Investigation of the Influence of Grain Size, Texture and Orientation on the Mechanical Behavior of Freestanding Polycry
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0924-Z03-13
Investigation of the Influence of Grain Size, Texture and Orientation on the Mechanical Behavior of Freestanding Polycrystalline Gold Films Liwei Wang, and Bart Prorok Mechanical Engineering, Auburn University, 275 Wilmore Laboratory, Auburn, AL, 368495341 ABSTRACT Polycrystalline gold thin films with thickness of 250nm, 500nm and 1000nm were deposited on Si substrates by means of both E-Beam evaporation and sputtering techniques. Highresolution SEM, including electron-backscattered diffraction (EBSD), was employed to provide a crystallographic analysis including grain orientation maps of the studied films. The Membrane Deflection Experiment (MDE) was employed to perform the microscale tensile testing. The Young’s modulus of gold films deposited by E-Beam evaporation was measured consistently in the range of 55-62 GPa while it increased to 68-72 GPa for sputtered films. Plastic yielding of the e-beam and sputtered films was contrasted due to varying microstructure of each deposition technique, which appears to assert a measure of control on the deformation mechanics. INTRODUCTION Thin film materials have been widely employed in microelectronic device and Microelectromechanical systems (MEMS) for many decades. Although the main purpose of many films in these devices is to impart particular electrical properties, their mechanical properties can be just as important as they can not only influence electrical behavior but also play a major role in their performance and reliability. To this end, many characterization methods have been developed to measure mechanical properties, including nano-indentation, micro-beam bending test, bulge test, etc. [1-5]. In this paper, the Membrane Deflection Experiment (MDE), developed by Espinosa and co-workers [6-9], was employed to perform the microscale tensile testing. The mechanical response of thin films depends on many factors. As the film dimensions begin to approach the scale of the material’s microstructure features, the mechanical properties begin to exhibit a strong dependence on the microstructure and specimen size [9]. The microstructure of thin films strongly depends on the deposition process used [10]. Characteristics such as grain size, crystalline orientation are affected by the conditions under which grain nucleation, growth, coarsening, and thickening occur. Two physical vapor deposition processing techniques, Ebeam evaporation and sputtering, are employed to grow films of varying microstructure. These films are characterized with electron backscattered diffraction (EBSD) and then tested by the membrane deflection technique. The results are compared and contrasted in terms of Young’s modulus and yield strength. EXPERIMENTAL DETAILS Sample Preparation: Gold films were deposited onto (100) Si wafers by both Ebeam evaporation and Sputtering. A CHA Mark 50 evaporation system and Denton Vacuum Discovery 18 sputter system were employed respectively. The gold target was purchased from Electronic Space Products Inc. with purity of 99.99% for the targets. The back
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