Mechanical and Electrical Properties of Nanocrystalline and Epitaxial TiN Films
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Mechanical and Electrical Properties of Nanocrystalline and Epitaxial TiN Films H. Wang, A. Kvit, X. Zhang, C. C. Koch, J. Narayan Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7916 ABSTRACT High-temperature materials such as TiN have been successfully applied as wear corrosion protection, decorative coatings, electrical contacts and diffusion barriers in electronic devices. However the poor toughness and ductility have limited some of these applications. To alleviate some of these problems, reduction of grain size can enhance grain boundary sliding and grain boundary diffusion related creep phenomena. We have investigated mechanical and electrical properties of TiN as a function of microstructure varying from nanocrystalline to single crystal TiN films deposited on (100) silicon substrates. By varying the substrate temperature from 25oC to 700oC during pulsed laser deposition, the microstructure of TiN films changed from nanocrystalline (having uniform grain size of 8 nm) to a single crystal epitaxial film on the silicon (100) substrate. The microstructure and epitaxial nature of these films were investigated using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Hardness measurements were made using nanoindentation techniques. Resistivity measurements were performed by van der Pauw method. The nanocrystalline TiN contained numerous triple junctions without any presence of amorphous regions. The width of the grain boundary remained constant 1 nm as a function of boundary angle. Similarly the grain boundary structure did not change with grain size. The hardness of TiN films decreased with decreasing grain size in nanoscale. This behavior has been modeled recently involving grain boundary sliding which is particularly relevant in the case of hard materials such as TiN. The dependence of resistivity of TiN as a function of the substrate temperature is discussed and correlated with hardness results. INTRODUCTION Because of their excellent corrosion and erosion resistance, high hardness, high thermal stability and desirable optical and electrical properties, TiN films are successfully applied as wearprotection coatings for tools and mechanical components 1,2, decoration coatings 3,4, electrical contacts and diffusion barriers in electronic devices. 5,6 However, there are disadvantages associated with these materials in terms of poor toughness and ductility which severely limit their applications. Poor toughness and ductility result from the lack of dislocations and mobility. To alleviate some of these problems, reduction of grain size can enhance grain-boundary sliding and grain boundary diffusion related creep phenomena. The characteristic of the microstructure produced by pulsed laser deposition, was that the dislocation density within the grains was quite high > 1011cm-2. In most materials, hardness increases with decreasing grain size. In metallic materials, which exhibit plastic deformation, hardness which scales
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