Microstructure evolution of gold thin films under spherical indentation for micro switch contact applications

• Published in: Journal of materials science Vol. 46; no. 18; pp. 6111 - 6117
• Main Authors: Arrazat, Brice, Mandrillon, Vincent, Inal, Karim, Vincent, Maxime, Poulain, Christophe
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.09.2011; Springer; Springer Nature B.V
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Contact; Crystallography and Scattering Methods; Cyclic loads; Deformation mechanisms; Diamonds; Dielectric films; Electron backscatter diffraction; Evolution; Failure mechanisms; Fatigue (materials); Gold; Grain growth; Grains; Indentation; Materials Science; Mechanical systems; Microstructure; Plastic deformation; Polymer Sciences; Radio frequency; Rotation; Solid Mechanics; Switches; Switching; Temperature effects; Texture; Thin films; Ultrasonic testing; Work hardening; Spherical Indentation; Micro Electro Mechanical System; Fiber Texture; Pole Figure; Crystallographic Texture
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-011-5575-8

RF MEMS (Radio Frequency Micro Electro Mechanical System) switches are promising devices but their gold-on-gold contacts, assimilated for this study to a sphere/plane contact, represent a major reliability issue. A first step toward understanding failure mechanisms is to investigate the contact metal microstructure evolution under static and cyclic loading. After static and cyclic loading of sputtered gold thin films under spherical indentation, high-resolution Electron Back Scatter Diffraction (EBSD) is used to investigate the contact area. Grain rotation against {111} fiber texture of 1-μm-thick sputtered gold thin film is a signature of plastic deformation. Grain rotation is observed above 1.6 mN under static loading using a spherical diamond indenter with 50-μm tip radius. The heterogeneity in grain rotation observed corresponds to a greater plastic deformation in the middle of the indent than at the edge. A 30° grain rotation due to cyclic work hardening is observed for a half-million mechanical cycles under 300 μN load using a spherical gold tip (20 μm radius). The same test in hot switching mode induces a grain growth in the contact area. Therefore, thermal effects occurring during hot switching are underlined.