Project report Project duration: Sep 2008 – Present Measurement of Damping in Thin Metal Films with Applications to Micro/Nanoelectromechanical Resonators Guru Sosale, Dorothée Almecija and Srikar Vengallatore (PI) Keywords : Q factor, MEMS, thin films, micromachined silicon cantilevers, damping Background and Significance Measuring structural damping due to internal friction in deposited thin films can generate valuable insights into the effects of size and confinement on the mechanisms of anelasticity, and provide useful guidelines for the design of high-Q micro/nanomechanical resonators used in microelectromechanical systems (MEMS) for sensing, communications, and vibration energy harvesting. However, accurate measurement of internal friction has been a long-standing challenge because of the difficulty associated with calibrating the background damping. Methodology: We have developed an approach based on a silicon microcantilever platform that resolves these difficulties. This approach is built upon the ability to operate silicon microcantilevers at the fundamental limits of dissipation established by thermoelastic damping (TED), and the ability to compute TED in metal-coated silicon beams without using any free parameters. Using this method, we are able to accurately measure internal friction in ultrathin films deposited by a wide variety of processes. Recent work included the first accurate measurements of internal friction at room temperature in sputtered films of aluminum, silver, and gold with thickness ranging from 50 nm to 500 nm. Of particular significance to the design of microelectromechanical resonators is that gold films dissipate less energy than either aluminum or silver between 100 Hz and 1.5 kHz. In all cases, internal friction is dominated by defect-induced processes occurring within the bulk of these films, and not at the silicon/film interface or at the free surface of the metals. Figure 1: (a) Scanning electron micrograph of micromachined Si cantilevers (b)Damping measurement setup: i) laser doppler vibrometer to measure dynamics of cantilever ii) piezoelectric base shaker, iii) vacuum chamber. Collaborators – Prof L Fréchette (Département de génie méchanique, Université de Sherbrooke) Selected publications - G. Sosale, S. Prabhakar, L. Fréchette and S. Vengallatore, “Effect of thin aluminum coatings on structural damping of silicon microresonators” Mater. Res. Soc. Symp. Proc., vol. 1222, 2010 - G. Sosale, S. Prabhakar, L. Fréchette and S. Vengallatore, “A Microcantilever Platform for Measuring Internal Friction in Thin Films Using Thermoelastic Damping for Calibration” Journal of Microelectromechanical Systems, (under review, 2011) Conference Talks: G Sosale, S. Prabhakar, L. Fréchette and S. Vengallatore “A New Approach for Accurate Measurement of Internal Friction in Thin Films: Applications to Microresonators used in MEMS” Symposium DD, MRS Fall Meeting. Boston, Nov 2009 Acknowledgement : NSERC, Canada Research Chair Program a) b)
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Project report
Project duration: Sep 2008 – Present
Measurement of Damping in Thin Metal Films with Applications to Micro/Nanoelectromechanical Resonators
Guru Sosale, Dorothée Almecija and Srikar Vengallatore (PI) Keywords: Q factor, MEMS, thin films, micromachined silicon cantilevers, damping
Background and Significance Measuring structural damping due to internal friction in deposited thin films can generate valuable insights into the effects of size and confinement on the mechanisms of anelasticity, and provide useful guidelines for the design of high-Q micro/nanomechanical resonators used in microelectromechanical systems (MEMS) for sensing, communications, and vibration energy harvesting. However, accurate measurement of internal friction has been a long-standing challenge because of the difficulty associated with calibrating the background damping. Methodology: We have developed an approach based on a silicon microcantilever platform that resolves these difficulties. This approach is built upon the ability to operate silicon microcantilevers at the fundamental limits of dissipation established by thermoelastic damping (TED), and the ability to compute TED in metal-coated silicon beams without using any free parameters. Using this method, we are able to accurately measure internal friction in ultrathin films deposited by a wide variety of processes. Recent work included the first accurate measurements of internal friction at room temperature in sputtered films of aluminum, silver, and gold with thickness ranging from 50 nm to 500 nm. Of particular significance to the design of microelectromechanical resonators is that gold films dissipate less energy than either aluminum or silver between 100 Hz and 1.5 kHz. In all cases, internal friction is dominated by defect-induced processes occurring within the bulk of these films, and not at the silicon/film interface or at the free surface of the metals.
Figure 1: (a) Scanning electron micrograph of micromachined Si cantilevers (b)Damping measurement setup: i) laser doppler vibrometer to measure dynamics of cantilever ii) piezoelectric base shaker, iii) vacuum chamber. Collaborators – Prof L Fréchette (Département de génie méchanique, Université de Sherbrooke) Selected publications
- G. Sosale, S. Prabhakar, L. Fréchette and S. Vengallatore, “Effect of thin aluminum coatings on structural damping of silicon microresonators” Mater. Res. Soc. Symp. Proc., vol. 1222, 2010
- G. Sosale, S. Prabhakar, L. Fréchette and S. Vengallatore, “A Microcantilever Platform for Measuring Internal Friction in Thin Films Using Thermoelastic Damping for Calibration” Journal of Microelectromechanical Systems, (under review, 2011)
Conference Talks: G Sosale, S. Prabhakar, L. Fréchette and S. Vengallatore “A New Approach for Accurate Measurement of Internal Friction in Thin Films: Applications to Microresonators used in MEMS” Symposium DD, MRS Fall Meeting. Boston, Nov 2009 Acknowledgement : NSERC, Canada Research Chair Program
a) b)
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