cycles plays a role on the lifetime of the test devices: larger stress amplitudes around a tensile mean stress reduce the fatigue resistance, mainly when a compressive stress is also present, in good agreement with a Wöhler curve.

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Thin Solid Films - Article in Press, Accepted Manuscript

Steven — Fri, 26 Dec 2008 11:55:16 +0800

Competition between dislocation nucleation and void formation as the stress relaxation mechanism in passivated Cu interconnects

J. Zhang^a, J.Y. Zhang^a, G. Liu^a, Y. Zhao^a and J. Sun^a

^aState Key Laboratory for Mechanical Behavior of Materials and School of Materials Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China

Received 6 March 2008; revised 26 November 2008; accepted 10 December 2008. Available online 24 December 2008.

Abstract

We perform systematic calculations to study the competition between the dislocation nucleation and void formation as stress relaxation mechanism in Cu interconnects under thermal stress, which is related to the aspect ratio (ratio of the film thickness to width) of the Cu lines. It is quantitatively found from both elastic-perfectly plastic model and kinematic strain hardening model that there exists a critical aspect ratio, below and above which the stress relaxation is dominated by the dislocation nucleation and void formation, respectively. The critical aspect ratio is revealed to modulate by both the length scale of the interconnects and the interfacial strength between the Cu lines and surroundings, suggesting potential application to achieve artificial controlling on stress relaxation mechanism in Cu lines. Calculations are in good agreement with available experiments.

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Thin Solid Films - Article in Press, Accepted Manuscript

Steven — Fri, 26 Dec 2008 11:52:55 +0800

Mechanical properties of porous silicon by depth-sensing nanoindentation techniques

Zhen-qian Fang^a, Ming Hu^a, Wei Zhang^a, Xu-rui Zhang^a and Hai-bo Yang^a

^aSchool of Electronic & Information Engineering, Tianjin University, Tianjin 300072, China

Received 29 August 2007;

revised 29 November 2008;

accepted 8 December 2008.

Available online 24 December 2008.

Abstract

Porous silicon (PS) was prepared using the electrochemical corrosion method. Thermal oxidation of the as-prepared PS samples was performed at different temperatures for tuning their mechanical properties. The mechanical properties of as-prepared and oxidized PS were thoroughly investigated by depth-sensing nanoindentation techniques with the continuous stiffness measurements option. The morphology of as-prepared and oxidized PS was characterized by field emission scanning electron microscope and the effect of observed microstructure changes on the mechanical properties was discussed. It is shown that the hardness and Young's elastic modulus of as-prepared PS exhibit a strong dependence on the preparing conditions and decrease with increasing current density. In particular, the mechanical properties of oxidized PS are improved greatly compared with that of as-prepared ones and increase with increasing thermal oxidation temperature. The mechanism responsible for the mechanical property enhancement is possibly the formation of SiO₂ cladding layers encapsulating on the inner surface of the incompact sponge PS to decrease the porosity and strengthen the interconnected microstructure.

Keywords: Porous silicon; Hardness; Young's elastic modulus; Nanoindentation; thermal oxidation

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Thin Solid Films - Article in Press, Accepted Manuscript

Steven — Fri, 26 Dec 2008 11:51:08 +0800

In-situ X-ray investigations of quench-condensed thin gold films

Dirk Lützenkirchen-Hecht^a, Sascha Gertz^a, Christian Markert^a and Ronald Frahm^a

^aFachbereich C- Physik, Bergische Universität Wuppertal, Gauss-Straße 20, 42097 Wuppertal, Germany

Received 21 December 2007;

revised 10 December 2008;

accepted 12 December 2008.

Available online 24 December 2008.

Abstract

Thin gold films were deposited on float glass substrates held at cryogenic temperatures down to 77 K and investigated in-situ using X-ray reflectometry and surface sensitive reflection mode X-ray absorption spectroscopy (XAFS). The combination of these in-situ X-ray methods with simultaneous electrical resistivity measurements yields information about the surface and volume microstructure of the deposited films as a function of the deposition temperature and their changes induced by a subsequent annealing treatment. The surface sensitive XAFS experiments clearly proved that the films exhibit a polycrystalline structure throughout the temperature range studied here. The data were fitted using a correlated Debye-model. The results show that for film deposition at low substrate temperatures < 130 K, a significantly decreasing Debye-temperature was found, reaching values of about 100 K in comparison to 165 K for the polycrystalline bulk material. This decrease was interpreted to be predominantly related to defective film regions with an increased static disorder.

Keywords: cryogenic temperatures; X-ray reflectivity; X-ray absorption spectroscopy; electrical resistivity

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Thin Solid Films - Article in Press, Accepted Manuscript

Steven — Fri, 26 Dec 2008 11:49:19 +0800

Modeling of creep deformation and its effect on stress distribution in multilayer systems under residual stress and external bending

Qing-Qi Chen^a, Fu-Zhen Xuan^a and Shan-Tung Tu^a

^aKey Laboratory of Safety Science of Pressurized System, Ministry of Education, East China University of Science and Technology, Shanghai 200237, P.R. China

Received 21 June 2008;

revised 26 November 2008;

accepted 4 December 2008.

Available online 24 December 2008.

Abstract

A general theoretical model was developed to predict the creep deformation and its effect on the stress relaxation and distribution in the multilayer systems under residual stress and external bending. Based on the proposed solution, a simplified solution for the special case of one film layer on a substrate is also presented. Finite element analysis was carried out to validate the presented model. Good agreements were observed between the finite element simulation and the prediction of the proposed model. In addition, the effects of film thickness on creep strain and stress distribution, the creep effect on neural axis location in the bilayer assembly subjected to the combination of residual stress and external bending were also discussed.

Keywords: Creep; Multilayer; Residual stress; External bending; Modeling

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Thin Solid Films - Article in Press, Accepted Manuscript

Steven — Fri, 26 Dec 2008 11:47:38 +0800

Mechanical and deformation behaviour of titanium diboride thin films deposited by magnetron sputtering

P.K.P. Rupa^a, P.C. Chakraborty^b and S.K. Mishra^a

^aNational Metallurgical Laboratory, Jamshedpur 831007, India

^bDepartment of Metallurgy and Materials Engineering, Jadavpur University, Kolkata 700032 , India

Received 20 September 2007;

revised 15 October 2008;

accepted 2 December 2008.

Available online 24 December 2008.

Abstract

Nanoindentation studies have been carried out for TiB₂ films deposited on Si, glass and steel by sputtering for studying the influence of the substrates. It was observed that the modulus of the film was influenced by the substrates from 30 nm onwards. Plastic energy analysis has shown that as load increases more energy is absorbed by the substrate. Quantitative indentation depth limits for obtaining film only hardness, using a combination of log-log plot of load vs displacement and load vs (displacement)² functions, have shown the dependence on the threshold load for crack formation. Comparison of the hardness data with composite hardness models has been performed. Fracture toughness of the coatings was also evaluated using two methods which resulted in comparable results.

Keywords: Thin films; Nanoindentation; Mechanical Properties; Sputtering; Titanium diboride

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J. Appl. Phys. 104, 123530 (2008)

Steven — Fri, 26 Dec 2008 11:46:04 +0800

Electrostriction in elastic dielectrics undergoing large deformation

Xuanhe Zhao and Zhigang Suo
School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA

Wedevelop a thermodynamic model of electrostriction for elastic dielectrics capableof large deformation. The model reproduces the classical equations ofstate for dielectrics at small deformation, but shows that someelectrostrictive effects negligible at small deformation may become pronounced atlarge deformation. The model is then specialized to account forrecent experiments with an elastomer, where the electric displacement islinear in the electric field when the strain of theelastomer is held fixed, but the permittivity changes appreciably whenthe strain changes. Our model couples this quasilinear dielectric behaviorwith nonlinear elastic behavior. We explore the consequence of themodel by deriving conditions under which the deformation-dependent permittivity suppresseselectromechanical instability. ©2008 American Institute of Physics

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Microelectronics Reliability - Article in Press, Corrected Proof

Steven — Fri, 26 Dec 2008 11:42:20 +0800

Experimental and simulation studies of resistivity in nanoscale copper films

A. Emre Yarimbiyik^a^,^b, Harry A. Schafft^b, Richard A. Allen^b, Mark D. Vaudin^c and Mona E. Zaghloul^a

^aThe Department of Electric and Computer Engineering, The George Washington University, Washington, DC 20052, United States

^bSemiconductor Electronics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8120, United States

^cCeramics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8520, United States

Received 13 April 2007; revised 3 November 2008. Available online 24 December 2008.

Abstract

The effect of film thickness on the resistivity of thin, evaporated copper films (approximately 10–150 nm thick) was determined from sheet resistance, film thickness, and mean grain-size measurements by using four-point probe, profilometer, and electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) methods, respectively. The resistivity of these films increased with decreasing film thickness in a manner that agreed well with the dependence given by a versatile simulation program, published earlier, using the measured values for the mean grain size and fitting parameters for surface and grain boundary scattering. Measurements of the change in sheet resistance with temperature of these films and the known change in resistivity with temperature for pure, bulk copper were used to calculate the thickness of these films electrically by using Matthiessen’s rule (this is often referred to as an “electrical thickness”). These values agreed to within 3 nm of those obtained physically with the profilometer. Hence, Matthiessen’s rule can continue to be used to measure the thickness of a copper film and, by inference, the cross-sectional area of a copper line for dimensions well below the mean free path of electrons in copper at room temperature (39 nm).

Keywords: Copper; Interconnect; Matthiessen’s rule; Resistivity; Size effects; Thin films

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Scripta Materialia - Article in Press, Uncorrected Proof

Steven — Fri, 26 Dec 2008 11:36:44 +0800

Micropillar compression studies on a bulk metallic glass in different structural states

A. Dubach^a^,^b, R. Raghavan^b^,^c, J.F. Löffler^a, J. Michler^b and U. Ramamurty^c

^aLaboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland

^bEMPA Materials Science and Technology, Feuerwerkerstrasse 39, 3602 Thun, Switzerland

^cDepartment of Materials Engineering, Indian Institute of Science, Bangalore 560 012, India

Received 10 November 2008; revised 3 December 2008; accepted 4 December 2008. Available online 24 December 2008.

Uniaxial compression experiments on 0.3, 1 and 3 μm diameter micropillars of a Zr-based bulk metallic glass in as-cast, shot-peened and structurally relaxed conditions were conducted. Shear band formation and stable propagation is observed to be the plastic deformation mode in all cases, with no detectable difference in yield strength according to either size or condition. The limitations of uniaxial compression tests in assessing the influence of various material conditions on plasticity, when it is inhomogeneous in nature, are illustrated.

Keywords: Compression test; Metallic glasses; Plastic deformation; Shear bands; Free volume

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